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)

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Final evaluating materialremoval

  1. 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. 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. 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. 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. 5. 6 Bibliography and Credits .....................................................................................................................275 Book ...................................................................................................................................................................................... 275 Articles: ................................................................................................................................................................................ 275 Seminar ................................................................................................................................................................................ 275 Contributors: ....................................................................................................................................................................... 276 Photo and Image Credits ................................................................................................................................................... 276 About the Author ...................................................................................................................................280
  6. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 27. Chapter 2 - Classification 28 Fig. 1. Type 0 Systems Fig. 2. Type 1 System
  28. 28. Chapter 2 - Classification 29 Fig. 3. Type 1 Systems, continued
  29. 29. Chapter 2 - Classification 30 Fig. 4. Type 2 Systems
  30. 30. Chapter 2 - Classification 31 Fig. 5. Type 3 Systems
  31. 31. Chapter 2 - Classification 32 Fig. 6. Type 3 Systems, continued
  32. 32. Chapter 2 - Classification 33 Fig. 7. Type 4 Systems
  33. 33. Chapter 2 - Classification 34 Fig. 8. Type 5 Systems
  34. 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. 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.

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