Unit 1 casting processes

CASTING
“Process of producing metal component
parts of desired shapes by pouring the
molten metal into a prepared mould and then
allowing the metal to cool and solidify. The
solidified piece of metal is known as a
CASTING”.
A plant where the castings are made is called
as Foundry.

Principle of casting Process
• Melt the metal
• Pour it in to mold
• Let it cool and solidify

History
• Casting dates back 5000 yrs
• Vannoccio B. (1480-1539), the “Father of
the foundry industry," in Italy. He is the
first man to document the
foundry process in writing.

History
Metal Casting History (India)
• 3000 BC Earliest castings include the 11 cm
high bronze dancing girl found at Mohen-jo-
daro.
• 2000 BC Iron pillars, arrows, hooks, nails
and bowls have been found in Delhi,
Roopar, Nashik and other places.

• 500 BC Processes of metal extraction
and alloying have been mentioned in
Kautilya's Arthashastra
• 500 A.D. Cast crucible steel is first
produced in India, but the process is lost
until 1750, when Benjamin Huntsman
reinvents it in England

Advantages
• Ferrous or non-ferrous.
• As the metal can be placed exactly where it is
required, large saving in weight can be achieved.
• Size and weight not limitation
• Tools required for casting molds are very simple
and inexpensive.

Limitations
• Dimensional accuracy and surface
finish
• Labor intensive process.

Applications of Casting:
Cylinder blocks
Machine tool beds
Piston
Mill rolls
Water supply pipes

Casting Terms:
1. Flask: A metal or wood
frame, without fixed top
or bottom, in which the
mold is formed.
• drag - lower molding
flask,
• cope - upper molding
flask,
• cheek - intermediate
molding flask used in
three piece molding.

Casting Terms:
2. Pattern: It is the replica
of the final object to
be made. The mold
cavity is made with
the help of pattern.
3. Parting line: This is the
dividing line between
the two molding flasks
that makes up the
mold.
Pattern

4. Pouring basin: A small funnel shaped cavity at the
top of the mold into which the molten metal is
poured.
5. Sprue: The passage through which the molten metal,
from the pouring basin, reaches the mold cavity. In
many cases it controls the flow of metal into the
mold.

6. Runner: The channel through which the molten metal
is carried from the sprue to the gate.
7. Riser: A column of molten metal placed in the mold to
feed the castings as it shrinks and solidifies. Also
known as feed head.
8. Gate: A channel through which the molten metal
enters the mold cavity.

9. Core: A separate part of the mold, made of sand and
generally baked, which is used to create openings and
various shaped cavities in the castings.
10.Chaplets: Chaplets are used to support the cores
inside the mold cavity to take care of its own weight
and overcome the metallostatic force.
11. Vent: Small opening in the mold to facilitate escape
of air and gases.

Metals and alloys commonly
used in Foundries:
FERROUS:
a. Cast irons
b. Steels
NON-FERROUS:
a. Copper alloys
b. Aluminium alloys
c. Magnesium alloys
d. Zinc alloys
e. Nickel alloys

Pattern Making:
A Pattern is a model or the replica of the
object to be cast.
Except for the various allowances a pattern
exactly resembles the casting to be made.
A pattern is required even if one object has
to be cast.

Functions of Patterns:
 Prepares a mould cavity.
 Patterns properly made and having finished
and smooth surfaces reduce casting defects.
 Properly constructed patterns minimize
overall cost of the casting.

Pattern Vs Casting
• Slightly larger than casting due to allowance.
• Carries Coreprints
• Different Material for pattern and casting.

Materials for making patterns:
WOOD
METAL
PLASTIC
PLASTER
WAX

Selection of Pattern Materials:
No. of castings to be produced.
Dimensional accuracy & surface finish.
Shape, complexity and size of casting.
Type of molding materials.
Nature of molding process.

The pattern material should be:
1. Easily worked, shaped and joined.
2. Light in weight.
3. Strong, hard and durable.
4. Resistant to wear and abrasion .
5. Resistant to corrosion, and to chemical
reactions.
6. Dimensionally stable and unaffected by
variations in temperature and humidity.
7. Available at low cost.

• Soft Wood Pattern : 50 Pieces
• Hard Wood Pattern: 50-200 Pieces
• Metal Pattern : 200-5000 Pieces

Types of Patterns:
Single piece pattern.
Split pattern / cope and drag pattern
Loose piece pattern
Match plate pattern
Sweep pattern
Gated pattern
Follow board pattern

Solid or single piece pattern
• Simplest pattern
• Made in one piece
• Cheapest pattern

Two piece or Split pattern.
• Withdrawal
• Length of Casting
• Made into two halves.
• It is also known as Cope and drag pattern

Match plate pattern
• Patterns are made in two pieces one piece
mounted on one side and the other on other
side of plate called match plate.
• Gates and runners are also attached.
• Produces accurate castings at faster rates.

Sweep pattern
• It is generally used for preparing large
symmetrical castings.
• It is made on wooden board and its sweeps the
sand in casting shape all around the
circumference.
• Hence it saves lot of labour and time.
• APPLICATIONS:
Symmetrical shapes such as wheels, rims

Segmental pattern
• It is used for preparing circular castings.
• In this type it does not revolve continuously
like sweep pattern, instead prepares the mould
by parts.
APPLICATIONS:
Used for circular work like rings, gears,
wheels, rims, pulleys etc.

Types of Pattern Allowances:
1. Shrinkage or contraction allowance.
2. Machining or Finish allowance.
3. Draft of Tapper allowances.
4. Distortion or Chamber allowance.
5. Shake or Rapping allowance.

1.Shrinkage Allowance:
All most all cast metals shrink or contract volumetrically
on cooling.
1. Liquid Shrinkage:
it refers to the reduction in volume when the metal
changes from liquid state to solid state at the solidus
temperature. To account for this shrinkage; riser, which
feed the liquid metal to the casting, are provided in the
mold.
Highest for Al
2. Solid Shrinkage:
it refers to the reduction in volume caused when
metal loses temperature in solid state. To account for
this, shrinkage allowance is provided on the patterns.
Highest for Brass

 Double shrinkage Allowance
 The metal shrinkage depends upon:
1. The cast metal or alloy.
2. Pouring temp. of the metal/alloy.
3. Casted dimensions(size).
• Cast Iron 10 mm/mt.
• Brass 16 mm/mt.
• Aluminium Alloys. 15 mm/mt.,
• Steel 21 mm/mt.,
• Lead 24 mm/mt.

2. Machining Allowance:
A Casting is given an allowance for
machining, because:
i. Castings get oxidized in the mold and
during heat treatment; scales etc., thus
formed need to be removed.
ii. Surface finish is required on the casting.
ferrous material require more machining
allowances than non ferrous material, because
they have scale on the skin.
Generally 1.6 mm to 12 mm

3. Draft or Taper Allowance:
 It is given to all surfaces perpendicular to
parting line.
 pattern can be easily removed from the
molding material tightly packed around it with
out damaging the mould cavity.
 More Draft needs to provided for hand
moulding machine as compare to Machine
moulding.
 10 mm to 20 mm/mt.
 Wax, mercury, polystyrene

4. Distortion or cambered allowance:
A casting will distort or wrap if :
i. It is of irregular shape,
ii. All it parts do not shrink uniformly i.e.,
some parts shrinks while others are
restricted from during so.
iii. It is U or V –shape
To Compensate this give a distortion of
equal Amount in the Opposite
Direction.
L/T L= length of leg

5. Shake allowance:
While removing the pattern from the mould, we
have to shake the pattern all around the vertical
faces in order to facilitate Easy removal.
In this process, the size of the cavity gets Enlarged
Hence, a –ve allowance is provided on the pattern
i.e., the pattern dimensions are kept smaller in
order to compensate the enlargement of mould
cavity due to rapping.
0.5-1.0 mm.

Properties of moulding sand
1. Porosity / permeability: ability of escaping air
or gas through the moulding sand
• Porosity is not present then blow hole may
produce in casting
How to increase it?
Silica sand particle size , reducing clay content,
additive, reducing ramming, providing Vent,.

• Cohesiveness: ability of formation of bond
between same material particles.
• Adhesiveness: ability of formation of bond by
sand particles with other material particles.
• Refractoriness: Ability of withstanding for
higher temp. without loosing hardness and
strength.

• Collapsibility: Ability of breaking the mould with
the application of little amount of the force.
• Flowability/ plasticity: ability of flowing of
moulding sand in each and every corner of a
mould.
• Green strength: Strength of sand in green of moist
condition
• Dry strength: Strength of sand in green of dry
condition

Molding Sand Composition:
Major part of Moulding material in sand casting
are
1. 70-85% silica sand (SiO2)
2. 10-12% bonding material e.g., clay
3. 2-8% water

1. Base Sand:
• Silica sand is most commonly used base sand.
• Other base sands that are also used for making
mold are zircon sand, Chromite sand, and
olivine sand.
• Silica sand - cheapest and easily available.

2. Binder:
• Binders are of many types such as:
1. Clay binders,
2. Organic binders and
3. Inorganic binders
• Clay binders are most commonly.
• The most popular clay types are:
–Kaolinite or fire clay and Bentonite
–Of the two the Bentonite can absorb more
water which increases its bonding power.

3. Moisture:
• Clay acquires its bonding action only in the
presence of the required amount of moisture.
• Correct amount of water develops good
strength, good tensile strength.
• Silica sand + clay+ water = Green sand
• Silica sand + clay+ Sodium silicate = Core sand

Additives
• To increase properties of moulding sand.
• Wood powder / saw dust: to increase porosity
and collapsibility.
• Coal Powder: to increase Refractoriness
• Starch or dextrin : to increase Strength or
resistance to deformation of the mould.
• (each added up to 2%)

Types of Moulding Sand
1. Green Sand / tempered / natural sand
(5 to 8 % water 15 to 30 % of clay)
It is fine, soft, light, low cost.
Used for Ferrous and non ferrous casting
2. Dry Sand
Green sand that been dried or baked.
Suitable for large casting.
3. Loam Sand
( 30-50% clay 18% water )
Large grey iron casting

4. Facing Sand :
Used next to pattern to obtain cleaner and smoother
casting surfaces.
Seal coal and coal dust
5.Backing Sand : (Black Sand)
Backs up facing sand, Reusable
Does not come in direct contact with pattern
6.Parting Sand :
Sprinkled on pattern to prevent adherence of molding
sand
Easier withdrawal of pattern.
Core sand: low clay content, Used for making Core

Mould making Methods:
• Hand moulding
• Machine moulding
Jolting
Squeezing
Jolt and squeezing
Sand slinger

Hand moulding
• If the force required for ramming of sand is
obtained by the human hand called as hand
moulding

Machine moulding
• If the force required for moulding is obtained
by machine it is called machine moulding

Squeeze Moulding Machine
• These machines may be hand operated or
power operated.
• The pattern is placed over the machine table,
followed by the molding box.
• In hand-operated machines, the platen is lifted
by hand operated mechanism.
• The table is raised gradually.
• The sand in the molding box is squeezed
between plate and the upward rising table thus
enabling a uniform pressing of sand in the
molding box.

Jolt Moulding Machine
• This machine is also known as jar machine
which comprises of air operated piston and
cylinder.
• The air is allowed to enter from the bottom
side of the cylinder and acts on the bottom face
of the piston to raise it up.
• The platen or table of the machine is attached
at the top of the piston which carries the
pattern and molding box with sand filled in it.

Jolt Moulding Machine
• The upward movement of piston raises the
table to a certain height and the air below the
piston is suddenly released, resulting in
uniform packing of sand around the pattern in
the molding box.
• This process is repeated several times rapidly.
This operation is known as jolting technique.

Jolting and Squeezing Moulding Machine

• It uses the principle of both jolt and squeezer
machines in which complete mould is
prepared.
• The cope, match plate and drag are assembled
on the machine table in a reverse position, that
is, the drag on the top and the cope below.
• Initially the drag is filled with sand followed
by ramming by the jolting action of the table.
• After leveling off the sand on the upper
surface, the assembly is turned upside down and
placed over a bottom board placed on the table.

• Next, the cope is filled up with sand and is
rammed by squeezing between the overhead
plate and the machine table.
• The overhead plate is then swung aside and
sand on the top leveled off, cope is next
removed and the drag is vibrated by air
vibrator.
• This is followed by removal of match plate and
closing of two halves of the mold for pouring
the molten metal.

Sand slinger
• In the slinging operations, the consolidation
and ramming are obtained by impact of sand
which falls at a very high velocity on pattern.
• These machines are generally preferred for
quick preparation of large sand moulds.
• A typical sand slinger consists of a heavy base,
a bin or hopper to carry sand, a bucket elevator
to which are attached a number of buckets and
a swinging arm which carries a belt conveyor
and the sand impeller head.

Sand slinger
• Well prepared sand is filed in a bin through the
bottom of which it is fed to the elevator
buckets.
• These buckets discharge the molding sand to
the belt conveyor which conveys the same to
the impeller head.
• This head can be moved at any location on the
mold by swinging the arm.
• The head revolves at a very high speed and, in
doing so, throws stream of molding sand into
the molding box at a high velocity.

TYPES OF SAND CONTROL TESTS
• The following are the various types of sand
control tests:
1. Moisture content test
2. Clay content test
3. Grain fitness test
4. Permeability test
5. Strength test
6. Refractoriness test
7. Mould hardness test

Moisture content test
• Moisture :the amount of water present in the moulding
sand.
• Low moisture content :does not develop strength
properties.
• High moisture content :decreases permeability.
Procedure:
1.50 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.
Percentage of moisture content = (W1-W2)/(W1)*100 %

Clay content test
• Clay influences strength, permeability and other moulding
properties.
• It is responsible for bonding sand particles together.
Procedures
1. Small quantity of prepared moulding sand was dried
2. Separate 50 gms of dry moulding sand and transfer wash bottle.
3. Add 475 ml of distilled water + 25 ml of a 3% NaOH.
4. Stir this mixture about 10 minutes with the help of sand stirrer.
5. Fill the wash bottle with water up to the marker (6 inches).
6. After the sand etc., has settled for about 10 minutes, Siphon out the
water from the wash bottle.
7. Dry the settled down sand.
8. The clay content can be determined from the difference in weights of
the initial and final sand samples.
Percentage of clay content = (W1-W2)/(W1) * 100

Permeability test
• Time taken for 2000 cc of air at a pressure of 980 Pa(10
g/cm sq.) to pass through standard specimen(5.08 cm
dia. and 5.08 cm hight) of sand.
• Permeability number (P) = ((V x H) / (A x p x T))
Where,
• V-Volume of air (cc) (2000)
• H-Height of the specimen (cm) (5.08)
• A-Area of the specimen (cm2) (20.268)
• P -Air pressure (gm / cm2) (5-10)
• T-Time taken by the air to pass through the sand (min)

1. Sample of dry sand (clay removed sand)
placed in the upper sieve
2. Sand is vibrated for definite period
3. The amount of same retained on each
sieve is weighted.
4. Percentage distribution of grain is
computed.
Grain fineness test

Core
Core: Used to produce Hallow Casting
eg. Holes, Recess, Projections, Internal Cavity.
Coreprints: region added on Pattern to Locate and Support
Core in Mould.
Characteristics of Core (Sand)
• High Permeability to allow an Easy Escape to gases
formed.
• High refractoriness to withstand high temperature of
molten metal
• Smooth surface.
• High collapsibility i.e. it should be able to disintegrate
quickly after the solidification of the metal is complete.

Horizontal Core
Usually in a cylindrical form
laid horizontally in the mold.
Vertical core
• The core is placed along a
vertical axis in the mould

Balance core
Suitable when the casting has
an opening only on one side
and only one coreprint is
available on the pattern.
Cover Core
• When the entire pattern is
rammed in the drag and
the core is required to be
suspended from the top of
the mold

Wing core
When a hole or recess is
to be obtained in the
casting either above or
below the parting line.
Hanging Core
• If the core hangs from
the cope and does not
have any support at
the bottom in the drag,
it is referred to as a
hanging core

GATING SYSTEM
• Channel through which the molten metal passes to
enter the mould cavity.
• The gating system is composed of
 Pouring basin
 Sprue
 Runner
 Gates
 Risers

REQUIREMENTS
Avoid sudden or right angle changes in
direction.
Fill the mould cavity before freezing.
Laminar Flow.
slag and other mould materials should not be
allowed
Aspiration of the atmospheric air is prevented.
Time taken to fill cavity should be minimum.
Full flow

POURING BASIN
Molten metal
from ladle is
poured into
pouring basin
from where it
moves in to the
sprue.
Act as a reservoir
Skimmer , Dam,
plug, Strainer

SPRUE
• A sprue feeds metal to runner which in turn reaches
the casting through gates.
• A sprue is tapered with its bigger end at top to receive
the liquid metal. The smaller end is connected to
runner.
• V= √ (2gh)
• Tapered sprue to Prevent Aspiration Effect

• Sprue Well: It changes the direction of flow
of the molten metal to right angle and passes it
to the runner.
• It serves to dissipate the KE of falling stream
of molten metal
• Splash Core: to prevent erosion of sand due to
strike of molten metal.

Runner : generally located in horizontal plane
Which connect sprue to gates.
Runner Extension: the extension is provided to
trap the slag in the molten metal.
Skim bob: it is enlargement along the runner
whose function is to trap heavier and lighter
impurities

Gates
• Top Gate:
• Metal enters from top, less time required,
• Maximum height of cavity up to which Top Gating
system used is 20mm.,
• suggested only for ferrous materials.

• Bottom Gate:
• Metal enters from bottom in drag,
• time required is more,
• less sand erosion.

• Parting Gate :
• metal enters the mould at the parting plane,
• For drag it is top gate and for cope it is bottom gate
• Easiest and most economical in preparation, Most
widely used gate in sand casting.

• Side Gate:
• Side gates are provided on either left or right side of
casting.
• Hence, metal enters into the mould cavity from sides.

Riser
• It feeds molten metal to the solidifying casting to
compensate for Shrinkage .
• To check complete filling of mould
• Requirements
1.It should have temp. gradient such that casting shall
solidify directionally towards riser.
2.Sufficient volume,
3.it must be last part to solidify

• Top Riser
• It is also called as dead riser or cold riser.
• It is located at the top of the casting.
• These types of risers fill up the coldest metal and are
likely to solidify before casting.
• By using this riser, there is more saving of material as
compared to other risers.

• Side Riser
• It is also called as live riser or hot riser.
• It is located between runner and cating.
• It is fitted at the last and contains the hottest metal.
• These risers are further classified as
a) Open Riser
b) Blind Riser

a) Open Riser
• These risers are open to atmosphere at the top
surface of the mould.
• The liquid metal in the riser is fed to
solidifying casting under the force of gravity
and atmospheric pressure till the top surface
of riser solidifies.
• It is connected either at the top of cope or on
the side of parting line.
• Generally open risers are cylindrical and easy
to mould.

b) Blind Riser.
• Blind risers do not break to the top of the
cope and are entirely surrounded by the
moulding sand.
• As it is closed at the top, a vent permeable
core at the top of riser may be provided to
have some expose to atmosphere.
• Blind riser is a rounded cavity and it
associates a slow cooling rate.
• These risers are more efficient.
• These risers are difficult to mould.

• Riser Design
• Risers V(volume)/ A(surface area) should be
high.
• Spherical shape : difficult to mould
• Cylinder
• Chvorinov‟s rule : Total freezing (solidification)
time for a casting is a function of ratio of
volume to surface area.
• Solidification time t= C*(V/A) sq.
• C= constant that reflects mould material, metal
properties like latent heat, temp.

• Best riser is one whose (V/A) sq. is 10 to 15 %
larger than that of the casting
• Since V and A of the casting are known
(V/A)riser.
• Generally ht. of riser = 1.5 * Dia. of riser is
Assumed.
Chvorinov’s formula is not accurate, since does
not take into account the shrinkage.

Melting and Pouring of Metals
Melting
• Different types of furnaces are used in foundry
for melting of metals depending upon the
metal to be melted, quality of metal desired,
type of fuel available and production volume.
• These furnaces essentially consist of a
refractory lined chamber which contains the
heat and the molten metal.
• The charge and fuel are introduced from
outside and suitable provisions are made for
removing the molten metal and spent material.

• The heat required for melting is obtained by
burning a solid or liquid fuel, electric arc,
electrical resistance or induction.
• The common types of melting furnaces used
in foundries today include cupola, crucible
furnaces, electric direct and indirect arc
furnaces and the induction furnaces.
• Of these the first two are the most common
for small to medium foundries.

Pouring
• Pouring of molten metal into the mould is
carried out with the help of several types of
containers known as ladles.
• Usually, the metal from the furnace is first
collected in a large receiving bucket or pit
from where It is distributed to smaller ladles.
• The ladle resembles a bucket with long
handles to facilitate it being carried by one or
two workers to the mould.

• Some ladles are provided with built in spouts
which allow metal to be taken out from the
bottom without disturbing the slag floating on
the top.
• The ladles are lined on the inside with fire
clay.
• Pouring of the molten metal into the mould
requires careful control.
• Pouring should be done continuously, at a
uniform rate till the mould, gating system and
the risers are full.

• For top risers, this will generally be indicated by
metal coming out of the riser provided the riser is
placed at the highest point in the casting.
• The temperature of the metal poured must be just
right. Too low temperatures may result in metal
solidifying before the mould cavity is completely
filled whereas too high temperature may lead to
evolution of too many gases resulting in
formation of blow holes and other defects.
• During pouring care should always be taken to
see that the slag does not enter the mould
otherwise defective castings may be produced.

• Bulk of the tonnage of gray iron castings is
produced from metal melted in cupolas. The
cupola is a simple and economical furnace for
melting pig iron and scrap needed for the
production of gray iron castings.
• Cupolas are also used for preliminary melting
for the production of malleables and ductile
irons.

Cupola Construction
• The cupola essentially consists of a cylindrical steel
shell lined on the inside with refractory bricks.
• The entire structure is supported on legs and is open
at top and bottom when not in use.
• At the bottom, doors are provided which can be
closed and propped to prepare a hearth for burning
coke.
• About 100 mm above the bottom of the shell is an
opening called the tap hole with a projecting spout for
taking out the molten metal.

• On the rear of the tap hole is a slag hole to drain out
slag. It is about 50 to 150 mm above the level of the
tap hole. This height decides the amount of metal that
can be stored in the cupola between taps.
• This height may be less if the cupola is fitted with a
receiver and the metal is continuously drained from
the cupola.
• About 50 to 150 mm above the slag hole are openings
through the shell into the cupola shaft called tuyeres.
These openings permit a blast of air from a wind box
surrounding the cupola shell around the tuyeres.
• These tuyeres are provided around the shell in one or
more rows to provide a balance supply of air.

• Air is supplied into the wind box from a blower
through pipes.
• The cupola shaft extends further up from the wind
box to a charging platform.
• The height of the cupola from the tap hole to the
charging platform is called the effective height. It is
about 4 to 6 times the internal diameter of the cupola
for small an medium size cupolas and about 3 to 5
metres for larger ones.
• At the height of the charging platform is a charging
opening through which the cupola can be charged in
operation.
• The cupola shaft extends further up by another 3 to 5
metres to give a chimney effect fc natural draft.

Fluxes
• In practically all melting operations certain amount of
slag is formed from coke ash refractory erosion and
oxidation of metal.
• Fluxes are added to reduce the melting point of this
slag and to make it less dense and more fluid to that it
floats on the surface of the molten metal and can be
easily removed.
• In cupola operation lime stone (CaCO3) is the most
commonly used flux.
• The weight of the flux is about 20 to 25 percent of the
coke charge. Other fluxes which may be used include
sodium carbonate (Na2CO3), fluorspar (CaF2) and
calcium carbide (CaC2)

Zones in Cupola
1) Crucible zone
This is the zone between top of the sand bed and
bottom of the tuyeres. This is also called well of the
cupola. Molten metal accumulates here between
taps.

2) Combustion or oxidizing zone :
• This zone is situated 150 to 300 mm above the top of
the tuyeres.
• The actual combustion of fuel occurs in this zone
using oxygen in the air blast.
• A lot of heat is liberated in this zone and is supplied
to other zones.
• Some heat is also evolved in this zone due to
oxidation of silicon and manganese.
• The temperature in this zone is of the order to 1550 to
1850°C.
• Because of this temperature molten drops of cast iron
pour into the hearth. The products of combustion in
this zone include C02, Si02 and MnOz.

3. Reducing zone :
• This zone extends from top of the combustion zone to
top of the coke bed.
• In this zone C02 produced in the combustion zone
reduces to C0 and the temperature drops to 1200°C.
• Because of the reducing atmosphere in this zone, the
charge is protected from oxidization.

• 4. Melting zone :
This zone extends from first layer of metal charge
above the coke bed upto a height of about 900 mm.
• The temperature in this zone is around 1600°C which
causes iron in the charge to melt.
• The molten iron picks up considerable carbon in this
zone by reacting with CO leading to formation of
Fe3C and CO2.

5. Preheating or charging zone :
• This zone starts from above the melting zone and
extends upto the bottom of the charging door.
• Alternate layers of coke, flux and metal charge are
preheated in this zone to temperature of about 1100°
C before entering the melting zone. „
6. Stuck zone:
• This rune extends from above the preheating zone to
the top of the cupola.
• This zone carries the flue gases and discharges these
gases to atmosphere.

• Crucible furnaces are mostly used for melting non
ferrous metals and alloys. The metal is melted in a
crucible which is a refractory vessel made of silicon
carbide, graphite or some other refractory material.
• Two kinds of crumble inmates are in common use :
• the stationary furnace and rotary type furnace.
• In the stationary kind of crucible furnace the crucible
with the metal is placed inside the refractory lined
furnace from outside.
• After melting the crucible is taken out for pouring. .
• In the rotary kind the crucible is permanently
cemented to the furnace and the furnace is tilted on
trunnions to take the metal out for pouring.

• Rotary furnaces are made for larger melting
capacities upto 500 kg or more. The stationary types
are used for small capacities upto 100 kg.
• Stationary furnaces may be above foundry floor or
built with refractory bricks below the foundry floor.
When built below the foundry floor these furnaces are
called Pit furnaces.
• Coke. oil or gas may be burnt in crucible furnaces, oil
or gas being more common.
• The metal in the crucible is ordinarily exposed to the
furnace atmospheres. It must be mentioned that most
non ferrous metals and alloys absorb gases, oxidize
and form dross readily when melted.

Classification of Casting Defects
Casting Defects
Visible Defects Internal Defects Surface Defects
Shift or Mismatch Blow Hole Scar
Shrinkage cavity Porosity Blister
Mis run Inclusions Swell
Hot tear Dross
Fin / Flash

Visible Defect
Shift or Mismatch
•The dislocation of upper and
bottom portion of the casting
across a plane is called
mismatch
Cause: mismatch of the cope and
drag or mismatch of split
patterns during the mould
making.
Remedy: Can be eliminated by
providing dovetail / lug pins so
that the cope and drag can be
properly located

Visible Defect
Flash / Fin
The additional material get
attached to the casting across
the parting plane is called flash
Cause: Improper closure of the
cope and drag will leave space
across the parting plane which
will be occupied by molten
metal and results in flash.
Remedy: Can be eliminated by
providing dovetail pins/ lugs
so that the cope and drag can
be properly located

Visible Defect
Shrinkage cavity
The open space produced in
the casting due to non
availability of molten metal
for compensating the liquid
shrinkages taking place
during solidification is
called shrinkage cavity.
Cause: non uniform heat
transfer from the casting.
Remedy: eliminated by using
chills

Visible Defect
Misrun
Non availability of molten metal
at a farthest point from the
pouring point is called Misrun
Cause: when the solidification
starts before complete filling of
casting cavity.
• Pouring temperature is too low
• Pouring is done too slowely
Remedy: By increasing the
Degree of Super heat.
By Minimizing the Pouring time.

Visible Defect
Hot Crack
Cause: Crack formed
during cooling after
solidification because of
internal stresses
developed in the casting
Remedy: maintain the
optimum cooling rate or
slow cooling will relieve
stresses without crack
formation

Internal Defect
• Blow Hole: presence of air or gas
bubbles inside the casting is called
Blow Hole.
Cause : Low porosity of molding sand
• Because of aspiration effect.
Remedy:
Increase the porosity property by
decreasing the ramming force
Increase the grain size of the sand
particles
Decrease the moisture content

Internal Defect
Porosity:
Presence of very small sized
air/gas particles inside the
casting is called Porosity

Internal Defect
• Inclusion/ sand Inclusion:
The presence of sand particles
inside the casting is called
inclusion.
• Causes: Due to sand erosion.
• (Sand erosion will takes place
due to turbulent flow of
molten metal.)
• Remedy: Ensure a laminar
flow by designing a proper
gating system.

Internal Defect
• Dross: Presence of
foreign particles or
impurities inside the
casting is called dross.
Remedy: the dross can be
eliminated by skim bob
and strainer.
•Making runner above or
below the ingate.

Surface Defect
Scar: is shallow blow
generally occurring on a flat
surface and is open to atm.
Blister: a scar covered with a
thin layer of metal is called
blister.
These are due to improper
permeability or venting.
Sometimes excessive gas
forming constituents in
moulding sand.

Surface Defect
• Swell: Under the
Metallostic Forces mould
wall may move back
causing a swell in Dim.
Of casting
• Faulty mould making
Procedure
• Proper ramming of sand.

Cleaning of casting
Inspection of Casting:
Destructive : Casting sample is destroyed
Tensile strength, hardness test
Non- Destructive :
Visual Inspection : Inspection by naked eye or
magnifying glasses.
Cracks, tears, swell
Dimensional inspection: to check dim. are with
in tolerance
Surface plates, height and depth gauges, etc.

Inspection of Casting
• Pressure Testing: to check Leakage, to check
resistance to bursting under hydraulic pressure
• Radiographic Inspection : Internal defects of
casting
• X rays and Gamma rays
• Eddy Current Inspection: supplying High
frequency Current, Electric Field induced which
will change its magnitude near defects
• Magnetic Particle Inspection: In case of ferrous
metal

DIE Casting
 Gravity die casting: if the flow of molten
metal in to the casting cavity is due to
gravity called as gravity die casting
 Pressure die casting: if flow of molten
metal in to the casting cavity is due to the
external pressure called as pressure die
casting

Permanent / Gravity Die Casting Process
• similar to sand casting process.
• used for pouring of at least one thousand
and up to 100000 casting cycles.
• Manufacturing metal mold is much more
expensive
• Ferrous and Non-Ferrous metals and alloys

•Special backing
powders are sprinkled
over the die surface
•The preheating is
done
•To avoid thermal
shock and
•To maintain the
metallurgical
properties &
•To avoid early
solidification of the
metal

• Cores (if used) are inserted
and mold is closed
• Molten metal is poured
into the mold, where it
solidifies

Permanent / Gravity Die Casting
Process
Advantages:
• Better mechanical properties
• Homogeneous grain structure and chemical composition
• Low shrinkage and gas porosity
• Good surface quality
Disadvantages:
• Costly mold
• Simpler shapes only

Hot Chamber Die Casting Process
Two main types
Hot-Chamber Die Casting
Furnace is integral part
Cold Chamber Die Casting
Metal is melted in separate furnace

Gooseneck (Cast iron)is used for pumping liquid
metal into Die cavity.
Plunger(alloy Cast Iron)
Nozzle is attached in between gooseneck and
sprue

• Casting metals: Al, brass, and magnesium
alloys

Pressure Die Casting Process
Advantages:
• Die casting is highly productive with low
dimensions tolerance
• high surface quality
Disadvantages:
• Expensive die
• Small parts (upto 15 kg)
• Complex and large machinery: expensive

Investment Casting
Advantages:
• Good dimensional accuracy
• Relatively inexpensive mold
• Rapid production rates possible
• Complex Shapes
Disadvantages:
• Long Production cycle
• Mold is not reusable

Centrifugal Casting
• Centrifugal Casting is a method of casting
parts having axial symmetry.
• The method involves pouring molten metal
into a cylindrical mold spinning about its axis
of symmetry. The mold is kept rotating till the
metal has solidified.
• The mold material Steels, Cast Irons, Graphite
may be used

Centrifugal Casting
• The mold wall is coated by a refractory
ceramic coating
• Pouring a molten metal directly into the mold
• The mold is stopped after the casting has
solidified
• Extraction of the casting from the mold

Centrifugal Casting
• Centrifugal force produced due to rotation of
the mould is used for distributing the molten
metal around the circumference of the mould
• hollow circular components without the usage
of the core.

Centrifugal Casting
• Typical materials that can be cast with this
process are iron, steel, stainless steels, glass,
and alloys of aluminum, copper and nickel.
• Two materials can be cast together by
introducing a second material during the
process.

Centrifugal Casting
Advantages:
• Large Cylindrical Parts
• Good quality
Disadvantages:
• Expensive
• Limited shapes

Centrifugal Casting
Typical parts made by this process are
• pipes,
• boilers,
• pressure vessels,
• flywheels,

Continuous casting process
• Molten metal is poured into vertical mould.
• Dummy starter is kept at bottom of mould.
• As metal level rises, starter bar is withdrawn at
rate equals to pouring rate.
• Water cooling is used for better Solidification.
• After solidification it is cut to desired length.

Continuous casting process
Application
Can Produce any shape of uniform c/s such as
rectangular, square, hexagonal, gear toothed
etc, either solid or hollow,

Unit 1 casting processes

More Related Content

What's hot

Similar to Unit 1 casting processes

Recently uploaded

Unit 1 casting processes