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
2.
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.
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
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
For external surface=10 to 25mm/m
For internal surface=40 to 65mm/m
4.0 Rapping or Shake 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. 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
20. 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
21. TESTING OF MOULDING SAND
9.0 Hardness test
Indicates the ramming density of the actual sand mould.
22. 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.
23. 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.
33. Pattern is machined from copper alloys, aluminium or
cast iron.
Mould materials contains 5 to 10% of phenolic resin
mixed with fine dry silica and dry oil or alcohol.(water
should not be used)
The pattern is heated to 230-600 C .
Applications:
* cams, cam shaft, piston and piston rings can be made.
35. Ceramic mould casting:
Ceramic slurry is prepared by mixing fine grained
refractory powders of
*zircon ZrSiO4 ,
*alumina Al2O3,
*fused silica SiO2 and bonding agent.
This slurry is applied over the pattern surface to form
thin coating around it and baked in less expensive fire
clay.
After pattern is removed, mould is heat further about
1000 c.
41. 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.
