Casting

 Casting
 Casting is a manufacturing process in which a liquid
material is usually poured into a mould, which contains
a hollow cavity of the desired shape, and then allowed to
solidify. The solidified part is also known as a casting,
which is ejected or broken out of the mould to complete
the process.

Steps Involved
inCasting : -
o Making mould cavity
o Material is first liquefied by properly heating it in a
suitable furnace.
o Liquid is poured into a prepared mould cavity
o Allowed to solidify
o Product is taken out of the mould cavity, trimmed and
made to shape

Advantages of
Casting :
• It can create any complex structure economically.
• The size of object doesn’t matter for casting.
• The casting objects have high compressive strength.
• All structure made by casting has wide range of
properties.
• All material can be cast.
• It is cheapest among all manufacturing processes.

Disadvantages:
 Along these advantages, casting has following
disadvantages.
• It gives poor surface finish and mostly requires surface finish
operation.
• Casting defects involves in this process.
• It gives low fatigue strength compare to forging.
• It is not economical for mass production.

 Flask: A metal or wood frame, without fixed top or
bottom, in which the mould is formed. Depending upon
the position of the flask in the moulding structure, it is
referred to by various names such as drag – lower
moulding flask, cope – upper moulding flask, cheek –
intermediate moulding flask used in three piece
moulding.
 Pattern: It is the replica of the final object to be made.
The mould cavity is made with the help of pattern.
 Parting line: This is the dividing line between the two
moulding flasks that makes up the mould.
 Moulding sand: Sand, which binds strongly without
losing its permeability to air or gases. It is a mixture of
silica sand, clay, and moisture in appropriate
proportions.

Casting
Terminology :
 Facing sand: The small amount of carbonaceous
material sprinkled on the inner surface of the mould
cavity to give a better surface finish to the castings.
 Pouring basin: A small funnel shaped cavity at the top of
the mould into which the molten metal is poured.
 Sprue: The passage through which the molten metal,
from the pouring basin, reaches the mould cavity. In
many cases it controls the flow of metal into the mould.
 Runner: The channel through which the molten metal is
carried from the sprue to the gate.

Casting
Terminology :
 Gate: A channel through which the molten metal enters
the mould cavity.
 Core: A separate part of the mould, made of sand and
generally baked, which is used to create openings and
various shaped cavities in the castings.
 Chaplets: Chaplets are used to support the cores inside
the mould cavity to take care of its own weight and
overcome the metallostatic force.
 Riser: A column of molten metal placed in the mould to
feed the castings as it shrinks and solidifies. Also known
as “feed head”.
 Vent: Small opening in the mould to facilitate escape of
air and gases.

Pattern
• Pattern : A pattern is made of wood or metal, is a replica
of the final product and is used for preparing mould
cavity.
• Except for the various allowances a pattern exactly
resembles the casting to be made.

Types of
pattern
1) Single piece pattern
2) Split piece pattern
3) Loose piece pattern
4) Gated pattern
5) Match plate pattern
6) Sweep pattern
7) Cope and drag pattern
8) Skeleton pattern
9) Follow board pattern

1. Single piece
pattern
 Single piece pattern is the cheapest pattern among all
other types of pattern.
 This pattern generally used in simple processes.
 It is applied in small scale production.
 In this pattern one surface is considered as flat portion.
This flat surface is used for parting plane.
 For making a mould, the pattern is accommodated either
in cope or drag.

2. Split piece
or Two Piece
Pattern
 It is the popularly used for intricate (complex) castings.
 This parting plane may be flat or irregular surface.
 In two- piece pattern half part is always moulded in drag
and other half part is moulded in cope.
 The cope part of the pattern has dowel pins. These
dowel pins are used to align the two halves of split piece
pattern. Holes in the drag half of the two- piece pattern
match exactly with dowel pins.
 Two- piece patterns are used where difficult to withdraw
casting and the depth of casting is very high.

3. Loose piece
pattern
 It is very difficult to remove one piece of solid pattern
which is above or below the parting plane having
projections from the mould.
 With the help of loose piece types of patterns projections
can be made by loose pieces.
 It requires skilled labour work as well as it is very
expensive.

4. Gated
pattern
 Gated types of patterns are used to make multiple
components inside the single mould.
 Gated pattern is nothing but the pattern consisting of one
or more patterns. For joining different patterns gates are
used.
 These are loose patterns where gates and runners have
already attached. These patterns are very expensive.
 Due to their high cost they are used for creating small
castings.

5. Match plate
pattern
 Basically Match plate pattern is a split pattern.
 Cope and drag areas are on the opposite faces of
metallic plate. This metallic plate is termed as Match
Plate.
 This type of pattern requires very less hard work and
gives very high output. Because the gates and runners
are also on the match plate.
 This is very expensive and gives accuracy as well as
high yield. This pattern is widely used for casting metals
like aluminium.

6. Sweep
pattern
 Makes use of a thin board of wood conforming to the
outer contour of the casting.
 It is used when the casting has a surface of revolution
contour such as cylindrical, bell shape, etc.
 It can be used for small or big castings and the number
of castings is not a problem.

7. Cope and
drag pattern
 Cope and drag pattern is a split pattern. This pattern has
cope and drag on separate plate.
 Cope and drag pattern has two parts which are
separately moulded on moulding box.
 After moulding parts, these two separate parts are
combined to form the entire cavity.
 Cope and drag pattern is almost like two-piece pattern.

8. Skeleton
pattern
 It consists of a number of wooden pieces assembled
together to form the desired shape.
 The assembly resembles a skeleton. The skeleton portion
is then covered with thin boards.
 This type of arrangement is used for heavy and big
castings and the numbers required is only a few.
 Material saving for the pattern is achieved and the cost
of pattern is reduced.

9. Follow
board pattern
 Follow board pattern consists of tool that is a simple
wooden board which is used for several reasons.
 The wooden board is used as a base in follow board
pattern for moulding process.
 This pattern is used in processes where casting
structures are weak and they may break after the
application of force.

Pattern
Allowances
 “The difference in the dimension of pattern and final
product of casting is known as pattern allowances.”
 Types of Pattern Allowances :
1. Shrinkage allowance
2. Draft allowance
3. Machining allowance
4. Distortion or camber allowance
5. Shake allowance

1. Shrinkage
allowance
 Shrinkage is defined as reduction is the dimension of the cast
during the cooling or solidification process.
 This is a general property of all materials. The magnitude of
shrinkage varies from material to material but every material
shrinks.
 This allowance when given on to the pattern, will increase its
size.
 Shrinkage is of three types:-
a) Liquid Shrinkage
b) Solidification Shrinkage.
c) Solid Shrinkage
Ex. Cast steel 3-5 mm per 100mm length
 Aluminium 3-4 mm per 100mm length
 Cast iron 2-3 mm per 100mm length

2. Draft
allowance
 Pattern draft is the taper placed on the pattern surfaces
that are parallel to the direction in which the pattern is
withdrawn from the mould (that is perpendicular to the
parting plane), to allow removal of the pattern without
damaging the mould cavity.

3. Machining
allowance
 Most of the castings will have more than one surface
that needs machining. The dimensions get reduced after
machining.
 Hence, the size of the pattern is made larger than
required. During machining, this extra material on the
casting is removed. This allowance depends on the
nature of the metal and the dimensions of the castings.

4. Distortion or
camber
allowance
 When the metal is in cooling process, stress is developed
in the solid metal due to uneven metal thickness in the
casting process.
 This stress may cause distortion or bending in the casting.
 To avoid this bending or distortion in casting, camber is
provided in the opposite direction so that when bending
occurs due to uneven thickness of metal, casting becomes
straight. This change in pattern shape to compensate
bending while casting is known as Bending Allowances.

5. Shake
allowance
 When the pattern is to be removed from the sand of
casting , the pattern will have to be shaken slightly to
remove it from the sand and this will cause a slight
increase in dimension of casting.
 To compensate this increase in dimension of casting, the
patterns are made slightly smaller from casting. This
change in dimension of pattern is known as shaking or
rapping allowances

Materials used
for Patterns:
 a) Wood – Well seasoned teak wood is used for the pattern.
Wood is soft, light and easy to work and takes the shape easily.
Used for producing smaller number of castings. Large and
small patterns can be made. It wears out faster, cannot
withstand rough handling and can absorb moisture.
 b) Metal – Is stronger than wood, but heavier than wood. Can
maintain dimensions accurately for a very long time. Does not
absorb moisture. Used to produce large number of castings.
Has longer life. It is difficult to repair. Bigger sized patterns
cannot be made using this.
 c) Wax – Is a low melting point material. Imparts good surface
to the mould. Can be recovered and used again and again.
Used in investment casting moulding. A combination of
paraffin, wax, bees wax, etc. is used for making the pattern.

Materials used
for Patterns:
 d) Plastics – Plastic material is a compromise between wood
and metal. Thermosetting resins like phenolic resin, epoxy
resin, foam plastic etc. are used as materials for making
pattern. It is strong and light in weight. Does not absorb
moisture during its use and storage. Gives good surface finish
to castings.
 e) Plaster – Gypsum or plaster of Paris is another pattern
material capable of producing intricate castings to close
dimensional tolerances. They are strong, light in weight, easily
shaped, gives good surface finish. However, they used for
small castings only.

BIS colour
coding of
Patterns:
 For easy recognition of different portions of the pattern,
standard colour codes have been recommended for the
finished wooden pattern. The standard colour code
adopted by the American Foundry men s Society ‟s
Society (AFS) is being used (AFS) is being used all over
the world. Each colour conveys how the castings will be.
Sr.
No.
Colour Casting position
1 Black Casting surface to be left unfinished
2 Red Surface of casting to be machined
3 Red stripes on
yellow
background
Loose pieces & seats
4 Yellow Core prints and seats for loose core prints
5 Diagonal black
stripes on a
yellow base
Stop offs (portions of a pattern that form a cavity which
are filled with sand before pouring). They are
reinforcements to prevent delicate portions of the
pattern.

CORES
 “Cores are used in the mould to produce mainly hollow
castings. It is the only method through which cavities
can be produced in the casting without machining.”
 Core sand is used to prepare the core. A core consists of
base sand, a binder and water if required.

Core Materials
 For making a core, proper mixing of some materials are
required in accurate proportions. The materials are as
follow :
1. Core sand or granular refractories
2. Core binders
3. Water (2 % to 7%)
4. Special additives ( corn flour, fuel oil , iron oxide etc.)
1. Core sand or granular refractories: main constituents of
core sand are clean, pure and dry silica sand, zircon,
olivin, carbon and charnotte.

Core Materials
2. Core binders : The main purpose of core binders is to
hold the sand grains together, impart strength and
sufficient degree of collapsibility. The common binders
given below :
 Core oil ( Veg. oils, mineral oils, animal oil etc.)
 Molasses ( for increase the hardness of core )
 Cereal binder ( for green strength, baked strength,
collapsibility)
 Dextrin
 Protein binders

Types and
positions of
core
(i) Horizontal Core: The core is placed horizontally in
the mould, it is known as horizontal core. The core prints
are provided at both ends of the core to rest in the seats
initially provided by the pattern. These core prints helps
the core to be securely and correctly positioned in the
mould cavity.
(ii) Vertical Core: The vertical core is placed vertically
with some of their portion lies in the sand. Usually, top
and bottom of the core is kept tapered but taper on the top
id greater them at bottom.

Types and
positions of
core
(iii) Balance Core: A balanced core is one that is
supported from its one end only. Such cores are used
when the cavity required is only to a certain depth.
(iv) Hanging Core: The core is supported from the top,
the core hangs vertically from the mould and the core may
be provided with a hole for molten metal to flow.

Types and
positions of
core
(v) Drop Core: Drop core is used when the axis of the
desired hole does not co inside with the parting line of the
mould, i.e., the core is required to be placed either above or
below the parting line.
(vi) Kiss Core: In some cases, pattern cannot be provided
with core prints and hence no seat will be available as a rest
for the core. In such cases, the core is held in position
between the cope and the drag by the pressure exerted from
the cope on the drag. Such a core is called a kiss core

METHODOF
MAKING
CORES
 Core making consists of the following four steps:
 1. Core sand preparation
 2. Core making
 3. Core baking
 4. Core finishing
1. Core sand preparation: The core sand of desired
type (dry sand) and composition along with additives
is mixed manually or using muller of suitable type.
2. Core making: Cores are prepared manually or using
machines depending on the needs. Machine like jolt
machine, sand slinger, core blower, etc., are used to
for large scale continuous production, while small
sized cores for limited production are manually made.

METHODOF
MAKING
CORES
 Core baking: Cores are baked in ovens in order to drive
away the moisture in them and also to harden the binder
thereby imparting strength to the core.
 Core finishing: The baked cores are finished by rubbing
or filing with special tools to remove any fins, bumps,
loose sand or other sand projection from its surface.

 The commonly used materials in moulding sand are as
follows :
1. Silica sand (60%to 95%)
2. Sand Binders ( clay biners, organic and inorganic
binders )
3. Additive materials ( sea coal, coal dust, wood flour,
dextrin etc.)
4. Water ( 2% to 8%)

Types of
Moulding
Sand:
 1. Green Sand:
 The green sand is the natural sand containing sufficient
moisture in it. It is mixture of silica and 15 to 30% clay
with about 8% water. Clay and water act as a bonding
material to give strength. Molds made from this sand are
known as green sand mould.
 The green sand is used only for simple and rough
casting products. It is used for both ferrous and non-
ferrous metals.
 2. Dry Sand:
 When the moisture is removed from green sand, it is
known as dry sand. The mould produced by dry sand has
greater strength, rigidity and thermal stability. This sand
is used for large and heavy castings.

Types of
Moulding
Sand:
 3. Loam Sand:
 Loam sand is a mixture of 50 percent sand and 50
percent clay. Water is added in sufficient amount. It is
used for large and heavy moulds e.g., turbine parts,
hoppers etc.
 4. Facing Sand:
 A sand used for facing of the mould is known as facing
sand. It consists of silica sand and clay, without addition
of used sand. It is used directly next to the surface of the
pattern. Facing sand comes in direct contact with the hot
molten metal; therefore it must have high refractoriness
and strength. It has very fine grains.

Types of
Moulding
Sand:
 5. Parting Sand:
 A pure silica sand employed on the faces of the pattern
before moulding is known as parting sand. When the
pattern is withdrawn from the mould, the moulding sand
sticks to it.
 To avoid sticking, parting sand is sprinkled on the
pattern before it is embedded in the moulding sand.
Parting sand is also sprinkled on the contact surface of
cope, drag and cheek.
 6. Backing or Floor Sand:
 The backing sand is old and repeatedly used sand of
black colour. It is used to back up the facing sand and to
fill the whole volume of the box. This sand is
accumulated on the floor after casting and hence also
known as floor sand.

Types of
Moulding
Sand:
 7. Core Sand:
 A sand used for making cores is known as core sand. It
is silica sand mixed with core oil (linseed oil, resin,
mineral oil) and other binding materials (dextrine, corn
flour, sodium silicate). It has remarkable compressive
strength.
 8. Molasses Sand:
 A sand which carries molasses as a binder is known as
molasses sand. It is used for core making and small
castings of intricate shapes.

Properties of
Moulding
sand
 1. Porosity:
 Porosity also known as permeability is the most important
property of the moulding sand. It is the ability of the
moulding sand to allow gasses to pass through. Gasses and
steam are generated during the pouring of molten metal into
the sand cavity. This property depends not only on the shape
and size of the particles of the sand but also on the amount of
the clay, binding material, and moisture contents in the
mixture.
 2. Cohesiveness:
 Cohesiveness is the property of sand to hold its particles
together. It may be defined as the strength of the moulding
sand. This property plays a vital role in retaining intricate
shapes of the mould. Insufficient strength may lead to a
collapse in the mould particles during handling, turning over,
or closing. Clay and bentonite improves the cohesiveness.

Properties of
Moulding
sand
 3. Adhesiveness:
 Adhesiveness is the property of sand due to which the sand
particles sticks to the sides of the moulding box.
Adhesiveness of sand enables the proper lifting of cope along
with the sand.
 4. Plasticity:
 Plasticity is the property of the moulding sand by virtue of
which it flows to all corners around the mould when rammed,
thus not providing any possibility of left out spaces,
and acquires a predetermined shape under ramming pressure.
 5. Flow-Ability:
 Flow-ability is the ability of moulding sand to free flow and
fill the recesses and the fine details in the pattern. It varies
with moisture content.

Properties of
Moulding
sand
 6. Collapsibility:
 Collapsibility is the property of sand due to which the
sand mould collapse automatically after the
solidification of the casting. The mould should
disintegrate into small particles of moulding sand with
minimum force after the casting is removed from it.
 7. Refractoriness:
 Refractoriness is the property of sand to withstand high
temperature of molten metal without fusion or soften.
 Moulding sands with poor refractoriness may burn when
the molten metal is poured into the mould. Usually, sand
moulds should be able to withstand up to 1650°C.

Properties of
Moulding
sand
 8. Green strength :
 The green sand after water has been mixed into it, must have
sufficient strength and toughness to permit the making and
handling of the mould.
 9. Dry strength :
 As soon as the molten metal is poured into the mould, the
moisture in the sand layer adjacent to the hot metal gets
evaporated and this dry sand layer must have sufficient
strength to its shape in order to avoid erosion of mould wall
during the flow of molten metal. The dry strength also
prevents the enlargement of mould cavity cause by the
metallostatic pressure of the liquid metal.

Testing of
MouldingSand
 Grain fitness test:
 The grain size, distribution, grain fitness are determined
with the help of the fitness testing of moulding sands.
The apparatus consists of a number of standard sieves
mounted one above the other, on a power driven shaker.
 The shaker vibrates the sieves and the sand placed on
the top sieve gets screened and collects on different
sieves depending upon the various sizes of grains
present in the moulding sand.
 The top sieve is coarsest and the bottom-most sieve is
the finest of all the sieves. In between sieve are placed in
order of fineness from top to bottom.

 Moisture content test:
 Moisture is the property of the moulding sand it is
defined as the amount of water present in the moulding
sand. Low moisture content in the moulding sand does
not develop strength properties. High moisture content
decreases permeability.
 Procedures are:
 1. 20 to 50 gms of prepared sand is placed in the pan and
is heated by an infrared heater bulb for 2 to 3 minutes.
 2. The moisture in the moulding sand is thus evaporated.
 3. Moulding sand is taken out of the pan and reweighed.
 4. The percentage of moisture can be calculated from the
difference in the weights, of the original moist and the
consequently dried sand samples.

Mould
 “A mould is a void or cavity created in a compact sand
mass, which when filled with molten metal, produces a
casting.”
 “The process of making mould or cavity in the compact
sand is called moulding.”

Types of
Mould
1. Green sand moulds
2. Dry sand moulds
3. Skin dried moulds
4. Air dried moulds
5. Loam moulds
6. Cement bonded sand moulds
7. Plaster moulds
8. Carbon dioxide moulds
9. Shell moulds
10. Metallic moulds

Types of
Mould
1. Green sand moulds : The green word indicates that the
moulding sand is in moist state at the time of pouring
of metal.
 “ A green sand mould is that mould in which the molten
metal is poured immediately after the mould is ready.”
2. Dry sand moulds : The word dry indicate that at the
time of pouring of metal, the mould is in dry state.
 Dry send moulds are actually made with moulding sand
in green condition and then moulds are dried in oven
before the molten metal is poured in them.
3. Skin dried moulds : These moulds are a compromise
between the green and dry sand moulds.
 In this case, the full mould is not dried, but only a
surface layer of about 12.5 to 25 mm of mould cavity is
dried by means of a gas torches or heaters and that’s
why, they are called skin dried sand moulds.

Types of
Mould
4. Air dried moulds : These moulds are similar to skin dried
moulds in the sense that their skin is dried, but they are not
artificially heated.
 After the mould has been made in the green state, it is open to
the atmosphere for certain period of time, during which some
of moisture from mould surface gets evaporated.
5. Loam Sand moulds: A loam mould is preferred for making
large castings. These moulds are built up with bricks and
iron reinforcements and are given a thick coating of loam
mortar all over.
6. Cement bonded sand moulds : The main advantage this
kind of mould is that they do not require ramming as the
setting of cement bond gives sufficient hardness and
strength.
 water ( 4.5 %) + cement ( 10 %)+ pure silica sand (85.5 %)

Types of
Mould
7. Plaster Moulds : The mould material in this case is
gypsum or plaster of paris and to this pop, additives
like talc, asbestos fibres, silica flour etc. are added in
order to control the contraction characteristics of mould
as well as settling time.
8. Carbon dioxide moulds : such moulds are made from a
mixture of clean, dry silica and sodium silicate ( as
binder).
 The moulding mixture thus obtained is rammed around
the pattern and gassed with 𝐶𝑂2. 𝐶𝑂2 gas is used only as a
mould hardener. The mechanism of hardening in carbon
dioxide mould is based on the fact that if 𝐶𝑂2 gas is
passed through a sand mixture containing sodium silicate,
the sand immediately becomes extremely strong bonded
as the sodium silicate becomes a stiff gel.

Types of
Mould
9. Shell moulds : The shell moulds are produced with the
help of heated steel pattern. These moulds are
prepared by heating a mixture of sand and phenolic
resin over the surface of metallic pattern. This enables
the production of a thin layer of uniform thickness
which, when separated from the pattern surface, forms
one part of shell. Two shells are assembled to form the
mould.
10. Metallic moulds: They are also known as permanent
moulds because of their long life.
 These moulds are generally made in two halves and they
are clamped to get the proper mould cavity.

Step involved
in making a
mould
 There are six steps in this process:
1.Place a pattern in sand to create a mould.
2.Incorporate the pattern and sand in a gating system.
3.Remove the pattern.
4.Fill the mould cavity with molten metal.
5.Allow the metal to cool.
6.Break away the sand mould and remove the casting.

Hand tools
used for mould
making
 1.Showel: It consists of iron pan
with a wooden handle. It can be
used for mixing and conditioning
the sand.
 2. Trowels: These are used for
finishing flat surfaces and
comers inside a mould. Common
shapes of trowels are shown as
under. They are made of iron
with a wooden handle.
 3. Lifter: A lifter is a finishing
tool used for repairing the mould
and finishing the mould sand.
Lifter is also used for removing
loose sand from mould.

Hand tools
used for mould
making
 4. Hand riddle: It is used for ridding of
sand to remove foreign material from it. It
consists of a wooden frame fitted with a
screen of standard wire mesh at the
bottom.
 5.Strike off bar: It is a flat bar, made of
wood or iron to strike off the excess sand
from the top of a box after ramming.
 Its one edge made bevelled and the
surface perfectly smooth and plane.
 6. Vent wire: It is a thin steel rod or wire
carrying a pointed edge at one end and a
wooden handle or a bent loop at the
other. After ramming and striking off the
excess sand it is used to make small
holes, called vents, in the sand mould to
allow the exit of gases and steam during
casting

Hand tools
used for mould
making
 7. Rammers: Rammers are used for
striking the sand mass in the
moulding box to pack it closely
around one pattern. Common types
of rammers are shown as under.
 8. Swab: It is a hemp fiber brush
used for moistening the edges of
sand mould, which are in contact
with the pattern surface, before
withdrawing the pattern. It is also
used for coating the liquid blacking
on the mould faces in dry sand
moulds.
 9. Sprue pin: It is a tapered rod of
wood or iron, which is embedded in
the sand and later withdrawn to
produce a hole, called runner,
through which the molten metal is
poured into the mould.

Hand tools
used for mould
making
 10. Sprue cutter: It is also used for the same purpose as a
sprue pin, but there is a marked difference between their use
in that the cutter is used to produce the hole after ramming
the mould. It is in the form of a tapered hollow tube, which is
inserted in the sand to produce the hole.

Moulding
Boxes or Flasks
 “It is a container in which sand is packed and rammed.”
 It can be made of either wood or metals.
 Following three types of flasks are widely used in
foundry:
1. Box type flask
2. Snap flask
3. Wooden moulding box

Box type flask
 It is also called tight or permanent flask.
 It is made up of wood or metal and is useful for making
small and medium castings.
 These flasks are removed after the casting has solidified.

Snap flask
 It is made of wood and generally used in the production
of small casting.
 These flasks are fitted with hinge at one corner and a
fastener (Nut and bolt) at the corner diagonally opposite.
 After mould has been made, it can be removed.
 So one flask is used for many moulds, therefore, this is
considerable economy.

Wooden
moulding box
 It is used for large casting in limited quantity.
 The side timbers are continued beyond the ends of box to
form two handles at each end.
 Cope and Drag portions are held together by suitable steel
lugs.
 The cross bars prevent the sand from falling out when the top
part of the box (i.e. cope) has been rammed up and is lifted
away from the bottom part of the box (i.e. drag).
 A moulding board and a bottom board complete the flask.

MOULDING
METHODS
 The various sand moulding methods are:-
 Bench moulding
 Floor moulding
 Pit moulding &
 Machine moulding
 Bench Moulding: Bench moulding is preferred for
small jobs and is carried out on a bench of
convenient height. The bench moulder (mould
maker) prepares the mould manually while
standing.

MOULDING
METHODS
 Floor Moulding: Floor moulding is preferred for large
size moulds that cannot be carried out on benches. In
most of the foundries, moulding is carried out on floors
irrespective of the size of jobs.
 Pit moulding: Large castings that cannot be
accommodated in mould box (flasks) are made in pits
dug on the floor. The pits form the drag part of mould
and a separate cope box is placed above the pit. The
mould maker enters the pit and prepares the mould. The
cope box is rammed using dry sand with risers placed at
suitable location. The walls of the pit are lined with
brick and the bottom is covered with moulding sand
with connecting vent pipes to the floor level for easy
escape of hot gases. A crane is used for handling the
cope box and other operations.

MOULDING
METHODS
 Machine moulding: In bench, floor and pit moulding,
all the operations viz., ramming, withdrawing pattern,
rolling flasks, etc., are done manually by mould makers.
But when large number of castings are to be produced
manual operations consumes more time and also
accuracy and uniformity of moulding varies. To
overcome this difficulty, machine moulding is used. The
operations perform by machines includes:
 Ramming moulding sand: By jolt operations or Jolt
squeeze machines.
 Rapping the pattern: Patterns are rapped in the sand with
vibrators that are operated electrically or by compressed
air.
 Removal of pattern: By raising or lowering the mould,
or by raising or lowering the pattern.

Moulding
Machines
 “Moulding machine is a device consisting of a large
number of parts and mechanisms which transmits and
directs various forces and motions in required directions
so as to prepare a sand mould.”
 Moulding machines performs the following operations:
i. Ramming of sand in the mould
ii. Lifting or drawing of pattern from the mould
iii. Rolling over or inverted the mould.
 Two main classes of machines are as follows :
A. Hand moulding machines
B. Power moulding machines

Hand
Moulding
Machines:
A. Hand Moulding Machines:
 Withdrawing the pattern from mould - Mechanically
 Ramming of sand – Manually
Hand moulding machines are following types :
1. Plane stripper type machine
2. Pin lift or push of type machine
3. Roll over type machine

Plane stripper
type machine
 The machine consists of a stationary table on which a
flask is supported, containing half pattern mounted on a
pattern plate.
 A stripping plate is incorporated between the pattern
plate and flask.
 Stripping plate has a hole/holes so that it fits accurately
around the pattern.
 The pattern is withdrawn through the stripping plate by
lowering the ram.

Pin lift or push
of type
machine
 The machine consists of a stationary table on which
pattern plate containing pattern is fixed. Four lifting pins
can be raised or lowered the table.
 The flask is placed around the pattern and is supported
on the lifting pins.
 For withdrawing the pattern, the flask is pushed upward
away from the pattern as the four pins are lifted up
through the holes in the table and pattern plate.

Roll over type
machine
Roll over type machine:
 It is considered to be more suitable for
withdrawing the patterns.
 It consists of a roll over frame on
which the pattern plate is fitted
containing the pattern.
 Flask or moulding box is placed
around the pattern and can be clamped
with the pattern plate.
 The whole assembly can swivel (turn)
on two trunnions.
 Roll over frame alongwith the mould
may be rotated by hand.

 Power moulding machines: these machines are
following types :
i. Jolt machines
ii. Squeeze Machines
iii. Jolt- squeeze machines
iv. Sand slinger
v. Diaphragm moulding machine

5. Diaphragm moulding machine :
 It is used to achieve uniform hardness of moulding sand.
 In this machine, the flask and pattern are mounted on a trolley
which can be moved along the machine bed ways by means
of an operated piston.
 In this, first flask is filled with sand and then the trolley and
flask is moved to the right side so that the flask comes under
the diaphragm head.
 The air pressure is now used to force the rubber diphragm
over the entire surface of pattern.

DieCasting
 Die Casting Process is a metal casting process that is
characterized by forcing the molten metal into a mould cavity
under the application of high pressure or under gravity.
 Because of the metal mould, the same mould can be used for
producing the infinite number of castings, hence the process is
also called a Permanent Mould Casting Process.
 Applications: Automotive connecting rods, pistons, cylinder
beds, electronic enclosures, toys, plumbing fittings.

Types of Die
Casting:
 Types of Die Casting:
 There are two types of Die Casting.
1.Gravity Die Casting
2.Pressure Die Casting
1. Gravity Die Casting:
• If the flow of molten metal into the mould cavity is due to the
gravitational force, then it is called Gravity Die Casting.
• In this process, the molten metal is to be poured into the
casting cavity via the pouring basin.
• Because of the problem of flow of the molten metal into
every corner of the casting cavity due to the gravitational
force, the gravity Die casting will be used for producing the
simple shape of the castings only.
• For example, IC engine piston made by aluminum alloys.

Pressure Die
Casting:
2. Pressure Die Casting:
• If the external pressure is used for molten metal to enter into
the mould cavity called Pressure Die Casting.
• Due to the external pressure, it is possible to flow the molten
metal into every corner of the complex shape of a cavity.
hence the complex shape of the casting can be easily
produced.
 For example, Carburettor body made by aluminium alloys
 Pressure Die Casting is classified into two types.
• Hot Chamber Die Casting
• Cold Chamber Die Casting

HotChamber
DieCasting
 In this Hot Chamber Die Casting Process, the
combustion area or the furnace is attached to the system
itself. The metal is to be placed in the pot such that it can
form into a molten metal by the application of furnace.
 When the molten metal is prepared then it has to be
injected into the cavity of the die so that the components
can be produced.
 The plunger moves upwards into the cylinder and
thereby the intake port opens which gives the entry for
the molten metal to enter into the cavity via gooseneck
pipe.
 The gooseneck pipe is insulated such that proper
solidification can be done. After it, the molten metal
passes through the nozzle into the die opening and
solidifies in the die.

HotChamber
DieCasting
 After solidification, the component is cooled and then it is
removed out from the die by moving the movable platen
towards its left. In this way, the components will be produced
in the hot Chamber Die Casting Process.
 Advantages of Hot Chamber Die Casting:
• Fast cycle time (approximately 15 cycles a minute) in Hot
Chamber Die Casting Process.
• There is a convenience of melting the metal in the hot
chamber machine itself.
• Zinc- tin and lead-based alloys were used.
 Disadvantages of Hot Chamber Die Casting:
• This process is applicable to low melting point metals only.

ColdChamber
DieCasting:
 The only difference between these two processes was the
presence or absence of the combustion chamber. As the
combustion chamber was attached to the machine itself in the
hot chamber die casting process.
 Whereas in the Cold Chamber Die Casting Process, the
molten metal is prepared away from the system and is
brought up to the system by means of a ladle/holding furnace.
Then the same procedure follows. i.e. the power cylinder
retracts the piston such that the molten metal enters into the
unheated shot chamber and then the piston/plunger is relieved
so that there is an application of force on the molten metal
such that it enters into the mould cavity via the nozzle.

ColdChamber
DieCasting:
 Advantages of Cold Chamber Die Casting:
• Cold Chamber Die Casting Process can be applicable for high
Melting Point metals.
 Disadvantages of Cold Chamber Die Casting:
• The cycle time was very slow compared to the hot Chamber
Die Casting Process.
• The cycle time was slow due to the need to transfer the
molten metal from the furnace to the cold chamber machine.
• Due to this, the productivity will be less.

Centrifugal
casting
 Centrifugal casting is the method of producing casting
by pouring the molten metal into a rapidly rotating
mould. The metal is thrown out towards the mould face
by the centrifugal force.
 It is a method of casting parts having axial symmetry.
 The mould is kept rotating till the metal has solidified.
 As the mould material steels, Cast irons, Graphite or
sand may be used.

 According the shape of the mould, the centrifugal
casting methods can be classified as follows:
1. True-centrifugal casting
2. Semi centrifugal casting
3. Centrifuge casting

True-
centrifugal
casting
 True centrifugal casting is used to create symmetrical
round hollow parts, such pipes and tubes.
 The process does not require the use of cores.
 It creates the parts through pure centrifugal force
generated by continuous rotation along the horizontal or
vertical axis.
 The centrifugal force drives the molten metal to the
outer walls while contaminants converge in the centre.
 Once the metal solidifies, the piece can be removed
from the mould and the unwanted materials removed
through machining operations.

Semi
centrifugal
casting
 When the moulds are rotated about the central vertical
axis and casting is symmetrical about the axis of
rotation, the process is called Semi centrifugal casting.
 The centrifugal force helps to flow of molten metal from
a central feeding sprue to fill the mould cavities.
 The centre of castings is usually solid, but if required, a
core may be used to produce central hole.
 The speed of rotation of these moulds is much lower
than that in true centrifugal casting.
 In this casting, it is not necessary to cast only one mould
at a time. Several moulds can be stacked together, one
over the other and fed simultaneously through a
common central sprue.
 Applications – gears, flywheels, track wheels etc.

Centrifuge
casting
 In this casting, the axis of mould and that of rotation do
not coincide with each other.
 Parts are not symmetrical about any axis of rotation and
cast in a group of moulds arranged in a circle.
 The metal is poured along this axis of rotation through a
central sprue and made to flow into mould cavities
through radial ingates cut on the mould interface under
the action of centrifugal force.
 A number of similar components can be cast
simultaneously.
 Applications- valve bodies, plugs, etc.

Gating system
 “The passage in the mould meant for carrying molten
metal to the mould cavity is known as gating system.”
 The molten metal from the ladle is not introduce directly
into the mould cavity because it will strike the bottom of
the mould cavity with great velocity and can cause
erosion of the bottom of mould cavity.
 Due to this, molten metal is introduce into the mould
cavity from the ladle through a gating system.

Elements of
GatingSystem
 The main elements of a gating system are as follow:
A. Pouring basin,
B. Sprue,
C. Runner,
D. Gates,
E. Risers.

Pouring
Basin/Cup
 The molten metal is poured into the pouring basin which acts as
a reservoir from which it moves smoothly into the sprue.
 The pouring basin may be cut into the cope portion directly or a
separate dry sand pouring basin may be prepared and used.
 The molten metal in the pouring basin should be full during the
pouring operation to avoid the atmospheric air and slag from
entering into mould cavity.
 The pouring basin also stops the slag from entering the mould
cavity by means of skimmer or skim core. It holds back the slag
or dirt which floats on the top and allows only clean metal
underneath it into the sprue.

Advantages of
Pouring Basin:
1. This eliminates aspiration.
2. This makes pouring easier.
3. This makes more control over the amount of metal
poured.

Sprue
 “The vertical passage through which molten flows down
from a pouring basin to the parting plane is called
sprue.”
 It connects the pouring basin to the runner or the gates.
 The basic requirements of a sprue are as follows:
1. The size of the sprue determines the rate of flow of
metal. So choose a adequate size that gives less speed,
splattering and fill the molten metal in the mould
cavity without any laps.
2. The velocity of the metal near the bottom of sprue is
considerably high than the velocity at the top of sprue.
Volume flow rate must be same at all points in the
sprue and the stream contracts as it falls.
 This contraction creates a partial vacuum between the
sprue walls and the metal stream and air is aspirated into
the metal.

Sprue
 This air aspiration can be eliminated by using taper shape sprue.
3. Due to high kinetic energy and abrupt change in the direction
of flow at the base of sprue, results in significant turbulence
and metal damage.
 This turbulence and metal damage can be avoided by using a
sprue well at the base of sprue.
 Sprue base : “Where a sprue joins a runner, usually, an
enlargement in the runner is made. This enlargement known as
sprue base or sprue well.”

Runner
 “In large casting, a runner may be used which takes the
molten metal from the sprue base and distributes it to
several gates around the cavity.”
 Runner may be located either in the cope or in the drag.
 The man advantages of putting the runner in the cope is
that it works as a riser also and it is not necessary to
attach an riser to the mould cavity.
 The runner located in the drag is only used while casting
of metals like aluminium or magnesium.

Gate
 “The opening or channel in the mould connected with
sprue through which the molten metal flows into the
mould cavity is known as gate.”
 The size of gate depends upon the rate of solidification.
 Types of gates:
1. Top gate
2. Bottom gate
3. Parting line gate
1. Top gate : it is sometimes also called drop gate
because the molten metal just drops on the sand in the
bottom of the mould. In top gating, the molten metal
from the pouring basin flows down directly into it.

2. Bottom gate : in this, the metal enters the mould
cavity from the bottom. A bottom gate is made in the
drag portion of mould.
3. Parting line gates : The runner and the gates which are
formed along the parting line separating the cope and
drag portion of the mould are called parting line gates.

Riser
 It is a passage made in the cope through which the
molten metal rises after the mould is filled up.
 Most common shape of riser is cylindrical.
 Advantages of riser :
1. In the starting of pouring, it allows the air, steam and
gases to go out of the mould.
2. On seeing the rising molten metal through it, it is
ensured that the mould cavity has been completely
filled up.
3. It acts as a reservoir to feed the molten metal to the
casting to compensate the shrinkage during
solidification.
4. Risers promote directional solidification.

 Thickest part of casting–last to freeze, riser should feed
directly to these regions.

Types of Riser:
 Depending upon location of the
riser, it can be classified into two
ways:
1. Top Riser: If the riser is placed
at the top of casting or at the end
of moulding cavity, it is called
as top riser or dead riser or cold
riser.
2. Side Riser : If the riser is
located between runners and
mould cavity, it is known as side
riser.
 It is also called a live or hot riser
since it is filled last and contains
the hottest metal.

Types of Riser:
 A riser may either be an open riser or blind riser.
1. Open riser : This type has its top surface exposed to
atmosphere.
 It is commonly employed on the top most portion of the
casting, or, alternatively, on the side at the parting line.
 Advantages of open riser :
i. These can be easily moulded.
ii. These serve as collectors of non-metallic inclusions
floating up to the surface.
Limitations :
i. These can be moulded only in the cope.
ii. Open risers are holes through which foreign matter
may get into the mould cavity.

Types of Riser:
2. Blind riser : A riser which does not expose to the top
of the cope and entirely surrounded by moulding sand
is known as blind riser.
 Advantages :
i. It can be removed more easily from the casting than
an open riser.
ii. It can be smaller than open riser.
 Limitations:
i. It is difficult to mould a blind riser.

Stages of
shrinkage/
contraction :
 When molten metal solidifies, contraction or shrinkage
in its volume takes place. The contraction of metal takes
place in three stages:
1. Liquid contraction : It occurs when the molten metal
cools from the temperature at which it is poured to the
temperature at which solidification commences.
2. Solidification contraction: It takes place during the
time the metal changes from the liquid state to the
solid. i.e. when the metal loses its latent heat.
3. Solid Contraction : it occurs when the metal cools
from the freezing temperature to the room
temperature.
 The shrinkage for stage 3 is compensated by providing
shrinkage allowance on pattern, while the shrinkage
during stages 1 and 2 are compensated by providing
risers.

Directional
solidification :
 Since all parts of the casting do not cool at the same rate
due to varying sections and different rates of heat loss to
adjoining mould walls, some parts tend to solidify more
quickly than others.
 This contraction phenomenon causes voids and cavities
in certain regions of casting.
 “The solidification of the molten metal in the mould
should start at points much farthest from the feeding
heads (i.e. sprue ) and that solidification should proceed
progressively towards the feedings which should be last
part to solidify. This type of solidification is called
controlled or directional solidification.”
 In this way, all the voids and cavities due to shrinkage
concentrate in the feeders and casting free from voids.

PIT FURNACE
 “A furnace made in pit for melting metal for taking
casting process is called a pit furnace.”
 It is used to melt small quantities of ferrous and non-
ferrous metals for producing casting.
 it is provided with refractory lining inside and a chimney
at the top.
 Coke is used as fuel. Broken pieces of metal are placed
in the crucible.
 Coke bed is ignited in the furnace and the crucible
placed into it is heated.
 Due to heating, metal gets melted in the crucible.
 After melting, crucible is lifted with the help of crucible
tong and placed in the ladles from where it is poured
into the moulds.

CUPOLA
FURNACE
 Construction:
 Cupola consists of a cylindrical steel shell with its interior
lined with heat resisting fire bricks.
 It consist of drop doors at the bottom after closing of which, a
proper sand bed could be prepared.
 This send bed provides the necessary refractory bottom for
the molten metal and coke.
 Immediately above the send bed is the metal tapping hole
which is initially closed with clay till the molten metal is
ready for tapping.
 Above the metal tapping hole, normally in a position opposite
to it, is the slag hole through which the slag generated during
the melting process is tapped.
 Above the slag hole is the wind box which is connected to air
blowers for supplying the air at a given pressure and quantity.
The air enters the cupola through the tuyeres.
 Above the charging platform is the charging door in the shell
from where the charge consisting of a combination of pig
iron, iron scrap, coke, and flux is put into the cupola.

CUPOLA
FURNACE
 Working of cupola:
1. Preparation of cupola : Clean out the slag and repair
the damaged lining with the mixture of fire clay and
silica sand. After this, bottom doors are raised ant
bottom sand is introduced. The surface of the sand
bottom is sloped from all directions towards the tap
hole. Slag hole is also formed to remove the slag.
2. Firing the cupola : A fire of kindling wood is ignited
on the sand bottom. After proper burning of the wood,
coke is added to a level slightly above the tuyeres. Air
blast at a slower rate is turned on.
3. Charging the cupola: After proper burning, alternate
layers of pig iron, coke and flux(limestone) are
charged from the charging door until the cupola is full.
Flux is added to prevent the oxidation as well as to
remove the impurities. Flux is 2 to 3% of the metal
charge by weight.

CUPOLA
FURNACE
4. Soaking of Iron: After charging the furnace fully, it is
allowed to remain as such for about 1—1.5 hr. During this
stage charge slowly gets heated up because the air blast is
kept shut this time and due to this the iron gets soaked.
5. Starting the Air Blast: The air blast is opened at the end of
the soaking period. The tap hole is kept closed till the
metal melts and sufficient metal is collected. The rate of
charging must be equal to the rate of melting so that the
furnace is kept full throughout the heat.
6. Pouring the molten iron : When sufficient metal collects in
the well, the slag hole is opened and the slag is removed.
After this, tap hole is opened to collect the molten metal.
7. Closing the Cupola: When no more melting is required,
the feeding of charge and air blast is stopped. The prop is
removed, so that the bottom plate swings to open. The slag
deposited is removed.

Oil FiredTilting
Furnace:
 It consist of an outer shell having a refractory lining
inside. The hollow portion around the crucible forms a
chamber through which burning fuel circulates.
 Working: Air from the blower and oil from the tank are
fed through respective pipes into a common chamber F
as shown in fig.
 Then mixture of compressed air and oil is made to pass
through the small nozzle, thereby, increasing its velocity.
Thus this mixture is fed into the furnace at a sufficient
high velocity.
 For starting ignition, a small piece of cotton waste or
cloth dipped in kerosene oil or similar other fuel is
attached at C and same is lit. The metal charge is placed
in the crucible and the fuel supply is started.

Oil FiredTilting
Furnace:
 The burning fuel circulate the crucible and the
temperature of metal rises, which ultimately starts
melting.
 When complete metal charge gets melted, the fuel
supply is cut off and the molten metal is collected in a
separate ladle for pouring.
 For collecting this metal, the furnace is tilted along with
the crucible by means of tilting wheel.

Electric
Induction
Furnace :
 Electric power to this furnace is supplied by an
induction coil placed around the crucible concentrically.
The coil is made of thick copper tube, inside which
cooling water is circulated. The crucible and coil are
packed in a rectangular box/ shell.
 The box is placed at a raised level in the platform and
has tilting mechanism for collecting the liquid metal.
 The normal frequency of 50 to 60 Hz A.C. can be used
for melting the iron.
 Medium frequency i.e. 200 to 5000 Hz is used for
furnace can be started cold.

1. Blow Holes :
 When gases entrapped on the surface
of the casting due to solidifying
metal, a rounded or oval cavity is
formed called as blowholes.
 Causes :
i. Lack of ventilation
ii. Excess moisture in moulding sand
iii. Low permeability and excessive
fine grain sands.
 Remedies:
i. Improve venting.
ii. Control moisture content.
iii. Mould should not be rammed
excessively hard.
iv. Increase grain size.

2. Pinholes:
 They are very small holes of about 2
mm in size which appears on the surface
of the casting. This defect happens
because of the dissolution of the
hydrogen gases in the molten metal.
When the molten metal is poured in the
mould cavity and as it starts to solidify,
the solubility of the hydrogen gas
decreases and it starts escaping out the
molten metal leaves behind small
number of holes called as pinholes.
 Causes :
i. High Pouring temperature.
ii. Less flux used.
iii. Low permeability
 Remedies:
i. Increase flux proportion.
ii. increase permeability

3. Fusion:
 Sand may fuse and stick to the
surface with a resultant rough glossy
appearance.
 Causes :
i. Lack refractoriness of sand.
ii. Excessively high temperature of
molten metal.
 Remedies:
i. Pour metal at proper lower
temperature.
ii. Proper refractoriness of sand.

4. Misrun and
Cold Shuts:
 “When the metal is unable to fill the
mould cavity completely and thus
leaves unfilled portion. It is called
misrun.”
 A cold shut occurs when two metal
streams do not fuse together properly.
 Causes :
i. Lack of fluidity in molten metal.
ii. Faulty gating system.
iii. Slow pouring of metal.
 Remedies:
i. Pour sufficiently hot metal.
ii. Make a rapid pouring.
iii. Modify gating design.

5. Shrinkage:
 Metals shrink as they solidify. If this
shrinkage is not compensated by
providing risers etc. voids will occur
on the surface or inside the casting.
 Causes :
i. Faulty gating and risering.
 Remedies:
i. Ensure proper directional
solidification by modifying gating,
risering.

6. Drop:
 An irregular shaped projection on the
cope surface of a casting is called
drop.
 This is caused by dropping of sand
from the cope into the mould.
 Causes :
i. Insufficient water content.
ii. Too soft ramming.
iii. Rough handling of mould.
 Remedies:
i. Mix proper quantity of water.
ii. Provide harder ramming.
iii. Handle the mould carefully.

7. Shift:
 The defect caused due to
misalignment of upper and lower
part of the casting and misplacement
of the core at parting line.
 Causes :
i. Misalignment of flask.
ii. Faulty Core boxes.
 Remedies:
i. Proper alignment of the pattern or
die part, moulding boxes.
ii. Replace the core boxes.

8. Hot tears:
 A crack that develops in a casting
due to high residual stresses is called
a hot tear.
 Causes :
i. Lack of collapsibility.
ii. Fine moulding sand.
iii. High moisture.
 Remedies:
i. Improve collapsibility.
ii. Increase grain size.

9. Scabs:
 Liquid metal penetrates behind the
surface layer of sand.
 Causes :
i. Too fine sand.
ii. Uneven mould ramming.
iii. High moisture content of sand.
 Remedies:
i. Increase grain size.
ii. Reduce moisture.

10. Swell:
 It is the enlargement of the mould
cavity because of the molten metal
pressure, which results in localised or
overall enlargement of the casting.
 Causes :
i. Defective or improper ramming of
the mould.
 Remedies:
i. The sand should be rammed
properly and evenly.

11. Sand
Inclusion:
 Holes in the surface of casting
usually filled with sand are known as
sand inclusions.
 Causes :
i. Low moisture
ii. Poor moulding Practice.
iii. Improper flux.
 Remedies:
i. Control moisture at correct
temperature.
ii. Use proper flux.
iii. Increase mixing time.

12. Warpage:
 Casting deform because of the stresses
set up in them internally due to
different solidification rates
experienced by different sections of
large, long and wire flat casting. This
deformation is called warpage.
 Causes :
i. Improper directional solidification.
ii. Faulty casting design.
 Remedies:
i. Facilitate Proper directional
solidification.
ii. Use correct casting design.

13. Cuts and
Washes:
 Casting surface resulted due to
erosion of mould surface by the
poured metal is known as a cut.
 Casting portion resulted due to a
portion of mould having been
washed by in-flowing metal is
known as a wash.
 Causes :
i. High moisture
ii. Improper gating system.
 Remedies:
i. Control moisture.
ii. Improve gating system.

14. Run Outs:
 Drainage of metal from the cavity is
called run out. It gives incomplete
casting.
 Causes :
i. Too large pattern.
ii. Excessive pouring pressure.
 Remedies:
i. Use correct size pattern.
ii. Moderate pouring pressure.

15. Rat Tails or
Buckles :
 Slight compression failure of a thin
layer of moulding sand is called as
Rat Tails and more severe
compression failure is called buckles
i.e. buckling of sand.
 Causes :
i. Excessive mould hardness.
ii. Improper casting design.
 Remedies:
i. Reduction in mould hardness.
ii. Modification in casting design.

Testing of
Defects/
Inspection of
castings
 Two methods are used for testing:
1. Destructive Inspection/Testing: In this method, the sample of
casting is destroyed during inspection. In this method, out of
the given lot of castings, a specimen piece is picked up and
is cut into two or more parts and then examined for internal
discontinuities.
2. Non-Destructive Inspection/Testing: In non-destructive
inspection method, inspection is done without destroying the
casting.
1. Visual inspection
2. Dimensional inspection
3. Pressure testing
4. Magnetic particle inspection
5. Radiographic inspection
6. Eddy current inspection
7. Dye penetrate inspection
8. Sound testing
9. Impact testing
10. Ultrasonic testing

Magnetic
particle
inspection
 It is used to detect surface or near surface discontinuities
in ferromagnetic materials.
 The principle used in this technique is that if a crack is
present in a magnetic material through which a magnetic
filed is passing, the lines of force will be distorted near
the fault. In case of piece without any crack, lines of
force will be uniform and straight.
 When the casting is magnetised, irregularities in the
material such as blow holes, cracks and inclusions
produce a distortion in the induced magnetic field.
 Such irregularities have different magnetic properties
than the surrounding metal and produce an abrupt
change in the path of the magnetic flux flowing through
the piece.
 This distortion in the magnetic flux can be detected by
the application of a fine powder of magnetic material,
which accumulated over such discontinuities.

 There are three basic operations in this technique:
1. Establish a strong magnetic field in the object.
2. Apply magnetic particles or powder to the test object
either in the dry form or suspended in the liquid.
3. Visually examine the test object.

Radiographic
inspection
 Internal defects in a casting such as cracks, voids,
cavities and porosity etc. as well as surface cracks can
be detected by this method using X-rays and 𝛾 gamma
rays.
 This is a non-destructive test. Radiographic examination
gives a permanent film record of defects that is easy to
understand.
 Working: In X-rays testing, short wavelength rays from
an X- ray tube are passed through a casting and recorded
on a special film held against the opposite face of
casting.
 If the casting has an internal defect, then the density of
the material at that spot will be less as compared to
surrounding material.
 This area will allow more penetration of the rays i.e. the
section of the casting with cracks will absorb a small
amount of X-rays as compared to fully dense material.

 This will result in the appearance of a dark shadow on
the X-ray film.
 𝛾 gamma ray testing is used for checking heavy walled
castings. Unlike X-rays, gamma rays from its source are
emitted in all directions, therefore, a number of separate
casting having cassette containing film fastened to back
of each casting are disposed in a circle around the source
placed in a central position.
 This way, many castings can be radiographed
simultaneously and overnight exposers may be taken
without continuous supervision.
Rays Source Remarks
X-rays High Voltage 200 kV – thickness up to 50mm & 1 million
volts for thickness from 50 to 180mm
𝛾 (gamma)
rays
Radium or its
salt and CO-
60
Heavy walled casting

Ultrasonic
testing
 It is based on the principle of reflection and transmission
of high frequency sound waves. It is more sensitive
method.
 Vibrational waves which have a frequency above the
hearing range of the normal ear are called ultrasonic
waves, which generally include all waves having a
frequency greater than about 20,000 kHz. Ultrasonic
waves are generally generated by the piezoelectric effect
which convert electrical energy to mechanical energy.
 A beam of ultrasonic waves is set up at one surface of a
casting. The waves travel through the part to the
opposite surface and are reflected back to the original
point.

 Any discontinuity in the path of waves scatters the
waves and the waves are reflected back sooner from the
defect that the waves from the defect free part.
 A CRO screen is used to see the reflected waves which
would give an indication of the location and magnitude
of defect.
 Two separate probes are there, one for transmitting the
waves and other to receive them after passage through
the casting.

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