Unit i METAL CASTING PROCESSES
- 1. METAL CASTING PROCESSES Sand casting – Sand moulds - Type of patterns – Pattern materials – Pattern allowances – Types of Moulding sand – Properties – Core making – Methods of Sand testing – Moulding machines – Types of moulding machines - Melting furnaces – Working principle of Special casting processes – Shell, investment casting – Ceramic mould – Lost Wax process – Pressure die casting – Centrifugal casting – CO2 process – Sand Casting defects – Inspection methods
- 3. SAND CASTING Casting is one of the processes used for making components of complicated shapes in large quantity. It is process of producing metal parts by pouring molten metal into the mould cavity of the required shape and allowing the metal to solidify. SAND MOULDS Mould is the cavity of the required shape made in moulding sand or in other material PATTERN It is model of the required casting made in wood, metal, plastics.
- 4. TYPES OF PATTERN Solid Split Pattern Loose Piece Pattern Match Plate
- 5. TYPES OF PATTERN Sweep Pattern Skeleton Pattern Segmental Pattern Shell Pattern
- 6. PATTERN MATERIALS 1.0 WOOD • Teak wood, white pine, rose wood are used. • Metal spray coating upto 0.25mm thick, coating materials Zinc and Aluminium to avoid moisture absorption and good surface finish
- 7. PATTERN MATERIALS 2.0 METAL • Mostly used when larger number of castings. • Cast iron, Brass, Aluminium are used.
- 8. PATTERN MATERIALS 3.0 PLASTER • Plaster of paris or gypsum cement is used • Plaster can be easily made into difficult shapes and easily worked. 4.0 PLASTICS • Plastics pattern is cast from a wooden pattern called master pattern. • Light weight but strong and not affected by moisture and more resistant to wear. • Poly acrylates, Poly ethylene, Poly Vinyle chloride etc. 5.0 WAX • It is used in investment castings.
- 9. PATTERN ALLOWANCES: Patterns are not made into exact size of the castings to be produced. Patterns are made slightly larger than the required casting. This extra size given on the pattern is called pattern allowances. Types of pattern allowances: 1. Shrinkage allowance 2. Machining or finish allowance 3. Draft or Taper allowance 4.Distortion or chamber allowance 5. Rapping or shake allowance
- 10. PATTERN ALLOWANCES 1.0 Shrinkage allowance • The extra size provided on the pattern for metal shrinkage is called shrinkage allowance. 2.0 Machining or Finish allowance • The pattern is made larger than the required casting for finishing purpose.
- 11. PATTERN ALLOWANCES 3.0 Draft or Taper allowance 4.0 Rapping or Shake allowance
- 12. PATTERN ALLOWANCES 5.0 Distortion or Camber allowance
- 13. TYPES OF MOULDING SAND 1.0 Green sand • Moist state is known as green sand. • 5 to 8% of water and 16 to 30 % of clay. • soft, light and porous. 2.0 Dry Sand • Prepared in dry stage. • Used for large casting • Mould does not cause defects which causes due to moisture. 3.0 Facing Sand • Used directly cover the surface of the pattern and comes contact with molten metal. • It contains Silica, Clay, Talc, Graphite etc.. 4.0 Loam Sand • It consists of fine silica sand, fine refractories, clay, graphite, fibre and water • It used for bell, roller, pulley etc. 5.0 Backing sand • It used for backup the facing sand and to fill the whole volume of the mould box. 6.0 Parting sand • It used when a casting is made up of two halves with cope and drag. It is sprinkled over the pattern to avoid sticking of green sand.
- 14. PROPERTIES OF MOULDING SAND 1.0 Porosity or permeability • It is a measure of moulding sand by which the sand allows the steam and gases to pass through it, otherwise casting defects such as blowholes will occur. • It depends on Quality and quantity of clays, Moisture, Degree of compactness. 2.0 Plasticity or flowability • It should flows around and over the pattern, uniformly fills the flask. 3.0 Adhesiveness • It sticks or adheres to moulding boxes. It does not fall out when the flasks are lifted and turned over. 4.0 Strength or cohesiveness • It should have sufficient strength so that the mould does not collapse during lifting, shifting, turning, pouring the molten metal. 5.0 Refractoriness • It should resist high temperature of molten metal and depends on purity of the sand, sizes. 6.0 Collapsibility • It should collapse easily after the casting solidifies.
- 15. Moisture content test Clay content test Grain fineness test Permeability test Strength test Deformation and toughness test Hot strength test Refractoriness test Mould hardness test TESTING OF MOULDING SAND
- 16. TESTING OF MOULDING SAND 1.0 Moisture content test a) Loss of weight after evaporation Moisture content = W1 – W2 % of moisture content = (W1 – W2) x 100 W1 b) Moisture teller method c) Based on chemical reaction CaC2 + 2H2O C2H2 + Ca (OH)2 Depending upon the amount of acetylene gas, moisture content is determined.
- 17. TESTING OF MOULDING SAND 2.0 Clay content test Sand + distilled water + 1% NaOH stirred 5 min and settle down 10 min sand + clean water. Clay content = W1 – W2, W1 – weight of sand before drying, W2 – after drying. % of clay content = (W1 – W2) x 100 W1 3.0 Grain fineness test
- 18. TESTING OF MOULDING SAND 4.0 Permeability test Tendency of sand which allows the escape of gases or air through it. Permeability number = VH / APT V = Volume of air (2000cc) H = Height of the specimen = 50.8mm A = Area of specimen = πd2/4 =20.268cm2 T = Time taken by 2000cc P = Pressure measured in manometer.
- 19. Permeability depends on grain size, shape of the sand grains, clay content or binder content, grain distribution, ramming capacity and water content Indirectly refers to the porosity of the sand Sand specimen rammer consists of crank lever, cam, weight gauge rammer rod and ram tube. Moulding sand mixture is filled in the ram tube up to the level marked on it. Then it is placed under the specimen pusher The pressure is applied by the weight through the specimen pusher over the moulding sand contained in the ram tube
- 20. TESTING OF MOULDING SAND 5.0 Strength test Measure of holding power or bonding power. a) Compressive strength b) Shear strength c) Tensile strength d) Bending strength
- 21. TESTING OF MOULDING SAND 6.0 Deformation and Toughness test Deformation – Plasticity of sand can be tested by applying compressive force. Toughness –The deformation of green compressive strength provides the quality of sand mix. 7.0 Hot strength test 8.0 Refractoriness test
- 22. TESTING OF MOULDING SAND 9.0 Hardness test Indicates the ramming density of the actual sand mould.
- 23. MOULDING MACHINES Moulding machines is used for mass production. Since the hand moulding is a slow process, only making few casting. For more castings, Moulding is done by using moulding machines. TYPES OF MOULDING MACHINES a) Jolting Machine Raised about 80mm and suddenly dropped.
- 24. TYPES OF MOULDING MACHINES b) Squeezing Machine The mould sand in the flask is squeezed between the machine table and squeezer head. c) Sand Slinger Impeller rotates, it will throw a stream of sand at great velocity into the flask.
- 25. MELTING FURNACES 1.0 CUPOLA FURNACE
- 27. 2.0 CRUCIBLE FURNACE a. Pit Furnace APPLICATIONS Used for melting cast iron and non ferrous metals and alloys in small quantity.
- 28. b. Coke Fired Stationary Furnace
- 29. c. Oil Fired Tilting Furnace Advantages
- 30. 3.0 ELECTRIC FURNACE a. Direct Arc Furnace
- 32. b. Indirect Arc Furnace
- 34. SPECIAL CASTING PROCESSES 1.0 SHELL MOULD CASTING
- 38. 3.0 LOST WAX PROCESS
- 40. 4.0 PRESSURE DIE CASTING a. HOT CHAMBER DIE CASTING
- 41. Applications: Household equipment's such as washing machine parts, vacuum cleaner body, fan case, store parts etc., Automobile parts such as fuel pump, carburetor body horn, wiper and crank case Components for telephones , television sets, speakers, microphones, record players Toys, such as pistols, electric trains, model aircraft’s etc., Advantages: Very accurate casting can be produced Casting with very good surface finish can be made Rate of production is high Casting with varying thickness can be made. Casting defects are less
- 42. b. COLD CHAMBER DIE CASTING
- 44. 6.0 CERAMIC MOULD CASTING
- 45. CORE MAKING
- 47. 7.0 CO2 PROCESS • Pure dry silica sand mixed with sodium silicate liquid use as a binder for making core. • NaSiO3 + CO2----------- NaCO3 + SiO2 • Moisture should not exceed 3%. • CO2 gas is passed through the core for 30 sec at a pressure of 140 KN/m2. • CO2 react with sodium silicate and forms sodium carbonate and silica gell. • Silica gell binds the sand grains together to provide strength and hardness to the core.
- 53. INSPECTION METHODS 1.0 Visual Inspection Common defects such as rough surface, obvious shifts, omission of cores and surface cracks 2.0 Pressure test The casting is filled with water, oil or compressed air. After that, the casting is immersed in a soap solution when any leak will be evident by the bubbles. 3.0 Magnetic Particle Inspection Fine iron powdered is sprayed on the surface of casting. If there is any crack, the flux lines will create a small north-south pole at the location of crack. The iron powder will be attracted to the crack. 4.0 Dye Penetrant Inspection It is used to detect invisible surface defects in a non magnetic casting. It is carried out by brushing, spraying into a dye containing a fluorescent material. The discontinuities in the surface indicated the presence of surface defects.
- 54. 5.0 Radiographic Inspection Internal defects such as cracks, porosity, blow holes, inclusions. 6.0 Ultrasonic Inspection Internal defects such as cracks, porosity, blow holes, inclusions 7.0 Thermography Inspection Nondestructive Evaluation (NDE)is to test and evaluate structural integrity without causing a physical damage to the component under inspection.