Introduction to manufacturing process

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This Presentation gives the information of Manufacturing process-1 of Mechanical Engineering course as per VTU Syllabus. Please write to me at: hareeshang@gmail.com for suggestions and criticisms.

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Contents are taken from several text books and compiled for academic purposes only. Author doesn't hold the copyright for the contents used in this presentation.

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Introduction to manufacturing process

  1. 1. 5/20/2016 1Hareesha N G, Dept of Aero Engg, DSCE
  2. 2. Unit-1: Introduction to manufacturing process • Casting Process: Introduction : Concept of Manufacturing process, its importance. • Classification of Manufacturing processes. Introduction to Casting process & steps involved. • Varieties of components produced by casting process. Advantages & Limitations of casting process. • Patterns: Definition, functions, Materials used for pattern, various pattern allowances and their importance. Classification of patterns. • Binder: Definition, Types of binder used in moulding sand. • Additives: Need, Types of additives used. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 2
  3. 3. Factors to be considered for selecting a production process a) Shape and size to be produced - For products with simple shape, machining is best suited. But for complex and intricate shapes, casting is preferred. The size of the product is also an important factor. For example, 'long' products such as rails or 'thin' products such as car-body panels can be best made by forming process compared to others. (b) Quantity to be produced - Both machining and casting can be used for producing large quantity products, but are not suitable for small quantity products, as they are not economical. (c) Type of material - Materials possess various properties like ductility, hardness, toughness, brittleness etc. Hard materials cannot be machined easily. Brittle materials cannot be mechanically worked (Forming process). In such cases, casting is preferred. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 3
  4. 4. Factors to be considered for selecting a production process (d) Surface finish and dimensional accuracy - Casting with expendable moulds does not yield good surface finish. However," if casting process is selected, it should be followed by machining process to obtain the desired surface finish and dimensional tolerance. (e) Quality and property requirements - A defect-free product with specific properties serve its purpose for long life. Properties of cast material are generally less when compared to that of mechanically worked materials. Also, casting gives a lot of defects. Hence, a process that gives better properties and quality should be selected. (f) Cost of the product - Customers often demand for products with more features and performance at reduced prices. Hence, a low cost production process should be selected, but at the same time, see that no compromise is made in terms of quality. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 4
  5. 5. CASTING PROCESS 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 5
  6. 6. Terms involved in casting 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 6
  7. 7. Terms involved in casting process • Mould box (flask) : It is usually a metallic frame used for making and holding a sand mould. The mould box has two parts: the upper part called 'cope', and the lower part called 'drag'. • Parting line/parting surface: It is the zone of separation between cope and drag portions of the mould in sand casting. • Sprue: It is vertical passage through which the molten metal will enter the gate. • Pouring basin: The enlarged portion of the sprue at its top into which the molten metal is poured. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 7
  8. 8. Terms involved in casting process • Gate/ingate: It is a short passage way which carries the molten metal from the runner/ sprue into the mould cavity. • Riser: A riser or feed-head is a vertical passage that stores the molten metal and supplies (feed) the same to the casting as it solidifies. • Gate/ingate: It is a short passage way which carries the molten metal from the runner/ sprue into the mould cavity. • Riser: A riser or feed-head is a vertical passage that stores the molten metal and supplies (feed) the same to the casting as it solidifies. • Mould cavity: The space in a mould that is filled with molten metal to form the casting upon solidification. • Core: A core is a pre-formed (shaped) mass of sand placed in the mould cavity to form hollow cavities in castings. • Core print: It is a projection attached to the pattern to help for support and correct location of core in the mould cavity.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 8
  9. 9. STEPS INVOLVED IN MAKING A CASTING The basic steps in making a casting are: (a) Pattern making (b) Mould preparation (including gating and risering) (c) Core making (d) Melting and Pouring (e) Cleaning and Inspection 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 9
  10. 10. a) Pattern making • A pattern is a replica of the object to be cast. • It is used to prepare a cavity into which the molten metal is poured. • A skilled pattern maker prepares the pattern using wood, metal, plastic or other materials with the help of machines and special tools. • Many factors viz., durability, allowance for shrinkage and machining etc., are considered while making a pattern. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 10
  11. 11. b) Mould preparation • Mould preparation involves forming a cavity by packing sand around a pattern enclosed in a supporting metallic frame called 'flask' (mould box). • When the pattern is removed from the mould, an exact shaped cavity remains into which the molten metal is poured. • Gating and risering are provided at suitable locations in the mould. – Gating - Passage through which molten metal flows and enter the mould cavity. – Risering - A reservoir of molten metal connected to the mould cavity to supply additional metal so as to compensate for losses due to shrinkage, as the metal solidifies. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 11
  12. 12. c) Core making • In some cases, a hole or cavity is required in the casting. • This is obtained by placing a core in the mould cavity. • The shape of the core corresponds to the shape of the hole required. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 12
  13. 13. d) Melting and Pouring • Metals or alloys of the required composition are melted in a furnace and poured into the mould cavity. • Many factors viz., temperature of molten metal, pouring time, turbulence etc., should be considered while melting and pouring. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 13
  14. 14. e) Cleaning and Inspection • After the molten metal has solidified and cooled, the rough casting is removed from the mould, cleaned and dressed. • This involves removing cores, adhered sand particles, gating and risering systems, fins, blisters etc., from the casting surface. • then sent for inspection to check for dimensions or any defects like blow holes, cracks etc. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 14
  15. 15. Components Produced by Casting Process • Casting is the first step and the primary process for shaping any material. • All materials have to be cast before it is put to use. • The ingots produced by casting process are used as raw material for secondary processes like machining, forging, rolling etc. • More than 90 % of all manufactured goods and capital equipment use castings for their manufacture. • To list the components produced by casting is an endless process. A few major components produced by casting are given below. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 15
  16. 16. Components Produced by Casting Process • Automotive sector - Nearly 90 % of the parts in automobiles are- manufactured by castings. A few parts include brake drum, cylinder, cylinder linings, pistons, engine blocks, universal joints, rocker arm, brackets etc., • Aircraft - Turbine blades, casing etc. • Marine propeller blades. • Machining - Cutting tools, machine beds, wheels and pulleys, blocks and table for supports etc. • Agriculture and rail road equipments. • Pumps and compressors frame, bushings, rings, pinion etc. • Valves, pipes and fittings for construction work. • Camera frames, parts in washing machine, refrigerators and air- conditioners. • Steel utensils and a wide variety of products. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 16
  17. 17. Advantages of casting process • Large hollow and intricate shapes can be easily cast. • Quick process, and hence suitable for mass production. • No limit to size and shape. Parts ranging from few millimeters to meters and few grams to tons can be cast efficiently and economically. • Better dimensional tolerances and surface finish can be obtained by good casting practice. • Castings exhibit uniform properties in all the directions - longitudinal, lateral and diagonal. • The casting process is usually the cheapest process. • Unrelieved internal stresses are absent in cast components. • Certain metals and alloys can be manufactured by means of casting only, e.g., Phosphor-Bronze.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 17
  18. 18. Limitations of casting process • Presence of defects in cast parts is a major disadvantage. • Casting process is not economical for small number of parts. • Properties of cast materials are generally inferior when compared to those made by machining or forging process. • Casting process mostly deals with elevated temperatures. • There are limitations regarding thin sections. • Casting process is not suitable for very small number of components. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 18
  19. 19. INTRODUCTION TO PATTERN MAKING • A pattern is a mold forming tool in the hands of foundry men. • A pattern is a model or the replica of the object to be cast. • Except for the various allowances a pattern exactly resembles the casting to be made. • A pattern is required even if one object has to be cast. • A pattern may be defined as a model or form around which sand is packed to give rise to a cavity known as mold cavity in which when, molten metal is poured, the result is the CAST OBJECT. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 19
  20. 20. Difference between pattern and casting • The main difference between a pattern and the casting is their dimensions. • A pattern is slightly larger in size as compared to the casting, because a pattern, – carries Shrinkage allowance, it may be of the order of 1 to 2 mm/ 100 mm. – is given a Machining allowance to clean and finish the required surfaces. – carries a Draft allowance of the order of 1 and 3 degrees for external and internal surfaces respectively – carries core prints. • A pattern may not have all holes and slots which a casting will have. Such holes and slots unnecessarily complicate a pattern and therefore can be drilled in the casting after it has been made. • A pattern may be in two or three pieces whereas a casting is in one piece. • A pattern and the casting also differ as regards the material out of which they are made. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 20
  21. 21. Functions of a patterns • A pattern prepares a mold cavity for the purpose of making a casting. • A pattern may contain projections known as core prints if the casting requires a core and need to be made hollow. • Runner, gates and risers (used for introducing and feeding molten metal to the mold cavity) may form a part of the pattern. • A pattern may help in establishing locating points on the mold and therefore on the casting with a purpose to check the casting dimensions. • Patterns establish the parting line and parting surfaces in the mold. • A pattern may help position a core (in case a part of mold cavity is made with cores), before the molding sand is rammed. • Patterns that are properly made and having finished and smooth surfaces, reduce casting defects. • Properly constructed patterns minimize overall cost of the castings. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 21
  22. 22. Pattern materials • The following factors assist in selecting proper pattern material: The number of castings to be produced. Metal patterns are preferred when the production quantity is large. The desired dimensional accuracy and surface finish required for the castings. Nature of molding process i.e., sand casting, permanent mold casting, shell molding, investment casting etc. Method of molding i.e., hand or machine molding. Shape, complexity and size of the casting. Type of molding materials i.e., sand etc. The high probability of changing the casting and hence the pattern in near future. Selection of pattern materials 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 22
  23. 23. Materials for making patterns • Patterns may be constructed out of the following materials. (a) Wood (b) Metal (d) Plastic (d) Plaster (POP) (e) Wax 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 23
  24. 24. WOOD • The most common materials for making patterns for sand casting is the wood. Advantages – Inexpensive. – Easily available in large quantities. – Easy to machine and to shape to different configurations and forms – Easy to join to acquire complex and large pattern shapes – Light in weight – Easy to obtain good surface finish – Wooden patterns can be preserved for quite long times with the help of suitable wood preservatives. Limitations – Wooden patterns are susceptible to shrinkage and swelling. – They possess poor wear resistance. – They are abraded easily by sand action. – They absorb moisture, consequently get deformed and change shape and size. – They cannot withstand rough handling. – They are weak as compared to metal patterns.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 24
  25. 25. Metal • Metal patterns are employed where large number of castings have to be produced from the same patterns. • Metal patterns are cast from wooden patterns. • The different metals and alloys used for making patterns are, – Aluminium and Aluminium alloys – Steel – Cast Iron – Brass – White Metal 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 25
  26. 26. Advantages of Metal Patterns – Unlike wooden patterns, they do not absorb moisture. They retain their shape. – They are more stronger and accurate as compared to wooden patterns. – They possess life much longer than wooden patterns. – They can withstand rough handling. – They do not distort – They possess greater resistance to abrasion. They have accurate dimensional tolerances. They are far stable under different environments. – It is easy to obtain smooth surface finish. – They possess excellent wear resistance and strength to weight ratio. Limitations of Metal Patterns – Expensive as compared to wood patterns. – Are not easily repaired e.g. (Aluminium patterns). – Ferrous patterns get rusted. – They (ferrous patterns) are heavier than wooden patterns, – They cannot be machined so easily as wooden ones. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 26
  27. 27. Plastic • Advantages – Durable – Provides a smooth surface. – Moisture resistant. – A plastic pattern does not involve any appreciable change in its size or shape. – Lightweight. – Wear and corrosion resistant. – Provides good surface finish. – It possesses low solid shrinkage. • Limitations – Plastic patterns are fragile and thus light sections may need metal reinforcements. – Plastic patterns may not work well when subject to conditions of severe shock as in machine moulding.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 27
  28. 28. PLASTER • Advantages – can be easily worked by using wood working tools. – Intricate shapes can be cast without any difficulty. – It has high compressive strength (up to 285 kg/cm2) • Disadvantages – Can be used for small castings only • Plaster Patterns Material: Plaster patterns may be made out of Plaster of Paris or Gypsum cement. • Applications: Plaster is used for making (i) Small and intricate patterns, and (ii) Core boxes. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 28
  29. 29. WAX • Advantages Wax patterns provide very good surface finish They impart high accuracy to the castings. After being molded, the wax pattern is not taken out of the mold like other patterns; rather the mold is inverted and heated; the molten wax comes out and/or is evaporated. Thus there is no chance of the mold cavity getting damaged while removing the pattern. • Applications • Wax patterns find applications in Investment casting process. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 29
  30. 30. PATTERN ALLOWANCES • A pattern is always larger in size as compared to the final casting, because it carries certain allowances. • The various pattern allowances are below (a) Shrinkage or contraction allowance. (b) Machining or Finish allowance. (c) Draft or Taper allowance. (d) Distortion or camber allowance. (e) Shake or rapping allowance. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 30
  31. 31. Shrinkage Allowance • Almost all cast metals shrink or contract volumetrically after solidification and therefore to obtain a particular sized casting, the pattern is made oversize by an amount equal to that of shrinkage or contraction. • Different metals shrink at different rates because shrinkage is the property of the cast metal or alloy. • The metal shrinkage depends upon • The cast metal or alloy. • Pouring temperature of the metal or alloy. • Casting dimensions (size). • Casting design aspects. • Molding conditions (i.e., mold materials and molding methods employed). • Cast iron poured at higher temperatures will shrink more than that poured at lower temperature. • Wood patterns used to make metallic patterns are given double allowance; one for the shrinkage of the metal of the pattern and the other for that of metal to be cast. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 31
  32. 32. Machining Allowance • A casting is given an allowance for machining, because – Castings get oxidized in the mold and during heat treatment; scales etc., thus formed need to be removed. – It is intended to remove surface roughness and other imperfections from the castings. – It is required to achieve exact casting dimensions. • How much extra metal or how much Machining allowance should be provided, depends upon: • Nature of metal i.e., ferrous or non-ferrous. Ferrous metals get scaled whereas non-ferrous ones do not. • Size and shape of the casting. Longer castings tend to warp and need more material (i.e., allowance) to be added to ensure that after machining the casting will be alright. • The type of machining operation (i.e., grinding, turning, milling, boring etc.) to be employed for cleaning the' castings. Grinding removes much lesser metal as compared to turning. • Casting conditions i.e., whether casting conditions result in a rough casting or a semi-finished one. Casting conditions include the characteristics of mold-materials etc. • Molding process employed. Die casting produces parts which need little machining (allowance) whereas sand-casting, require more machining allowance. • Number of cuts to be taken. Machining allowance is directly proportional to the number of cuts required for finishing the casting. • The degree of surface finish desired on the cast part.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 32
  33. 33. Draft or Taper Allowance • It is given to all surfaces perpendicular to the parting line. • Draft allowance is given so that the pattern can be easily removed from the molding material tightly packed around it without damaging the mold cavity. • The amount of Taper depends upon – Shape and size (length) of the pattern in the depth direction in contact with the mold cavity. – Molding method. – Mold materials. • Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 33
  34. 34. Fig. shows two patterns — one with taper allowance and the other without it. It can be visualized that it is easy to draw the pattern having taper allowance, out of the mold without damaging mold walls or edges. Taper on external surfaces = 10 to 25 mm/metre. Taper on internal surfaces = 40 to 65 mm/metre, 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 34
  35. 35. Distortion Allowance • A Casting will distort or warp if: – it is of irregular shape, – all its parts do not shrink uniformly i.e., some parts shrink while others are restricted from doing so, – it is U or V-shaped, – it has long, rangy arms as those of the propeller strut for the ship, – it is a long flat casting, – the arms possess unequal thickness, – one portion of the casting cools at a faster rate as compared to the other, etc. • Distortion can be practically eliminated by providing an allowance and constructing the pattern initially distorted i.e., outsize in the opposite direction so that the casting after cooling neutralizes the initial distortion given on the pattern and acquires the correct shape. • The amount of distortion allowance may vary from 2 to 20 mm depending upon the size, shape and material of the casting. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 35
  36. 36. Shake Allowance • A pattern is shaken by striking the same with a wooden piece from side to side. This is done so that the pattern is loosened a little in the mold cavity and can be easily removed. • In turn, therefore, shaking enlarges the mold cavity which results in a bigger sized casting. • Shake allowance is normally provided only to large castings because it is negligible in case of small castings and is thus ignored. • The magnitude of shake allowance can be reduced by increasing the taper. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 36
  37. 37. TYPES OF PATTERNS 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 37
  38. 38. • For selecting a particular kind of pattern for making a casting, one may consider the following points: – Quantity of castings to be produced. – The size and the complexity of the shape of the casting to be produced. – Type of molding method to be used (i.e., hand or machine molding). – Problems associated with the molding operation such as withdrawing the pattern from the mold etc. – Other difficulties resulting from poor casting design or pattern design. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 38
  39. 39. • The different types of patterns commonly used are: – One piece(Solid) pattern – Split pattern – Loose piece pattern – Match plate pattern – Cope and Drag pattern – Sweep pattern – Gated pattern – Skeleton pattern – Follow board pattern. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 39
  40. 40. One Piece (solid) Pattern 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 40
  41. 41. One Piece (solid) Pattern • It is the simplest type of pattern. • As the name suggests the pattern is made from one piece and does not contain loose pieces or joints. • It is inexpensive. • It is used for making a few large size simple castings • One piece pattern is usually made up of wood or metal depending upon the quantity of castings to be produced. • For making the mold, one piece pattern is accommodated either in the cope or in the drag. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 41
  42. 42. Split Pattern • Patterns of intricate (shaped) castings cannot be made in one piece because of the inherent difficulties associated with the molding operations (e.g. withdrawing the pattern from the mold etc.) , such patterns are, then, made as split or two piece patterns. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 42 The upper and the lower parts of the split pattern are accommodated in the cope and drag portions of the mold respectively. Dowel pins are used for keeping the alignment between the two parts of the pattern. The parting (surface or) line of the pattern forms the parting (surface or) line of the mold. Patterns for still more intricate castings are made in more than two pieces for facilitating their molding and withdrawing. A pattern having three pieces will require a three piece flask for the molding purposes
  43. 43. Loose Piece Pattern • Certain patterns cannot be withdrawn once they are embedded in the molding sand. Such patterns are usually made with one or more loose pieces • Pieces for facilitating their removal from the molding box and are known as loose piece patterns. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 43 Loose parts or pieces remain attached with the main body of the pattern, with the help of dowel pins. The main body of the pattern is drawn first from the molding box and thereafter the loose parts are removed, the result is the mold cavity. Loose piece patterns involve more labour and consume more time in the molding operation. Loose Piece
  44. 44. Match Plate Pattern • A match plate pattern consists of a match plate, on either side of which each half of (a number of) split patterns is fastened. • A number of different sized and shaped patterns may be mounted on one match plate. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 44 The match plate with the help of locator holes can be clamped with the drag. The match plate has runner and gates also attached with it. After the cope and drag have been rammed with the molding sand, the match plate pattern is removed from in between the two (i.e., cope and drag.)
  45. 45. Match Plate Pattern • Cope and drag are then assembled and this completes the mold. • Patterns, match plate, runner and gates — all may be made up of aluminium, because it is light and relatively inexpensive. • Match plate patterns are normally used in machine molding. • Match plate patterns are preferred for producing small castings on mass scale. • They produce accurate castings and at faster rates. • Piston rings of I.C. engines are produced with the help of match plate patterns.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 45
  46. 46. Sweep Pattern • A sweep pattern is just a form made on a wooden board which sweeps the shape of the casting into the sand all around the circumference. The sweep pattern rotates about the post. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 46 Once the mold is ready, sweep pattern and the post can be removed Sweep pattern avoids the necessity of making a full, large circular and costly three dimensional pattern. Making sweep pattern saves a lot of time and labour as compared to making a full pattern. A sweep preferred for producing large castings of circular sections and symmetrical shapes. The manufacture of large kettles of cast iron requires a sweep pattern. Image courtesy: METAL CASTING AND JOINING By K. C. JOHN
  47. 47. Gated Pattern • Gated patterns are usually made of metal which increases their strength and reduces the tendency to warp. • The sections connecting different patterns serve as runner and gates. This facilitates filling of the mold with molten metal in a better manner at the same time eliminates the time and labour otherwise consumed in cutting runners and gates. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 47 A gated pattern can manufacture many castings at one time and thus it is used in mass production systems. Gated patterns are employed for producing small castings.
  48. 48. Skeleton Patten • A skeleton pattern is the skeleton of a desired shape. The skeleton frame is mounted on a metal base. • The skeleton is made from wooden strips and is thus a wooden framework. • The skeleton pattern is filled with sand and is rammed. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 48 A strickle (board) assists in giving the desired shape to the sand and removes extra sand. If the object is symmetrical like a pipe, the two halves (of the pipe) can be molded by using the same pattern and then the two molds can be assembled before pouring the molten metal. Skeleton patterns are employed for producing a few large castings. A skeleton pattern is very economical as compared to a solid pattern, because it involves less material costs. Castings for turbine castings, water pipes, channels, etc., are made with the help of skeleton patterns.
  49. 49. Follow Board Pattern • A follow board is a wooden board and is used for supporting a pattern which is very thin and fragile and which may collapse under the pressure when the sand above the pattern is being rammed. • With the follow board support under the weak pattern, the drag is rammed, and then the follow board is withdrawn. • The rammed drag is inverted, cope is mounted on it and rammed. During this operation pattern remains over the inverted drag and gets support from the rammed sand of the drag under it. • Ultimately, the pattern is removed and the cope and drag are assembled.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 49
  50. 50. MOLDING SAND BINDERS • Binders produce cohesion between the molding sand grains in the green or dry state (or condition). • Binders give strength to the molding sand so that it can retain its shape as mold cavity. • Binders (to the molding sands) should be added as optimal minimum. • Increasing binder content reduces permeability of molding sand. • Increasing binder content, increases green compression strength up to a limit; after which green compression strength remains practically unchanged with further increase in binder content. • Clay binders are most commonly used for bonding molding sands. • The best clay is one which imparts the optimum combination of bonding properties, moisture, life and cost of producing the required casting.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 50
  51. 51. MOLDING SAND BINDERS • Clay binders are most commonly used for bonding molding sands. • Clay binders can be classified as: – Fire clay – Bentonite • Sodium montmorillonite • Calcium montmorillonite – Illite – Kaolinite • Bentonite: – The most commonly used clay binders are Bentonites as they produce strongest bonds in foundry molding sands. – Bentonite deposits are available in India in Rajasthan and Bihar – Bentonites are the weathered product of volcanic ash and are soft creamy white powders. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 51
  52. 52. • Fire Clay: – Fire clay is a refractory clay usually found in the coal measures. – Fire clay particles are about 400 times as large as compared to those of Bentonite ; hence the same percentages of fire clay produce lower strengths. • Illite – Illite is the decomposition product of micaceous materials due to weathering. – Illite is found in natural molding sands. – Illite has softening point of about 2500°F. – Illite does not swell in the same way as bentonite but gives reasonable strength. – Illite particles have thickness and width of 20 and 100-250 milli-microns respectively. • Kaolinite – Kaolinite is the residue of weathered granite and basalt. – Kaolinite binder has its composition 60% kaolinite, 30% illite and 10% quartz, – Kaolinite gets Very low swelling due to water and is non-gel forming. – Kaolinite particles possess thickness and width of 20 and 100-250 milli-microns respectively. MOLDING SAND BINDERS 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 52
  53. 53. WATER • The amount of water may vary from 1.5 to 8%. • water is responsible for the bonding action of clays. • Water activates the clay in the sand and the clay-sand mixture develops strength and plasticity. • Water added to the sand mixture, partly gets adsorbed by clay and partly remains free and is known as Free Water. • The absorbed water is responsible for developing proper bond and the green strength. • The free water acts as a lubricant, • It increases plasticity • It improves moldability, but It reduces strength of the sand mixture. • For a given type of clay and its amount, there is an optimum required water content. • Too little water will not develop proper strength and plasticity. • Too much water will result in excessive plasticity and dry strength. • The amount of water required to develop the optimum properties can be found out experimentally. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 53
  54. 54. ADDITIVES • The basic constituents of molding sand mixture are; – Sand – binder and – water • Materials other than the basic ingredients are also added to molding sand mixtures, of course in small quantities, in order to – enhance the existing properties. – To develop certain other properties. – to give special qualities like resistance to sand expansion, defects etc. • Some of the additive materials along are given below. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 54
  55. 55. • Facing materials: – Facing materials tend to obtain smoother and cleaner surfaces of castings and help easy peeling of sand from the casting surface during shake out. – A few facing materials are • Sea coal • Graphite • Coke • Silica floor • Cushion materials: – Cushion materials burn when the molten metal is poured and thus give rise to space for accommodating the expansion of silica sand at the surfaces of mold cavity. – In the absence of cushion materials, large flat surfaces of castings may buckle due to thermal expansion of silica sand grains. – A few cushion materials are: • Wood floor • Cellulose • Other special Additives: – Finely ground corn floor, Iron oxide, Boric acid, diethylene glycol 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 55
  56. 56. Disclaimer: Contents are taken from several text books and compiled for academic purposes only. Author doesn't hold the copyright for the contents used in this presentation. 5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 56

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