Special Casting Processes Centrifugal Casting Semi centrifugal casting Centrifuging Die Casting Gravity Die Casting Pressure die casting Hot chamber die-casting: Submerged plunger die casting Air blown or goose neck die casting machine Investment Casting Defects in Casting Blow holes Casting Defects Shrinkage Crack Inclusions Lift and shift Swell Fins Misrun and cold shut Metal Penetration Hard spot Run out Drop Warpage

1. Special Casting Processes

2. Centrifugal Casting
• The mould is rotated and the
molten metal is distributed to
the mould cavity with
centrifugal force.
• This process makes hollow
product.
• Following are centrifugal
process:
1. True centrifugal casting
process
2. Semi centrifugal casting
process
3. Centrifuging process.

3. Centrifugal Casting
1. True Centrifugal casting
process:
• This process is also classified
as horizontal, vertical or
inclined at 70 to 90°.
(A)Horizontal axis machine :
• With this process better
quality casting is achieved
and speed control is also
possible.

4. Centrifugal Casting
(B) Vertical axis machine:
• The axis of rotation of mould is
vertical.
• Here molten metal is poured from
the top of axis of mould, so due to
centrifugal force it will stick on
mould wall.
• Small length castings are produced
with appropriate thickness.

5. Centrifugal Casting
2. Semi centrifugal casting:
• The casting like symmetrical
shape, pulley, wheel, disk,
gear like big shape products
manufactured.
• More than one casting
achieved.
• Here vertical axis machine is
used. In center the hub is
provided to create hollow
core.

6. Centrifugal Casting
3. Centrifuging:
• This process is used for non-
symmetrical castings having
intricate details and also for
precision castings.
• The centrifugal force provides
high-fluid pressure to force the
molten metal into mould cavity.
• A number of similar
components can be cast
simultaneously.

7. Die Casting
• Die casting utilizes two blocks
of heat resistant metal machined
to meet along the plane of the
parting line.
• Fine vents are cut to allow air to
escape as the metal centers.
• Molten or semi molten metal is
either poured under gravity or is
forced under high pressure into
a die and pressure is maintained
till solidification stage.

8. Die Casting
1. Gravity Die Casting:
• feeder is incorporated so that
when the level of the metal
in the feeder is above that at
the highest point of the
casting.
• head of liquid in feeder
forces the metal into all parts
of the mould cavity.
• Aluminum, Copper, Lead,
Magnesium, Zinc products
are produced.

9. Die Casting
2. Pressure die casting:
• In pressure die casting metal flows under high pressure
• Also as the die is metallic, the casting rate is high and thus mass
production is possible.
The following are the types of pressure die casting
(A) Hot chamber die-casting
(1) Submerged plunger die casting
(2) Air blown or goose neck die casting
(B) Cold chamber die casting.

10. Die Casting
(A)Hot chamber die-casting:
(1) Submerged plunger die casting:
• Generally 125 kg/cm2- pressure is
applied.
• The castings from zinc, tin and lead
alloys are produced having low
melting temperature.
• When plunger comes down, ‘C’ port
closes and required pressure is
applied in ‘B’ chamber.

12. Die Casting
(2) Air blown or goose neck
die casting machine:
• with this process the metals
having low melting
temperature like lead, tin,
zinc ore to be cast.
• In this machine the cast-
iron goose neck chamber is
used.

13. Advantages of die casting
• Advantages:
• Thin section (0.5 mm thickness) can be easily made.
• Impression or complicated design can be achieved on component
walls.
• The production rate is high (300 per hour approx).
• Die set can be used many times.
• All non-ferrous products are produced with this method.
• Better surface finish is achieved.

14. Disadvantages of die casting
• It is not economic for small quantity of production.
• It is used for only small casting (10 kg weight approx).
• Initial cost is high for die and other equipment.
• Only non-ferrous products are casted.
• If proper care is not taken then the defects like blow hole can be
possible.

15. Investment Casting
• This process is called the lost-wax
process or precision casting. The
following are the different stages
(1) Die making
(2) Making wax pattern
(3) Precoating the wax pattern assembly
(4) Investment the wax pattern in mould
box
(5) Removal of wax pattern
(6) Pouring molten metal
(7) Cleaning of casting

16. Advantages Investment Casting
(1) Very smooth surface of casting without parting lines are achieved.
(2) Machining of intricate shape can be manufactured.
(3) Die casting can be replaced when short runs are involved.
(4) Castings are sound and have large grains as the rate of cooling is
slow.
(5) It represents the only method suitable for manufacture of precision
shaped castings of high melting point metals which would cause too
rapid die failures is normal die casting process.

17. Disadvantages Investment Casting
(1) It is expensive process and hence is adopted only where small
number of intricate and highly accurate parts particularly high melting
point alloys are to be manufactured.
(2) This process is suitable for small size parts.
(3) This presents some difficulties when cores are to be used.

18. Defects in Casting
• Casting defects, their causes & remedies:
(1) Blow holes
Holes on casting surface is blow holes. This defect occur because of air
comes out from surface.
Causes: Moisture level is high in mould sand, improper baking of core.
unnecessaryy carbonic binder, unwanted ramming, small vent hole, fine
sand etc.
Remedies: Proper moisture level, proper baking of core, proper use of
binder, proper ramming, proper vent hole with vent rod, selection of sand
particle.

19. Blow holes Casting Defects

20. Casting defects, their causes & remedies
(2) Shrinkage
When metal transfer from liquid to sold its volume will decrease.
During this process if it will not get more molten metal then in the
internal surface of casting voids are developed, that is known as
shrinkage.
Causes: Defective runner, gate and riser, molten metal's pouring
temperature.
Remedies : Proper arrangement of runner, riser and gate for proper
directional solidification. If required, the design can be changed,
maintaining proper molten metal temperature.

21. Shrinkage Casting Defects

22. Casting defects, their causes & remedies
• (3) Crack :
• Due to solidification metal shrinks in mould. The improper shrinkage
develops stress on surface, due to that cracks propagates on surface
also known as pull.
• Causes: Non availability of collapsibility property of mould and core,
improper design, hard ramming of mould.
• Remedies: Collapsibility property can be improved, design can
improved. properly ramming of mould.

23. Crack casting defect

24. Casting defects, their causes & remedies
• 4) Inclusions :
• Unwanted ingredients such as metal oxide, slag, sand particles give
defects known as inclusions in metal castings.
• Causes: Improper gating system, improper pouring, low quality
mould and core sand, improper ramming, impurity in metal charge.
• Remedies: By modifying gating system, turbulence free pouring,
using good quality mould and core, proper ramming of mould sand,
proper and pure metal charge should be used and by using oxide free
molten metal crucible.

26. Casting defects, their causes & remedies
• (5) Lift and shift :
• Some part of casting gets distortion known as lift and shift.
• Causes: Improper alignment of pattern parts, improper support of core, improper clamping of mould box,
improper strength of mould sand.
• Remedies: By aligning the mould box with help of dowel pin, properly supporting core in mould, properly
clamping of mould box, providing proper strength mould and core sand.
• (6) Swell
• Due to molten metal the some part of mould cavity become large so the casting becomes larger than required
which known as swell.
• Causes : Pressure of molten metal on surface, improper ramming of sand, low strength of core sand.
• Remedies: By properly ramming of sand, by increasing core strength so molten metal can easily flow in
mould.
• (7) Fins
• Thin edge on casting known as fins. Generally it is on parting line.
• Causes: Improper clamping of mould b0x, improper arrangement of mould and core.
• Remedies: Properly clamping of cope and drag, proper assembly of mould and core.

27. Casting defects, their causes & remedies
• (8) Misrun and cold shut :Molten metal cannot reach in all the parts of mould, so this improper filled
casting known as misrun. Molten comes from different sides, sometimes cannot mix each other. This
defect known as cold shut.
• Causes: Defective design of gating system, low fluidity of molten metal, thin wall of casting, non-
continues pouring of metal.
• Remedies: Modification of gating system, increasing temperature of molten metal, continuously
pouring of molten metal, increasing porosity of sand.
• (9) Metal Penetration: Surface of casting becomes rough due to metal penetration.
• Causes: Bigger size of sand, less ramming, low strength of moulding sand and core, higher
permeability.
• Remedies : Fine grain sand, proper ramming of mould sand, proper mixture should be used to increase
moulding and core porosity.
• (10) Hard spot: Some part of casting solidifies very fast and that surface becomes tough, that known as
hard spot.
• Causes: Bad casting design, improper métal composition, improper use of chills.
• Remedies: Proper design of castings so metal solidifies in same time, proper metal Composition, proper
use of chills in design.

28. Casting defects, their causes & remedies
• (11) Run out: While pouring, molten metal comes out (leaks out) from casting known as run out.
• Causes: Defective mould box, defectively moulding process.
• Remedies Moulding box should be changed, modification in moulding process.
• (12) Drop: A drop occurs when cope surface cracks and breaks, thus the pieces of sand fall into the
molten metal.
• Causes Due to either low green strength or improper ramming of the cope flask, improper reinforcement.
• Remedies: Proper mixing of binder for strength improvement, proper arrangement of steel rod for
reinforcement in core and mould, proper ramming.
• (13) Warpage: After or before solidification casting may twist or change shape known as warpage.
• Causes: Improper design, lack of directional solidification, internal stress.
• Remedies: Proper design of casting to get directional solidification. By proper heat treatment the stress can
be removed.