Casting processes and defects

MANUFACTURING PROCESS I
Unit No 3
Casting Processes & Defects
Prof. P. B. Borakhede

Contents
 Introduction
 Permanent Mould Casting
 Slush Casting
 Die casting
1. Hot Chamber
2. Cold Chamber
3. Vacuum Chamber
 Centrifugal casting
1. True Centrifugal Casting
2. Semi centrifugal Casting
3. Centrifuge casting
o Casting Defects

INTRODUCTION
 The utility of casting processes is wide and a large
quantity of castings is produced through these methods
only.
 A large number of developments have taken place in this
field and various new moulding and casting methods
have been evolved to serve certain specific purposes.
 These new methods have helped in one way or the other
in increasing production rate, effecting greater economy,
improving quality of casting, eliminating or minimizing
need of further machining, providing better dimensional
control, production of better surface finish.
 These methods are termed as special casting
methods.
Prof. P.B. Borakhede, MGI-COET, Shegaon

The special casting methods are as follows:
1. Permanent Mould Casting
2. Slush Casting
3. Pressed Casting
4. Die casting
5. Centrifugal Casting
7. Investment Casting
8. Continuous Casting

 This casting is also known as gravity die casting.
 It differs from sand casting because in this the mould
is permanent and is neither destroyed nor remade
after each cast.
 Highly heat resistant fine grained alloy iron and steel
are the commonly used materials for making
permanent moulds.
 Pouring is permanent moulds is done simply due to
gravity, ie without any external pressure, and hence
name Gravity Die Casting.
 This process is used for large quantity production.
 It has very high rate of production.
1. PERMANENT MOULD CASTING

Construction
 These moulds are generally made in two halves, hinged
together to facilitate quick opening and closing and
ejection of casting
 Parting surface of two halves is in vertical plane.

 Grey iron or steel cores are used for producing cavities
or hollows in castings.
Moulds after solidification of castings are opened by
hand lever or through mechanical devices.
Rapid and efficient clamping has to be provided on the
mould on the mould.
 The mould consists of several blocks joined together.
Form block and base block together forms actual mould
cavity, where as runner block contains runner and riser.
In order to enable easy removal of casting, runners and
risers are kept on parting line.
 Cores are normally employed for producing holes more
than 10 mm.

 Core is hold by base block.
Stages in castings
 The mould is preheated to a temperature of about
400◦C through suitable means.
 After attaining correct mould temperature the first
casting is poured.
 Cores are removed as soon as metal are begins to
solidify, `otherwise it may shrink on the surface of the
metal cores to lock them within casting.
 The mould is then cleaned by blowing, coated with
refractory coating, cores assembled in position and
closed again for pouring.

Advantages
 It is a very speedy process and each cast takes
between 2 to 4 minutes time only.
 Permanent moulds have very long life as one mould
can be used for producing 3000 to 10000 castings.
 Surface finish is better than sand casting.
 For the same amount of production it required less floor
area than sand casting.
 Less skill is required of the operator than in sand
casting.
 Many defects found in sand casting are eliminated
totally.
 Castings in large quantities can be produced more
economically.

Disadvantages
 These moulds are much costlier than sand moulds.
 This method cannot be economically used for small
quantity production. The minimum economical figure
required 500 castings.
 Castings of only 120Kg can be made through this process.
 It cannot be used for castings of very high melting point
alloys.
 Shapes of castings may offer very complicated problems in
mould design.
 Gates, runners and risers cannot be shifted anywhere.

 It is basically a permanent mould casting process used
for producing Hollow Castings without using Cores.
 It is normally employed for producing such articles in
which dimensional accuracy is not important but the
outer surface is to have an ornamental appearance.
 The process consists of pouring the molten metal into
the mould, retaining it there for some time to allow the
outer shell to solidify and finally turning over the mould to
drain out the inner molten metal into receiver.
 The thickness of solidified shell depends upon the
chilling efficiency of the metallic mould and the duration
for which the metal is allowed to remain in the mould
before turning over.
2. SLUSH CASTING

 Lower melting point alloys, like tin, lead and zinc base
alloys, are commonly used as casting materials in this
process.
Advantages
 This casting can be used for decorative or ornament
manufacturing.
 Reusable mould and fast cooling rates.
 Good surface finish and good surface detail.

Disadvantages
 Lower melting point alloys.
 Variable wall thickness.
 Requires manual labor.
 Time consuming process.

 Die casting is a metal casting process that is
characterized by forcing molten metal under high
pressure into a mould cavity.
 Molten metal under high pressure is poured in cavity by
the use of mechanism.
 Within a fraction of second, the fluid alloy fills the entire
die, including all the minute details.
 The advantages of die casting lie in the possibility of
obtaining castings of sufficient exactness and in the
facility for casting thinner sections that cannot be
produced by any other casting methods.
 The accuracy attained is so high.
3. DIE CASTING

Types of Die Casting Machines
There are four main types of die casting machines
1. Hot chamber die casting machine
2. Cold chamber die casting machine
3. Air blown die casting machine
4. Vacuum die casting machine
A) Hot Chamber Die casting Machine
 This is operated by hydraulic plunger.
 This plunger acts inside a cylinder formed at one end
of goose neck type casting.
 A port is provided near the top of cylinder to allow the
entry of molten metal into it.

 When bottom of the plunger is above the port, molten
metal is entered in the chamber through this port.
 Down stroke of plunger closes this port cuts off the metal
supply and applies pressure on molten metal present in
goose neck to force the metal into die cativy through
injecting nozzle.

 After certain period of time, the plunger is raised up and
port in opened, again molten metal falls in chamber and
process continues.
 After the metal in dies solidifies, the dies are opened by
ejector pins and casting is ejected.
 Zinc based alloys, aluminum alloys are cast in this
machines because they have low melting point.
B) Cold Chamber Die casting Machine
 In this horizontal cylinder is used into which injector
plunger works.
 In this metal is melted separately in a furnace and
transferred to them by means of a small hand ladle.

 After closing the die the molten metal is poured into the
horizontal chamber through metal inlet.
 Plunger is pushed forward hydraulically to force the metal
into die.
 After solidification, the die is opened and the casting is
ejected.
 The plunger is again drawback, molten metal is poured in
cylinder and same process is continued.

 These machines are widely used for casting aluminum
and alloys and brass which cannot be cast in hot
chamber machines as they require higher pouring
temperature.
Advantages and disadvantages of Die casting
Advantages:
1. Very high rate of production is achieved.
2. Close dimensional tolerances of the order of 0.025mm
is possible.
3. Surface finish of 0.8 micron can be obtain.
4. Longer die life.
5. Less floor space is required.

Disadvantages
1. Not economical for small production.
2. Only economical for non ferrous alloys.
3. Heavy castings cannot be cast.
4. Cost of die casting equipment is high.
5. Die casting usually contain some porosity due to
entrapped air.

C) Vacuum Die-casting Machines
 Complete evacuation of air from the die prior to metal
injection is necessity for preventing the air entrapment in
casting.
 This difficulty is overcome in the vacuum die casting
machine.
 This method is used to reduce porosity in casting.
 This is a modified form of the previously described Hot
chamber and cold chamber machines.
 In this the die cavity is completely air free before molten
metal enters in cavity.
 The additional equipments are required in both hot
chamber machine and cold chamber machine around
the die blocks.

 A vacuum valve is connected to the cavity to evacuate air
in cavity.
 Valve is connected to vacuum pump.
 Vacuum pump is started just before plunger started
applying pressure.
 As vacuum pump starts it applies vacuum in the die
cavity, the air in the die cavity is removed.

 Also the speed of molten metal is increased because of
vacuum effect.
 The valve is closed when molten metal is filled completely
in cavity.
Advantages
 Complete evacuation of air from die cavity and chamber.
 Production of smooth casting .
 Free from defects like air porosity.
 Also enables rapid feeding of molten metal in die cavity.

Advantages and Disadvantages of die casting
Advantages
 Most of non ferrous alloys can be cast.
 The production rate is as high as 300 to 500 casts per hour in
hot chamber process and 75 to 150 casts per hour in cold
chamber process.
 Very close dimensional tolerances can be held.
 Very thin sections can be cast.
 Very high surface finish can be obtained.
 Intricate shapes can be easily cast.
 Holes up to minimum 1.6 mm diameter can be easily
cored.
 The process requires less floor area .
 For large quantity production, this process is very
economical as compared to others.

Disadvantages
 Every metal and alloy cannot be cast.
 Machines and other equipment used are very costly.
 This process cannot be economically employed for
small quantity production.
 The maximum size of the casting is limited.
 Unless special precautions are adopted for evacuation
of air from cavity, some air is always trapped in
castings, causing porosity.

4. CENTRIFUGAL CASTING
 The process of centrifugal casting is also known as liquid
forging.
 It consist of rotating the mould at a high speed as the
molten metal is poured into it.
 Due to the centrifugal force the molten metal is directed
outwards from the centre, towards the inside surface of
the mould, with considerable pressure.
 As a result of this, a uniform thickness of metal is
deposited all along the inside surface of the mould,
where it solidifies, and the impurities being lighter remain
nearer to the axis of rotation.
 This process enables the production of castings with
greater accuracy and better physical properties as
compared to sand casting.

 Many different shapes can be cast through this process
but those with symmetrical shapes are best suited for it.
 Better physical properties are achieved because denser
or cold metal is automatically forced towards the outer
side of the casting by centrifugal force.

The centrifugal casting methods can be classified as
follows:
1. True centrifugal casting
3. Centrifuging
A) True centrifugal casting
 The main features of true centrifugal casting are that
the axis of rotation of the mould and that of the casting
are the same.
 Also the central hole through the casting is produced
by the centrifugal force without use of a central core.
 The axis of rotation of the mould may be horizontal,
vertical or inclined at any suitable angle.

 End cores are usually employed at the two ends of
mould to prevent molten metal from being thrown out at
the ends.
 Applications are iron pipes, gun barrels bushing etc.
 A typical horizontal true centrifugal casting is shown in
figure.

 It is shown having a large cylindrical mould for casting
cast iron pipes.
 Similar equipment can be used for other cylindrical
items.
 The mould consist of an outer metallic flasks provided
with a rammed sand lining inside.
 Mould is rotated between two sets of rollers. Bottom
rollers are mounted on a shaft driven by a variable
speed motor mounted at one end.
 Pouring in the mould is over, the mould is rotated at a
slow speed.
 Pouring in the mould is done through a pouring basin
form on the body of the trolly.
 Initially during pouring the mould is rotated at a very slow
speed.

 After the pouring is over, the mould is rotated at a very
fast speed to effect even distribution of the metal inside
the surface of the mould and proper directional
solidification.
 After solidification, flask is replaced by a new one
process repeated.
 Wall thickness of the castings is controlled by the volume
of molten metal poured into the mould.
 Pouring temperature range between 1482 to 1649 C.
 For successful casting, the application of correct spinning
speed is necessary.
 Slow speed will not allow the molten metal to adhere to
inside surface of the mould and too high speeds will
develop high stresses in the castings.

B) Semi centrifugal Casting
 This is process is also known as profile centrifugal
casting is widely used for relatively large castings
which are symmetrical in shape such as discs, pulleys,
wheels, gears etc.
 In this the mould is related about a vertical axis and the
metal poured through a central sprue.
 In this one or more castings are molded at a time.
 Several mould can be stacked together, one over the
other and fed simultaneously through a common
central sprue.
 This provision increases the rate of production
considerably.

 The centrifugal force is used to feed the metal outwards
to fill the mould cavities completely.
 The speed of rotation of these moulds is much less than
that in true centrifugal casting.
 With the result, the pressure developed is too low and the
impurities are not directed towards the centre as
effectively as un true centrifugal casting.

 The moulds used may be of green sand, dry sand,
metal or any other suitable material.

C) Centrifuging
 This is also known as pressure casting.

 In this the axis of rotation and that of the moulds do not
coincide with each other, as the moulds are situated at a
certain distance from the central vertical axis of rotation
all around the same.
 Shapes of castings do not carry any limitation in this
method and a variety of shapes can be cast.
 A number of small mould cavities are made around a
common sprue and connected to the same through
radical gates.
 For higher rate of production stack moulds can be used
with advantage.
 Like semi centrifugal method in this method also mould
assembly is rotated about a vertical axis and centrifugal
force used to force the molten metal from central sprue
into the mould cavities through the radial gates.

Advantages and Disadvantages of Centrifugal
Castings
Advantages
 Castings produced are clean as most of the impurities are
collected on the inner surface and can be removed.
 Castings acquires high density and high mechanical
strength.
 Gates and risers are not needed.
 Formation of hollow interiors without cores.
 High output.
 High production rate.
 Thin sections and intricate shapes can be easily cast.

Disadvantages
 All shapes cannot be easily cast through this process.
 The complete equipment requires a heavy initial
investment.
 Its maintenance also is quite expensive and its operation
needs employment of skilled labor.
 Many other casting processes are much better than
centrifugal casting.
 Area occupied is high.

5. INVESTMENT CASTING
 This casting method is also called as Lost Wax Casting.
 This method is came in practical during World War II.
 The process broadly consist of preparing an expandable
pattern of wax, plastic by pouring it into a metal mould or
die. This pattern is used for making mould of investment
material, which consist of refractory material and liquid
binder.
 The complete procedure consist of following steps.
1. Die making 2. Making wax Pattern
3. Assembling the wax pattern 4. Investing
5. Removal of wax Patterns 6. Pouring and casting
7. Cleaning and inspection.

a) Die casting
 The first step is to make a suitable metal die in which
the melted was is poured to produce the pattern.
 These dies can be made either by using a metallic
master pattern or by directly machining the required
shape through a pair of steel blocks.
 Steel die have more life than other type.
 Dowel pins and holes are provided on the mating
surfaces of the two halves of dies.
 Pouring gate is provided with adequate draft to
facilitate easy opening of the die.

b) Making Wax Patterns
 The die halves are closed and properly clamped.
 Molten wax is then forced into the die, under pressure
by means of a Wax-injection Machine.
 After some time the wax is solidified and it is removed
from die.
 Solidification process may takes 1 to 2 minutes.
 Likewise number of same pattern are formed.
c) Assembling Wax Pattern
 The next step is to weld a number of small wax patterns
to a common wax gating system ( wax sprue) so that
they can placed together in one mould.
 This is done by an instrument hot wire welder.

 It consist of small piece of resistance wire heated by
electric current to a temperature just sufficient to melt the
wax.
 The complete assembly is then placed in a metal box
called flask, which contains the investment material.
d) Investing
 The investment material can be applied around the wax
pattern assemblies to form the moulds in any of the
following three ways:
i) Mix or Pour Method
 It consist of making slurry of finely ground refractory
grains by mixing them with a suitable liquid binder and
pouring this slurry into the flask surrounding the pattern
assembly.
 After setting of slurry mould is ready for baking.

ii) Dip-coat Method
 It consist of providing a thin coat of the refractory slurry
on the pattern surfaces of the same type as above.
 After it is dried, a cheaper and coarser investment
material is applied around it.
 The initial fine coating provides a smooth finish on the
casting.
iii) Multiple Dip coat Method
 It is also called ceramic shell method.
 In this method, repeated thin alternate coats of fine
slurry and coarser investment material are provided on
the pattern assembly.
 Usually 5 to 8 layers are provided and 3 to 6mm
thickness is formed.

 The binders commonly used are sodium silicate, ethyl
silicate and gypsum plaster.
 Powdered refractory material is mixed with is may be
silica, magnesia, alumina.
e) Removal of Wax Patterns
 The wax patterns can be removed by placing heaters
near wax assembly at heating increasing temperature of
heaters so as the wax in the mould converted into liquid
form.
 The wax is automatically removed from mould by sprues
and common runner.

f) Pouring and Casting
 The prepared moulds are preheated to a suitable
temperature depending upon the metal is to be
poured.
 Preheating providing advantages
1. Remaining wax in the mould if any is vaporized and
evacuated.
2. Preheating of mould causes expansion of mould
cavity which in turn compensates for the solid
shrinkage of the casting.
3. Preheating of mould will help the metal to flow easily
and fill up all the details.
 The metal is melted in furnace and poured into mould
under gravity, under air pressure, under centrifugal
force or by creating vacuum.

 After some time the metal poured in the mould get
solidified as temperature of it decreases.
g) Cleaning and Inspection
 After the mould gets cooled, the investment material is
then broken through hammering or vibrating the moulds
to separate itself completely investment material.
 Gates and risers are then chipped off.
 The chipped spots are then grid to provide smoothness.
 They are inspected through the specified inspection
method.

Advantages and Disadvantages
Advantages
 Used for manufacturing different parts like cams,
machinery components, turbine blades, dental fixtures,
jwellary, gears etc.
 High dimensional accuracy with very close tolerances
can be achieved.
 Complex contours and intricate shapes can be easily
cast.
 Extremely this sections, can be successfully cast through
this process.
 Castings are quite sound and free from most of the
casual defects.
 Surface finish is very high so need of further machining
is eliminated in the most of the cases.

Disadvantages
 Size of the castings to be made is limited and cannot
be varied.
 Large castings cannot be produced through this
method.
 One mould can be used for only one casting. This
increases cost of production.

6. CONTINUOUS CASTING
 This process consist of pouring the molten metal into
upper opening of a vertical metal mould, open at both
ends, cooling it rapidly and removing the solidified
product in a continuous length from the lower end of
the mould.
 This process is largely applicable to brass, bronze,
copper, and aluminum and to a limited extent to cast
iron and steel.
 A number of processes have been developed for
continuous casting of various metals and alloys are as
follows:
1. Asarco Process 2. Reciprocating Mould
3. Williams Process 4. Alcoa Direct Chill Process

Of the processes the most popular method is Asarco
Process.
Asarco Process

 In this process the pouring die and cooling jacket are
made integral with furnace.
 It also incorporates an integrated valve to stop the
metal flow into the mould when desired.
 The molten metal flows into the mould from below the
metal surface so that no impurities are included into it.
 As it flows down it is cooled rapidly by quick dissipation
of heat by the circulating water in the jacket around the
metal mould.
 Withdrawing Rolls below the mould help in pulling down
the solidified casting at a controlled speed.
 Below the rolls the saw is fitted to cut the product to
desired lengths.

 This process is vastly used for copper and bronzes.
 Many popular shapes like round, square, rectangular,
hexagonal and fluted etc can be cast.
Advantages and disadvantages
Advantages
• Continuous casting allows manufacturing metal slabs
or bars in large amounts by short time.
• Sprue, runner, riser not use thus, no waste metal this
leads to 100% casting yield.
• Mechanical Properties are high and extremely
reproducible.
• Increased use of purchased scrap when.
• Product has good reliable soundness.

Disadvantages
• Continuous and capable cooling of mould is required.
• Only simple shapes can cast which should have a
stable cross section.
• Large capital investment is necessary to set up process.
• Not proper for small amount production.
• Requires large ground space.

Shell Moulding
 This process have been developed by Germany during
World war II.
 It is also called Corning Process.
 It makes use of a mixture of fine sand and phenolic
resin binder as the mould material. The same mixture is
used for shell cores.
 Fine silica sand is mixed with about 5% synthetic resin
to form the mixture.
 The mould is made in two halves as thin shells and
baked.
 These halves are then clamped together to form the
complete mould before pouring.

 The material used for mould and core making is
permeable, which eliminates need of additional venting
and minimizes the chances of Blow holes.
 For preparing the mould a metallic pattern is prepared
and positioned on a metal plate, combining runners,
gates and risers.
 This unit then heated to approximately 232◦C and
sprayed with the silicon release agent.
 This agent prevents the shell from striking to the pattern
and the plate and enables its easy removal after it is
ready.
Advantages
 Very high class surface finish is obtained.
 Less skill is required.

 Moulds can be made at any convenient time and stored
for future use.
 Due to high permeability gases escapes readily through
them.
 Complete automation of the process can be done.

CASTING DEFECTS
 A large number of defects occur in Sand Castings
produced through various methods.
 The defects pose a great problem to the foundrymen
because if casting defects are more 10%, the lot is
rejected.
 There are various reasons of casting defects such as
lack of skill, carelessness, Lack of coordination etc.
 Factors which are normally responsible for the
production of these defects are as follows:
1. Design of casting 2. Design of pattern equipment
3. Moulding and core making equipment
4. Mould and core material 5. Gating and rising
6. Moulding techniques 7. Melting and pouring.

Various Defects, Their Causes And remedies
1. Blow Holes
 They appear as cavities in a casting.
 When they are visible on the upper surface of the
casting, they are called open blows.
 These blows are normally rounded and have smooth
wall.
 Blow holes are due to entrapped bubbles of gases in
the metal and are exposed only after machining.
Causes:
• Excess moisture content in moulding sand leads to
production of large steam inside the cavity.
• Cores are not sufficiently baked.
• Use of rusted or highly moisted chills, chaplets or
other metal inserts.

• Excessive use of organic binders results production of
high amount of gases.
• Cores not adequately vented.
• Moulds not adequately vented.
Remedies:
• Moisture content in the moulding sand should be
properly controlled.
• Cores should be adequately baked.
• Chills, Chaplets and metal inserts should be clean.
• Organic binders should be used with restraints.
• Cores and moulds should be adequately vented.
• Moulds should not be excessively rammed hard.

2. Porosity
 This defect occurs in castings in the form of Pinhole
Porosity or gas Porosity.
Causes:
 These porosities are caused by the gases absorbed by
molten metal.
 Gases commonly absorbed are hydrogen, nitrogen,
oxygen.
 Mainly hydrogen is responsible for pinhole porosity.
 During solidification, gas is released and in driving
itself out of the metal it creates very small voids
throughout casting, called pinholes.
 They are very small in size and can be detected by
Xray examination of a machined surface of casting.

Remedies:
 Proper melting temperature should maintained.
 Adequate amount of flux should b used.
 Casting should be made to solidify quickly by proper
gating and rising.
 Permeability should be increased and moisture content
should be kept as low as possible.
3. Shrinkage
 During solidification there is a shrinkage.
 Alloys always shrink when changing from molten to
solid.
 This is because the density of a casting alloy in the
molten state is lower than that in the solid state.

 Too much shrinkage may lead to cracks, known as hot
tears.
Causes:
• This defect occurs on account of inadequate and
improper gating, rising, and chilling, due to which proper
directional solidification does take place.
Remedies:
• Shrinkage can be removed by design a running (gate)
system with risers that ensure a continuous flow of
molten metal.
4. Misrun and Cold shut
 When the molten metal fails to reach all the sections of
the mould such that a certain part of it remains unfilled,
resulting an incomplete casting, the defect is known as
Misrun.

 When two streams of molten metal approach each other
in the mould from opposite directions establish a
physical contact between them, but fail to fuse together,
resulting discontinuity between them, it is known as a
Cold shut.
Causes:
They occurs due to lack of fluidity in the molten metal and
faulty design, incorporating very thin sections.
Remedies:
They can be eliminated by improving the design and
adjusting the pouring temperature to ensure proper
fluidity.

5. Inclusion
 Any separate non-metallic foreign material present in
the cast metal is called an Inclusion.
 These inclusion may be in form of oxides, slag, dirt,
sand and gas.
 Sometimes the atmospheric and other gases absorbed
by molten metal in furnace, laddle or during flow in
mould, if not allowed to escape will weaken it.
 The atmospheric and other gases absorbed by molten
metal in furnace, laddle or during flow in mould, if not
allowed to escape will weaken it.
Causes:
• Faulty Gating and pouring
• Dissolved gases in molten metal

• Soft Ramming of Mould
• Rough handling of mold and core etc.
Remedies:
• Gating and pouring system should be proper
• Unwanted material in the molten metal should be
removed before pouring in the cavity
• Gases in the molten metal should be escape
• Ramming should be complete.
6. Hot Tears
 This is one of the main defect.
 It is also called hot cracking or hot shortness.

 The main reasons of hot tears is the low strength of
metal after solidification, causing the metal to fail in
coping up with excessively high stresses set up by solid
shrinkage of the metal.
 These cracks are external or internal.
 They are harmful when they are present internally.
Causes:
• If the solidifying metal does not have sufficient strength
to resist tensile forces during solidification, hot tears will
appear.
• Lack of collapsibility in the core and mould.
• Hot tears are mostly caused by poor mold design.
Remedies:
• Mold design should be proper
• Material should be resistant to stresses, strain.

7. Metal penetration
 This defect occurs as a rough and uneven external
surface on the casting.
 It takes place when the molten metal enters into the
space between the sand grains and holds some of the
sand tightly with it even after Fettling.
Causes:
• Faulty gating
• Large grain size sand used
• Soft ramming of mould
• Moulding sand or core have high permeability.
• Pouring temperature of metal too high.

Remedies:
• Improved gating system
• Use sand having finer grain size
• Provide harder ramming
• Increase strength to required extent.
8. Shifts/mismatch
 A shift is a misalignment between two mating surfaces,
leaving a small clearance between them and changing
their relative location.
 This may occurs at the parting surface between two
parts of the mould, or at core prints, providing a gap
between core and core seat.

Causes:
• Worn out or bent bent clamping pins
• Misalignment of two halves of pattern
• Improper location of core
• Faulty core boxes
• Insufficient strength of moulding sand and core.
• Continuous large flat surface on casting
Remedies:
• Repair or replace dowels causing misalignment
• Provide adequate support to core
• Locate the core properly
• Repair or replace the core boxes
• Increase strength of moulding sand and core.

9. Fusion
This defect appears as a rough glassy surface over the
casting.
When molten metal enters the mould cavity, it comes in
contact with the sand and the latter, under the action of
excessive heat of metal, melts and gets fused to the
casting surface.
Causes:
• Low refractoriness in the moulding sand
• Faulty gating
• Too high pouring temperature of metal
• Poor facing sand

Remedies:
 Improve refractoriness
 Modify gating system
 Use lower pouring temperature
 Improve quality of facing sand.

Important Questions
Explain continuous casting process with its applications.
Explain various steps involved in Investment Casting
Process.
Describe 'Centrifugal Casting Process'. Discuss different
type.
Discuss the advantages and applications of shell
moulding process.
Write notes on following defects:
i) Porosity ii) Hot Tears iii) Blow Holes iv) Shift/mismatch v)
Fusion vi) Metal Penetration vii) Inclusion.
Explain die casting processes.

Casting processes and defects

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