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Final evaluating materialremoval
Final evaluating materialremoval
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Final evaluating materialremoval

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Deburring and Finishing Processes explained by AF Kenton a long-time process developer and OEM (Original equipment Manufacturer)

Deburring and Finishing Processes explained by AF Kenton a long-time process developer and OEM (Original equipment Manufacturer)

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  • 1. Nova Finishing Systems ▪ PO Box 185, Hatboro, PA 19040 www.novafinishing.com ▪ 215-444-9981 ▪ 800-444-4159 ▪ Fax 215-444-9982 novafinish@earthlink.com ISBN - 978-0-615-85574-5 Evaluating Material Removal and Surface Modification Systems, by A.F. Kenton Copyright 2013
  • 2. Table of Contents Chapter 1 - Abrasives.................................................................................................................................7 Introduction ............................................................................................................................................................................ 7 A Brief History of Abrasives ................................................................................................................................................. 7 Abrasives ............................................................................................................................................................................... 10 Chapter 2 - Classification ........................................................................................................................19 Surface Finishing and Preparation ..................................................................................................................................... 19 Classification: ........................................................................................................................................................................ 23 Type – Equipment Classification (first or first 2 numerical digits) ................................................................................ 24 Explanation of Location ....................................................................................................................................................... 26 Equipment ............................................................................................................................................................................. 35 Chapter 3 – Type 0 Equipment ..............................................................................................................37 Alternative Deburring Systems .......................................................................................................................................... 37 Chapter 4 - Type 1 Equipment ...............................................................................................................40 Automation: .......................................................................................................................................................................... 40 Wheel and Belt Systems ....................................................................................................................................................... 40 Human Factors...................................................................................................................................................................... 45 Variable Factors .................................................................................................................................................................... 45 Debris ..................................................................................................................................................................................... 46 Size/Diameter ........................................................................................................................................................................ 46 Automated Abrasive Wheel Deburring System ............................................................................................................... 47 Automated Abrasive Belt Machines .................................................................................................................................. 50 Non-woven ............................................................................................................................................................................ 51 Non-Woven Material Systems ............................................................................................................................................ 51 Selection ................................................................................................................................................................................. 58 Organic materials ................................................................................................................................................................. 60 Other Natural Materials ...................................................................................................................................................... 60 Abrasive and polishing compounds .................................................................................................................................. 66 Felt .......................................................................................................................................................................................... 69 Flap Wheels ........................................................................................................................................................................... 70 Discs ....................................................................................................................................................................................... 70 Comparison ........................................................................................................................................................................... 75 Inorganic Abrasive Belt Systems ........................................................................................................................................ 76 Chapter 5 – Type 2 Equipment & Mixed Technologies ....................................................................82 Abrasive Blasting: ................................................................................................................................................................. 82 Air and Dust .......................................................................................................................................................................... 83 General ................................................................................................................................................................................... 84 Suction System: ..................................................................................................................................................................... 85 Safety ...................................................................................................................................................................................... 88 Pressure System: ................................................................................................................................................................... 88 Other Media .......................................................................................................................................................................... 93 Small Systems ....................................................................................................................................................................... 94 Cryogenics: ............................................................................................................................................................................ 96 Shot Peening Media ........................................................................................................................................................... 100
  • 3. 4 Chapter 6 – Type 4 Equipment ............................................................................................................102 Wet Blasting or Water Hone: ............................................................................................................................................ 102 Water Jet: ............................................................................................................................................................................. 104 Ultrasonic Deburring ......................................................................................................................................................... 107 Abrasive Flow Media ......................................................................................................................................................... 112 Chapter 7 – Type 5 Equipment ............................................................................................................114 Thermal: ............................................................................................................................................................................... 114 Chapter 8 – Type 4 Equipment ............................................................................................................116 Chemical Milling: ............................................................................................................................................................... 116 Electro-Polishing................................................................................................................................................................. 117 ECD/Electro-Chemical Deburring.................................................................................................................................... 118 Chapter 9 – Type 3 Equipment ............................................................................................................123 Mass Finishing Equipment................................................................................................................................................ 123 The Barrel: ........................................................................................................................................................................... 125 Large Barrel Systems: ......................................................................................................................................................... 131 Medium or Open End Barrel Systems: ............................................................................................................................ 132 Open End Bottle.................................................................................................................................................................. 134 Small Barrel Systems: ......................................................................................................................................................... 136 Loading and Unloading Systems ..................................................................................................................................... 138 Vibratory Systems: ............................................................................................................................................................. 141 Separation ............................................................................................................................................................................ 151 Wet systems......................................................................................................................................................................... 152 Bowl Shape Vibratory Mills: ............................................................................................................................................. 153 Vibratory Bowl System Eccentric Weight Control Adjustments ................................................................................. 156 Machine Capacity ............................................................................................................................................................... 157 Continuous Flow Tube ...................................................................................................................................................... 162 Multi Pass ............................................................................................................................................................................ 164 Compartment Processing .................................................................................................................................................. 166 Part Impingement ............................................................................................................................................................... 167 Unloading ............................................................................................................................................................................ 167 Dam Operations.................................................................................................................................................................. 168 Small Bowl Systems ........................................................................................................................................................... 171 High Energy Centrifugal Systems: ................................................................................................................................... 173 High Energy Barrel Systems: ............................................................................................................................................ 174 High Energy Disc Systems: ............................................................................................................................................... 177 Input/ Output ...................................................................................................................................................................... 179 Comparison of Disc vs. Barrel .......................................................................................................................................... 180 Other Mass Finishing Systems:......................................................................................................................................... 181 Drag Finishing .................................................................................................................................................................... 183 Spin Finishing ..................................................................................................................................................................... 184 Turbo-Abrasive: .................................................................................................................................................................. 184 Orbital Beam or Sonic Beam: ............................................................................................................................................ 187 Orbital .................................................................................................................................................................................. 187 Magnetic: ............................................................................................................................................................................. 188 Magnetic Disc Finisher ...................................................................................................................................................... 190
  • 4. 5 Chapter 10 – Technology & Equipment Summary ..........................................................................191 Conclusion of Equipment .................................................................................................................................................. 191 Surface Finishing Options ................................................................................................................................................. 195 EQUIPMENT CLASSIFICATION EVALUATION BY CATEGORY ........................................................................... 200 Equipment Burr Class Location ................................................................................................................................ 200 Wheel and Belt Systems 100 – 151 .............................................................................................................................. 204 Abrasive Blasting 250 - 253 ......................................................................................................................................... 204 Cryogenic Blasting 5200 - 5233 ................................................................................................................................... 204 Chapter 11 – Surface Finishing Standards ........................................................................................205 Surface Finish Quality Control: ........................................................................................................................................ 205 Other Terms and Measurement........................................................................................................................................ 207 Chapter 12 – Media ................................................................................................................................212 Media Supplies ................................................................................................................................................................... 212 Random Media ................................................................................................................................................................... 213 Media Size ........................................................................................................................................................................... 215 Preformed Shaped Media .................................................................................................................................................. 226 Steel media: ......................................................................................................................................................................... 231 Organic media: .................................................................................................................................................................... 237 Dry shapes ........................................................................................................................................................................... 238 Random Organic Materials ............................................................................................................................................... 239 Blended or mixed media ................................................................................................................................................... 244 Pumice.................................................................................................................................................................................. 244 Other inorganic additives .................................................................................................................................................. 245 Antique Appearance .......................................................................................................................................................... 245 Felt and Miscellaneous ...................................................................................................................................................... 246 Temperature ........................................................................................................................................................................ 246 Media Shapes: ..................................................................................................................................................................... 247 Media Guidelines ............................................................................................................................................................... 253 Chapter 13 - Liquid Systems ................................................................................................................254 Chemical Compounds ....................................................................................................................................................... 254 Liquid Flow Systems: ......................................................................................................................................................... 256 Additives: ............................................................................................................................................................................ 258 Chemical Accelerators: ...................................................................................................................................................... 260 Chemical Control/Monitoring: ......................................................................................................................................... 261 Alternative Processing Methods: ..................................................................................................................................... 264 Chapter 14 – Selection Guidelines & Cost Factors ..........................................................................265 Waste Treatment: ................................................................................................................................................................ 265 Applications ........................................................................................................................................................................ 266 Quick Guideline Briefs For Mass Finishing System Processing ................................................................................... 266 Required Part Information for Proper Processing ......................................................................................................... 267 Equipment Requirements .................................................................................................................................................. 269 OPERATION COST ESTIMATE ...................................................................................................................................... 270
  • 5. 6 Bibliography and Credits .....................................................................................................................275 Book ...................................................................................................................................................................................... 275 Articles: ................................................................................................................................................................................ 275 Seminar ................................................................................................................................................................................ 275 Contributors: ....................................................................................................................................................................... 276 Photo and Image Credits ................................................................................................................................................... 276 About the Author ...................................................................................................................................280
  • 6. 7 Chapter 1 - Abrasives Introduction The purpose of this book is to cover the subject of all material removal processes or surface finishing type modification equipment on parts and finished product. Basically this subject matter involves the classification, explanation, and use of energy forces in a form of negative actions to achieve positive results. In this case, surface finishing is the positive result of the removal of material, which is actually a negative accomplishment. The information given is technical, yet general purpose, with hands-on type applications designed to help one select the best method and/or equipment to achieve the results one is looking for. The title of this book is Evaluating Material Removal and Surface Modification Systems. Most material removal processes and equipment use mechanical methods and solid abrasives to accomplish surface profile modifications; however, there are also other methods and means of accomplishing this task. Historically speaking, the term or word abrasives is well known and is normally well understood to represent small solid materials capable of effecting other materials when force of pressure is applied in relationship to one another. The word “abrade” means to remove or modify the surface of an object with that of another material object by physical movement or force. Most people equate abrasion with that of a break down or the destructive action of one form of solid matter to affect that of another form of solid matter in a relationship to those objects involved. In this process, the objects involved get smaller and/or the overall object or larger objects normally get modified and smoother. Given the consistency of the objects involved, there is a relationship or a controlled rate of break down given the same amount of force, but that may not be necessarily true. In all cases, abrasion is a removal process caused by the use of abrasives, which alters or changes an edge or surface profile of one physical object with and by that of another. A Brief History of Abrasives The history of abrasive materials goes back a long way to the dawn of man. When one thinks of the early man, he thinks of the cave man and his Stone Age mentality possessing only the basic skill for survival. How man survived and became the dominant species here on earth was through his intelligence and the use of tools, which were created or enhanced with the use of abrasives. Archeologists indicate that even the earliest man used tools to help him kill his food, cook it, and clothe himself. That means that man had the basic knowledge of how to make things to help him help himself and that required the use abrasives. Early man possessed few skills and he used what he could from nature; therefore, wood and stone became his basic materials to make tools. With use, man began to modify these tools by using harder substances to chip away at both wood and stone items. In time, blunt wood and stone devices, when chipped and rubbed, became sharp cutting and piercing tools and weapons. So very early on, man learned that rubbing or grinding of one object or stone against that of another affected both objects, but more important he created and learned through trial and error the early phases of abrasive technology and surface refinement.
  • 7. Chapter 1 - Abrasives 8 As man improved his tools and weapons, he also discovered that his cutting tools had a two-way action. That is, not only did the tool cut the object he was working on, but it sometimes cut the person using the tool. In most cases a sharp edge was desired and care was exercised; however, as people began to make other objects not designed to cut, the sharpness was not desired and had to be removed or modified. A sharp edge in the wrong spot can cause failure of the intended object or tool itself. Edge removal processing really didn't get much attention until the Bronze Age and/or when metal working became a more common tool making process, but even then creating the sharp edge was more important than removing it. In those early days of metal working, the creation of sharp edges on metals often produced end result of sharp, rough, or irregular edges that reminded people of sharp or rough, prickly fruit and/or plants that protect themselves with thorns or burrs. Consequently, at some point in history, these sharp, unwanted inorganic fragmented projections also became known as burrs. Like their plant counter parts these burr projections had to be avoided and removed before the tool or product could be used properly and safely. The creating of a sharp edge requires the thinning of materials being worked. Although a lot of materials could be sharpened, they would not hold up over a long period of time. The materials, which provided the best results, were metals, because they maintain a smooth continuous surface with an acute angle; however, metals were also the most difficult material that could be worked. To properly work metals and achieve the desired result one had to have the knowledge of both the metal and the abrasive. Through mostly trial and error, it was learned that different mineral abrasives and sizes had different physical effects or characteristics to other materials and they produced different results depending on how these abrasive materials were used or applied. In short, man learned about the hardness of one material in relationship to affect that of another. In the early days, most metal modifications and/or edges were accomplished by blacksmiths using heat and hammers. Pounding and reshaping were the primary methods used to obtain the desired shape and edge. After shaping, the final edge was dressed or worked by hand using a flat grinding stone, a round wheel, or fine loose abrasives applied by leather and lubricant. Because sharpening and the surface finishing process was achieved slowly, burrs were not known to be a problem back then. If they were a problem, little is known or written about them. As mentioned, the knowledge of abrasive materials goes back a long, long way. Way before the time of blacksmiths and metalworking. More than likely, stone finishing and wood working trades knew how to use abrasives and this knowledge carried over into metalworking. However, unlike these other trades, metal working and finishing presented special problems not common in those other trades. The characteristics of stone and wood are not the same as metal. Metal is tougher or stronger and more cohesive in thin sections than those of other materials. The burr problem requires special handling or treatment and more aggressive abrasives and procedures.
  • 8. Chapter 1 - Abrasives 9 Just when man learned how to use abrasives in a more controlled and productive way is unknown; however, there are stone monuments in ancient Egypt and other parts of the world that that have been worked smooth and uniform and that is not found in nature. That means that early-civilized man found ways to work and create relatively smooth surfaces through repetitive means. However, the basic idea of using abrasives for creating smooth surfaces probably came about by observing a number of exceptions in nature. More than likely, man observed and tried to duplicate the erosive effects that water and waves had on stones in creeks and shorelines or how desert sand and wind effected nature and manmade objects in arid regions of the world. Man could not duplicate the type of energy forces of nature and therefore probably had to rely mostly on hand pressure and crude turning devices. To aid hand working, he used types of cloth with or without hard support backing and other mechanical methods to apply greater pressure to the abrasive in contact with the end product materials. The first known successful mechanical method, other than hand and the grinding wheel, to apply a continuous force on parts may have occurred in ancient China and Egypt. It is known that they did use barrel tumbling methods with stones to work metal, but there isn’t much information on these methods or processes. The need and development of mechanical pressure for making contact between the abrasive and the work piece resulted in new application methods and other materials being tried for improving surface finishing speeds and results. At some point uniformity and repeatability in both parts and supplies were discovered to be important factors. Due to scarcity of uniform abrasive supplies and suppliers man basically used whatever was available to him in either organic or inorganic materials and noticed that these different particle sizes and materials produced different results. Because of the variance and characteristics of these different working materials, they all became known as a media or a medium, which is a means of conveying or to get to something else, or is a transmitting or transfer device. I guess you can also call this period of time, early research and development. Along with the understanding of abrasive materials, man discovered that the speed and surface finishing end results could be manipulated using different mechanical contact devices of cloth, fiber, or leather, which could be impregnated with abrasives. Most application methods were mechanical rubbing or lapping type operations done by hand, but it was also observed that finishing results were affected by the size and hardness of the abrasive particles used, and the way in which the energy forces were applied. However, time was not considered a big factor back in the early days of metal working, labor was relatively cheap and plentiful and craftsmen took pride in their work. In addition to the type of energy force, the process, and the mechanical contact device, the transfer means of application and the moisture content associated with the use of the abrasive were found to have an effect on final surface finishes. Lubricants and/or liquids were used to improve the abrasive process and help prolong the life of these mechanical contact or transfer devices, the abrasive, and to improve the general working conditions that man
  • 9. Chapter 1 - Abrasives 10 experienced while working with these products. Liquids were used to reduce the dust and heat transfer problem caused by mechanical actions necessary to get good finishing results. So very early on in our civilization, it was discovered that a lot of different factors affected surface refinement, and metal finishes and as technology improved over the ages, there was a growing need for higher quality surface finishing for functional and mechanical applications. Along with the need for abrasives for removing burrs and creating edges was the need for smooth surfaces and/or low RMS 1 or flatness, which produces reflective mirror finishes. To get smooth surface finishes required the use of finer types or sizes of abrasive materials, more energy, and longer time processing. That is, the need to improve surface features required different qualities or characteristics of an abrasive and the size of abrasives was important to produce the desired result. Again, the method of application was also often different as well as the processing time. Mirror finishes were used a lot by people in the armies of old for a number of reasons. The idea of a bright, shiny sword or metal armor, besides not only aesthetically pleasing, was believed to have a defensive value to reflect light and interfere with the enemies ability to see properly. Therefore besides fit, form, and function, bright finishes were desired on metals and to accomplish the task of polishing required a wider range of finer, softer abrasives and additives to prevent oxidation. It is interesting to note that a lot of abrasive technology originated out of the needs of the military. So you see, the more things change, the more things remain the same. Abrasives There has almost always been a need for different methods and materials to perform special metal finishing tasks and that makes the abrasive industry and finishing one of the oldest industries still in use today. Deburring and polishing are both material removal processes that are relative to size. Polishing is more of a surface modification using little if anything typically considered abrasive materials because of its small size, but their function is the same. Both require the use of abrasive materials of different size, shape, characteristics, and methods of application. For deburring, the general rule of thumb is the larger and harder the abrasive the more material is removed in the shortest period of time; however, it also leaves the roughest surface finish. For polishing, the best results are obtained using a series or progression of smaller and smaller and softer abrasives. Naturally these are over simplified statements that do not take into account part size, material, and what is the desired result. The term abrasives, is a general or generic term used to describe a lot of different mineral compounds. The word abrasive is not a specific item in itself because just about any physical substance found on earth will effect or do material modification, if given the right tools and pressure applied to an abrasive particles and the material being worked. Why I mention this 1 RMS means Root Mean Square. It is a standard unit of measure for surface profile or roughness. See chapter 11
  • 10. Chapter 1 - Abrasives 11 now is because an abrasive classification or product works a limited range of surface irregularities and produces specific results. To a large extent, these surface modifications depend on the material being worked. The material removal rate of all abrasives is normally rapid at first then tapers off until no major material removal rate is noticeable and that is because the abrasive particle size itself becomes smaller and less effective. This surface finish situation may occur way before the desire finish is achieved. As stated, in the past the abrasive material used for deburring were usually determined by the hardness of the mineral or abrasive particle and the part being worked. Large hand-held stones or files were used to rub or deburr material edges. For surface finishing and bright finishes, leather or cloth and a fine abrasive paste or rouge where preferred to produce smooth shinny metal. Technically, both deburring and polishing involves nearly the same abrasive materials, but the amount and way in which the energy is applied to the abrasive and transfer system determines the characteristics of the metal finish or end results. Normally removal of a lot of material can best be accomplished on outside edges of a part. That is because access to outside dimensions are relatively easy to reach and extreme force can be concentrated and applied to an edge to remove material very fast; whereas, flat surfaces require the same amount of pressure or more to produce relatively little noticeable material removal. The reason for the difference is the amount of pressure spread over a point versus a broad flat area. An analogy of energy forces used here would be that of a riffle versus that of a shotgun. Both guns work the same or do the same thing, but they are used for different applications. In one of our abrasive applications, the process is done to remove the sharpness of the material, the other is done to remove porosity of the material or to create a smooth surface. One process requires the use of more rigid application of abrasive and the other requires a more flexible application of those same abrasives or smaller abrasive particle sizes. Abrasive pressure can be more easily concentrated in a rigid manner and there is less resistance to the force of a metal edge than that of a surface area where pressure is spread out over a relatively larger area. The cohesiveness or surface tension of metal is more difficult to overcome in a broad flat state, given the same abrasives and tools. Normally application considerations are not a problem and never in conflict. That is, we are talking about two different requirements. Edge removal is done for primarily safety and functional reasons and normally doesn’t require a fine uniform surface finish. A flat surface is already safe and functional, but does require surface refinement for better environmental protective treatments or coatings. A refined finish will be a mirror image of that base metal, but will be capable of better adhesion qualities or will produce more uniform molecular structure for a protective chemical treatment. In most cases, function and/or longevity are the primary reasons for making parts out of metal. Parts must conform to specific dimensions in order to work properly. The size and outside dimensions are important for clearance to other parts, but these dimensions may also be controlled by inside holes that fasten parts together to function as an assembly. Any overlap or
  • 11. Chapter 1 - Abrasives 12 sharp edge may interfere or damage adjacent parts or materials. Therefore, edges must be rounded or modified reasonably smooth and this amount of material removal is usually determined by a combination of abrasives, friction, mass, and energy that work together to modify the outer layer of the metal to conform to the finalized part and its working environment. The general surface appearance of metal appears relatively flat, but under magnification, the physical surface profile of the metal is composed of uneven peaks and valleys. To deburr or modify parts, an abrasive must be used that will remove or blend in these surface irregularities. Very hard abrasive materials with large molecular crystals may produce a shinny surface appearance, but they may also do more scratching or tearing on a micro level of the metal than the smoothing or removal of the surface. Hard abrasive materials are actually better for polishing when the material is of a very small particle size and/or worn down so that the edges are rounded or removed. Worn or a round abrasive particles permit more mobility and a kind of rolling action that is more desirable for burnishing, which is more of a lapping or deforming of the surface irregularities than a removal process. The smaller and harder the abrasive used with mechanical application devices, the more pressure one can exert on the abrasive and this normally means the smoother the surface; however, this is not necessarily true. Given the same size abrasive mineral, an abrasive harder than the metal will work or create a profile of the metal nearly equal to the size and shape of the abrasive particle used. That is because the abrasive may not break down, but will drag along the surface of the part to be worked thereby creating a mirror image of its particle size. If the abrasive is loose and able to roll, it actually flows with the profile and to some extent compresses, laps, and/or deforms the peaks of the metal profile. This action creates a denser top micro level surface that is more shinny or smoother, but the metal will still have an irregular, less pronounced surface profile variation. When an abrasive is used that is softer than the metal being worked, the abrasive will break down or decompose as it is being used and generally will create a smoother over all surface profile. That is, when the softer particles hit the profile, the particles meet resistance in excess of their crystal size and strength and in the process of breaking down into smaller particles; some of the metal profile is modified and/or removed. The rate at which the particle breaks down and the crystalline molecular structure of the abrasive determines the overall surface finish profile of the metal. If the abrasive breaks down too fast without any pressure against the irregular profile, then there is little material removal. However, softer materials that break down are normally smaller in particle size and are somewhat more flexible thereby creating an overall smoother surface profile finish, but not necessarily a bright shinny finish. To do a good job of metal removal the best abrasive materials are the ones that break down and exposed new irregular or flat shaped sharp mineral crystals. This break down characteristic seems to be a better gauge of a good abrasive than hardness; yet, hardness gives greater life or longevity to the abrasive materials. Therefore, the measure of a good abrasive, besides hardness, requires the knowledge of other characteristics such as the molecular structure of the mineral, its crystal structure, and/or its chemical composition and in some cases,
  • 12. Chapter 1 - Abrasives 13 its behavior in water and chemicals. Hardness is still a very important factor to consider for abrasive characteristics, so much so, that knowledge was protected and shared only with people who worked with abrasives that were respected craftsmen or tradesmen. At times, these people had to share some common information to gain reliable sources of good mineral sources and sometimes they had to trade technical information as well. Like any trade or industry, there was and is a need to distinguish materials and create standards. Because uniformity produces repetitive results the importance of descriptive information for determining materials and hardness, a universal measurement scale was desired and needed. The classification of minerals seems to be pretty well clear cut and dry and is determined by a relatively fixed chemical composition; however, there are different grade variations or forms of hardness within a range of minerals that can be distinguish even within these fixed grades. Minerals are naturally occurring compounds formed under the physical forces of pressure and heat; therefore, different conditions can produce different variations of the same mineral. This variation is normally distinguished by density, but it also can be a result of the sub atomic molecular crystal structure caused by heat and pressure. Normally hardness and density are closely related, but they can be different because of the atomic bonding structure. The physical size of a particle is easy to identify and classify with mechanical means; however, hardness and density are relative terms and can be difficult to classify using any fixed set of standards or means of measurement. That is because there are a number of ways to measure hardness, but no one single method works well in all cases over a complete range of minerals. In the early 1800’s, a hardness scale was developed by a Friedrich Mohs. The Mohs scale rated all known minerals from 1 to 10, with the talc mineral as the softest at a 1 the diamond being the hardest at a 10. The basis of this scale is the ability or relationship of one mineral to scratch the surface of another. The original scale only showed or rated 10 common minerals of the day. At a much later date a modified Moh’s scale was created that numbered minerals from 1 to 15. More recently, decimals were also added to create a more defined scale or relationship of one mineral over another. The modified version of this scale is a fraction chart with the only other numerical consideration as a .5 or a half whole number for determining sub category hardness. Even though these other versions of this scale are acknowledged, unless specified as the modified Mohs scale the measurement most people still use is the old 1 to 10 system. More recent precision hardness measurement scales are the Brinell, Rockwell, Vickers, and Knoop scales. All of these scales depend on resistance to permanent indentation of a specific shaped contact tool device, such as a ball or pyramid, under pressure against the mineral or material in question. The most common scale used in the USA, besides the Mohs, is the Knoop scale that identifies minerals using a numerical value of 1 to 7000 for the same 1 to 10 Mohs classification. Even though the Knoop scale is more detailed, it is rarely used in the abrasive finishing industry. All of these scales are excellent for determining metal hardness, but
  • 13. Chapter 1 - Abrasives 14 because of mineral hardness, there are fracturing problems; therefore, most people still refer to the original Mohs scale when talking about hardness. In addition to the hardness of metals scales mentioned, there are still some other lesserknown hardness scales which can be used or shared within the industry. The Scleroscope test or scale is based upon the height of a rebound of a contact tool. Supposedly, this test measures the loss or transfer of energy of the sample. Another test or scale is known as Microhardness. This is a low-pressure indenture test similar to all of the other common metal tests; however, this is done at low pressures and requires the use of a microscope. For softer materials, there is the Shore Durometer scale or test that uses a spring loaded contact tool. Other scales not commonly known or used by the general public are the eddy current test that measures electrical properties, the Sonadur test that uses a sound resonance, and the Eseway test that uses impact via an ultra sound sensor. None of these other tests are being used to any extent in the abrasives industry so we will not go into them in any more detail. Mohs Scale Of Hardness Material Scale Talc. …………………………………………….. 1 Gypsum. ……………………………………….. 2 Calcite…………………………………………... 3 Fluorite…………………………….…………… 4 Apatite………………………………………….. 5 Orthoclase…………………………………….... 6 Quartz. ………………………………………….. 7 Topaz…………………………………………….. 8 Corundum………………………………………. 9 Diamond……………………………………….. 10 I do not know of any study of metal or material hardness to correspond to the mineral hardness and pressure or its relationship to the Moh’s scale; however, there is probably a correlation. There is the Rockwell standard for measuring metal hardness, but again, there is no relationship to the Moh’s scale. That means that there is no scientific relationship for selecting one abrasive over another other than the recommendations from abrasive suppliers and most abrasives that are used are determined by cost and availability which in turn is normally determined by raw material suppliers. That also means that hands on experience knowledge is one of the best sources for determining abrasive usage. The variable qualities of both materials and abrasives make the selection and finishing process systems sometimes appear unscientific, but there is a relationship. Most knowledge of abrasives, deburring, and finishing are just not taught, but are picked up with experience.
  • 14. Chapter 1 - Abrasives 15 Hardness of minerals is an important factor in material removal rates and processing times. However, they are not the only factors. In fact, size and friability are very import in relationship to the metal hardness. Because of specific gravity, resistance, density, and molecular structure, a physical part is normally larger than the abrasive used and therefore more resistant to significant physical changes. That means that an abrasive is affected and subject to change as well as the parts surface finish; therefore, an abrasive harder than the material being worked is desirable. The stronger the crystal structure of the abrasive mineral and larger the size of the particle the greater the amount of kinetic energy that is released. Not only do you have energy from an outside source to create the pressure and contact with the part, you also have energy from an inside source. Outside forces are easy to explain. That is the whole purpose of machines and that is what all abrasive machines systems do. Inside kinetic energy is different. The latter is similar to what happens in an earthquake or explosion. Besides the actual release of energy in the form of heat, there is also violent radical molecular movement. Physical displacement and forces are amplified in extremely short rapid movements of the remaining material on a molecular level that creates tremendous pressures against whatever they are in contact with. As abrasive particles break down and become smaller, they require greater outside energy or force to do the same amount of material removal. That is both a true and false statement. What happens is that because the abrasive particles become smaller there is actually more surface contact, friction, and greater resistance. That breakdown process generally produces less bulk and weight per particle. That in turn, reduces the size of the material particles being removed. That is the true part of the statement. Where the difficulties or false part of our statement, “same amount,” comes in is in the load characteristics of the material removal process. Given the same density or hardness, the larger mass will always affect the smaller mass first of either the size of the abrasive or the materials surface profile irregularities. That means that the material removal rate maybe in the same ratio of particle size to material removal, but the ability or load characteristics increase making it more difficult to remove larger surface irregularities in mass. This is false according to our first statement and goes back to an earlier statement that the surface profile can only be as smooth as the smallest abrasive particle. The molecular cohesive force or bond of an abrasive tends to lose its ability to remove, carry, and convey other materials as they get smaller and this relates to mass and/or specific gravity. However, this problem is somewhat overcome by the mass as a whole, which behaves like a flexible solid. Then again, this size and mass behavior makes it more difficult to remove greater surface irregularities without the use of more energy or force. All abrasives will work up to a certain point and then slowly decrease, based upon the elements of weight, mass, and density. As long as there is a transfer mechanism in place to apply pressure to both the part and the abrasive, then there will be material removal. However, because we are talking about normal working conditions or processing time, an efficiency point is reached way before the life of the abrasive is used up. In short, the smaller the particle size, the greater the energy force and/or pressure is required to maintain the same material removal rate.
  • 15. Chapter 1 - Abrasives 16 With the exception of a flat smooth surface, irregularities in a materials surface profile will always exist to some extent on a plane of reference, if only because of the porosity of the material involved and the relationship of bonding molecules. In most cases, surface finishing systems do not have to create a perfectly flat material profile. In fact, when parts require a heavy coating over the finished part, a smooth finish is not the desired end result. The size and/or amount of a surface profile irregularity can be reduced and will continually decrease to a measured zero point or where the size of the abrasive will not work efficiently. There are limits to abrasive mechanical methods or processes. At some point, which depends upon the characteristics of the abrasive used, the break down rate or friability of the abrasive becomes a more important factor than weight, mass, and density. The reason for that is because the breakdown process releases kinetic energy forces and any movement of a solid against another solid does surface modification. This may still be a difficult technical concept to understand, because the relationship of the abrasive to the material’s surface profile can vary greatly; however, a lot of common sense is involved here. That is, at first larger, fewer, and heavier surface profile irregularities are removed during a mechanical deburring process, then as the part’s surface becomes smoother, material removal size becomes smaller in size and volume to both the abrasive and the material being worked. That break down process gives the visual appearance of little or no surface modification. In actuality, the material removal rate remains nearly constant, but physical perception is deceived. However, if you go strictly by the weight of the part to the material being removed, then this is a false statement. A lot of this measuring and evaluation depends on what measuring scale you are using. Typically, depending upon the deburring or surface finishing systems used, most large irregularities that offer resistance to the abrasive are removed first, followed by smaller and flatter surface features. The smaller the abrasive particle size, the deeper it can penetrate into the material profile of the part; however, if the particle size is too small it too can get trapped in that same profile if there is no larger particles to dislodge it. The smaller the mass, the less force it has to do material removal and that also means the finer the surface finish. The only way to compensate for this factor is to impart or increase more energy or weight to smaller abrasives than is required for larger mass size. This particle lodging situation happens a lot with blasting systems. The only other way to get around the rule of particle size that affects the surface profile rule is to allow the abrasive to float or give in relationship to the pressure applied to both the abrasive and the material being worked. If an abrasive has the ability to be flexible, or allowed to drag and/or be compressed along the surface of the material to be worked, it can accomplish a finer surface finish than its normal particle size. However, because abrasives are basically dense solids, there is little ability for this material to float unless you add air or water to the process or to somehow bind the abrasive into a flexible or larger softer abrasive mass shape. Then again, if any abrasive is permitted to free float without controlling the part contact, there is no absolute assurance that this will still produce a uniform finish finer than the abrasive used.
  • 16. Chapter 1 - Abrasives 17 It is necessary that the abrasive particle does change or break down in order to carry away burrs, debris, or any surface irregularities. The result of not breaking down or becoming smaller, is excessive energy imparted onto the abrasive that is transferred to the part causing a condition resembling an orange peel surface. When that happens, the material surface becomes more dense where impacting occurs and that creates a condition that is called work hardening which is similar effect produced by heat treating materials. In an abrasive process, large particles can deform the material surface being worked, given enough mass, creating either visual or microscopic indentations and that can leave the surface rougher than what its surface profile started out. This is another common condition that results from blast finishing systems. As mentioned, the smaller the average size of the abrasive particles used to modify the surface, the finer or smoother the material finish. Another way to produce smoother surface finishes is to use softer or more flexible abrasives. A smooth finish can also be accomplished by using some kind of liquid or some bulky filler mass as a means to cushion the abrasive or to encapsulate it make it more flexible. Lastly, the slower the movement and pressure of the media against the part or surface the finer or smoother the finish. Naturally, there is a point of economics involved with all of these processes, so time is normally another factor or requirement for finishing. The energy force factor must be considered in any material removal system for speed and the finishing results desired. At some point greater energy force or pressure and smaller particle sized abrasive is required to perform finer or smoother surface modifications. When this point is reached, one should consider the concept of step processing which is a condition where an abrasive ceases to work efficiently to produce the desired surface smoothness. When that point is reached another abrasive is chosen to produce the next finishing requirements. The point where the performance of abrasive particles appears to decrease rapidly is when a new or different abrasive should be changed in order to maintain efficient material removal rates. More energy or pressure can only be applied to the abrasive up to the point where that energy can be transferred in relationship to the material removal process or the required part finish. To produce finer material or edge finishes requires smaller abrasive sizes and longer or more aggressive processing times. It was mentioned that the fastest way to get to a smooth polished finish is to prepare or refine the edge or surface features with coarse or larger abrasives first. Depending on the roughness of the initial part and the finish required, the part or area is then reworked with consecutively smaller abrasive grit sizes using a multiple number of steps or passes until the surface finish is achieved. This step procedure is a slow process, but it is also faster than using a single small abrasive size to accomplish the same finishing task. With the exception of a measurable flat smooth surface, irregularities in material surface profiles will always exist to some extent on some plane of reference, if only because of the porosity of the material. However, the size and/or amount of the irregularity can be reduced and will continually decrease to a point where the size of the abrasive media will not work efficiently. Weight and mass are the most important factors to remove large amounts of surface irregularities. However, a point is reached where weight and mass become a liability. At some point, which depends upon the characteristics of the abrasive media used, the breakdown rate
  • 17. Chapter 1 - Abrasives 18 or friability of the media becomes a more important factor than weight and mass. Technically speaking, you cannot get a smoother surface feature better than the abrasive particle size you are using, because the particle, if it does not break down into a smaller particle, will actually produce irregularities that correspond to the physical abrasive particle size in use. As mentioned, the only way to get around this rule of size is if the abrasive material is allowed to float or give in relationship to the pressure applied to both the abrasive and the material being worked. However, because most abrasive particles used are made into fixed shapes or bonded to a rigid surfaces there is little ability to float, unless you add air or water to the process. Then again, if abrasives are permitted to free float this may not produce a uniform surface; therefore, contact pressure is very important in material removal rates and surface finishes, where time is important. Now, that means that how energy is applied and transferred to the abrasive particles and the parts being worked are also very important to material removal processes. Another factor to consider is the hardness of the materials being worked and the abrasive particle hardness, because there are different friable breakdown rates or crystal structure of abrasive materials. You need an abrasive that will wear away and remove surface irregularities before the abrasive particles lose their ability to abrade and/or transfer energy. Energy force, or how energy is applied to the materials surface must be considered in all surface modification systems. There are a number of systems and options on how this energy is to be applied and they all achieve different results. The concept of energy or force uniformly applied to abrasive particles is an important factor both in surface finish quality and the speed of the process. However, there are tradeoffs. Consistency and repeatability are important. Therefore, not only does one have to consider the abrasive and size to use, but he needs to know the finishing characteristics and quality in relationship to the equipment or process, plus the economics that can be achieved using these energy transfer systems.
  • 18. 19 Chapter 2 - Classification Surface Finishing and Preparation Before the age of mass production or standardized parts, most parts were custom made, worked, and finished by hand. That normally meant that no two parts were actually identical and not necessarily interchangeable. They may have looked and functioned the same, but dimensional variations were common; therefore, finishing requirements were not that important or critical, especially if the parts could not be seen. Appearance and being smooth to the touch was probably more important than dimensional tolerances. If the metal part could be seen, a mirror or reflective finish was usually desired, since this was normally a sign of good craftsmanship. However, most metals and surface finishes that were exposed to the environment and not protected were and are subject to oxidation. Therefore, no matter what the appearance of the finished part, a protective coating was desired to cover the surface finish from oxidation and deterioration. Use of the word surface finishing opens up a whole new can of worms, which I avoided earlier. Depending upon whom you talk with, the term “surface finishing” means different things to different people. Depending upon the application or relationship to the person in question, it can mean: preparation, plating, painting, coating, or our usage meaning surface profile modification or the smoothness of the material. Each application or meaning involves another industry or technology, which is different from one another and has its own set of rules and requirements. Unfortunately, like so many of words in the English language, the proper terminology depends upon the industry you are talking about and since they are all related, it makes it extremely confusing at times. See conclusion chapter. Surface finishing and surface preparation mean two different things, but to the average person they are sometimes used interchangeably. A surface finish can mean the final result of a manufacturing processes and/or the final appearance of the part at any stage of manufacturing or it can be the final condition after any additional protective coatings are applied. In some cases, a surface finish does not have to be protected and can be the same as that final appearance of the part. Surface preparation is the final surface appearance of the part prior to being coated with some kind of protective film or coating. Surface preparation is never the final appearance of a part, unless you consider thin chemical coatings or treatments. In the latter situation, a thin coating such as anodizing or alodine, the part’s surface appearance or dimensions remain unchanged; therefore, it is both a surface finish and surface preparation. It is the mechanical systems and changing conditions or inconsistency of a part’s surface at any point is what causes much of the confusion and usage of these interchangeable terms. Now, although we have just tried to make a distinction between these two words, common usage confuses them. That is, we have just said earlier that no matter what the appearance, coatings are necessary to protect a surface finish from oxidation, but a surface finish only represents a current condition of the part. That means that almost all parts are
  • 19. Chapter 2 - Classification 20 finished to what is called a surface preparation condition. Interpretation of these words basically now means that any metal part that appears to be metal is the surface finish or surface profile; whereas, surface preparation now refers to perhaps a surface condition prior to being coated with a thick film, or at least cleaned in some soluble solution. Perhaps another visual aid is that a surface finish is usually a lot smoother than a surface preparation, because roughness or porosity is a desired quality for most heavy thickness coatings or films to adhere too. Before we get into equipment classification and energy force systems, let’s take a look at the options for the common term surface finishing. In mechanical finishing, there are 3 types of options. The option one chooses depends mostly on how the part is to be used, or in what environment it will be working in. These options are as follows: 1. Surface preparation for heavy or thick coatings such as paint or plastic based film products, 2. Surface preparation for thin film chemical coating or treatments, 3. Polished or smooth finishes are for aesthetic appearances or are done to reduce bacteria hazards and medical requirements. In most cases, design engineers will specify surface finishing requirements based upon the end use criteria. Once the surface finish requirement is determined, the method to achieve that surface preparation needs to be selected. The following are some guidelines for surface preparations. Surface Finishing Options Type 1 Surface preparation for heavy thickness coatings A. Surface finish will be the roughest of all options and the finished part will exceed the parts final dimensions because of the coating. B. Surface finish should be as rough as possible to increase the surface area for good adhesion properties and/or wear characteristics or longevity of the coating. RMS 35 or higher. C. Roughness of surface should not exceed in height the profile of the thickness of the film or coating to be placed on part. D. Surface should be as clean as possible from debris, oils, and oxidation. Therefore, cleaning should be done immediately before coating, but part(s) should be dry. Type 2 Surface preparation for thin film coatings A. Surface finish normally requires a secondary modification and that will be the final dimensions of the part, but it can be on the plus side of the tolerance depending on the film or coating. B. Surface finish requires a smoothing or modification of the part to improve uniformity of the surface profile of the finalized processed part. Normal RMS range is 12 to 20. C. Roughness profile is not as critical for most chemical treatments; however, the smoother the surface, the more uniform the treatment. See Type 1, C & D above for non-chemical coatings.
  • 20. Chapter 2 - Classification Type 3 21 Polished finishes A. Surface finish will be the smoothest of all the options and close to the final dimensions of the part, but on the minus side of the tolerance. If a thin film coating is still required, dimensions may exceed final part size. B. This process is not considered surface preparation, but a modification procedure or material removal process. The finalized part will either have a textured pattern or mirror finish in the RMS range of 2 to 18. C. Surface finish is mostly a question or porosity or for appearance sake; however, coatings can still be applied for protective reasons. In making a part, most manufacturing time is devoted to making the part. That is, a part is made from raw material that can be molded, cast, or rolled into square or round bar, it is then machined, milled, drilled, turned, ground, etc. In most cases, little thought or time is devoted to the final surface finish of the machined part. That was the thinking in the past and this same thinking process seems to have extended into the present. Production facilities seem to spend a lot of time concentrating on the machining operations and then rush the deburring and finishing operations. Too little engineering thought is devoted to the final finish. Whereas, with some proper planning as to how a burr or roughness is formed a lot of deburring and surface finishing can be avoided or lessened. The combination of a good engineer and machinist, with the proper knowledge of feeds and speeds, equipment, and tools can create a program that can eliminate almost all deburring and surface finishing. See “Deburring and Edge Finishing Handbook” by La-Roux Gillespie 1997 Generally speaking, any part that is machined, formed, or worked usually results in sharp edges and that is not normally an accepted finished part. Therefore, some secondary operation or process is normally required to remove the sharp edges and/or smooth out surface irregularities before the part can be used in its final application. A secondary operation means that some form of energy or force must be used to remove or modify the part’s edges and surface. What force one uses and how that force is applied is the understanding of deburring and mass finishing. In mechanical finishing, the concept of energy or force uniformly applied to abrasive particles is an important factor both in the surface finish quality and the speed or rate of the material removal process. In addition to speed one has to consider the factors of consistency and repeatability and the economics that can be achieved using these energy forces. Other factors are limitations of part size and shape as well as the abrasive used and the finishing characteristics in relationship to the equipment. How energy or how equipment uses energy is critical to the processing element, time, and the final results. There are at least two elements or forms of energy that are used for material removal in mechanical systems. These are: speed or velocity and pressure or friction. These are related terms, but they can also be thought of as 4 elements. Speed and velocity are related to movement. Pressure and friction can be related to compression and contact. So, in simple terms,
  • 21. Chapter 2 - Classification 22 for material removal you need to move the part and abrasive under pressure in a uniform contact fashion against one another. That basically brings us up to finishing equipment. How energy or equipment uses energy is critical to the processing element. Now, although there are two forms of energy required, there are 5 basic energy or equipment systems that do surface finishing or material removal, 6 if you consider hand operations. Of the original 5, only 3 are mechanical systems which involve abrasives. The other 2 systems deal with liquids and temperature. These will all be discussed at length shortly. Naturally, manual hand work is all very labor intensive, time consuming, and surface finish quality varies a great deal from item to item because of tools, methods, and the human factor. This lack of uniformity and repeatability in early times was not normally a problem, because most useable physical items or material goods were basically one of a kind type products considered custom made and not made to with interchangeable parts. Therefore, because of the time element and costs, surface finishing of goods were not a major prerequisite, unless you were talking about items specifically to be shown and seen by royalty or people of money. In the latter cases, a great deal of extra time was required and spent on surface finishes. As machine assisted cutting tools came into use, burr removal became more and more of a problem. Shortly after the industrial revolution began, the terminology used to describe the process of sharp edge removal or surface refinement became known as deburring, or to burr, and/or meaning the negative form of a burr. Burr, in turn is the analogy of the sharp thorny projections of burr type plants previously mentioned. Many high speed production machine systems using cutting tools create sharp edges and/or produce slivers or fragments of metal that resemble, behave, and feel like the thorny burr. Most metal working processes create burrs for a number of reasons. The primary reason is the fact that when metals reach a certain thickness or rather thinness, they cease to behave like the parent metal, but bend and/or behave like a flexible solid, yet stiff enough to create problems of safety and possible performance of the part. One way to reduce this extra material deburring removal is to use the proper cutting tool and speed in the machining operation. It is possible to machine a part without any sharp edges or burrs, but it is usually more cost effective to separate the fast machining operations or main material removal processes from the slower secondary finishing operations. Because time is money, most companies trade off production speed and incur the problem of burr removal to a separate metal working process as a standard practice. The deburring process then is necessary to actually finish the machine cutting operation, or to improve the surface finish of the machined area, or to achieve a proper profile or edge. Primarily the part must conform or meet fit, form, and function criteria within safe handling parameters and maybe appearance. The actual removal process then is the burr removal or the word deburr, even though we may be talking about surface preparation or finishing. Hand powered tools and surface finishing was not known to exist or be of any significance until the invention of steam powered machines. Even then, it was really electricity
  • 22. Chapter 2 - Classification 23 and air powered equipment that became the main source of mechanical energy systems that reduced and improved hand labor surface finishing operations. In the early 1900's, the industrial revolution changed the way a lot of things were done. With standardized parts and/or production lines came the need or requirement for the uniformity of parts and finishes. Even with advent of powered hand tools, the surface or edge finish of an end product depended upon who was operating the hand tool, the size, type, and condition of the abrasive that were used or specified, and to some extent the inspection procedures which set the standards of acceptability. The end results or finishing procedures still varied to some extent depended upon the person and/or pressure applied to the tool, the abrasive, and the part. As long as parts were not designed for close tolerance precision fit and as long as they looked nearly alike, most of these finishing procedures were acceptable. As quantities and/or volume of parts being produced began to increase, reliability and quality of the part became a major factor. Therefore, it was necessary to develop new ways to surface finish all parts alike and in the shortest amount of time, energy, and economically. Hence, hand tools gave way to automated systems, except where work areas were too difficult for efficient abrasive tools and procedures. A number of different ideas were incorporated into technology applications to try to produce uniform finished parts, but most of these involved the use of abrasive materials. Abrasives were and are the main source of mechanical material removal systems. In talking about abrasive deburring and finishing systems today, we are talking about a great many different types of mechanical applications of abrasives and machine systems. All of the abrasive systems developed have certain advantages and disadvantages depending upon what has to be done to the part and the end result desired. The general basis of all of these systems can be narrowed down into three different categories of machine applications or how the media and energy force is used in relationship to the orientation of the part. That is, we know that size, shape, and composition of the abrasive affect the final results of a part, but the way in which the energy force is applied to the media and/or orientation of the part also effects the final results. Classification: Because there is no central engineering organization that wants to get involved with setting standards for determining all deburring and finishing systems, I created my own version of a workable system for clarification and understanding of these material removal systems. Before we begin to start to explain the equipment classification system, we also have to set some other parameters as to what constitutes a burr or rough surface finish. Therefore, our classification numbering system will cover the equipment involved, the size of the burr or roughness and where or how the parts must be worked to achieve the results desired. Instead of a single form of identification, we are talking about a number of separate systems combined to create a single three or four digit classification number. This numbering system works for all material removal systems, but it is not a good representation of extremely small parts under a half inch in size and that will be discussed at length because of special
  • 23. Chapter 2 - Classification 24 problems associated with size. Burr removal is functional or proportionate to the size of the part; therefore, although this system is good for parts above a half inch in size or larger there is a relationship to parts on a smaller scale. Again there is no precedence. The equipment classification system will be composed of a single 3 or 4 digit identification number. It will identify the energy system involved, the size of the burr or roughness of the part and the location of the burr or where the work has to be done. Because this information will be general in nature, to cover all systems, the classification system developed throughout this book will show a numerical range for the equipment and not a single digit number which can be developed for a specific machine systems. Then again, the size of the media also affects the amount and size of the material removal process itself; therefore, a numerical classification number also depends on the media being used and because of that, the equipment cannot be isolated to a single number. Type – Equipment Classification (first or first 2 numerical digits) To classify all deburring systems and equipment, we will try to keep it simple and say that there are perhaps five classifications, so equipment classification will begin with only the numbers 1 through 5. Even though I said I was going to keep it simple, there is an immediate problem. To classify all deburring and surface finishing systems, I have to start out with a Type 0 classification. This zero indicates that there is no equipment involved here and the work is done by a manual hand operation. The zero plus five makes a total of 6 classifications. Another problem here that needs immediate explanation is that some material removal systems use a combination of methods or processes which are hard to classify with a single digit classification; therefore, two digits may be necessary to properly identify the type of equipment involved. An example of this is water honing equipment systems that use a combination of water and abrasive; therefore, the number of this equipment begins with 42XX, which represents both a liquid and a blast type energy system. That means that our classification numbering system should be composed of a total of 4 digits, but in many cases only 3 digits will show instead of 4 because we have dropped any classification number beginning with a zero. Before we identify these 6 deburring systems in detail, there are some other important factors to consider that determine or effect the equipment. Therefore, let us look at the last two digits in our numbering system first. Burr Class (second digit from right to left) The next number in our classification number is a single digit that represents the class of burr. I have created an artificial size range, which is based upon a general thickness measurement and surface roughness based upon the RMS surface profile. Again, we start out with the same zero problem. This zero digit is done to indicate that there really is no burr, but a surface modification or finish is required or the determining factor rather than burr removal. The system classifies 5 categories of burrs and stops at an arbitrary thickness I think is appropriate. The zero plus five denotes 6 classifications of burrs and roughness.
  • 24. Chapter 2 - Classification 25 Burr Location (last digit to far right)) The last number in the classification number denotes the location of where the work is to be done or what area of a part is worked best by this equipment. This is a very general category, but there again is a relationship, which is important. Again a zero indicates only surface modification is required. The zero plus the three burr locations brings the total to four classifications. Explanation of burr class “Class 0” burr indicates that while no burr is present, some further mechanical or surface finish is required. In most cases this will involve burnishing or polishing, but textured finishes may also be called for either on grounds of aesthetics or to improve adhesive bonding. No assigned RMS will be given to this classification. “Class 1” burr will be considered any material with a sharp edge that may or may not be capable of cutting human flesh or a mating part or assembly. The equivalent surface roughness would be 0 to 8 RMS. I am concerned here with the cutting of wire, cables, or tubing over a period of time due strictly to weight, pressure, or movement against a sharp edge. Class 1 burrs can usually be improved or modified sufficiently in a polishing or burnishing operation to remove or modify the surface or edge enough so as not to create cutting possibilities. A surface finish or 0 to 8 RMS is extremely smooth and normally requires no surface improvement, but may require a polished reflective mirror finish. Jewelry and medical implants are common surface finished parts. “Class 2” is any burr or fragment of material that can be removed with ones fingernail and resembles thin aluminum foil. Class 2 burrs can be removed with fine abrasive methods. The equivalent surface roughness would be anywhere from 8 to 16 RMS. At or about a 16 RMS is desirable for a good quality plated part. “Class 3” is any burr that cannot be removed by ones fingernail and measures about .010 to .020 inches thick. Class 3 burrs require medium abrasive methods. The equivalent surface roughness would be from 16 to 24 RMS and is the range of most parts that require a thin film surface treatment. “Class 4” is any burr that is .020 to .032 inches thick and is not considered parent metal*2. This is relatively thick and rigid material and requires coarse aggressive abrasive methods. The equivalent surface roughness would be from 24 to 35 RMS and is generally not suitable for thin film treatments, but is acceptable for heavy thick coatings. ‘’Class 5’’ is any burr over .032 inches thick and is often referred to as parent metal. Parent metal is any material that cannot be moved by hand without the use of a tool or is something like a tear where the metal is distorted. Class 5 burrs should not be considered as a candidate for normal deburring equipment or methods unless a great deal of time is available to 2 Parent metal is hard to define because it changes in relationship to the material in question, but generally speaking it is a burr that can not be removed without excess multiple forces.
  • 25. Chapter 2 - Classification 26 work the part. In fact, class 5 burrs should be returned to the supplier of the part or machine center for rework. The equivalent surface roughness would be over 35 RMS, which is about the finest surface finish that can be achieved using blast type equipment and methods. This surface finish is good for all heavy thickness surface coatings. Burr Classification Class 0 burrs surface modification only, no burrs present. Class 1 burrs are sharp edges which can cut one’s finger or cut wire or tubing over a period of time and/or vibration. Approx. 0 to 8 RMS. Class 2 burrs are thin irregularities of material which can be removed from a part with one’s finger nail. Material thickness approximately 0 to .010. Approx. 8 to 16 RMS. Class 3 burrs material irregularities that require greater pressure than the unaided hand alone. Material thickness approximately .010 to .020. Approx. 16 to 24 RMS. Class 4 burrs or material irregularities that require a lot of pressure and force on media and part. Material thickness approximately .020. to .032. Approx. 24 to 32 RMS. Class 5 burrs exceed .032 in material thickness and RMS surface profile roughness. Not recommended for most deburring equipment or removal methods but RMS is good for surface preparations or coatings. Explanation of Location Before we leave the realm of burr classification, we should also consider a second number to indicate where the burr is located. To clarify that statement, we know in the manufacturing process of producing a part that there are normally specific problem areas that occur because of the way the part is produced. That is, we are concerned with burrs that occur either on outside or inside dimensions. Internal burrs are primarily caused by drilling; If the drill exits the part, they are considered outside burrs. As 0 above, so too do we carry a 0 for surface modification even though we do not specify a location it will be the same as 3 or all locations. The difference between 0 and 3 is that 0 will be surface profile improvement and 3 will be just for burr removal. The numbers are in the order of difficulty. Some deburring methods are better than others in working these specific problem areas. Burr Location 0 for surface modification only. 1 for outside dimensions. 2 for inside or internal dimensions. 3 for both inside and outside dimensional burrs. Explanation of equipment classification With the above information, we are ready to get back to our original intention of classifying all deburring equipment systems. These systems are based upon the application of
  • 26. Chapter 2 - Classification 27 energy in relationship to the part. The size, shape, and configuration of a part plays an important role in the selection of one of three abrasive deburring or finishing equipment systems, or the material removal systems based upon liquids or temperature. For the mechanical abrasive methods we will classify them as either a type 1, 2, or 3 system. Type 1 systems uses abrasives in a parallel plane, or the main energy force is in contact with a rotating transfer device that is controlled by pressure as it slides along the surface of the part. Type 2 systems involve air born abrasives that are propelled or transfer energy forces at an angle or perpendicular to the surface of a normally fixed part. Type 3 systems mix the orientation of the part and the abrasive to achieve a mixture of nearly equal energy forces in an x, y, and z axis movement under pressure. Because we are talking about all deburring and polishing systems, we must also include here, type 4 liquid or chemical systems and type 5 temperature modification systems which involves heat or cold. Equipment Classification Type 0 system is for manual hand working of parts only. Energy is directed downward and movement is back and forth or in a circular pattern with a fine abrasive. Type 1 system is for relatively flat materials where the energy force is directed down and parallel or horizontal in a wiping action to the materials surface via a wheel, disc, or belt. Type 2 system is used primarily for surface preparation or textured finish to take a heavy thickness coating. This abrasive blast equipment transfers energy force into solid abrasive particles which are air or liquid born and directed perpendicular or at a slight angle to the materials surface from a short distance away from the material being worked. Type 3 system is used in mass finishing type equipment. Energy is transmitted uniformly into abrasive particles or preformed shapes in a random combination or a mixed pattern of movements relative to free floating parts within the mass. Type 4 system is primarily a liquid energy transfer method directed through a liquid to help modify part burrs and surfaces. This can either be a pressure system, a molecular reaction system, or it can involve material transfer by an electrical current. Type 5 systems is an air based energy transfer method that uses extreme temperatures to help modify part burrs and surfaces.
  • 27. Chapter 2 - Classification 28 Fig. 1. Type 0 Systems Fig. 2. Type 1 System
  • 28. Chapter 2 - Classification 29 Fig. 3. Type 1 Systems, continued
  • 29. Chapter 2 - Classification 30 Fig. 4. Type 2 Systems
  • 30. Chapter 2 - Classification 31 Fig. 5. Type 3 Systems
  • 31. Chapter 2 - Classification 32 Fig. 6. Type 3 Systems, continued
  • 32. Chapter 2 - Classification 33 Fig. 7. Type 4 Systems
  • 33. Chapter 2 - Classification 34 Fig. 8. Type 5 Systems
  • 34. Chapter 2 - Classification 35 Equipment Type 0 system involves hand operations or the manual application of energy to the abrasive device. Hand labor normally orients and works parts in one direction or uses abrasives in a parallel plane to the material being worked for aesthetic reasons. By maintaining a rubbing action or energy force in the same direction as the part or in the direction of the greatest amount of material the abrasive or transfer device is more efficient than circular or cross movements. Generally speaking all manual processing methods do not normally produce fast, good looking, or smooth surface finishing results. Type 1 system is the same identical method used by the type 0 system except the task is accomplished using powered buffing wheels or belts to contact the part and this accomplishes the same results, but faster than hand labor operations alone. The wheel or belt systems use coated abrasives that travel over the part, or vice-versa, parallel to its surface. This movement produces a long continuous sliding stroke or contact pattern with the part. With the exception of pressure applied by the operator, less human labor is required and therefore processing is normally faster with better results than type 0 systems. The amount of material removal of type 0 and 1 systems is controlled by the amount of pressure exerted on the transfer device and abrasive. For material removal, rigid systems work best, but are hard to control. In both systems, flexible methods are usually favored for the control factor and for polishing. Flexibility allows for more surface coverage, over lapping patterns, orientation of the part, and the transfer device. It should also be noted that any long fiber, grain, filament, or any fine abrasive with broad flat grain orientation will generally produce more smoother, lower RMS, or shinny parts. Type 2 systems are often called cleaning systems but are used mostly for surface preparation treatments for coatings because they can produce the roughest surface profile which is good for adhesion of paint and other heavy thickness coatings. In fact the finest surface finish that can be achieved using this technology is only around a .032 RMS. Other benefits of blast type systems is that they can also be used to stress relieve and work harden the surface metal of parts. With the advent of air pressure equipment, abrasive blasting became and still is a very popular means of surface modification. In type 2 systems, the main energy force is transferred to the abrasive that becomes air born and propelled in a controlled concentrated blast pattern a short distance from the part being worked. Even though we have stated that these systems apply force nearly perpendicular to the part orientation, the angle can vary to incorporated any angle to the part, but the optimum efficiency angle is about 60 degrees. In a number of automated or semi-automated systems the parts are in a fixed position. Movement of the part or abrasive orientation is also within the realms of this definition. Type 3 systems are very flexible systems. Unlike the above systems that basically work with stationary flat oriented parts, type 3 systems do not require any prerequisites for handling or fixturing of the parts being worked. Parts can move freely within these systems and the equipment can use both loose random abrasives and/or preformed shapes in different sizes, shapes, and compositions. Because of the multi directional energy forces, pressures and part
  • 35. Chapter 2 - Classification 36 versatility, these flexible systems accomplish normally faster more uniform results more economically. In this category are machine systems that rotate, shake, spin, and vibrate. Generally speaking, these processing methods are considered mass finishing systems, because they can accommodate a batch of parts in a work chamber with no special handling or orientation. Mass finishing systems then refers to the batching of parts in mass in a machine or work chamber with abrasives. Type 4 systems cover a range of technologies. Energy and force are not directed or transfer to another media, but is the result of molecular reactions or electrical movement. In its simplest form, it can be nothing more than a liquid tank of water; however, normally a chemical additive is required to create molecular movement. If that chemical is concentrated, it can cause a reaction that will affect the sub atomic molecular structure of the material in the solution. Typically in the plating industry, a controlled electrical current is introduced into a weak solution that assists in transferring material coatings or to remove material. If acoustics are introduced into the liquid to produce ultrasonic cavitation then the mechanical energy forces or movement of molecules increases the effects of the chemical media. Lastly, water under high pressure, liquids can be used to use to remove material. Type 5 systems use air and extreme temperatures. Mostly we are talking about extremely high or low temperatures. Extreme temperature processes create a condition outside the normal characteristics of the material being worked and that makes it easier to remove the irregularities. Heat can be used as a medium in a special piece of equipment designed to contain a controlled mini explosion which melts or burns away fragments of material. On the opposite side, there are other systems that use extreme low temperatures that freeze fragments to make them brittle so that they can be removed more easily using some additional movement or abrasive methods. Deburring equipment and technology have advanced rapidly over the last several years; however, this has not been the case in past history. Up until the late 1800’s processing methods were slow to change from their introduction because labor was very cheap up until the mid nineteen hundreds. As labor costs continue to increase more than the material costs they stimulate new processing innovations. Now systems have changed and evolved over the years in cost and speed of operation. There are now so many deburring and polishing systems that one needs a score card to understand and determine which is best finishing system for what end product. Hopefully, this information will help you with that determination. There are many options and methods of deburring parts that are being used and each method or system has advantages and disadvantages; therefore, the knowledge of these alternatives can help one decide the best method or alternative equipment to use given the proper circumstances and/or resources available. However, mass finishing systems are probably the most versatile of all finishing systems because the abrasive media and equipment are so diverse; therefore, this book will go into great detail on all mass finishing systems. However, just briefly, there are now three basic types or generations of mass finishing systems that go under the type 3 classification and that needs a little explanation. These finishing systems are referred to as the 1, the barrel, 2, vibratory and 3, high energy centrifugal systems, and to some extent there is a fourth related technology system called drag or spin finishing systems.
  • 36. 37 Chapter 3 – Type 0 Equipment Alternative Deburring Systems Hand-held tools and mechanical systems used to improve surface finishing were of no significance until the introduction of steam power. Crude and cumbersome drives allowed for limited material removal by turning rather large abrasive wheel and belt contact systems. It wasn’t until the introduction of electricity and pneumatic air systems that the use of type 1 power tools became wide spread in the deburring industry. With the introduction of more complicated part designs and functional requirements, plus standardized parts, automation, and light weight portable tools, did productivity demands have a significantly effected on finishing operations and the popularity of type 2 and 3 systems. Even with the advent of powered deburring tools, the surface or edge finish of a product depended upon the control of the tool by the operator, who decided what size, type, and pressure to apply to the abrasive system and part. Most finishing operations are considered dirty and supposedly do not require a lot of technical knowledge and because of that, work has been delegated to the some of the most inexperienced workers. Unfortunately the human factor effects the elements of pressure, speeds, and replacement tools and all of these elements effect mechanical surface finishes. Sometime, the logic of some very complicated expensive parts delegated to some of the most inexperienced operators leaves a lot to be desired. In addition to working the parts, the human factor is also involved in the visual inspection procedures. Without standard of acceptability, that also means that most parts can fall within a wide range of surface finishes and/or profiles. Most companies are more interested in precision dimensions than surface finishes; however, as production quantities continue to increased and become more common place, product uniformity and consistency demands also increase. Without adding more and more people to meet these demands, most industries chose less and less work that is not machine automated. For the repeatability factor, mass finishing systems are perhaps the best and cheapest way to produce uniform surface finished parts in volume. Other alternative deburring systems may still be required to work some difficult to reach areas, but mechanical abrasive systems seem to be the basis of most material removal systems. Upon reviewing the various deburring and finishing systems in use today, one encounters many variations of the same systems we have classified. Each system has strengths and weaknesses based upon a range of part sizes they can accommodate as well as production volume based upon size and time. The classification system developed effectively sets limits that reflects the manner in which the abrasive or medium utilizes energy input in relation to the material removal rate and the parts orientation to produce specific surface finishing results. Initially, I tried to organize alternative deburring systems into a logical progression from the relatively simple to the more complicated systems. In this order most equipment systems will usually give you some idea of costs, but technology and equipment accessories can get involved and effects costs radically, especially the addition of automated material handling
  • 37. Chapter 3 – Type 0 Equipment 38 systems. Therefore, simple systems can get quite complicated. This section will try to be a brief glimpse of equipment and processes to compare material removal rates or surface modification with mass finishing systems. Hand Tools: This category of deburring tools takes on two sub-headings. They are manual and automatic. I did not break down automatic into semi or full automation. In most cases, parts to be worked still have to be loaded and unloaded somehow; therefore, although the equipment performs an automated function, the positioning and handling is not considered automated. Truly automated equipment normally includes self loading and unloading systems. Manual Systems: The manual systems for deburring involve the use of physical manpower for its primary energy source. That is, it requires a human to apply pressure to some form of tool to abrade or polish some object which he holds or fixes in place. Then again, the tool can be fixed in place and the part can be pressed against the tool. These systems are probably the oldest, most time consuming, reliable, and maybe still the fastest of all metal removal systems. However, besides fast and reliable, manual systems are also probably the least accurate to control because they rely on the human factor and that is also true of all power tool systems that are not automated. Repeatability of pressure, contact, time, and coverage can only be accomplished by automation; however, even with power tool systems the application device does wear out and changes its material removal performance characteristics with use. Therefore hand and automated tool systems quality or finish can vary from piece to piece and operator to operator over the same given period of time. The most common tools in this manual category are the file, rubs, abrasive discs, belts and/or sand paper. These hand methods can handle a wide range of from 0 to 5 type burrs in our equipment classification numbering system. In addition to these popular contact devices is a relatively new tool called an edge deburring or swivel tool. I will start my classification system with this swivel deburring tool, because it does not fit a logical progression of hand tools. This is a type 0, manual hand-held tool equipment classification. Using our burr classification system, this device can only be used on class 1,2 and maybe 3 burrs and only on outside #1 locations. That makes this tool a Type 0 system, with a maximum burr classification of 3 in location 1, or is a 001 to 031 class tool. This hand-held edge deburring swivel tool is nothing more than a handle with an irregular bent shaped sharp squared off or sharp edged heavy carbide metal wire that is capable of swiveling to the contours of the part to be worked and the force applied. It is something like a file, but it maintains its position on the part by itself by way of a ball or bent hook like end piece upon which pressure and contact are applied. Normally the operator of the tool holds the part in his other hand so that he can turn the part and keep the tool on the edges of either holes or the O.D. edges of the part. If you noticed, actually pressure is applied in two directions simultaneously; therefore, some dexterity is required to operate this tool. While with hand held
  • 38. Chapter 3 – Type 0 Equipment 39 sand paper or a file, pressure is usually applied in only one direction, or backward and forward or in a circular motion over the same path using more energy than the swivel tool. Fig. 9. Manual Hand Deburring Tool This is a hand-held tool that is used to deburr the edges of a part. The tip or blade of the tool swivels freely as it is pushed or pulled by the operator along the edge of the part. Because of the configuration of the carbide tip, it tends to drag along the blunt edge of the part thereby shaving the sharp edge of the metal. Most of these tools have inter-changeable tips for multi function jobs. Because hand tools such as the file and sand paper have been around so long, I don't think it necessary to go into any explanation of these tools. However, I will say that new developments in bonding techniques for abrasives in wheels, coated belts, and new fiber materials, plus artificially made synthetics have made significant improvements to hand tool products and accessories. Synthetic materials have especially improved the cutting ability, life, and performance of all of these devices. This book and classification system will not cover any of these manual systems, but they do fall within the limits of a 2-digit classification system such as the swivel tool.
  • 39. 40 Chapter 4 - Type 1 Equipment Automation: Probably the most labor intensive and most popular form of deburring in use today are wheel and belt systems which fall under our type 1 equipment systems. This type of equipment covers the widest range of part burrs, hence its popularity. The reason for this is because these systems use direct pressure and contact between a mechanical power or energy source, the abrasive tool or transfer device and the parts being worked. Based upon our classification system, this equipment handles 0 to 5 burrs in type 1 locations. Actually these systems can probably work burrs a lot rougher than our classification range of up to 5; however, this is excessive and inefficient use of manpower. Using our numbering system, this type of equipment is normally designated a 1 and handles burrs 0 to 5, in location 0 to 1, or they have a classification range of from 100 to a 151 system. Note, the above classification is again general in nature, meaning that most applications fall within this common realm of O.D. or surface profile applications. There are other variations, such as small I.D. wheel systems that would be considered an equipment classification of up to 153; however, these systems are not within the normal application of this system. Most internal deburring wheel systems are not as universal or easily dedicated to work all variations of I.D. holes and have a very limited size range, because of the hole size and environment in which they have to work. The more rigid the abrasive tool or system, the greater the material removal rate given the same pressure. That means that coated inorganic belt or rigid disc systems are much more aggressive and can handle the upper limits of this classification better than can most organic or synthetic wheel systems. That also means that belt and rigid disc systems are used primarily on flat parts and outside surfaces. Organic wheel systems on the other hand can lap or polish parts better because of the flexibility of the wheel. Also, because of the flexibility factor of most organic wheel systems, they can handle both a portion of inside holes and outside dimensions as well as a wider range of part shapes and configurations than can belts. Versatility sometimes over comes speed. Wheel and Belt Systems General Information I call wheel and belt equipment, forms of automated deburring systems, but in reality they are more comparable to a hand tool. The only difference is the power source. That is, energy is applied in some fashion to a rotating wheel and pressure is applied by a person to the work piece, by hand, against the wheel or belt, or vice-versa. The industrial terminology for hand-held work piece processing is called “off-hand,” because the work is done off one’s hand. It is the person or operator who determines, by one's pressure and manipulation of the work piece in relationship to a fixed position wheel or belt, the time in which the work will be accomplished and to some extent the quality of the finished product. Hand-held tools are not considered off-hand work, because the hands are not controlling the part, but the power tool
  • 40. Chapter 4 - Type 1 Equipment 41 device. Because of the human factor this type of equipment is not a truly automated system, but it is still a great improvement over a manually powered hand operations. Semi-Automatic Wheel System The machine system shown here is a basic double axial buffing machine, which has a centrally located energy power source for rotating the wheels. In this case it is used for buffing, but abrasives or solid non-woven or filament wheels can be used on this machine for deburring also. I call this system, semi-automatic because it requires manual material handling and finishing techniques. Fig. 10. Semi-Automatic Wheel System Do not under estimate the human factor. A skilled operator who knows and understands the mechanics of pressure, loading, and/or the flexing of wheels and belts can normally out produce a fully automated production line. Also, nothing seems to match the quality of the surface finish as a good hand buffed part. A hand buffed part is still the industrial standard by which all other processes are measured. All other methods and systems use or compare their best surface finished parts to a hand buffed part.
  • 41. Chapter 4 - Type 1 Equipment 42 Speeds/Energy Source I suppose any electric motor can be fitted with any abrasive wheel, belt, or polishing buff to work parts. But a lot of motors cannot hold up to the side pressure or end-thrust energy forces exerted on the motor bearings by the wheel system by an operator; therefore, there are a number of factors and operating conditions required for selecting a good motor. Most stationary or hand-held wheel systems are heavy duty ball bearing motors that operate between 1200 to 3600 RPM. However, more important than RPM maybe the horsepower and bearings of the motor. The speed at which a wheel turns or RPM’s relates to energy transfer and/or friction and heat in most cases. Side pressure created by hand pressure of the part against a moving wheel can affect the speed of rotation and bearings significantly. Without sufficient horsepower, one may actually stop the wheel from turning completely by applying too much pressure against the rotation force. Such a situation is not good for the part, the operator, the motor, or production. Therefore, motors or equipment should be reviewed for adequate horsepower and the application. An important factor to consider besides the RPM of the motor is the speed of the outer edge of the contact device. That is, the speed of the motor turns a wheel that is larger than the shaft of the motor; therefore, the size or the diameter of the contact device in turn translates into a higher RPM rate of speed than the motor or linear feet per minute. A 2400 RPM motor with a 12 inch wheel will produce a linear rate of travel or turn at twice the speed of a 6 inch wheel on its outer edge. The optimum speed of most wheel and belt systems is approximately 1000 surface feet per minute. The processing cycle time to produce an acceptable part is determined by the roughness of the part, the pressure applied to the belt, the abrasive used, and the desired end results, which can be expressed as follows: 1. Force or applied pressure x the distance traveled or surface feet per minute = energy input. 2. Amount of material remove = energy input. These equations relate material removal to energy input. They do not deal with the time factor, which can be related to: 3. Rate of energy transfer = surface feet minute x pressure or force. Cycle time is then inversely proportional to the linear surface feet per minute and the applied pressure or force. That means that the temperature limit may be reached by the operator, the abrasive, or the material, well before the part is complete. Heat Gain All type 1-equipment systems transfer energy from the motor RPM’s to the contact device and then into the part in the form of heat. Too much pressure or temperature will adversely affect the color or appearance of a part and may change the hardness of the metal being worked. At extremely high temperatures, metals can oxidize and react like parts being
  • 42. Chapter 4 - Type 1 Equipment 43 heat treated, resulting in either work hardening or loss of temper. In fact, the subject of grinding, which we are not going to classify or explain, is designed for large amounts of material removal. This equipment uses a multi pass means of lapping and liquid quenching the part because of the heat transfer problem. As mentioned, the optimum speed limit of most motorized belt deburring systems today is equal to about 1000 surface feet per minute. The speed or cycle time of the operation is also determined by pressure. That is, to achieve the desired end results, one has to remove the burr or material to an acceptable condition. The more pressure you place on the work piece against the wheel or belt the shorter the time cycle for the burr as well as the belt or wheel. However, too much pressure can also cause problems and/or over correction, rework, and possible damage to the transfer device, the work being done, and possibly the operator. Another limiting factor for wheel speeds are the formulated dressing, lubricating, and abrasive compounds that are used primarily on the organic fiber wheels. These compounds are designed to deburr or polish and operate within a certain temperature range that is indirectly controlled by the RPM speed at which a motor operates. As mentioned, pressure of the part against the wheel system by the operator determines the amount of material removal and the friction or the amount of heat generated, which is transferred to the part and operator. That heat problem means that an abrasive or buffing compound used on a wheel system must be formulated or selected to hold and transfer a proper mix of abrasive and lubricant to work the part properly and that depends on the material and the finish desired on the part. Belt systems don’t have the same exact problems as wheels, but they can to a limited degree use lubricant compounds. On wheel systems, low temperature compounds may not hold the abrasive in place to work at high speeds and pressure, whereas high temperature products may not adhere to the wheels at slow speeds. Because belt systems are rigid, the heat can cause either an adhesion problem where it can load up with debris or it will lose its own abrasive and can become an ineffective abrasive tool. For every action, there is an equal and opposite reaction. Energy transfer is one of these reactions when type 1 equipment is involved. Besides the heat factor, vibration is also being transferred to the operator and the part. As mentioned too much pressure can produce too much heat and that will affect the operator, the tool (wheel or belt), and the part as well. The heat factor refers mostly to relatively small to medium sized parts. Parts larger than a person can handle in weight or length requires a fixtured tool or part plus a material handling system; therefore, heat will not normally affect the operator, but the operator can affect the metal part. Typically, burrs are on the outside edges of parts, and wheels and belts only work a relatively small amount of material or surface area; therefore, heat is not normally a factor. However, to work a large flat surface, especially buffing operations, heat is a major factor. If a small hand-held part becomes too uncomfortable for a person to hold, he can't properly control the part's surface finish. Also, if that operator presses too hard on the abrasive wheel or belt, he may damage or compromise the transfer devices performance factor. That is, if
  • 43. Chapter 4 - Type 1 Equipment 44 too much pressure is applied, a wheel will lose its uniform integrity and cease to work properly and a belt will load up with the material being removed. Normally, using a light amount of pressure on a proper wheel or belt will provide a quick good clean abrasive surface finish. Too much pressure will create a glazed uneven coating on the transfer device and part and slow down or stop the material removal system. If this happens to belt systems, the best thing to do is to change the belt, but sometimes wheels can be re-dressed. Operator technique and a proper balance of speed and pressure are required to accomplish a good surface finish or deburred part with type 1 systems. Heat Loss Just as there is a rise in temperature due to the conversion of mechanical energy into thermal energy due to friction, there is also dissipation. The three main ways to lose heat are through conduction, convection, and radiation. To understand these methods, one can, to some extent, overcome one force with that of another. Conductive Heat Loss: is the process of energy transfer through that which is in contact with the energy source, which is primarily another solid. Heat will migrate from its source and will seek a balance within the material being worked to its ambient environment; therefore, it will to some extent dissipate some of the heat within the part or material itself. If the part is in contact with the transfer device, some of the heat will go into this device as well as the part. Also if there is a work platform, this too will absorb some of the heat. Other conducting factors that affect heat transfer are the materials being worked, the size of the part or its surface area, and to some extent the characteristics of the abrasive product itself. Those materials that conduct electricity also seem best for conducting heat. Copper and aluminum are well known for their heat conducting properties. Some abrasives that break down fast can carry away a lot more heat than more cohesive materials, Also, the more and the larger the size of the material removed, the better the heat transfer away from the part being worked. Convection Heat Loss: is the heat energy transfer through air, a liquid, or solid. When a transfer device is in operation, it does so in an ambient environment of air. The density and weight of a solid effects the immediate molecules of air that indirectly passed on to that heat energy to the surrounding air to a lesser degree. That means that the less denser air around the work being performed is effected by the transfer device and it too absorbs heat. To increase the efficiency of convectional heat transfer, water or liquid may also be used. The physical geometry of the part itself also plays a part in how it holds or losses heat. A thin flat part, like a heat sink which are specifically designed to loss heat, losses more heat faster than a solid cylinder or rod, because the surface area is less. Therefore, the configuration of the part or surface volume plays an important factor in heat transfer into the environment. Radiant Heat Loss: is similar to convection heat, except it is primarily air born energy transfer. Radiation is a transfer method not necessarily effected by the physical movement of molecules, such as cohesive effect and movement of air around the transfer device or a
  • 44. Chapter 4 - Type 1 Equipment 45 movement caused by the pressure of heavier to lesser density of air created by the density of molecules as they expand. Heat transfer by radiation is actually more like a atomic molecular transfer of heat, similar to or almost like a chemical chain reaction without physical movement. Human Factors The effects of heat and vibration on the human operator are important elements of both a positive and negative nature. On the positive side, a good operator can out produce and is more flexible than a fully automated belt or wheel system. On the negative side, a poor operator can damage equipment, parts, and himself. The human operator must be considered to be at least 50% of the overall performance of type 1 equipment where material handling is absent. That means that most wheel and small belt systems are primarily controlled by the operator from start to finish. That also means that the working environment is an important factor to be considered. Operators are exposed to a number of physical stresses related to this equipment. Safety from heavier debris and the close proximity to the rotational force are inherent dangers that one must expect to face using this equipment and precautions and care should be taken when and where possible. Prolonged and constant handling of parts and pressure can cause white knuckle or carpal tunnel muscle related physical symptoms in humans. Also, in proper air and dust collection systems can cause lung related illnesses, all of which can incapacitate a human; therefore, operator comfort is not so much a luxury as it is a necessity. Variable Factors Because of the speed at which a wheel or belt system operates, a lot of material can be removed in a relatively short period of time. Of course, the amount of material removal has a lot to do with the type and size of the abrasive wheel or belt used. That makes these systems very versatile and capable of handling all types of burr classifications. However, it should also be known that there are some variable factors that also cause slight variations that effect surface finishes using these systems. A new rigid wheel or belt, before it is broken in or used for production will operate more aggressively before it stabilizes. That is, it will remove a great deal of material and produce a rather rough finish in comparison to parts worked by this same system a short time later. This difference is more noticeable on belt system than on wheels, because most flexible wheels use what are called a rouge or lubricating sticks to coat or treat the wheels which effect material removal. Belts on the other hand already have the abrasive added to the contact device. Rigidity or stiffness of a transfer device tool initially increases contact pressure; therefore, the amount of pressure to the work pieces needs to be constantly increased over the life of the tool to maintain the same cutting or deburring rate and surface appearance of the part. In either case, there is a noticeable difference in first piece parts versus a part taken from production at a later time in either a fully automated system or parts done by hand. Because of this known problem of uniformity or surface finishes, most first piece parts are often set aside and then reworked with this same tool after the wheel or belt is broken in.
  • 45. Chapter 4 - Type 1 Equipment 46 As a wheel or belt is used, there is still an ongoing break down of both the abrasive particle size on the transfer device tool and the material being worked. Again, this effect is more noticeable on belts than flexible wheel systems, because you are normally always adding an abrasive paste to a wheel whereas a belt uses up what it has. Debris In any mechanical abrasive process there is an end product, that being a finer surface finish of the materials you started with. With the exception of precious metals, most of this finer end product of metals and abrasive is completely useless and has no value. In fact, it is a liability and/or necessary evil. If abrasives don’t break down, they don’t work. If parts don’t conform or function properly they don’t work properly. Therefore, the whole principle of deburring is based upon negativity, or the negative destruction of both the media and the excess material or burr to achieve a good positive acceptable result. The debris created from deburring operations has to go somewhere. In most cases the heavier particles fall on the floor, but a large amount of the debris is so fine that it drifts in the air around the work area and in some cases, some gases can be given off from the materials being worked or the abrasive binder. In large amounts of volume to air ratio, or given a little amount over a long period of time, this debris material can become hazardous to one's health. Therefore, pre-cautions are necessary in a work environment to protect the employees. That means that the operator and those nearby should wear a protective air filtering device to protect their health, and/or a dust collection system should be installed near the machinery work area to suck out and vent the contaminates to a safe collection source. Size/Diameter As mentioned above, the wheel or belts selected to perform material removal plays an important part in obtaining the desired results. Solid rigid wheels and belts made of inorganic materials seem to cover a wide range of abrasive grit sizes and use different bonding agents in their composition. These transfer tool devices can vary in diameter but are relatively thin in relationship to the material to be removed because of the heat transfer problem mentioned earlier. Most standard off the shelf rigid inorganic wheels are relatively thin and under 1 inch in thickness. If they are thinner than 1/8 of an inch and solid they are known as cutting wheels. Some solid wheels can be up to 2 or 3 inches in width, but this is not common. As a contact device surface area increases so too does heat transfer become more of a problem; therefore, it is usually easier to work with small surface areas than larger contact systems. This smaller size also permits working more detailed areas of a part and normally greater flexibility of part sizes. Besides rigid inorganic wheel systems, there are both organic and inorganic composite or flexible filament wheel systems. The flexible inorganic composite systems can be made to handle very wide parts with some minor contours, but they are mainly used for flat sheet metal parts with a lot of shallow holes or special applications. These automated deburring machine systems work and look something like a street sweeper, but the parts pass through a series of
  • 46. Chapter 4 - Type 1 Equipment 47 abrasive rotating wheels on both the top and bottom sides of the part as it passes through the machine. Adjustments can be made to the brushes to apply the proper pressure for surface finishes and compensate for brush wear. Most of these brush type systems use water and cleaner to properly process parts. Like any machine with moving parts, the machine is completely enclosed, vented, and in most cases uses water to control dust and temperature of the parts and the environment of the operation. Automated Abrasive Wheel Deburring System Most common automated deburring systems are designed for processing relatively flat sheet metal parts and/or in-line production. Also, due to the violent nature of the material removal process and energy forces at work, a lot of these systems are designed to be run wet in order to keep dust and debris confined. In fact, most machine systems are completely enclosed for safety reason so no human can come in contact with any of the moving parts; therefore, little can be seen of the actual wheels and mechanisms that do the work as seen in the following machine systems. With few exceptions and because of costs, most machines are built or dedicated to in line high volume production or parts that are relatively similar in size because adjustments, other than the deburring wheels, to such a machine is costly due to down time and tooling. Fig. 11. Automated Abrasive Wheel
  • 47. Chapter 4 - Type 1 Equipment 48 Fig. 12. Automated Abrasive Wheel Machines Below are two versions of in-line abrasive wheel systems. The normally larger “dry” system is used for deburring or polishing machined parts that have more surface variation. The smaller “wet” systems are used for sheet metal parts, or in this case printed circuits. In a number of cases units can be made to use both dry and wet technology for processing parts. This can also include provisions for cleaning and drying parts. Fig. 13. Dry system
  • 48. Chapter 4 - Type 1 Equipment 49 Fig. 14. Wet system Some automated belt deburring systems can also be made to be very wide and can move or feed parts. These systems have greater heat transfer problems than the wheel systems because there is more contact area than the brush systems. However, in most cases no human touches the part until it comes out of the machine and this heat is dissipated relatively fast. Care is still required in handling these parts. The main problem of these machines is the fast accumulation of debris and the need for frequent and proper cleaning. It should be noted that fires and explosions have been known to occur in cases where poor maintenance is practiced. Most of the big automated belt systems are designed to handle large sheet metal parts 3 or 4 feet wide. They also have the ability to control the amount of pressure or tension on both the top and bottom rollers, as well as the backup padding under the belt to effect surface texture, on the part as it moves through the machine. Because of the amount of material removal most of these large belt systems have dust collection systems built into the equipment to collect debris particles. Optional wet systems are also available and that helps cut down on a lot of the debris problems.
  • 49. Chapter 4 - Type 1 Equipment 50 Automated Abrasive Belt Machines All automated abrasive belt systems can only process flat 2 dimensional sheet metal parts. These systems are capable of deburring the top and bottom of holes in relatively thin sheet metal and they leave a textured grain appearance on all parts. The main feature of these machines is their wide abrasive belts and their in-line adjustable pressure sensitive conveyors. Shown below are both the dry and wet systems. Fig. 15. Dry system Wet system Probably the fastest high-speed material removal system is accomplished with solid inorganic rigid wheels. However, most of these wheels are not used in offhand applications. That is because it is difficult to maintain a consistent, even pressure between the wheel and the part without mechanical assistance. Hand-held parts will cause rigid wheels to bounce or chatter against a part and results in a rough and possibly irregular surface finished part. This condition is also a safety issue to the operator; therefore, most of these systems are automated so that constant pressure can be applied to both the part and the wheel. As mentioned, greater resistance causes greater heat; therefore, most of these automated solid inorganic rigid wheel type systems use liquid lubricants to speed up processing by maintain proper working temperature and to remove debris. These systems do deburr, but are more commonly used for what is called lapping or grinding a part to a specific thickness. The term lapping is used to indicate a multi step, back and forth, movement or layering process to remove small amounts of material until the desire thickness is achieved. I mention these grinding wheels here, but I will not go into a lot of detail on them. They are not part of standard deburring or surface finishing practices. But, because they do remove material they should be mentioned. Usually these systems produce a very smooth, flat surface finish or work type 0 burrs. This type of operation is not normally used for mass production
  • 50. Chapter 4 - Type 1 Equipment 51 because parts are usually handled one at a time. There are some flat disc lapping machines with multiple spindles that can do large volume production; however, parts are still feed one at a time into the machine. Therefore, this type of equipment is not common in high volume parts production unless dimensions are critical to the part's performance. These machines are normally used for making precision part's rather than to do deburring. Non-woven There is a relatively new category of light weight solid wheels and belts which are used for offhand applications called non woven products. These are very abrasive materials and are composed of both organic and inorganic materials. Because these products can be very aggressive and don’t load up with debris they are used on up to a type 3 burr, but they can also work other lesser burrs. These non-woven abrasive products are composed of synthetic polyurethane fibers in a flexible foam like fibrous composite imbedded with inorganic abrasives. Non-Woven Material Systems As abrasive go, non-woven products are a relatively new comer to the deburring industry. This material is composed of minerals, resins, and fiber that are made into wheels, sheets, belts, and other composite materials. The formulation provides great rigidity and flexibility for a very effective and efficient abrasive medium. Fig. 16. Mineral, Resin and Fiber: Synthetic fibers and abrasive particles are combines and bonded to form a conformable, three-dimensional, open-web material Surface Finishes Mineral type A A A S Grade Course Medium Very Fine Super Fine Finishes Generated (Micro-Inch Range) Aluminum Stainless Steel 130-150 62-72 80-100 32-40 16-35 6-12 8-12 4-6 Coated Abrasive Grade Equivalent 80-150 150-180 220-320 320-600
  • 51. Chapter 4 - Type 1 Equipment 52 These non-woven wheels are made with different percentages of abrasives as well as different abrasive particle materials and sizes. Naturally the finer and softer the abrasive, or the smaller the percentage of abrasive in the wheel the finer the surface finish. These wheels are normally always run dry and they produce less heat to the operator in offhand production than do the inorganic solid wheels. Non-woven wheels are basically solid and rigid, but they have some flexibility to them that gives them better off-hand control than other inorganic rigid wheels. Also, because of the rate at which the wheel breaks down, they produce more dust or debris and that carries away more heat, which is transferred into the debris. Non-woven products have greater rigidity than most fabric or flexible brush type wheels but the material characteristics of this type of abrasive material also gives them greater contact control and contour flexibility. This semi cushion type quality allows the operator to get more coverage and better pressure and/or performance of material removal and surface finishing of the part. That means that less heat, energy, and vibration are transfer to the operator than with inorganic rigid wheels, bit less than flexible organic wheels. Depending on the part in question, these wheels probably remove as much material in the same amount of time as some coarse grit solid wheels, but hardness of the material or part does play a big factor in this generalization. The biggest advantage of the non-woven wheel is that it won't load up with the work removal material, because it breaks down at a relatively fast rate and as mentioned, they do produce a lot of dust and material debris. There are tradeoffs. Filament and wire In talking about inorganic composites, we were talking about basically rigid wheels. There is also another category of inorganic wheels, which are considered flexible brush and are not non-woven. The flexibility of brush wheels is a direct result of the construction and density of fiber materials in a radial pattern. That is, most of the wheel is composed or encompasses a greater portion of air than actual filaments. These fibers or strands can be made from metallic wires, and abrasive filled nylon or polymeric composite materials that are extruded. These materials are then cut to length, shaped, formed and/or crimped, and then fastened in a radial or straight pattern configuration series or uniform rows of fiber. Fig. 17. Deburring Wheels
  • 52. Chapter 4 - Type 1 Equipment 53 Fig. 18. Filament Brush Systems Most industrial filament brushes are made up of individual strands or filaments in a radial or circular construction, but reciprocating flat brushes are also available. Filaments are made from straight or crimped cut metal wire, encapsulated wire and polymers, or non-metallic composites of abrasives and polymers of round or rectangular shape filaments. Because of the wide variety of materials and sizes, a simple wheel is very complex; therefore, the following is terminology, specifications, and application information. (a) Geometry of conventional circular filamentary brush, (b) wire filament geometry, and (c) nylon/abrasive filament geometry. Fig. 19. Filament Geometry
  • 53. Chapter 4 - Type 1 Equipment 54 Fig. 20. Brush Characteristics
  • 54. Chapter 4 - Type 1 Equipment 55 The advantage of brush filaments is that they bend under pressure and this again helps the operator to have better control of the wheel and the part. These wheels are better at working recesses than non-woven products, but are still not good on parts with a lot of deep recesses and holes. That is because the actual deburring work is done at the end of the filament or that portion of the filament that is in contact with the part. Basically, if the fiber is flexible enough, it can and will drag along the surface of the part creating an overlapping uniform smooth pattern. Filament and wire wheels are also used to create textured artistic patterns on primarily metal parts. Naturally, the straighter and thinner the filament, the more flexible the brush and the softer and finer the material removal pattern. Also, normally the fewer the number of filaments the softer the wheel. On the opposite side, the thicker the filament or the greater the number of filaments, the greater the rigidity and the more material removal capability; however, to increase stiffness, some wire wheels are composed of knotted or twister groupings or bundles of wire. As mentioned earlier, new unused wheels or flatter, squared off end bristles remove more material or work faster before they are properly broken in. Speed or RPM’s of the wheel and size are also important considerations. In addition to the actual material specifications of the filament is the pattern or how the filaments are held in place and how they are grouped in different pattern variations. Besides wheel brushes are cup, end, internal, wide, and maybe very small micro brushes. Each of these brush systems are constructed or fabricated to perform different functions and/or work specific application problems. The older and more common brush wheels used for deburring are made from metal wire and the most common shape is called the circular or radial brush. The following are recommended applications.
  • 55. Chapter 4 - Type 1 Equipment 56 Filament Power Brush Material Applications Of the 5 basic types of filament brushes, there are 4 charts and/or recommendations based upon work piece materials. Wheel an d wide brush charts are used interchangeably. (Courtesy of Osborn Brush) Wheel Brush Selection Guide Matching the WORKPIECE material to the brush material End Brush Selection Guide Matching the WORKPIECE material to the brush material The Best Brush Material Is: The Best Brush Material Is: CRIMPED WIRE Aluminum Brass Copper Iron Plastic Steel Stainless Steel Wood Steel OK OK Stainless Steel VG OK OK BC OK OK NR BC NR OK NR OK BC OK Nonferrous OK BC BC OK VG OK OK OK Steel NR OK OK BC NR BC NR OK Stainless Steel NR OK OK OK NR OK BC OK Nonferrous VG BC BC OK VG OK OK OK Aluminum Brass Steel NR VG Stainless Steel VG VG Nonferrous VG BC BC Steel NR NR Stainless Steel NR NR Pliant Polymer KNOTTED WIRE CRIMPED WIRE Copper Iron Plastic Steel Stainless Steel BC BC VG VG NR BC NR NR VG BC NR OK OK OK NR BC NR BC NR NR VG NR VG BC NR NR NR BC NR BC BC Rigid Polymer NR NR NR BC NR BC BC VG VG VG VG BC BC BC BC BC BC BC VG BC BC KNOTTED WIRE TY® ENCAPSULATED WIRE TY® ENCAPSULATED WIRE Pliant Polymer NR NR NR BC NR BC BC NR Rigid Polymer NR NR NR BC NR BC BC NR NATURAL FIBERS NATURAL FIBERS (With Abrasive Compounds Only) Tampico- Treated Tampico Untreated VG VG VG OK VG - Treated VG VG Sisal VG VG Nylon OK Abrasive Nylon BC BC BC OK VG VG VG OK OK BC BC NR SYNTHETICS OK OK BC NR Abrasive Nylon OK OK NR OK OK OK OK BC BC VG VG BC BC VG SYNTHETICS
  • 56. Chapter 4 - Type 1 Equipment 57 Filament Power Brush Material Applications, continued Cup Brush Selection Guide Matching the WORKPIECE material to the brush material Internal Brush Selection Guide Matching the WORKPIECE material to the brush material The Best Brush Material Is: The Best Brush Material Is: CRIMPED WIRE Aluminum Brass Copper Iron Plastic Steel Stainless Steel Wood STRAIGHT WIRE Aluminum Brass Copper Iron Plastic Steel Stainless Steel Wood Steel BC BC BC BC NR BC BC BC Steel VG VG VG VG NR VG VG NR Stainless Steel VG VG VG VG NR VG BC NR Stainless Steel VG VG VG VG NR VG BC NR Nonferrous VG VG VG NR OK OK OK VG Nonferrous VG BC BC VG OK OK VG NR Steel NR OK OK BC NR BC NR NR Steel VG VG VG BC NR VG BC OK Stainless Steel OK OK OK VG NR VG BC NR Stainless Steel VG VG VG VG NR VG BC OK Nonferrous BC BC BC NR NR OK OK NR Nonferrous VG BC BC VG OK VG VG OK OK OK OK BC NR BC OK NR BC BC BC BC BC BC BC BC KNOTTED WIRE CRIMPED WIRE TY® ENCAPSULATED WIRE TY® ENCAPSULATED WIRE Pliant Polymer NR NR NR BC NR BC BC NR Rigid Polymer NR NR NR BC NR BC BC NR Pliant Polymer SYNTHETICS SYNTHETICS Abrasive Nylon Abrasive Nylon BC BC BC BC VG BC BC BC Legend VG is typically the BEST CHOICE for the combination is typically VERY GOOD for the combination OK is typically SUITABLE for the combination NR is NOT RECOMMENDED for the combination BC
  • 57. Chapter 4 - Type 1 Equipment 58 Fig. 21. Filament Brush Applications Selection Brush type is determined by how the strands of filaments are held in what position or arrangement. Basically there are five types of filament brushes: wheel, cup, end, internal and wide brushes. The brush selection is determined by the type of work to be done, the equipment to be used, and it’s RPM speed, and the surface profile or finish desired. The composition of the filament strands is determined by the workpiece material, equipment RPM and the finish required. The size of the brush is determined by the part’s size and configuration, equipment RPM and the finish required Typically the larger the brush diameter, the more efficient the brush. However to select the maximum allowable size, you must consider RPM machine speed. RPM speeds over 6000 should not exceed a 6” O.D. Shorter filaments have the ability to flex and conform to irregular surfaces better.
  • 58. Chapter 4 - Type 1 Equipment 59 Fig. 22. Brush Types for Applications Getting back to composite filament brushes, the most common synthetic wheels are normally made from nylon with either a silicon carbide or aluminum oxide material added to them to make the flexible filament more abrasive. These brushes consist of about 40% of organic material and can be made with a number of different abrasive particle sizes. The coarsest, most abrasive size is about a maximum grit size of 46 to the smallest of about 500 grit. Because of the relatively low melting temperature of around 600 degrees for nylon, these brushes have limited applications for deburring. This may sound like a high temperature, but it is relative to pressure, meaning that it can easily exceed this temperature very quickly at the contact point. Consequently, these wheels are used more for cleaning purposes along with straight nylon material fibers, polymeric, polypropylene, and the natural fibers of tampico and palmyra. Most brushes have relatively short bristle lengths which are easier to control and work better than longer ones because pressure deforms the bristles. The inherent flexibility of all filament and wire wheels allows them to work extremely well on contour parts and again type 0 to 1 burrs. However, because of their construction, they can produce noticeable patterns or textures on the finished parts and may leave flat surfaces rougher than they were before they were worked. Then again, some of these finishes are considered artistic in themselves and can be found to decorate trucks and the most notable use was on the Spirit of St. Louis airplane. The deburring performance of such brush wheels depends on the overall diameter of the fiber, the width of the bush, the type of material, the length of the fibers, and the number of fibers filaments, and the wheel or design application. A general rule of thumb is the larger the diameter of the filament and the shorter its length the rougher the surface finish produced and the more material removal capability. Also the greater number of filaments a brush has the more uniform and finer the finish pattern or texture.
  • 59. Chapter 4 - Type 1 Equipment 60 Organic materials Lastly, there are the flexible organic cloth type wheels. These wheels have greatest amount of flexibility and that does not lend itself to a great deal of material removal. These wheels may also have the greatest amount of construction and material variations. Generally speaking, most of these wheels are used to deburr and polish, or buff, type 0 burrs but can be used for some minor deburring on type 1 burrs. The amount or aggressiveness of the organic wheel or material removal depends mostly on the compound used with the wheel rather than the actual construction of the wheel. Organic fabrics are composed of strong, almost hollow, inter-connecting and woven cellular fibers that tend to have greater flexibility and therefore softer qualities than solid, rigid inorganic materials. This flexibility lends itself to surface refinement, rather than material removal. Fig. 23. Organic Wheel Materials The following are some of the more common compositions and materials used to make buffing wheels. Flannels Domet flannel (with nap on both sides) and Canton flannel (nap on one side and twill on the other) in various weights are used where other fabrics fail to produce a high enough luster. Coloring of jewelry products is a typical application for such buff materials Sisal Sisal is a natural hemp fiber used for fast-cut buffing of steel and stainless steel. It is a coarse fiber twisted into strand groups and frequently woven into a fabric. It has a much lower thread count than cotton muslin, sometimes five by seven per inch, and offers the advantages of greater surface defect removal. Combination Sisal/Cloth buffs are effective designs. The sisal plies are often cloth covered to omit the tendency of the sisal to cut the cotton threads of adjacent cloth plies. Alternating cloth and sisal improves compound retention, reduces unraveling and moderates cut. Kraft paper alternated with sisal also has applications. Other Natural Materials Occasionally, other materials are used to form buffs. For example, woven wool buffs are used on plastics, soft metals, and sterling silver. Sheepskin buffs are used to avoid surface drag or smear when buffing metals that contain lead. Russet (bark-tanned) sheepskin is used for cut. White alum (alum-tanned) sheepskin is used for color buffing.
  • 60. Chapter 4 - Type 1 Equipment 61 Pieced Buffs Pieced buffs are less expensive because they are made from lower priced materials. The buffs are made of colored segments, unbleached segments, and occasionally bleached material. Combination Buffs Often different materials are combined, especially sisal and cloth, and occasionally paper as well as cloths of different specifications. Synthetic Fibers Unwoven nylon and other synthetic fibers, because of their water resistance, may be used wet or dry or with wax or grease lubricants. Buffs made of synthetics are usually operated at low speeds, Typically 2,500 sfpm, to prevent melting and streaking of surfaces. In the finishing industry, the term polishing basically refers to metal removal and is done with anything that modifies a surface profile which is the same definition we use for deburring. That also means that almost anything can be considered an abrasive, even the smoothest material that can be used to rub or contact another surface. To make some distinction of terminology, the finishing industry uses the word buffing to refer to a specific desired brightness or high luster surface finish, but this does not necessarily mean a smooth surface finish. The most common, general purpose, polishing wheels are made from cotton, but can be muslin, canvas, felt, or leather. Wheels are fabricated in layers sewn together or held together with adhesives of silicate of soda or animal based glues. The quality of the wheel is determined by thread count per inch in the fabric, which weights between 2.5 and 3.5 linear yd./lb. of 40inch wide materials. These materials can be treated before or after assembly of the wheel. Harder and stiffer treatments provide faster cutting and deburring. Softening makes them more flexible and provides longer life. Some treatments provide better adhesion for lubricants and compounds. Most treatments are done to the buffs to make them fire resistant and retard burning. Buffing wheels are normally die cut and pieced together in layers like a sandwich. Without a means to hold the layers together, the buffs unravel or fray easily. However, in this condition, they are cheap and good for polishing. Most wheels are sewn together in various ways. Concentric sown wheels tend to be stiff near the stitch section, then loosen after the stitch wears through and this may cause an uneven textured surface on the finished parts. A spiral stitch results in a more uniform density of the wheel and produces more constant results. Square sewing creates more pockets to retain more buffing compound. Other sewing patterns are radial, radial arc, tangent, parallel, ripple, zigzag, cantilever, and petal. These patterns provide strength and longevity to the wheel and also increase its cost.
  • 61. Chapter 4 - Type 1 Equipment 62 Organic Wheel Fabrication Fig. 24. Wheel construction The following shows the sewing patterns and/or fabricating construction of most of the buffing wheels in use. Unsewn Buffs Conventional, full-disk buffs are made with die-cut cloth disks. Unsewn, conventional full-disk buffs may be used for luster. Loose disks are turned to allow the threads of the material to lie in different directions. This results in more even wear, avoiding a square shape after being put into use. One disadvantage of this conventional design is that the fabric can fray or ravel. When held against a wheel rake, a cloud of threads may fly off. This shortens buff life, increases compound consumption, and adversely affects finish. Also available are solid bias sisal buffs, with every other layer being cloth, and rebuilt buffs made from reclaimed material. Conventional Sewn Buffs Conventional, full-disk buffs for heavier buffing (cut) are sewn in various ways. Closer sewing is specified for cutting harder metals and for removing deep imperfections. Concentric dewing causes a buff section to become harder as it wears closer to the sewing and softer after wear causes the sewing to break through. Spiral sewing results in more uniform density. Square sewing produces pockets that help the buff wheel to retain more buffing compound. Radial sewing, sometimes called sunray sewing, and radial arc sewing provide other variations. Tangent, parallel, ripple, zigzag, cantilever, and petal sewing are used for similar reasons. Special sewing, other than spiral, which is done on automatic machines, involves more labor in the buff manufacturing process, thus increasing the price per buff. Folded or Pleated Buffs Folded buffs consist of circles of cloth folded twice to form a quarter circle, resulting in a “regular-pocket” buff (18 ply), or, for more cut, three times, to form eighths of a circle to constitute a denser “superpocket” (34 ply). The segments are laid down to form a circle, with each segment overlapping the previous segment. They are sewn around the arbor hole and partway to the periphery. The folds form pockets that hold compound and flex sufficiently for contour-following capacity. Folded buffs share three design deficiencies: lack of center ventilation, a tendency to fray, and waste of material in the unused center. Pleated Buff Airway buff cloth may be accordion pleated to present more angles of material to the surface of the product to be finished. Pleating results in more cloth angles to reduce streaking and improve coloring characteristics. Better cutting is also achieved in some applications. Packed Buffs Buffs may be packed with spacers consisting of cloth or paper inserted between the larger diameter plies. The same spacer principle is used between buff sections. Both measures result in a softer wheel face. The packed buff construction is effective in contour buffing applications. A version of the packed buff, for threaded, tapered spindles (2-12-in. diameter), is used in the jewelry industry. The center is hardened, usually with shellac. The sides of the buff may be reinforced by leather disks. Pieced Buffs Pieced buffs may be used in place of sewn full-disk buffs. They are made from remnants of cloth left over in the manufacture of other textile products. Such buffs require one of the types of sewing used for full disks in order to stay together in use. The chief virtue of pieced buffs is their higher value owing to the lower cost of materials. They usually are sold by the pound (see Table).
  • 62. Chapter 4 - Type 1 Equipment 63 Approximate Weight - Spiral Sewed Pieced Buffs Diameter (in.) 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 REGULAR Approx. 1/4 in Thick Lbs. Per Sections 100 Per 100 Sections Lbs. 7.4 1351 11.5 870 16.6 602 22.1 452 29.4 340 36.5 274 46.0 217 55.6 180 66.3 151 77.7 129 90.2 111 103.5 97 117.7 85 132.9 76 149.0 67 HEAVY Approx. 5/16 in. Thick Lbs. Per Sections 100 Per 100 Sections Lbs. 8.2 1220 12.8 781 18.4 543 25 400 32.7 306 41.3 242 51.0 196 61.7 162 73.5 136 86.2 116 100.0 100 114.8 87 130.6 77 147.4 68 165.3 60 Extra Heavy Approx. 3/8 in. Thick Lbs. Per Sections 100 Per 100 Sections Lbs. 11.1 900 17.3 578 24.9 401 33.0 303 44.1 227 54.8 182 69.0 145 83.4 119 99.5 100 116.6 86 135.3 74 155.3 64 176.6 57 199.4 50 223.5 45 Conventional construction wheels and sewing patterns may also incorporate folds or pockets of fabric and/or gaps. These segmented pockets hold compound and flex for greater contour following capability. There are also the pleated patterns that provide more cloth angles to reduce streaking and improve coloring capabilities and cutting in some applications. There are also what are called packed buffs. These are wheels that are packed with spacers of either cloth or paper inserted between larger diameter layers or plies of fabric. All of these wheels have a relatively small I.D. hole that can have flanges. Fig. 25. Organic Wheel Designs In addition to the stitching or sewing pattern of organic buffing wheels, there is the arrangement of the fibers and how those fabric materials are held or gathered together
  • 63. Chapter 4 - Type 1 Equipment 64 Fig. 26. Cloth Buffs Bias buff (left) versus conventional buff (right). Thread configurations of bias buffs alternate warp and filler threads. Biasing provides design efficiency by exposing all thread ends to the surface being buffed, reducing fraying of the fabric. Cloth bias buffs in order of increased density from closed Face (left to right: 0,2,4,6) to open face (far right) design. Open cloth sisal buff Spoke unit or finger sisal buff. Bias pattern construction wheels are more frequently used than conventional buffs because they naturally run cooler and therefore resist burning. As mentioned, a lot of cotton buffing wheels can catch on fire with or without lubricants or compounds. Temperatures produced in buffing can exceed the combustible ratings of most fabric materials and that is why most buffs are treated with fire retardant chemicals. That still does not insure that fire is not possible in buffing operations; therefore, care should be taken in and around such high production work areas. The main construction difference in fabric buffing wheels is the orientation or layering of the plies of fabric composing the wheel. Less expensive construction wheels use a simple X Y pattern which is capable of unraveling. Most production wheels use bias material threads which are held at 45 degree angles when assembled. This construction orients all the fabric ends so that they face the outside edge from a large I.D. or center section that supports the inside edge. This popular wheel is also convoluted with puckered pockets. The higher the number the greater the cloth content, density, and convolutions. Another wheel is the open-face cloth buff, which prevents loading and streaking. The bias sisal wheel is good for longer life, the open cloth bias wheel and the open double cloth wheel is good for contoured parts, the spoke unit or finger wheels have great cutting power as well as contour capabilities. As you can tell, there are a number of buffing wheels with special applications unique to each design and/or construction; therefore one requires some knowledge of these variations and applications to select the proper buffing wheel that will hold up to the part or application necessary.
  • 64. Chapter 4 - Type 1 Equipment 65 Fig. 27. Organic Wheel Applications Below are some of the more common applications for wheels shown. In most cases, to get a good quality finished part requires a number of different wheel applications or abrasive qualities not found in one wheel alone. As mentioned, each wheel has certain qualities and/or advantages over that of another. Therefore, in most production facilities there is more than one polishing station and these are normally set up with different wheels to achieve different results. That means that most parts can or should be worked with more than one wheel abrasive or polish. For production speed, a part is done in steps or stages until it is acceptable and the fastest way to achieve this is by various steps rather than can be accomplished in one operation only.
  • 65. Chapter 4 - Type 1 Equipment 66 Abrasive and polishing compounds To accomplish either a deburred or buffed part using flexible organic wheels requires that the wheel to be coated with either an abrasive compound or rouge. Some wheels are treated with chemicals to enhance their performance, but they still need an abrasive or rouge compound applied to the wheel to do the type of surface finishing work required. The wheel provides the mechanical energy for the abrasive or rouge to work. Compounds normally come in a solid bar form that becomes a semi liquid form coating when applied to a moving wheel system. These compounds must be periodically applied to the wheel to replenish or improve the working performance of the wheel or compound. The type of wheel is also important in the retention and performance of the compound. The compound in bar form contains a binder and an abrasive. Most binders come from animal or vegetable materials that can be made into fatty acids, tallows, or glycerides, and will produce saponified water-soluble soap film which will dissolve when combined with alkali cleaning solutions. Petroleum, mineral oils, and waxes can also be used, but are unsaponified and are more difficult to clean than water-soluble products. Besides cleaning, binders control frictional heat or slip, lubricity, degree of hardness and/or resistance, and the adherence properties of the compound. To apply the proper compound to the wheel, the solid bar is pressed against the flexible soft wheel buff and the friction generates heat that liquefies the compound and transfers it to the wheel. Some newer automated methods spray a liquid compound on the wheel or parts as they travels through a number of wheels. Typically, an abrasive compound would be composed of a pumice, fused alox, or silicon carbide. An intermediate step or compound might be "Tripoli" or fine silica, and a final polish would be an iron oxide, aluminum oxide, or chrome based compound. Aluminum oxide compounds are the most popular products used in deburring and buffing and are normally white in color. There are a lot of different grades of aluminum oxide in use. It rates an 8 or 9+ in its various oxide forms on the Mohs’ Scale. When this raw material product is heated at low temperatures of 950 degrees centigrade, it is considered fused aluminum oxide or calcined alumina and is still considered soft material and is used for buff polishing of all materials. At temperatures of 1250 or 1850, this product is used more for its cutting qualities. Naturally, the larger the abrasive grain size, the faster it will cut, but the hardest fused aluminum oxide is generally used in the making of abrasive belts. Silicon carbide is the hardest material used in a compound and it rates a 9.6 on the original Mohs’ Scale and is normally used for abrasive cut down. It is made from mixing coke and silica in an electric furnace at approximately 1900 to 2400 degrees centigrade. It is used primarily for abrasive cutting processes and can be gray in its color or compound. Another cut down compound is Tripoli. It is a name used for naturally occurring microcrystalline silica. It is used for cut down of mostly non-ferrous materials of aluminum, brass, copper, zinc, and other white metals. Because this is a silica product, it requires protective breathing precautions of a
  • 66. Chapter 4 - Type 1 Equipment 67 mask and/or ventilation. This is a relative soft material rating a 7 on the Mohs’ Scale and can be yellow in color in its compound form. Besides abrasive cutting compounds are buffing compounds, which really don’t remove material as much as they modify surface finishes by lapping or micropolishing. Chromium oxide, also called green rouge, is used for buffing and can achieve mirror finishes and/or color finishes on stainless steels, chromium, and nickel. Its oxide is rated a 9 on the Mohs’ Scale. Iron oxide or ferric oxide is also called jeweler’s rouge or red rouge is also a popular buffing compound. It is 99% pure iron oxide and is used a lot on non-ferrous metals of brass, copper, gold, and silver and is usually red in color. It is a lot softer oxide rating only a 6 on the Mohs’ Scale. Abrasive and Buffing Compounds For Organic Wheel Systems To determine what compounds to apply to organic wheels, the following guidelines are recommended. First, what is the hardness of the material to be worked? Second, what is the hardness of the abrasive in the compound? Third, what is the RPM speed of the equipment being used? Fourth, what is the desired surface finish? In addition to these questions, one should also know the size of the abrasive particles and temperature range of the compound. Hardness of Abrasive Materials Abrasive Type Chemical Symbol Mohs’ Scale Aluminum Oxide (fused) AL2O3 8-9+ Aluminum Oxide (calcined) AL2O3 8-9+ Tripoli-silica SiO2 7 Silicon Carbide SiC 9.6 Iron Oxide Fe2O3 6 Chrome Oxide Cr2O3 8-9 Wheel Speeds for Hand Buffing, sfm Cutting Down Luster Buffing Carbon and Stainless Steel 8,000-9,000 7,000-9,000 Brass 6,000-9,000 6,000-9,000 Nickel 6,000-9,000 6,000-8,000 Aluminum 6,000-9,000 6,000-7,000 Zinc & Other Soft Metals 5,000-8,000 6,000-7,000 Chromium - 7,000-8,000
  • 67. Chapter 4 - Type 1 Equipment 68 Production Buffing Techniques Material to Finish Aluminum Satin Finishing Cutdown Buffing Color Buffing Aluminum oxide greaseless compound light head of Dry Tripoli bar. Loose or ventilated buff or string wheel, 3,000 to 5,000 sfm Aluminum oxide greaseless compound. Loose or ventilated buff, string wheel 3,500-5,500 sfm Aluminum oxide greaseless compound. Loose buff 5,000 to 6,500 sfm Tripoli bar or liquid compound loose or ventilated buff, 6,000 to 8,000 sfm Rouge silica unfused aluminum oxide bar or liquid compound loose or low-density ventilated buff, 6,000 to 8,000 sfm Tripoli bar or liquid compound. Ventilated loose or sewn buffs. 5,500 to 8,000 sfm Chromium Decorative Plate Lubricated silica greaseless compound, loose buff, 3,000 to 4,500 sfm Copper Aluminum oxide greaseless compound. Loose or ventilated buff string wheel, 4,500 to 6,000 sfm Aluminum oxide greaseless compound. Loose or packed buff, string wheel, 3,000 to 5,000 sfm Aluminum oxide greaseless compound. Loose or ventilated buff, 5,000 to 7,500 sfm For burnt areas: Combination fine fused and unfused aluminum oxide bar, loose or ventilated buff, 6,500 to 8,000 sfm Tripoli bar or liquid compound. Loose sewn or ventilated buffs, 5,500 to 7,500 sfm Tripoli bar or liquid compound. Loose or ventilated buff, 5,000 to 8,000 sfm Tripoli bar or liquid compound. Loose sewn or ventilated buff, 5,000 to 8,000 sfm Rouge silica unfused aluminum oxide bar or liquid compound loose or low-density ventilated buff, 5,000 to 8,000 sfm Chromium green oxide or unfused aluminum oxide bar or liquid compound, loose or ventilated buff, 5,000 to 6,500 sfm Chromium green oxide or unfused aluminum oxide bar. Loose or ventilated buff, 6,500 to 8,500 sfm Brass Hard Chromium Copper Plate Nickel and Alloys Nickel Plate Decorative Aluminum oxide greaseless compound. Loose or ventilated buffs, 4,500 to 5,500 sfm Steel and Stainless Steel Silicon carbide or aluminum oxide greaseless compound. Loose or ventilated buff, 4,500 to 6,500 sfm Zinc Aluminum oxide greaseless compound. Loose or ventilated buff, 5,500 to 6,500 sfm Aluminum oxide bar or liquid compound. Ventilated, sewn, sisal finger or Tampico buffs, 8,000 to 10,000 sfm Tripoli bar or liquid compound. Loose ventilated or sewn buffs Rouge, silica, or unfused aluminum oxide bar or liquid compound, loose or low-density ventilated buff, 5,500 to 7,500 sfm Chromium green oxide or unfused aluminum oxide bar or liquid compound, loose or ventilated buff, 5,000 to 8,000 sfm Lime bar, or chromium green oxide, or unfused aluminum oxide bar or liquid compound, loose or lowdensity ventilated buff, 6,500 to 7,500 sfm Chromium green oxide and/or unfused aluminum oxide bar or liquid compound, loose or ventilated buffs, 8,000 to 10,000 sfm Silica or unfused aluminum oxide bar or liquid compound, loose or low-density, ventilated buffs, 6,000 to 8,000 sfm
  • 68. Chapter 4 - Type 1 Equipment 69 In more advanced automated systems, parts may be spray coated with a liquid form of rouge as they pass on a conveyor belt line into a fixed series of buffing wheels. The liquid compounds used are all water based products or oil/water emulsions. Stability of the product is achieved through density, viscosity, and suspension. Because this is a liquid compound that is accurately proportioned per part, wheel speeds can be lower and uniformity is more consistent to the operation. In general, liquid systems are a lot more simple to operate and maintain and maybe the trend form in the future for all systems; however, these are automated systems and the initial coast is a whole lot more than using bar compounds. As mentioned, in wheel systems it is the compound that does the actual material removal or surface modification, the wheel only provides the pressure and/or mechanical energy that acts somewhat like a catalyst in the operation. That is, it helps the operation, but it is not the primary agent in the process. Pressure, friction, type of wheel, and compound is what produces a polished or abrasive surface finish. Again, a lot of different compounds and wheels produce a wide variation of finishes. As long as we are talking about finishes again, let me say that nearly all flexible wheel systems produce a luster on parts. As mentioned earlier, these wheels can be composed of different materials, thickness, length, texture, and/or grades that produce highly reflective mat, textured, or satin type finishes. There are also the composite synthetic brush type wheels that produce excellent material removal or polishing type results, but not generally a mirror finish. Reflective surface finishes can be achieved using abrasives and other means; however, to achieve a reflective mirror finish requires a soft wheel and compound with a lot of lubricity to improve the material surface profile of the material being worked. A smooth, flat buffed surface is normally required and desired for medical parts to avoid contamination from microscopic organisms and sometimes on high tech parts for precision performance. Felt Now, after making that statement, I am going to make an exception to what I just said. Another good polishing wheel that is not exactly soft and is an exception to rigid wheels are those made of hard organic cotton felt. There are a number of grade densities of felt that are manufacturer that are determined by pounds. The harder grades of organic felt material have some minor flexibility even though they are basically stiff rigid wheels. That means that these solid rigid wheels are similar to non-woven materials in characteristics and performance but are not considered as such because they are not composed of a blend of mixed abrasive materials and synthetics. Felt wheel products are made in different densities and the harder the felt the longer it lasts. Also, density determines how these wheels perform. The problems with these wheels are the same as those of solid inorganic wheels; it is difficult to maintain constant, even contact with a part without a chattering effect. Therefore, a lot of felt wheels are very popular for small power tools and especially the jewelry industry for achieving mirror finishes. Because of the fine quality of this material, these wheels can be used with or without rouge.
  • 69. Chapter 4 - Type 1 Equipment 70 Flap Wheels The flap wheel is another type of radial wheel and is composed of separate individual square flap segments of coated abrasives of fabric, sisal, and cloth material that are set at a right angles to the direction of rotation. Because of this construction, the wheel tends to be more rigid and therefore more aggressive. Basically they behave the same as filament and wire wheels, but are more easily controlled and normally produce smoother results. Fig. 28. Types of Inorganic Flap Wheels Discs Disc type abrasive products look and behave like wheel systems; however, unlike radial wheels, they work on one of their flat sides, instead of the width of the edge or face. The abrasive is only coated on one side of the disc like a belt system. They are similar to a flap wheel, but they do not work with the tips of their edge and they do not rotate like radial wheels. The disc can be flexible or rigid, but normally that is a function of the backing or support backup mounting plate. The hand tool that use discs are also more difficult to control, because they are used at right 90 degree angles to the work piece and that causes them to follow a changeable circular pattern. That is, the pattern is a variable factor influenced by the rotation of the disc and controlled by the operator that can be anywhere from perpendicular or an almost flat angular drag. Also because of the circular pattern, it is very difficult to create a uniform surface finish. This system uses a single disc or a flexible flap type of construction and it operates in close full contact with the work piece. That means that when the abrasive wears down the disc will have to be replaced. That also means that the surface profile will also change, because the abrasive has also changed. The working part or flap of these wheels are made from coated abrasive belt products and can be backed up with either rigid or flexible formed materials for better control and contact.
  • 70. Chapter 4 - Type 1 Equipment 71 Besides the abrasive type sandpaper belt materials being the same as a disc, the shape and behavior characteristics are definitely different from a radial wheel system. When a disc is mounted vertically fastened to a fixed motor and platform system, the results are good for working thin edges of parts, but not large flat areas. Even this type of equipment and processing method does not produce good uniform material removal or deburring results. This problem is even more noticeable when using a handheld portable power tool on larger flat parts. The circular shape of the disc and the pressure an operator applies to it in a free or non-rigid plane of reference normally creates an irregular surface finish or angular drag pattern. Material removal is accomplished in a circular manner, but because of the speed and the control factor, only a portion of the disc is in contact with the surface profile at one time, thereby creating an overlapping half moon pattern. In other words, the portable hand tool or disc grinder is good for large flat parts, but it still produces uneven results and patterns because of the control factor. Beside circular disc, there are now some triangular shaped discs with holes in them to help relieve the heat and remove debris or what is called loading caused by excessive pressure to a disc. Loading is the condition where the abrasive and the material being removed from an almost flat profile thereby not allowing the abrasive to be in surface contact with the material to be worked. As mentioned previously, in order for abrasives to work, they must themselves have a surface profile capable of material removal. Technically, the use of a disc is not a normal finishing system, because of the control factor. Most disc systems are used for small part lots or reworking materials.
  • 71. Chapter 4 - Type 1 Equipment 72 Fig. 29. Inorganic Abrasive Disc The transition from radial deburring wheel systems to belts uses another type of wheel know as the disc. Instead of using an in line wheel face, the disc uses a single side or uniform abrasive face that operates in a circular rotary pattern 90 degrees to the movement of the tool. Instead of working a relatively small section of part with good visual reference, the disc covers a much wider area and obscures the work section, then again, the radial wheel is used to work smaller off hand parts and disc are primarily used on much larger parts. Instead of taking parts to the wheel, the wheel is taken to the parts. The most common disc construction uses a thin abrasive belt product, normally round in shape and designed for quick changes by snap on fasteners, screws, or glue. The more rigid the disc construction or the support backing the more aggressive the wheel system. There are now some solid triangular shaped discs for reciprocal type equipment and a new triangular AVOS disc with holes that allow operators to actually see the product or problem area they are working. These new design discs tend to generate less heat and use less power.
  • 72. Chapter 4 - Type 1 Equipment 73 Other variations of the disc, besides the standard flat are: slotted, scalloped, raised bump, and stars. Some more bulky configurations are square or round pads, cross, and butterfly. Another shape that is used to work I.D holes are the cartridge rolls, cylinders that are uniform or tapered, and cone shapes. We have already talked about the flap wheel, but I guess it can be classified as either a wheel or a disc belt. They can also be constructed with an inter mix of nonwoven pads, designed to remove a lot of material in a short period of time, from type 0 to type 3 burs. Wheels using the non-woven materials as filler, produce excellent polished finishes, but not a buffed finish. Each of these shapes are constructed to handle special applications or work difficult to reach areas for deburring. Perhaps I should mention that up to this point, we have talked about RPM’s and rotation as the power source to accomplish material removal… There is another way and it is common with these disc type transfer or contact devices. There are what are called reciprocal motor systems. These systems work in a back and forth motion and are more closely related to a vibration method. Technically, both the contact device and the power source remain relatively stationary, but because of the fast back and forth movement of less than an inch, the system creates an over lapping pattern for which the abrasive can work and modify the part. The reciprocal systems are used a lot at home to improve surface removal. They are not normally used in industry for production because they are relatively limited in their abilities and applications. They cannot designed to handle burrs over a type 2; therefore, this equipment would have a maximum range or classification of 100 to 121. This is the only application of reciprocal power source equipment.
  • 73. Chapter 4 - Type 1 Equipment 74 Fig. 30. Inorganic Abrasive Shapes All abrasive belt construction wheels and standard reciprocal shapes start out as flat and nearly square shapes. They are then either cut into special shapes and/or folded into special shapes. Following are a few common applications.
  • 74. Chapter 4 - Type 1 Equipment 75 Before I go much further, I think I should say something about discs versus belt systems. I grouped wheel and belt systems together because they are used to work parts or materials in a horizontal or parallel plane to the surface of the materials they are working. That is, the surface profile material of a part is moved perpendicular to its original position or along the same parallel plane as the part. Wheel and belt systems use abrasives and compounds differently, but achieve nearly the same results. In operation, wheel and belts do not behave the same, but discs and belts use the same abrasive materials and do behave the same. The only difference between belts and discs are their shape and the way the energy forces are applied. Belts normally work a broad flat area in one direction and produce a uniform surface finish. Most discs can work with their whole surface diameter, but normally operators use just their edge and rarely achieve 100% contact. This method of operation produces a swirl pattern and this is normally never uniform. The reason for this problem is the way the transfer device tool is held and the difficulty of the operator to apply pressure and control over the tool and the surface being worked. Therefore, discs are used more for heavy material removal in small areas and in excess of type 4 burrs. As a general statement, disc systems are almost used more like a cutting tool instead of used for surface finishing. Comparison Earlier, I began this section talking about type 1 systems which are both wheel and belts and then I proceeded to tell you a lot about wheels. Even though these systems are related by the way they work or move horizontal or parallel to the materials surface profile, they are different to some extent. Belts have different characteristics from wheel systems. Wheels seem to be softer, more flexible, because they are composed of a lot of loose materials separated by air and therefore they are used more for buffing or what I think most people call polishing, meaning to produce a bright shine. However, polishing terminology used by wheel people means material removal and buffing is the proper term for a bright surface finishing. Belts are more rigid and seem to have greater surface contact and abrasive density and that relates to more material removal or deburring than wheels. I would also say that probably, wheels work better on contour parts and belts work better on flat sheet metal type parts. Belts also do not use a lot of compounds to control material removal and surface finishes therefore they tend to be simpler systems. Once a belt is selected you are pretty well locked into a uniform finish, depending upon the abrasive used, that a belt will produce. Again, you do have the break in situation factor were the belt is more aggressive initially and then stabilizes. What I just said about belts being a simpler system is and is not exactly true. Although the contact belt is relatively simple compared with the wheel systems, belts have a couple of variables. First of all the belt has a power source motor not necessarily directly in contact with the belt. Usually the system has a drive wheel or contact wheel, the belt itself, and an idler or tension-tracking wheel, all of which are designed to control the belt. So, even though we are talking about a wheel versus a belt, we are also talking about other mechanical features that
  • 75. Chapter 4 - Type 1 Equipment 76 control the process. That makes the actual equipment system more complicated mechanically, but the application and/or results are simpler or easier to obtain. Inorganic Abrasive Belt Systems Although powered by motor and wheels, belt systems are mechanically more complicated, but produce more consistent finishing result. Belts work like wheels in that they operate in a linear mode, but tend to be more rigid and have greater surface area. Besides the type and size of the abrasive construction of the belt, the hardness of the contact wheel also effects the final surface finish of the part. Compounds are not as important in obtaining final results. All belts have at least two wheels and most use three. Work area is either against a contact wheel or a stuff contact backup point between the contact and tracking wheel. Fig. 31. Contact Wheels Surface Material Hardness and Density Purpose Wheel Action Comments Cog Tooth Rubber 70-95 Durometer Heavy Grinding Standard Serrated Rubber 55-95 Durometer Medium to Heavy grinding Very aggressive, retards dulling Excellent stock removal, not as severe as cog tooth Plain Face Rubber 40-95 Durometer Light to medium grinding “X” Shaped Serrations Flat Rubber 35-70 Durometer Compressed Canvas Flat Solid Sectional Cloth Buff Section Cloth Available several densities from extra soft to extra hard Available five densities, 50 to 90 plies per inch Variable Polishing to light grinding Polishing For heavy stock removal such as gates, risers, etc.. Not as aggressive as cog tooth, depending on land to groove ratio. Most common type For flat surfaces or where belt might be punctured with serrations More applicable for nonferrous parts Bench-type grinder oriented. All around wheel Flat “Middle-of-the-road” type wheel, finer surface roughness than above For very mild contours and light stock removal Varies with density from light stock removal to fine polishes Polishing Uniform polishes for contoured work Excellent for all types of finishing. May be preshaped Contour polishing Conformable for polishing contours and irregular shapes Adjustable for width and density
  • 76. Chapter 4 - Type 1 Equipment 77 Like wheel systems, belts use pressure applied both to the part and the transfer tool device or belt. Therefore, motor requirements are nearly the same and can be inter changeable. Unlike the wheel system, the surface finish using a belt cannot be regulated to any great extent by compound additives, but it can be regulated by changing the contact drive wheel under the belt. Given the same abrasive belt using a soft contact wheel versus a hard wheel, the belt will work faster to remove more material the harder the contact wheel; however, that will also result in a rougher surface finish. Cloth and soft contact wheels have greater contour capabilities and will result in finer surface finishes. Fig. 32. Inorganic Abrasive Belt Applications Belts are manufactured to include different abrasives and sizes, backings, bonding, splices, and types of flexing. Abrasive grains are classified into grades or grit sizes ranging from 16 coarse to 1500 fine. Two systems are normally used: FEPA for aluminum oxide and silicon carbide abrasives and CAMI for zirconia alumina (see chart. Typical applications and speeds are as follows:
  • 77. Chapter 4 - Type 1 Equipment 78 Fig. 33. Suggested Surface Speed and Abrasives for Various Metals Lubricant Contact Wheel Type Dry Cog tooth or serrated Hardness/ Durometer 70-95 duro. 4,0007,000 Dry or Light Grease Plain face rubber, canvas 40-70 duro. Medium 180320 4,0007,000 Heavy Grease or Polishing oil Plain face rubber, canvas, cloth Soft ZA or A/O 36-60 3,0005,000 Dry Cog tooth or serrated 70-95 duro. Polishing ZA or A/O 80150 3,0005,000 Dry or Light Grease Plain face rubber, canvas 40-70 duro. Fine Polishing A/O or S/C 180240 3,0005,000 Heavy Grease or Polishing oil Plain face rubber, canvas, cloth Soft Grinding 24-80 4,0007,000 Light Grease Cog tooth or serrated 70-95 duro. Polishing ZA,A/O or CAO Fine Polishing A/O or S/C 100180 4,0007,000 Light Grease Plain face rubber, canvas 40-70 duro. Medium A/O or S/C 220320 4,0007,000 Light Grease or heavy grease Plain face rubber, canvas, cloth Soft Grinding A/O or S/C 36-80 3,0007,000 Light Grease Cog tooth or serrated 70-95 duro. Polishing A/O or S/C 100150 3,0007,000 Light Grease Plain face rubber, canvas, cloth 40-70 duro. Medium Fine Polishing A/O or S/C 180320 3,0007,000 Light Grease or heavy grease Plain face rubber, canvas, cloth Soft Grinding ZA,A/O or CAO 24-80 5,0007,000 Light Grease Cog tooth or serrated 70-95 duro. Polishing A/O or S/C 100180 5,0007,000 Light Grease Plain face rubber, canvas, cloth 40-70 duro. Medium Fine Polishing A/O or S/C 220320 5,0007,000 Light Grease or heavy grease Plain face rubber, canvas, cloth Soft Grinding ZA,A/O or CAO 24-60 2,0005,000 Dry Cog tooth or serrated 70-95 duro. Polishing A/O or S/C 80150 2,0005,000 Dry Serrated or plains 40-70 duro. Fine Polishing A/O or S/C 150240 2,0005,000 Dry or Light Grease Plain rubber Soft Grinding ZA or S/C 36-60 1,0002,500 Dry Cog tooth or serrated 70-95 duro. Polishing S/C 80120 1,0002,500 Dry or Light Grease Plain face rubber, canvas 40-70 duro. Fine Polishing S/C 150240 1,0002,500 Dry or Light Grease Plain face rubber, canvas, cloth Soft Material Operation Abrasive Grits Hot and Cold Rolled Steel Grinding ZA,A/O or CAO 24-60 Polishing ZA,A/O or CAO 80150 A/O Grinding Fine Polishing Stainless Steel Aluminum Copper and Copper Alloys Nonferrous die casting Cast Iron Titanium Belt Speed 4,0007,000 Tensioning devices are important in belt performance and the proper running or centering of the belt. These devices are slightly crowned in the center and should not be a flat
  • 78. Chapter 4 - Type 1 Equipment 79 tension wheel for the proper tracking or positioning of the belt. If the tension on this idler/tension wheel is too tight a belt may wear or deteriorate very fast and created very rough finishes. Too lose a belt may slip and therefore not work properly, but in some cases may be good for processing contoured parts. A proper tension is dictated mostly by the type of contact wheel that is selected for a desired finish which the contact wheel is designed to produce. Belt Composition The abrasive belts or discs are made from sandpaper. Other than the fact that there is no sand or paper involved in making these belts, this statement is correct. The generic name of paper is used to describe some coated products; however, these are actually compositions of either man made or natural fiber materials and are developed from paper type products. In addition to these paper based products are cloth materials which are stronger and normally water resistant. Fabric materials seem to hold abrasives better and generally last longer than paper. Cotton again is the choice of most abrasive belts or discs; however, polyester fibers offer greater tensile strength, last longer, and are more resistant to fraying and tearing. Common abrasive particles used are garnet, flint, and emery. More recently, the newer man made materials of aluminum oxide, silicon carbide, zirconia alumina, and ceramic aluminum oxide are becoming more popular. New synthetic inorganic materials and bonding agents are being developed everyday and are producing faster, longer life products. The backing or bonding agent used to attach the abrasive to the belt is very important. Typical binders are glue, phenolic and urea resins. Glue bond products are less resistant to heat. Resin over glue are used for good flexibility and all resin bonded products give the maximum durability and aggressiveness. Generally speaking, the greater the thickness of the bonded coating, the less flexible the belt. Lastly, the orientation of the abrasive on the belt or disc is also becoming a very important issue. Up until very recently, most belt materials were and are random shaped particles that conformed to a specific particle size that are basically glued together and bonded to a flexible belt material. Most belts use a system called open cut distribution of random dispersing of the particles to the backing material or giving the belt about 50 to 70% abrasive coverage. This is normally a single layer on a flat surface. There have been some recent developments that can actually orient the abrasive particles to allow the greater mass or full abrasive coverage to be in contact with the paper material, thereby producing more uniform products and finer surface finishes. This system is what is called close cut and is complete coverage and can have a specific pattern or orientation of abrasive applied to the belt. In addition to dispersal is now a new manufacturing belt process that can micro replicate a specific size and shaped particle and create an orientation pattern on a belt in multi layers similar in appearance to that of a metal file. The abrasive micro replicated composites are a patented and complex process that creates a precise replicated abrasive shape and pattern. As the abrasives wear, they expose other layers of abrasives until a color change becomes noticeable with wear thus indicating the belt needs to be replaced. This construction and pattern
  • 79. Chapter 4 - Type 1 Equipment 80 uniformity produces faster, more exact cut rate, and even surface finishes throughout the longer life and higher cost of the belts. The abrasive orientation also reduces loading problems or produces more debris and or liquid removal. Naturally, the more complicated or complex the bonded product, the more expensive the belt. Construction of the more common, open cut, coated abrasive belt products can take one of four forms. They are as follows: 1. J construction is flexible lightweight cloth belts used mainly for contours. 2. X construction is heavier than J weight and is used for heavy stock removal. 3. Y construction is a newer coated abrasive belt that is stronger and more rugged than X weight. 4. S construction is a special material designed to make wide belts. The faster a standard abrasive belt is run, or surface feet per minute, the more heat is generated causing it to deteriorate faster also. Too fast a belt speed will cause excessive loading of any material being removed to stick to the belt and will stop abrading entirely. Sometimes, the abrasive in an over loaded belt can be restored with a hardened metal dressing wheel. However, the simplest means is to let the belt cool down and then contact it again very hard and for a short duration with another part. Pressure causes the fracturing of the abrasive grain and exposes new crystallized material. To prevent over loading, improve the finish, extend the life of the belt, and to increase aggressiveness, lubricants can be used on a dry belt. Like the buffing wheels, grease sticks can be applied before the work has begun to the belt and during its operation. These lubricants do not decrease material removal and they do retard over loading as well as provide finer surface finish results. Normally liquid coolants or water is not used with belts except in the larger automated systems mentioned earlier.
  • 80. Chapter 4 - Type 1 Equipment 81 Fig. 34. Inorganic Abrasive Belt Construction Abrasive usage and belt construction has come a long way since early times. Up to recent times, abrasives were selected based upon hardness and size. Past refinements of belt materials have centered on the application medium backing and/or bonding along with harder synthetic abrasive materials. Today’s technology has now gone into the design and replication of the abrasive shape, it’s construction, and how this shape is arranged in patterns. While higher rates of abrasion are not necessarily achieved, more consistent surface finishes; cooler temperatures and longer belt life are the results at slightly higher costs. Three-dimensional structures uniformly distributed over the entire surface
  • 81. 82 Chapter 5 – Type 2 Equipment & Mixed Technologies Abrasive Blasting: Abrasive blasting is a type 2 equipment system for class 5 burrs only, primarily at 0 and 1 locations, but can handle some 2 locations; therefore, I’ll give it a 3 rating. That makes this a 250 to 253 system. It is probably one of the most popular forms of surface preparation or finishing in use today. It is also probably one of the oldest finishing systems. In short, this system duplicates the effects that occur more slowly in arid wind driven deserts. That is, abrasive blasting uses air pressure to propel an abrasive or non-abrasive particle at materials that require some kind of uniform surface finish. The results are good clean parts with a textured, indented, or irregular increased surface area profile finish, provided that either the abrasive is harder or the energy pressure is greater than the material being worked. About the best surface finish that can be achieved using this equipment is somewhere around a 32 RMS. To achieve that fine a surface finish requires special fine media and a good dry air source. As mentioned earlier in the section on abrasives, it is difficult to achieve a surface finish finer than the size of the abrasive particle that one is using. That means that the particle size and how the energy is applied determines the surface profile of the material being worked. Blast type systems cannot properly process abrasive particles finer than 320 girt, which is equal to around 32 to 35 RMS. In addition to media particle size, a part finish can vary to some extent by just the positioning of the part in relationship to the direction of the air pressure and/or blast pattern. If parts are done at a consistent and proper angle to the abrasive blast gun nozzle, the results are good clean, relatively smooth material finishes with a semi gloss type appearance. If the part is worked in a direct line of sight or close to 90 degrees to the abrasive, the results are more dimpled rough surface finish. The first method is considered surface finishing and the second surface preparation. In the first method, processed parts normally can be used in an as is situation and/or chemically treated; whereas, the second method requires the part have another operation, or is used mostly for good paint or coatings adhesion. The elements of the abrasive, pressure and positioning are the determining factors using blast equipment. The best results are achieved when the blast pattern produces a scrubbing pressure wave type action, determined by weight, pressure, and volume, of the media. If the work or gun nozzle is not positioned at the proper working angle, you might want to compare this type of technology to that of the blacksmith of old, because what you may get is a pounding or hammering of the surface by a lot of small particles. The wrong angle will peen the part and produce work hardening as well as reduce the life of the media. Abrasive blasting is not a true deburring system per se, because it really doesn't remove the burr as much as it modifies it so that there are not a lot of sharp edges. That is a common problem in all abrasive blast systems, because the size of the particles being used, their shape, and the random energy force controls the pattern of the surface profile and that matches the
  • 82. Chapter 5 – Type 2 Equipment & Mixed Technologies 83 abrasive being used. A better descriptive word or terminology for this type of equipment is surface cleaning or preparation. After making this statement about cleaning, I should tell you that actually the part or parts being processed should be washed or cleaned prior to being worked by blast type equipment. The reason for this cleaning is that dirt, oils, greases, from parts processed will eventually be re-deposit on the materials being worked. Because most of these systems are closed loop systems the abrasive particles doing the surface modification are re-cycled and reused; therefore, any abrasive will become a carrier or act as a transfer agent for the contaminates and find their way back onto parts later on in the processing. Most blast systems are generally used in a closed loop cabinet and are not really conducive to high volume production environments because of the problem of processing one part at a time*3 which is the same problem that the automated buffing or polishing production lines encounter. Again, the more automated systems can handle larger volumes of parts if they are tied into a conveyor belt or material handling system, but that still requires loading and unloading the holding device or fixture that positions the part. In most cases, abrasive blast systems are faster and cheaper per piece using manpower than wheel buffing systems, again depending upon the size and configuration of the parts. Small hand-held parts still maybe faster with a wheel system. However, the surface finish or the end result is also very different. Wheel systems are normally used to produce bright shinny parts as an end result; whereas, blast systems are used to produce a satin or frosted appearance on parts and/or parts that have to have other surface finishes or coatings put on them. Perhaps the greatest advantage blasting has over a buffing wheel type systems is that the abrasive blasting can work more detailed parts and/or more recessed machined areas than can fixed diameter wheel or belt systems. Blasting is a more flexible system because you do have the capability of using multiple nozzles that can achieve almost complete coverage of the part except where or how it is mounted on the material handling system. Again automation can possibly re-position part orientation. Air and Dust Besides the need for an air supply system to operate blast equipment, another companion piece of equipment is also necessary to operate the system properly. Besides the actual blast cleaning equipment, which is usually a closed loop cabinet, there is the need to vent the dust, dirt, and debris to the outside or a safe containment source. This is called a dust collector. Naturally this device slows down and filters the air to an acceptable condition before releasing it and stores the solid fine waste while the main bulk of the abrasive is re-cycled prior to the dust collector. Depending upon the volume of the machine system, the spent air can normally NOTE: An exception to all of this are some machines that have accessory baskets that rotate on an angle inside the cabinet. This system accommodates and upsets a batch of parts while the gun nozzle is fixed. Parts 3 tumble either continuously or on a timed cycled .
  • 83. Chapter 5 – Type 2 Equipment & Mixed Technologies 84 be allowed back into the work environment. Larger systems need special handling and disposal procedures. Another companion piece of equipment required is an air supply system. Most companies already have air compressors for other needs within a machine shop; however, it there is no source to create air pressure that is also needed. Naturally that also means the necessary plumbing of pipes to transport the air to the location of the equipment and a sufficient volume of pressure and air supply. On top of all of this is the need for in line filter systems to eliminate an accumulation of water or moisture associated with compressed air systems, plus possible oils. The drier the air, the better the operation of the equipment. General It is difficult to image anyone not knowing what abrasive blasting is or what it does. However, just to be sure, let me say this, it is a mechanical means to surface finish all materials by way of using air pressure and fine abrasive inorganic or organic particles. Unlike the mechanical wheel/belt systems that do surface removal by means of applying direct contact pressure from an abrasive transfer device to the work piece, abrasive blasting applies pressure to the air born abrasive particles only, not another transfer device. In blast equipment, abrasive particles abrade by way of an impact or a one way type scrubbing action caused by mechanical energy and resistance, resulting in friction, abrasion, and heat. The abrasive impact pounds and/or shatters the abrasive as well as the effecting the surface of the part or object being worked. The impact pressure of the particles dislodges surface materials on the part being worked and again there is kinetic energy that is released when the abrasive media breaks. Instead of a continuous contact pattern that may produce a grain type appearance, blasting is a more mobile means or fine random contact of material removal with no major discernable surface finish pattern if done properly. At the same time, there is definitely a textured finish to all materials being worked. Abrasive blasting creates a satin, glossy, or dimpled finish appearance similar to the effects produced by wind driven sand on objects in a desert. I imagine that somewhere way back in history that this observation resulted in the idea for sand blasting. Such a system could have been tried with some success using a gravity feed type system suspended above the work to be processed. But without the pressure, such a system would have been a long drawn out process. I have never heard or read where this was done, but it is possible. Speaking of pressure, that is the main difference between the two commonly used air blasting systems available to do this type of finishing. There is the vacuum or venturi system referred to as suction and the pressure system. Both systems perform relatively the same amount and type of work; however, the vacuum systems have been around a whole lot longer, are good for small to moderate production volume, and are a little less expensive.
  • 84. Chapter 5 – Type 2 Equipment & Mixed Technologies 85 Fig. 35. Abrasive Blast Systems Comparison Below is a comparison of the two main operating systems used in abrasive blast finishing. The end results achieved using this equipment are nearly the same; however, there are mechanical, internal, and pressure differences. Suction System: This system works by using a high pressure air line and an abrasive feeder line, both of which connect to a nozzle or gun type device that mixes the air with the abrasive particles. That is, they unite the two separate lines within what is called a gun. It is called a gun because of its resemblance and function as one. Air and abrasive are combined within this mixing chamber or a metal Y fitting design in a ratio of 2:1. That is, the air line is normally twice as large as the abrasive feeder line right before the point of discharge through a nozzle. Air pressure in this type of system can be used to regulate speed or pressure of the abrasive, but pressure or air volume can also be regulated by means of the abrasive feeder line itself. This system is designed in such a way that allows air to enter the system by way of another hole opening on a metal tube over which the flexible hose connects to the abrasive reservoir. If the hole is fully uncover by the hose, you will get almost all air flow only. Fully closed, you will get all media. This adjustment regulates abrasive volume at any pressure.
  • 85. Chapter 5 – Type 2 Equipment & Mixed Technologies 86 The Venturi suction system works by both negative and positive pressure. It allows high velocity air pressure to pass over the abrasive feeder line. That movement in turn creates a negative pressure over the abrasive feeder line and that basically sucks the abrasive through the smaller hose and combines it with air pressure at the back of a nozzle, resulting in a positive air flow. The gun nozzle is a tapered smaller orifice, which then speeds up the combined flow and sprays out the abrasive under positive pressure in a relatively narrow focused and/or fixed pattern of discharge. During this mixing of the abrasive and air some energy or pressure is lost in this negative suction process, but because of the nozzle restriction, it is again speeded up. As the air pressure and abrasive are increased in the system the resistance of the nozzle also increases. That means more wear and tear on the nozzle. Naturally, the I. D. hole of the nozzle determines its spray or work pattern and if the hole increases by abrasion, so too does work area increase and pressure must be adjusted accordingly. Along with pressure is air volume. One affects the other. This is a cause and effect relationship or catch 22 that should be known for proper control. Because of this wear rate, nozzles have to be watched and replaced periodically. This should be done when the I.D. of the nozzle becomes 1 ½ times its original size. The nozzle in a blast gun behaves something like a drill bit. That is, it is a perishable, disposable tool. It can be used up to some point, then it loses its ability to work properly. In most cases this is a quick change, fixed rigid insert, usually made of hard high tensile strength tungsten carbide or boron carbide steel, or hard ceramic, positioned in the nozzle assembly or gun. The gun, in turn is small and flexible enough to be a hand-held mechanism; however, it is still restricted in movement by the attached air and abrasive hoses. The maintenance and replacement procedures for these nozzles are simple easy to use mechanisms that make this system appealing. Hoses also wear out, but have a great deal of life compare to the nozzles. Probably the next most frequent replacement item are the hand gloves and maybe the glass observation window in the cabinet which can get obscured because of the abrasive. As mentioned, the actual spray pattern or work zone of the gun is controlled by the inside diameter or hole in the nozzle, and the distance from the work piece, and the air pressure. In suction systems the inside hole diameter of the nozzles range from 1/4 of an inch I.D. to 7/16 of an inch. As the I.D. becomes larger so too does the amount of air pressure and volume required to do the same amount of material removal. The larger the I.D. the greater the spray pattern or coverage area that can be worked in proximity to distance in one pass. Usually straight through bore I.D. hole nozzles are used for close up work, or 10 to 12 inches in distance. Tapered nozzles are better for distance beyond that and are tapered from the larger inlet to smaller exit. In most cases, the outlet is also tapered at the reverse angles to direct the spray pattern. For working parts with I.D.’s there are some nozzles that have multiple side vents. See charts.
  • 86. Chapter 5 – Type 2 Equipment & Mixed Technologies Fig. 36. 87 Abrasive Blast Comparison, Pattern and Pressure Suction-Blast Air Requirements (SCFM) 30 40 50 60 70 80 90 100 ¼” nozzle, 3/32” air jet Pressure (PSI) 6 7 8 10 11 12 13 15 ¼” nozzle, 1/8” air jet 10 12 15 17 19 21 23 26 5/16” nozzle, 5/32” air jet* 15 19 23 27 31 37 38 42 7/16” nozzle, 7/32” air jet 31 38 45 52 59 66 73 80 *Unless otherwise specified, this nozzle is supplied. GUN ID 4 SCFM = 1 compressor horsepower Distance from Workpiece 6" 1/4" 1-3/8" 5/16"* 1-1/2" 7/16" 2" 12" 2-5/8" 3-1/2" 3-3/4" 1-3/4" 2" 18" 2-3/4" 4-1/2" 4-1/2" - 1" 3-3/4" 3-3/4" Pressure-Blast Air Requirements (SCFM) Pressure (PSI) 1/8” nozzle 3/16” nozzle* ¼” nozzle 5/16” nozzle 3/8” nozzle † 20 6 15 27 42 55 30 8 18 32 50 73 40 10 22 41 64 91 50 13 26 49 76 109 60 14 30 55 88 126 80 17 38 68 113 161 100 20 45 81 137 196 120 25 55 97 152 220 Hotspot Brush-off *Standard nozzle * Unless otherwise specified, this nozzle is supplied. † This nozzle supplied on FaStrip cabinets. 4 SCFM = 1 compressor horsepower Compressors should be sized to the next larger nozzle to allow for nozzle wear. Nozzle Distance from Workpiece ID 6" 12" 18" 1/8" ¾” 1” 1” 1-1/2” 1-1/8” 3/16"* 1-1/4” 1-3/8” 1-1/2” 2” 1-5/8” 2-1/2” ¼" 1-1/4” 1-1/2” 1-7/8” 2-¼” 2-1/8” 2-3/4” 3/8”† 1-5/8” 1-3/4” 2” 2-1/4” 2-1/4” 3” Hotspot Brush-off *Standard nozzle
  • 87. Chapter 5 – Type 2 Equipment & Mixed Technologies 88 Safety Because of the abrasive characteristics of blast type processing and the velocity of discharge of the abrasive, the operator must or should wear protective clothing and rubber abrasive resistant gloves. In self contained closed cabinets, all of these safety features are supplied as standard equipment. Blast systems designed to be used outdoors, or in large open environments, or enclosed blast rooms, need extra safety protective clothing and air breathing systems. All of these systems are regulated by OSHA and EPA rules that make safety equipment and/or clothing necessary for an operator of this type of equipment in all environments. However, the biggest concern or emphasis is on air born breathing apparatuses rather than physical injuries from the blasting. Initially sand blasting systems were the most popular form of abrasive blasting out doors and had few regulations. However, sand is a composite of different minerals and it is composed mostly of silica. Under current regulations any material containing silica requires safety precautions due to its carcinogenic properties and because blasting is primarily an air based system, that requires air breathing devices. Eye protection gear is also required and a major concern against air born particles. Lastly, because all parts and materials contain residue debris these contaminates as well as spent abrasives must be disposed of properly and not just left on the ground at an unprotected blasting site. In manual closed cabinets, safety or protective gloves are designed or permanently fixed to the cabinet in such a way as to make the systems completely air tight. In these manual type cabinet operations the operator can move the gun nozzle, fix it or the part in place, or turn the part in a close proximity to the gun nozzle within the sealed cabinet. Normally one hand holds the part and the other hand directs the gun or abrasive at the part. The operator observes what he is doing through a glass window in the sealed cabinet and does not need special eye wear, because that too is fixed into the cabinet. The closed loop cabinet system also has a continuous flow of air, which sucks the debris and finer particles into the dust collector and the larger media is re-cycle by gravity feed to and from the bottom of the machine. Nearly all debris is in the form of a dust and goes into a collection system which must be purged and disposed of on a periodic bases per regulations and/or specifications of the equipment manufacturer. Caution and proper maintenance is required for debris and dust collection. If not properly done or performed, explosions and fires can happen. The use of aluminum oxide and working of metals such as aluminum and magnesium are very susceptible to these types of problems. Pressure System: As the name implies, this is a systems that combines the air and abrasive particles into a single feeder line and has a much more simple nozzle discharge tube. With fewer parts and lines, this type of system usually works up to four times faster than suction systems because you can get greater pressure and twice as much velocity to the particles and/or
  • 88. Chapter 5 – Type 2 Equipment & Mixed Technologies 89 discharge with much less air pressure. In fact, air pressure is the only way to regulate a pressure system. Pressure systems have a higher abrasion ratio or factor than suction systems, because the abrasive particles are pushed by a positive energy force rather than pulled by a negative vacuum system. That means that there is more energy or force to the abrasive particle at the discharge nozzle and that allows the operator to work at lower air pressures. That also means that the gun hose will have to be replaced more frequently, but because of reduced pressures, nozzle should wear longer. No air is wasted in this positive flow process system, which is the direct use of air pressure to the blasting nozzle gun. Besides higher energy impact of the abrasive, other benefits are longer media and nozzle life and shorter time cycles and maybe better control and performance than with the suction type systems and at these reduced air pressures. Therefore, long range cost savings usually warrant the extra cost of this type of system. Pressure systems will remove heat treat scale at 60 PSI where the suction system may not, even at a higher pressures. The spray pattern or nozzle inside dimensional holes are usually smaller than suction systems. The I.D. range is normally from 1/8 inch to 3/8 of an inch and the spray pattern is smaller and more controllable. Other than the method of applying pressure to the abrasive, the operation and re-cycling of these systems are the same.
  • 89. Chapter 5 – Type 2 Equipment & Mixed Technologies 90 Fig. 37. Abrasive Blast Systems Abrasive blast equipment only provides the mechanics to effect product. That is, the equipment cannot work or clean a part properly without manual or mechanical movement to either the part or the equipment in relationship to the part. Therefore, movement is very important in abrasive blast systems. Most inexpensive systems are consider a closed loop cabinet where the operator opens a door inserts the part(s), closes the door, put his hands through the cabinet gloves to get to and hold the parts, and then looks through a glass window as he processes the parts. Visuals show the typical requirements of a closed loop abrasive blast system and two small-automated barrel tumbling systems.
  • 90. Chapter 5 – Type 2 Equipment & Mixed Technologies 91 Fig. 38. Automated Abrasive Blast Systems Because of the human factor and dwell time, parts may not get a uniform surface finish; therefore, when volume or uniformity are of concern, material handling or movement systems are desired over human processing. These systems can be as simple as a rotating barrel or table, some form of in-line movement, multiple or moving nozzles or any combination of these methods. The following illustrations depict some of the more common material handling systems. The letter G represents parts being processed.
  • 91. Chapter 5 – Type 2 Equipment & Mixed Technologies 92 Abrasive media Besides the equipment to provide the pressure or work energy, the abrasive blast media is the next most important ingredient in this mechanical system. Here we begin to change the terminology of the word abrasive or abrasive particles and use the more common term for most mechanical processes to media, because not all materials used to modify or do material removal are solely abrasives. Again, different sizes and hardness of media materials produce different results. Early on, the use of sand was the most commonly used media because of its known abrasive qualities and/or characteristics. It was also abundant and cheap. It was so common that most people still refer to this equipment and technology as sand blasting. However, it was also discovered that sand media had a relatively short life expectancy. That is, it could only be re-cycled about once or twice at about 60 PSI air pressure before it is completely used up or loses its mass and/or ability to abrade. Air pressure controls the speed or impact energy of the particle and/or material removal rate as well as the rate of decomposition of the media. A real low air pressure may get you a second or third re-cycling of sand media, but because of material volume and general maintenance and up keep, sand is not cost effective or commonly used or recommended for abrasive blast systems. Then again, if you lived out in a desert, it probably would be your first choice. Abrasive media selection should depend upon the type of abrasive or mineral, its size, shape, density, hardness, and friability and not cost. Unfortunately cost often dictates the media, instead of the other way around. Other features to consider depend upon the amount of air pressure one wants to use, the attrition rate of the media (which includes media size), the angle of the gun nozzles, and the type of material and/or surface finish desired. It should also be noted that by re-cycling the media over and over again, the pattern or texture of the finished product will change, because the media will also change. That is, with use and re-cycling, media will get smaller and smoother with use which is the same condition experienced with wheels and belts, but not as dramatic a change. The greater the angle of the blast guns, from 90 degrees, the greater the life of the media and the greater the volume of media impact to the stationary work part, which also produces a smoother surface finish. The material removal rate efficiency of the media is greatest between 45 and 60 degrees. As a rough guideline, large glass beads at high velocity provide a deep matte finish; whereas, low velocity produces smoother, brighter surfaces. A smaller particle size will generally produce a brighter smoother surface. When the size of an abrasive particle is doubled, so too is its kinetic energy. When velocity is doubled, its kinetic energy is quadrupled. The more common abrasive media in use today for most metal modification or burr removal is aluminum oxide and glass beads.
  • 92. Chapter 5 – Type 2 Equipment & Mixed Technologies 93 Other Media Some media used in this equipment is not really designed to be abrasive. Glass bead is manufactured from lead free, soda lime type glass that contains no free silica. This material is then made into a preformed ball shape that produces a much smoother brighter type finish than angular abrasive. Glass beads hardness is about a 6 on the Mohs scale and can be re-cycled maybe 30 times at 60 PSI. The media is virtually chemically inert and therefore it is a happy medium for high efficiency and an environmentally acceptable method of metal cleaning or surface finishing when properly controlled. Glass beads are the most common, general all purpose media and comes in a wide variety of sizes. See table showing comparison chart of other impact abrasives for cleaning, finishing, peening, and to some extent deburring applications. The heaviest abrasives used for blasting are from three main metal groups and are steel, malleable iron, and cast iron in either round shot or angular grit. Steel can be recycled 200 times or more, whereas, cast iron may be between 50 to 100 times and malleable iron falls somewhere in between these two. The hardest material is normally cast iron with a Rockwell C scale of up to 65. Both iron materials cost less than steel and break down faster and tend to be more aggressive than steel, but the life of steel makes it more cost effective. Steel shot is significantly heavier than glass bead and therefore achieves similar surface appearance on parts, but it produces a more noticeable dimpled pattern in a shorter period of time. Even with this heavy media, little or no burr is effectively removed and therefore this system remains a class 0 to 1 deburring system. Steel grit, silicon carbide grit, and garnet all produce fast results but because of the irregular angles of this media, the surface appearance is very dull. They are normally used to prepare or produce a rough surface texture which is good for secondary coatings to adhere. Aluminum oxide is probably the most popular abrasive media in use today because of its costs, its longevity, and its hardness. Besides glass beads, this media is probably the most common abrasive used in blast finishing and surface preparation. At 120 pounds per cubic foot of material, it is heavy and carries a lot of kinetic energy to the work piece. It rates an 8 on the Mohs scale. More gentle abrasive media for blast finishing are the organic materials of walnut and other shells plus corn cob. These organic materials are usually used in smaller machines or to work non-ferrous metals and plastics. Choosing the right media is not that difficult. There are relatively only a few options. However, as I say that, I also know that wheat starch, rice hulls, nut shells, fruit pits, sodium bicarbonate, ceramics, plastics, nylon and other synthetics have been used with good success. Perhaps the most important factor to remember is the larger the media particle the more material it will remove and the softer or finer, the smoother the surface finish. There are some special applications that may be of interest using abrasive blasting techniques. I mentioned corn cob as a soft gentle media, its specialty is in the use of paint stripping. However, more recent plastic media is now more commonly used to strip paint,
  • 93. Chapter 5 – Type 2 Equipment & Mixed Technologies 94 especially on aircraft. In fact special blasting gun nozzles for aircraft are now available to that includes a method of sucking or collecting the paint particles and abrasive debris in a vacuum type glove or bag type mechanism that hugs the surface of the material being worked or stripped. Instead of a cabinet that uses a gravity feed mechanism to recycle, this seems to do everything all in one and this produces a cleaner working environment. Actually the system is the same as a normal closed loop cabinet; however, the active or mobile head mechanism is open on one side to work the material and the hoses to and from the head are longer and further removed from the actual power and feed source. Small Systems Another special version of the pressure type equipment are small bench top systems. The working cabinet of these systems are a little bigger than a bread box, or close to two feet square. Some of these cabinets are even equipped with microscopes. This system deserves some special attention because it has a number of special features. Like their big brothers, these systems do require the work cabinet and a dust collector. Unlike the bigger systems, these systems cannot normally use air, but requires very dry air sources, of carbon dioxide, or nitrogen, which also should be filtered for sub micron particles. Because these are small systems, the nozzle or gun is also very small and looks something like a pencil that can easily be handled with one hand. The normal nozzles of these unites are very small, with an I.D. orifice of .005 up to .045 and are made of tungsten carbide or a synthetic sapphire. Other sizes and configurations are also available. The maximum flow rate of media is around 40 grams of material per minute. Naturally because of this small size and volume, production is usually limited to deburring, cutting, and drilling of small high tech parts, used in the electronics industry, but is also used for deflashing, cleaning, etching glass, and working small areas in other industries. Perhaps the biggest difference of these small systems, besides their air supply is the media and its applications. The media used in these systems are fine powders of aluminum oxide, silicon carbide and glass bead that can vary in size from 10 to 50 micron in size. Because of the size of this fine material, the supply source or feed of this material must first be vibrated before it is feed into the blast system. Also, the media is not re-used; rather it flows into the dust collector. The relatively low volume of media and debris does not load up the system very fast.
  • 94. Chapter 5 – Type 2 Equipment & Mixed Technologies 95 Fig. 39. Small Abrasive Blast Equipment Equipment size makes a lot of difference in finishing results, time, and area coverage. Although the media remains nearly the same, the abrasive particle size is normally a lot smaller and the results are therefore proportional. There are four variables affecting the cutting speed in small abrasive blast systems, which can be precisely controlled for maximum efficiency. They are: (1) distance to nozzle from the work piece, (2) rate of abrasive flow, (3) propellant gas pressure, and (4) the type of abrasive used. Although the figures below demonstrate experiments conducted on glass, the relationships are similar to other materials. Fig. 40. Technical Data of Variables Affecting Cutting Speed
  • 95. Chapter 5 – Type 2 Equipment & Mixed Technologies 96 Cryogenics: Another variation of abrasive blasting or type 2 equipment was initially developed for very soft and flexible products in the synthetics industries. Normal abrasive blast systems will not economically remove the burr or deflash rubber and plastics parts because of their flexibility; therefore, temperature is used to change the quality characteristics of the parts being worked. Under our classification system, this is both a type 2 and 5 system, because it uses both direct particle energy transfer and temperature to effect class 0 to 5 burrs in 0 to 3 location. Because the abrasive method of operation is somewhat secondary to the environmental controls our classification will be a four digit number to reflect how the equipment is different from abrasive blast equipment and that makes this a 5200 to 5253 system This burr classification covers a wide range of surface finishes and may need some explanation. Cryogenic blast equipment is used primarily to clean parts. Most cleaning systems do not normally effect the existing RMS of a part, because media made with gases or semi liquids will flow or deform upon impact with the material being worked. As long as the material being worked is harder that the media, there is no or little surface profile change. Some soft materials may still achieve a slightly higher RMS due to the media mass and impact energy of even these soft materials. Type five equipment systems represent the newer technologies that use cryogenics or below freezing conditions to effect material removal behavior. The equipment operates in a closed loop system just like abrasive blast systems, but it is designed to operate at extreme cold temperatures. There is a definite advantage in operating at temperatures below 32 degrees Fahrenheit, especially with organic materials and soft flexible materials such as rubber or plastic. These systems are especially good on molded parts. That is because thin parting lines, flash material, and/or minor burrs on primarily molded parts become stiff, rigid, and weak at low temperatures. The advantage of this lower temperature is that it takes less energy or impact pressure to remove these thin and normally flexible burrs. You might like to relate this equipment system to that of a functional refrigerator or ice making cabinet in that the work environment and parts are processed at below freezing temperatures, but the operator stands outside the cabinet without special protective clothing. The parts are loaded into the machine and pre-treated with liquid nitrogen, before being worked. The blast media must also be pre-treated before being used. The cabinets are made with double wall construction and insulated as well as the gloves to conserve the working temperature. Care is still required in handling parts in the cabinet as well as after they come out of the machine. These systems are very expensive due to the fact that this equipment uses liquid nitrogen and requires some additional features and items not common to air blast systems. Some early cryogenic equipment that are no longer used, use to also makes their own blast media which is CO2 gas in a solid pellet form. The carbon dioxide media use to act and behave just like organic abrasive particles. The most interesting feature about this media was that there was no waste or residue from the media itself. Any remaining media not destroyed in the impact soon
  • 96. Chapter 5 – Type 2 Equipment & Mixed Technologies 97 evaporated afterwards. The only material left was the excess flash or burr. Problems and costs are associated with these systems. Most of the media used in cryogenic deflashing systems today is plastic or nylon and again used on rubber and plastic products at low temperatures. There is virtually no use of this technology for working metal, because of cost and inefficiency. The media can be propelled by air or airless blasting mechanics. Also, it should be noted that the actual processing time of parts should include a pretreatment phase of cooling the part as well as the media. In addition to the liquid nitrogen machine systems, there are also some machines that still use CO2, dry ice or just normal frozen water, or wet ice to operate, naturally these are less expensive systems and they don’t operate as efficiently. Fig. 41. Cryogenic Blast Equipment Cryogenic blast equipment is used primarily on soft, very flexible materials such as rubber and plastics, but it can also be effective for cleaning very viscous covered materials. The system operates like a normal abrasive blast system except the work chamber environment or main ingredient functions at extremely cold temperatures. Surface finishing is not as important as removing excess, unwanted materials that normally occur with molding processes. The three main elements of the system are: velocity or pressure of the media, which is normally plastic shot, for the proper length of time, and at a low enough temperature to stiffen or freeze the excess materials.
  • 97. Chapter 5 – Type 2 Equipment & Mixed Technologies 98 Wheel or Airless Blasting: This equipment still falls under the classification of type 2, blast cleaning equipment. However, what makes this equipment different from air blast systems is that it is not propelled or controlled by air pressure but a mechanical energy force. The impact energy transfer system puts this equipment into a class 5 burr removal system in 0 and 1 locations. That makes this a 250 to 251 system. This system does the greatest amount of molecular material modification, produces the roughest surface profile, well over 35 RMS, and it can handle a 52 burr, but it will not remove it in a good clean and smooth way, which is typical result of all blast systems. This system is used primarily for surface preparation or treatment rather than deburring. What makes this equipment so different from blast equipment is that it is propelled or controlled by mechanical speed or velocity of a wheel mechanism alone. This system utilizes a mechanical spinning wheel movement or energy force to propel heavy weight media at high velocity speeds against a machined part or casting to descale, modify, or treat the parts surfaces. Remember our earlier statement. When velocity is doubled, kinetic energy is quadrupled. These systems are capable of blasting parts with 2600 lbs. of steel shot per minute over a broad work surface area, for as long as the media supply can hold up. Again, there is deterioration of the media that must be considered, but most parts are worked in a relatively short period of time. This equipment behaves almost exactly how the old blacksmith process worked, but without the heat problem. This is not so much an abrasive blast type system as it is a malleable surface conditioning process. The energy forces produced by weight and the high velocity of steel ball, pellet, or grit media does treat and change the hardness of the metal and/or relieves molecular stress from the manufacturing or machining operation of the parts being processed. Instead of effecting the molecular structure of the part as is accomplished in heat treating, this system uses impact weight to condense the outer molecular structure of the part in question. What happens here during this process is the surface becomes microscopically condensed and/or harder due to the dense re-arrangement of the molecules of metal. This can be achieved to some extent by using air blasting equipment, but wheel blast systems are special machines designed to employ the use of malleable impact knowledge technology or the movement and flow of metals under pressure to strengthen and/or stress relieve parts and weldments. The process can also be referred to as shot peening and the machines are called wheel or airless blast cleaning equipment. This system uses primarily mechanical energy forces caused by a rotating blast wheel which can be controlled by a fixed or variable speed motor from 1800 RPM to 3600 RPM. The blast wheel can be positioned or moveable and reversible, or there can be multiple wheels within the system fixed above or below the work piece. The blast pattern produced by the wheel within the machine can be adjusted; however, its greatest efficiency is located directly below the impeller and slightly to the side opposite the center line of the wheel rotation. The actual release point of the shot is at the 11 O’clock position prior to the throw line or where the media leaves the impeller.
  • 98. Chapter 5 – Type 2 Equipment & Mixed Technologies 99 Fig. 42. Wheel or Airless Blasting Equipment Wheel or airless blast equipment derives its energy from a wheel that transfers RPM’s to the velocity of the media at a designated rate, direction, and force. The media hardness, weight, and mechanical forces involved in turn effects the materials being worked. Because of the greater media weight more energy can be transmitted to the work and larger work pieces than other blast systems.
  • 99. Chapter 5 – Type 2 Equipment & Mixed Technologies 100 Because of this energy force, the work chamber and parts being processed by this equipment have to be rugged and thick, or else they may be distorted and will self destruct by this process. The machine cabinet is normally made out of ½ to 1 inch thick manganese which has good work hardening characteristics itself and becomes harder with use. There are even more expensive impact resistant construction metals available for longer life than the manganese. In addition to the special emphasis on the construction of this equipment, like the air blasting systems, these systems still require all of the same support accessories. That is, they require an air supply, the dust collection, and the abrasive material handling systems. The media used is normally larger than that found or used in air blast equipment. The terminology cleaning is often referred to, for this type of equipment, is not exactly the same as air systems or water based systems. Cleaning here usually refers to the descaling of heat treated parts, which are commonly processed by these systems. As stated, these machines are designed to produce clean work hardened parts, but because they do effect dimensions of the part or parts, they also produce uniform surface conditions which looks similar to a sand blasted finish. This type of equipment is not specifically engineered to do any deburring but is again only a surface modification processing that does reduce surface problem areas and burrs. Because of the tremendous energy forces and aggressiveness of these machines, these are rather large and heavy duty machine systems constructed with thick plates. Therefore in order to justify fabrication costs and construction large volumes and/or part sizes or special surface treatment problems are necessary to support the high costs of fabrication. Unlike sand blast equipment, most wheel blast cleaning machines are almost fully automated, except for the loading and unloading of parts by an operator. This automation is almost necessary due to the high energy forces of the media and impact debris. The machine is designed to isolate the work chamber to work normally one part at a time on a horizontal turntable and unless the table has a special fixture for moving the part, only one side of the part can be worked at one time. Some of these machine systems are designated as batch equipment and processes a small volume of parts. The work chamber of these batch machines allows the parts to tumble freely like the sand blast barrel type systems or they have a flexible chain type of convey belt that operates vertically within a closed chamber. There are still other machines specifically designed with more than one wheel and blast chamber to work some rather large parts or continuous parts and more than one side of a part at a time. However, a great many machines are fully automated for continuous straight pass through or rotary table type systems because of the potential safety problems or forces the operator can be exposed too. See application diagrams below. Shot Peening Media Shot peen or blast media varies from abrasive blast media in that it is less abrasive and is normally larger, more uniform in size and shape and therefore heavier. That is because the desired end result is to work harden or modify a part surface and not necessarily remove material. The more spherical the shape the better the surface finishing results and the more
  • 100. Chapter 5 – Type 2 Equipment & Mixed Technologies uniform the surface treatment. Broken or sharp edge particles can damage a parts surface resulting in an uneven non-uniform treatment. Fig. 43. Peening Media 101
  • 101. 102 Chapter 6 – Type 4 Equipment Wet Blasting or Water Hone: This is a type 2 and 4 equipment system that handles class 0 to 5 burrs from 0 to 3 location. Since this is a dual energy related system and its main source of energy comes from liquid under pressure, therefore, I have inverted the classification number to reflect that environmental relationship. That makes this a 4200 to 4253 system. Just like the cryogenic blast equipment, this classification number covers a wide range of surface finishes, because it is used more often for cleaning parts than producing surface finishes. Like all blast systems, the surface finish will normally exceed 32 RMS; however, because of the liquid element, the energy forces and abrasive particles will flow and/or deform on impact. That means that there will be little if any surface modification, provided the parts are harder than the abrasive used in the process. Wet blasting equipment uses an abrasive and a liquid energy transfer method system; therefore, the proper terminology for this system or process is called water honing. This equipment is basically the same as abrasive pressure blasting systems; however, because we are dealing with a liquid system and an extremely fine abrasive this process generally produces smoother surface finishes because it has more flexibility and/or buffing action to the media. The energy of the particle size is, to a large extent, absorbed by or into the liquid; therefore, the impact of the media to the part isn’t as great as an air blast system. In fact, the blast processing is similar to cleaning parts with high pressure water or heavier more viscous water. This process produces less contact impingement than air blast systems and generally produces no compressive stress or work hardening on parts. In most cases, the finer media used in a wet system would not be able to be processed by normal air blast systems because of its surface tension. That is, small media can reach a point where it behaves like glue or wants to become a solid again and air pressure alone would not be enough to keep it flowing. Given the same media size particles, pressure, and time used, a wet system produces results that are smoother, brighter, and have more shine; however, contaminates and/or oxides can still produce dull gray finished parts. Lastly, even though the wet system does not require a dust collector, the pumps, and controls necessary for wet blasting normally makes this equipment more costly than air blast systems. Actual operation and costs are comparable, but there are more maintenance problems. Then there is the need to treat or change the liquid system periodically. Like the air blast system that self purges out smaller particles in a dust collector, a wet system has to use liquid filters.
  • 102. Chapter 6 – Type 4 Equipment 103 Fig. 44. Wet Abrasive Hone Wet abrasive hone equipment looks exactly like an abrasive air blast system except the cabinet system is watertight. The closed loop cabinet and operations uses water instead of air to move the media which is an extremely fine abrasive powder and this results in less material removal and a finer surface finish to parts.
  • 103. Chapter 6 – Type 4 Equipment 104 Water Jet: This is a type 4 stand alone system, suitable for class 2 and 3 burrs to handle in type 1 location only, but it can do some work in 2 and 3. Because this is a limited pass or has very little dwell time on a specific area of a part, it has relatively no effect on the RMS surface finish or profile of that part. This equipment has limited applications and range that will make this a 421 to 431 system. It has been known for some time that water alone does do material removal work of soft or soluble materials. High pressure water jet systems have been used for some time for cutting metal similar to either plasma or flame cutting equipment. Water pressure systems are not commonly used for deburring, but there are trends that indicate they are gaining popularity as more machines are being used that have improved surface coverage to do deburring. They are not to the point of a dishwasher, but they are getting there. Water jet technology will not radius existing edges, but it will remove lose fragmented burrs effectively. Usually these machines are specifically designed to wash or clean parts first and deburr as a secondary operation. The first machines specifically designed to do deburring were introduced in Germany in 1974. A typical water jet deburring machine system operates at pressures of about 5000 to 9000 PSI. At pressures greater than these, this equipment is used for cutting; but just the same, care must be exercised not to dwell on a part for any extended period of time for even at these pressures materials will be worn away or cut to some extent, especially softer non-ferrous metals. There are two principle methods of operation for water jet deburring equipment. The more common system that is more effective, uses a rotating nozzle holder, fitted with two nozzles that rotate at high speeds of 200 to 850 RPM and moves in a set direction which is computerized to create multiple over lapping patterns. The other basic system is used more on flat parts and uses a set of broad fan like nozzles that again travel or move the part in a set pattern. Because the latter spray pattern is more spread out, it has less concentrated pressure to deburr the parts, but it lends itself to continuous pass through type systems. Water jet technology is relatively new, therefore the pumps are also new and still being developed and improved. That means that there may be significant maintenance time required to keep the system functioning properly. However, the greatest equipment wear is in the nozzle orifice, with the broad flat fan spray nozzles being effected first at about 100 hours of operation. To improve or protect both the part from wear and oxidation and the nozzle life, chemical detergents and inhibitors are added to the deburring liquid. Some more powerful water jet cutting equipment utilizes extremely fine abrasive media to improve or speed up their cutting ability. Therefore, the addition of abrasives is likely to be more common in the not too distant future of water jet deburring equipment as well. Again, the major problem is the wear resistance of the nozzles. Material limitations and the extremely high pressures wear the nozzle orifices relatively fast, therefore, improvements in this area are expected.
  • 104. Chapter 6 – Type 4 Equipment 105 As long as we are talking about primarily a water system and before we move on to more abrasive removal type equipment, we should talk about ultrasonic applications. The water jet uses straight water under pressure to deburr or modify materials. In the near future, these systems may include the use of very fine abrasive particles or liquid enhancers to give more density, bulk, or energy to work faster. It is a lot more difficult to excite or agitate water or energize water to do material removal; however, it can be done on a microscopic level. Water Jet Deburring Water is the simplest and cheapest medium that can be used to deburr, but great pressures are required for abrasion to take place by way of a narrow jet or focused concentration of water. The molecular structure of water allows it to penetrate the densest of materials and modify whatever it comes in contact with; therefore, pressure, pattern concentration, and dwell time determines the effectiveness of material removal of water jet equipment. Fig. 45. Methods of obtaining broad jet coverage In essence, the following methods are used to achieve the extensive deburring and cleaning of component parts.  Spraying with rotating nozzle holders, fitted with circular jet nozzles  Spraying with flat jet nozzles arranged in a row
  • 105. Chapter 6 – Type 4 Equipment 106 Ultrasonic Deburring/Polishing: In lieu of inline water pressure created by pumps, water can be mechanically excited or energized without great inline pressure. Boiling is one way to energize water and electromagnetic excitement is also possible. Ultrasonic cleaning system have been know and used for years as the best method to clean the porosity of all materials and as we said earlier, cleaning is actually the removal of semi-solids. There is no one machine system designed and marketed today as yet to do straight ultrasonic deburring in a liquid tank system. However, it can be done, but the results are normally better accomplished faster, cheaper, and easier using other methods; therefore, there is no equipment and no rating. To clarify my statement, ultrasonic tank systems can and have been used for cleaning and that is a material removal system for contaminates and soils. It should also be mentioned here that a test of a good ultrasonic cleaning system is to place aluminum foil into a tank to check its power. A good system will put holes in the foil; therefore, with the proper concentration and direction of energy, ultrasonic applications can remove or modify solids on at least a small scale. Deburring can be accomplished using this technology and therefore should be mentioned with or without a rating system. Remember, before the laser was invented, there were only forms of the incandescent light bulbs. Ultrasonic cleaning utilizes the principle of electro-mechanical energy to power or energize water to remove soluble material contaminates. To create that force, an electric current or a modulated electric current is introduced to a quartz crystal called a transducer. A pulsed current causes the crystal to expand and contract very rapidly and that transmits a low power radio signal that effect the water molecule. Present equipment operates at a range of 23 kilohertz to about 80 kilohertz, but its energy is measured in watts. Ultrasonic crystals are normally manufactured in a cone shape to direct the energy to the large end of the transducer which is sealed to the underside of a liquid tank. Because we are dealing with solids, the electrical connections and the seal must be properly bonded. The electro-mechanical energy then focuses energy up through the transducer and the tank wall, and that in turn agitates the water molecules and creates standing energy waves inside the liquid. Present technology says the lower the frequency, the more powerful the energy is transmitted in standing waves. That means that unless a part is moved, there will be gaps or voids of no work on the part in question; therefore, some newer systems use a modulating frequency range than one set power output. The water is effected by the ultrasonic energy wave vibrations and causes the water molecules to break down and implode similar to how solids release kinetic energy. As this implosion occurs there is also very violent movement occurring in positive directions as well as negative movement. This violent movement on a microscopic level produces an extremely good mechanical movement or action to clean all material immersed within the agitated liquid. The terminology cleaning is more associated with using ultrasonic energy systems than with deburring. That is because this process equipment uses mostly chemicals to get a reaction
  • 106. Chapter 6 – Type 4 Equipment 107 with the materials being worked. That is, the liquid in the process is more of a controlled chemical action and reaction rather than a mechanical abrasive system. To do any abrasive deburring and/or polishing using this equipment or system requires a delicate balance of a solution capable of suspending an abrasive particulate. An alternate method would be to somehow move the liquid just enough to keep the abrasive in suspension and not interfere with the ultrasonic energy that produces energy waves. Remember, the energy wave force only effects the water molecules that in turn moves the particulate. Therefore, that also means that any abrasion must be relatively light. Ultrasonic Deburring Water based systems are very effective methods for cleaning or dissolving soluble materials; however, it is rarely used to deburr parts without using a great deal of pressure. Yet, on a microscopic level, water agitated by ultrasonic does exert great energy that can do minor material removal. Ultrasonic equipment at present is only used for cleaning and not deburring. Fig. 46. How Ultrasonic Deburring Works In an ultrasonic cleaning system, cavitation bubbles form and grow under the influence of negative pressure in the rarefaction portion of the sound wave. As the sound wave progresses, negative pressure is replaced by positive pressure in the compression portion of the sound wave, causing cavitation bubbles to implode, which releases mechanical energy in a “jet” or shockwave. This energy release enhances and facilitates cleaning processes
  • 107. Chapter 6 – Type 4 Equipment 108 Ultrasonic orbital system There is now a machine system on the market that claims the right to be called an ultrasonic orbital system. Unlike the previous mentioned ultrasonic systems, this system uses primarily solid forms to transmit energy and behaves like a reciprocal motor. Like other previous ultrasonic systems, we are still talking about relatively light deburring, but this equipment is used mostly for very limited polishing work type applications or class 0 burrs in type 1 locations. The equipment still falls under our classification 4 system; however, it is a modified type 4 system or 4 and 2 system, making this a 4200 system only. The RMS range is very limited using this equipment. The surface improvement range will only be about 0 to 8 RMS. That means that normally parts being processed have to be smooth or under 20 RMS before they are processed. Even this number does not describe this machine system adequately, because the liquid used in this process is really a slurry of liquid and a fine abrasive that is energized perpendicular to the work piece. Typical applications are for polishing molds and finishing blind cavities. The equipment uses contact pressure, combined with a unique blend of liquid, abrasives, and a moldable rigid tool. As mentioned, this equipment behaves similar to a reciprocal disc system and employees both mechanical and electro-mechanical energy forces. Material removal rates normally do not exceed .0005 of an inch or less and can achieve surface finish improvements of 5:1 to 10:1 and as smooth as 4 micro inch. The machine system looks something like a hydraulic press. The main work tool is a special shaped transducer attached to a probe type extension which in turn holds a piece of graphite or glass that works the part. The transducer behind the tool is electrically excited and produces mechanical energy forces that are transmitted to the end piece tool. This end piece is then placed onto the part that has to be worked. The probe and the stationary part are then immersed in a fine abrasive slurry. When the tool is activated the graphite or glass end piece is ultrasonically agitated and because of the contact pressure, it molds itself into the work piece and in so doing it also modifies the work piece. There is some periodic movement of the tool up and down in order to bring new abrasive slurry to work the part. The neat thing about the probe is that it does not require a pre-shaped tool or special alignment. Everything is done and functions automatically. The abrasive slurry that is used in conjunction with the ultrasonic probe uses a 300 mesh or finer abrasive material. Normally, silicon carbide is used; however, a lot has to do with the hardness of the material being worked. In some cases harder materials and fine diamond abrasive must be used. A lot of the materials used are diluted forms of materials used in the next category of equipment called Extrudehones or abrasive flow systems.
  • 108. Chapter 6 – Type 4 Equipment 109 Fig. 47. Ultrasonic Polishing Proper finishing of molds and blind cavities has historically been a labor-intensive, time-consuming and expensive procedure. The ultrasonic process achieves a polishing action by vibrating a brittle tool material such as graphite or glass into the Workpiece at ultrasonic frequencies and relatively low amplitudes. The polishing action occurs as the fine abrasive particles in the slurry abrade the high spots of the Workpiece surface, typically removing 0.0005 inch (0.013 mm) of material or less. The extent of polishing required is determined by the initial surface roughness of the Workpiece and the finish required after polishing. Typical surface improvements range from 5:1 to 10:1; finishes as low as 4 μ inch(0.1 μm) Ra can be achieved. In orbital polishing, controlled material removal occurs by the Workpiece being oscillated orbitally in the horizontal plane while being fed vertically into a containment cylinder of abrasive media. The advance rate of the Z axis (vertical axis) is controlled in an adaptive mode, where the Z axis federate is predicted on pressure feedback. As the Workpiece is inserted into the media cylinder, pressure rises causing the media to conform to the geometry (of virtually any reasonable configuration) and to become semi-solid, three-dimensional sandpaper, improving surface finish and removing burrs.
  • 109. Chapter 6 – Type 4 Equipment 110 Abrasive Flow: Abrasive flow or extrude hone technology is relatively new and follows the pattern of abrasive materials as the main source of material removal, but in a modified form. The abrasive media is a cross between a liquid and solid that flows under pressure. Because the media is unique, I am showing this process and equipment as a separate category, but it may be considered an extension or progression of the wet blast system previously mentioned. That is evident by the use of the terminology honing which is used to describe wet processes of material removal. Really this is an abrasive flow machining process. However, because of heavy viscosity or cohesiveness of the abrasive media used in this system, this is more an extrusion process than a true honing system, hence the name. For sake of classification, I will call this a 4 and 2 or 42 type system, which handles class 0 to 4 burrs in type 3 locations. That makes this a 4200 to 4243 system and a surface finish from 10 to 24 RMS depending on the processing media. This equipment utilizes a mechanical means of using abrasives in a semi-solid form closely resembling putty or silly putty. Because of the flow characteristics of the media, this system tends to work best in confined internal passageways or inner dimensions, but with proper fixturing, external areas can also be worked. Positioning of the part and the proper control and direction of the semi-solid media is very important to achieving the desired finishing results. Under hydraulic pressure the media is energized or forced to move or flow through a fixed stationary part. The abrasives are dispersed and suspended in a gelatinous putty like polymer matrix that flows under pressures from about 100 PSI (7 bar) to 3,200 PSI (200 bar). Normally the higher the pressure the faster the flow and material removal, but it also depends on the viscosity of the media. Because of part design and material construction some parts may not be able to take the high pressures exerted by this equipment; therefore, there are some limitations as to what parts can be efficiently processes using this technology. The abrasive hone works something like the hydraulic cylinder which is used to move the media. That is, the whole machine behaves like one big hydraulic cylinder, except in this case the work chamber is completely filled with media and is under pressure, or the media is directed or allowed to flow through the part and then exit. The movement applied to the heavy viscous abrasive material is forced through and/or around the fixtured part in a two stroke up and down flow cycle of the hydraulic cylinder. The resistance and pressure of the abrasive in the media putty then modifies the part where the media is allowed to flow. If the media does not flow, that section of the part will not be worked; therefore, this will not work blind holes or dead end passages.
  • 110. Chapter 6 – Type 4 Equipment 111 Fig. 48. Abrasive Flow Machine Process Schematic In a standard abrasive flow process, two vertically opposed cylinders extrude abrasive media back and forth through passages formed by the Workpiece tooling. Abrasive action occurs wherever the media enters and passes through the most restrictive passages.    The major elements of the process include: The tooling which confines and directs media flow to the appropriate areas; The machine which controls the media extrusion pressure, flow volume and if desired, flow rate; The media, which determines the pattern and aggressiveness of the abrasion action that occurs. By selectively permitting and blocking flow into, or out of, Workpiece passages, tooling can be designed to provide media flow paths through the Workpiece that restrict flow at the areas where deburring, radiusing, and surface improvement are desired. Frequently multiple parts or passages are processed simultaneously. In a linear abrasive flow system, flowing abrasive media moves through workpieces in only one direction. Some advantages: The tooling need only provide a seal at the inlet to the Workpiece allowing simpler tooling and more convenient loading. The outside of the Workpiece is not surrounded by media during processing, which means easier unloading and cleaning. Media removal from the processed passages of the part can be accomplished in the processing station, collecting and returning it via the same hopper and in the same location stream as the processed media. Since media can exit freely from the part, there is less flow resistance that isn’t performing useful work, consequently processing is faster and less heat in produced in the abrasive media.
  • 111. Chapter 6 – Type 4 Equipment 112 Fig. 49. Abrasive Flow Variation Another newer variation to this abrasive flow system is a faster one way machine that automatically re-cycles the spent slurry. Tooling is very important and/or can be selective in working some areas and not others. That is, it can restrict flow to only the area that needs to be worked. Tooling is not only for holding the part, but to restrict and direct the flow of the putty like media. Tooling can channel the pressure and/or abrasion to the burr area of the part provided the part is adaptable to the parameters mentioned and can accept the pressure, frictional heat, volume, media, and multiple strokes. This technology is especially good and useful for deburring parts that have a lot of internal, deep, inter-connecting cavities. Abrasive Flow Media The media used in an abrasive flow process is a very special synthetic polymer putty like material that can vary in viscosity to achieve different results. The more solid, denser, or lower the viscosity of the media the slower the movement and the coarser the surface finish and higher the material removal rate. The higher the viscosity, the faster the process and the finer the finish. Media viscosity, extrusion pressure and passage dimensions determine the media flow rate, which are calculated by dividing the flow volume by the processing time. The abrasive used in the polymer is typically silicon carbide with a particle size of .0002 up to .060, but boron carbide, aluminum oxide, and diamond can also be used. Time cycles of 1 to 2 minutes are common, but finer results may take up to 7 minutes per cycle. The life span of the media depends upon the amount of materials processed and its efficiency will decline until it needs to be replaced in a couple of weeks. In addition to deburring parts, there is yet another slight variation to this equipment called an orbital polishing machine. As the name implies, this equipment is designed
  • 112. Chapter 6 – Type 4 Equipment 113 specifically to polish. The equipment to do this work is similar to the deburring equipment, except that there is a mechanism that produces a horizontal oscillation between the tooling, the work piece, and the slurry. The speed of oscillation and orbital amplitude is 400 to 1200 RPM and the tooling is usually made of nylon or polyurethane. The height or amplitude of the oscillation determines the amount of material removal; however, this dimension cannot exceed the height of the surface variation to be worked. The polymer slurry used to polish is of a higher viscosity than that used to deburr and does not flow while in use from one chamber to another, rather it moves or flexes in place. Like the previous technologies, the abrasive flow machines or Extrudehones are still a one on one type machine system. That is, the number of parts that can be processed are determined by the tooling fixture or fixturing. This type of system is adaptable to production line technology, but requires a lot of automated material handling systems which can increase productivity by loading and unloading and/or the use of multiple cylinders for processing. Also, just like abrasive blast type systems that require a dust collection system, the abrasive hone type system may require the use of a clean and wash cycle as part of its production to remove the polymer residue. This does not have to be built into the machine or dedicated to this specific manufacturing process, but is recommend for high volume production. Therefore, this equipment can and is quite costly.
  • 113. 114 Chapter 7 – Type 5 Equipment Thermal: This is a good opportunity to explain another relatively new technology called thermal deburring. This system is classified as a type 5 equipment process, but it can only work up to class 2 burrs effectively in 3 locations, and it will not affect the overall surface finish of the part. That makes this a 500 to 523 system classification. Although heat is involved only, this system processes parts or produces parts similar to abrasive extrusion, except the work medium is primarily an air plasma instead of viscous solid. This system is good for parts with the same deep internal holes, cavities, and/or hard to reach burrs. Deburring takes place in the same uniform manner as how the flow of abrasive putty material works its way through a part, except instead of a semi-solid abrasive material as the work tool, the tool here is heat caused by pressurized air and combustible natural gas. In fact, it is not a mechanical process of burr removal at all. It is a short thermal heat cycle induced system and/or controlled combustion system that burns away excess burrs. If you define the word burn, it is a very rapid or violent form of oxidation similar to an explosion. In the case of thermal deburring, a batch of parts can be placed loosely in mass into a basket or fixture which then goes into a work chamber that is sealed with a clamping force of 200 to 400 pounds. For more uniform finished parts, placement or orientation of the part is sometimes helpful for processing. If the parts are not restrained, they may fly out of the container during the rapid combustion and/or subject to possible damage. These systems are relatively small or accommodate small parts. The larger work chamber machine systems measure about 10 inches by 6 inches; therefore, capacity is limited. Smaller systems are more powerful and efficient. The work chamber when sealed is filled with natural gas and oxygen which are pumped in under pressure and then ignited. The mixture of gas to air can be from 2.5:1 to 9:1. Some machine systems feature a dual shot capability. The result is an instant combustion like explosion, burn, or oxidation, which reaches temperatures of 6000 degrees Fahrenheit that lasts approximately about 2 milliseconds. This heat burst is so intense that sharp edges and burrs vaporize into an oxide powder and gases. Normal processing time is usually less than 1 minute. Why the heat effects the burr instead of the part is because of the high ratio of surface area of the burr to part mass. Also, the time cycle is so short that the heat cannot penetrate or damage the rest of the basic part. However, there can be a residue oxide coating from the burr that can and will deposit on the part during the cooling cycle. Large burrs may produce small molten round ball like weld splatter and excessive burrs may just round off like an incomplete molded shape. Because this is not a mechanical system that uses pressure and resistance to remove the burr, what you get is a slightly modified version of what you started out with. That is, flat surface areas will not be effected nor improved by this process. The only areas that will be effected are the sharp edges or burrs created in the machining of the part and should this be an
  • 114. Chapter 7 – Type 5 Equipment 115 irregular burr varying in thickness, the finished product may still be similar to an irregularity. Almost all applications are on metal parts, but with proper adjustments, plastic can be worked also. Thermal Deburring Temperature has an interesting effect on all materials. Earlier we discussed cryogenics that made soft flexible parts stiff, brittle, and weak for media to work easier. Now we come to the opposite category. Extreme high heat temperature for a short duration can literally evaporate solid materials. The following explanation describes this process more thoroughly Fig. 50. Thermal Deburring
  • 115. 116 Chapter 8 – Type 4 Equipment Chemical Milling: This is not so much a physical piece of equipment as it is a process, just as the name implies. This is classified as a type 4 process that uses chemicals for the removal a class 0 to 3 burrs in 3 locations. That makes all chemical processes variations of a 400 to 433 system. It is not a mechanical abrasive process. That also means that basically what you start within the way of a surface finish is what you are going to end up with but with slightly less material or an etched part and it can be bright and shiny or dull. If the part is rough or around 35 RMS (average of the surface variation determined by a profilometer measuring root mean square), it will end up roughly the same or maybe slightly better. This is because this process involves the reaction of chemicals and solids, which dissolves or removes small amounts of material in an etching type operation controlled by the concentration of chemical, temperature, and time. A good part of the actual material removed goes into solution, heavier debris settles to the bottom of the tank, and some material is transferred into heat and gas. Using a straight chemical process, a number of parts can be grouped together in a batch type operation, tumbled in a basket, or just immersed in the acidic or caustic chemical for a relatively short period of time. Even though I have just explained this process of material removal, there is almost no use of this technology for deburring purposes because of the hazards involved and/or the lack of good controls over the process, chemicals, and parts. There is a slight variation of this process used called ECD or electro-chemical deburring which we will talk about shortly. On the positive side, this is the first technology we have talked about that can be considered a type of mass finishing process if it utilizes a rotating chemically resistant barrel system of operation. However, in a straight chemical process, most parts have to be oriented for the work to be done properly and requires the use of good liquid circulation or part movement. This form of batching can also utilize a material handling system that works in batches or continuously, but again due to the hazards and lack of controls there are no machine systems designed to do a straight chemical milling process. There is one popular form of chemical milling, machining, or deburring to work class 0 burrs which is used to produce electronic computer circuit boards. Technically, we are talking about a cutting operation here rather than deburring, because the end product is composed of a flat composite material that has basically no observable burrs. Why it is still considered as a deburring process is because we are dealing with extremely fine micro burrs. This is a popular method for burr removal in the computer industry. Control is achieved with masking materials that are required for precisely controlling where the chemical will perform its work to create good clean clear and isolated or delineated circuit lines and pads. Printed circuit boards are sensitive to electrical current, so normal plating methods are not used. Burr or material removal is limited to microscopic burrs over a wide broad area.
  • 116. Chapter 8 – Type 4 Equipment 117 When chemically milled parts are done, they must be rinsed in order to stop the reaction from taking place. If the rinse process is done improperly, too much material removal may cause more problems or create more burrs than they correct. Therefore, time, temperature, and the concentration of the chemical is important in controlling the rate of material removal or burr or it will create a larger burr problem. Technical knowledge of metals and chemicals are very important because of reactions and/or the release of gases and by products. This technology is primarily a liquid system, which involves a series of cleaning, rinsing, chemicals, and more rinsing tanks. This system requires a large processing area and support equipment to maintain safety and the integrity of the chemical processes. Such systems are more often associated with plating type company operations rather than an in house manufacturing operations, unless it is part of a large volume parts producer. This is true, primarily due to the major fact that this industry is controlled by a lot of safety regulations involving both people and the environment. Again, this process is very specialized, regulated, technical, needs a lot of support, and is relatively expensive. Before we leave the category of chemical processing, we should say that we are talking about plating industry processes. However, most plating companies are concerned with putting on a coating, not taking something off. To be short and sweet, the difference between a straight chemical systems and the next subject of electro-chemical deburring is the use of an electrical current. Like thermal deburring, electro-chemical deburring will attack burrs or irregularities first. The speed of material removal depends upon the chemical, its temperature, current density, fixturing, and the metal alloy to be worked; however, the addition of electricity does speed up material removal and does make it a more controllable deburring process than straight chemical milling applications. There are a number of variations in electro-chemical deburring. It can be used with or without acidic solutions and stationary electrodes to remove metals. Often the parts are passivated or surface hardened against oxidation during the deburring process, because of the chemicals used. The parts can be fixtured, racked, or tumbled in a barrel. There is one process in mass finishing that uses graphite ball media in a barrel, with parts that can conduct an electric current, and an electrode. As the barrel rotates, the balls both act as an abrasive as well as a conductor of the electric current, which works with the chemical to remove the burrs. Electro-Polishing Nearly all forms of chemical surface modification all fall under the same equipment classification range of 400 to 433. Electro-polishing is a form of electro-chemical deburring that uses an acidic electrolyte and an electrical current that can be used on most metals, but will not work well with alloys containing silicon. It is actually a deburring system, but it leaves the entire surface of the metal bright and shiny; therefore, it is sometimes used just for the final appearance of the part. This process differs from electro-chemical machining by using a heated chemical bath combination of phosphoric and sulfuric acid chemicals and requires a anode and cathode plating technology or fixturing of parts in a bath.
  • 117. Chapter 8 – Type 4 Equipment 118 The process works by using an electric current to create a very thin monomolecular film of gas that builds up on the part, and any burr or material sticking up through this gas tends to burn off. Besides burrs, high profile surface features or material peaks are first effected in this process. Given enough time, other significant material removal will occur on flat surfaces because of the chemicals involved. Metal surface finishes will normally be brighter on all areas of the part. Surface finishes will not be as smooth as mechanical processes, but they may look better. ECD/Electro-Chemical Deburring Another deburring process using liquids is called electro-chemical deburring or ECD. It is the most popular form of chemical deburring, because it is fast, accurate and can handle up to class 3 burrs. It is different from the electro-chemical polishing I mentioned earlier, because the liquids used are not strongly acidic and do not etch or passivate the metal. This material removal process is also very selective and is different because electrical current does most of the work. In an ECD process, the liquid is a simple 20% salt solution of sodium nitrate or chloride mixed with water which is called an electrolyte and has a pH of around 7 or is neutral. The solution only conducts a direct electrical current and/or a flow of electrons and metal ions from positive to negative anodes. In addition to an electrical flow the electrolyte is also designed to flow under a pressure of 5 to 40 PSI. The liquid flow and current can be adjusted to increase the speed of the deburring process, which is extremely fast. Parts are normally processed in seconds, but material handling takes up significant time. Fixturing is very important in this process. The normal gap between the part and the anodes is approximately .020 to .060th of an inch, but can be .010 to .020. The smaller the gap, the faster the process works; however, the gap depends on the size of the burr, liquid flow, current, and time. Opposite the fixtured part is an electrode designed to conform to the finalized size and shape of the parts dimensions. To activate the process, a direct low voltage electrical charge is introduced into the liquid bath tanks via the anodes and directs a flow of electrons that travel through and from the part through the liquid to a negatively charged anode. This process is very fast and selective. Deburring is localized to where or what has to be removed. That means that tooling plays a major role in deburring. In all cases, the parts to be worked have to be fixtured onto a specialized rack type system which is then immersed into an electrolyte solution. Then, an electrical current, which is reduced through a rectifier, must be allowed to complete an electrical circuit which dissolves the burr. There are no other physical changes to the part or liquid during this process. However, the fixtures and solution must be cleaned and properly maintained continuously. Chemicals used vary with the metals being used, but surprisingly a lot of these products are proprietary. Also, this process can only be used on metallic parts. Most machine systems are automated to a point where the operator loads a fixture while another fixture is being processed.
  • 118. Chapter 8 – Type 4 Equipment 119 The results of ECD processing are fast, from 10 to 30 seconds, and can be controlled a lot better than straight chemical milling or electro-chemical milling, but the additional support equipment and material handling can be a whole lot greater and more costly than the other systems. Some variations of this process move the parts or have moving electrodes or brushes to pass over the burr area instead of moving the liquid and some even use an electrode mesh that is laid on the part and dissolves in the burr. The benefit of ECD is in precision control of the material removal process, plus the chemical solution is very inexpensive and is relatively safe; however, the accumulated waste and debris must be neutralized before disposal in solid waste fills. Fig. 51. Electro Chemical Deburring Electro chemical deburring (ECD) works almost identically to thermal deburring except that it operates in a chemical liquid bath. Temperatures, but mostly opposite electrostatic charges work in opposition to each other to remove loose or thin sections of non-parent material. To operate efficiently, the positioning and/or tooling representing the anode or cathode are very critical to the performance of this type of system. (see diagram) Unlike chemical milling, which takes a long time cycle, ECD works in seconds. Picture Shows the sectional view of a simple EC deburring fixture where we deburr the intersecting holes on the Workpiece (10) A) The lower fixture with the baseplate (1), the Workpiece locator (4), the electrode with the connecting bus bar (10) and (2), the electrolyte connection with the internal cavities (3) B) The upper fixture consisting of base (5), positive anode contact (8), anode spring (6) and electrical connection (7). The entire fixture will be attached to the machine feedhead, advanced to make contact, and will charge the part positive. If applicable, it will also place the electrodes in relationship to the Workpiece. Retracting the upper fixture after the deburring cycle is completed will clear the lower fixture so finished parts can be unloaded and undeburred parts loaded. Burlytic ECD Process There is another variation of ECD with the trade name called Burlytic deburring. This is a more forgiving process similar to what is used in the plating industry and is almost identical to the first electro-chemical deburring/milling process I described earlier. This system uses a large
  • 119. Chapter 8 – Type 4 Equipment 120 tank systems and rather simple tooling procedures. Unlike normal ECD, the Burlytic process electrolyte chemical is run at ambient or cool temperatures and is somewhat of a selective deburring system over that of ECD and requires no special tooling. Also the electrolyte does not need to be pumped under pressure, but must be agitated and the electrical current application is different. Instead of low voltage over a given period of time, this process uses high voltage in a pulsed method of operation. Actual time to do the material removal is about the same. ECD does work faster, but because of the method of current distribution, the actual material removal rate is about the same. The Burlytic process is a computer controlled system; therefore, it is a more expensive than ECD. Its actual tooling is quite simple and inexpensive; therefore, its overall operating expenses are less than ECD and it can also work a wider range of both ferrous and non-ferrous metals. The process produces normally bright polished looking finishes with surface refinement or smoothness of 4 to 8 RMS thereby making it a little more versatile than ECD. Fig. 52. ECD Processing Equipment Systems The term electro-chemical deburring can also be referred to as electro-chemical machining. The process utilizes the flow of an electrical DC current through a liquid chemical bath or tank. The difference between most systems varies how the parts are attached to fixtures and/or electrical connections, power requirements, time, and the liquids used. Below are two widely used systems
  • 120. Chapter 8 – Type 4 Equipment 121 Fig. 53. Burlytic Process About the Burlytic Process The Burlytic process uses a patented electrolyte solution and a computer controlled energy source to achieve a new level of performance in electrolytic deburring. The electrolyte has a high electrical resistance. When a machined part is immersed in the solution and a low DC voltage charge is applied between the part and a stationary cathode, an electrostatic charge is concentrated at the sharp features (burr) on the part. In high-density areas of the electrical field, burrs are dissolved and carried away by the electrolyte. By applying voltage in controlled pulses it is possible to provide polishing action over an entire Workpiece or focus the deburring activity to just the edges of the part. Small ECD System: As indicated, most ECD systems require a lot of space and to some extent support equipment. There is one slight exception to this type of system. There is a small hand-held one man machine that can do the same job, but only one piece at a time. This machine's tank is roughly 2' square by 6" deep and contains and re-circulates an electrolyte salt solution. Attached to this tank is a rectifier generator that conducts the electrical current between a hand-held wand and the part. The wand is hollow and allows the solution flowing through it to complete the electric circuit. The part to be worked is placed in the work tank against a metal base plate and the wand is then placed on or near the burr to be removed. The liquid flow and a metal gap between the tip of the wand and the metal part and plate permits an electrical current to disintegrate the material as the wand passes over it. It is a relatively small, inexpensive simple system that works or behaves like a welders torch, except with a liquid.
  • 121. Chapter 8 – Type 4 Equipment 122 Fig. 54. Small ECD System As an alternative to large processing tanks is a small portable mini ECD deburring system that is good for low volume or multiple configuration parts. This unit is not as powerful as larger systems, but it has universal applications and does not require special tooling. Rather, this system relies on a hand-held guided electrode wand or stylus that serves as the tooling. The electrode is a brass and plastic tube assembly that is easily replaced or modified for special applications. All work is performed within a 25 inch square x 5 inch high tank and powered by a separate generator attachment. The electrolyte solution is normally a non-hazardous sodium nitrate that works well with most metals
  • 122. 123 Chapter 9 – Type 3 Equipment Mass Finishing Equipment We have finally reached the classification of type 3 mass finishing equipment or deburring mills. The latter name of mills is not commonly used, but that is their function to grind or exert abrasive pressure in a free or loose state via mechanical energy forces and gravity. It is the only equipment or machine systems to employee energy flow patterns to move the entire mass of abrasives and parts as a single unit, hence the origin of the name. It is also the only system that uses gravity as a primary pressure source of energy along with mechanical energy movement applied to the largest size of abrasive media in an unrestricted free flow pattern. The type 3 systems can handle from 0 to 5 class burrs primarily at mostly number 1 locations or the O.D.’s of a part, making the equipment range from 300 to 351 in our classification system. I am tempted to give them a 353 rating; however, solids going through holes is not normally a good idea, because of the possibilities of media irregularities and or multiple shapes getting stuck within the part being worked. However, even though they are not recommended for internal deburring or surface modifications, they are still better than type 1 systems and maybe type 2, with the exception of abrasive flow systems. These systems can achieve close to a 4 RMS surface finish starting from around 35 RMS in multiple sequential step processing. Anything above 35 RMS is not recommended for processing. The terminology or mass finishing reference is due to the fact that a large volume of parts can be processed in a batch or continuous flow with or without abrasive media in a free tumble process movement or X,Y & Z dimensions within a work chamber. The handling of parts in mass is one of the biggest advantages of this equipment over all other systems. It is versatile, quick, easy, and requires relatively little direct or indirect labor, just machine time. These systems normally do not require any special preparations for cleaning or holding the parts, but can be adapted for special applications. Most systems can process a wide diversity of part sizes, shapes, materials, and weights. The size of the part processed is only limited by the size of the machine and the range of the surface finish is only limited by the abrasive media shape and particle size. Most machines in use are manually loaded and unloaded, but fully automated systems are available. The primary purpose of automation is to lift the media and parts to the height of the work chamber for processing. Most machines will unload without much help. The equipment provides the mechanism to apply abrasive energy forces to the mass, or is the vehicle used to remove material, or to get to a certain designated surface finishing point and/or achieve the desired end results on parts. Mass finishing systems transfer or use energy forces that are applied to a work chamber to create uniform energy patterns within the mass that effect the parts and materials placed into the work chamber of the equipment in relationship to abrasive materials and gravity. It is a mechanical abrasive process. How the energy or force is applied to the abrasive determines the speed or processing time cycles and
  • 123. Chapter 9 – Type 3 Equipment 124 that distinguishes the difference between these mass deburring systems, but there are still some other factors besides energy considerations as well. Generally speaking, mass-finishing equipment can be broken down into 3 generations of technology improvements or types of equipment. These equipment systems are the barrel, vibratory, and high energy or centrifugal systems. There are other machine variations or systems that use the same abrasives and use mechanical energy forces, which are indirectly related to these systems, but unless the parts can be processed in mass, they are not a true mass finishing system. For those reasons mentioned, the following systems or equipment will be listed in their order of historic lineage, speed of operation, and price. What primarily makes these machine systems different from one another is their speed of operations and this is the result of the technology used to exert energy forces to the abrasive and parts within their work chambers. All these systems can produce nearly the same end results; however, it is a question of time. As a general rule, the rotating tumbling barrel system takes the longest time to process parts. That is followed by vibratory systems, which improves processing times by a factor of 10 and then there are the high energy centrifugal system that improve processing time by another factor of 10 over the vibratory equipment. The use of gravity is very important to mass finishing systems. If it weren’t for gravity, none of these systems would work. Gravity is translated into weight, force or friction, and pressure. All mineral abrasives have different weights and molecular density and that is expressed as a value known as specific gravity for all materials (see tables for abrasives). Parts too have weight, density or harness and size, but these are variables that are not distinguishable with a scientific constant. The greater the weight of the mass the greater the force, friction, and material removal. That greater the concentration or density of the abrasive and parts, meaning the height of the mass, the greater the downward pressure and friction in the work chamber. The speed of the mass movement and how the energy is applied is also important. The only thing the equipment does is to create a flow pattern or movement to the solid abrasives and parts in a uniform pattern. Basically you have a solid mass moving in a limited or restricted work chamber and this exerts energy on a smaller sized particles and mass and that produces pressure resulting in friction. It is the weight of the mass that exerts the pressure on the parts and the larger the abrasive shape and particle size of the media the more the material removal. What you put into a machine determines what comes out of it. What media you use determines how the parts and mass are modified. By increasing the speed of rotation or gravity one increases the energy forces and improves the pressure and speed of material removal process. All mass finishing systems have some form of a work chamber or container for the work mass. The barrel is nothing more than a large sealed container that is turned, rotated, or moved on a stationary frame in a fixed position. It turns or rotates the contents within at a speed that does not exceed the force of gravity which is 32.174 ft. per second square. Vibratory systems move or oscillate the work container and contents inside from an outside energy source that creates a moving vertical amplitude that does not exceed a half an inch in height and creates a pressure of about eight times the force of gravity. High energy centrifugal systems use both
  • 124. Chapter 9 – Type 3 Equipment 125 external and internal forces to apply pressure to its work contents also. An internal disc spins the mass and that transfers energy directly to the parts, up to 25 times the force of gravity. The high energy barrel systems uses counter rotating barrels to increase the pressure up to 30 times the force of gravity within the work chamber and that is then transferred to the mass and parts. Naturally the more advanced high energy centrifugal systems have the shortest finishing time cycles and are probably the most aggressive systems now, but they are also the most costly. Although vibratory systems are somewhat slower, they have quick unloading or material handling advantages over the manual high energy systems. The barrel systems are still popular because of slightly lower prices than vibratory and they get good polishing results even though they are slow. A lot of engineers compare the processing technology of mass finishing systems to that of a three-legged stool. That is, the equipment provides the mechanical energy forces, the media performs the work, and a liquid4 keeps everything functional. If one of these three factors is not performing well, the parts to be processed will not achieve the desired end result. Therefore, of all of the systems mentioned so far, perhaps mass finishing equipment is the most difficult to master, because of the three variables. Some people even call mass finishing systems technology black magic or black art and is one of the reasons why a number of companies do not like to use this type of equipment or processing system. That is because it is possible to work a batch of parts which will be processed the same and uniformly, but the next batch or another batch some time later can have some variation if something in the process has changed. Like any new piece of equipment, there is a learning curve. It takes time to master all the variables. Even though there may be problems from time to time, these systems usually out perform all other methods of deburring by a long mile in relationship to cost savings or processing costs per piece. As mentioned, the main advantage to mass finishing equipment is the fact that parts can be handled or worked in mass and can produce consistent uniform finishes per batch of parts, if done properly. These parts do not have to be racked, placed in a fixture, orientated, or done one piece at a time. Also, the parts do not normally have to be cleaned prior to placing them into a machine. The liquid and chemical used in the processing can usually handle most contaminate problems. Therefore, mass finishing systems lend themselves very well to high volume production and a wide range of part sizes and materials without much labor and maintenance. The Barrel: Now, at some early point in history it was discovered that a true bowed barrel shape allowed people to move great weight from place to place fairly easy. Because of the round barrel shape, only a small portion of the barrel actually touches the ground, acting like a big wheel, and that allows for relatively easy movement over flat surfaces. In the movement process NOTE: Besides a liquid as the main source of cleaning or lubrication, small dry inorganic or organic particles can be used to take the place of liquids and chemicals. 4
  • 125. Chapter 9 – Type 3 Equipment 126 it soon became evident that the rotating barrel also had the ability to effect the contents inside, especially loose objects not tightly packed. In most cases, especially food stuffs, this was not a desirable intent of the barrel design. On the positive side, it was thought to be a good probable means to effectively work surface conditions of objects and modify sharp edges within the barrel. By simply holding the barrel in place and allowing it to rotate with abrasive and materials inside, it became a tool to work other harder materials, formerly worked by hand. That concept created the advent of mass finishing barrel tumbling systems for deburring parts which remains one of the principle methods of working parts even today. Operating Principle of the Barrel A barrel system works by rotating a closed work chamber containing parts and abrasive media in a one directional mode of operation. As the barrel rotates, a work action or slip of the mass occurs inside the barrel by the raising of the contents or work load to a height where gravity over comes inertia and any cohesive properties of the mass itself. This movement creates a spill down zone or a continuous slide in primarily one direction or motion, but some side movement and/or tumbling action can take place. The original bowed wooden barrel had some minor compression and greater side tumbling capabilities than the more recent straight barrel designs built for efficiency and longer wear. Most barrels used in production are built symmetrical for simplification of construction and made from metal that can be coated, not like the bowed wooden barrels of old. To improve the action or movement within this type of equipment, large barrel systems have broad flat hexagonal sidewalls that create a greater degree of lift or aggressiveness to the media and parts within. A single uniform curved barrel surface is constantly trying to rebalance the load within, whereas rotating flat areas create a more rapid pulse type movement to the workload. Most smaller barrel systems are made in a round shape for cost purposes. Prior to the decline of popularity of all the barrel systems, some barrel designs began tapering or bowing the ends of the tumbling barrel to get more x and y movement and compression or friction to the work mass. Another innovation tried was to vibrate the barrel while turning it in order to speed up or improve upon barrel processing times and finishes. Unfortunately, most of these innovations could not significantly improve processing times to justify the cost of these features.
  • 126. Chapter 9 – Type 3 Equipment 127 Fig. 55. Mass Finishing Systems Barrel Tumbling Equipment Barrel tumbling systems go way back to ancient times. They are simple, they are easy to operate, and they have been around for a long time and will continue to be around for a long time. Probably the only new addition to the barrel system over the years was the introduction of electrical power. The diagrams below illustrate the principles of operation and a picture of a large single and double compartment machine system. The tumbler corners lift the load until it reaches a point where it slides down the hill. The bumping and scraping against the stones (or themselves) abrades the parts. At least 90% of the work is done in the upper 1/3 of the load Barreling Action Capacity The actual working capacity of a barrel is approximately 50% of the volume size within the barrel. That is, a normal 5 cubic foot barrel holds two and half cubic feet or approximately 250 lbs5 of media and work mass. Of the weight and volume, only about 50 to 60% of the work mass is parts; therefore, the classification of capacity is somewhat confusing. That is, some manufacturers rated their equipment by working capacity based upon parts and some used the size of the work chamber to identify their capacity. In either case, the standard unit of measure was based upon volume rather than weight or liquid capacity. For this example, we used 100 lbs. equal one cubic foot; however, media does vary for 55 lbs. minimum for plastic, 90 lbs. avg. for ceramic, to 330 lbs. for steel. 5
  • 127. Chapter 9 – Type 3 Equipment 128 As the barrel system rotates, the actual active work zone in the barrels work chamber only occurs on the top level of the media or about 1/3 of the mass inside. The other 2/3 of the work mass is virtually dormant or inactive. Typically, the load level or capacity of a barrel, at 60% of its volume, with the liquid level one inch below the mass level should produce an abrasion rate of 150 surface feet per minute. Fig. 56. Barrel Processing Equipment Speed The speed at which a barrel rotates is very important, because the slide of work load depends upon the diameter of the barrel, the R.P.M.'s., the height of the media and work load mass, and the height of the liquid level. The normal speed of rotation of our example machine is very slow with an optimum speed of around 27 RPM's or about 150 SFPM (surface feet per minute) for polishing and good part finishes. Processing cycle time depends on the size of the barrel and also affects the surface finish of the parts. See chart: R.P.M. for Barrel Diameters RIM or Surface 40 Feet/min 50 60 70 80 100 120 135 150 165 180 200 225 250 4.8 5.7 6.7 7.6 9.5 11.4 13 14 16.2 17 19 22 24 36 32 30 28 24 23 20 17 16 15 13 12 11 5.3 6.4 7.4 8.5 10.5 12.7 14 15 18 19 21 24 27 6 7.2 8.4 9.5 12 14.3 16 18 20 22 24 27 30 6.4 7.6 8.9 11.3 12.7 15.2 17 19 21 23 25 29 32 6.8 8.2 9.5 11.7 13.6 16.3 18 20 23 25 27 31 34 8 9.8 11.3 12.9 16.1 19.4 22 24 27 29 32 36 40 8.3 10 11.7 13.3 16.7 20 23 25 28 30 33 38 42 9.5 11.5 13.3 15.3 19 23 26 29 32 35 38 43 48 11.5 13.6 15.9 18.2 22.7 27 31 34 38 41 45 51 57 12 14.3 16.7 19 24 29 32 36 39 43 48 54 60 13 15.3 17.8 20.5 25.6 31 35 38 42 46 51 58 64 14.7 17.6 20.6 23.5 29.4 35 40 44 48 53 59 66 74 16 19.4 22.6 25.8 32 38 44 48 53 58 64 72 81 18 21.4 25 28.6 35.7 43 48 54 59 64 71 80 89
  • 128. Chapter 9 – Type 3 Equipment 129 A good barrel system has a speed control that can regulate the RPM’s of the barrel. This is important because some burrs, if subjected to a energy forces of a normal deburring cycle speed, can be deformed and or rolled over to one side quickly, making them more difficult to remove later. That means that a good machine operator will first start the machine at a lower speed to avoid this problem and then increase its speed 10 to 15 minutes later. Small barrels require faster speeds to equal the same amount of SFPM. Faster speeds maybe desirable for deburring parts, but these faster speeds may overcome the force of gravity and interrupt the constant even slide zone within the barrel and that in turn may cause part impingement, pitting, or an orange peel effect, and/or damage to the parts being processed. Instead of the parts tumbling, they may get air born and get pounded or showered with heavy particles causing impact damage. Where the part surface finish is not important and shorter time cycles are more desirable this may be acceptable process, but it is not the best use of the equipment. Continued use at high RPM’s will shorten the life of the media, by breaking it up faster, and/or effect the inner walls or liner of the work chamber as well. The standard barrel systems efficiency to deburr or polish depends on the ability of the work mass (parts and media) to slide down a slope created by gravity. As mentioned, if the slope is broken up by too fast a speed the parts may become air born causing part damage and/or the barrel system becomes ineffective. Too slow a speed does not hurt the parts but it just makes the time cycle longer. When faster speeds are desirable, make sure there is a greater quantity of water and chemical compound in the barrel to give more cohesion to the mass and this will also soften or buffer the impact or hammering effect of the media on the parts. Barrel tumbling systems have been around a long time, but are not as popular as they once were, mainly because of their slow speed of parts finishing, operator intervention, and the need for material handling. However, they probably still produce the best polished parts of any mechanical system using dry organic materials, that is because barrel systems produces long smooth slide patterns against the part, similar to the effects of a buffing wheel. Barrel systems are still very popular for burnishing or bright finishes. Steel ball burnishing media is also use for work hardening parts, especially the smaller systems that operate on rollers. Because these systems are considered closed loop, they work well where chemical treatment of parts or harsh chemicals are desired. Lastly, some of the older chemical compounds that foam a lot seem to work better in barrel systems and produce better end results than the newer chemical formulations that go into more aggressive finishing equipment. Liquid The reason for the popularity of barrel systems is due in part to their simplicity and the heavy construction of the work chamber barrel. They hold up to a lot of abuse and weight as well as strong chemical concentrates. This type of machine can handle a large volume or liquid content and the chemical factor is used very effective in metal burnishing. The normal water and compound solution for a barrel system is one gallon per hundred pounds of media. For deburring, less water or a level of 1 to 3 inches below the mass level is desirable. For burnishing, more water is preferred or 1 to 3 inches above the mass. Care is required when using strong
  • 129. Chapter 9 – Type 3 Equipment 130 chemicals, especially when unloading the barrels after processing is complete. Be sure to slowly pre-release any sealed hatch cover prior to opening due to chemical reactions and/or pressure caused by heat generated during processing. Getting back to the ruggedness of the equipment, perhaps we should spend a little time on the work chamber liners. Because barrels are designed to abrade parts, the abrasive materials and parts used in the process also abraded the wall construction of the work chamber. Early on, barrels were made completely out of wood and some were designed to run with water in water. These systems date back to ancient Egypt and China, but there are still some in use today that uses a barrel design that permits water to flow in and out of the barrel. These systems have limited use and are used mostly for cleaning and to some extent polishing. Inner Wall Construction More heavy-duty barrel construction is from metal, but some are still lined with wood. This wood acts as insulation and allows a buildup of heat and it also cushions heavy parts so that damage is less likely to the part. These wood lined barrel systems are still in use today and are preferred for gentile light weight parts and dry organic media processes designed to polish plastic parts and restoring clarity to clear cut plastic. Naturally woods is not a good barrel liner for abrasive deburring work or long wear. They should not be used for extremely heavy parts unless the deburring or polishing media is greater than 80% of the mass volume. Wood liners also have to be replaced often to prevent more serious damage to the outer metal barrel itself. Such maintenance repair or replacement work does become quite costly. Therefore, for more aggressive abrasive processes a one-piece interior coating or a more flexible abrasive resistant liner is recommended or necessary to prolong the life of the work chamber. The first practicable abrasive resistant liners used to coat these work chambers were made from neoprene rubber based materials. Unfortunately these liners don't stand up to a lot of the chemicals used in the processing of parts with the media. Eventually, most of the liners then changed to PVC or polyvinyl chloride based materials. These worked exceptionally well; however, their life span was not as great as the neoprene. Next came the urethane liners that are now the most popular of all the liners used for all mass finishing equipment. These latter liners last extremely long and are chemically resistant; however, the PVC materials still seem to give a little better traction to help the media rotate. Therefore, you will still see some PVC and to some extent neoprene liners in smaller barrel system. Barrel systems are still popular for removing a lot of material on outside surfaces and rounding edges, or putting a radius on parts over a long period of time. Time cycles may take days. On the positive side, barrels still produce maybe the closest finish to a hand buffing operation than any other mass finishing machine system. On the negative side, besides speed being a factor, the one directional mode of operation also affects material finishes. That is, in the actual tumbling operation very little media gets into the inner dimensions of a part. That means that the outside edges of a part get worked very hard or aggressively while the inside
  • 130. Chapter 9 – Type 3 Equipment 131 dimensions get barely touched; therefore, barrels are not recommended for deburring parts with machined recessed surfaces, slots, or grooves. Large Barrel Systems: There are three basic designs of barrel systems in popular use. They all rotate parts in a one directional mode, but how they do it is slightly different. The most common system, as stated above, is usually a hexagonal barrel attached to a frame with a shaft secured to the center portion of the outside barrel or it can be a through shaft axle type. This barrel can be one, two, three, or more closed compartments with secured access hatch covers on each to allow multiple parts processing at the same time. Each work chamber can have a different media and part; however, if they are different, then the processing time cycles may also be different. Probably one of the most annoying problems of a large barrel machine is the loading and unloading of the barrel. Because barrel systems are the oldest form of mass finishing machines around, most large production systems did not and still do not have very good positioning controls. This positioning problem is also a result of the chain and sprocket drive design. That automatically means that there is linkage and gearing that behaves like a digital system, or that there are just so many spaces and voids where the barrel can stop. The number of gear teeth and size of the linkage determines the position of the barrel and there are just so many teeth. To load these machines, there is only one access hatch to the work chamber and it must be in the right position for both loading and unloading. The problem of not being in the right position results in spillage and time delays. To position or jog a barrel takes a quick button push of an on-off electric switch and visual attention. That action creates a short jerky movement of the barrel. Because of the weight and load position of the mass within the barrel and the lack of a good dead stop or brake, the barrel tends to want to re-position or move itself back to its original position after its power is cut. That means that positioning is not always easy to control; consequently, as mentioned, there may be rapid lurching and missed positioning of the hatch cover which can cause problems and time delays as well as extra clean up. To load the machine, the barrel must be manually jogged or stopped at least 45 degrees to its upright position for optimum loading. Media and parts must then be brought up to that level of the opening and hopefully the container is not larger than the hatch opening. Large barrel systems should take at least a minimum of 50 pounds of parts and maybe up to 1000 pounds or more per batch. All large systems should have hoist or material handling accessory assisted systems. The height of the barrel opening can vary to some extent, but it is usually at least 4 feet from the floor level and even at this height, repetitive motion and weight can be strenuous if this is done manually. To unload parts, the access hatch must first be stopped again at the top side, then the access hatch removed and/or replaced with a screen hatch cover. In any lower position, or straight down, the inner contents of the mass will exert a pressure that will interfere with removal of the hatch as well as cause a possible safety problem to the operator. Another problem of the hatch cover is that it only allows access to the barrel, a barrel with its opening
  • 131. Chapter 9 – Type 3 Equipment 132 straight down may not completely unload its contents, because a hexagon shaped barrel will retain parts and media on the flat section adjacent to its hole opening. After the appropriate processing time to work the parts, the barrel or work chamber is stopped, then jogged or rotated by a drive mechanism and positioned perpendicular to gravity. Without the use of gravity, barrel systems cannot work. With the screen hatch cover in place, the barrel can be slowly rotated allowing its contents to be spilled or jogged again to direct its liquid contents, debris, or media to the ground, a screen deck, or container. The fastest way to unload and separate parts is to dump everything onto a separator screen deck. With a screened hatch cover in place smaller media can go through and the parts will still be left in the barrel, but the restricted opening can still leave some media mixed with the parts. In lieu of the hatch cover application, some barrel machine systems have provisions for detachable screen decks built into the machine below the barrel. Because of liquid problems, most big barrel machines have a specially designed area with sloping floor and drains. Provisions must be made to catch or direct the liquid, media, and/or parts. As mentioned, to speed up material handling operations, the entire contents of the barrel are dumped onto a separate screen separation system. In all cases, problems of liquids and the positioning control system does not making dumping of the processed liquid or slurry simple. Also, in most cases, the liquid can contain chemicals and contaminates which again presents problems for the operator and maybe in and out plant environment. For more immediate safety reasons, operators wear a lot of waterproof safety clothing and possibly a respirator. Because of the viscosity and chemical composition of the affluent, special plumbing and holding tank systems are common. This is normal procedure for large machines over 5 cubic foot capacity or more. Medium or Open End Barrel Systems: I chose to call this section of machines medium size capacity or open end barrel systems, because the typical machine in use is relatively small to medium at about 5 cubic foot capacity which is about the most common. This is a popular machine system because it works well in a manual mechanical mode with human physical power supplying most of the machines loading and unloading movements. There are larger systems which have automated tilt features of up to 9 cubic feet, but the majority of machines in use are of a medium size capacity. This design variation of a barrel system has only one axis point and is normally always open on the other end. This can be considered a cantilever mount design, which looks like a cement mixer; however, unlike the mixer, this barrel has a greater number of flat sides and like the mixer, it is slightly larger at the bottom mount area than the top. Most of these systems are designed so the barrel work chamber and motor are inter connected in a fixed position and attached via a bevel gear. The motor is mounted and moves on the opposite side of the tilt mechanism from the barrel. In this position the motor acts as a counter weight and somewhat offsets the weight in the work chamber. Still, some machines have additional weight added to the motor area to offset the mass weight within the barrel.
  • 132. Chapter 9 – Type 3 Equipment 133 The biggest advantage of this equipment is the quick loading and unloading capabilities of the machine system. The barrel can be emptied very quickly and manual loading is normally about the same height as the horizontal barrel or at a person’s waist level, before the work chamber is re-positioned in the operational mode. The tilting mechanism on all cantilever systems allows for quick dumping of parts and media. Positioning or tilting of the barrel is done by hand and can be adjustable from straight up to straight down, or complete turned around until fixed into position. Because this dump and load system is normally done manually, these machines are not big systems like the horizontal units; rather, they are maybe 5 cubic foot maximum to about 1 cubic foot in capacity. The manually lifting and controlling of the work chamber or weight movements basically determines the sizes of these machines. That also means that a lot of these systems are used for drying or polishing of parts with organic materials, because organic media is lighter in weight. The work chamber or barrel normally operates on a 45 degree diagonal line of rotation. Actually they can be adjusted from zero to 90 degrees or at any point in between as long as the parts and media don’t fall out as the barrel rotates. This angle produces a media or mass flow that is similar to a vortex pattern common in all mass finishing equipment. While in operation, the one directional cascade of the mass is the same as horizontal machines, but the slide pattern of the media in this machine, can vary anywhere from 60 to 30 degrees. At 45 degrees, the slide zone within the barrel movement maybe slightly greater than that of a horizontal barrel system, but there is not as much weight or mass; therefore, time cycles maybe slightly greater than horizontal barrel systems. These systems usually operate without a cover or sealed hatch because the media does not reach the opening while in operation, which is not true of the bigger horizontal systems. In this operating position the opening allows for quick visual inspection of the parts and processing without stopping the machine. The machine is fixed in place or stationary while in operation, but it can have wheels and is easily moved around to different shop floor locations. Another versatile feature is that the machine is capable of tilting 180 degrees thereby allowing the machine to be loaded on one side or very close to another machine, processed, and dumped to the opposite side. When parts are added to these open end barrel systems, there is a tendency for the flow pattern to change and because of gravity the parts seek the bottom of the greater portion of the elongated mass within the barrel system. Unlike cement mixers, most of these machine systems normally don't have vanes to upset the parts, but they could have them. In fact, fins or lifters can help achieve better mixing of the media and parts provided the parts do not get stuck on them or damaged due to contact. The main reason for these machines not to have lifters is because of the possibility of part damage due to the parts hitting the next moving lifter. A movement of the lifter vane is opposed by the gravity and flow pattern of the mass and therefore two opposing forces produce a great deal of force and possible damage. If the parts and lifters are completely submerged under the
  • 133. Chapter 9 – Type 3 Equipment 134 media, then the risk of damage is drastically reduced. The flat sides of the typical barrel normally provide sufficient energy and mass movement within them as to not require lifters. Open End Bottle Another problem with any barrel design is that mass movement within the work chamber is somewhat restricted. That means that part separation can occur in relationship to the mechanical motion and gravity if the parts are extremely heavy. Speed will only improve part movement and media pressure on the part to a certain degree, beyond which there is no improvement and inefficiency. To make barrel system more aggressive there is a special shaped barrel system called a bottle tumbler. These barrel systems have work chambers with large bottoms and small top openings similar to that of a bottle, hence the name. In addition to increasing the mass mixing or rotation of the parts, the bottle shape design also produces greater, more uniform compression forces on the mass within. As the load rotates in primarily one direction there is also much more tumbling motion in X, Y and Z directions caused by the shape of the barrel. Therefore, these barrel systems are sometimes referred to as triple action machines. Bottle tumbler machines are not very common because of the higher fabrication costs of the work chamber. Also this bottle shape design was introduced about the same time as other more aggressive deburring systems became available. Another reason for their scarcity is because their actual working capacity is about 1/3 rd of their rated size. That is, if the machine is called a 3 cubic foot machine, its actual working capacity with parts and media is about one cubic foot. Barrel Shape Designs and Applications Most barrel tumbling systems operate in uniform of symmetrical shaped horizontal barrels. When barrel system use a vertical of angular rotating position, they tend to have a larger dimensional configuration at the bottom of the work chamber and a narrower open top. Better surface finishing results can be achieved with a horizontal barrel system, but they are not as user friendly as tilt barrel barrels. Also, parts having a greater length than width or thickness have a tendency to tumble end over end in tilt barrel designs which result in excessive wear on outside dimensions and ends. Therefore, the bottle-shaped tilt barrel design creates a more aggressive triple action flow pattern within the work chamber and mass resulting in shorter time cycles and a more uniform finish to parts.
  • 134. Chapter 9 – Type 3 Equipment 135 Fig. 57. Tilting Tumbler Machines The tilting tumbler is a versatile machine suitable for wet or dry barrel finishing procedures. An old favorite for finishing, it offers the advantages of fast loading and unloading as well as rapid inspection. This is especially useful with runs of short duration. This particular machine features a tapered octagon shaped barrel for maximum tumbling action. The barrel is metal and watertight. If necessary, the barrel can be lined with wood or seamless vinyl. The tilting device will swing the barrel a full 180˚, the barrel is automatically locked in any position. The tumbling dryer machine combines tumbling action and heat to dry and clean parts with corncob grain or sawdust. A heated barrel speeds drying time and lengthens the life of the drying agent (corn cob grain or sawdust). Open-end bottle or triple action barrel mixes parts and media similar to a horizontal barrel
  • 135. Chapter 9 – Type 3 Equipment 136 There are some very small open end barrel systems that are less that 1 cu. ft. capacity in size, but most of these machines are not what I would call industrial production machines, unless you are talking about very small parts less than a half inch in size. Because of cost factors, these small systems are made at a fixed angle and the whole unit, with the motor, is picked up and tilted to empty the contents. Again, because of these limiting factors, most of these machines are typically used as parts drying systems, but they can also be used to perform wet deburring operations as well. Small Barrel Systems: The last type of barrel system is for smaller machine systems, usually under 1 cubic foot. These barrel systems can be just smaller versions of their big brothers, but more often than not, they normally run on rollers and bars, which are turned by a separate power source. That is, there is a separate power rail system that rolls and turns the barrels as they sit on the rotating rails and that bar movement turns the barrels. The barrels are separate and only held in place by gravity. Like the medium barrel systems the weight of the barrel and its contents basically determine the maximum size of these systems. That is, you can only lift just so much weight onto one of these power rail systems unless you use a secondary material handling or lifting device. Most of these barrels are made of one piece, light weight, molded polypropylene. For ease of loading and unloading, the barrels have a large hatch cover opening on the side of the barrel. Most of the power rails are designed to accommodate one to eight of these barrels at a time. These detachable barrels do not normally exceed one cubic foot capacity in size and can get down to .10 cu. ft. The versatility and light weight of these systems make them popular in the jewelry industry and/or used a lot for small parts batching.
  • 136. Chapter 9 – Type 3 Equipment 137 Fig. 58. Small Barrel Tumbling Systems All of the tumbling systems on the following page operate with removable barrels. The upper right system uses a central shaft that clamps the barrels and holds them in place. The other unit’s barrels rotate by riding on rails that turn the load. They are held on by gravity.
  • 137. Chapter 9 – Type 3 Equipment 138 Loading and Unloading Systems Loading and unloading of these machines is always a slow process in that the media and parts must be placed in the machine and then dumped to sort out the media from the parts each time the machine is used. That is because the systems with hatch or door mechanism have a somewhat restricted opening to get parts and media into and out of the barrel. By the way, and that also means that an additional operation must be performed that requires another accessory piece of equipment. Without a separating screen or sorting device the separation of parts from media can be very time consuming operation. As mentioned, some large barrel systems may have a special door hatch cover that can be replaced with a screen to allow media to fall out and the parts stay in during a slower rotation cycle, prior to unloading, but I have never seen a very fast effective system. Most large barrel machine systems have accommodations for flat screens to be installed slightly under the rotating barrel. Besides the screen deck, two containers are required. One to catch and hold the media and the other for the parts. This feature permits all the contents of the barrel to be dumped at one time and allows the machine to be refilled and started again while sorting can take place below the horizontal barrel. While this is technically possible, moving equipment in close proximity to an exposed rotating piece of equipment is now regulated by OSHA standards and may no longer be an acceptable condition. Self powered mobile screen systems may be utilized and acceptable to speed up unloading; however, because of the safety cover or cage around the machine that must be place before the machine is started, even this accessory may be a problem or restricted during machine use. Therefore, sorting must take place either immediately upon dumping, before the machine is restarted, or moved to another location for separation. Dumping the entire contents of the barrel usually saves time; however, not always. No matter what unloading system is used, there is going to idle machine down time. Another interesting feature about parts separation is a great reliance on hand picking of parts out of the media mass, especially when the media used is nearly the same size as the parts or larger than the parts. It is an extremely slow process. That is, it is slow if the parts are smaller than 3/8 of an inch and when there is a large quantity of parts involved. When parts are big in comparison to the media is the fastest method of separation. However, more often than not, people tend to think that they can manually separate parts from media faster than accessory devices. In most cases this is a false assumption. Flat screen separators are the most common separating devices that are used and as stated earlier, some of these are built onto large barrel systems. These manual or stand alone screens are good separation systems up to a certain point. As stated, when there is a big difference in part size and media, separation is relative quick and easy. When the parts are less than twice the size of the media, or the hole size of the screen opening is less than twice the size of the media there may be difficulty in properly separating parts from media. The most important thing to remember is to get a screen with the greatest amount of open area in relationship to solid part of the screen.
  • 138. Chapter 9 – Type 3 Equipment 139 Mechanical Screen Separators US std Tyler Micron Size Inch Size Mesh Mesh Approximate Approximate 4 4 4760 0.185 6 6 3360 0.131 8 8 2380 0.093 12 10 1680 0.065 16 14 1190 0.046 20 20 840 0.0328 30 28 590 0.0232 40 35 420 0.0164 50 48 297 0.0116 60 60 250 0.0097 70 65 210 0.0082 80 80 177 0.0069 100 100 149 0.0058 140 150 105 0.0041 200 200 74 0.0029 230 250 62 0.0024 270 270 53 0.0021 325 325 44 0.0017 400 400 37 0.0015 All screen systems are designed to separate parts from media. For large volume production, powered vibrating screen systems are favored over manual systems, especially where large volume and weight are involved. In most applications, the parts are larger than the media. Normally, for speed, all the contents of a mass finishing system machine are dumped onto the screen deck, which has a raised edge or border to funnel and direct the parts. Some systems are extensions to existing internal screen ramps or decks. Most screen systems only use one size screen to separate the parts from the media, but multiple screens can be used to sort the media for critical tolerance problems either with the parts or the media. All of these systems have a place for containers(not shown) to collect parts and media separately. Some of the more common screen hole sizes And/or standards are shown here. To improve separation there are automated stand alone systems which are designed to vibrate by themselves and are usually mobile or easy to move around. These systems are relatively fast, provided there is a substantial size difference between the media and the parts. If there is not a big difference in size of media versus parts, separation maybe a little more difficult, especially in separating parts smaller than the media. Media that has been worn or random media may still get through these screens and mix with the smaller parts. Another problem of flat screens is that even with vibration assisted shaking of the screen, there may still be problems of media laying or sitting on top of parts. If a part has a recess configuration, media can get stuck in these areas or just rest on top of the part during separation. Therefore, in nearly all cases, even with screen systems, manual hand labor and monitoring may still be required for complete and proper part separation. The only sure way of removing all media from a part is to upset the part during the separation process from the media by rotating the entire mass before allowing the part to exit the screen. The rotary screen looks like and is a large diameter perforated tube that turns on normally powered rollers. Because of media and part size, a number of screen tubes maybe require. However, a rotary screen separator can handle a lot of volume, heavy loads, and is
  • 139. Chapter 9 – Type 3 Equipment 140 much faster, more efficient, and can take up less floor space or be much shorter than a flat screen system. Therefore, if efficiency, speed, and space are a factor, one should consider the rotary screen separator over other systems, provided the parts volume warrants the extra cost of such a system. Tubular Rotary Screen Separator This screen system is made from the same flat stock as standard screen separators, except the material is rolled into a tube. This shape has many advantages. One, it is fast and two; parts and media get tumbled as they pass through a rotating screen in a gravity feed operation. That means that it is difficult for the screen to get blocked by media and parts shed most excess media on top of them. Fig. 59. Tubular Rotary Screen Separator
  • 140. Chapter 9 – Type 3 Equipment 141 A couple of comments about barrel finishing that may be of some interest. Of all the mass finishing systems used, barrel finishing equipment costs are normally cheaper than other systems. They also have longer media life than other systems, primarily because they are slower than other systems. That also means that longer time cycles involving chemical additives are subject to more discoloration or darkening of the metal parts due to chemical reactions. Lastly, because this is a closed loop system, parts may come out dirtier or with more debris than other processes; therefore, they may still need a secondary rinse or cleaning. This is about as far as I want to go with the barrel system. There have been some new developments with what are called high energy barrel systems; however, I want to cover them under another heading called high energy systems. But, before we leave barrel systems I should say something about a another transition machine system that is not made any more. At one time, there was a barrel machine that not only rotated but also used a shaking or vibration motion that could work independently of or simultaneously to the rotational motion. These machines did not produce a good vibratory action, but they worked well in the unloading and/or separating operation when the machine was stationary. Again, the advantages and technology did not warrant the extra expense. Vibratory Systems: Unlike the barrel, the work chamber of a vibratory system does not rotate or move to any extreme degree. Instead, the work chamber is suspended on springs under its outer edge, flange, lip, support platform, or work chamber so that the work chamber can float freely about in a limited way. Rather than apply energy to rotate the work chamber, the energy force is directed to the work chamber by way of an eccentric weight attached to power drive shaft normally located centrally under the work chamber. The free-floating suspension system of springs and the off balance eccentric counter weight tilts the work chamber to create a continuous circular movement. At a cross section static point, the work chamber is lifted and dropped in short vertical movements to compensate for the off balance eccentric weight and that creates an energy flow pattern or rhythmic movement to the eccentric weight*6. The energy and force is transferred from the work chamber to the contents through the solid media and parts mass to create a mechanical movement and pressure, which performs a grinding or milling action within the work chamber. In addition to this physical work action movement caused by the eccentric energy forces are some other internal vibrational harmonics caused by the design of the work chamber, the construction materials, and by the media. These other forces are relatively weak secondary energy forces to the main energy pattern of the eccentric movement. Most of the dissimilar harmonics are caused by the media; however, chamber design and construction materials can also effect energy transfer. Again, energy forces travel best through a solid and excite or vibrate the work chamber and that energizes anything within that chamber. This is energy force is more NOTE: There is one mechanical energy system that uses electro-magnets to create the same material flow as that produced by an eccentric, but this is only found on tub type machine systems. 6
  • 141. Chapter 9 – Type 3 Equipment 142 obvious or can be better seen in how a fluidized bed system or ultrasonic system works, except this is physical movement of solids and/or transfer of mechanical energy. The vertical height or amplitude movement of a vibratory work chamber is normally less than one inch above and below the stationary top or the spring line at the work chamber base, which serves as the centerline for the movement. The movement of the work chamber is a direct function of the eccentric weight mechanism and work mass. An eccentric weight is specifically designed to produce a movement or force away from a central axis of the drive shaft as it turns. This creates a certain continuous moving energy wave, point, or position that causes a positive and opposite negative constant moving radial bump type force away from the center axis of the drive shaft. The physical weight and/or location of the eccentric determines the amount of amplitude or force of this energy bump within the machine. Therefore, amplitude adjustment is normally accomplished by the adding or subtracting of weights in relationship to the total work mass, but it can be a matter of just moving and fixing the weights out away from the center of the rotating shaft or at angles to opposing weights. It is possible to add too much weight or amplitude adjustment to a machine system process. Too much weight will produce an uneven flow or no flow of the media mass within the machine and will cause the mass to bounce in place and possibly damage the parts being processed. Too little weight will just increase processing time, but will also produce a generally smoother type surface profile finish. The movement of the eccentric weight produces or generates an X force of tremendous energy which is up to eight times the force of gravity. That force moves the media mass out from the center of the machine to the outside vertical wall of the work chamber in a radial pattern. The eccentric also produces a Y force that creates a vertical lift exactly where the eccentric weight is under the work chamber and another sub-secondary force of lesser energy directly opposite the eccentric. Actually, the eccentric energy forces produce an equal xy pattern that moves the media up before it tumbles backward as it also moves in a confined limited way until it reaches the outside wall. The backward movement of the media is a result of the eccentric weight energizing the media mass, lifting it, and then letting it settle back down in a new position. Actually, because the media cannot move as fast as the eccentric weight, it passes its energizing vertical point and begins to settle and to fall backward before the next energy wave moves it again in a continuous manner. So even though the work mass appears to be and is in constant motion, the energy forces are really short energy bursts or pulses that create a wave or movement within the work chamber.
  • 142. Chapter 9 – Type 3 Equipment 143 Fig. 60. Vibratory Systems Fig. 61. Vibratory Energy System All vibratory mass finishing systems operate by creating an out of balance energy force which creates an energy flow or pattern within an attached work chamber. This energy is created by a motor, with either eccentric weights attached to a vertical drive shaft, or it turns a belt or flexible shaft that turns another shaft with eccentric weights attached to the work chamber. Above pictures show the construction of a direct drive motor system which is centrally located in the machine with its eccentric weight attachment assembly. Depending upon the machine and work load, weights can be added or removed. Also shown is the typical mechanical flow pattern created by the eccentric weights within a vibratory bowl system. A tub type unit has its drive shaft and eccentric weight assembly located horizontally below its work chamber. Most tub systems are run by belts (not shown).
  • 143. Chapter 9 – Type 3 Equipment 144 The energy force from the offset eccentric weight is a single point or line within a 360 degree circle. That means that there is more dead space than impulse; therefore the greater media movement within the work chamber is away from the energy wave or opposite the rotation of the eccentric weight. When the media reaches the outside wall of the machine it then moves in the direction of least resistance, which is up and slightly in the opposite direction of the eccentric weight movement and this causes a spiral action. The equal X Y forces produce a circular movement to the media within the work chamber around the outside wall and down to the center of the machine or mass. This movement also produces an even continuous circular horizontal and vertical orbital movements flow to the media. Too fast of an RPM speed of the motor or too heavy an eccentric weight versus the weight load ratio will cause the load to vibrate in place and be ineffective. The energy forces produced by a vibratory system are a lot stronger and faster and energizes the entire work mass than a barrel system. Barrels rotate and rely on gravity to create pressure from the movement of the media and this is only active in one third of its total mass at a time. Therefore, vibratory systems are more efficient and more powerful, and at the same time, the way the processing energy is applied to do the work makes the equipment safer, more user friendly, and requires less space than a barrel machine of the same capacity. Barrel systems are normally enclosed with a stationary safety cover because its movements are greater than one inch and cannot be touched or handled during its operation without some possible harm to one's hand or operator. It is possible to put one's hand on to a vibratory machine and actually into the media and/or work mass without any major problem for safety while in operation. As you can tell from this description of mechanical energy forces, the barrel needs a hatch cover secured at nearly all times on the larger horizontal systems to retain the work mass while in operation. A vibratory system usually operates without any top or security device, because it always operates in an upright position. In fact the larger machine systems have no means to hold the work chamber to its machine base except its weight, the weight of the contents, and either an external or internal method to hold the springs in place. An optional cover device can be used to quiet the machines noise when in operation and/or to hold down dust if the machine is using dry media. The noise is actually a result of the media movement within the machine. Most vibratory systems use motors that operate between 950 RPM to 1800 RPM. These can be fixed or variable speed motor systems, with the most common speed for deburring at 1400 RPM for large machines and 1725 RPM for smaller machines. Greater speeds do not seem to produce the results of this speed range without some negative results. Like the barrel systems, the greater RPM's usually result in part damage and/or impingement. Higher RPM's and/or energy requirements may be desirable for heavy weight to load ratio processing or doing what is called burnishing. Some steel burnishing machine systems operate at 3600 RPM and this is only done because of the weight mass that retards its actual movement. That is, steel media requires a lot of energy to get it to move and continue moving; therefore, the RPM of this work mass is probably the same as ceramic in slower RPM machines.
  • 144. Chapter 9 – Type 3 Equipment 145 Like barrel systems, slower RPM speeds are also not recommended only because it takes longer to accomplish the same results. As mentioned in the footnote, there is one vibratory tub type machine system that uses electro-magnets to energize and create the vibrational energy forces. It looks and operates the same as eccentric motor system, but it uses electro-magnets to create a physical pulse movement to the work chamber. Because the movement is linear this system has only been used on the tub designed equipment systems. The system also requires the use of a separate variable voltage transformer and control panel to regulate the movements and adjust the amplitude of the electro-magnets. Burnishing is not a material removal system per se, but it is like the sand blasting system in that it modifies rather than removes the burr. Any material removal is a result of metal flexing or fatigue, but most of the burr is still there, rolled over to one side or flattened. This process uses a non-abrasive preformed ball shaped media of steel or porcelain and does require a lot of energy to move this weight mass and get good rotation. Because of this weight mass element, most of these machine systems are built special to handle the extra stress, weight, and power requirements. Because porcelain ball media is lighter, it can be used in almost all vibratory machines to accomplish burnished parts, but it will take longer than steel because of its weight. See the section on media for specifics. Noise and Vibration The noise factor can be quite significant in vibratory equipment depending upon the media and the amount of liquid being used. That is because this type of machine normally operates with an open top work chamber and it is so much more aggressive than barrel type equipment; therefore, sound covers are sometimes used to cover the machine in operation. These sound covers can be either permanently attached or lowered into place to encompass the top of the machine or the whole machine. Another solution is usually to dedicate a separate room to isolate the noise and/or vibration. Noise and vibration are really two separate problems. Although sound can be annoying, vibration can be just as disturbing or worse, both to people working around the equipment area and to other machine systems. That is, vibration can travel a significant distance with enough force that it upsets delicate equipment and instruments within the same building. In fact, it is recommended that large machine systems be given their own cement slab to isolate the vibrations from other nearby equipment. In lieu of a separate slab, cushion type isolators are also recommended, but are never as effective as bed rock type isolation. Vibrational energy forces must go somewhere and if a machine is not designed properly and this energy is not transmitted to the work load and/or chamber properly, this force will travel the shortest route possible. This often means that it will back up or down into the whole machine stand or base. This will also mean more functional problems than normal for the machine in a relatively short period of time. If the media does not get moved and work properly, something else will get moved or be effected and this is normally negative reaction.
  • 145. Chapter 9 – Type 3 Equipment 146 A good abrasive deburring operation produces about 80 decibels of sound vibration or more with ceramic media. More aggressive machines operate at higher decibels, but all noise levels can be adjusted or controlled by the use of media and liquid. Then again, noise indicates the aggressiveness of the system. To intentionally decrease the sound level by changes in media or liquid levels will effect time and performance also. Therefore, sound levels are a good indication of the process operating properly. However, government rules and regulations do require protective head or sound gear at or slightly above the 85 decibel vibration level for anyone working in or near this type of environment. A vibratory machine does process parts a lot faster than that of a barrel. If a barrel takes 10 hours to work a part properly, it would take a vibratory system maybe 1 hour to do the same job. Deburring cycles of 10 to 15 minutes are common. Also, this type of machine produces more uniform finished parts because of more equal X - Y energy forces applied through the abrasives in direct contact with the parts. This difference in surface finish appearance is especially noticeable if the parts have internal cavities or recesses. Surface finishes are uniform wherever the media can reach or make contact. There are two basic variations of vibratory machines. What I am referring to here is the work chamber configuration, commonly called a tub or bowl. There is also a difference in the way energy forces are applied and the types of parts that can be processed. However, as the names implies, one is designed like a bowl, donut, or angel food cake mold; whereas, the other is a rectangular tub shape. Most bowls use a center cone section to separate the media during its circular rotation and this also directs the flow of media and parts into a continuous circular channel or creates a dual movement function. The tub is already a single channel and moves the mass predominately in one direction. Both vibratory machine systems produce a two directional movement to the media or an X - Y motion to the media mass while it circulates. There are some comparable differences in the time cycles of a bowl versus a tub type system. Given the same size machine capacity and media weight, tubs produce 20% to 30% more energy forces that result in slightly shorter processing time cycles. The major difference can be accounted for due to the fact that the channel depth is normally greater in a tub than a bowl, thereby allowing greater weight and pressure on parts at the bottom of a tub than can be gotten in a shallower bowl channel. Weight is a big factor in processing times. The more media and parts you can get into a machine the shorter the time cycles, because the greater the mass, the greater the weight, and the greater the pressure. Besides cycle times, there are also some significant implications of the work chamber shape in regards to the parts being processed. The biggest difference is usually in the size or length of the parts capable of being processed. Tub units can process rather long parts that tumble freely, but retain their orientation within the mix occasionally hitting or touching one another or the tub walls. Whereas, in a bowl unit, the parts move in an equal X-Y spiral motion and are less subject to part and/or wall contact, provided that they are smaller in size than the bowls channel width.
  • 146. Chapter 9 – Type 3 Equipment 147 Flat parts are a special problem with tub or bowl type units. Both designs have relatively flat walls, especially at their top opening. Tubs have two short flat walls and both have smooth curved surfaces. Flat, two dimensional, parts and flat walls do like each other a lot; therefore, they are not a good combination for wet processing. Water can create or cause problems with what is called surface tension between both the part, the work chamber, and water resulting in adhesion between parallel surfaces and especially parts. Water adhesion is a situation where water loses its memory and thinks and behaves like glue. This is a problem with flat parts, light weight parts under a ½ inch in size, or parts with at least one large flat surface, but it is not a concern with most other machined parts or applications. Most large machine systems are designed so that their work chambers have serrated or textured areas near the open tops to allow the breakup of water surface tension on parts. This design helps the problem of surface tension between the parts and the machine wall, but it doesn't help part on part adhesion problems. Sometimes a quick temporary fix for water or part adhesion problems is to add a little alcohol to the process to reduce surface tension. In any case, the bottom line is that flat designed equipment and parts do not lend themselves to good uniform deburring in a wet mass finishing processes. Material Handling Systems Another major difference between a tub and bowl is the material handling system. In fact, in most manual or semi-automatic mass finishing systems the bowl has more advantages than a tub system and even some high energy systems because of parts handling capabilities. That is because a bowl machine is normally designed with a dam or ramp which leads or diverts the work mass to a raised screen deck that will separate the media back into the bowl and allow the parts to be directed to a container outside the machine. This is the most efficient separation system available in mass finishing, even today. However, for additional costs automated systems will outperform even this simple design. A bowl machine system behaves more like a continuous flow type processing machine than a closed loop batch type system than most other mass finishing systems. That means that the machine can continue running uninterrupted thereby allowing the machine operator to dump a new load of parts in the same media, if they are compatible to the media being used. That saves a lot of machine down time. In barrels, tubs, and high energy systems, finished parts have to be dumped onto a separate screen deck and then be re-directed to a container. After this, the media and new parts must be put back into the machines work chamber and unless this material handling system is automated, this is a lot of indirect hand labor. Tub Shape Vibratory Mills: We will start with the tub type unit, because this was developed and introduced before the bowl type machines. The tub design is actually made into the shape of an elongated letter "U" that maybe tilted slightly at an angle and some may have one long wall slightly curved. The tub is suspended on springs under the flange or lip at the top of the letter U. The other distinguishing feature that identifies tub type machines is how the machines are powered
  • 147. Chapter 9 – Type 3 Equipment 148 or energized to create the vibration for mass motion. Because there is no real name designation identification to the tub shapes, I will give them my own identification, which is not part of any equipment classification system: Type 1A is the basic tub shaped machine. We will keep it simple and just say that this unit is powered by a single rotational shaft attachment with an eccentric weight that is slightly off center to the work chamber and runs length wise underneath the tub. This off center eccentric is indirectly powered by a belt driven motor7, a flexible coupling, or a constant velocity coupling from the motor to the shaft. Belt systems alone retard the free floating tub; therefore, these drive systems are normally only found on smaller less expensive machines. On some larger machines, weights can be added or subtracted to improve the amount of vibration or amplitude of the vertical motion of the machine. This offset eccentric position produces energy forces that bring media and parts up one side of the long tub wall and falls down to the other side. During the process, the media movement pattern is slightly deformed or elongated and not symmetrical as it rotates the whole mass. In this processing, there is good side motion and part movement or tumbling. It is not exactly an equal X - Y motion, but it is close and it does a good job. Fig. 62. Tub Type Systems The basic tub type mass finishing vibratory system produces an energy wave or pattern that has a primary flow pattern as well as a secondary pattern. Where the energy is applied to the work chamber determines the flow characteristics of the media and parts within. The first illustration shows the longer primary flow pattern of the media and the smaller circular lines show the action within the media mass. The eccentric weight moves the work chamber in a circular pattern. Energy is transmitted to the media and parts, which flow in a predetermined pattern, which allows the smaller, and usually lighter media to move faster than the larger parts. This movement causes a scrubbing or abrasive action against the surface of the parts as they too move. The action or movement is very uniform throughout the entire work mass. NOTE: One exception to this is a machine that is powered by electro-magnetics that vibrate up to 3600 cycles per minute manufactured by a company called Vibrodyne. This unit requires a separate control panel that includes a variable voltage transformer. 7
  • 148. Chapter 9 – Type 3 Equipment 149 Fig. 63. Typical Tub Type Configurations Type 1B tub looks the same as 1A, but it is a dual shaft machine with two eccentric power drives, located or attached along the outside of the long tub walls. Naturally there is more aggressiveness to the work mass and the results are slightly shorter time cycles. There is also a greater capability to run heavier parts and for those parts to be lifted or moved higher in the work mass which is better for recovery or unloading by hand or a lifting mechanisms. Some
  • 149. Chapter 9 – Type 3 Equipment 150 dual shafts machines are powerful enough to run heavy steel burnishing media applications, but steel ball burnishing is not normally done in a tub because of the weight factor and the extreme power requirements. Type 1C tub is an overhead cam type machine which has its eccentric weight system attached and located to the top side of the machine. This system can also be a single or dual shaft system. This machine is capable of working extremely large parts and does lift them up to the top surface of the work mass. These overhead machines also seem to have slightly different media performance against the part. The action is more of a scrubbing motion rather than a beating action found in type 1A and 1B tubs. Generally speaking, this action results in an overall smoother surface profile or finish to the part. Type 1D is a Continuous In-Line Tub. These machines are another separate category or modification of the basic tub type system. As the name implies, this machine system uses a long tub type work chamber, but it is designed to re-circulate the media like a bowl machine. The machine is designed in such a way that the media and parts are feed into one short side of the machine, they travel down a slightly inclined channel, over a screen deck and come out the other side. Parts are continuously moved in the long direction of the machine as they circulate or processed in the short direction of the tub until they exit over a screen where the parts are separated from the media. The media is then conveyed back to the front of the machine and is reused and is continuously recycled, hence the name. Because of all the mechanics involved these machines usually run from a five cu. ft. at 12" x 72" up to a size of 125 cu. ft. or 48" x 288" or bigger. The big advantage of this type of equipment is that parts can be feed into the machine and processed without touching each other, they can also be integrated into a continuous production line. The disadvantage is the machines large size and the large volume of media that is required and that means less flexibility of using different media without significant down time for change over. Continuous Tub Type System Another variation of the tub type system is the continuous, in-line or linear flow through system. This system operates like all the other tub systems except the tub is usually longer to increase dwell time in the abrasive and it is slightly inclined to make the media and the parts flow in a specific direction. As the mass exits the machine, it is dumped onto a screen deck that separates parts and media. The media is conveyed back to the start of the machine in a continuous loop. This machine system is rather large due to accessory conveyers and separators, but parts maintain good separation and therefore it works well with automated production lines.
  • 150. Chapter 9 – Type 3 Equipment 151 Fig. 64. Continuous Tub-type System Separation I have mentioned how large parts can be processed and removed from all the different work chamber tubs mentioned above; however, I did not say anything about smaller parts. Smaller parts of less than 1/2 inch in size require a special material handling system rather than the hand pick type method. Part separation can become very time consuming as well as cause machine down time. Therefore material handling or unloading deserves a lot more attention than meets the eye. On nearly all tub type units, one of the short walls of the tub contains a door mechanism. When the parts are properly deburred and ready to be unloaded, the operator can open a hatch or door which empties the complete machine. The media and parts are then dumped onto a conveyor or a secondary screen device which is normally use to separate the parts from the
  • 151. Chapter 9 – Type 3 Equipment 152 media. The parts go on to their next process and the media is put back into the machine for reuse or another media is put into the machine for processing with different parts. That means that the machine is idle until it is re-started with the next load. All of this handling requires additional manpower and/or labor as well as time. Wet systems A brief statement here about the liquid application during the mass finishing process. This subject will be covered in detail later. All of these tubs, bowls, and high energy systems have drains and inlets for adding chemicals and liquids. Some can be complicated devices for monitoring the chemicals and/or contaminates. In most cases, they are simple systems. In some machines, you have a continuous flow of liquid in and out of the work chamber and mass at about the same flow rate. In other batch type operations, you can put a set amount of liquid in and retain it for nearly the entire cycle, this is especially true of nearly all barrel systems. Normally, it is suggested that if you use the batch type system in vibratory equipment, just drain and rinse the media mass for the last 5 or 10 minutes with water. This rinse can also be done with the barrels, but you must stop them first, drain, and re-fill them with the clean rinse water. In all machines, you have a main source of liquid input that may or may not be connected to the work chamber and maybe a series of smaller exit drains at the bottom of the work chamber that are inter connected. Normally the more amount of liquid into and out of a machine the nicer looking or the cleaner the parts. With proper compound additives used in processing, the parts do not require further cleaning or assistance to stop chemical reactions or oxidation. Strong chemical solutions may be used to work parts faster; however, most commonly used products are extremely weak or diluted so that they can be disposed of down a drain. However, even the weakest compounds must be checked with local disposal procedures. Some deburring wastes and/or metals require special handling. Stainless steel is made with chromium which can go into solution and may have to be handled differently. See section of liquids. An adequate amount of liquid into a machine is determined by the machines size. That is, large machines require a greater flow of liquid than do smaller machines. In most cases, you want to see a good amount of liquid in the media mix to keep everything flowing freely. Too much water flow will slow down the deburring action of the machine system. A good guideline is about 5 to 10 gallons of liquid per hour in machines over 5 cubic foot capacity. You do not want to see a lot of debris or a heavy milky solution. Also, you do not want to see liquid splashing out of the media mix. In the later case, you may want to check your drain system to make sure they are not clogged and retaining liquid. For that reason, a good drain system should be able to discharge twice the amount of the maximum input. There are exceptions to almost everything I am saying here, but until you learn the basics, it is difficult to explain these variables. One last thing about drains, the actual size of the holes in the drain plate covers determines the size of the parts that you can work. That is, the larger the drain hole, the less
  • 152. Chapter 9 – Type 3 Equipment 153 likely it is to get clogged and the faster the liquid drains. But, if you have a drain hole of say 3/8 inch diameter, that is about the minimum size of the part and/or media you can run in this machine before it too goes down the drain. Lastly, there are some cases where it is desirable to run a dry organic media mix. Normally this media is relatively small. That means that the drains will get clogged very easy; therefore, special precautions must be taken to seal the drains before using the machine with this dry organic materials. Bowl Shape Vibratory Mills: Motor systems As tub type units are mostly distinguished by the location of their power drives, so too can the bowls; however, the round bowl shape is the dominant feature of these systems. Although these two designs visually appear quite different from one another, they actually function almost identical, in that the media and mass still travels up the outside wall and down toward the center of the machine. The bowl design has a more noticeable center section, whereas, the tub center is within the work chamber or mass itself. The bowl shape design feature actually creates a more linear flow to the mass that can be controlled easier than a tub type machine system. Although we are talking about linear, which is normally considered straight, the bowl shape is a circular channel through which the mass travels around in a straight flow line. Unlike the tubs, that have their power drives and eccentric weights mounted in a horizontal position parallel along the tub bottom or walls, bowls have their drive and weights mounted in a vertical position through the center of the machine. That means that a tub unit accentuates the moving energy bump in a vertical plane, whereas, the bowl does the same thing on a more horizontal plane. The tub machines are slightly more aggressive because the eccentric moves in harmony with gravity forces and therefore intensifies the movement and forces of the mass. Most large bowl systems have only two options on their power drive and they have nothing to do with the way energy is applied to the work chamber. The distinction is that the motor system is either a dual shaft direct drive, or an indirect driven pulley and motor system. Dual does not mean two separate shafts, but one shaft or axis that goes complete through the center of the motor or machine. In both cases, there is usually a top and bottom shaft with eccentric weights. In a sense, the dual shaft mechanism behaves like a gyroscope with limited intentional vertical movement to which the work chamber center line or center of gravity is attached. The direct drive, dual shaft motor system has weights attached to both motor shaft ends and is positioned or attached directly to and through the center hub of the work chamber. There are two indirect drive systems that use a transfer system. In one, the motor drives a belt and pulley system with upper and lower weights attached to or through the center hub to activate the work chamber. The other indirect drive mechanisms use a constant velocity, flexible coupling do the same thing as the belt. The flexible coupling seems to be the more common system in use today. Both indirect drive systems make repair and replacement of motors and drives easier than direct drive systems, because they are easier to get at.
  • 153. Chapter 9 – Type 3 Equipment 154 A direct drive system uses a dual shaft motor which is rigidly attached vertically within the machines work chamber or center hub section, making the power source and work chamber one. That means that the assembly above the springs is extremely heavy because of the motor weight, bowl construction, liner, and media within the work chamber. Most of these bowl machines are designed in such a way that even without the eccentric weights in place, the greater weight of the machine is the motor system which is centered or slightly below the bottom level of the work chamber. This is done to offset the weight of the media mass within the bowl. As mentioned, the direct drive motor location also means that the motor is more difficult to get at and repair if anything should go wrong. It even means the changing or adding of weights for amplitude adjustments is also a little difficult. Belt and coupling systems have the motor located to one side or attached to the chassis of the machine and that makes replacing parts and adjustments a lot easier. On smaller equipment or the centerless hub machine there is only a single shaft and lower eccentric weight attachment. Both machine systems operate the same but there are more adjustments and performance factors that make the dual shaft system more desirable and controllable. Fig. 65. Vibratory Bowl System Direct Drive The following semi-transparent visual of a typical direct drive vibratory bowl system and placement of motor, weights, in enclosed chassis which is accessible by a door. Top weights are accessible by removing top cover shown closed. Also shown are suspension, drain, and exit or screen deck ramp systems.
  • 154. Chapter 9 – Type 3 Equipment 155 Adjustments In the bowl design the energy forces are somewhat different than the tub. Although the eccentric counter weight systems are attached differently and the forces are applied differently they behave similar, in that the media moves in the opposite direction to the eccentric weights movement. In the tub, the eccentric weight is attached directly parallel to the tub. Whereas, the counter weight system of the bowl effects and directs the energy perpendicular to its movement. A bowl moves or tilts down to one side in an act-reaction type energy force movement, perpendicular to wherever the eccentric energy force is directed. This causes a constant circular spiral motion perpendicular to the bowls level orientation. Besides the moving or adding and subtracting of weights, there is no control or adjustments to a tub machine to adjust the x - y flow or motion of the media within. A bowl system has much more control over how materials are processed because there are weights on both the top and bottom side of its eccentric shaft whose angles can be adjusted in relationship to one another. These weights are also balanced in relationship to the mass within the work chamber. Positioning of the eccentric weights does make a difference in the x - y movement or way in which the media and parts behave in the machines work chamber. In a bowl design, the bottom weight controls the vertical mechanical action of the machine and because of that, the bottom weight always leads the top weight in the direction of rotation. Adjusting the bottom weight controls the amplitude or vertical lift motion of the machines media or work mass. The top weight controls the degree of the rotational loop or roll action which is the distance or amount of horizontal travel in relationship to its vertical lift movement. In other words adjustments can be made to control either a very tight short spiral or a long spiral of the work mass. Naturally, a tight spiral is desirable for what is called single pass processing and/or even multi-pass machine systems; however, too tight a spiral can cause more part on part contact. The tight spiral or slow feed rate adjustment concept is incorporated into some machines for the sole purpose of only allowing a part to pass or move in one direction and exit the machine. That means that any batch type machine system can be adjusted and utilized to make it a continuous in line or pass through type system. Part movement in and out of a machine can be controlled or regulated to process parts to a pre-designated time cycle determine by the weight system alone. The closer together the top and bottom weights are to each other the tighter the spiral. The maximum adjustment is 180 degrees apart for a long spiral. See diagram for details.
  • 155. Chapter 9 – Type 3 Equipment 156 Vibratory Bowl System Eccentric Weight Control Adjustments The amount of bowl movement or aggressiveness of a machine system over 2 cubic feet capacity is controlled by adjustable top and bottom eccentrics weights sometimes called a flywheel. These weights control vertical lift or height of the bowl movement. This is called amplitude. Weights can be added or subtracted to compensate for the workload within the bowl. The heavier the mass, the more energy is required to move it. Too much energy may damage parts. The relationship or position of the top and bottom weights is adjustable within 180 degrees of each other and controls the rotation or spiral of media and parts mass. The maximum effective range of the weight separation is approximately 150 degrees. Other than adding weights, the bottom weight position is normally and the top one is the one that is changed because it is easier to access. Because the bottom weight cannot be seen when adjustments are made to the top, there are normally markings to indicate the position of the bottom weight. Adjustments of weights control the speed, travel or movement of the mass around the bowls channel and the amount of roll or spiral and/or separation between parts. The closer together the weights, the tighter the spiral. Because machines may differ in the direction of rotation, the bottom weight always leads the top weight. (See diagrams) Fig. 66. Counterweight Adjustment Although we have talked about the power drive system of bowl machines first, a more common way to distinguish bowl type systems is in the actual shape or fabrication of the bowl. This shape description does distinguish them from tub type machines, but bowl machines are also designed different from one another. When these machines were first introduced in the
  • 156. Chapter 9 – Type 3 Equipment 157 early 1950's, fabrication simplicity was the rule that controlled costs and designs. Therefore, most bowl machines were built with flat bottoms and sides, which were molded or lined with a heavy 1 to 2 inch coating of urethane. As indicated earlier, flat walls, water, and flat, light weight, two dimensional parts don't get along very well for uniform processing. Therefore, eventually most bowl designs eventually evolved into the more common curved wall machines. Most bowl systems now use the curved wall shape, not only to keep media and parts from adhering to the sides of the bowl, but this shape also aids in the performance of the media mass. Because of the media flow within a bowl is directed up the outside wall and down toward the center cone section of the bowl, a curved wall restricts and/or compresses the media mass exerting more pressure and energies to the mass which abrades parts faster. In a normal straight wall channel bowl design, the media loses energy and pressure as it expands in the vertical lift of the media. If the media is restricted near the top of the bowl before it falls into the center, it retains greater more uniform pressure transfer to the mass. Machine Capacity Besides shape as a determining factor for performance, it also determines the capacity of the machine system. That goes for both tubs and bowls. In the mass finishing equipment industry there is no uniform code to determine capacity. What seems rather clear cut to the average non-user is not that simple for comparison purposes. This problem may be related to the working capacity of the barrel systems. What is said to be a 5 cubic foot capacity machine maybe the total fill volume or the proper working capacity for parts, not the size of the work chamber. To determine capacity size, one must take into account a number of factors. Capacity can be given in size, weight, volume, or liquid. It can also be given as the total mass, the media or part mass only. Another confusion is the relationship of the media to the parts ratio or percentage. That difference means that because media and parts vary in density or weight a machine can have several different capacities depending upon which media you want to use to determine a standard unit of measure. Simple? As mentioned, the terminology of working capacity can be different from machines total capacity. This term usually refers to a machine in a condition that would be considered ideally loaded to perform at its optimum processing cycle. In a vibratory system, this ideal work chamber capacity is usually 2/3 to 3/4 full of both parts and media. Again, this can be a variable condition depending upon what media and materials will be necessary to do proper deburring and/or processing. Therefore, be careful when trying to compare. You may be mixing apples and oranges. One more note about size. When determining what size part that can be worked in a bowl machine is not determined by the overall size of a bowl; rather, it is determined by the channel width of this type machine. The maximum part size that goes into a tub should be at least an inch or two shorter than the total length of the tub and the part will probably be in
  • 157. Chapter 9 – Type 3 Equipment 158 contact with the walls of a work chamber. In a bowl machine, the part length should not exceed the short width of the channel for good uniform finishing. Parts in any machine system should be is smaller than the channel width so they will not be in contact with the wall or work chamber. To exceed the width of a channel is possible; however, that means that the part will always be in contact with either the outer or inner wall of the bowl. That also means that the part may not get good rotation which may result in a nonuniform finish and excess wear to the work chamber liner. Curved walls help minimize the amount of contact with any part shape or configuration. Besides curved walls effecting the performance of vibratory machines, there are other shapes that have processing advantages and disadvantages. As mentioned, tub systems use primarily the application of energy forces to distinguish design variations. The following are some of the variations in bowl designs. Work Chamber Bowl Channel Designs The following illustrations show a progression of bowl configurations from early square designs to the more common curve pattern. Fabrication is from the simple to more complex. Curved designs increase the amount of pressure on the media and parts to work more aggressively throughout the complete cycle or movement; whereas, the square design encounters more resistance and uneven flow patterns. Even the curved bottom bowl loses energy and pressure as the mass rises up the outside wall of the bowl’s channel. Normally, the greater the restriction and movement the more aggressive the abrasion of the parts and the shorter the time cycle. Fig. 67. Bowl Designs Arena Bowl Shape Now, in addition to curved walls to get additional pressure to the media there is an elongated bowl system called the arena bowl, also known as the race track design. This bowl design can have curved walls, but its main source of media compression comes from its shape. This design was one of the first machines created to compete with in line continuous tub type
  • 158. Chapter 9 – Type 3 Equipment 159 machines. The longer channel length permitted greater dwell time before the parts exited the machine in one pass. Supposedly this machine produces the same horizontal and vertical X - Y motion as any other vibratory system; however, just like a race track, the mass runs faster with less rotation in the straight away in longer channel section of the bowl before the turn increases pressure around the shorter curves. Parts have a tendency to bunch up at the short ends of the machine and this increases pressure that can cause somewhat uneven processing and possible part impingement or damage. Originally, this machine was designed with one motor or direct drive located in the center of the machine to power the whole machine. This did not provide enough movement and action and a second eccentric drive system was used with one motor located at the opposite end. Later, the motor was relocated to the center of the machine and drives went to both eccentric systems at either end of the machine. In more recent years, the arena bowl has also been modified into a two motor and eccentric system to increase the power and performance of the machine. Fig. 68. Vibratory Bowl Equipment Variations Arena Bowl – A variation to the standard bowl is an elongated work chamber bowl that looks similar to a racetrack or arena. On of the advantages of this design is to give parts more separation and more travel or dwell time before a part makes a complete trip around the bowl. By adjusting the eccentric weights, parts can be made to exit the machine in one pass. Also, instead of continuous pressure of the curved bowl design the configuration concentrates greater pressure at the two end areas of the bowl. When two motors and eccentric systems are used in this machine, the increased vibration improves the aggressiveness of the media and material removal process for shorter time cycles.
  • 159. Chapter 9 – Type 3 Equipment 160 Spiral Bowl As long as we are talking about bowl shapes, it might be a good idea to tell you about two more bowl configurations. One is called a spiral bowl and is shaped like a lock washer. This design along with the eccentric movement pushes the media mass up an inclined fixed bottom plane until it reaches an offset portion of the bowl. Once at the top of the offset, the media drops back down and starts all over again. At the point of the offset, a screen deck or exit screen is attached so that parts can continue and media be returned to the bowl channel without stopping the machine The greatest advantage of this bowl design is the ease of parts separation and unloading. This design is also a good one-pass continuous cycle type system, which is dedicated to parts that enter the low end of the machine and exit at the top. The media movement and motion is controlled by the top eccentric weight, which governs vertical movement or dwell time cycle. On the negative side or in more common use the machine is very aggressive because the drop off increases a more violent work action in relationship to the parts and that may cause some minor marking or damage to some parts, which may or may not be desirable. Fig. 69. Spiral Bowl This is a true bowl design; however, instead of the bottom of the bowl being uniformly level, this bowl design tapers or rises like a lock washer. Naturally at a certain point the bottom drops off and the media begins a new travel cycle. The advantage of this design is that it is much easier to unload parts without losing any due to being trapped anywhere. This machine can also be adjusted for a single pass cycle. Another advantage of the drop off is to concentrate pressure on the parts and shorten processing time; however, the drop can also cause possible damage to delicate or critical dimensions.
  • 160. Chapter 9 – Type 3 Equipment 161 Centerless Bowl Another less common bowl design is called a centerless bowl. This is a bowl that essentially does not have a typical center cone or hub section. The center portion of this bowl is slightly raised to some extent, but not enough to be considered a center cone. Technically speaking, without a center hub, parts can be processed larger than channel width. When this machine is in operation, the media flow is basically the same as a machine with a center cone, in that there is a center gap where the eccentric energy is so intense that it causes the media to flow back out before it can come together. A slightly raised center section aids in a more even flow and compression of the media. This machine design has the greatest curved walls and compression of any vibratory machine being made today. These extremely curved walls do provide more uniform compression and pressure on the media to work faster. On the other hand, there is no top weight eccentric; therefore, there is no control on the vertical rotation or spiral. Adjustments are made with the bottom eccentric weights only. Centerless Bowl – This is one of the more unusual bowl system designs. This machine is called a Centerless bowl; however, there is a raised lower center section, but no central core or hub. The advantage of this design is to create a greater curvature to the bowl walls to increase pressure on the work mass which shortens processing time. The lower center section allows for a little easier access to the mass and it also allows for processing some longer parts than the normal channel width, but it is not normally recommended. Other than the bowl design, the machine works and behaves like a standard bowl system Fig. 70. Coreless and Conventional Centerless Bowls
  • 161. Chapter 9 – Type 3 Equipment 162 Continuous Flow Tube Just as tub machines have continuous pass through systems, so too do the bowl machines. There is one machine system called a tubular vibratory finishing system that looks and behaves similar to a bowl machine; however, instead of a straight through or circular one pass system, this machine looks like the coils of a water cooler or spiral spring. The machine has a series of completely enclosed tubes in a double spiral that allows the media and parts to travel down three circular levels and then back up to the same entry level. This design minimizes the need for large floor space like the continuous tub system and increases travel distance in a relatively short space. Typically, these machines range in size of 6 to 16 cubic foot capacity and require 5 to 6 ½ feet diameter of floor space. In this design, parts are feed in the top of the machine near where they exit. Separation takes place on the top side of the machine in an open space of 5 ½ to 7 feet in length. Part size is limited to the diameter of the tube, which is either a 4 or 6 inch inside diameter. Tube construction is almost one inch thick made from a reinforced molded rubber product. Parts longer than the inside diameter of the tube can be processed; however, that means that the parts will be rubbing against the tube I.D and therefore can possibly get stuck. The tube design exerts excellent compression or working pressure on the parts provided the correct working level of media is maintained. Media level is critical to proper functioning of this machine system. If the is not maintained and filled to the proper working capacity, the media and parts will not complete its closed loop flow. Continuous Bowl Type Systems Just as the vibratory tub type machine systems have their continuous in-line flow through system, so too do bowls. As mentioned a couple of times, eccentric weights can be adjusted in such a way to increase dwell time or the time it takes a part to make one complete revolution of the bowls channel. Long cycle times are possible in almost all bowl systems and average around 15 to 20 minutes. Unlike the tub that requires a large space for conveyors, bowls take up less space for in-line production systems. That means that machines can also be arranged empty into another machine with different media or longer time cycles
  • 162. Chapter 9 – Type 3 Equipment 163 Fig. 71. Tubular Vibratory Finishing System This machine looks something like a vibratory bowl system, but instead of an open processing channel, this machine uses interconnecting spiral tubes to form an extra long continuous work chamber. There is one short area at the top of this machine where media and parts can be seen and/or loaded and unloaded. This design is probably the ultimate design for media compression. Besides the above features, this machine system looks and behaves like a normal vibratory bowl.
  • 163. Chapter 9 – Type 3 Equipment 164 Multi Pass In recent years, a number of manufacturers have developed another continuous flow through bowl system called a multi pass bowl type machine. This machine looks more like the standard bowl systems than the tube type machine. Also, unlike the tube system design, the multi pass systems are all top load media and travel systems. Instead of one large channel, these machines can have a number of smaller channels or a smaller continuous spiral type channel in the space of one big over all work chamber. Basically, the multi pass is a regular normal bowl machine with a least one continuous spiral channel or two side by side segregated channels. This design allows for the use of more than one media or where parts can travel in one continuous flow through these two media processes. Normally the channel width and depth are a lot less than the standard bowl design and processing takes longer because these machines don't get as much pressure on the mass; therefore, they are better adapted for running small sized parts. The advantage of this machine system is that if there is more than one channel, more than one media can be used for processing the same part. The channels can be configured in such a way that the part(s) can move back and forth from one channel to another by themselves. That also means that a two or three step process might be performed on one type of part in one processing machine cycle. As mentioned earlier, separation and processing time can be achieved or adjusted to suite the process by re-arranging the eccentric weights to permit longer time cycles or dwell time of the parts in the media.
  • 164. Chapter 9 – Type 3 Equipment 165 Multi-Pass Continuous System This is another variation of a vibratory bowl type system. Again, this machine looks and behaves the same as a normal vibratory bowl. The only difference is that this bowl is designed to have a single continuous spiraling channel, but gives the appearance of a number of smaller width channels, side by side. Actually, the machine can be designed to have more than one separate channel with inter connecting ramps so that more than one media can be used to process a part before it exits the machine. The main advantage of this system is increased part separation and a dwell time of up to 30 minutes or the optional second step media operation for a finer surface finish. On the negative side, part size is normally smaller due to the reduced channel width. Fig. 72. Multi-Pass Configurations
  • 165. Chapter 9 – Type 3 Equipment 166 Compartment Processing Not related to the bowl shape is another interesting design patented by a company to keep parts separated from one another is a free floating separation device that looks similar to an old fashioned Merry-Go-Round. This device fits into the bowl of their machine system to separate individual parts and is used to minimize part impingement or damage. This device uses a single one piece unit fixture that has a series of rotating mobile compartments that are attached to the center of the machine like a spooked wheel. A single part is designated per compartment and allowed to circulate within the closed work channel and the limits of the fixture spacing. The compartments allow for the circulation of the part and the media, which is confined to or within that compartment while it in turn circles the channel width of the machine. This device keeps parts separated so that there is no part on part contact and at the same time provides enough space for a uniform finish to the part. The fixture or compartment sizes are usually made to order and are not normally adjustable to accommodate different sized parts. These compartment systems are usually dedicated to specific parts and/or product lines. Vibratory Bowl Fig. 73. Part Separation Partition System The biggest problem of all mass finishing systems is the problem of unwanted marks or damage due to part on figure contact. This is more part 55 noticeable on heavier or larger parts than our category B size. The ideal processing method is to run parts through a continuous in-line system with sufficient space between parts to enter and exit. If a continuous system cannot maintain enough part separation then one can use a fixed partition to insure individual part separation and integrity. In a tub type machine system, inserting and fixing the position of the partitions is relatively easy because of the common rectangular shape. However, every partition system still needs to allow media to flow or travel from one partition to another. Without this interaction the energy forces and weight mass involved will destroy the partitions. One of the more popular batch type bowl separation systems is the floating merry-goround. This system looks like a spoked wheel which is inserted into the channel width and it is allowed to travel and move with the work mass.
  • 166. Chapter 9 – Type 3 Equipment 167 Part Impingement I keep talking about part contact or part impingement, but I have never spoken in length about it. Basically, impingement is a condition where one part contacts another and in so doing results in some form of marking or damage to both parts. This condition can be caused when the process or eccentric weights are not adjusted correctly or there are too many parts to the volume of media and/or where amplitude is too great. The word impingement is used primarily to describe a condition of marks on polished parts or where aesthetics are concerned. Sometimes impingement or part on part contact is a desired process where parts alone are used to deburr each other without the use of media. This latter processing method, the word impingement isn't even used to describe the process; rather it is referred to as part on part processing. This processing method is used a lot on flat small parts and/or where media separation or lodging is a problem. The results are often parts with a bright finish, no burrs, and no extensive labor for separation, but these parts may still have marks on them. In most cases, impingement is not desirable condition. Normally parts are processed in a ratio or percentage of parts to media. These figures can vary, but the normal percentage for deburring can be 50:50 to 60:40, media to parts. For polishing, it can be anywhere from 70:30 to 90:10, media to parts. Why this is important is because of the nature of the efficiency of the abrasive process and part impingement. That is, at a percentage of more parts to media than described, part impingement is likely to occur. This condition can cause damage and/or is not aesthetically pleasing. Unloading Probably one of the most import features of mass finishing parts in a bowl system is the unload mechanism. This device is extremely simple and yet quite unique to vibratory bowl systems only. Bowl systems are the only machines that are capable of unloading themselves without secondary pieces of equipment or expensive automated material handling systems. That also means that the machine does not have to be shut down and the media reloaded as long as the next batch of parts are the same or does not require a different size or type of media. That is because the media always stays in the machine even when parts are taken out of the machine. To do this type of unloading, there are three different design variations that work or aid in the process for internal parts separation as well as the old standby complete dump via the door hatch mechanism. There is the interrupt-dam, the inclined-ramp and the reverse dam. They all require the use of a raise screen deck above the media and are normally fixed within the work chamber channel. For this system to work properly, the parts must be bigger than the media so that the media can pass through the screen deck holes back down to the work chamber channel. The longer the deck the more thorough the separation of the media from the parts. Generally speaking the deck only encompasses less than 1/3 rd the diameter of the bowl or channel and can extend out another foot or two beyond the bowl so that a container can be positioned underneath. The gap between the media and the upper screen deck can be anywhere
  • 167. Chapter 9 – Type 3 Equipment 168 from 4 inches to 12 inches or more. If parts are extremely large, they can stick out of the media during rotation and can interfere with the screen deck and vice versa. That means that they can become stuck on the underside of the deck and if not caught in time, they may damage to part, deck, or both. Some screen decks and dams are designed as separate inserts that fit into special mating parts or locking devices built into the machine. Also, there are some bowl designs which have a bump or raised bowl section on the bottom of their channel to meet a dam half way. This design helps smooth the incline up the ramp to improve media flow, but it also reinforces the rigid seal of the dam. The greater the perpendicular angle of the dam, the less efficient it is to properly circulate the total mass. Dam type separation systems work very well and efficient, but because of the interrupted flow of the mass they still may not achieve 100% parts separation; therefore, be aware of part stragglers. Dam Operations When a dam is activated and properly in place, it stops the flow of the work mass causing it to take the path of least resistance. Dams are designed to stop the flow of media and parts around the work channel and divert the flow up to the raised screen deck until it reaches and travels over it. In all cases, the dam must close and seal the channel and direct the media up to and over the screen deck. The dams can be made straight up and down vertical, flat or horizontal, or most are made to interrupt media at an angle. When not in use, most dams are located slightly in front and hinged to the screen deck in the same horizontal position; however, they can also be separate from the deck or be located on the bottom of the bowl and raised up. A lot of dams are set in place manually by a big leverage type handle located on the outside of the bowl connects the dam and the lever directly opposite the dam through the work chamber. Manual dams cannot be set in place to work when the machine is not running, because it is impossible to physically seal off the channel properly through a stationary solid. Even when the machine is running, the manual dam can only be started or inserted just so far, then the force of the work mass will complete the activation or seal. Again, manual insertion of the dam is sometimes difficult and may take a lot of physical muscle; therefore, a growing number of machines are being automated to do everything hydraulically. Without a complete channel seal, you cannot get proper separation. Dams can be manually activated or automatically powered. On some machines the work flow rotation can be stopped and the motor and media flow reversed. This stopping and reversing the rotation can actuate the dam, which makes it easier to insert or automate the unloading sequence. The interrupt dam works best on flat bottom machine systems. The reverse dam works exactly the same way as the interrupt dam except the machine comes to a complete stop first and then the motor and media is reversed, after a time delay. The dam is inserted into the work mass and the movement of the media completes the sealing of channel and diverts the mass onto the screen just as the interrupt dam system.
  • 168. Chapter 9 – Type 3 Equipment 169 Fig. 74. Vibratory Bowl Internal Screen and Dam Systems The same screen systems that are used on barrel tumbling systems can normally be used for part separation on vibratory systems provided they have an exit door that is reasonable located or matches the screen height. However, in addition to the exit door, most vibratory bowl systems have a screen separation system built into each machine and that does not require the emptying of the entire contents of the machine. Although these separation systems are built in, they do not have to be used until the processing is complete. To accomplish unloading and separation, a dam or lever can be activated to close the processing channel and redirect the mass over a screen deck and exit parts to outside the bowl. There are a number dam and screen designs that are used. The system below shows a basic dam that is inserted when needed. Note: to active a dam, the machine should be running, because of the density of the work mass, it is not possible to properly place the dam and close the channel. When the dam is placed to block the channel, the media builds up or is directed up a ramp to the deck. That means that the dam interferes with the flow pattern of the work mass and creates an uneven weight distribution which can interfere with all the mass exiting over the screen deck. The problem of part accountability is almost non-existent with the spiral bowl design (bottom) because the dam and screen are nearly the same or it is a continuation of the bottom channel profile and that does not interfere with the basic flow pattern of the work mass. The inclined ramp is only found on spiral bowl systems where the channels are all slightly inclined like a lock washer and is described above. Because of this inclined design, this dam is more like a bridge or an extended bottom channel which serves as a screen deck that exits the machine. This system requires a lot less energy to move the media mass and is the best system for achieving almost total separation of the media from the parts. That is because there is no interruption of the materials part flow and everything must pass over or through this dam unrestricted. All the other dam systems may trap parts and/or not result in 100% separation because of blockage and mass flow. Even with this screen system there is still a possibility media can fall into the parts container if there is a large number of parts with media resting on top of them.
  • 169. Chapter 9 – Type 3 Equipment 170 Lastly, there are still a number of machines in use that do not have any kind of internal parts separation systems. The lack of a separation systems on these machines may be due to the size and/or configuration of the parts that need to be worked or just a cost factor. To unload all of these machines, there is still the old reliable stand by door or hatch that purges the whole contents of the machine. All big machines with or without dams have a door to quickly changing the media in a machine before refilling and starting the next batch of parts. This is the same way a big barrel machine is used. The dumping of a machine's contents onto a secondary transfer device or screen is a fast method of unloading and separation. A word of caution. If these big doors are used too often, there is a tendency for wear and tear and the watertight seal may eventually leak and become a problem due to constant use. Let me take a quick minute here to go over another area related to separation. Just in case you are unaware of the differences and the need for different screen sizes and holes, I thought I would cover this subject a little. As stated, in mass finishing systems you normally want a screen that has holes smaller than the part, but large enough to allow the media to fall through. When the media is nearly the same size as the part, round perforated holes are preferred over square or diagonal wire mesh because it controls the exact dimensional limit of the part being separated out of the media. Sometimes a long or elongated slot is also desirable for long parts, but wire mesh has or accepts a lot of part and media variation. Screens are used to let media pass and parts to stay on top of a screen separation system. Normally parts cannot have a smaller dimension than that of a round hole unless it has a shape to it or is extremely long. Sometimes the physical limitations of screen sizes can be fooled and the parts captured by the way in which the media and mass enters the screen. Most undersized parts will fall through a round hole; however, there are a good percentage of parts that can be recovered provided they are at least twice as long as they are wide. Long thin parts are best separated through long slots. When parts are smaller than the media, it may be necessary to do what is called reverse separation. That is a condition where the media stays on top of the screen and the parts fall through. Movement of the separation screen is necessary to direct the media to a separate container. During this screen separation, or machine processing, or unloading of the machine the media may get broken or chipped. That means that there is still a possibility of media chips still getting into the parts. If this happens, the ceramic or plastic chips can be blown away with air pressure. This type of separation process is usually done away from the machine discharge, because time and attention needed to this operation. The key for getting excellent separation under normal working conditions is to have the largest amount of open area to the solid portion of the screen or frame material. That usually means that wire mesh should be the preferred screen; however, as mentioned, it is sometimes difficult to determine odd shaped parts or media through square holes. The relationship of the hole size to part size is important as well as the moving of the mass over the screen separation system.
  • 170. Chapter 9 – Type 3 Equipment 171 Most of the screens that come with standard bowl machine designs have a hole opening size of 1 to 1 1/2 inches. Naturally, that means that the parts being separated should be larger than the size of the hole openings. Additional screens or other screen hole sizes can be purchased for smaller size parts to fit the deck. However, most screen systems lose their efficiency below 1 inch in size. That is mostly due to the heavy thickness and construction of the deck system itself. That basically means that the ratio to open area is less than 50%, which is not good for part separation. On top of all of this is always the problem of storage, maintenance, the changing, and the wear and tear on fasteners. Lastly, smaller ferrous parts may be more easily separated from the media by use of magnets than screens. Manual magnets can be used to separate large parts from a machine while the mass is in motion. Other magnetic systems can be adapted to remove parts from the media when place above the existing screen system. The more automated systems look something like a chain conveyor and are not normally built into machines but are accessory systems that attach to or are in close proximity to the existing separation system. Small Bowl Systems Perhaps a brief note should be added here about small vibratory deburring machines. These machines are usually one cubic foot or smaller and are becoming very popular for a number of reasons. The cost of this equipment is relatively inexpensive because a lot of the materials are plastic, but they perform almost as well as their big brothers. The major design difference, besides a one piece bowl construction, is that they do not normally have an adjustable counter weight eccentric system on both the top and bottom side of the motor. This is done for fabrication simplicity and costs, but it works and functions nearly the same as the large machine systems. Some of these machines are built so cheaply that they do not hold up to long term industrial use. Make sure you check machine specifications, especially the motor, and warranty to compare systems. Normally you do not want a machine system with a motor smaller than 1/4 horsepower, and if they do not advise you of the horsepower, you know these machines are not meant to last. Machines below 1/10 horsepower are for infrequent or light duty hobbyist use. On the positive side, because of this inexpensive construction, these machines do not normally need any maintenance or lubrication, as do the larger systems. The biggest advantage of these smaller machines, besides costs, is the ability to do batch work on parts smaller than one inch and are extremely good on parts under a half inch in size. To unload most of these machines and/or their contents the machine must be manually dumped onto a secondary screen type device. However, there is one finishing system that can separate parts from the media in less than 30 seconds without dumping the entire contents of the machine onto a secondary piece of equipment or screen. This patented device is called an "Inseparator" and it can separate parts down to .030 in size, provided one uses the appropriate media. Most of these small machine systems are easily convertible from wet to dry media operations very quickly. Lastly, these machines seem to polish parts almost as well as hand
  • 171. Chapter 9 – Type 3 Equipment 172 buffing. The only major difference is their limited capacity; therefore, they are very popular with small parts manufacturers and jewelers. Fig. 75. Small Internal Parts Separation System Most small vibratory deburring systems usually use a cheap and dirty separation screen on top of a 5-gallon bucket to separate parts from media. There is only one internal separation system and that is considered semi automatic. It is a frame and interchangeable screen system called an “Inseparator” that operates like a basket. It is a very fast manual put and take-out system that claims 100% part separation in less than one minute. Because of the size limitations of this equipment, this is especially good on small parts under category B or 2 inches in size down to .030 minimum.
  • 172. Chapter 9 – Type 3 Equipment 173 High Energy Centrifugal Systems: This type of equipment is considered the third generation of mass finishing machines. As vibratory systems were a significant improvement over barrel type machines, so too are high energy, centrifugal systems over vibratory. If it takes a barrel system 10 hours to properly work parts, it might take a vibratory unit 1 hour to do the same job, and a centrifugal system 6 minutes. That’s fast! Surprisingly the motor speed or RPM’s on these machines are actually slower than that of most vibratory equipment, yet we call these high energy systems. That is because, even though high energy motors operate at slower speeds, they use a different principle of applying energy forces than vibratory machines. That is, instead of indirectly applying energy forces by an eccentric, that lifts and drops or bumps and grinds, high energy systems apply a constant force directly to the whole media mass at once. Vibratory is just that, it vibrates, oscillates, or pulses by moving the mass in short movements and uses gravity to help it create a flow pattern. High energy systems apply a direct, constant, circular energy force of great pressure to the media, therefore, it operates faster than vibratory systems. High-energy systems move the media mass in a constant sliding type motion and this creates uniform pressure greater than gravity itself within the work chamber. That is, because of the speed of rotation, an artificial gravity of its own is created greater than natural gravitational forces. Rather than the short impulse movements that are found in vibratory equipment, highenergy centrifugal forces move the mass and maintains a uniform pressure greater than gravity. You might want to compare the appearance and function of this system in action to that of an amusement park Ferris wheel ride on its side, or better yet, the ride where the bottom drops away after it reaches a high speed of rotation. Upon analyzing this high-energy equipment, the movement relates closer to that of an abrasive belt or wheel system than it does how vibratory equipment works. Yet, like the vibratory, the flow within the work chamber is similar to the toroidal action of that equipment. What is different about high energy systems is the movement of the media or height it attains as it is lifted by the velocity of the rotation before gravity over comes the vertical height and pressure. Again, while this motion and action is similar to vibratory, the force is more constant, uniform, and greater. Like the mass finishing systems previously mentioned, there are variations to the centrifugal systems as well. There are basically two types of high energy systems in use today. These are the barrel and the disc finishing systems. The barrel systems look something like the original barrel type machines of old; however, there are some noticeable differences. Whereas, the disc finishing systems look like a big food blending machine without the stirring devices in the bottom.
  • 173. Chapter 9 – Type 3 Equipment 174 High Energy Barrel Systems: Like the old barrel systems, these machines can be rather large and are completely enclosed for safety reasons. The machine will not operate without the safety cover being closed and this cover seals off all access to the moving barrels inside. Because this system uses counter rotating barrels, there are a number of high-energy forces and stress factors that requires a well engineered machine with proper safety precautions. This is not a machine that can be taken lightly. As previously mentioned, instead of one large barrel rotating very slowly, the centrifugal systems consist of a number of smaller barrels which are designed to spin in the opposite direction of the main rotational force. That is, the carriage frame that contains the barrels rotates in one direction up to 250 RPM and the barrels are also powered to rotate in the opposite direction up to 60 RPM. The speed of the counter rotating barrels can be anywhere from a 1:1 ratio to a slower 4:1 ratio of turns of the barrel to one revolution of the carriage. Naturally, the more turns of the barrel the more G forces, gravitational forces, applied to the work mass within. These counter rotating movements can produce up to 30 times the force of gravity to the barrels contents. This system creates the greatest pressure of all mass finishing systems and makes this the fastest deburring equipment available. Unlike vibratory equipment that have equal X-Y forces and works with gravity, centrifugal systems have X-Y-Z forces. The dominate Z force is gravity and pressure. The first machines to use the high energy centrifugal forces came out in the 1950”s and saw limited use because they were very big and tall machines that required a lot of space. Besides big in height they had relatively small barrels and little working capacity. Also, because this energy principle was new, these early machines experienced problems due to the highenergy forces and material failures.
  • 174. Chapter 9 – Type 3 Equipment 175 Fig. 76. High-Energy Mass Finishing - Centrifugal Barrel Systems Most centrifugal machines are equipped with 4 barrels spaced evenly on a heavy-duty spinning turret. Position or the direction of spin can be horizontal or vertical and it can spin like a paddle wheel, boat, a roulette gambling wheel, or a windmill. As the turret is rotated in one direction, the barrels rotate in the opposite direction affecting a 1:1 ratio. When turret speed exceeds60 RPM, the barrel is subject to high compressive forces of up to 30 times the force of gravity. This speed causes the work mass to slide to the furthest inside wall of the barrel. The energy and pressures created in this process produces extremely fast material removal or surface modification far exceeding either normal barrel or vibratory systems. Today, the barrel systems seem to vary in the design of the securing devices and/or arrangement and size, shape, and access covers of the barrels. Most systems use an equal number of balanced barrels, the most common number being four, but it is not necessary to run all the barrels at one time or even put or keep them in the machine. These barrels are normally mounted horizontal or length wise, parallel to the floor, but smaller versions can be mounted vertically on a rotating disc. The newer horizontal barrel systems seem to favor a slightly tilted barrel system where the barrels are mounted on a diagonal line inclined toward the main central axis. This latter configuration supposedly helps create a figure 8 type flow inside the sealed barrels which results in a better flow pattern, more travel, and/or a supposedly better finish and shorter time cycles.
  • 175. Chapter 9 – Type 3 Equipment Fig. 77. Barrel Finishing Systems Most barrel finishing systems look and behave similar to the older barrel methods of years ago, except for speed. However, internally within the barrel, the work action is completely different because of the high gravitational forces at work; therefore, construction requires more precision and balancing for safety and performance. With some slight changes in the shape and alignment of the barrels within the machine, different workflow patterns can be achieved. As mentioned, 1,2, or 3 barrels can be used in these systems. There are also smaller 2-barrel systems that require a lot less space because they spin on a flat vertical wheel or plane. Barrel shapes and size vary a great deal, but because of the aggressive nature of these systems most work chamber barrels utilize a replacement liner concept. 176
  • 176. Chapter 9 – Type 3 Equipment 177 Besides the technologies used for the counter rotation and securing of the barrels in this equipment, the basic function of the machinery is the same as a standard barrel system. That means that material handling or the loading and unloading are exactly the same as previously mentioned; therefore, extra barrels are recommended for faster more efficient use of these systems. Also, because of the higher energy forces and heat generated by these systems chemical reactions are more common and that creates pressure in the barrels that must be relieved prior to the opening of the door or hatch on the barrel. High Energy Disc Systems: These machines are relatively simple and that makes them easy to operate. The most complicated part of this machine is the precision dimensions required in manufacturing and fitting the bottom disc to the work chamber. Like a vibratory machine, these machines all sit upright in operation, but like the cement mixer type barrel system, they can be dumped. The smaller machines can be operated without a safety cover and needs no special precautions. Most of the smaller machines, less than 8 cubic foot capacity, can be dumped by hand. The larger automated systems normally are fully enclosed for safety and because of the material handling design and conveyor systems. The work chamber design on this machine system is very simple, with either straight or slightly curved walls which always stay stationary. There is no true center cone section to this work chamber like the vibratory machines; therefore, there is no channel width to restrict the size of the part entering the bowls shape. But, because of the media flow, parts should not exceed half the bowls diameter in order to get uniform finishing. The only moving part on this machine is a conical dome shaped bottom disc of the work chamber, from which the machine derives its name. This bottom disc turns at speeds of 80 to 300 RPM which equates to a peripheral velocity of 800 to 1200 surface feet per minute. This is nearly the same speed at which a buffing wheel operates. The action or motion within the work chamber of the disc machine is similar to that of a vibratory machine, except the media travels in the same direction as the rotation of the bottom disc. Therefore, this system can be considered a direct drive action type machine system rather than the indirect drive reaction type vibratory machine systems. Also, we are talking about higher speeds of media rotation that increase the weight and/or pressure of the media work mass to accomplish more material removal in a shorter period of time. This machine system is approximately 10 times faster than most vibratory equipment, but not quite as aggressive as the high energy barrel systems.
  • 177. Chapter 9 – Type 3 Equipment 178 Fig. 78. High Energy Mass Finishing Systems Centrifugal Disc Systems How It Works Most centrifugal disc finishing machines look similar to conventional bowl systems. However, instead of the bowl moving by an eccentric weight, the bottom of this machine looks like a dish or disc, hence its name, which spins and the outside walls stay stationary. The is no large or raised center cone to this machine. Although the RPM’s of this machine are less than vibratory equipment, the spinning disc subjects the media and work mass to greater energy and compressive forces of up to 25 times the force of gravity at a low noise level. This machine works fast, but not as fast as the centrifugal barrel system. One advantage over the barrel system is the size and capacity of the work chamber can handle more and larger parts than the barrel. The illustration shows the mass and flow pattern within the work chamber. A typical disc finishing machine system can normally be manually tilted and its contents dumped out (at left, below). A fully automated system (below, right) has material handling capabilities: (1) container movement, media and parts loading plus liquid input systems. (2) is the bowl type work chamber in both its normal working condition and (3) its dump mode. (4) shows the screen separation system and (5) the rinsing system.
  • 178. Chapter 9 – Type 3 Equipment 179 There is one more interesting feature to the disc machine which should be talked about and that is precision gap of the bowl and spinner (disc). Abrasives and precision is not commonly talked about in this industry, but relatively speaking, these machines are built with a high quality control standards and have a gap of .020 in width between the rotating disc and the fixed outer bowl. This tightly controlled gap is still subject to particles lodging and that can affect the wear of these mating parts. This can be a major problem with any small parts or media, but can happen with any size due to the nature of the material removal process itself. Input/ Output Without sufficient water flow to cool and lubricate the gap, this machine can seize up very easily, because deburring generates friction and heat. Unless that heat is dissipated, materials will expand to absorb that heat. Dry processing can also present special problems of heat and particle size; therefore, it is not normally recommended for dry organic processing, but there are variations of this equipment specifically designed to run dry media. Care and maintenance of this inherent problem determines the life and/or replacement of these disc parts. Because of this gap problem on all disc systems, there are a number of approaches to compensate for this potential condition. The most interesting is the liquid input and drain system for wet processes. Most disc machines add liquid from the top and drain out the bottom through the gap. Some companies use this bottom gap to add water and compound up through this gap to the media mass while in operation. The idea is to reverse the liquid flow pattern to remove debris from this critical dimension area. The bottom input systems can use a side drain above the gap plus it uses a center drain which exits down through the center drive shaft. The size and location of these drains determines the amount of liquid that can be used in this equipment. All liquid systems that carry away debris have inherent problems that can cause blockage; therefore, there does not seem to be any real clear advantage to either liquid drain type system.
  • 179. Chapter 9 – Type 3 Equipment 180 Fig. 79. Disc Gap and Drain System There are two basic gap and drain systems in use with disc finishing systems. Type A is the more common method of circulation, where liquid and compound enter into the top portion the machine and drains through the gap between the disc and the stationary wall, to the exit drain under the spinning disc. The number 1 shows the flow of the work mass and 2 the flow of the liquid. In type B systems, the liquid enters the work chamber through the gap from below, which is the reverse of type A and exits via the hollow center shaft. This method B supposedly balances the disc hydraulically and allows for generally smaller gap dimensions under .020 with this up flow design and this also reduces seal failures. The flow pattern shows entry and movement of the liquid within the mass only. Both systems may also use an extra drain positioned near the bottom of the outside wall. In either case, the gap is subject to lodging by particles smaller than gap because of pressures exerted by the high gravitational energy forces at work. For dry organic processing in disc machines, the input system is basically the same, except air can be introduce or blown through the gap. This seems to work fairly well; however, better provisions must be made to cover the top and purge the air and collect the air born dust particles. Most machines are not interchangeable to run wet and dry systems. That is because liquid drain holes are too small and therefore are not easily adaptable to be able to handle the proper flow of air in a dry system. Basically, what you are talking about is a special modified design that reverses normal drain systems and increases the flow to accomplish dry processing with the minimum of problems. Comparison of Disc vs. Barrel There is little over all processing time difference between the high energy barrel systems and the disc systems from part input to separation. Perhaps the main difference between these machines is the material handling and/or the work load capacities. The centrifugal barrel works faster, but material handling time makes it slower than the total time and labor of a disc machine. The larger barrel system may require special handling and the positioning of the barrels for both loading and unloading, plus the labor needed to take off the hatch cover, dump, and separation nearly equals the amount of time required by the disc machine to do the same amount of work. To get around this down time problem, extra barrels can be purchase to load and unload while the machine is still in operation.
  • 180. Chapter 9 – Type 3 Equipment 181 As to capacity, the disc machine normally can handle a lot more volume and larger parts than the barrel system. The barrel on the other hand seems to work faster and achieves better results using dry organic polishing media and can work smaller parts than the disc. Therefore, you make the call. Again, there are tradeoffs. A fully automated disc finishing machine system can easily be more cost effective and efficient provided there is enough part volume to justify the cost of the automation. Then again, such a machine is a lot more costly as are all the centrifugal machines versus the vibratory equipment. They basically all do the same thing, it’s just a matter of time and money. The question is, what do you want to do? What volume? In what time frame? And how much can you afford or are willing to pay? Other Mass Finishing Systems: This section is really an extension of the mass finishing equipment, but these systems are variations that are distinct enough to warrant their own categories. In other words, these machine systems are not as popular as those above, but there are advantages enough to mention their differences and/or their advantages or disadvantages. The major link or similarity is that they can all use the same abrasive media that is used in mass finishing equipment. Spindle and Drag Finish Machines: These are two different related technology machine systems and are somewhere in between a disc machine and a vertical high energy barrel system. These machines usually fall under the terminology of mass finishing equipment; however, the machine can only handle one part or a group of parts per fixture or spindle. These machines are all classified as type 3 equipment systems and can handle up to class 5 burrs very effectively, but only on 1, outside locations. So, like the vibratory and high energy systems, these are also 300 to 341 systems. This is not a free tumbling parts system that is used in mass finishing. The parts are rigidly attached or allowed to move within a confined space of only the fixture or how it is attached to the fixture. The number parts or group of parts able to processed at one time is limited to the number of spindles a machine has. The only similarity to mass finishing equipment systems is the abrasive media that is used in processing and to some extent the way that media is used. However, the resistance and pressure caused by fixtured parts speeds up processing or finishing time a great deal and can be somewhat selective in where the greater material removal takes place. Every part has to be loaded and maybe unloaded manually to or from a fixture. There are not too many universal fixtures that can handle all part sizes and configurations; therefore, a lot of the processing depends on the design of the fixture and part. Once a fixture is designed, there is the need to reasonably balance the weight and position of the part or parts onto the fixtures so they are as nearly balanced as possible so they get properly finished. Because of a lot of direct labor time is involved, most of these machines have extra spindles for loading and unloading during processing. The fixturing of the parts or spindles takes about the same amount of time as the loading and unloading of high energy barrel
  • 181. Chapter 9 – Type 3 Equipment 182 systems, the only difference is the number of parts that can be processed. Although this is a time consuming problem for material handling, processing time is relatively short. Most of the bigger machines look something like a standard vibratory machine. The system contains a work chamber that sits vertically like a vibratory or disc machine, but they have armatures called spindles that hang down from an independent separate mechanized rack type device, or it can have motorized attachments that fastens to the outside of the machine. The spindles are hand loaded and/or unloaded with parts and the fixture is placed into the tub or barrel only when the media is in motion. Instead of parts being placed inside a machine and allowed to be process freely, parts are fixed onto vertical spindles and these spindles are then placed into a normally wet media mass. There are at least two main differences in the drag finishing systems. Most systems rotate the work chamber while others rotate the parts. In very early systems, vibratory equipment was used and parts immersed into the work flow. Then, specific versions of this equipment were designed so the tub or bowl rotated and the spindles with parts stay stationary. In either system, the violent movement of the stationary spindles and parts caused media to fly out of the work chamber upon impact with the fixtured spindles and parts. Because of the great resistance of the media around the parts as well as up the walls of the work chamber, most of these older machines had high protective barriers around the bowl or machine. These early drag machines produced a disruptive media flow and that resulted in an uneven effect or material finish on the parts. To compensate for this effect, some stationary spindles were manually reversed, or the parts were rotated on the spindle. Other drag systems that use a stationary work chamber, reverse the part rotation of the parts for an equal amount of time in the opposite direction to get more uniform surface finishing. Because of this reversing and manual attention problem, the fixtured spindle systems began to get motorized and automatically rotated the parts in the work chamber Rotating or spinning the parts allowed these machine systems to use slower work chamber rotation speeds and/or media movement. By rotating the part more energy is transmitted to the part instead of the media. Eventually, this processing became known as spin finishing. Drag finishing is exactly the same process; however, instead of the parts spinning in place, they are drag through the media. Newer spin finishing machine systems look and operate differently from the older systems. Most of the spin finishing machines have their motor located on the top of the machine and the spindles and fixtures are designed to come down from the top into the work chamber. Then, either the work media is raised up to the parts or the parts are lowered into the media. Some spindles can rotate the parts in place within a moving barrel, rotate the part on the spindle only, or some machine systems actually drag and spin the parts through stationary or moving media one way and then reverse the spinning. There seems to be a number of new variations of this equipment. Some early machines perform or function as mentioned above and in some cases, the spindles go up and down as well as spin. In some machines, the spindles don’t rotate but the media can be rotated in both
  • 182. Chapter 9 – Type 3 Equipment 183 directions. Some spindles hold the parts rigidly in place so they cannot move, others allow the parts to be attached to the spindle having but a single point of contact; thereby allowing the parts to move in a limited way. Speed of rotation also varies. The tendency now is to rotate the media slow and spin the parts fast. Some systems spin the parts and the barrel up to a 6:1 ratio. This is an extremely fast speed and material removal system. Most drag systems run large parts in wet systems and used with large abrasive media. The newer spin finishing systems are equally impressive and do primarily smaller parts using dry organic systems for polishing. The aggressiveness of any drag or spin finishing system lends itself to polishing work and the use of dry organic materials; therefore, the latter systems are very popular with jewelers right now. Drag Finishing Drag finishing is an older technology than spin finishing. Neither process is a true mass finishing process because both require the placing of parts on fixtures, which is a hand type operation. However, the process is usually classified as a mass finishing because it uses the same abrasive media. The main difference between the two systems is that in drag finishing, the media is in motion and the fixtured parts normally remain stationary and in spin finishing it is just the opposite. Because parts are rigidly in place, drag resistance is normally greater than spin systems. To achieve a uniform finish requires the equal movement of the media in both directions or a slow rotation of the parts either manually or automatically. Fig. 80. Drag Finishing Technically speaking, almost any previously mentioned mass-finishing system can be used as a drag or spin finishing system, that is because any systems can be adapted to handle fixtured parts. But, the bottom line is that all of these machine systems require the use of spindles to fixture parts in order to increase pressure and speed up the material removal processing times by creating greater resistance and pressure against the abrasive media. In turn,
  • 183. Chapter 9 – Type 3 Equipment 184 that fixturing time requires labor and that limits production volumes. Again we have a trade off of speed or time versus labor in the way of material handling and volume. Spin Finishing Spin finishing is the natural progression of drag systems. That is because parts must be turned to achieve uniform results. To increase or improve results, why not spin the parts at higher speeds? Most spin systems still move the media and some also incorporate an automatic reverse cycle to rotate the parts. The spin can be accomplished in either a horizontal or vertical motion to the fixtured parts and the spindles can also move up and down in the media to give an x and y axis movement to the parts. Fig. 81. Spin Finishing Equipment The selection of media is the same criteria used for other mass finishing systems; however, because of energy forces and fixturing, most media used is relative small in size and therefore, more random abrasive particles can be used than the more expensive preformed shaped type media. Also, as mentioned, smaller size media lends itself and this type of equipment to smoother, lower RMS surface finishes, and/or polished finishes. Turbo-Abrasive: This is another variation of the spindle machine systems; however, this machine system uses exclusively dry inorganic media and can handle up to class 4 burrs and is also classified the same as other mass finishing equipment as a 300 to 341 system. The turbo-abrasive performs
  • 184. Chapter 9 – Type 3 Equipment 185 similar to drag and spindle systems, except that the spindles and fixtures rotate only and operate horizontally completely within a fixed media and barrel container. There is another more important technology used in this process that contributes to its increased performance and that is what is called the fluidized bed concept. This fluidized bed principle introduces air into a mass of solid relatively small particles and that changes the characteristics of the media mass to behave like a liquid. Once the air is shut off, the media mass again behaves as a solid; therefore, air pressure is used to adjust the resistance of the media to the part. Air pressure plays a considerable role on the speed of this operation. Instead of controlling the speed of the parts movement to shorten time cycles and processing, air pressure can be used to regulate to some extent the same task. Air pressure is sometimes used in pulses to improve material removal rates and too much air will slow down the operation. Another result of too much air pressure is that it also purges the media of smaller particles and debris caused by the operation. Like drag and spin finishing equipment, all parts must be fixture onto spindles. The turbo-abrasive machine can be made with one or more spindles up to eight depending upon the size or range of the parts that need to be worked. The most common size range of parts are from a half inch to about 4 inches in size. The high speed of the spindle rotation can be adjusted to 5,850 surface feet per minute and/or produce metal removal rates of .08 to .2 thousandths per minute. The media used to perform most turbo abrasive deburring is a combination of alumina, zirconium, and titanium, plus other variations of this mixture. Like the air blasting systems, an air supply is needed and some form of dust collection is required for this equipment which is built into this machine system. The abrasive particle size still plays an important part in material removal rates and again air pressure must be compensated for this size and weight factor. These fast cycle times do not result in a lot of heat generated because the induced air pressure also acts as a coolant and dissipates the heat; therefore, no precautions are necessary in the handling of parts coming out of the process.
  • 185. Chapter 9 – Type 3 Equipment 186 Fig. 82. Turbo Finishing Large turbine discs with fir tree slots deburred and finished with turbo abrasive equipment TF-500 Turbo-Finish Machine with horizontal spindle for processing 1-4 parts simultaneously, each of which can be up to 20 inches in diameter Fir-tree slots in same turbine component after Turbo-Abrasive processing Close-up of Fir-tree slots on turbine disk or ring prior to processing with TurboAbrasive equipment Assorted consumer articles and hand-tools processed with Turbo-Abrasive equipment
  • 186. Chapter 9 – Type 3 Equipment 187 Orbital Beam or Sonic Beam: This machine came way before the turbo-abrasive system, but it used a similar concept. That is, they both insert the part into a media mix after the media is energized. This machine design was a radical departure from mass finishing concepts and never really caught on as a viable processing system because of limited applications; therefore, it is no longer made. The technological approach used was unique and worth mentioning. The motor or energy source was also unique and was the first system to be powered by electro-magnetic solenoids. Using our classification system, this would have been a type 3 system that could only handle up to class 2 burrs, or maybe class 3 in 3 locations, making this a 300 to 323 system. In this machine system, processing is specifically designed to handle two separate energized systems at one time. The machine looks something like a telephone pole with two cross beams or a dual cantilever mechanism. The media mass is contained within two stationary square containers on opposite sides of a horizontal beam. There is no resemblance to a normal mass finishing work chamber. There is no center cone section, eccentric, or spinning disc. Rather, the small random shaped abrasive media is rotated within a square container which is energized from below caused by electro-magnets that are energized or rapidly pulsed to create a mechanical movement. Normally a large single part was fixtured to each side of another horizontal beam that energized and vibrated. The parts are immersed into stationary tubs, or the tubs were raised up to the parts. Because of the high frequency of the energy transmitted to the media, the mass became fluidized and the parts buried themselves into the media. This machine system had a very brief introduction in the mass finishing industry and saw very limited use, around the late 1960’s or 70’s manufactured by the former Wheelabrator company before it was broken up. This was not a very popular machine system, but it might be considered the first type of high energy system and it was the first use of a electro-magnetic machine system. It was also the first vibratory system capable of deburring deep inside holes and cavities commonly found in automobile transmissions castings. Unfortunately no visuals are available on this equipment. Orbital This machine uses the name orbital, similar to the last machine system; however, it is a much smaller system that works completely different. It looks and behaves similar to a paint shaker and it is also called a shaker-mixer. It is a type 3 system that can handle up to class 3 burrs in 1 locations. That makes this a 300 to 331 system. The only difference between a paint shaker and this machine is that the work chamber is a clamping device that holds a sealed, removable container that moves in and out as it shakes back and forth. This system and movement is essentially a modified barrel system, except the barrel/ container moves back and forth in a violent action, but it does not make a complete revolution. The work chamber is a separate sealed container or barrel, just like a can of paint. The in and out action of the drive shaft, which is also shaking back and forth, creates a figure 8 movement of materials within the work chamber or an orbital pattern, hence its name. Because of the violent nature of this action, this machine is completely enclosed. Because of the energy forces involved, most of these machines are relatively small in size making it acceptable to jewelers and other small parts manufacturers.
  • 187. Chapter 9 – Type 3 Equipment 188 Fig. 83. Orbital Shaker-Mixer The orbital machine system resembles and works similar to a paint shaker. The energy forces produced by this equipment move back and forth and in and out which creates a figure 8 movement within the work container which is detachable from the machine. When in operation, the machine cover completely encloses the shaker movement. Magnetic: Probably the newest technology principle used in mass finishing systems today utilizes magnets to energize the work mass to do burnishing only. Common terminology for this system is a magnetic tumbler; however, it is actually a centrifugal system that primarily uses special small stainless steel rod media. Magnetic systems were first introduced into Europe in the late 1980’s to burnish and to some extent minor deburring of small parts. Because of the limited size and power of these systems they can only work class 1 burrs, maybe class 2 in 1 locations. This system falls under our type 3 mass finishing classification and rates a 300 to 321. I am tempted to make this a 4300 to 4321 system because more than half the work chamber mass volume is liquid, but it is the media that actually does the surface modification work or effects the part. The system has no observable moving parts; however, it works by spinning magnets below a cover plate or platform on which the work chamber rests. Except for an outside raised lip restriction on the top plate of the machine, the work chamber is not physically attached or fastened. Rather, it is held in place by the magnetic attraction of the media inside the bowl and the magnets below. The machine system uses strong rare earth rotating permanent magnets fixed to a motorized rotating disc that operates at 1725 to 3600 RPM in close proximity to the media mass.
  • 188. Chapter 9 – Type 3 Equipment 189 The energy force of the magnets has a limited range to influence both ferrous and to some extent non-ferrous metals of drawn stainless steel wire; therefore, these systems are very small or perhaps a better word would be shallow and can only handle small parts. Anything over 2 inches in size would be a difficult task for this equipment. The work chamber of these machines are filled with mostly water and chemical to approximately 2 to 4 inches of work height. The most common media used is special stainless steel pins on or about .5mm x 5 mm maximum or small light weight ferrous materials that would take less than 1 pound to fill a large 8 inch diameter size machine system. Existing small steel or stainless steel balls will not work. The proper proportions of media to liquid in the work chamber is very critical to the proper operation of this equipment, but the most important factor is the extremely thin and long stainless pins or cut wire which is very expensive. Even though the media is special, it is still subject to problems of discoloration and or darkening if not properly treated or maintained. You may have noticed that we have been talking primarily about stainless steel media and magnetism. Normally stainless steel is not a magnetic material; however, when any metal is drawn to such a small size, its molecular structure changes or becomes aligned. This alignment makes all materials then subject to magnetic influences. This machine is primarily a burnishing system that uses stainless steel metal pins or cut drawn wire to initiate surface finishing by way the pressure and impact created by metal movement within a liquid mass, thereby energizing the solid contents of the work chamber. Because of mass and attraction, this system will not work properly, if the parts are made out of ferrous or magnetic metals.
  • 189. Chapter 9 – Type 3 Equipment 190 Magnetic Disc Finisher The magnetic disc finisher has no noticeable moving parts. It works by spinning permanent magnets just below a non-magnetic cover plate on which the work chamber sits. There is no fixed attachment of the bowl to the cover except for the magnetic attraction of the magnets and the media within the container. It works by the spinning magnets, which in turn moves the stainless steel cut wire pins within a container of liquid. Normally stainless steel is not magnet; however, when the material is drawn or its atoms become aligned it is magnetic. Because the media is metal, it is non-abrasive. That means that this system is used primarily for burnishing, but it can remove excess some material because of the small media size and force. Even though there is x & Y movement to the media the parts may not rotate well in this system; therefore, a number of systems have an automatic reverse or spin cycle. Fig. 84. Magnetic Disc Finisher This centrifugal machine system behaves more like a disc finishing machine which produces a lapping work flow pattern type action. A good magnetic system also generates a lot heat to the work chambers contents to uncomfortable levels within 15 to 20 minutes. These machine systems are being used mainly for burnishing type work, but they also do light deburring by impacting parts or removing loose burrs. By mixing the steel with other materials in a ratio capable of being driven by the steel, some abrasive deburring can be accomplished. This is a good system for burnishing jewelry and small parts, but they are extremely limited to small mostly non-ferrous type parts .
  • 190. 191 Chapter 10 – Technology & Equipment Summary Conclusion of Equipment At the beginning of this book, we talked about the history of abrasives and the application of abrasive methods to improve and remove surface variations. Primarily, we were mainly concerned with creating and deburring of sharp edges resulting from the working of metal parts. Basically, we said that there were a number of ways to achieve surface modification or metal removal, and we arrived at a classification system that used 6 different applications of energy to do material removal. Very early on, we tried to set parameters to indicate the amount of material removal or treatment by indicating at least three forms of acceptable standards for conditioning or surface finishing modifications in relationship to the surface profile of the material being worked. Those surface modifications being, surface preparation or the conditioning of the surface to accept a thick protective coating, the removal of excessive burrs and the preparation of the surface to receive a thin protective coating, and the smoothing or polishing of a surface profile. To achieve these three forms of surface conditioning or modification, we came up with a classification system that identifies 6 types of processing, 5 use equipment. The first system, or our type 0 system, is a manual hand labor method of applying or supplying physical force to an abrasive to do surface modification or material removal. This type 0 system involves no equipment but does involve an energy transfer device; therefore, we include it within the system, but give it no numerical value or a zero rating. In addition to the use of hand labor, three other systems involved the use of mechanical forces and abrasives. Two involve the use of non-mechanical methods. All of these systems involve the use and transfer of energy to apply force or molecular changes to the parts to be modified. Technically speaking, energy can be transfer through a solid, liquid, or air. Naturally the greater the weight or mass, the greater the amount of energy that can be transferred and the greater surface modification that can be accomplished in the shortest period of time, normally that also results in the roughest surface profile of the finished part. Therefore, the greatest amount of material removal can be accomplished with rigid solid abrasives, then liquids, and then air. Next, the size and composition of the abrasive is then the next factor in the amount of material that can be removed. Lastly, how the energy force is transfer to the part is the last factor that determines surface removal rates and speed of operation. How energy is applied is the criteria for our equipment classification system. All of the mechanical abrasive equipment systems are energy transfer devices designed to increase the speed and velocity of the abrasive in relationship to the parts and this increases pressure, which improves abrasion and material removal. The increase in speed or velocity in a linear straight-line mode is different from rotational energy forces, meaning that speed does not necessarily result in greater pressure. Pressure is more easily achieved when it encounters resistance at high-speed centrifugal forces. The formula for centrifugal force is: force equals the mass times velocity square divided by the radius (F=mV2/r), or force equals the mass times
  • 191. Chapter 10 – Technology & Equipment Summary 192 gravity (F=mg). So, if you double the RPM's, you double the velocity and quadruple the gravitational forces or pressure. If you double the radius or diameter while keeping the velocity constant you would get half the gravitational force. Double the RPM's and double the radius, you double the velocity and gravitational forces. The most economical way to increase the speed and pressure of mechanical abrasives systems is by increasing the gravitational forces using the principles of rotational devices or centrifugal forces. For every action, there is an opposite reaction. Along with increased speed comes friction and heat. Systems that use air and liquids dissipate most of their heat via these methods and therefore most parts are relatively unaffected by the heat of the processing. At some point, all of these systems can reach an upper limit were heat will affect the part processing; however, more than likely the equipment will reach its functional level or limitation before the parts will. All of these systems achieve increased pressure by wheel movement in a direct or indirect application or transfer of energy. Although rotation is directly involved in type 1 systems, the speed of rotation is not as important as the pressure on the abrasive transfer device by the operator. Type 2 systems are the most indirect method or use of speed, because rotational forces have to be converted to air pressure, which in turn energizes the abrasive. The application of rotational energy is most notable in type 3 high-energy mass finishing systems. In type 1 equipment systems, the energy of rotation is applied to a solid or transfer device, be it a wheel or a belt, in direct contact and/or works parts parallel to the surface profile of that part. This is almost the identical motion and action used by manual hand labor operations, except this system uses primarily a flexible powered transfer device. Without automation assistance, man is still the primary source of applying the pressure to the transfer device and this effects the final surface finish because of his manipulation and use of this equipment. Because of the simplicity of the equipment and/or tools, this system is probably one of the most popular methods of achieving material removal and modification. Of all the mechanical systems, it is the oldest and cheapest methods, excluding manpower, with one of the widest ranges of material modification; therefore, it is still a very popular method of achieving surface profile modification. In our type 2 equipment classification, the energy of a solid is applied by air pressure and projected at the surface profile of a part in close proximity to the energy release point. This is a indirect method of energy contact or transfer which is diffused at nearly a perpendicular angle to the part to be worked. Because of the angle of attack of the solid abrasive, this method normally increases the surface profile of the part being worked and produces rougher surface profile results, no matter what media is used; therefore, this equipment is used primarily for surface preparations. Unlike type 1 systems, where the pressure being applied is by human manipulation of the equipment, man only controls the position of the part in relationship to the abrasive flow and the pressure is constant to what settings are used or required by the human. In type 3 equipment systems, we return to the energy of rotation of a solid applied by a solid in a direct contact method that uses rigid solid abrasives in a free floating mass that is
  • 192. Chapter 10 – Technology & Equipment Summary 193 capable of multiple applications of pressure and angels of attack by the media shape. This equipment uses the largest form of abrasive particles and greatest amount of energy force than any other system. It also has nearly no human interaction that controls the part finish, except selection of what abrasive to use. This is the most aggressive method of uniform material removal of the entire surface finishing systems and it does not require automated material handling systems to work large volumes of parts. This equipment is used primarily to remove excessive burrs and surface modification for plating applications and smooth surface finishes. Type 4 equipment systems use a liquid to transfer energy to a solid part and this can be done in a number of ways and/or in combination with solids or air. Because of the density and cohesive effect of water molecules, which are very small, water by itself is a poor medium for transferring high-pressure energy and has little abrasive force by itself. Water needs a great deal of energy input to get an effective output and again, because the molecules are small the effect is less than that obtained by solid abrasives. Any 4 digit machine systems beginning with the number 4 means that these systems do not removal as much material as the basic 3 digit prime number system which follows this first digit. In our equipment classification, a four digit number beginning with the number 4 means that this is a combination method process which normally produces smoother surface finishing result and is less aggressive for removal a lot of material. Type 5 systems are not good primary equipment systems that do a lot of material removal. Type 5 systems use temperature extremes to do limited burr removal and not good for surface modifications. Basically you have extreme heat and cold that can only effect relatively relative thin sections of materials and are not good on surface profile modifications. On the high heat side, energy transforms thin solids into vapor or lighter, less dense material deposits, but can work difficult to reach areas. On the cold side, a negative energy system weakens thin metal and plastic materials, making other solid applications or combination systems work more efficiently to removal flash and burrs. Presently mass finishing equipment is the most popular means of deburring and surface finishing of parts and the least expensive overall process for doing surface modifications. It is also popular for producing bright shiny burnished and to some extent polished parts; however, when aesthetics are in question, probably the hand buffing type wheel systems are still the most popular and produce the best looking results. For external or heavy coatings, blast systems are the most popular processing method. For hard to reach and micro to small light burrs, liquid or chemical and thermal systems seem to be more effective. Simplicity seems to be the key to getting people to use tools and the less direct labor the greater the probability of the system to be used. That also means the more automation and/or material handling systems get tied into other equipment finishing type systems, the more common deburring done by hand and mass finishing systems will likely decline in large production facilities. Yet, the demand for smoother polished parts may actually increase due to the concern of material porosity and medical concerns; therefore, surface refinement may become a greater requirement than deburring.
  • 193. Chapter 10 – Technology & Equipment Summary 194 The reason for the possible decline of deburring may be because the simplicity of mass finishing equipment is only over shadowed by the complication of abrasive media selection and the variables that control surface finishing. Actually, newer equipment systems and processes are becoming more specialized, less complicated, and easier to work with. It is the media, not the equipment, that really determines or makes mass finishing systems a precision instrument or predictable processing method of achieving the desired end result of a part finish. A finishing system is only as good as one’s knowledge of the media and/or the control one has over the end process. As automated machining centers increase their programming capabilities, which improves their accuracy and performance, they may eventually include deburring tools. That means, there will be less need or requirements for material or edge removal, but more concern for surface finishes. There are still a lot of deburring and polishing applications that automated machine tools or programming systems can’t work properly; therefore, I think there will always be a need for abrasive mechanical systems. Even if the volume of deburring applications decreases, polishing applications will probably increase because of bio medical concerns. Generally speaking, most machine centers cannot achieve the uniform surface profile finishes or smooth edge radii or blending requirements that mechanical system can. Also, if the machine center can achieve the desired deburring results, the speed and time required to keep up with production volume may not be competitive to a mechanical secondary operation. Lastly, without sophisticated follow up machine systems to monitor surface profiles and tooling, machine centers will constantly turn out parts that will vary slightly from one piece to another. Tooling and wear is a major factor that must be taken into consideration and that affects uniformity of finished parts. So, where do we go from here? Let’s review our equipment classification system and take into account what a novice person may want to consider when they are in need of producing a better surface finished part. What equipment should be used? What are some of the standard parameters required or should be taken into consideration when selecting how to do these secondary operations? What determines how I finish this part? One of the first things to take into consideration for determining equipment is the size of the part. Another factor is the configuration of the part and what has to be achieved as the final surface profile. Actually that was two factors; however, the second part of that factor may have to be clarified. That is, what has to be achieved is largely determined by how the part will be used. Engineers will usually specify what surface requirements are needed based upon the environment the part will be used in and how the part is to be used. That means that there are usually 3 different parameter options. We have mentioned these options earlier, but it may be a good time to review these again. The three main options for a part finishing systems are as follows: 1. Surface preparation for a heavy or thick coating, such as paint or plastic based film products, 2. Surface preparation for a thin film chemical coating or treatment, 3. A smooth, or bright, good looking aesthetic finalized surface appearance on a part. Once one of these factors has been determined, then the
  • 194. Chapter 10 – Technology & Equipment Summary 195 finishing equipment can be determined. There are exceptions to almost all processes as to what is best and that is determined a lot of times by what one has to work with in the way of equipment in house. However, because we are not locked into this limitation, we will make recommendations based upon our classification system. Surface Finishing Options Type Description 1 Surface preparation for heavy thick coatings 2 Surface preparation for thin film coatings 3 Polished finishes Our equipment classification system is a generalization for all finishing equipment systems and parts processing. In the following chart, the numbering system is basically listed in the order of how technology has evolved to some extent; it reflects costs and the order of the aggressiveness. Variations, supplies, and improvements in this equipment have provided or designated us with a “Range” or limitations. In the last column of our chart, I have included “Surface Finishing Options” as a quick reference guide. This series of numbers appears in the order of the equipment’s best performance capabilities from the list above. Both designations are generalizations and are only suggested as a reference. There are some additional charts to follow which may also be helpful for narrowing or selecting the finishing system for your particular application. Again, this is not absolute. Deburring Equipment Classification - Surface Finishing Options System Wheel and Belt Systems Abrasive Blasting Cryogenic Blasting Wheel Blasting Wet Blasting Water Jet Ultrasonic Abrasive Extrusion Thermal Chemical Mass Finishing Systems Spindle/Drag Finishing Turbo-Abrasive Orbital/Sonic Beam Orbital Magnetic Range 100 – 151 250 – 253 5200 - 5233 250 – 251 4200 – 4233 4200 – 4231 4200 – 4211 4200 – 4243 500 – 533 400 – 433 300 – 351 300 – 351 300 – 351 300 – 323 300 – 331 300 – 321 Option 3 -2-1 1–2 2 1 2 2 2-3 2–3 2 2–3–1 2–3–1 3–2–1 2–3–1 2 3–2 3
  • 195. Chapter 10 – Technology & Equipment Summary 196 The primary systems used to achieve type 1 surface finishing options or preparations are classified as type 200 equipment systems. This also includes 4200 and 5200 systems to some extent. These are all blast type systems and are also know primarily as cleaning systems that produce parts with finishes that have a greater over all surface profile or surface area which has better coating adhesion qualities. Blast finishing systems normally leave surface finishes rougher than what one starts out with. These same surface qualities can be achieved to a lesser extent by using very coarse grades of ceramic media in mass finishing equipment and abrasive belt and wheel systems, in that order. Type 2 surface finishing options are more general applications of all three types of equipment classifications. That is, using a medium to fine grade of abrasive in any one of the designated equipment systems mentioned will produce results which are normally acceptable for thin chemical films or treatments. Naturally, the finer the abrasive used, the lower the mass and pressure which results in a smoother surface profile or finish to the part. A smoother surface profile is more desirable for thin uniform coatings because there is less surface profile exposure to the environmental elements. Rough surface profiles are susceptible to uneven coatings and penetration by material protrusions. Type 3 surface finishes can also be accomplished using all three abrasive equipment classification systems; however, all 200 equipment systems should not be used, unless you are looking for a frosted texture or satin type finish. A better result can be accomplished with 4200 systems. That leaves all 100 and 300 equipment system as the primary means of achieving polished, low RMS surface profile finishes. Again, a low surface profile reduces the effect of biological agents and eliminates possible contamination problems. Now, before we talk about aggressiveness, which relates to time, I think we need to talk about volume. If you do not have a lot of parts that need a secondary finishing operation, your options are either limited or not, depending upon how you look at things. Small volumes of less than a dozen or so parts are normally limited to hand type operations, because most systems are not built to handle so few parts. That means that parts are either worked by hand or processed using wheel or belt type systems. If the part configuration is relatively simple and has easy accessibility to the area that needs to be deburred, then relatively more parts can be processed probably more quickly by hand than can some automated systems or even mass finishing equipment. Total time is a big factor for determining cost effectiveness or feasibility. Other factors include equipment maintenance, wear, and set-up time. The complexity of a part configuration and accessibility are also important factors to consider in determining equipment. Whereas, we have shown that volume is not the sole determining factor for equipment selection, this same statement has its opposite counterpart. That is, if a part has a complex geometry or the burrs are located in difficult to reach areas and are time consuming to work by hand, then there may be enough repetitive business to justify a lot more expensive processing system. Most complex configurations of parts have internal cavity burrs that cannot be easily reached or seen and that is why we have incorporated this burr location into our numerical classification system.
  • 196. Chapter 10 – Technology & Equipment Summary 197 The numbers 0, 1, 2, or 3 appear as the last digit of our equipment designation system. However, there are really only two choices here. Again the number 0 means that no or little material removal is necessary. As far as I know, all equipment systems will deburr outside accessible #1 locations relatively easy; therefore, you will not normally see a machine system ending only with a number 1 type location. As mentioned, the most difficult areas to reach are internal number 2 dimensions. This problem and location is especially noticeable with mechanical abrasive systems, because solids do not move well in confined spaces. The number 3 is the ability to work both area locations. There is no one system that does both ID and OD areas equally well. Our equipment classification system distinguishes aggressive features or traits by the second to last digit in our numbering system. This number reflects or determines the range or capability for material removal, with the number 5 being the highest classification of material removal. Again, material removal in excess of .030 is possible with a number of these machine systems, but it is not recommended and not the efficient use of the equipment. Burrs or material removal in excess of .030 are best accomplished with better machining practices. Aggressiveness of a mechanical machine system relates to time. The more aggressive a machine the faster the equipment or the greater the pressure is applied to the process. Remember, the machine system is only an energy transfer device to the medium that does the material removal. Therefore, in larger mechanical machine systems, the larger, heavier, and more rigid the mass or solid the media used by the equipment, the more aggressive the equipment system. So, aggressiveness can relate more to the solid abrasive than it does the equipment, but how the energy is directed and how much energy is transferred is the function of the machine system. Now, because of progress and machine improvements, there are a number of variations in equipment and system designs that determines equipment aggressiveness. In type 1, wheel and belt systems these differences are somewhat clear, cut, and dry. There are relative no or little use of solids by these systems; however, the wheel or belt itself does behave like a solid form of media, or is the transfer medium. Besides this factor, other variations or improvements to these systems are mostly in the form of automated material handling systems. Speed or RPM's of the drive wheels can only achieve a fixed rate of energy transfer. The operator applies or determines the pressure to the part or work and that causes heat which is a factor that is effected by pressure. Besides pressure, the other controlling factors are the compound additives, coolants, and abrasives that determine a system performance. In blast type systems there are more aggressive control variables. Also, there are different parallel blast systems technologies operating side by side. The aggressiveness of blast equipment is determined by the amount of energy transfer or pressure. There are just two ways to apply energy to air born particles and only one way with the addition of liquids. The greater the pressure and the heavier and larger the media, the faster, more aggressive the equipment system.
  • 197. Chapter 10 – Technology & Equipment Summary 198 To determine the aggressiveness of blast systems is to look at the media that is used with the equipment system and the amount of force used to energize the media. The amount of material removal of these systems is greatly affected by the size and type of the media used on the part or material being worked. Increased pressure means that the part and media size is or will be significantly modified as pressure increases, but coverage or dwell time will decrease. So blasting has to take into consideration two factors for aggressiveness, not just the aggressiveness equipment, but that of the media being used. In mass finishing systems aggressiveness is also a product of pressure and these differences are known as generations of equipment or the form or type of energy used to perform the work, such as barrel, vibratory, or centrifugal. Although these systems use energy differently, pressure is determined by the application of rotational energy forces or factors of gravitational forces and by the use of larger heavier media. As with blast equipment, media is a major factor that effects the amount of material removal, time, and the surface finish. Unlike blast systems, mass finishing technologies are significant progressions and warrant different names or titles. The energy forces transferred to the parts are different in a barrel, vibratory, and high energy systems. Each system works by almost a factor of 10 times faster than its previous name sake or generation of equipment. The end results are almost identical but the processing speed is the major determining factor plus cost of the equipment. Once a part is processed, it is of little use until it is sorted or isolated by itself. Separation is another factor that enters into time cycles; therefore, processing time is not solely dependent on speed or aggressiveness of the equipment. Material handling is always something to be considered. Perhaps one the better deburring equipment systems is the abrasive flow type machine. These systems combine or utilize the attributes of solids and liquids in direct contact with the part. The energy transfer medium behaves similar to a solid but it flows more like a liquid. This is an extremely efficient and somewhat aggressive deburring system that does well on surface profile material removal. Because of the flow characteristics of the heavy viscous slurry media, this is the best system for working parts with internal cavities and dimensions The down side of abrasive flow equipment systems is that they are slow, require special fixtures, and require some massive support equipment and pumps; therefore, it is probably the most costly equipment system of all that are listed. Some variations of this equipment produce excellent or improved surface profile finishes, but generally most of these machines for removing hard to reach burrs. The technologies of thermal and chemical deburring systems would seem to be more easily controlled or regulated than blast or mass finishing equipment, because they do not involve the mechanical systems or the use of a solid media in relationship to the part. These systems use the mediums of air and water which are less dense energy transfer system; therefore, the equipment is used more for selective type material removal work than the more difficult task of surface profile modification.
  • 198. Chapter 10 – Technology & Equipment Summary 199 Adjustments or aggressiveness to these systems involve primarily one energy transfer system which should not vary significantly; however, volume and the mass or part size is more of a controlling issue or factor. Relative to other equipment systems, parts processed by these methods are generally smaller and the process removes less material than other deburring systems mentioned. Even though these systems are rated very aggressive in our classification chart, they are rarely used for major deburring or surface modification. These systems are similar, but a lot less costly than the abrasive flow machines that do almost the same type of material removal. As you can tell, there are degrees of aggressiveness and there are variable factors influencing the use of different deburring or finishing system. There are a lot of gray areas here and/or variations. Therefore, enclosed is another evaluation chart that is a little more detailed than the equipment classification chart only. This should help you decide a little better the strengths and weaknesses of the different type of equipment and material removal processes involved. Like all good flexible processing systems, there are a lot of variables that enter into this more detailed chart. That means that selection depends upon how you want to use the equipment. Naturally, the more uses or variation in parts you have or want to process through a machine system, the more down time will be experience in set up time or change over down time. No system is completely idiot proof. The more variations you have or want to have, the greater the flexibility of the equipment system and the greater the chance of encountering additional problems. With that thought, below is a more detailed chart for equipment selection and part processing:
  • 199. Chapter 10 – Technology & Equipment Summary 200 EQUIPMENT CLASSIFICATION EVALUATION BY CATEGORY Equipment Burr Class 1 System Wheel & Belt Abrasive Blasting * Cryogenic Blasting Wheel Blasting Wet Blasting Water Jet Ultrasonic Abrasive Extrusion Thermal Chemical Mass Finishing Spindle Turbo-Abrasive Orbital Beam Orbital Magnetic 2 3 4 Location 5 G G G G G G P G G S G G G VG VG VG G G G G 2 3 4 5 0 1 2 3 G G G S G P G P G VG VG G G P P S S G S P S G P S VG VG G VG S G 1 VG VG G 0 VG G G G G G S S S G S S S P G S P P S G S G G G G G P S P G S G G G S VG G S G G G G G G G G G VG G G G G S G S VG G G S G S P G G G P S S P S G S P S S G G G G S G G G G VG G G G G G G S P P G S G G S S G S S S Explanation of letter symbols VG Very good G Good S Some P Poor Left Blank not recommended for application or classification * Rating based upon material removal, not surface finish. I alluded to size as a determining factor in equipment classification earlier; however, I did not go into any details. Part size is a very important factor for determining equipment and processes, not only for determining or maintaining production rates, but also for controlling accountability of the parts. In most industrial applications, assembled parts are relatively large in comparison to electronic, medical, and jewelry type parts. Why I mention that is because almost every material removal system discussed so far has alternative smaller systems which have different specifications and cost factors. Finishing equipment is built to reflect different size parts and volume. Small parts can get lost in large capacity machines and never found again and large parts in small machines may not be processed properly or achieve a uniform surface finish. Selection of a finishing system is mostly determined by capacity which in turn is determined a lot of times by a mixture of parts that must be processed as well as volume. Why choose a 10 ton press when a hammer will do? In addition to size of the equipment, part size is another major determining factor, which is especially evident in mass finishing equipment. Generally speaking, there are about 4 sizes or ranges of parts in most metal processing systems. To make it simple, I’ll just say that if a part
  • 200. Chapter 10 – Technology & Equipment Summary 201 can be held in the palm of one hand and can’t be seen, then that is one size. If a part can be held in one hand and weights less than about 2 pounds, that is another size range. If a part exceeds the two hand or the 2 pound range, then that is the third size of parts. Any parts that need mechanical loading help would be a fourth size group of parts. This part size analogy creates another classification system and equipment chart. As in drafting that has drawing sizes, our hand-held part now equates to what we will call” A” size parts, or parts under a half inch in size. Parts capable of being held in one hand are “B” size parts and will be over a half inch in size to approximately 8 to12 inches in length, or about a 8 inch cube. Parts capable of being handled by a single operator using two hands unassisted are C size parts and are somewhere over 12 inches in length or over the 8 inch cube size. D size parts are any parts that are difficult for one person to handle and/or control and are more subject to weight limitations than size limitations. In short, D size parts need material handling devices. Each one of these part sizes constitutes a specific range of recommended equipment. Classification of Part Sizes Letter Measurement Description A ½” or smaller parts Can’t be seen in closed hand B ½” up to 12” length Can be held in one hand C weight Need 2 hands, or over 2 lbs. D weight Need material handling assistance Finishing equipment systems are built to reflect different size parts and/or volume. That means, one size does not fit all. The only except to that rule are the chemical deburring systems that depend primarily on size and capacity of the liquid tanks, but even here, the electric generating equipment are sized to a certain mass or volume of parts. Therefore you can shop for equipment size and function as well as price in a lot of instances. So, not only do you have alternative material removal processes and equipment, you also have different size systems to accommodate the part sizes A through D mentioned above. Also mentioned is the problem of accountability, which is a very important factor for some parts. Even though the size of a part maybe smaller, the cost of producing them may not be; therefore, greater care is required for the overall quantity of the parts as well as the quality of the surface finish produced or required. Below is another generalized chart indicating equipment classification and the part size range these systems normally handle.
  • 201. Chapter 10 – Technology & Equipment Summary 202 Fig. 85. Equipment Classification by Part Size System Wheel & Belt Abrasive Blasting Cryogenic Blasting Wheel Blasting Wet Blasting Water Jet Ultrasonic Abrasive Extrusion Thermal Chemical Mass Finishing Spindle Turbo-Abrasive Orbital Beam Orbital Magnetic A B C S S G VG VG G S VG G G G G G VG G G G G S G G P VG S G S S S S G G VG VG VG G S S G G S VG S Explanation of letter symbols VG Very Good G Good S Some P Poor Left Blank not recommended for application D G VG S G S
  • 202. Chapter 10 – Technology & Equipment Summary 203 Now, we have talked about part size to some extent and have made some recommendations. Sometimes size is not a good quick reference guide in the selection of mass finishing equipment. In addition to part size and equipment size, we have also talked about capacity in cubic feet as a way to measure equipment. All these previously mentioned guides normally require some calculations in order to come up with what volume of parts can be processed in what system. In my opinion, the quickest way to come up with capacity figures is by weight of parts in a machine system. As another quick reference capacity guide for mass finishing equipment, I’d like to give you some rough guidelines in terms of weight of parts in a machine system that also takes into account a media capacity of 50 to 60% which is good for deburring. Do not use this guide for dry media or processing. As a side note, as machine systems become smaller, so too do the energy forces; therefore, the smaller the system the longer the time cycle to produce the same results. Fig. 86. Weight Capacity of Parts Pounds of Parts 10 100 250 500 Cubic Foot Capacity ¼ Cu. Ft. 1 Cu. Ft. 5 Cu. Ft. 10 Cu. Ft. Part size is an important factor for determining equipment and processes. In most industrial applications, assembly parts are relatively large in comparison to electronic, medical, and jewelry type parts. Why I mention that is because almost every material removal system discussed so far has an alternative smaller systems, which has different specifications and cost factors. Equipment is built to reflect different size parts and/or volume. So, not only do you have alternative material removal processes and equipment, you also have different size systems. Each system has a range or limiting factors to consider. There you have it. These are the primary options for deburring and polishing. We have covered the most popular processing methods and machinery for deburring and polishing. This explanation of equipment basically serves as a guideline to advise you of advantages and limitations of different systems. All systems will work or do something to some extent. How material removal systems work and the efficiency of their operation are the determining factors that should guide you. Of the mechanical energy force options, mass finishing systems and their relationship to abrasives and/or media as well as parts being processed are probably the most aggressive and popular. The following chart is a summary of the systems we have reviewed.
  • 203. Chapter 10 – Technology & Equipment Summary 204 Deburring Equipment Classification Chart System Range Wheel and Belt Systems 100 – 151 Abrasive Blasting 250 - 253 Cryogenic Blasting 5200 - 5233 Wheel Blasting 250 - 251 Wet Blasting 4200 - 4233 Water Jet 4200 - 4231 Ultrasonic 4200 - 4211 Abrasive Extrusion 4200 - 4243 Thermal 500 - 533 Chemical 400 - 433 Mass Finishing Systems 300 - 351 Spindle/Drag Finishing 300 - 351 Turbo-Abrasive 300 - 351 Orbital/Sonic Beam 300 - 323 Orbital 300 - 331 Magnetic 300 - 321 We can now go into the explanation of media, liquid systems, and the processing of materials, specifically designed to be used with and control mass finishing processes. But before we do that, perhaps we should explain a little about the ways and means for determining surface finishes. If we do not set up any ground rules of what you are trying to achieve and what type of ruler we are using to try to maintain standards of performance or uniformity, we are not going to achieve apples and apples.
  • 204. 205 Chapter 11 – Surface Finishing Standards Surface Finish Quality Control: An acceptable finished part is normally concerned with three things. They are fit, form, and function. If a finished part does not conform to at least one of these criteria, it is not an acceptable part. It is a reject. The main reasons for part rejection are burrs or surface variations that affect how a part fits, its overall dimensions or form, and how it functions in relationship to other mating parts. If we are talking about a part that can be seen, we may also be talking about a surface appearance. What is an acceptable part is determined by engineering. They in turn determine the parts final dimensions. They do not necessarily determine the most appropriate method of making the part, just how it is to operate and its final dimensions. Other people or engineers decide how a part is to be made and what is an acceptable surface finish based upon its function, use, and its operating environment. Now, the measurement of a part seems to be pretty straight forward and simple, but it is not. That is, a parts basic outside and inside dimensional shapes are somewhat simple to measure, because we are talking about mainly the separation or measurement of two points. However, the flatter surfaces or planes in between these dimension is just one or a multitude of points that also need a certain amount of uniform conformity which can also be measured. To determine the acceptability of a part is to a large extent determined when that part is designed. That is, the materials are specified to conform to its function. Then specific dimensions are machined or formed into the part and the surface finish is determined by the environment in which that part is to work. To protect that part, increase its life, and to function in that environment requires a secondary process which is either a chemical treatment or coating, or the absence of any secondary operation. The secondary protective coating is only as good as the materials surface preparation. Because of manufacturing options and cost factors of raw materials, forming, and/or machining, every part can be somewhat different from one another. That also means that edges, surface finish, and burrs can also vary slightly from one part to that of another and from batch to batch and from machine to machine. There are a lot of different ways in which a part can be made and this somewhat effects the final results, in good or bad ways. That also goes for whatever processing method, equipment, and media is used to correct material or machining irregularities. In mass finishing systems, surface preparation or finish is determined by the type of energy forces exerted on the part by an abrasive or media and particle size. Again, external dimensions are relative easy to determine, but how a parts surface finish is measured is determined by the way in which it is made and what is acceptable. The way it is measured or inspected to conform to predetermined specifications or critical dimensions is also another factor to consider. The most common means for determining a surface finish and/or surface irregularities besides visual appearance and feel, is an instrument called a profilometer.
  • 205. Chapter 11 – Surface Finishing Standards 206 The profilometer is device that measures the peaks and valleys of the surface of an object by moving a stylus ball type probe over a pre-set measurable surface. The read out measurement of this device is related to a calculation of the average surface variations of the peaks and valleys of a given measurable surface and is called RMS or Rq. RMS stands for the mathematical term root mean square determined in micro inches or micrometers. A micro inch or micro meter is one millionth of an inch or meter which is equal to .000001 of which ever scale you are using. Depending upon the part, usually 5 readings or measurements are taken over different center lines of the part and should be approximately the same length. RA (Roughness Average) Rq/RMS (Root Mean Square) These terms are derived from mathematics to indicate a relationship of overall flatness of any surface material. In the US, this surface is measured in millionths of an inch or microinch, 1 microinch = .000001. The illustration shows a surface profile of a part with shaded peaks and valleys in relationship to a centerline average. A number of terms are used interchangeably to describe certain aspects of a surface profile. The more common term used to measure flatness is RA. This is the arithmetic average roughness profile measurement of the surface profile of the material from the centerline to the maximum height of the profile. The RMS is the geometric average of the roughness profile and is derived by taking the square root of the squares of the average vertical distances. Rq is the more current terminology being used in place of RMS. Although these two terms and measurements are related, they are not compatible. In most cases, the relationship is 1.11RMS to 1 RA when in fact is a variable that can go from 1.11 to 2.10:1. Fig. 87. Surface peaks and valleys: centerline average
  • 206. Chapter 11 – Surface Finishing Standards 207 Other Terms and Measurement From the centerline or mean average, other forms of measurements can be established. Each of these terms or measurements serves a purpose, but the bottom line is to establish a dialog of universal or a standard form of measurement. The following show some of the more common terms used. Rv is the maximum valley depth in a profile below the mean line of the measured area. Rp is the maximum peak height of the profile above the mean line of the measured area. Rt is the sum of Rv & Rp or the maximum peak to valley height or total roughness of the profile of the measured area. Rsk is the measurement of asymmetry (skewness) of the profile of the measure area. As stated earlier, when a part is designed, a lot of the pre-determined qualities of a part are specified and those critical qualities that are more important than others may be checked or determined for acceptability. For surface finishing, there are measurement parameters or standards for amplitude or surface variations in height as well as spacing and/or a combination of both. A measurement tolerance or a range of acceptable surface variations is normal for determining this acceptability. Most finishing processes can only control amplitude parameters. As a general rule, normal mill steel or sheet metal after processing averages about 35 RMS or Rq. As the number becomes less or down to zero, the surface finish becomes finer or smoother.
  • 207. Chapter 11 – Surface Finishing Standards 208 Fig. 88. Components of Surface Finish Measurement parameters are basically designed to identify roughness (height), waviness (spacing0, and form (hybrid). Each standard serves a special purpose. With the advent of a world community, European ISO standards are being integrated and updated to reflect more universal measurements. The following are some examples of working standards. RsK – Skewness – is the measure of the symmetry of the profile about the mean line. It will distinguish between asymmetrical profiles of the same Ra or Rq Rz - Also known as ISO 10 point height parameter, is measured on the unfiltered profile only and is numerically the average height difference between the five highest peaks and five lowest valleys within the traverse length. S - is the mean spacing of adjacent local peaks, measured over the assessment length (A local peak is the highest part of the profile measured between two adjacent minima, and is only included if the distance between the peak and it’s preceding minima is at least 1% of the P + V of the profile. HSC – The high spot count is the number of complete profile peaks (within assessment length) projecting above the mean line, or a line parallel with the mean line. This line can be set at a selected depth below the highest peak or a selected distance above or below the mean line. Sm - is the mean spacing between profile peaks at the mean line, measured over the assessment length. (A profile peak is the highest point of the profile between an upwards and downwards crossing of the mean line Pc – The peak count is the number of local peaks which project through a selectable band centered about the mean line. The count is determined only over the assessment length though the results are given in peaks per cm (or per inch) The peak count obtained from the assessment lengths of less than 1 cm (or 1 inch) is obtained by using a multiplication factor. The parameter should therefore be measured over the greatest assessment length possible.
  • 208. Chapter 11 – Surface Finishing Standards 209 To achieve a good surface finish acceptable to a secondary chemical treatment or anodize finish coating, usually a measurement of 16 to 18 RMS is required. Paint coatings can be rougher than 20 RMS; however, if a good flat paint appearance is required, then the finish should not exceed 22 RMS. In mass finishing systems, a mirror finish parts can be achieved at almost any RMS using steel media; however, most engineering people think in terms of smoothness and brightness. That is, even though bright finishes can be achieved with rough surface finishes, once they get dirty, they are hard to restore to brightness because of the roughness of the surface finish. Therefore, mirror finishes and/or acceptability is normally around 8 to 12 RMS. Lastly, perhaps the best surface finish that can be achieved, without lapping, is probably about a 2 to 4 RMS using mass finishing systems, and step processing. Another common terminology used to measure surface finishes is Ra, which stands for roughness average. This is the most commonly specified standard for machine shops in the USA. This measurement standard would seem similar to RMS, because it is a measurement of only the peaks of the roughness profile from the center line average. Therefore, as a general rule, most shops have been using a conversion factor or RMS of 4 times greater than of an Ra. That means that a normal mill finish on materials of 30 to 35 RMS would be equivalent to an Ra of 120 to 140. Now, what I just said is about the conversion factor may be true, but it is not correct. In reality, this is a variable ratio that depends upon the process used to create or manufacture the surface profile. This ratio is actually a minimum of 1.11 RMS, Rq to 1 Ra up to 2.10 to 1. See the following conversion table. Ratio of RMS to Ra Actual ratios of RMS, Rq to Ra for various processes: Turning 1.17 to 1.26 Milling 1.16 to 1.40 Surface grinding 1.22 to 1.27 Plunge grinding 1.26 to 1.28 Soft honing 1.29 to 1.48 Hard honing 1.50 to 2.10 Electrical Discharge Machining 1.24 to 1.27 Shot peening 1.24 to 1.28 For most processes 1.25 to 1 For honing 1.45 to 1 In addition to the terms RMS and Ra are a number of different other measuring parameters. The following are a few popular examples. The term Rp is used to determine the average peak height profile from the centerline. This information is sometimes more helpful for
  • 209. Chapter 11 – Surface Finishing Standards 210 determining how well the surface profile may wear. Rv is the average valley depth of the profile below the centerline. This information is helpful for determining how well that surface may retain lubricant. Rt is the maximum peak to valley height profile and high lights the extreme surface features. The term Rsk is a measurement of asymmetry or skewness of the surface profile in relationship to the centerline. This information tells you the direction of the profile to positive, neutral, or negative, which is desirable for a good bearing surface. As stated, there are probably countless numbers of measurement scales, plus both new and old terminology, which complicates things. Other scales which may affect burrs, but are not covered in any detail here are those which are used to measure hardness, waviness, sharpness, lay, texture, slope, etc. This book was written and/or expresses all measurements in RMS; however, this term may become obsolete shortly and replaced with Rq. I mentioned Ra which measures a surface profile, but this too may become obsolete, in order to be more specific or limiting. This is a new scale developed for Europe and is a ISO 10 point height parameter, or a 10 point Ra. That is, it is an average measurement, which specifically covers readings over 5 peaks and 5 valleys within a traverse length. The function or performance environment of a part may require special considerations or quality control standards that are more important than just surface smoothness. Therefore, there are other scales that may be necessary for checking the parts acceptable performance, but not necessarily a condition that can be controlled by mass finishing systems. Other technical information or standards may be necessary to meet contract obligations or performance requirements. That means being on the same page of the play book as everyone else to meet the working conditions of the part, but again, these standards may not be requirements of surface finishes which we are concerned with. Mass finishing can effect a lot surface and edge conditions, but it cannot correct a badly made or machined part. Again, this information is for reference only and cannot be effected by mass finishing systems. For simplification, our references will all relate to RMS in inches for the rest of this book. The following media selection information is directed at how to accomplish the best surface finish results using abrasives and mass finishing equipment and media. We will start off with media selection and or guidelines for processing certain type of materials and/or parts. Then we will cover the liquid chemical side of this processing as a separate segment issue, which it is. Equipment will only provide the energy forces for the media and liquid to do their work.
  • 210. Chapter 11 – Surface Finishing Standards 211 Surface Finishing Standards The following chart is a good reference guide for a number of standards used for surface profile measurements and their relationship to one another, if any. Surface Profile Parameters Parameter Name Height Parameters Ra Roughness Average (Ra) Rq Root Mean Square (RMS) Roughness Rt Maximum Height of the Profile Rv, Rm Maximum Profile Valley Depth Rp Maximum Profile Peak Height Rpm Average Maximum Profile Peak Height Rz Average Maximum Height of the Profile Rmax Maximum Roughness Depth Rc Mean Height of Profile Irregularities Rz (ISO) Ten Point Height Ry Maximum Height of the Profile Wt, W Waviness Height Spacing Parameters S Mean Spacing of Local Peaks of the Profile Sm, RSm Mean Spacing of Profile Irregularities D Profile Peak Density Pc Peak Count (Peak Density) HSC High Spot Count a Average Wavelength of the Profile q Root Mean Square (RMS) Wavelength of the Profile Hybrid Parameters a Average Absolute Slope q Root Mean Square (RMS) Slope Lo Developed Profile Length Ir Profile Length Ratio ADF and BAC Parameters Rsk, Sk Skewness Rku Kurtosis Tp, Rmr(c) Profile Bearing Length Ratio (Material Ratio of the Profile) Htp, Rc Profile Section Height Difference H Swedish Height Rk Core Roughness Depth Rpk Reduced Peak Height Rvk Reduced Valley Depth Mr1 Material Portion Mr2 Material Portion Vo “Oil-Retention” Volume Rpq, Rvq, Rmq Material Probability Curve Parameters Standards Related 1,2,3,4 1,3,4 1,3 1,3,4 1,3,4 1 1,3 1 3,4 4 4 1,2,3 Pa, Wa Pq, Wq Pt, Wt Pv, Wv Pp, Wp 4 1,3,4 4 1 Pz, Wz, Rtm Ry, Rymax, Rti, Rz Pc, Wc Rt, Pt PSm, WSm, Sm 4 4 1,3 1,3 4 4 Pa, Wa Pq, Wq Ir Lo 1,3,4 1,3 1,3,4 Psk, Wsk Pku, Wku Pmr(c), Wmr(c), Pmr, Rmr, Wmr 1,3 Htp, Rt 5 5 5 5 5 Rpk* Rvk* Rmr(c), tp Rmr(c), tp
  • 211. 212 Chapter 12 – Media Media Supplies The word media is a very generic catch all word. It is a proper noun that acts more like a descriptive verb. It can mean virtually anything that is used to convey or transfer some kind of result, be it good, bad, or indifferent. Early on in this book we talked exclusively of abrasives and this is a form of media, because an abrasive transmits energy from one source to another and in the process, it causes mechanical movement and friction. When this movement is controlled in a uniform way with uniform abrasive materials, this produces predictable results. In addition to being an energy transfer system or process, this can also be considered a destructive system or process. That is because whatever media or parts are placed into these energy systems there is an expected modification result to the media and parts. Within the text of describing all mechanical deburring equipment, we eventually added and changed the word abrasives to media or used the words inter changeably. However, in mass finishing systems, media is the most common term used to describe any material that is used to produce a modified or altered appearance to a part. This usually refers to an abrasive, but it can still be anything that will abrade, polish, clean, or separate parts. Media can be random stone or mineral aggregate, preformed shaped ceramics, plastics, steel, or alloy metals and all forms of organic materials. In other non-mechanical material removal processes it can also be a liquid, or extreme heat. Most of the media talked about in mass finishing systems are inorganic materials used in what are called wet processing operations; however, there are also dry organic materials that do light material removal and polishing. Given one specific part, run in different media compositions of the same size in the same machine, or similar technology machines, you will get different results over the same period of time. That is because each media system has different abrasive qualities, wear rates, and surface finishing characteristics, but the surface profile of a part is also effected by liquids, chemical compounds, and machine adjustments. Therefore, that means that the selection of a media requires some knowledge of both the equipment being used and the abrasive media and that discourages a lot of people from using mass finishing equipment. An analogy of abrasive media here is that it behaves like the numerical controls of a computerized machine system. However, instead of pushing buttons or numbers to control movements and tools, the operator physically puts in or installs the proper size, shape, and composition of media and this determines the parameters of the final surface profile and the rate of material removal. Depending upon the parts to be worked, almost anything can serve as deburring media. In a pinch or in an extreme need, you can go outside and dig up some gravel and put it into a mass finishing machine and it will achieve some kind of results. The trick is to find and use that same consistent media to produce the same predictable results you are looking for, in the shortest period of time, and hopefully produce acceptable uniform results over and over again.
  • 212. Chapter 12 – Media 213 As mentioned, not only do you have to worry about selecting the right media, you have to be concerned with its size, shape, and composition. Other factors to be concerned about are the life or wear of the media, and what kind of end results or surface finish that has to be achieved. There is no single cure all media that will work on all parts or materials and having and storing of a lot of different abrasive media is sometimes not practical. There are tradeoffs. The following are some general rules or patterns that can help you select the right media for the right part. Here then are some rough guidelines to help your selection process. Random Media First of all, let's narrow down some basics. Long ago, most abrasives used in any kind of material removal process were random aggregate of mixed stone materials. It was soon found out that without controlling the type of mineral aggregate used, different results would be achieved using different batches from even the same material or source. Therefore, the aggregate was identified to a specific mineral content. If the mineral was a mixture of different particle sizes of the same material, non-uniform results were also possible due to the inability of the random mix to achieve good uniform surface contact on the part or material being processed. That difference of particle sizes also effected the processing time and surface finish of the part; therefore, abrasive suppliers began to be classifying minerals into a particle size range. The random shape or nature of crushed aggregate makes it almost impossible to come up with a singular specific uniform size or weight per particle; however, it is possible to come up with a size range. Classification even within a size range still does not exactly end up with a 100% uniform particle size. That is because over 90% of the particle size falls within the x and y or length and width dimensions of the screen size, but that it does not control the z or height of the particle size. However, the parameters of the classification and the remaining materials are normally within 5 to 10% of that size range and that is close enough to produce good uniform or predictable results within limits. Just as a note, random aggregate generally has a spherical or elongated shape to it and that limits its access to certain part recesses, inside dimensions, and corner angles. Depending upon the abrasive material, approximately 90% of the aggregate particles will conform to a screen size hole opening. The screen serves as the classification method and is used as the standard to measure crushed random aggregate particles. Any material that passes through a specific size screen is classified as being that size, but it also has a lower screen upon which and from which that media is taken. A secondary screen, below the first screen somewhat controls the lower minimum size of the particle or aggregate classification. That also means, the finer the screen, the better the conformity of the particle size. In the manufacturing process of making abrasives products, rock mineral is crushed and allowed to fall through a series of wire mesh screens stacked one on top of another. Wire is used because of the efficiency of open area to solid wire; therefore, the hole size is not exactly a true indicator of particle size. The proper classification of abrasive particle size is separated by a series of screens which block out larger materials from passing through a screen and catching
  • 213. Chapter 12 – Media 214 the size range which is allowed to pass through the upper screen and retained on the next smaller size screen. As stated before, perforated holes or screens are better for more uniform media classification, but it has too much solid mass to be efficiently used in separation systems. Square holes are better, but although they have fixed X and Y dimensions, they also have a larger diagonal dimension. In most cases, the classification of aggregate usually comes off of a group of screens, especially on small sizes, giving a range or a two number type grade or classification, but it can be a single screen size or number. In addition to a size range, there is normally an abrasive mineral range. Minerals have a molecular crystal bonding structure that affects the cohesive nature or hardness of the particles within the material description. If a mineral product is consistent, or produces consistent results, one does not normally question the purity of the abrasive mineral, provided it achieves the final surface finishing results. Unless one absolutely needs a pure form of a specific mineral, which is not likely, there is also a range of mineral product and this is determined by natural availability. Particle size is controllable by man, but mineral conformity or content can vary from different sources. There are mineral variations and because of this, there are products sold as a blend rather than a straight mineral. These blends may have a specific name, but they are still composites of a group of minerals. The main advantage to blends is a reduced cost factor rather than a performance factor. Because of all these variables the abrasives industry was established to control more uniform standards of classification for sizes, mineral grades, and blends. Today, not a lot of people question the size and/or content of the abrasive product they use, because most of the variable characteristics of the abrasive are known, or the limits or range of the product is known. In some extreme cases letters or certificates of quality can be obtained to conform to the product purchased. Generally any product sold must conform to specific quality standards set by the industry. Besides quality, if the cost of a product changes drastically, and/or new safety hazards are discovered, such as the problems associated with silica or gypsum, this may require a person or company to consider a new alternative product with similar performance capabilities and the industry should have ready alternatives. Then again, alternatives are readily available because of stocking. That is, unless a company is buying from a manufacturing source, it is buying from a warehouse that stocks a number of items from different manufacturers. If the product is not available, or costs have changed, normally one can select another particle size, or another product with similar material characteristics. Loose random abrasive materials of different sizes or a size range has certain application limits. That is, for cost purposes, this industry makes a mix or blend of sizes of a specific product in order to accommodate specific applications. If this standard size range is not acceptable to the end user, then additional screening operations can take place to control the size of the particle needed; however, that also means additional handling and costs.
  • 214. Chapter 12 – Media 215 The economics of supply and demand, plus the sorting operation and the manufacturing or quality control of screens determine the accuracy of these sizes and their cost. The next biggest cost factor is freight and maintenance or storage costs. The availability of mineral sources and the law of supply and demand really controls what is produced and sold. That law may also be superseded by technical knowledge of availability versus costs. I suppose that both cost and usage of a mineral product are shared or determined by the distributor and the user. A company that uses abrasives is basically dependent upon a supply source for information. Therefore, if they do not have the information or it is unknown, then they or you are locked into what you can get or have knowledge of. That means that what is sold comes back to the statement that the more commonly used abrasive materials and size ranges that are stocked by the manufacturing source and their distributors. What abrasive is common or sold is or should be what works best. However, on the other hand, if a manufacturing source doesn’t have high labor and maintenance cost to produce a product then the cost factor becomes very important and they can pass on the savings to the end user. If a company doesn't have to make many processing changes and has a good source for the raw material, and it doesn't present a safety hazard when used, then it is cheaper to process that single abrasive product than it is to process several different sizes or products. Even though I just used the word products, most mineral sources are geographic in nature and there is only one product mined and processed. Media Size Why is abrasive particle size so important? Because all parts are designed to function to accomplish some desired end and their design is dictated to certain pre-determined dimensions and/or shape plus function. Part shapes must maintain certain dimensions that when machined can be quite complicated. That is, they must have fixed equal distant points or angles. That means that abrasive materials have to pass freely around or through these points to deburr the part properly without effect the critical dimensions of the part. Simple right? Not exactly! Unfortunately, most parts are engineered and designed to perform a function with little thought about the manufacturing or surface finishing problems associated with the finished product. Parts can and should be made to take into account both machining and finishing limitations. That means that parts should be designed to avoid as many recesses, pockets, holes, or sharp angles as possible or within reason. Again, there are tradeoffs. The design engineer does not normally take into account the material finishing requirements. He usually leaves that up to a mechanical engineer who tries to work with existing equipment systems. It is usually only after the ME determines that the company does not have the proper machine or enough machine capacity to work the part does he look at new or alternative equipment. When it comes to the surface finish profile of the part, most engineers leave that decision up to a process engineer or worker on the floor. Normally, a finishing system is the last consideration of any manufacturing operation and is not considered an important issue.
  • 215. Chapter 12 – Media 216 I purposely spent some time here to show you some of the steps prior to surface finishing to emphasize the problems and/or delegating of responsibilities here. What I hope you see is a trend to shrug off responsibility to normally lesser and lesser qualified or trained people. Then again, the operator using the equipment may ultimately be way more knowledgeable of the equipment limitations and finishing capabilities than the engineer responsible for the final product. Finishing problems are determined by use and conveying the importance of what is critical or important to the finished part. For instance, why polish a part, if it will never be seen. From the stand point of processing only, the following is just good sense. For simplification, efficiency, and ease of separation, one usually selects a media that is smaller than the part, because it is easier to let the media pass through a separation screen than the part. At the same time, you do not want to select a media that will get stuck or lodge itself within the part. Also remember that multiple pieces of media can get jammed or get stuck as easily as one piece. A good rule of thumb is to select a media that is larger than the smallest hole or dimension that has to be deburred. If inner dimensions have to be worked or deburred, select a media size that is not too close to a half size of those dimensions because of the multiple pieces jamming problem. Abrasives or media breaks down and becomes smaller with use. Therefore, another guideline or the best rule to follow is that the larger the size or the heavier the media, the faster it will work because the specific gravity or weight of the media will apply more pressure to the work the part. Why media larger than the part is not commonly used is because it cannot contact the part uniformly. Media size must be selected that is able to reach into all areas of the part that must be worked to produce uniform results. If the media selected to work the part is larger than the part the deburring process works faster because there is more bulk, weight, and pressure in the process; however, it is also more difficult to separate the parts from the media. The larger the media the faster the material removal and normally the rougher the surface finish. That also means that thin or soft parts may be susceptible to damage or marks caused by heavier and larger media. As for separation, that normally means that the media will have to be handled at least twice, or at least differently, because the media itself may become smaller or fracture causing a wide range of sizes both larger and smaller than the part. The process of removing parts from larger media is called reverse separation. There is no standard machine built that I know of that can automatically remove smaller parts from larger media, unless the parts are magnetic. Fully automated systems can and have been built with multiple screen systems for this purpose, but they are not common. The cost to build such automated equipment does not seem to warrant the extra benefits of using larger media than the part. If reverse separation is needed, it is normally cheaper to dump both the parts and the media onto an inclined secondary screen device to allow the parts to fall through and be captured by one container while the media goes into another container off to the side. Because of media breakdown, you may still not end up with 100% parts after this type of double screening, especially if the media and parts are nearly the same size. Also, this practice is inefficient because the machine from which everything came must be refilled.
  • 216. Chapter 12 – Media 217 For inorganic random media to be effective deburring parts over 1 inch in size in mass finishing systems, its minimum size should be over 1/2 to maybe 3/4 inches in over all dimensions or grit sizes 3 to 2. Media can be up to 2 inches or 00 grit size, provided there is a good way to separate parts from media. A good size range between media and parts is desirable for part separation rather than abrasive characteristics. Media smaller than a 1/2 inch or under a 3 grit size for this application example will not be efficient economically because of time; however, given the same media composition, the surface finish will be smoother. The same basic rules apply for parts smaller than 1 inch down to about .030 in size or approximately 24 grit. At this small size, mechanical systems are not very effective. Standard Inorganic Grit Sizes Grit Size # 4 5 6 7 8 10 12 14 16 20 24 30 36 46 54 60 70 80 90 100 120 150 180 220 Micro Grit 240 280 320 360 Mesh USS** 3.5 4 5 6 7 8 10 12 14 16 20 25 30 40 45 50 60 70 80 100 120 140 170 200 Mesh 200 Microns (Average) 5600-4750 4750-4000 4000-3350 3350-2800 2210 1845 1600 1346 1092 940 686 559 483 356 305 254 203 165 145 122 102 89 76 63 Microns 50-53.5 40.5-44.0 32.5-36.0 25.8-28.8 Inches (Average) 0.187 (nom) 0.157 0.132 0.111 0.087 (av.) 0.073 0.063 0.053 0.043 0.037 0.027 0.022 0.020 0.014 0.012 0.010 0.008 0.0065 0.0057 0.0048 0.0040 0.0035 0.0030 0.0025 Inches 0.00200 0.00154 0.00122 NOTE: As grit size becomes smaller the size range becomes more in line with the screen size hole openings used to separate and classify the mineral.
  • 217. Chapter 12 – Media 218 Because of dimensional irregularities of larger inorganic random media shape, there are multiple dimensional factors, which may vary substantially. Therefore, the larger the size of random media the larger the possibility of random size media to get stuck. Any random media size over a 1/4-inch may not pass freely around a machined part without getting stuck or lodge in specific locations within a part design. Most random media used for deburring is in a size range of .120 to .030. There are just too many variables that cannot be controlled by using random media. Therefore, greater control of media dimensions is desirable and accomplished by preformed shaped media. Loose random abrasive media is commonly used in all composite abrasives, belts, and rigid wheels. It can be found in a lot of re-formulated compounds or hard coatings. By its self, it is used mostly in abrasive blast systems, but is not that common in mass finishing systems. The main reason for its usage has to do with how the energy is applied. That is, in abrasive blast systems, energy is transferred to air born particles of a specific size of random media in an indirect application of energy and that impacts the part. Upon impact, energy is diffused rapidly to both the abrasive and the part or materials surface, resulting in a spot or contact point. In mass finishing systems, there is a direct application of energy in the form of pressure and friction that causes material removal in a line of force rather than a particle spot. Again, how energy is applied is the reason for the different forms of deburring and surface finishing systems and equipment technologies. Abrasives are the most popular media form used in mechanical processes to transfer energy and remove materials. However, there are new developments in manmade synthetics that improve the abrasive characteristics and longevity of transfer devices even though they may cost more. Normally, manmade media is normally a more pure mineral form or variation of a naturally occurring abrasives, but have better control over abrasion, size, and wear life. Preformed Shaped Media Because of the problems of random media dimensions and/or its tendency to get stuck in parts, manmade preformed shapes were developed that specifically control outside dimensions of the abrasive media shape. The preformed media shape is also designed to control the rate of material removal, media wear, and performance. It is the advent of the preformed shape that made material removal and surface profiling an exact science and for the popularity of mass finishing processing equipment. Technically speaking, a preformed shape is a part, but because its purpose is to work other parts, it is never referred to as a part, but it does have fit, form, and function just as the part being worked. Instead of being called a part or a proper noun, it is referred to how this man made material is used, that being media or abrasive. In the trade, the manufactured abrasive media is just referred to as a preform or the shape that the preform is made into. Composition A preformed abrasive is a rigid molded shape or cut extrusion shaped part usually made with either a ceramic or plastic based bonding agent somewhat like cement or an epoxy blend.
  • 218. Chapter 12 – Media 219 Besides the bonding agent, which is designed to break down or deteriorate at a fixed rate of usage, the shape contains a specific size of random abrasive particles. The size of the abrasive normally determines the amount of material removal from the part and the bonding agent determines the rate of material removal. That means that there can be a lot of formulations for a specific size and shape of that preformed media. Although mineral particle sizes can vary to some extent in a preformed shape, but it is the bonding formulations that vary the most and control the rate of media and part breakdown. The shape contains a uniform matrix of smaller abrasive mineral particles, rigidly held in place by the bonding agent to do the material removal work. The abrasive particles in the preform shape behave like a series of small chisels or the teeth on a hacksaw that abrade the material being worked. As mentioned, the abrasive particles that go into these preformed shapes are a specific size of loose random abrasive particles. However, unlike random shape media, the abrasive particles in these compositions don’t exceed .060 in particle size. As the media shape is used, the smaller abrasive particles in the preformed shape lose their roughness or ability to cut or do material removal to the parts due to either rounding off or fracturing of their exposed abrasive particles within the preformed shape. One of the advantages of preformed media is that the bonding compound is formulated to continuously recede and expose new or more abrasive particles that are more pristine or sharp. These shapes are capable of maintaining a relatively consistent efficient material removal rate over at least half the life or size of the preformed media shape. Actually, the media retains its cutting ability until it is used up; however, because of the weight factor being reduced, the media shape loses its effectiveness and shape characteristics around it half life. A quick word about the terminology, “life.” Media can be used up to the point it completely disappears by itself down the drain. However, prior to this point, there may be additional problems. Therefore, I like to talk in terms of half life. You know that radioactive materials have half lives, well so too does everything else. Half life, in my opinion, is about the best mileage or usage you can get out of a preformed shape. In most cases, based upon a 40 machine hours week, the half life of a fast cut preformed shape is about 3 or 4 months. This time frame can change depending upon the bond or composition of the preformed shape. A fine cut media is probably closer to 4 or 6 months life and ceramic porcelain media is measured in years. Getting back to half-life. Why I chose this point is because at this size the preformed shape looses significant weight and energy mass to do the same amount of work as it did when it was new. Therefore, as media gets smaller, it takes longer and longer to do the same amount of work. Also, at half-life, the media shape is virtually gone. That means that the media is subject to getting stuck a lot easier and holes become a major problem for lodging. At this half life point, if you want to continue to use this media for other smaller parts, you should re-sort, separate, or classify the media to know what new size part it can work without getting stuck. A preformed shape does not guarantee that the media will not get stuck in a part, but it does minimizes the potential for such a problem, if one sizes the media to the part properly. The human factor still plays a big part in this potential lodging problem. That is, the media selected
  • 219. Chapter 12 – Media 220 must still meet certain criteria of compatibility before it should be used. Also, as I indicated earlier, there is no one shape for all media that will or can do the job on all parts. On top of that, it is nearly impossible to maintain a stock or inventory of all of the different media sizes and shapes needed or necessary to work all of the parts that most companies have to process. All of this means that somewhere down the line tradeoffs or compromises have to be made on what to stock and use in your mass finishing equipment. The two main problems for media selection that should be address first are: 1, What composition media to use for the application? 2. What size and/or shape to use for the application? For deburring, there are two main selections and these are determined or involve the nature of the part to be worked. Are the parts to be deburred ferrous or non-ferrous materials? Ferrous materials almost always use ceramic preformed shapes. Non-ferrous parts normally use plastic or synthetic preformed shapes. Non-metals can normally use either depending upon the results one wants to achieve. Part size is an important factor that effects media selection. For processing small parts under a 1/2-inch in size, dry organic materials are normally recommended and can be used that have a fine abrasive in them. There is also a new organic shape media that is also used dry. Some inorganic media shapes can be used in some cases, without a liquid, but are not normally recommended. When inorganic materials are used dry by themselves there is a relatively fast breakdown of the preform shape and contamination has no place to go and it can become a problem. Preformed ceramic media is made and available down to 2 millimeters in size for wet processing and 1 millimeter porcelain balls are available for burnishing. However, water and small lightweight parts do not work properly in the recommended proportions of normal mass finishing guidelines. This is especially true of any size of heavier flat parts as well. The next problem is basically you do not want the media to get stuck in the part configuration, recesses, or holes and at the same time it has to get into the problem areas to deburr or surface finish all areas of the part. Ceramic Media: The most common abrasive performed shaped media is made with ceramic based materials and is capable of working harder carbon steel materials than plastic bonded shapes. Because of its hard rigidity and composition, it is more abrasive than plastics and therefore transfers its energy and weight more directly to the parts in question. Also, ceramic media normally has greater weight than plastic, at around 80 to 120 pounds per cubic foot of media, and is capable of working materials relatively fast. The preformed media shape size, particle size within the shape, and the mineral composition of the preformed shape determines the surface finish. Normally, the larger the particle size, the faster the material removal. Plastic and synthetically formulated based preformed shaped media weights around 55 to 90 pounds per cubic foot and is softer, lighter, and more flexible than ceramic. Some newer formulations exceed 100 lbs. per cubic foot of material. A fast cut ceramic with .060 particles, will generally leave processed ferrous metal parts with a dull galvanized texture appearance
  • 220. Chapter 12 – Media 221 and so does a coarse plastic on non-ferrous materials. Plastic media shapes on ferrous parts will take an extremely long time cycle and may not properly deburr the part no matter how long your process time. If you do try to use plastic media on carbon steel, what you will get are parts with a glossy uniform finish, but not necessarily smoother. On the other hand, ceramic media on nonferrous materials will chew up your parts in a short period of time, maybe in 5 or 10 minutes. Also most ceramic compositions will probably leave your non-ferrous parts with a rougher surface finish than what you started out with and that may not be suitable for a secondary thin coating or anodizing. Earlier, we talked about abrasive particles and their relationship to specific gravity or weight. We said generally the larger the size and weight of the particle, the faster it works. This same principal applies to preformed media shapes, except you have a number of other factors to consider and all of these effect the characteristics of preformed media and its ability to remove or abrade other materials, how fast it works, and what kind of surface finish it will produce. The following criteria are used to determine a good preformed media shape. Preformed Shape Media Factors 1. First is the hardness and weight of the abrasive particles. This is the same as characteristics for random media. 2. Second is the bonding agent, which controls the rate of breakdown of the media wear, amount of abrasive particles, porosity, and general hardness of the media. 3. Third is the size of the abrasive mineral particle within the compound matrix and media shape. 4. Fourth is the actual manufacturing process and/or how the media is made. 5. Five is the temperature at which the media is cured. We have talked about specific gravity and weight of random media before; therefore, we will start out with the second factor, which are the inorganic bonding materials used in the manufacturing process. These ingredients are all trade secrets, but nearly 100% of a man made preform is naturally occurring inorganic clay type materials which are designed to lock up or bind everything together and therefore control the rate of breakdown or wear rate and/or hardness of the preformed media shape. These bonding additives have certain characteristics that control the amount or percentage of abrasive particles and their size in the matrix and control the porosity and/or absorption rate of these bonding materials. The number of inorganic bonding ingredients or compositions are normally limited to about seven different standard blended formulations of materials per manufacturer and are designed to perform in a certain manner on specific materials or parts and have certain expected abrasion characteristics and/or surface finishes. The number of formulations is only governed by the ability of the manufacturer and/or customer on a supply and demand bases. That is, any number of formulations is possible, but the cost goes up if it is not a standard stock formulation.
  • 221. Chapter 12 – Media 222 Dramatic deburring finishes can be achieved that involve the bonding agent only. That is, given the same abrasive particle size in a different bonding composition, the rate of cut can be significantly greater or faster using a different bonding agent that breaks down faster. At the same time, the overall surface finish will normally be rougher than a slower rate of cut or break down. Preformed media shapes must break down in order to do material removal properly and in a reasonable period of time. If the media shape does not break down, it will lap or burnish a part rather than deburr it and/or the cycle time will be greatly increased to accomplish nearly the same end results. In this case, the result of burnishing is more the deforming of the parts surface profile. Burnishing basically flattens or moves surface features rather than removes them. Ceramic porcelain media is nothing more than a very hard formulated bonding agent made into a preformed shape. Preformed media shapes made with a soft or loose bonding agent normally produces a fast cut rate on parts. Again, particle size is also important in the amount of material removal, but generally the bond is very important. The faster the breakdown of the media the greater the costs and economics of the material and maintenance of the process. Again, there are tradeoffs of speed versus costs, or the cut rate of the abrasive versus the wear rate of the media. No deburring media will last forever. All this means that the economics of media usage may not be as important as the economics to produce a good acceptable end product. We talked about half-life before, but it deserves mentioning again. A typical wear rate for media is somewhere around 3 or 4 months, based upon a 40 hours per week, before half life sets in (see application section for specific attrition rates.) and/or where the media becomes too small, in most cases, to be effective on the parts for which this media was originally selected. There is the inherent problem of the media becoming smaller and smaller and eventually small enough to cause lodging within the parts being worked and this maybe way before the half life time cycle sets in; therefore, other factors need to be considered other than direct labor or material costs. The third factor of size was explained earlier. The larger the size the more aggressive. The smaller the particle size, the finer the surface finish. Rough finish versus smooth finish. Fast, short time cycles versus long time cycles. The fourth factor that controls a preformed media shape is the actual manufacturing process. The amount of pressure and/or how it is applied to the preformed shape affects the density and weight of the media. In the manufacturing of preformed shapes, pressures of 7,000 PSI to 20,000 PSI can be applied by extruding or pressing the preform into a shape. Naturally, the greater the pressure, the harder and denser the preformed media shape and this normally relates to wear resistance or longevity of the media. Some preformed media shapes are made from what are called sintered materials. This manufacturing process causes materials to react or bond under pressure to create a preformed shape, without liquid additives. These preformed shapes have very high wear rates or longevity and are used mostly for burnishing because they are so hard, but they are also capable of some light deburring. On the negative side, because of porosity of sintered media, leaching of finer
  • 222. Chapter 12 – Media 223 microscopic abrasive particles occurs and this may tend to discolor or darken the materials during processing. The fifth factor that effects preformed media performance is the curing of the media. That is, all media begins as a slurry mix, except sintered materials, of ingredients with just enough moisture to hold a shape or configuration. Then this green or uncured media is baked in ovens at temperatures between 2,000 degrees to 3,100 degrees Fahrenheit. All of these inorganic materials are heated to reach a point short of absolute melt down were fusion or the binding of the matrix compounds takes place. The way in which the heat is applied and/or cooled also plays a part in the media wear rate and hardness. Media cured at higher temperatures normally are harder porcelains and are used for burnishing. By the way, all ceramic media is gray or brownish in color. The harder and/or a finer the abrasive compound preformed, normally the lighter the color. A porcelain or burnishing media is normally pure white and a very abrasive media is usually a dark gray or dark brown in color. Before choosing a preformed media shape there are other factors to consider. Besides all of this technical background on the media and selection, one’s choice may still not be a one shot deal. That is, one size, shape, and media composition may not achieve the end results you are looking for on a specific part. If you have multiple parts, multiple materials, or your part requires a very low RMS and/or polished finish, then you may not achieve the results you are looking for using one size, shape, or media composition alone. This is especially true if you are trying to achieve very low surface finishes. In the latter case, you will need to change media compositions before you achieve the results you are looking for, if you want to do the processing in the shortest quickest most efficient time. This is true of any and all abrasive media deburring systems. There are surface finish limitations designated by the characteristics of the abrasive particle size within the preformed media shape. That means that you may need to use more than one media in a series of steps or operations to achieve the end results you are looking for. You cannot combine media of different compositions within the same work chamber or process and achieve the desired end results. To achieve a surface improvement of over 8 to 10 RMS or get to a certain point or surface finish under 12 RMS, it is normally faster to achieve that surface improvement by using more than one media composition in a series of operating steps. For economical reasons these operational steps are usually limited to 3 steps, but 5 or 7 are possible. This is what is called or referred to in the industry as step processing. More detail will be said about this latter. This multiple processing is part of that black art we talked about at the beginning of this book. But, it is also the same criteria used to produce fine finishes using buffing wheels. The most common abrasive used in a ceramic and plastic preformed shapes is aluminum oxide, it is very hard and therefore effective for fast deburring. Also, as you learned earlier, there are different grades or hardness depending on the type of aluminum oxide that you use to make the preformed shape. Silicon carbide is sometimes preferred over aluminum oxide for faster cutting action, especially on hard materials or ferrous parts that become weldments.
  • 223. Chapter 12 – Media 224 Another abrasive that is popular for fast deburring is zirconia, but it is more expensive. Less abrasive is straight silica sand and quartz which also cost less. Other special abrasive mineral formulations can also be made to order but need minimum weight production runs. Another media selection factor to consider is based on contamination. The bulk of the bonding agent of the media breaks down and is heavy enough to settle out of solution. Some of the media waste breaks down and becomes so fine that it can become microscopic in particle size. This particle solution can penetrate and get trapped in the porosity of the materials being abraded; therefore, some quality control requirements will not allow the use of aluminum oxide or silicon carbide abrasives on some metals for other technical reasons. Other processing factors to consider besides media formulations are the problems of using the same media, or re-circulating the same liquid for both ferrous and non-ferrous parts. Mixing metals, media, or liquid are not recommended because they are all good transfer devices for contaminating dissimilar metals or parts and producing potentially undesirable end results. Earlier, I mentioned that manufacturers usually make about seven formulations of media in different sizes and shapes. In most cases, users of media want to deburr a part in the fastest shortest period of time possible to keep costs low. That means that the customer wants the largest size media possible with the largest abrasive particle in the preformed shape. What limits or prevents the use of the largest media is the size of the part and all of the areas of the part that have to be worked. You should consider limiting your selection to a media that will not get stuck or jam in the part and will not bend or distort the part and yet work all the areas that have to be worked. For simplification and/or classification I will arbitrarily say that there are only coarse, medium , and fine grades of ceramic media. That is not true, but it is a simple example. Starting with a normal mill finish carbon steel formed part with about a 35 RMS, a fast cut coarse media will, in about a 5 cubic foot capacity vibratory machine system, takes 5 to 20 minutes to deburr most metal parts. This variance in time depends on the hardness of the material, the severity of the burr, and the configuration of the parts. The finished part from this media should have a surface finish or profile of around 24 to 32 RMS. Multiple this time factor by about 10 for older barrel systems and divide by 10 for high-energy mass finishing systems. Again, this is not exactly true, but it is close. The visual appearance of this part will look very dull and have a galvanized textured appearance. Stainless steel, machined parts, metal castings, and some flexible synthetics may take longer than our carbon steel example. To accomplish a finer finish, suitable for most paint coatings, a medium grade abrasive media is normally required after the abrasive fast cut media. The normal range of this media, after the coarse media, will achieve a surface finish of around 22 to 28 RMS. The end results will have a finer appearance or a dull satin type finish with no major noticeable abrasion pattern. These results can be accomplished in about 15 to 45 minutes when used as a second step process and using the same parameters mentioned above. If this media is used as a first step, starting at 35 RMS, the finer finish will probably take more than twice as long and may take as much as 2 to 4 hours to accomplish in a vibratory machine system.
  • 224. Chapter 12 – Media 225 Normally, any part that needs to be plated requires a fine finish of around 16 to 22 RMS. To achieve these results, a third step may be required using a fine cut media. Parts with a surface finish of 22 to 24 RMS processed with this media, after the second step mentioned above, will take 20 minutes to 1 hour to achieve at least an 8 RMS improvement or result using the vibratory equipment. The visual finish on the part will be a bright looking luster, but far short of a mirror finish. Naturally, if you start out with this media, instead of the steps indicated above, the processing time will take well over 4 hours. Maybe triple that time or more. The above three-step process is typical for parts requiring a fine finish prior to plate. It is not absolute. There are variables that may affect time cycles and surface finish. That is why there are so many variations and/or varieties of abrasive media. It may not be a simple and or choice for media. Future technology and abrasive compositions may change, but for now that is how fine surface finishes are accomplished using mass finishing systems and that is one of the areas that few engineers or management understands. Excluding material handling of parts and the cost of replacement media, liquid compound, and water, that is the fastest most cost efficient deburring way to process parts requiring a fine surface finish of around 8 to 12 RMS. Before I move on to plastic media, I will say that there are new formulations being produced all the time. A lot of these new products are designed or formulated to try to find a good media that will work both ferrous and non-ferrous parts equally well. One company has come close, but again there are tradeoffs. There is a good new hybrid product that does work both ferrous and non-ferrous materials, but it does not work either one very well. But it does come close to being a universal acceptable media for both materials and it is very helpful for companies that use and process a lot of mixed metals or just non-ferrous producers who are not concerned with a fine RMS finish. The term used to describe this hybrid media is called light weight ceramic. This media weights around 61 to 65 pounds per cubic foot rather than the normal 90 to 100 pounds for most other ceramic deburring media. Because of this lighter weight and low density or porosity of this new media it can maintain good cutting ability to the part and it maintains relatively good wear characteristic to the media. This material still has some problems such as ferrous parts take longer to achieve good results, and non-ferrous parts normally result in rougher finishes. When this product was first introduced, the wear or attrition rate was so fast that that the media replacement cost made this media questionable to recommend. However, improvements to this product now make this a very competitive product which I would now recommend, providing one can live with the problems indicated earlier. Again there are tradeoffs.
  • 225. Chapter 12 – Media 226 Preformed Shaped Media Fig. 89. Ceramic Media Ceramic preformed shaped media bonds are extruded and more rigid than plastic. Ceramic shapes are used for deburring and/or surface removal of hard ferrous metals or where a lot of material needs to be removed. Ceramic shaped media comes different angles of the same shape and in compositions or shades of gray or brown, the lighter the color the finer the cut. Some of the more common shapes are shown below. The more the geometric straight lines of the media, the more resistance or force is needed to move the mass. The rounder the lines, the more mobile the mass. Mobility Resistance Plastic Plastic preformed shaped media bonds are molded and used to deburr mostly on nonferrous metals. The bond is softer and more flexible than ceramic and therefore produces normally smoother RMS surface profiles. The plastic bond compositions can be made with either polyester or urea plastic resin formulations, which are usually distinguished by bright colors. Fig. 90. Plastic Media Mobility Resistance
  • 226. Chapter 12 – Media 227 Plastic media: For a good number of years, random media and later ceramic preform media shapes were the only choices available to most people using mass finishing equipment. In the 1940's plastic preform media was developed to produce better surface finishes on non-ferrous aluminum and brass parts. Even though ceramic media deburrs non-ferrous parts, the surface finish was not fine enough to produce a good surface finish capable of accepting a uniform chemical alodined or anodized sealing coat to protect against oxidation. It was found that by changing the hard bonding agent of ceramic media to plastic, better or smoother surface finishes could be achieved on non-ferrous parts because of the softer more flexible characteristics of plastic. Because of this less rigid quality and significantly greater processing time, this media is not recommended for deburring ferrous materials. Hard materials and soft media are not normally a good combination. Usually the media gets worn out and produces questionable results versus costs. However, plastic media has also become the choice for processing precious metals and jewelry because of its finer surface finishing characteristics. Except for the bonding agent used in the manufacturing of plastic media, almost everything that was said about ceramic media above can be said about plastic media. Just as there are five steps that effect the manufacturing and final product of ceramic preformed shapes, so too are these same steps a factor with plastic media. However, preformed plastic media has a bonding agent made from synthetic chemical compound variations, which deserve maybe some additional information. First of all, most common plastic media is made with a polyester plastic based bonding agent. Polyester has a tendency to break down and produce a white milky residue which has a greater tendency to go into solution as microscopic particles finer and lighter than ceramic residue and more difficult to settle or filter out. Also, that residue can cause foam to form and harden in the discharge waste of a holding container if it traps air. This harden foam residue is flammable under some normal disposal conditions; therefore, appropriate safety precautions are required especially where people smoke. It is not exactly highly flammable, but it does burn rapidly and may be difficult to put out because of its lightweight feather like qualities. Unlike ceramic media, which uses basically one inorganic type of formulation, plastic comes in two basic formulations. We talked about polyester based performs, the other formulation for plastic media in use today is a formulation that uses a urea plastic bonding compound. This media is made with formaldehyde and in its raw state before manufacturing can be very hazardous. However, after this manufacturing process is complete there is virtually no hazard of formaldehyde in its use or problem for its disposal. The advantage of this urea formulation is that it is softer, more flexible, and will not foam as much as polyester based plastics. That means that it is less likely to leave marks on finer, softer materials, or precious metals. Also, urea is less likely to work as fast as polyester. All of these differences are minimal; therefore, there is relatively little difference in performance characteristics. Cost wise, urea is less expensive than polyester and therefore it is gaining greater popularity and usage. Application information for plastic media is basically the same as you find for ferrous and ceramic media; however, as stated, non-ferrous materials usually require finer surface
  • 227. Chapter 12 – Media 228 finishes. Step processing using plastic media is also commonly used in processing non-ferrous parts. In fact, it is probably used more than ceramic step processing. That is because normally non-ferrous products require finer finishes so that secondary operations can be preformed to improve their surface hardness or put a protective coating on the parts. If we compare plastic step processing to ceramic, a wider range of surface finishes are possible than with similar ceramics equivalents. Using the same criteria as the ceramic example, the following results can be obtained using plastic media. A fast cut abrasive polyester plastic media can probably result in a 26 RMS or an 9 point improvement from the normal 35 RMS in 15 to 20 minutes in a five cubic foot capacity vibratory machine. The appearance of the part will have a fine dull galvanized pattern. The medium plastic used after the fast cut, will produce a 16 to 18 RMS in about 30 minutes and will have a uniform luster to the part. To start out with the medium cut media first would take 2 to 3 hours to accomplish the same RMS finish. Using the finest grade of plastic media available after the medium cut, probably an 8 to 12 RMS may be achievable in about one hour or more and will appear to have a bright luster. To achieve a 12 RMS using fine media only might take 6 to 8 hours or more of processing time. Another advantage of plastic media versus ceramics is that the media is available in more shapes and sizes and as stated before, more bonding compositions. The reason why more plastic preformed shapes are available than ceramic shapes is because they are made from molds and most ceramics are cut extrusions. An explanation about shapes will be covered in a separate section or heading. One of the disadvantages of plastic media is the aging factor. That is, all media shapes continue to dry out after manufacturing and that effects its moisture content. If plastic media is not used routinely, it is more susceptible to cracking or drying out with age. Therefore, shelf life for storage is limited or less than that of ceramic under more dry conditions, but we are still talking about years rather than months. If plastic media is stored in humid or damp conditions, its shelf life maybe over 10 years or exceed the life of ceramic media. The use of colors makes plastic media more easy to identify the different abrasive compositions than that of ceramic media; however, each manufacturer has their own color code. There are no standard uniform color codes in this industry. Therefore, in most cases, you need to know who the manufacturer is before you can identify the abrasive composition and/or wear qualities of the media by color. However, even color is not an absolute within a manufacturer because they will produce whatever color a customer requests. The only sure way to identify composition is by seeing or reading the part number on the box from which the media came in. Once it is in the machine, there is no way to be sure what composition it is; therefore, identification after use is also important. Generally speaking the darker the color of the preform plastic shape, the more abrasive the media. A red color use to indicate a more aggressive media than say a blue. A green was normally used to indicate a medium cut, but this is not necessarily true now. Reds and greens seem to be inter changeable by different manufacturers. Any color can be added to any abrasive formulation and therefore, color should not be used to identify media compositions alone. If this
  • 228. Chapter 12 – Media 229 trend continues, perhaps, besides ordering plastic media by composition, you will also be able to select your own color as well. About the only thing the manufacturers seem to agree on is the description of the size and shape of the preform media. Every manufacturer of preform media shapes have their own description for their make of preform shape, abrasive, and composition. Some companies designate their part number description to denote the size of the abrasive particles in the composition. In this case, the lower the number, the larger the abrasive particle and the higher the number the finer the particle size. A number of manufacturers use letter designations to identify their media compositions. Outside of the letter P for porcelain which seems to be common usage for this item, there is no other discernable patterns in use. Again, there are no industrial standards. See comparison charts. Ceramic Media Comparison Chart Manufacturer Abrasive Finishing (Fortune) Ceratech Rosemont Ceratech Tumblex U.M.Abrasive Vibra Finish Washington Mills Wisconsin Porcelain Abrasive Media Composition Equivalents AXPV-25 AX-65 AH-41 C-46 44& 90 1 2 3 4 5 RC 100 RC 200 RC 300 RC 400 RC 500 N L J K &G C P LL MC FC P M F XF SF XXF UC SC 10 20 30 40 50 FB/F C XC SC SP-3 F-33 6 RC 600 DM H DF HE HE C60 NOTE: Chart reads from left to right in the degree of abrasion or coarseness. Exception is C60, which is a special fine hard burnishing media. Plastic Media Comparison Chart Manufacturer Abrasive Media Polyester Composition Equivalents Almco 100 Ill.Electro 5000 200 Polyflow XX 3271 2000 1500 D70 4000 X D10 3104 1000 H-10 H-20 H-30 H-40 D30 D50 D165 D155 D154 D150 Rosemont R500 R600 R650 R700 R800 R900 R1250 R3600 R3700 R3800 Superfine LD1 LD2 LD3 LD4 LD5 LD6 LD7 HD1 HD2 HD3 PS 400 PFQ PJQ PAO Ultramatic U.M. Abrasives XFF3 Vibra Finish VF-V FF1 VF-B VF-X HD4 FC1 VF-XV VF-AO VFXX3 VF-Z1 0 VF-Z2 VF-Z3 NOTE: The cross reference comparison charts used to compile the above come from a number of manufacturers and may not or do not match up exactly, except for the last 4 vertical columns to the right. Also, the above are the most common products produced; there are a number of formulations still not shown. Lastly, there is no comparison chart available to compare urea formulations with the polyester resins shown above. Chart reads from left to right in the degree of abrasion or coarseness.
  • 229. Chapter 12 – Media 230 As shown and stated, these charts are for reference only, they are not a 100% match up, but a close relationship. I would have also liked to have included a third chart to show attrition rates of the media breakdown with usage; however, there is additional difficulty in presenting such information in chart form. I have included an attrition chart in the back of the book under the sub-heading category call applications. However, this information is not very accurate for comparing one product against or with one another; rather it is for use in determining costs of operating equipment. It is not a good indication of comparisons or really media wears, because of questionable testing procedures, but it is a start. Because abrasive deburring preformed shaped media is the most commonly used abrasive in all mass finishing processes, that is the reason for the comparisons charts. They are close proximity's. The charts do not show any burnishing media or dry organic materials, because these are not normally abrasive products and/or there is little wear or difference from one make or supply source of media to another. Let me explain a little more about the difficulties in providing detailed comparisons. First of all, as stated, there is no one central organization like the abrasives industry to regulate or enact standards. Therefore, almost all information derived for publication is from the actual manufacturing source. That means that the information is biased or shown to indicate the positive attributes of their product in the most optimistic terms. Therefore, in conducting tests no one company is about to devote a great deal of time and resources for impartial testing. To do so is or can become quite costly. Therefore, with no immediate positive monetary results no or few companies want or are willing to undertake such testing. Although mass-finishing systems is somewhat an exact science, it can also be used or considered as smoke stack type industry. That is, it gets results based upon trends that can be used to manipulate results. You are already aware of at least three factors governing mass finishing as that of the equipment, the media, and the liquids. Each one of these factors can be affected or can control the end results to some degree. In addition to these factors are a lot of other variables that can be controlled to make this an exact science. To do proper testing for scientific results of a consistent nature, one must first determine the equipment to be tested or the media composition or shape to be tested. If one is comparing equipment, then the same media must be used in each of the machines using the same amount, size, shape, composition, liquid control, and the parts to be processed. If you vary any one of these factors, the results may change drastically. In determining attrition or wear rate of a media in use, one machine system capacity size and machined part must be selected for use in all tests. However, the results will only be applicable for that type of equipment and part used. Technically each machine system will have a different result from one another and the work chamber size or weight factor of the work load effects the results a great deal. Since no two competing systems has exactly the same capacity size, comparisons are still somewhat difficult to come by, but there are indicating trends. The ideal test parts should be a round bar or object about half the work chamber channel in width and maybe anywhere from a half inch to two inches in thickness to get good
  • 230. Chapter 12 – Media 231 movement or rotation within the work mass. Its weight should not allow it to sink to the bottom or float to the top during processing. That means that the part should not be effected substantially by the media shape or configuration. Unfortunately, there are no universal type parts; therefore, test results can vary from part shape or material to some degree. Parts too can have a dramatic result on the processing and wear rate, because they can to some degree, control the flow and movement of the media. Again, there is a relationship of variables. The media used in each test must be new and weighted. If the media where to be used over again on another test, there will have been some wear rate and that means that the media has to some extent begun to change its configuration and/or become smaller. As media becomes smaller, its actual surface contact with the part increases. For impartial test results, the media should be new each time a test is begun. Perhaps the biggest problem with accurate test results for media is moisture content. To get a good wear rate the media must be weighted before and after each test. Also the liquid used during the test must be consistent and be monitored for the same volume per test. Upon competition of the test period, the media must be dried to the same conditions that existed before the tests were performed or some exact cut off time period point so noted. Because it is difficult to duplicate the moisture content of the media before the test and to restore it to that same condition after the test is nearly impossible. Maybe a better way to proceed with such a test is to soak the media in a predetermined amount of water and/or include the weight of the water before and after the tests. Once all of these variables have been monitored and regulated, then, and only then will you begin to see consistent repetitive and/or similar test results that can be translated into wear rates or attrition. So you see, it is not that easy to come up with comparison or attrition rate charts. Also, you can’t blame the manufacturers for their presentation of the information that they supply. A lot of factors are know within limits. A lot of factors are too costly to determine accurately. But, in determining comparisons, you, in effect, have just learned a little more about a number of other factors that can and do effect mass finishing processes, preform media, and the ideal part size. Steel media: In addition to abrasive media, there is non-abrasive burnishing media. We have already talked about ceramic non-abrasive porcelain media and a sintered aluminum oxide material called XM. Besides inorganic ceramics, inorganic metals of carbon steel and stainless steel are also made into preform shapes for the specific purpose of burnishing or brightening parts. Again, it does not polish per se, but does roll or lap the materials being worked almost like how sheet metal is made or finished between two rollers. At about 300 lbs. per cubic foot, steel media movement does modify or shine all materials in a relatively short period of time. Porcelain can produce the same results but it weights anywhere from 100 to 150 lbs. per cubic foot and takes 3 to 4 times as long to do the same job. Because of this weight factor for steel, certain precautions must be taken to properly adjust the energy transfer of mass finishing equipment to use this media. First of all, not a lot of
  • 231. Chapter 12 – Media 232 equipment is capable or properly designed to handle or work this heavy weight media. Again, we are talking about a lot of force and energy required to start things moving, keep them moving, and then the extremely violent movement associated with the start up and shut down. If not properly reinforced, machine systems not specifically designed to run steel will either not move the media properly or will incur pre-mature break downs. Systems that are capable of running steel media have to be adjusted properly. That is, too high an energy transfer action to the media may result in the parts being impacted too violently and thus leaving a pocked mark or orange peel appearance commonly associated with shot peening equipment. In some cases this may be acceptable, but the more gentle or uniform the rolling action, the smoother the surface finish. As an interesting statement only, it is said by some manufactures of burnishing media, that in order for steel preform media to move or roll properly, there must be a little oxidation or rust on the media. Without oxidation, the media will continuously slip and not create a rolling movement or action, which is desirable for the performance of this media. I suspect that this statement may be true; however, I also believe that such oxidation is not noticeable to the eye. But if this statement were true, there is still the question of stainless steel media. That is, I suppose oxidation has to take place on stainless steel, the same as carbon steel, but again there would not be any noticeable oxidation. A little while ago I mentioned a condition causing a shot peening surface condition. In addition to this problem, we should also say something about the other effects of steel media on the finished part. While steel media is often used to produce bright shinny parts, it also does a good job of work hardening and stress relieving parts, either intentionally or unintentionally. That means, that because of the weight factor, there may be some distortion to the physical shape, surface profile, or dimensions of thin, lightweight, or soft metal parts. The surface finish of a work-hardened part is almost equal to a plated part in hardness; therefore, if precision is critical to the performance of a part, the use of this media must be monitored closely. Once a part has been work hardened, it is difficult to correct or remove burrs that have been distorted by weight. By the way, this work hardened coating is a very thin microscopic layer of denser parent metal, almost like the case hardened coating on the media itself. As mentioned, the weight factor of steel media is so great in relationship to other media that most manufacturers of mass finishing equipment specifically design or make a special heavy duty version of their machines to handle this media. They also advertise the fact that their equipment can run steel media. That is because the amount of energy required and the construction and suspension of the work chamber are critical to the performance of any mass finishing equipment using this media. That also means that not all machines can run or hold up to the effects of steel media. This is the acid test for all good mass finishing equipment. If a machine cannot run steel media, it normally does not have a good life span, is under powered, or is poorly designed, or all of the above.
  • 232. Chapter 12 – Media 233 In describing media up to this point, we have been talking about grades or the abrasive quality of different formulations of preform media. With steel media, we drop the classification or grades of coarse, medium, or fine for primarily size and shape as the controlling factor for governing performance. We can use the term grades to denote different formulations of steel and stainless steel which are used to make preform shapes for burnishing; however, the characteristic of metal grades are not significantly different from one another. That is, their performance and wear rate are nearly identical to one another. There is a difference of cost and maintenance of steel versus stainless steel, but generally the term grades is not used to distinguish differences of steel media. In addition to these metal grades are the less common non-ferrous media products. As the size of steel media becomes larger, it also works faster, because of this increased volume and weight factor. As stated before, size and weight are also factors with abrasive media, but with steel we are talking about a surface treatment of primarily performing a rolling or burnishing operation to aesthetically brighten parts, not to remove any material. Any actual material removal is a result of metal fatigue than abrasion. In fact, burrs may still be present, but in a modified or distorted form. Therefore, if critical dimensions are required, care must be taken using this media. I mentioned earlier that steel media is available in a preformed shape. Most people think in terms of steel shot or the ball shape as the most commonly used shape for achieving a bright uniform finish. But it also should be noted that better or greater mobility is achieved with a mixture of balls of different sizes. The ball shape does lend itself to great mobility, but it is not a good shape for getting into corners and it really has a small point of contact with which to do surface modification. When uniform ball media is used, surprisingly, they do not roll as well as a mixture of different sizes. The reason for this is due its limited uniform point of contact with the part and other balls. When a mass of identical shapes are used, there are a lot of equal stress points that require a lot of energy to make them move, versus unequal points cause faster, greater movement in a shorter period of time and less energy. In addition to the standard ball shape are the oval balls and the eclipses which are balls with flats, both of which have more surface contact than the ball. For getting into tight spots are, ballcones and cone shapes, both of these look like the planet Saturn, but the ballcone is not symmetrical and is more pointed at one end. The diagonal shape is an angle cut cylinder that is used to get into corners and angles. The pin shape has both ends that come to a point and is used to work detail. A mixture of primarily pins plus other small shapes are used a lot by jewelers and is for working detail designs in jewelry parts; there it is called a jewelers mix. Earlier, under the heading of equipment, we talked about magnetic tumblers. The media used in this equipment is made from extruded stainless steel wire cut to length. It is similar to pin media, but not as thick. That is, it is stainless steel wire made from .02 to .05 diameter to 2 or 3 times that in length. That makes it very thin, light weight, and relatively expensive. Probably because this is new technology type equipment requiring special media and it is in demand and the supply is limited, the cost is very high. Normal stainless steel media is not magnetic, but when any non-magnetic material is drawn thin, it re-aligns its molecules to become susceptible
  • 233. Chapter 12 – Media 234 to magnetism. Most of these magnetic machines use less than a pound of steel media in their operating capacity, but the cost of this new media can exceed $300 a pound. Normally, we think of steel media for burnishing only; as mentioned, any material removal or true deburring is only through metal fatigue or the flexing of the burr until it cracks and/or falls off. There is however, one manufacturer who produces a form of steel cylinder media made with a high nickel content that is formed with serrated or knurled edges that is specifically designed to cut or deburr parts to a limited extent and for a limited time period. The life expectancy of this configuration is said to be about 2000 hours with proper maintenance. In some cases any burnishing media can be used with fine inorganic abrasive particles to accomplish some deburring; however, it is not recommended because carbon steel media is in a condition called case hardened. This case harden condition is a thin dense hardened layer of metal with a Rockwell rating of about 55 on the C scale for 1045 steel or C 60 for 1018 steel; therefore, if this layer is removed or damaged, the media wears very quickly. If abrasives are added to steel media, they will deburr, but the weight of the media still has a tendency to flatten the burr, rather than to remove it. Most people and companies take the easy way out by deburring with either ceramic or plastic media first, then burnishing with steel as a secondary operation. If this media is used with abrasive particles, it must be run by itself to smooth itself before it can be used to burnish again, provided the case hardening is not affected. Normally all burnishing media requires a break in period or reconditioning cycle so that it is smooth and will perform polishing. Not only is this necessary after the use with abrasives, but also any length of time where this media is allowed to sit idle, especially if no precautions are taken to protect against oxidation. Perhaps the biggest problem of steel media, beside its expensive cost is the amount of maintenance required to keep the media in prime working condition. That is, carbon steel media not properly dried and protected after every use will rust, pit, and eventually begin to stick or adhere to one another. If properly cared for, steel media will last almost forever; however, because of handling, more media is lost through poor handling practices than for any other reason. If not properly maintained, some carbon steel media may only have a life span of 500 hours. Also, any operation using steel media taking longer than 4 hours does or should require a purging and replenishing of the liquid compound in the process to avoid chemical reactions that darken parts and effect the media itself. Lastly, this heading refers to steel media for the purpose of describing the most common burnishing media used to brighten parts. However, it should be known that other metals, such as brass and aluminum can be made from cut wire, shaped into ball form or other shapes and used to perform the same task as steel media. Whatever these metal based materials of these other media shapes, they are normally used to process parts of the same basic alloy so that no metal contamination takes place. Cut wire of any alloy can be used but rarely is any other alloy formed into shapes for burnishing.
  • 234. Chapter 12 – Media 235 There seems to be an interest in aluminum for both deburring and burnishing. There is an aluminum cylinder or heavy cut wire shape as well as a star shaped media that weighs 65 pounds per cubic foot. The star is used primarily for deflashing and working aluminum die cast parts, but it can be used for burnishing after it is well worn. Another interesting feature of this aluminum media is that it has no problems for disposal like other metal waste by-products and processes. The only waste problem that might occur is from the parts being worked. It should also be mentioned here that steel or stainless steel media shapes are the most expensive of all the preform media shapes. Stainless steel prices can be more than double the cost of carbon steel media and both steels can be up to 3 or 5 times the cost of ceramic or plastic media. This is the initial purchase price only. You should consider this price or cost as an investment, because the media normally never has to be replaced over one's life time with proper maintenance procedures. Another interesting benefit feature of using stainless steel media instead of carbon steel is that you can use a magnet on ferrous parts to remove them from this media after processing is complete and you don't have to remove the media from the machine. A combination of steel parts and media does require a screen separation system; therefore, another factor must be considered. As mentioned, but not emphasized, perhaps the main reason for most media replacement is due to poor material practices than any other reason. Steel media, especially ball shapes, behave like a super ball when dropped or spilled. They will scatter to the 4 winds as quickly as you blink your eye. Therefore, designated barriers should be considered when handling this media in or around the mass finishing equipment. Even with good maintenance and handling practices this media can deteriorate and lose some of its mass over a period of about 10 years plus or minus. A special note should be added here also to advise you that there are a number of applications where parts are sometimes used as media to work, or massed together to work each other. That is, formed parts are run en mass to deburr and to some extent brighten each other as well without the use of media. This is sometimes done to eliminate the problems caused by lodging or the need to separate parts from media. This method of part processing is not considered deburring, because it is a metal on metal operation which should fall under this category of burnishing, but it does deburr. Not many parts are good candidates for this type of processing. Most parts get stuck or tangled with each other, or don’t get all the areas that need to be worked because of part configuration, but sometimes such problems are better than the alternative problems. Another factor to consider is that the surface finish may not be improved or may in fact become rougher using part on part deburring processing.
  • 235. Chapter 12 – Media 236 Steel Media Shapes All steel and stainless steel media is derived from cut wire stock, formed, deflashed, heat treated, ground, and finished. Other raw materials are available in ball form and molded aluminum mill star shapes are also available. The following constitute nearly all media shapes: Fig. 91. Steel Media Shapes 1) Balls – Round balls without flats for more critical finishing requirements. 2) Balls, Eclipse – Round Balls with slight flattening at the poles (Precise roundness is not required for most steel media finishing operations) Pole flattened balls are less expensive to manufacture and purchase. 3) Oval Ball – This shape introduces an oscillating motion to the finishing mass and provides more surfaceto-surface contact than balls 4) Diagonals - Beveled edges of diagonally cut ends provide effective finishing action in corners. Cylindrical body offers wide area contact. 5) Pins, Slim (S) – Tapering to pointed ends, pins reach into recesses and grooves, deflash through holes and clean threaded areas. 6) Pins, Taper (T) – See 5 7) Cones – Center flange and tapered crowns provide contact in angles and on curved surfaces. Small sizes are ideal for ornamental designs. 8) Ballcones – This design combines the burnishing abilities of balls and cones into one scientifically proportioned shape. 9) Abcut Cylinder or Rod - Patented abrasive surface puts teeth into finishing for fast heavy deburring, burnishing and material removal 10) Aluminum Mill Star – Molded aluminum alloy media shapes are designed to punch trough and deburr thin sections of molded parts.
  • 236. Chapter 12 – Media 237 Organic media: The last major category of deburring and polishing media is organic. It was interesting to find out that the earliest barrel tumbling operations of the 1900’s did not use water or liquids to deburr parts. However, it was soon discovered that inorganic and water did improve the speed of cutting and improve the appearance of parts. Prior to water based systems, sand was used as a lubricant with larger abrasives to improve material removal and that also improved the surface appearance of the part by carrying away dirt. However, sand or solid materials are not very absorbent and organic materials began to be used with fine abrasives particles. These organic materials proved to better at cleaning and polishing than the inorganic materials; however, because of their lightweight, they also proved to require greater processing time. Again, the trade-off factor. Organic materials are the least expensive of all media, because they do not involve a forming process or a lot of labor prior to distribution and use. Organic materials are naturally occurring materials that are easier to process than the solid inorganic materials. Organic materials are basically hollow cellular structures of former living vegetation which don't have a lot of weight or mass and because of its weight or bulk by volume it tends to be the least expensive per cubic foot of material. A rough guide line average for all loose granular dry organic media is 21 to 35 pounds equals about one cubic foot of material; whereas, plastic is about 55-90 lbs. and ceramic weights around 100-120 lbs. The most common organic materials used as media are corncob, wood, and nutshells. Until just recently, materials derived from naturally occurring cellular organic materials could not be made into preformed shapes. Organic Shapes Dry organic hard wood is a special exception to the generalized statement that organic materials cannot be made into shapes needs clarification immediately. Fine grain hard wood is commonly cut into preform shapes; however, instead of being formed as all the previous preformed materials. Wood is first cut to thickness and then cut into specific length and width sizes and shapes for bulk and/or to serve the same function as a manufactured preform ceramic or plastic shape media form. The basic shapes that wood is cut into is a cube, a diamond, and either a one sided pointed peg or a two sided wedge type peg. The residue of this same fine grain wood shape or sawdust is also used, but not as a preformed shape. With the exception of the cut wood shape, nearly all organic materials are ground up and sifted into size classifications similar to random media and abrasive particles and used in that form. There are at least three different sizes or classifications of the saw dust form of wood; however, there can be more variations than this. Normally fine organic materials like wood saw dust is not sold as a finished product as it is classified; rather, it is treated with either an abrasive or polishing additive and then sold as a treated compound to be used with the wood shape or by itself.
  • 237. Chapter 12 – Media 238 Fig. 92. Organic Media Shapes Up to relatively recent times, all organic shapes were basically 2 dimensional wood shapes cut to thickness. Media shapes that have a shaped point are formed before they are cut. See below silhouettes. About 1996, a new process was developed that takes fine gain loose or random size organic materials and combines them in a viscous resin bond to form shapes similar to how plastic media is made. The new media formulations can actually have more organic abrasives than organic materials and are very abrasive, but they are still used dry without water. There are no visuals of the three media shapes, which come in triangles, squares, cylinders of different sizes and compositions. Media, Actual Size Dry shapes Now, there have been some rather recent developments in dry organic finishing that a lot of people do not know about that should be of interest to everyone. Around 1996, a company developed a patented method for making dry organic preformed media shapes with abrasives materials found in ceramic and plastic media shapes. These preformed shapes look and behave just like ceramic and plastic deburring media shapes, but it is used dry. The key to this product is the resin bond that holds both organic and inorganic materials together. In fact, because of this bond, it is possible to have more inorganic abrasive materials than organic materials in its composition; therefore, it is hard to classify. Because the shape contains organic materials and is only run in a dry process, it falls under our dry organic category.
  • 238. Chapter 12 – Media 239 Formulations of these preformed shapes weight between 65 to 85 pounds per cubic foot. In addition to improving the cutting or material removal speed of organic media, it can work or modify a greater range or surface profile than can most other ceramic or plastic media formulations. That also means that parts usually achieve a smoother surface finish in less time. The biggest advantage of this new preformed shape is that the media lasts 5 to 20 times longer than that of most wet preformed inorganic media. Along with the weight factor, this media gives you more bang for your buck. Like any new product on the market, there are pluses and minuses. Presently, there is only one source for this preformed shape and therefore it is somewhat expensive at about $12 per pound. However, at the same time, it has a lot of advantages that make this media very attractive. If you take into consideration the cost of attrition, water, waste treatment, chemical, maintenance, and labor relating to wet processing, the cost of this new product is very competitive. Some other indirect tangible savings are: there are no water marks on parts, no rusting, no sticking together of flat or light weight parts, and basically smoother, brighter, dry, clean parts ready for their next operation. Random Organic Materials With the exception of the above dry shapes, organic materials are extremely light weight in comparison to both random and preformed inorganic shape media. Because of this weight factor, random organic materials do not have a lot of energy mass that can be transferred onto the parts being worked. It is for this reason that this media is normally used as a last step polishing operation. For random media to be effective, parts should first be reduced to about 18 to 20 RMS surface finish by other processes or media, the finer the surface finish the better. Organic media can achieve surface finishes as smooth as 2 RMS, but 4 to 8 RMS is more easily achievable. In the opposite direction, additives can make organic materials very abrasive to do relatively faster material removal work, or create an antique look, or can be used to help shorten the time period of the final polish. Polish here refers to the material being flat or smooth, rather than a bright mirror finish. Because we are talking about natural occurring materials and relatively small or fine particles that are very absorbent. That means that this category of materials is normally run dry. In some instances organic wood shapes can be used as a filler material in a wet processes to soften the action of abrasive preform plastic or ceramic media, or for obtaining smoother finishes. However, it is not normally recommended and is not good practice because the media will deteriorate quickly and the small organic particles will clog the drain system. All of the other preformed and random media materials prior to this category or group of abrasives are normally run in a water and chemical solution. Most mass finishing systems are designed and built to run wet processing. Therefore, to run a dry media may require some changes to existing equipment before these materials can be used properly. Specifically, we are talking about the drain system and the open top of the machine. The drain must be taped or sealed before usage to prevent clogging of the drains with the fine small breakdown particles
  • 239. Chapter 12 – Media 240 that eventually behaves like cement. However, eccentric weight systems may also have to be changed or adjusted to accommodate the lighter weight load. In a wet deburring equipment system you have the waste byproducts of the deburring operation plus the ceramic or plastics, plus metals and miscellaneous dirts and oils. With dry materials you do not get that much amount of waste byproducts, but you do get dust problems. That is, as one runs a dry process, the organic particles break down and become finer and finer and a lot of it can becomes airborne. Therefore, precautions must be taken to either vent the air or cover the machine or both. Another less serious problem is the disposal of used organic media. Normally 90% or greater of the original sawdust like compound media behaves in a self cleaning or self destruct mode. That is, it breaks down, becomes finer, and dusts to the atmosphere. A good portion of the organic material clings to the parts being processed and/or is therefore called drag out. That means that you normally never have to remove any organic media or waste. In fact, it is common practice to always add new dry media to the existing machine operation every time a new batch process is started to replace the loss from break down of the previous materials and replacement of the spent compound or additives. Replacement material should be a small cup per cubic foot of the machine capacity being used, per batch. Naturally cross contaminates of metals and soils is always a problem. Most manufacturers of treated organic products recommend changing this type of media as soon as it becomes dark or black. To them, this is an indication that this material has used up its ability to perform its task of either polishing or deburring. Where quality is an issue, this is probably a very good practice. Another good practice is to try to maintain a separate batch of organic material per type of material being processed. You don’t normally want to polish brass after stainless steel or aluminum. Cross contamination of metals is probably a more common problem than achieving a fine surface finish. When the quality of the end product is not an important issue or a specific finish is not specified, this organic media can be used for a long period of time. I have been using a batch of dry organic polishing mix for over 10 years. I better qualify that statement. I am using a special organic blended mix that I keep adding new replacement material per batch of parts. As far as I can remember, I have never disposed of any dry mix that I have started with; however, as stated, when quality is an issue, I always start out with a new blend or mix. Any disposal of organic media is because it becomes so contaminated with the debris from parts being worked that it turns black and gummy and interferes with the movement of the media or work mass. If too much moisture or liquid additives are used to improve the performance of the mix, parts may come out with white dimples, or it may result in the media creating balls or deposits on the side walls of the work chamber. All of these problems are a result of too much compound additive treatment creating a saturation point either on the part, work chamber, or within the media itself. This saturation or loading condition does not hurt the part, but it does not help it either. Unless the media and part can maintain good surface contact in a non-sticking mode, the
  • 240. Chapter 12 – Media 241 process will not improve the surface finish. Instead of improving the surface the compound will behave and act like a magnet, creating conditions center around the excess compound. If this condition occurs the disposal of this excess or contaminated waste is recommended over the adding of new dry material. The waste can normally be disposed of in paper trash; however, if it contains concentrations of metals and oils then care should be taken to conform with local disposal procedures. Loose Random Dry Organic Media Most loose random shaped dry organic materials are made from the cellular structures of former living plants; therefore, their shape and size are determined by what part and/or size of the plant was. That means that the most materials used are of relatively small size so they can flow freely when they are made into uniform particles. Shell particles are normally larger and harder than fibrous wood products, but both can be made into very small almost powder like sizes. In their natural state, the weight of these products do not vary much except when liquid and/or solid additive compounds are added to the products to assist the materials in either polishing or to increase their abrasive qualities. Visuals show actual size of some common materials. Fig. 93. Common Organic Media Corn Cob Of these organic materials, corn cob is the lightest grain or cellular structure size particle at about 23 to 33 pounds per cubic foot and is normally the softest of the dry media. Ground up cob has been used for a long time as a drying agent for spills because of its absorption qualities and is used in vibratory and the older barrel systems for that same purpose. In fact, there are special designed inline drying machines that use corn cob to follow parts washers. These are usually more efficient than hot air blow off dryers, or centrifugal systems, because they are still a solid mass in relationship to the part being processed. Because corncob media makes contact with the part it also has the ability to do light cleaning and brightening of surface features, which technically is deburring to some extent and that's also why a cob drier is more efficient than hot air type system alone. This light cleaning or abrasive characteristic of the media is important because all tap water retains minerals in solution and consequentially it does leave spots when it dries or even if it sits for any short period of time without being wiped dry. Water stains are a common problem with polished metals; therefore, the soft organic nature of corn cob media makes it ideal as a drier and cleaner for most parts processing.
  • 241. Chapter 12 – Media 242 Because of the lightweight of corncob, it is often used on non-ferrous soft metals such as aluminum and/or delicate and detailed parts. As stated, the media does have some minor abrasion qualities by itself. Where it really is superior to most wet media is when it is blended with other additives of inorganic abrasives or chemically treated to perform certain tasks. The absorption qualities make it an ideal candidate to soak in, retain, and transfer polishing compounds. Organic materials can also be pretreated to retain, hold, or suspend some fine abrasive particles provided another bonding agent is used to enhance its ability to stabilize the mixture. In some cases, where the materials are nearly the same specific gravity weight of the particle size to create a homogeneous blended mix, additives may not be necessary. Lastly, dry organic materials can be pre-soaked with waxes, lacquers, and dyes to transfer these products evenly and uniformly to other parts or products in barrel tumbling systems. When either a liquid or polishing paste is added to corn cob, the processing results are nearly equal to a hand buffed finish. Unlike burnishing media that is used to get bright but rough finishes, organic media does remove microscopic amounts of material and does polish and smooth parts to a very low RMS finish. This can be as low as a 2 RMS or better provided other operations are preformed first and this also depends upon this and previous processing steps and time cycles. In most mass finishing systems, polishing results take a long time. In fact, normally the longer you run a part in this media the finer the finish. Also, the greater the percentage of media to parts the better the end results. To polish parts, the proper mix is about 80% media to 20% parts by volume. This mix can be changed to more media to parts, but at some point the quantity of parts per batch and the time cycle does effect costs adversely. To get good mirror surface finishes using dry media, parts normally have to be run in a step process. Dry media should only be considered for polishing after the parts being worked have a surface finish of 18 RMS or finer. Starting from this 18 RMS and soft non-ferrous metals in a centrifugal high energy barrel systems, a mirror finish of about 8 RMS can be accomplished in about a half hour to one hour and a 4 RMS in about two hours. In vibratory systems good results of 12 RMS can be achieve in 2 to 4 hours with good mirror finish of 8 RMS in 8 to 12 hours and about 24 hours for a nearly hand buffed type finish of 2 to 4 RMS. Old barrel systems may take 24 hours for a 12 RMS and about 48 hours for an 8 RMS and maybe 120 hours for a 4 RMS result. Another common organic polishing media are nutshells with walnut being the dominant choice of most users because it is about the hardest and heaviest of all organic materials. Again, when mixed with polishing additives, the results are spectacular. This media is commonly used in the jewelry industry because of its excellent results when treated with polishing additives. However, because of its hardness, some care must be taken to regulate the amount of energy or amplitude, vibration, or RPM's of the equipment to prevent what is called an orange peel effect of the media impacting the metal surface. This effect is similar to what can occur using steel media, but it is not nearly as bad.
  • 242. Chapter 12 – Media 243 Wood In addition to the granular organics of cob and nut products is wood. There are some unique qualities to wood that have both positive and negative benefits. The most common wood used to make up this media is beech and birch. These woods have dense fine grain structures and are therefore considered hard woods. Wood in saw dust form is fibrous and/or occurs in long strands of short cellular fibers. In that state, given the same volume, it is actually lighter than corn cob and weights between 20 and 25 pounds per cubic foot of material and also depends upon the moisture content of the product. The long cellular fiber quality of wood means that this material behaves or produces results more like that of cloth buffing wheel. It has more of a wiping action than do the granular organic particles. It cannot create the dimple patterns or orange peel effect of grain type particles. On the negative side, the fiber is somewhat elongated and that causes it to adhere or stick to most materials being worked either assisted by moisture from the air or from the additives. This adhesion problem is also caused in part by static electricity. Wood shapes in cut form behaves similar to extremely fine plastic media when used with non-ferrous metals. It does not abrade alone by itself, as does plastic, without some additives. In fact it has a tendency to polish or clean a little by itself. If some of the saw dust particle form of wood were to be added to the cut wood shapes, the results, without additives would be somewhat abrasive in nature, until the materials break in or becomes smooth through usage. This break in period is actually a process of the closure of microscopic pores of the material. With polishing additives and with or without the fine particle saw dust form, and properly broken in, wood shapes do an excellent job of polishing almost all materials. Most dry organic polishing mixes are a combination of the dry organic particles plus a polishing additive, which is blended into the mix, but is still dry and free flowing. This additive is usually a paste type product that requires additional time to mix and be dispersed within the organic materials; however it can also be a liquid or a powder. The blending process produces what is called impregnated or a treated product. As mentioned earlier, these products can and do work the same as buffing compounds in almost the same way except no manual labor is involved using mass finishing equipment. The resulting surface appearance is almost equal to a hand buffed finished appearance. As parts are processed in any dry organic media blended mix, the temperature does rise and this helps the additive to coat the parts and the organic materials wipe and smooth them. Usually after each batch of processed parts, new materials or additive must be added to the process due to loss and break down of both the organic material and the additive. In some cases when the mixes become too dusty, water can be added sparingly. Too much water will drastically shorten the life or organic materials. That also means that care and storage of dry blended materials is of some importance and concern. Moisture Content Perhaps another interesting thing should be mentioned here about moisture content of dry organic materials and machine systems. Some blended formulations or dry organic mixes
  • 243. Chapter 12 – Media 244 can have more moisture content and while that sounds good, it causes them to adhere or cling to everything. This moisture content is especially not good for centrifugal type systems because this equipment amplifies the adhesion properties that cause the particles to cling together more than they would in barrels and vibratory equipment; therefore, newer formulations of treated organic materials are blended with dry forms of polishing additives. Moisture content also seems to have an indirect effect on plastic parts. The combination of wood saw dust and wood shapes plus a proper polishing additives is commonly used to polish and restore clarity to clear plastic parts that have either been saw cut or sanded to shape. However, because of the light weight of these materials, we are again talking about a long time cycle of may 24 or 48 hours in a vibratory system and almost twice that long for barrel systems. However, given enough time the appearance from a barrel system will be superior to a vibratory machine, because of the longer slide motion of the media. Moisture adds weight to dry organic materials and this can have a beneficial effect; however, weight can better be accomplished with bulky wood shapes added to any fine grain organic particle to provide more mass. Bulk and volume increases any mass finishing process or shortens processing times greater than treated dry organic media alone. At the same time, wood shapes can also create impact deformity on plastic parts if the equipment is not properly adjusted. In addition to bulky wood shapes, other preformed shapes of plastic and porcelain can also be added to dry organic mixes and achieve good results in shorter periods of time; however, adjustments must be made to compensate for this increased weight factor. Blended or mixed media Up to this point, we have talked about adding polish to organic materials and I have described some of the results. Fine inorganic abrasives can also be added to organic materials to do deburring and material removal and/or create a surface texture. In all cases, the random organic particles provide the bulk of the mechanical energy requirements; however, because of the weight differential, sometimes a glue like binder must also be added to the mix to properly suspend the inorganic abrasives. This deburring process is more commonly done with the wood products, because the fibrous form of wood plus a sticky additive of wax or oil creates a type of filament matrix that behaves similar to sand paper or a metal file. Organic particles materials are more rounded and don't have the same good results as do the wood fibers. Pumice The most common abrasive additive used to work with organic materials is pumice because of its lighter weight than the organic particles. Other materials can be used; however, if their weight or size is significantly different than the organic media particles the inorganic abrasives will not stick or stay bonded to the organic materials. Sometimes, without the use of special bonding agents, separation can take place within the work mass. That means that you may get a situation where the media mix can be in two distinct levels rotating in the same work chamber and that may not work parts uniformly. Sometimes this condition can be good for processing parts, but it is a tricky situation and is normally avoided.
  • 244. Chapter 12 – Media 245 Because of the lightweight, porosity, and hardness of pumice it is the primary abrasive used with organic materials. However, it also has the fastest breakdown rate of any inorganic material in use. Pumice will out cut aluminum oxide, silicon carbide, or zirconia in a dry process operation. The reason for this is that it is a very friable and porous material which breaks down into smaller long slivers that cling to both parts and other materials equally. This break down characteristic makes it ideal for relatively fast surface refinement in a relative short period of time especially on soft non-ferrous materials. On the negative side, a batch of parts gets modified as well as the media mix itself. The constant replacement of replenishment of pumice makes it difficult to properly control. It is for that reason why pumice alone is not commonly used. In special cases, pumice can be used by itself to perform deburring and surface modifications both in an all dry process or when used with liquids. That means that a wider RMS range is possible using pumice with other preform shapes. By itself in a dry state, it is a slow process that works well on soft non-ferrous metals, especially small parts under a half inch in size. When used wet by itself, it is very effective in working plastic materials, because it produces a rough finish very fast and then it begins to produce finer and finer surface finishes without adding or changing the liquid. However, to get a superb finish, you should change to a burnishing chemical compound. Other inorganic additives Other abrasive materials and particles sizes can be added with varying results to dry organic materials. Probably the heaviest weight abrasive used with dry organic media is zirconia. On ferrous metals this works well up to a point, then it has a tendency to start polishing. The abrasive particles are so hard they begin to round off and become smooth; rather than break down and stay as an abrasive. Therefore, new zirconia material must be added or blended with bulk shapes or pumice to maintain its abrasive quality. Other small size inorganic materials have the same problem as zirconia. That is, without the use of water to aid in their decomposition, the materials themselves round off their edges and/or load up and begin to polish. The parts being worked may also have some influence over the inorganic abrasive media by glazing or sealing up whatever porosity the abrasive might have had before it was used. Therefore, although inorganic materials can be small enough to do the same work as organics, they do not have the same polishing or abrasive qualities as treated organic materials. Antique Appearance The appearance of parts processed with abrasive organic blended mixes is similar to the results produced by sand blasting systems, but without the fine dimple pattern. It can also be compared to that of a wire brushed or satin finish. A lot of new antique looking parts are done in this way. Antique looks can be accomplished by blackening the metal first and then processing the parts in a dry abrasive organic mix or inorganic blend.
  • 245. Chapter 12 – Media 246 With abrasives added to dry organic materials, normally a wider range of surface finishes and textures can be accomplished with the preform shapes used in wet processing. Dry abrasive organic media blends seem to produce good results between 22 to 12 RMS starting from 35 RMS. That means that in most instances, everything that wet preform shapes can do, so too can dry organic materials with abrasives. Besides the lack of water, chemicals, and debris, the only difference between wet and dry processing is the increased amount of processing time and the finer surface finish that organic particles will produce. Felt and Miscellaneous Besides the more common uses of organic media described above, there are also some more infrequently used media materials that can be used. One of these is felt. A very hard felt, cut into square shapes, is used in some instances to perform polishing tasks that require extreme delicacy and/or smooth surface finishes. Most felt materials tend to break down and become one big ball of cotton felt; therefore, be careful to get the hardest grade or density of this material. Like most organic materials, felt does take and hold polishing additive chemicals very well. However, felt is not normally sold for use as a media and can be difficult to find and expensive to buy. In addition to felt are a class of weird materials of which I will just mention one. A number of years ago, I saw a barrel process using big gummy type rubber based erasers being used to clean up plastic parts and small light weight aluminum parts. I mentioned earlier that almost anything can be used as a media and have some effect on whatever it is you are trying to do or accomplish in the way of mass finishing. This is one of those way out applications. Today it is not impossible to run with completely dry mass finishing processes only. In fact, this seems to be a trend that high energy equipment is taking. In addition to improvements in mass finishing equipment performance, there are improvements in new CNC machine centers and equipment. That means that parts are being worked to finer surface finishes and tolerances due to better tool control. That also means that these parts need less deburring and better more refined surface finishes. These factors plus the concern of water pollution, and other controlling rules, regulations, and the restrictions being placed on chemicals all add up to the popularity and trend toward dry organic media. Temperature Lastly, while we are talking about dry organic media and blends, we should also mention the fact that when this media is run, it does not behave as wet systems do. What I mean by that is the fact that water, besides being a lubricant and conveyor for chemicals, also acts as a coolant. On the other hand, dry organic materials run considerably warmer. This elevated temperature aids in the performance of the polishing additives similar to how a buffing wheel works. That is, as the temperature increases, so too does the efficiency of the buffing compounds within the mix. In fact, the same buffing compound used on wheels, can also be used with dry organic materials; however, the bar form must be changed to either a powder form or liquefied some way to add and or be disperse within the media.
  • 246. Chapter 12 – Media 247 The greater the temperature within the work chamber of the mass finishing system, normally the better the polishing results up to the range or point limitation of the additive compounds. There are also relatively low flash points to organic materials; therefore, too high a temperature may be undesirable. This is especially true when heated corn cob is used for drying parts. Normal temperature range of long processing cycles of 24 hours using dry media can get up to maybe 100 degrees Fahrenheit in closed barrel type systems, to 120 degrees in vibratory equipment, and up to about 150 degrees in high energy type systems. While dry organic media is not harmful or hazardous to the environment or for use around people, what you put into the media may be. To clarify that statement, the media is not the problem. The problem is either the parts being worked or the additives being used to impregnated the dry organic media. Because of EPA and OSHA requirements, abrasive or polishing compounds are not normally a problem. That leaves the process itself or the materials being worked as a potential problem; however, even this situation is a very remote possibility. The process problem is nothing more than a good housekeeping problem of airborne particles and good maintenance. Any form of dust can become a problem if it is not properly controlled and any waste disposal from dry processing can normally be placed into the paper trash. However, like any trash disposal, you should check with whoever regulates such things in or out of your company. Media Shapes: I choose not to include the physical description and dynamics of media shapes earlier in the descriptions of media because we were talking mostly about abrasion characteristics. I did provide visual information; however, I decided that shapes needed a category all by themselves. Media shapes do play a part in the amount of material removal, but it is not the determining factor like abrasive particles are in determining the end results. That is, you know now that weight is a very important factor in mass finishing and the fastest way to alter weight in a preformed shape is through increase size and/or shape as well as media composition. Shape is more a determining factor that controls mobility and accessibility, or how and where a part is worked. Mobility maybe somewhat easy to understand, but accessibility needs clarification. The term access is just that. Unless a preformed media shape can get into all of the areas of a part that have to be worked, it cannot perform its function of deburring and/or surface modification. Even if the area doesn’t have to be worked, it basically needs surface conditioning to produce uniform results. That is, if say a media is selected that cannot get into corners of a part and it later gets anodizes in a secondary operation, there may be a definite noticeable appearance to the part due to different surface profile finishes. Shape determines access to the work area and the ability of the preformed shape to work without getting stuck. That last word stuck is a very important word in the mass finishing industry. Probably the most single important factor in mass finishing is the ability to select a preformed media shape that is the most universal in size, shape, and composition, that will work as many different parts as possible without getting stuck. Such an ideal selection is next to impossible.
  • 247. Chapter 12 – Media 248 Just the sheer size or scope of part configurations makes it extremely rare that one can get away with one media size and shape size fits all. Consequently, most companies select a number of different sizes and shapes of media to perform different tasks and/or produce different finishes. Even though the proper practice is to maintain some diversity of media size and shape, this is still not very common until you get into larger companies or companies that do a lot of deburring and surface finishing. As mentioned, the cost of storage and maintenance maybe traded off in the name of some additional material handling or cost effectiveness. In selecting media shapes, there are usually compromises that have to be made to live with a certain amount of potential lodging in parts, but time is money; therefore, selection must be based on part configuration first and/or the volume of that part versus other parts. That is, common sense tells you to select the media that will work your most numerous parts first, but if critical dimension parts are less numerous but cost a whole lot more to make, you don’t want to trade off volume for cost considerations. On the negative side, if you have a certain number of parts that require a lot of hand work to remove media that gets stuck, then you may want to consider another size and shape just to eliminate this problem. Basic shapes The following are some rough guidelines to follow for media shape selection. As a general statement only, there are really only two choices or shapes from which to make a selection. My own slang terminology for these shapes are steamrollers and bulldozers, or just rollers and pushers. The basic media shapes roll and crush the burr or scrape and push the burr. One selects either mobility or pressure. The greater the diameter or roundness of the media shape the easier it rolls and moves both the media and the parts. The greater the geometric straight lines a media has, the greater the pressure, force, or resistance the media and parts encounter. All shapes work and perform the task of material removal almost equally well. The more symmetrical and/or uniform the shape of the media, normally the greater the mobility of the media. In this category are: cylinders, spheres/balls, and cones. In mass finishing equipment, these shapes behave something like both a fixed wheel and a mobile wheel. That is, as these shapes move, they rotate en mass and by themselves. These shapes work extremely well where you have a lot of holes and the shape can poke itself slightly into the hole and rotate a little before it moves on. Because these shapes are so mobile en mass, they do not hold, support, or restrict parts from reaching the bottom of the work chamber. That characteristic means that the full weight of the media mass is utilized on the parts. The only negative of this shape is that you cannot work inside corners or inside angles very well and that can develop a shadow appearance. Given the same mass finishing equipment, the more geometric the shape, such as triangles, pyramids, tetrahedrons, and the straight wedge, the slower and noisier they rotate. The reason for this behavior is because there are more points of surface contact with the parts and other media. Sharp edge media movement is restricted due to the alignment of edges and that resistance causes the mass to push and scrape along. Instead of using weight and mobility, these shapes tend to transmit this resistance into greater pressure to the parts being worked.
  • 248. Chapter 12 – Media 249 Because of this resistance factor, parts in the media mass maintain relatively good separation, maintain their position, and they do not sink to the bottom of the mass. In addition to these two basic shapes, there are combination shapes that try to incorporate the best attributes of both configurations. Probably the most common geometric characteristic shape used in both configurations is the angle cut. Naturally, ball media has no angles; however, cylinder ends are cut on an angle and a cone incorporates an angle into its shape. Most geometric shapes have sharp edges and can easily incorporate an angle into their shapes. Because ceramic media came first and were extruded, it was discovered that instead of cutting the shape straight up and down or perpendicular to the extrusion, the finished product shaped worked better and reached more areas if it was cut on an angle. Hence the term and popularity of the angle cut shapes. Most plastic media is molded and instead of cutting the media on an angle, the media shape incorporates the angle into its design. The angle cut can vary from shape to shape and within the same shape, but it is normally cut at 22 degrees. A lot of the angle shapes depend upon who the manufacturer of the media is. The same shape made by a different manufacturer can be anywhere from 20, 22, 25, or a 30 degree angle cut. For special applications and deeper penetration, there are also 45 and 60 degree angle cuts. Naturally the more angle, the thinner the shape at the point. That also means, the sharper the angle, the thinner and the weaker the material is at that point. There are tradeoffs. Angles are actually commonly found on all media shapes and help perform special functions. Angular shapes have the ability to penetrate into holes, and work corners, and sharp recesses very well. The angle works or behaves similar to a knife blade or a triangular file. The sharper the angle, the deeper the penetration and the tighter the area or detail it can work. Even though I mentioned the weakness of the point area, there is not too much fear of the media shape breaking because of its hardness, even with 60 degree angle cut media. Angle cuts are recommended for whatever media shape you do select. There is another interesting problem associated with angle cuts and that is how the shape is measured. All preformed media is measured and specified by length, width, and height. The basic shape of media is really in two dimensions; therefore, because of the angles, the media dimensions normally exceed that of the shape. This can be confusing and sometimes needs clarification, especially before you buy a 3/8 inch 60 degree angle cut triangle. When you receive that shape, you will find out that it has an actually length of about 3/4 of an inch that extends from point to point. Now, the angle cut is a very effective shape for deep penetration and the cylinder is very effective shape for mobility. When these two attributes are combined with a different type of angle cut or cut to a point instead of parallel, you come up with another very interesting hybrid shape described as a V cut cylinder, a cylinder wedge, or a tricyl. What is so special or unique about this shape is how it behaves and where its center of gravity is.
  • 249. Chapter 12 – Media 250 Perhaps the cylinder wedge shape is the best of both worlds or a good media for most general purpose deburring applications. The cone shape is also a good mobile media, but it has limited surface contact. The cylinder wedge shaped media seems to be the best of both worlds, because it is cut to a point like a piece of pie when looked at from one side and is completely round from the other 90 degree side. That means that this shape has great mobility and has a lot of contact with broad flat areas. The cylinder wedge and the cones are popular choices and are the only media shapes that come in both ceramic and plastic compositions. Balls and cylinders and especially cone shapes have great mobility, but the cylinder wedge shape seems to be the most mobile and it still maintains a sharp angle with two broad flats which are good for surface profiles, heavy material removal, and deep penetration abilities. Unlike all of the other shapes mentioned so far, all of the other media shapes have their center of gravity right in the center of the shape. As mentioned, the center of gravity controls the movement of the mass and/or media shape. All other shapes are very stable and don't move too far away from the energy source and they do work their way into tight spots and can get stuck. The cylinder wedge shape is the only shape that actually has its center of gravity of the outside edge of the shape. That means that the cylinder wedge is very unstable and moves a lot. This unstable mobility can best be proven by placing a piece of media on its rounded edge a move it slightly. This shape is the only shape that will continue to rock back and forth for some time after being energized. That mobility also means that it is less likely to work itself into tight spots and stay there. Like Murphy's Law, if media can get stuck, it will get stuck because of the mobility factor. The lodging problem is less likely in the case of the cylinder wedge, because that shape has a lot of material that extends to one side beyond the geographical center of the shape. See chart Operating Characteristics Preform Plastic and Ceramic Media Shapes Media Shape * Lodging Sphere Cylinder Wedge Cylinder Cone Pyramid Elliptical Triangle Diamond Tetrahedro ns Tri-Star 1 1.2 4b 4 1P 5F 5 5 5 5 1 5 16 24 2.5 3 3.5 3.5 5 5 5 4C 5 3 4 3a 3a 1b 2L 2L 5F 3FL 5F 4F 4FL 4 5 2d 4 4 4 2 5 5 4 5 4 4 4 3 3 4 3 5e 4e 4 18 20 18 19 21 19 15 5 3a 3FL 3 4 4 17 Mobility Surface Contact Area Retain Shape Surface Finish Process Time Total Score Rating NOTE 1: * Lodging column is not added or part of overall score, but the lower this number the less likely this media is to get stuck. The Total Score Rating is the sum total of all other columns and which is based upon a numerical score where the lower the number the less
  • 250. Chapter 12 – Media 251 versatile the media is, and the higher the number, the more versatile it is in processing applications. NOTE 2: Sub letter designations and explanations are as follows: (a) Mobility factor works best when the media dimensions are closer to a square, bulky, or equal X Y rather than elongated or thin dimensions. (b) These shapes display peculiar qualities when used in bulk. That is, when used in uniform sizes, this media shape absorbs energy offering greater resistance and decreases its mobility significantly. (c) Shape looses mobility when the length to width ratio exceeds 2 : 3. (d) The edges wear down and become a tapered elliptical shape. (e) A thin flat shapes work more aggressively than bulky shapes. P Point contact, or extremely small surface contact. F Primarily Flat broad surface contact. L Primarily Line surface contact FL Primarily Flat broad surface contact but also Line contact. Based upon a chart developed by Sam Thompson. In the selection of a media shape, some general rules to remember are that geometric shapes that have a lot of bulk, straight lines, and/or angular edges to them also have a tendency to work faster on outside surface areas. These are relatively sharp shapes that encounter more resistance between themselves and the parts being worked. The broad flat ceramic shapes of triangles, tri-stars, pyramids, tetrahedrons, and straight wedges are all good selections for this type of work. Geometric shaped media movement is not very smooth flowing or mobile because the energy force is somewhat locked up in short burst of energy that behave similar to an ice flow breaking up on a river. In fact, this can be noticed by just listening to the noise emitted during the deburring process. This media will run very noisy because of the resistance factor, but it will also do an excellent job of removing a lot of material from outside edges and flat surface areas more than most rounded shapes. For deburring I.D. and O.D. holes in parts, cylinders seem to be the shape of choice. They offer greater mobility than flat configurations, but give way to heavy parts en mass allowing them to sink to the bottom. In some cases this is good for obtaining the greatest weight of the media mass or energy to deburr, but it is bad if you want to retrieve small parts by hand after the processing is complete. One more feature of this shape is the amount of surface contact can be actually greater with this shape if the part has a lot of contours than a straight geometric shaped configuration. Because this shape has basically a broad line or point on point contact that rotates, the material removal process maybe less than the flat configurations.
  • 251. Chapter 12 – Media 252 As mentioned, cylinders can be selected either to pass through holes and recesses or penetrate deep enough into a hole to do edge removal or work a problem area. This is similar to how a larger drill bit is used to chamfer smaller I.D. holes. To do this deep deburring, most cylinders are cut on either a 22 or 25-degree angle, but as mentioned, they also can be gotten in 45 and 60-degree angles for this problem of penetration. These angles are normally cut parallel to one another to give them uniform balance and performance. Getting back to holes. Holes present an interesting problem. If you want the media to pass through the hole, select a cylinder media, if possible, that is about 1/8 of an inch smaller than the smallest hole being worked. However, be careful that you don't have some holes exactly twice the size of the media, because two pieces or more of cylinder media can jam as easy as one. The safe procedure is to select a media larger than the hole sizes and work the burr from outside or above the surface of the hole. Even though we have talked about the more common shapes and various configurations, perhaps I should say more about plastic media. The reason for this is that there are many more shapes made from plastic than there are from ceramics. The reason for this is that more plastic media is made with molds. One exception to this is a special formulated plastic composition and machine that works like a Hershey kiss candy-making machine that produces the curly top. Besides the kiss shape, they also make a four-sided pyramid kiss shape with the same top. Most ceramic media is normally extruded and cut to thickness. Molded shapes tend to have more points or protrusions that can get into tight spots. Besides the plastic cone and cylinder wedge shapes mentioned above are flat wedges, pyramids, tetrahedrons, triangles, tristars, arrowheads, coniforms, and tetraforms and some minor variations to these configurations. Because molded media shapes normally have more angles in their configuration, some thought must be given to the wear of all of these shapes. That is, as a shape wears down, it loses some of its sharpness or cutting edges. That also means that it cannot reach into angles or recess areas as well as it did when it was new or had an sharp edge. Angle cut media does help preserve a shapes configuration during this wear rate; however, most angular molded media becomes more of an irregular oval shape mass with use. Therefore, when a media reaches or wears to half its original size, its shape cannot normally be determined readily. That means that the life of the media may be a lot less than its actual half life or functional life. This situation occurs in about 3 or 4 months based upon use of 40 hours per week in an average vibratory machine system. With all of that in mind, the following are some guidelines to use in selecting deburring and polishing media for mass finishing equipment:
  • 252. Chapter 12 – Media 253 Media Guidelines 1. For rapid or large amounts of material removal from parts in the shortest period of time, you need the largest preformed shape available, which will get into and work all the areas that have to be modified. It should also be the coarsest abrasive particle size with a fastest break down bonding agent. 2. The preformed shape you select depends upon the configuration of your part and/or what burr or surface finish is required. Mobility, resistance, size, and abrasion characteristic are the determining factors for media selection. 3. For the smoothest surface finish, you want either a fine abrasive preform shape in a small size and a good hard bonding agent, or you may want to do a step down process of more than one media preform operation. Which way you go depends on where you start. That is, the optimum abrasive range for deburring or surface modification using media shapes is somewhere around a 10 to 15 RMS improvement. That is about the limit of all preformed shapes except the new dry organic shapes. 4. Ferrous metals should be run in ceramic preformed media. Plastic parts should also be run in ceramic media for speedy short time cycles and when appearance is not a factor. 5. Non-ferrous parts can be run in ceramic if surface appearance is not important and where short time cycles are desirable. If a part is to be anodized or plated, medium to fine grades of plastic or synthetics should be used. Normally all non-ferrous parts are run in plastic based media. 6. Do not mix metal parts or materials of different compositions in the same media without thoroughly rinsing or cleaning the work chamber, especially after batch type processing. Microscopic debris may contaminate, react, or discolor the next batch of materials. You don't want aluminum parts with iron rust spots on them. 7. For bright finishes on all surfaces or materials, without regard to roughness, steel or porcelain preformed shaped balls is the preferred shape in most applications with a good liquid compound. 8. For the brightest smoothest surface finish possible, dry organic media impregnated with a polishing additive is recommended. 9. Flat parts and parts under a 1/2 inch in size should be run with dry organics for both deburring or polishing for uniform finishes. The surface tension of water tends to glue flat parts together and small parts to the work chamber walls. 10. For the best, shortest time cycles in all machines fill your machines work chamber to its maximum working capacity and to the proper proportion of media to parts ratio. Weight and pressure are the two most important elements for deburring using mass finishing equipment.
  • 253. 254 Chapter 13 - Liquid Systems Chemical Compounds As mentioned earlier, mass finishing systems are like a three-legged stool. It takes three elements to properly deburr or polish parts. We have talked about two of these elements of equipment, and media. The third element is chemical compounds or solutions. To achieve the best results in mass finishing systems, water and chemicals must be added, properly monitored, and/or regulated to produce good clean acceptable parts, or for dry processes there are dry organic compounds. For simplification, the remainder of this section will deal only with wet processing chemicals. Of the three principles governing mass finishing processing results, chemical compounds are probably the most difficult to nail down or control. Why chemicals are so important and yet so difficult to recommend or be specific about is because of all the variables prior to the parts getting to the deburring stage. All manufacturing companies do things differently. That means they use different production equipment, supplies, and processing methods. That also means that they normally all require the use of chemical lubricants in making of their parts. Not only do companies make parts out of more than one material, they may use more than one chemical lubricant or oil in the production of a single part. Some companies may even go as far to change lubricants due to cost factors. To complicate matters even more, these companies may also buy parts from someone else that has other lubricants different from their own. Knowing what has to be cleaned helps a great deal in selecting the right chemical cleaning or deburring compound for wet processing. Again, if the lubricants and oils are known, the chemical base is relatively easy to determine and that means that a cleaning product can also be properly selected. Without the knowledge of the contaminates, all of this adds up to a lot of possible unknowns and guess work and that sometimes makes it difficult to find a chemical cleaning compound that will clean, deburr, and protect the finished part in a fast economical way. For consistent accurate finishing results a simple answer for the processing problem or chemical selection of a deburring compound is to wash all parts prior to them entering the mass finishing equipment, but rarely is this ever done. A mechanical cleaning process is actually better at removing all contaminates either known or unknown. The pressure and surface contact exerted by media, chemicals, and water is a very efficient method of cleaning; therefore, most companies do not clean parts prior to mass finishing. The purpose of a chemical deburring compound is to maintain lubrication and the suspension of contaminated debris and soils off the parts being worked and the media itself. Without this liquid purging action, cutting oils and debris will stick to the parts and glaze up the surface of both the part and the media. If the porosity of either the part or media gets coated with contaminates it makes it more difficult to deburr because it reduces the abrasive relationship and thereby significantly increasing the processing time. On the up side, perhaps a
  • 254. Chapter 13 - Liquid Systems 255 side benefit of this media glazing over is that the parts will come out brighter, shinny, and maybe smoother, but they will still be dirty. Media which has become glazed requires a significant amount of time to be reconditioned or restored to its original abrasion qualities once this glazing has occurred. The actual restoration requires the use of a good strong degreasing chemical and/or cleaning cycle. In this process, the media can lose as much as 20 or 30% of its mass and require a significant amount of time; therefore, this is not a recommended or desired procedure. Normally it is more cost effective to just replace the media. The best way to correct the problem is not to create the problem. Water alone will not prevent media from loading up with contaminates. Chemical additives must be used to clean the parts and the media. Generally speaking cleaning involves the dissolving of contaminates and their suspension in a soluble solution; however, because of molecular attraction, surface contaminates may require some additional help to remove these materials. To do that, chemicals are chosen that react with the metal parts to help purge the surface contaminates. This cleaning action is best accomplished by controlling the pH of the solution or the chemical additive. The pH of a liquid substance is considered either acidic or basic. The pH scale is the logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity in gram equivalents per liter. The pH scale measures from 1 to 14 with water as neutral, but has a rating of 7. Anything above this number is considered basic or a soap and anything below this number is considered acidic. Again, generally speaking, acidic solutions seem to work well with nonferrous materials and basic solution work well with ferrous materials. This is not a hard and fast rule and there are a lot of exceptions with liquids depending upon what you trying to achieve. Besides the compound affecting the solution, water itself is a major factor in mass finishing. That is, water is not a constant everywhere in the world, or for that matter, within a mile of each source. Water contains minerals, which are leached out of the soil from which it comes and then stays in the solution. This mineral content, called hardness, effects the performance of media, but even more so the chemical additives. That means that given the same chemical additive for processing to a company in one part of the country may not work as well as that same product for another company somewhere else. All of the above factors concerning liquids makes a simple problem more difficult. That also means that most companies will have to do some experimenting on their own with chemicals even though there are guideline recommendations. Another factor complicating the proper mixing of solutions is that there are a lot of chemicals to choose from and each has their own formulations, recommended dosage, or dilution rate. Probably the first thing one should look at after the pH or the product and before selecting a chemical additive is the concentration or dilution rate of the chemical compound. A quart of chemical solution with a dilution rate of 640:1 is actually better than a 55 gallon drum of user strength chemical, unless you are not prepared to monitor, mix, or regulate the solution properly.
  • 255. Chapter 13 - Liquid Systems 256 In a concentrated form, a chemical is normally a better deal for storage and probably price, but the inconvenience of mixing and adding the chemical may cause addition problems and/or costs. Most chemicals are now designed to be biodegradable and that means that if you do nothing with them over a period of time they will cease to be of any use. The best chemical compound in the world will not work if the solution is not properly maintained. Also, too much dilution will change the pH of the product and it may not work properly. Besides pH and dilution rate as criteria for selecting a cleaning compound is the question of another additive within the chemical itself. Because mass finishing systems are mechanical abrasion processes, they do remove materials from whatever is being worked or abraded. That also means that in effect, this material removal process is recreating new raw surface features that have never been exposed to oxygen and/or the oxidation process found in nature. All of this means that another additive is usually incorporated into a chemical cleaner that does help seal or protect new exposed metals and material against oxidation. This product is often referred to as an inhibitor. An inhibitor is not a cure all protective coating, but is more of a retardant against oxidation. Too much inhibitor or too heavy of a coating will also affect the performance of the media just like glazing will; therefore, a diluted solution of an inhibitor is recommended to prevent flash rusting of parts prior to follow up coatings. Flash rusting is a more noticeable problem as either outside temperatures increase or parts are heated to dry faster. If parts sit for any length of time prior to their next operation, too little inhibitor will not protect the parts long enough. Dilution rates or secondary coatings may have to be adjusted periodically because of environmental and storage factors. Liquid Flow Systems: Besides the chemical, another controlling aspect of liquid solutions is the proper rate of flow into the mass finishing systems. Without the proper amount of liquid to lubricate and carry away cutting residue and debris, parts will become dark or black and may develop imbedded abrasives and scratches. The flow rate or liquid volume is a variable factor governed by the size of the machine, the media, and the drain system. In addition to these factors is the way in which a process is run. In smaller equipment systems under 1 cubic foot in size and any barrel system, the liquid and chemical are normally a one shot deal where you add the chemical solution to a batch or work, close up the system, and then empty it when the process is over. If a close loop or batch system is used, then a secondary rinse is suggested for the parts and/or media to clean off any debris or residue on both the parts and the media and to stop any chemical reactions. A second type of closed loop system is a re-circulating system. This system is the same as a batch process, but it re-circulates more volume of the solution. Usually these are relatively small systems of 30 to 50 gallon capacity where the solution is constantly used over and over again until it becomes ineffective because of the chemicals reacting with materials being worked, oils, other contaminates and the deburring debris. Even though these closed loop
  • 256. Chapter 13 - Liquid Systems 257 systems can become contaminated, the volume of the liquid solution is very effective for a longer period of time than batch type operations. A large, closed loop single chamber holding tank with a capacity of 20 to 50 gallons will normally provide 5 to 10 days of good reusable solution based upon 40 hours of processing time. Longer life is possible up to one month; however, most biodegradable chemical solutions begin to lose their effectiveness at about 10 days in solution. More common closed loop tank systems used to re-circulate the liquid are usually separated into two or three partition segments called weirs that stagnate or slow the liquid allowing the heavier particles to settle out. The tank can also have some kind of oil capturing device that screens, transfers, or collects the oils and other light weight materials so that the solution will have a longer life and the contaminates will not get re-used or screw up the process. A pump is used to collect the least contaminated solution in the last weir and returns it to the mass finishing system. The third system is called a flow through, which is not considered a closed loop system. This system constantly provides a new supply of solution and it drains to an outside source. Some of these outside sources are still much larger version of the closed loop system mentioned above; however, they do not re-circulate the spent or used liquids without purifying them. This third system still requires the use of chemicals to be added to the mass finishing equipment and this addition can be done in a couple of ways. One way to control chemical input is to manually pre-mix a large container of a user strength solution either by using a concentrate of liquid or powder form and use it as a reservoir until it is complete used up and start all over again. The capacity of the tank or solution can be determined by a flow rate of about a gallon per hour per cubic foot. On large equipment, over 5 cu. ft., this is not recommended. Another automatic form of the same tank system uses an orifice to regulate and control incoming liquid or the chemical compound additives to water in a pre-mixing tank with a control float to monitor liquid level. This is a relatively inexpensive system for medium size machine systems. Once an orifice size is selected and a chemical or liquid supply is hooked up, this system requires no maintenance provided the liquid flows do not change. Lastly, there are the more expensive metering pumps that do the same thing as the orifice system can but these are not dependent on flow. They regulate liquid chemical compounds and water flowing into a machine system. These are more expensive systems, but they are the simplest input systems that take the guesswork out of liquid control. With the exception of the batch type closed system, the re-circulating and flow through systems still need to maintain a proper flow through the mass finishing equipment and process. In new start up operations where the media has never been used or has drier out, the initial flow requirement may be greater in the first 5 to 10 minutes of processing than the normal amount of solution while in operation. After the moisture content of the media is reached, a good liquid flow should be about 1 to 2 gallons of liquid per hour per cubic foot of media or
  • 257. Chapter 13 - Liquid Systems 258 machine capacity. So, even with fixed liquid controls in place, the intervention of the machine operator may still be necessary The flow into a machine should nearly match the flow out of the machine. Because of debris from the deburring operation, there are inherent problems of clogged drains. Therefore, long processing cycles should be checked periodically to make sure the drain systems are working properly. Most manufacturers account for this potential problem by putting in normally 2 or more drains with a 2 to 1 output drain capacity than the liquid input. An obvious sign of a clogged drain is the noise or sound level of the process system itself which decreases and it may be possible to observe water splashing up into the air and/or around the machine. When chemical compounds were first introduce into mass finishing equipment, a good rule of thumb for chemical usage was, the more suds, the better the product and/or end result. This is no longer true. Most chemicals used in these operations no longer have high suds rates. In closed barrel type systems, suds are still acceptable and can be used effectively; however, as indicated, formulations have changed primarily because in most other equipment foam or suds is not desirable. What is visually looked for now in a good chemical compound is a slight temporary bubble observed between the media as it moves. Too much suds as well as too much water in a mass finishing process will slow down the action of the equipment and process. Suds may produce nicer looking parts in some cases and may lessen the chance of part on part impingement, but it will also take a lot longer time to process the parts. Additives: Most chemical compounds in use today are liquid; however, at one time, powders where the preferred choice of the end user. The main reason was and is cost. Chemicals in the form of powder are normally easier to store and are more concentrated. Other than cost, dry powders still have some advantages in products that contain fine abrasive and organic materials used in polishing. In the case of dry organic compound additives, one advantage is that these products can usually be used in both wet and dry applications. Most liquids too can be used in wet and some dry applications, but their formulations are not the same and they may not be effective for dry organic materials. Normally, polishing additives used in dry processes contain waxes or oils that do not dry out and work well in dry processes. Most liquids cannot suspend these same ingredients properly and they would probably cause a glazing situation to occur with a preformed shaped media. For liquids to work properly, they must be able to be uniformly soluble. If liquids contained or retained organic materials in suspension a biological reaction would take place which would make the compound or organic materials in the solution deteriorate quickly and would create other problems. The popularity of liquids are also due in part because of the ease of handling, dispensing, and/or metering by pump to achieve proper dilution rates. Liquids contain and hold inhibitors better than powders and are a lot easier to control and dispense into equipment than powders. Most equipment systems are not capable of handling powders and they must be premix by
  • 258. Chapter 13 - Liquid Systems 259 hand and due to the safety factor and handling procedures, powders are not used much anymore. Deburring and burnishing compounds contain a number of surfactants to improve the performance of water. The word surfactant is a very generic word used a lot in the chemical industry to mean almost anything they want it to mean. I used the word, but by itself, it means nothing. A surfactant is nothing more than another additive to water that effects the waters behavior or performance. It can be anything organic or inorganic. By itself, water alone does not have or allow for good surface contact or penetration of the materials porosity. If the water cannot get into the pores of the material, it cannot dissolve or clean the part. Surfactants are basically ingredients that work on the surface tension of water and they react or interface between the media, metals, the solution, and air. For safety reasons, products are formulated in such a way as to have a minimum concentration level below which the product becomes ineffective. Most deburring products are alkaline in nature and contain an inhibitor that re-deposits a protective coating on parts after cleaning them. Surfactants can be almost anything added to water to make it work better. Therefore, the solubility of a chemical and water solution is very important. Equally important is the nature of dirt and or debris. The longer contaminates stay on a part the more difficult it is to clean. Some contaminates can interact with a metals porosity and bond to it. To remove bonded contaminates one needs a product with a good surfactant ingredient or good wetting agent. That is, it should have a chemical that makes the water wetter so that it can penetrate and displace the contaminated soils on the parts being cleaned. In a sense, a wetting agent breaks up the attraction process of the soil and the parts substrate. In some cases, an emulsion surfactant is more desirable where you have thick, grease like, insoluble soils. This type of chemical product produces a milky solution that causes the dispersion of the contaminates and holds them in suspension. A saponifier is another type of product similar to the emulsion process chemical, but is better for use on the cleaning of animal fatty acids. The latter products usually contain a significant amount of sodium or potassium hydroxide. Naturally, the higher the temperature of any chemical solution the better and faster it will work. Even pure water, at a high enough temperature will dissolve most contaminated soil. Getting back to mass finishing compounds, the difference between a burnishing compound and a deburring compound is that the burnishing product contains a significant amount of microscopic chelating agents which seeks out metal ions, encapsulates them and suspends them in solution for easy disposal. The problem of chelating agents is in the disposal and treatment of the waste water. The bonding qualities of chelating products makes it extremely difficult to break up; therefore, the use of this agent may increase the problems of the waste disposal with possible long term effects of the debris or costly recycling treatment. Another important ingredient of a burnishing compound, and to some extent deburring products, are ingredients that provide lubricity. Lubricity is very important in steel ball burnishing. Not only does lubricity additives help the mechanical action of media, it also creates
  • 259. Chapter 13 - Liquid Systems 260 or encapsulates the media with a charge that allows the compound to cling to the media. In effect, it seals, glazes, or buffers any possible abrasive action to a limited extent. In effect, it provides a buffer zone that is extremely thin and does not allow any abrasive particles to work. Lubricity ingredients also provide a little more mobility to the contact shape and mass. A single, one chemical fits all does not exist. Most chemical compounds used in mass finishing systems are low foaming alkaline. Acid based products are still popular for working non-ferrous materials of stainless steel, some aluminum, copper, and brass alloys. An ideal chemical deburring product would be free of chromates, phosphates, silicate, fluorides, chelators, nitrites, and cyanide. Also, it should be non-caustic, solvent free, emulsifier free, low foaming, non-carcinogenic, biodegradable, environmentally safe, and have a pH of around 7.0 to 9.0. Also, the product selected besides cleaning the material being worked must not attack that material and cause it to deteriorate. Other than these few desirable qualities, selection of a chemical cleaning compound is easy. In mass finishing systems sometimes there are instances were chemical reactions are desirable to speed up deburring operations. A lot of strong alkaline or caustics are used to create a surface condition called embrittlement which affects burrs very quickly and causes them to become stiff and break off relatively fast. Acidic compounds can also be used to assist deburring operations in a similar way and are usually desirable for processing aluminum parts. The negative side, strong concentrates of chemicals require care and special handling or disposal of waste by-products. Also, concentrated chemical solutions tend to turn parts dark or black if left in batch or closed loop systems too long. If a mass finishing process takes over four hours, or the chemical is used over a period of four hours, both the parts and chemical should be monitored in some way to check the effectiveness of the process. Flow through systems that do not use the liquid over again but dispense chemical on a proportioning bases are about the safest way to process strong chemicals over a long period of time. Chemical Accelerators: We have just talked about the use of strong concentrates of chemical compounds in mass finishing equipment and how they affect parts and the potential problems associated with them. There is another category of chemical deburring and polishing compounds called accelerators which are similar to the chemical concentrates mentioned above, but these products are specifically designed to react with parts and produce fast metal removal and low RMS surface finishes, without major harmful chemical effects or waste treatment problems. Accelerator chemicals are formulated to produce different results on different materials in a fast and efficient manner. The companies who are making these accelerator products claim to be able to remove 150 to 80 grit sanding belt lines in 3 to 7 hours and produce 2 to 6 RMS surface finishes. Typically, these chemical products are formulated and used on heavy metal removal, especially hard materials such as Inconel, titanium, Waspalloy, and some stainless steels, but there are also formulations for aluminum, brass, and zinc.
  • 260. Chapter 13 - Liquid Systems 261 These accelerators are chemical concentrates, which require care in handling but are diluted when in use and are recommended to be used with non-abrasive high-density porcelain preformed media shapes. The products are designed to produce chemical reactions with the metal, which in turn produce an inert soft surface metal coating or salt film, which is called blackmode. The name is derived from the metals appearance before the part is processed. Unlike other strong chemicals, chemical accelerators do not etch the metal and the salt that is produced is not an oxide. When in use, the media is constantly removing this reactive surface coating without having or producing the normal abrasive slurry debris of the media. If the media cannot get into or contact this soft salt like film, no surface refinement can take place and the remaining salt will retain its parent metal hardness. As the chemical accelerator works, it removes a lot of surface roughness in a relatively short period of time, and then it slows as the surface becomes smoother. It will always continue to work to some extent, but at some point it does not become cost effective to continue. Normal time cycles are about four hours in vibratory equipment to achieve extremely fine surface finishes. It is interesting to note that when this surface finish is achieved by the first chemical, a second burnishing chemical accelerator can be successfully added or used to achieve brightness, without the machine being shut down or cleaned between these processing steps. Besides the increased speed of metal removal the chemical accelerator process also has the additional side benefit of using media with long life or wear than the normal deburring media used in vibratory processes producing the same results. In addition to the media life is the cost savings of not having to use more than one step and having to change the composition of the preform media shape. Chemical accelerators can have a pH as low as 2 on the acidic deburring side to about a 9 pH on the burnishing compound side. That means that these products are stronger concentrates than normal deburring compounds and that some precautions must be taken by employees who work around these products constantly. It is mandatory that all personnel who work about chemicals wear impervious boots, gloves, clothing and protective eyewear. Also like all processing fluids and waste products they must eventually wind up being treated before being disposed of; therefore, safety and treatment cost must be weighted with the increase processing speed or time element. Again, there are tradeoffs. Chemical Control/Monitoring: As stated earlier, all manufactured parts can vary from one batch to another; therefore, one should always monitor the process and results and, if necessary, adjust the chemical additive accordingly. Again, the black art or witch craft returns. Perhaps the simplest way to work with and select a chemical compound for mass finishing is to try it. Take a recommended product and use it as directed. If the product works, stay with it and use it. It is also a good suggestion, once a chemical is selected, to cut the dilution rate in half and see if it continues to work well. If a chemical product does not work well initially, try doubling the concentration and then cut back. This cutting in half or doubling is probably the only sure way to get the proper solution based upon your water hardness.
  • 261. Chapter 13 - Liquid Systems 262 The dispensing of chemical compounds by metering pump systems make the process of dialing dilution rates a whole lot easier than it used to be. Without the use of metering pumps, there are pumps that can siphon chemicals in proportion to water usage that can be controlled by orifice fittings designed to proportion the chemical in a direct relationship to the water input. Lastly, there is still the pre-mixing of chemical by hand in batches and either dispensed with pumps or gravity feed into the equipment being used using the proper solution flow. However, any premixed or pre-measured tank still requires monitoring over a given period of time. Talking about monitoring, once a chemical or chemicals have been selected, their use or consistency must be monitored periodically. Some products deteriorate faster than others and concentration has a lot to do with actual performance of the product. Omitting all the selection criteria for the chemical compound product, there is still a need for the proper maintenance controls of the solution while in use or storage. That is, like preform deburring or polishing media that deteriorates with use, so to do liquids lose their characteristic properties to lubricate and clean the media, the part, and to some extent the equipment. As mentioned, there are metering systems to regulate a proper constant flow of chemical and water mix through processing equipment and you can say that these systems are in a sense already being monitored, controlled, and/or being maintained based upon the process of selection. These flow through systems are normally concerned with an input only. However, batch systems that re-circulate liquids over and over again must be concerned with an ever changing solution that must be monitored and maintained periodically. If the processing chemicals do not change per batch of parts, then the chemical should still be checked every four hours of operation for their pH value. Although pH is the most important measure of a chemicals strength and life, it is not the only factor. Without going into elaborate testing equipment, most chemical solutions can be tested with hand-held electronic digital read out measuring meters. Some of these devices are not as accurate as others; therefore, some care must be taken for selecting a meter. Before selecting a meter know what are its parameters or sampling criteria and/or in what are the units or increments being read. Also check to see if there is a way to re-balance or zero out the meter or is there a pre dip solution to get a proper base line correction. Lastly, there is care and maintenance of the meter to consider. The simplest way to monitor a solution is with litmus paper. However, most of these products are not very accurate and are not precise enough to use as a monitoring device. There is one company who makes a good quality, narrow range, of pH papers. This company makes a number of products that measure from 0 to 14 pH. Each paper strip measures a chemical solution range of 1.5 pH in step increments of 0.2 or 0.3, by using visual color code matching. Using this observation method, it is possible to be accurate to within .05 pH. Another tricolor product measures a wider range of pH values from 1 to 11 in whole pH units to the nearest .25 pH unit using this color code method.
  • 262. Chapter 13 - Liquid Systems 263 Fig. 94. Liquid Monitoring Devices The least expensive method for testing chemical solutions is by a variety of treated pH or litmus paper products. Sticks of paper can measure a pH range of 1.5 units in steps of .2 and .3 pH for accurate readings to within .05 pH of the chemical solution. Tricolor rolls can measure a range of 1 to 11 in whole units for readings to within .25 pH. For ion detection, liquid chemical reaction kits also use the color change or visual color principle against chart standards to determine the existing current test range of a chemical solution. There are also now a number of more costly small fountain pen size mechanical devices with either visual or digital read outs to perform these same tests. Filtration and degreasing or oil skimmers are also important in re-circulating systems. Filtration itself is a very complex science. Rather than go into a lot of detail on this subject, I will only say that we are primarily dealing with waste water that has a lot of large size heavy particulate and it will setting out of solution very quickly. That also means that for recirculating purpose, we do not need a great deal of high or fine quality water purification. In fact, such quality is uneconomical and a waste of money, unless we are talking about large volumes of liquid. Therefore, the biggest concern of a filter system is not to allow the recirculation pumping system to get jammed up with an accumulation of waste. Most mass finishing systems do not need pure, clear water for clean parts. Oils are another problem. In most cases, lubricants and oils float to the surface of the waste water. Although it spreads across the top surface of the waste water, it can be confined, directed, and controlled. If it is allowed to pass through most filtering systems, it will eventually screw up the filter system and stop it from working properly. The confinement of oils can be accomplished by a containment tank weir and then removed by a continuous wheel or belt that picks up and deposits the oil into a separate container. Other systems allow the confinement of the oils in a closed off area or spill area. All of these methods and/or removal devices require monitoring of proper liquid levels periodically. Anything in the solution that is not water will react or change a chemical product over a given period of time. The more debris or foreign particles in a solution the faster it will deteriorate. All of these factors or particulate weakens the strength of chemicals and are constantly inter reacting with one another. Therefore, the more contaminates that can be
  • 263. Chapter 13 - Liquid Systems 264 removed from a system while it is in use or in process, the better and longer the chemical compound will work. Alternative Processing Methods: As mentioned, beside wet processing there are dry organic mass finishing systems. Fine dry organic materials, or any fine grain material acts and behaves similar to water up to a point; however, the very nature and cellular form of organic material particles give them a rather interesting characteristics that allow them to clean by a slightly abrasive method. Their small size or upper limit size range allows it to flow just like water and as stated earlier, chemicals can be added in the same manner, but not proportionate, to organic materials as it can be added to water. The only thing that fine organic materials cannot do is dilute or dissolve materials; otherwise it behaves the same as water in mass finishing systems. Organic materials can get extremely small and they do become ineffective at a particle size range of under .010 to .020 in size unless used with other bulky materials. Certain inorganic materials around .010 to .050 can also be run as a dry process operation; however, dust can be a problem. A pretreatment can be added to some inorganic materials to control dusting, but it is still difficult to control both the cutting, glazing, and the dusting problem. Normally dry organic operating procedures are almost mandatory on parts smaller than a half inch diameter or square, because of the problems that water adhesion creates. Getting back to liquid systems, we talked about batching systems, closed loop recirculating systems, and flow through systems for controlling abrasion and cleaning of parts in mass finishing systems. Each of these systems have advantages and disadvantages and a lot depends on the machinery involved. However, because of government regulations, nearly all systems, even flow through are no longer flow through systems as they were known before. That is, nearly all systems are closed loop systems either dedicated to this specific equipment or product line or to the manufacturing plant as a whole. Even though most of the waste and by-products of mass finishing operations are harmless they do contain metals in solid and solution form which must be treated. If nothing else, the waste solids do behave like cement and they will eventually clog a drain system; therefore, proper maintenance is required and drain access should be considered during installation. A couple of thoughts might be appropriate here regarding how to improve the performance of liquids in special cases. Normally cost prohibits the implementations of these ideas, but you should be aware of them. It is possible to improve or speed up processing time and/or chemical reactions by using hot water instead of normal ambient tap water into mass finishing equipment. In closed systems, this occurs naturally to a point; however, in bigger open systems this does not occur. Also, deionized and distilled water has greater cleaning and penetrating abilities than tap water and can also be used to improve the cleanliness of the end product substantially.
  • 264. 265 Chapter 14 – Selection Guidelines & Cost Factors Waste Treatment: Let’s get back to the disposal of wastewater from mass finishing equipment operations. It is suggested that all liquid waste materials first enter a settling tank with baffles like all standard close loop systems. Because we are dealing mostly with inorganic materials, approximately 80 to 90% of the waste is heavy enough to settle out. Suspended solids in solution eventually accumulate at the bottom of the collection tank and these solids must be removed and disposed of in some fashion. When dealing with primarily precious metals this solid waste can be quite profitable. Most of the remaining liquid waste and contaminates must be filter or treated to comply with local, state, and federal regulations, before allowing it to be disposed of as run off to the environment or public sewer system. To help you comply with new rules and regulations, the following is a checklist for your review to seek approval for discharging effluent wastewater from mass finishing systems directly into a sewer system: Before contacting your local municipality, you should have the following information available for review. Waste Treatment Guidelines 1. 2. 3. 4. 5. 6. 7. 8. 9. Estimated number of gallons, both the minimum and maximum, to be discharged every 24 hours. Estimated cost of the water for that discharge. Determine water hardness level, if possible. Get a copy of standard municipal limits from sewer department. Get copy of municipal guidelines and/or submission form. If submission form does not list following, obtain information for: i. COD - Chemical Oxygen Demand ii. BOD - Biological Oxygen Demand iii. FOG - Fats, Oils, and Grease iv. SS Mg/L - Suspended Solids in milligrams per liter. OSHA approved MSDS sheet for media being used. OSHA approved MSDS sheet for chemical compound. OSHA approved MSDS sheet for materials being worked in mass finishing machine. 10. All of the above should be reviewed for compliance to standards plus any local regulations. 11. 12. Obtain or create typical wastewater sample. Submit sample to municipal sewer department. It is suggested that you may want to have an outside testing laboratory review sample first, before submitting to sewer department. This may eliminate any undo concerns or scrutiny by regulators.
  • 265. Chapter 14 – Selection Guidelines & Cost Factors 266 13. Install mass finishing equipment upon acceptance of effluent disposal by sewer authority. Set up and adjust water flow through settling tanks or filtration system. Check SS Mg/L. Adjust PH and chemical usage to help ensure bio-degradable breakdown of all waste products. 14. Establish a monitoring schedule for cleaning the system and disposal of the solid and liquid waste. Applications I have discussed guidelines for media selection earlier; however, I would like to cover some of the more common generalized guidelines concerning all mass finishing systems. They are as follows: Quick Guideline Briefs For Mass Finishing System Processing Rule #1. There are no hard and fast rules for achieving immediate good surface finishing results every time, unless a lot of information is known about the parts and the operations prior to mass finishing. Rule #2. All mass finishing equipment will work faster, more aggressively when the equipment is filled to its maximum working capacity or capacity so designated. Weight and pressure are the major factors for fast material removal. Note: Barrel systems cannot operate properly with a full barrel, there must be room for proper movement. Rule #3. To achieve the fastest, shortest time cycles, use the coarsest media possible that will get into all the areas that have to be worked without getting stuck or distorting the part. Rule #4. Normal procedure for media selection is as follows:  Ceramic media is used for ferrous metals.  Plastic media is used for non-ferrous metals.  Steel or porcelain media is used to achieve a bright shinny burnished finishes materials.  Dry treated organic media is used for smooth, polished mirror finishes on all materials. on all Rule #5. Extremely small or flat parts tend to stick together in a wet processes; therefore, they are better processed with dry abrasive mix products. Rule #6. Multiple step processing is recommended to remove the most amount of material in the shortest amount of time. Rule #7. The higher or lower the pH of the liquid chemical compound from 7.0 (neutral), the cleaner the parts and media; therefore the faster the deburring process will work. Also the more concentrated the chemical compound, the faster it will work up to a point where excessive foam will slow down or retard movement of the process. Rule #8. To achieve good clean looking parts, use an ample flow of liquid through the work chamber liquid system or use a filtered close loop system rather than to close loop batch
  • 266. Chapter 14 – Selection Guidelines & Cost Factors 267 parts. If a batch system is used, drain and rinse the parts and media the last 5 or 10 minutes of the processing cycle. Rule #9. Too much liquid and/or chemical will slow down deburring action, but maybe useful to reduce or cushion part on part contact or for burnishing operations where the chemical is very important. Rule #10. To achieve a fast bright finish on part, use a heavy non-abrasive burnishing media after deburring. Rule #11. To achieve the finest, smoothest, mirror finish and lowest RMS use a dry organic polishing media after deburring. Most chemical compound additives contain inhibitors that will protect parts for a short period of time, maybe 24 hours, but some parts need additional protection. Rule #12. All parts should be cleaned and protected as soon as possible after processing to prevent oxidation. I have tried to emphasize in rule #1 the importance of knowing as much as possible about the part or parts prior to the finishing process. Maybe we should create a check list of things that should be known that can effect part finishes and determine which finishing method is best to use. The following is such a list, but is not the total list, because there are other factors which in turn are dependent upon the finished product itself. Some of the information required here is the same as that above; however, the above information relates more to equipment than the actual processing of that equipment. Required Part Information for Proper Processing 1. What is the part made out of? A. Ferrous metal B. Non-ferrous metal C. Plastic D. Composite E. Organic F. Other 2. What is the hardness of the material? 3. How was it made? A. Cast or molded B. Forged C. Machined D. Sheet 4. What is the weight of the part or cubic foot of parts? 5. How big or small is the part? 6. What quantity of parts have to be processed?
  • 267. Chapter 14 – Selection Guidelines & Cost Factors 268 7. What time cycle is required? 8. What is the configuration or part volume? 9. Are there any interior dimension or recesses? A. What is the smallest I.D. Dimension? B. Does the part have any thin material areas under .020? 10. What is the desired finish? A. Part needs to be deburred only B. Part has to be chemically treated C. Part has to be painted D. Part has to be polished E. Part has to be protected against oxidation only 11. What is the existing surface finish? 12. Are there any tight measurement tolerance requirements? 13. Are there any cost restraints? 14. What equipment , if any, is available? 15. Were there any chemical coolants or lubricants used to manufacture part? 16. How long have parts sat idle before required surface finishing? 17. Has oxidation of part started to occur? 18. Were parts subject to any gases or dust? 19. Can or have parts been subject to extreme temperatures? 20. Will temperature effect part? 21. Are there any problems using chemicals to process part? 22. Is contamination a problem in processing? In addition to these mass finishing guidelines for processing and part information, there is still another list needed for equipment requirements for the end customer. This list takes production needs into account more than the part or the process. The first thing one needs to do is analyze the needs of customer or end user for mass finishing equipment. That is, let’s take a look at what is normally needed to make a logical and reasonable decision as to what is needed in the way of equipment, media, and compound necessary to accomplish a specific task of mass finishing. Again, there may be some repeated items from the above lists here. The following are some guidelines for determining equipment needs:
  • 268. Chapter 14 – Selection Guidelines & Cost Factors 269 Equipment Requirements 1. What is the size of the part to be worked? Length, width, and height? 2. What is the weight of the part? 3. What material is the part made from? Metal, plastic, composite, other? 4. What quantity has to be processed? Per year, per month, per lot, per shift, per day, per hour, other? 5. What is the basic part function? 6. Burr requirement: Slight edge break, remove sharpness, remove burr completely, burr removal plus edge break, other? 7. Finishing requirement: Smooth only, specific RMS, bright, mirror finish, other? 8. Will part be painted or plated? 9. Critical tolerance considerations: None, corner and edges, holes, diameter or thickness, other? 10. Other parts considered for this processing? 11. Mixed metals? 12. Current needs? 13. Future needs? 14. Cost limitations? 15. Electrical power requirements? Once these questions have been answered an intelligent engineer maybe able to make a proper recommendation on equipment, media supplies, and compound to do mass finishing. However, if there are monetary limitations or there is a need for future planning to acquire new or additional equipment and supplies, then an operating cost estimate might have to be prepared. The following are some guidelines for determining estimated costs:
  • 269. Chapter 14 – Selection Guidelines & Cost Factors 270 OPERATION COST ESTIMATE* Parts: Produced Required DATE per shift ______________________ Company per hour ______________________ Part # per month ___________________ per ____________________ ________________________________________________________________________ Part Length Actual Displacement______Cu. Inches Part Width Indicate # of parts________Cu. Feet Part Height Working # of parts* _______Cu. Feet Part Weight Cu. Ft. pts. in machine______Cu. Feet Number of parts in batch________Qty *80%of Indicated # of parts. Ratio of media to parts Machine Used:______________________________ Capacity________Cu. Feet Machine hourly cost(See Table Below) Machine cost /hour Power Cost__________Horsepower at $.065† per HP hour Compound cost at __________ per ounce per cu. ft. Media Used:_________________________________________________________ Media in machine__________ Cu. Ft. Weight per Cu. Ft.__________ Pounds in machine_________ Lbs. Cost per pound__________ Cost media in machine___________ Attrition rate per hr.__________% MEDIA COST / HR.____________________ TOTAL MACHINE HOURLY COST _______ Load Cost: Load Process Time_____Hours______ minutes __________ Labor Rate___________Per Hour X Labor Rate_____ minutes __________ TOTAL COST / LOAD __________ TOTAL COST / PART __________ TOTAL COST / 1,000 PARTS. __________ NOTE 1: The information contained on this page are also available on a Windows 95 computer program available upon request from author’s company. All numbers appearing to the right after the solid line under the part description are automatically calculated by the program. For those who do not have the program, the following description explains in better detail what these figures mean. †Based on Michigan job shop data in Michigan in 2000. Results will vary, depending on local electric power rates.
  • 270. Chapter 14 – Selection Guidelines & Cost Factors 271 After part length, width, and height are multiplied, the total is divided by 1728 to get the actual displacement in cubic inches. In the program, parts per cubic inch are rounded off to one tenth. On the computer program, it is a 5 digit number. The figure from this calculation is then divided into 1728 to get the indicated number of parts per cubic foot. Now, parts do not and should not fit or stack neatly into a mass finishing work chamber system; therefore, an 80% figure of the indicated number of parts is used to get a good, free flowing working number of parts. The ratio of media to parts is an arbitrary number based upon what kind of finishing requirements you want to achieve. I usually use a percentage of media to parts; however, most large machine systems use a ratio to determine volume displacement. So, for abrasive deburring instead of 60% media to 40% parts, this equates to about a 3.5 : 1 ratio of media to parts. To convert percentage to ratio or vice–versa add the total number of both halves of a ratio and divide into 100. For polishing this 90% media to 10% parts becomes about 9 : 1 ratio. Based upon the arbitrary ratio you need, this number is divided into the size of the machine system you have, need to have, or expect to have for future needs. So, if you have a 25 cubic foot machine and you have a 4 : 1 ratio of media to parts, the function of this ratio is 5 and you divide that into 25 to get the cubic foot of parts in the machine. (As an added note here, most of this book talks about percentages rather than ratio. Therefore, to covert either percentage to ratio or vice-versa, take the function number and divide it into 100 to find out what the number one equals.). To get the total number of parts in the batch or load capacity per processing cycle, you multiple the number, in this case 5 times the working number of parts per cubic foot. NOTE 2: Machine hourly cost figures below are based upon averages computed over 2,500 hours of machine operation per year and include: rent, heat, light, insurance, supervision, and general overhead. A depreciation rate of five years and an average maintenance costs were also used. To be more accurate, you may use the following estimate sheet to compute actual costs. All Vibratory Equipment: Machine hourly cost rate* 1 cu. ft. includes screen and reloading accessories…………………….. $ 0.50 2 cu. ft……………………………………………………………………… $ 0.58 3 cu. ft……………………………………………………………………… $0 .93 5 cu. ft……………………………………………………………………… $ 1.40 10 cu. ft……………………………………………………………………… $ 2.23 15 cu. ft……………………………………………………………………… $ 3.36 20 cu. ft……………………………………………………………………… $ 4.45 25 cu. ft……………………………………………………………………… $ 5.57 35 cu. ft……………………………………………………………………… $ 6.36 *Based on Michigan job shop data in Michigan in 2000. Results will vary, depending on local electric power rates.
  • 271. Chapter 14 – Selection Guidelines & Cost Factors 272 To determine the hourly machine cost, you can use the figures provided under NOTE 2, or calculate them on the following spreadsheet. To use the later requires yearly cost figures and accounting numbers for depreciation. To arrive at the final cost figure is a simple straight forward calculation. Enter this number under machine coast per hour. Power cost is based upon the horsepower of the machine system selected. Again, this number can be calculated from your existing records, or it can be gotten from your local power supplier, or you can use the figure which is provided above of $.065 per horsepower per hour. The compound cost figure is based upon the following information. For this figure, a common compound use rate for processing is one ounce per gallon of water. The displacement or size of the machine. Example: 20 cu. ft.= 20 gallons per hour. Divide the cost of the compound by 128 ounces to get the cost of compound per ounce per cubic foot, then multiply this figure to get the machine cost per hour. Media selection is important as mentioned in another section of this book. Your selection of a composition, size and shape, pretty well locks you into a lot of the following information. The pound in 50-pound boxes, which is standard packaging, normally sells media and sometimes this equates to about 1 cubic foot of media. The latter information is only a rough estimate and should not be used in these calculations. Media capacity may be slightly difficult to determine because of variable standards also mentioned elsewhere in this book. That means that the size of the machine is not the media capacity of the machine; therefore, get that capacity information from the equipment manufacturer. Example: A 20 cu. ft. machine at a normal 3 : 1 ratio of deburring media to parts equals 15 cubic feet of media in the machine. Multiple this capacity figure times the weight of the media per cubic foot, which is normally given by the supplier or manufacturer, to get pounds in the machine. Multiply the pounds in the machine by the cost per pound to get the cost of media in the machine. The Attrition rate per hour percentage is based upon a series of tables enclosed, see NOTE 3, supplied by the manufacturers of the media. These are figures from the most common suppliers of media. However, this does not have all of the suppliers. NOTE 3: The following comparison chart is a composite of information provided by manufacturers as to the wear characteristic of their media. Most of the figures were derived from tests from a high energy Harperizer machine system; however, some tests were also conducted in vibratory equipment. Unfortunately, that means that the results may not be 100% comparable because we are not comparing apples and apples. Also the equivalent compositions are just that, they are approximately the same , not exactly the same. However, this is the best we can do to arrive at reasonable figures. Again, there is no one standard or central organization which can make these determinations.
  • 272. Chapter 14 – Selection Guidelines & Cost Factors 273 Attrition Rate Chart for Media Abrasive Finishing (Fortune) Ultramatic Composition Composition Rate Washington Mills Rate Composition Wisconsin Porcelain Rate Composition Rate AX – 90 .3 LL .2 D – 20 .3 AX - 65 .4 MC .4 D – 30 .4 XC .4 AH - 41 1.0 FC .6 D - 40 1.3 H 1.3 AX – 44 .1 D - 10 .1 F .1 CS - 46 .6 GC .7 C .3 SC .4 D - 50 .44 N .001 HD .1 I 40 .02 XB .005 XM UL H – 33 .6 .4 F – 36 LW .3 SP – 3 .003 .2 F – 33 .5 .3 .5 Once the machine operating costs are known, one can calculate the hourly machine costs or general administrative costs of operating this equipment. Most of this costs are not specifically related to the equipment, but the overall costs of one’s business and labor. That means that even though the equipment or machine system costs the same for everyone buying that same system, it will have different hourly operating costs because of the company itself.
  • 273. Chapter 14 – Selection Guidelines & Cost Factors 274 Determination of Machine Hourly Cost Rate A. Floor Space Costs Add costs per year for floor area where machine is located Cost per year Rent $__________ Heat $__________ Light $__________ Insurance $__________ General Overhead $__________ Supervision $__________ Total Cost of Department Floor Space Total $_____ X Sq. Ft. needed for operation = Floor Space Cost Per Year Sq. Ft. in department B. Depreciation and Maintenance Total Cost of Equipment $__________ Divided by _____ Years of Depreciation $__________ Maintenance Cost Per Year $__________ MACHINE HOURLY COST RATE Total of A & B above = $_________ Hours Used Per Year________= $ ________ Per Hour Well, that concludes deburring and mass finishing systems to a great degree. I will not say that this finalizes future possibilities. There are a lot of relatively new systems discussed earlier in this book and just as mass finishing systems have evolved into basically 3 generations of equipment, so it is possible that these other technologies may also. The simplest system for deburring would be the best, because generally speaking no one likes to do deburring or polishing work, especially by hand. Most companies or supervision think and practice a negative bias toward deburring systems. That is, they put their least skilled workers on this task or equipment because it is generally dirty work supposedly requiring no special talent. As you can see from the amount of material we have covered in this book, this is not a true statement, nor is it far from being idiot proof! You would think that the time and money spent to achieve the making of precision parts should deserve some attention and expense for a good and proper finish. That is, some parts cost literally hundreds or thousands of dollars and yet they can be relegated to the most unskilled people and tools to do the final surface finishing. I think that is a potential for disaster. Hopefully, this book might help to shed some light on this profession and clean it up.
  • 274. Bibliography and Credits Bibliography and Credits Book Metal Finishing Guidebook and Directory Issue 98 & 99 January 1998 Volume 95, Number 1 & January 1999, Volume 97, Number 1 Articles: Polishing and Buffing by Al Dickman and Bill Millman Buffing Wheels and Equipment by Stanley P Sa xSurface Conditioning Abrasives by Jan Reyers Belt polishing by George J. Anselment Filament Brushing Tools for Surface Finishing Applications by Robert J. Stango Blast Finishing by Daniel Herbert Impact Blasting with Glass Beads by Robert C. Mulhall and Nicholas D. Nedas Mass Finishing Processes by David A. Davidson Seminar 5th International Conference on Deburring and Surface Finishing Copyright 1998 Deburring Technology International, Inc. San Francisco, CA. Sept. 1998 Turboabrasive Machining-Automated Technology for Finishing of Part Prof. Zinoviy I. Kremmen, St. Petersburg, Russia Advanced Abrasive Flow Technology Ralph Resnick, Extrudehone, Irwin, PA. Electropolish Deburring Peter Marcilese and John Stackhouse, Dynetics, Woburn, MA. Developments in High-Pressure Water Jet Deburring Klaus Berger, Daimler Benz, Stuttgart, Germany 275
  • 275. Bibliography and Credits 276 Contributors: Michael, Mark, & Scott Cantwell Finishing Associates Inc. 320 Constance Drive, Unit 2 Warminster, PA. 18974 David A. Davidson Pegco Process Labs Bartlett, NH 03812 James Randal , retired Jenex Corp. Chelsea, MI 48118 Bob Kramer 47 Chestnut Hill Rd. Roslyn, N.Y. 11576 George Bull Electrohone Technologies, Inc. P.O. Box 317 Crystal Lake, IL. 60039 Sam R. Thompson Retired, Ultramatic Equipment Corp. Wallingford, CT 06492 Stanley A. Mayer SMC Systems Inc. San Diego, CA 92117 Dave Arber Omni Finishing Systems Inc. 163 Railroad Drive Ivyland, PA. 18974 Dave Koster & Robert Schaeffer ThermoBurr 6310 Wall St. Sterling Heights, MI. 48312 Bill Neibiolo REM Chemicals, Inc. 325 West Queen St. Southington, CT. 06489 Mark Singer P.O. Box. 434 Morristown, NJ 08057 Vibrodyne 2853 Springboro West Dayton, Ohio 45439 Photo and Image Credits 3M Industrial Abrasives Div. 3M Center 223-6NW-01 St. Paul, MN 55144-1000 Fig. 16, Fig. 17, Fig. 28, Fig. 29, Fig. 30, Fig. 34 Abbott Ball Co. Illinois Railroad Ave. West Hartford, CT. 06133-0100 Fig. 91 Almco Inc. 902 E. Main St. Albert Lea, MN. 56007 Fig. 73, Fig. 80, Fig. 81 C & M Topline Manufacturing 5945 Daley St. Goleta, CA. 93117 Fig. 58 (bottom) CAE Ultrasonics PO Box 220 Jamestown, NY 14702 Fig. 46
  • 276. Bibliography and Credits Cryogenic Systems & Parts 3595 Cadillac Ave. Costa Mesa, CA 92626 Fig. 41 DEWALT Industrial Tool Co. 701 E. Joppa Road Baltimore, MD 21286 Fig. 3 Diston Corp 87 John Dretsch Sq. North Attleboro, MA 02760 Fig. 7, Fig. 54 Dreher Corp. 57 George Leven Dr. N. Attleboro, MA 02760 Fig. 93 Empire Abrasive Equipment Corp. 2101 West Cabot Blvd. Langhorne, PA. 19047 Fig. 4, Fig. 35, Fig. 36 Extrudehone 8075 Pennsylvania Ave. Irwin, PA. 15642 Fig. 47, Fig. 48, Fig. 49 Farr Mfg.& Engineering Co Williamstown WV. 21687 Fig. 14 Fill-Chem Inc. PO Box 90833 Raleigh, NC 27675 Fig. 94 277 Finishing Associates Inc. 1610 Republic Rd. Huntingdon Valley, PA. 19006 Fig. 6 (center and bottom), Fig. 64, Fig. 76, Fig. 77, Fig. 78, Fig. 79 Glen Mills Inc 395 Allwood Rd. Clifton, NJ 07012-1794 Fig. 74 Grav-l-Flo Corp. 400 Norwood Ave. Sturgis, MI 49091 Fig. 68, Fig. 69, Fig. 80, Fig. 81 Guyson Corp. of USA E.J. Grande Ind. Park Saratoga Springs, NY 12866-9044 Fig. 38 ICM Inc. 10630 S. Garfield Ave. South Gate, CA 90280 Fig. 44 Illinois Electro-Deburring 9393 Seymour Schiller Park, IL. 60176 Fig. 90 Jackson Lea 75 Progress Lane Waterbury, CT 06720-0071 Tables on page 67 and 68 Jenex Corporation 13550 Luick Drive Chelsea, MI 48118 Fig. 66, Fig. 90 Kersarge Peg Co.,Inc. P.O.Box 158 Bartlett, N.H. 03812 Fig. 92
  • 277. Bibliography and Credits Kmeech Corp. 1 Oak Hill Rd. Fitchburg, MA 01420 Fig. 53 Kramer Ind., Inc. 1189 Sunrise Highway Copiague, N.Y. 11726 Fig. 5, Fig. 58 (top), Fig. 10, Fig. 37, Fig. 55Fig. 57, Fig. 59, 0 L.A. Abrasive Products 400 Sibley Blvd. Harvey, IL 48209 Fig. 27 Metal Improvement Co. Inc. 10 Forest Ave. Paramus, NJ 07652 Fig. 43 MSC Industrial Supply Co. 75 Maxess Road Melville, New York 11747 Fig. 3 (top) Noga Engineering Ltd. PO Box 55 Schlomi, Israel 22832 Fig. 9 Norton Corp. Worcester, MA 01615-0008 Fig. 31, Fig. 32 Nova Finishing Systems, Inc. 1610 Republic Rd. Huntingdon Valley, PA 19006 Fig. 1, Fig. 6 (top left, side view drawing), Fig. 75 278 Osborn Brush 5401 Hamilton Ave. Cleveland, OH 44144-3997 Fig. 2, Fig. 11, Fig. 18, Fig. 19. Fig. 20, Fig. 21, Fig. 22 Rampart Finishing Equipment Co. 632 E. 152nd St. Cleveland, OH 44110 Fig. 58 Rose Training Systems Inc. 6161 Cochran Rd., Ste. 0 Solon, OH 44139 Roto-Finish 1600 Douglas Ave. Kalamazoo, MI. 49007 Fig. 6 (top right), Fig. 67, Fig. 72, Fig. 74 S.S. White Ind.Products Pennwalt 151 Old Brunswick Rd. Piscataway, N.J. 08854 Fig. 39, Fig. 40 Sommer & Maca Ind., Inc. 5501 West Ogden Ave. Cicero, IL 60806-3507 Fig. 2, Fig. 11, Fig. 12 Stanley P. Sax Corp. 101 South Waterman Detroit, MI 48209 Fig. 23, Fig. 24, Fig. 25, Fig. 26 Sugino Corp 1700 Penny Lane Schaumburg, IL 60173 Fig. 45 Surftran Bosch Group 30250 Strephenson Highway Madison Heights, MI. 48071 Fig. 8, Fig. 50 - Fig. 52
  • 278. Bibliography and Credits 279 Sweco, Inc. 8029 US Hwy. 25 Florence, KY. 41022-1509 Fig. 6 (top left), Fig. 60, Fig. 65, Fig. 74 USF Surface Preparation Group 1605 E. Hwy 34, Ste. A Newman, GA Fig. 4 The Wheelabrator Corp. 27 Amlajack Blvd. Shenandoah, GA. 30265 Fig. 42 Vapormatt Ltd. Rue a Chiens St. Sampson’s, Guernsey Channel Islands GY24AG Fig. 12, Fig. 44 Timesavers Mass Finishing Div. 5270 Hanson Court Minneapolis, MN. 55429-3111 Fig. 3 (bottom), Fig. 15 Tipton US Corp. 8411 Seward Rd. Hamilton, Ohio 45011 Fig. 12, Fig. 13, Fig. 70, Fig. 71 Turbo-Finish Corp. 25 Williamsville Rd. Barre, MA 01005 Fig. 82, Fig. 84 Ultramatic Equipment Corp. 8502 E. Via De Ventura #210 Scottsdale, AZ. 85258 Fig. 62, Fig. 63 Vibra Finish Co. 8491 Seward Rd. Hamilton, Ohio 45011 Fig. 90 VSM Abrasives Corp. 1012 E. Wabash St. O’Fallon, MO 63366-2774 Fig. 33 Washington Mills Ceramic Corp. 20 North Main St. North Grafton, MA. 01536 Fig. 89
  • 279. About the Author 280 About the Author Anthony (Tony) Kenton went to college at Indiana University, Bloomington, Indiana, and Temple University Philadelphia, PA. He worked for a number of manufacturing companies in engineering capacities before he entered sales. In the 1980’s he had a lot of hands on knowledge and experience in the finishing and abrasives industry. So, in 1988, with a lot of help from friends and business partners, he started his own company now called Nova Finishing Systems Inc. Originally this company made vibratory deburring machines he designed for small surface finishing applications. He has expanded this to include one registered separation patent and has acquired and now builds centrifugal deburring systems formally manufactured by R.N. Hutson Co. Mr. Kenton takes pride in the fact that he is constantly improving his products and designing new systems. In addition to being a leading innovator, he is a well published technical writer on abrasive and processing systems for the industry and has been featured in nearly all US trade publications. he is also an author, and respected consultant for the finishing industry. In this book, Evaluating Material Removal and Surface Modification Systems, he wants the reader to know as much as possible about options and alternatives on how to accomplish their desired end result. Mr Kenton not only designs equipment, but he has designed a classification system similar to the Dewey Decimal system for surface finishing. His book and system employs the KISS principle by reducing all processing methods into a total of six classifications based upon how energy is applied. A simplified equation of this principle is found on the front cover of his book, “The application of energy + pressure + hardness of media and material = the rate, amount, and time of material removal and surface modification.” ISBN - 978-0-615-85574-5 Evaluating Material Removal and Surface Modification Systems, by A.F. Kenton

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