Introduction about metal casting process

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 PLASER
• 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
1.0 Shrinkage allowance
• Metal shrinks on solidification and contracts on cooling to room temperature.
2.0 Machining or Finish allowance
• The pattern is made larger than the required casting for finishing purpose.

10. PATTERN ALLOWANCES
3.0 Draft or Taper allowance
4.0 Rapping or Shake allowance

11. PATTERN ALLOWANCES
5.0 Distortion or Camber allowance

12. 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.

13. 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.

14. 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.

15. 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

16. 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.

17. 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

18. TESTING OF MOULDING SAND
6.0 Deformation and Toughness test
Deformation – Plasticity of sand can be tested by applying compressive force.
Toughness – Deformation of green compressive strength provides the quality of sand mix.
7.0 Hot strength test
8.0 Refractoriness test

19. TESTING OF MOULDING SAND
9.0 Hardness test
Indicates the ramming density of the actual sand mould.

20. 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.

21. 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.

22. MELTING FURNACES
1.0 CUPOLA FURNACE

23. 2.0 CRUCIBLE FURNACE
a. Pit Furnace
APPLICATIONS
Used for melting cast iron and non ferrous metals and alloys in small
quantity.

24. b. Coke Fired Stationary Furnace

25. c. Oil Fired Tilting Furnace
Advantages

26. 3.0 ELECTRIC FURNACE
a. Direct Arc Furnace

28. b. Indirect Arc Furnace

29. c. Induction Furnace

30. SPECIAL CASTING PROCESSES
1.0 SHELL MOULD CASTING

32. 2.0 INVESTMENT CASTING

34. 3.0 LOST WAX PROCESS

36. 4.0 PRESSURE DIE CASTING
a. HOT CHAMBER DIE CASTING

37. b. COLD CHAMBER DIE CASTING

38. 5.0 CENTRIFUGAL CASTING

39. 6.0 CERAMIC MOULD CASTING

40. CORE MAKING

42. 7.0 CO2 PROCESS
• Pure dry silica sand mixed with sodium silicate liquid use as a binder for making core.
• 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 jell.
• Silica jell binds the sand grains together to provide strength and hardness to the core.

43. DEFECTS IN CASTINGS

48. 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.

49. 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.