Casting Processes

UNIT-I
METALCASTING
PROCESSES
2

Manufacturing Engineering
engineering
Manufacturing
includes product design and
manufacturing system design as
well as operation of the factory.

Manufacturing Process
Raw materials
Working
Process
Finished
goods
Manufacturing process is
science and technology by which a
material is converted into a useful
shape, with a structure and
properties.
Manufacturing Process

Types of Manufacturing Process
The manufacturing process can be
classified into four major types.
They are
(i) Casting
(ii) Material removal
(iii) Deformation processes
(iv) Consolidation processes

(i) Casting
 Expendeble mould
 Sand casting
 Shell casting
 Investment casting
 Lost wax casing
Multiple – use mould
 Die casting
 Permanent mould casting

(ii) Material removal
 Mechanical machining
 Turning
 Milling
 Drilling
 Boring
 Sawing
 Non – traditional machining
 Etching
 Electro polishing
 Electro discharge machining
 Water jet machining
 Abrasive jet machining
 Laser beam machining

(iii) Deformation process
 Hot bulk forming
 Forging
 Rolling
 Extrusion
Cold forming
 Wire drawing
 Swaging
 Roll forming
 Deep drawing

 Welding
 Oxyfuel
 Arc
 Plasma
 Resistance
 Laser
Brazing
Soldering

Adhesive bonding
Mechanical joining
Discrete fasteners
Integral fasteners
Press fit
Shrink fit

1. Metal casting processes
 A casting may be defined as a “metal
object obtained by allowing molten
metal to solidify in a mould” , the
shape of the object being determined by
the shape of the mould cavity.
 Casting (or) foundry is a process of
forming metallic products by melting
the metal, pouring in to a cavity known
as the mould, and allowing it to solidify.

 When it is removed from the mould,
it will be same shapes as the mould.
 Many parts and components are made
by casting, including
carburetors, engine
cameras,
blocks,
crankshafts, automotive components,
agricultural equipments, road
equipment, and pipes.

Advantages of casting process
Some of the reasons for the success
of the casting process are:
The most intricate of shapes, both
external and internal, may be cast.
Extremely large, heavy metal objects
may be cast when they would be
difficult or economically impossible to
produce.

 Because of their physical properties,
some metal can only be cast to
shape since they cannot be hot-
worked into bars, rods, plates, or
other shapes.
 Construction may be simplified as a
single piece.

 Metal casting is a process highly
adaptable to the requirements of
mass production
 Some engineering properties are
obtained more favorably in cast
metals.

2. Sand Casting
 Sand casting is used to produce a
wide variety of metal components
with complex geometries.
 These parts can vary greatly in size
and weight, ranging from a couple
ounces to several tons.
 For sand casting, the most common
materials are iron, steel, brass and
aluminum.

 With these alloys, sand casting can
produce small parts that weigh less than
one pound or large parts that weight
several tons.
 It is a cost effective and efficient process
for small lot production, and yet, when
using automated equipment, it is an
effective manufacturing process for high
– volume production.
 Sand casting is also common in producing
automobile components, such as engine
blocks, engine manifolds, cylinder heads,
and transmission cases.

Advantages
 Low cost of mould materials and
equipment.
 Large casting dimensions may be
obtained.
 Wide variety of metals and alloys
(ferrous and non – ferrous) may be
cast (including high melting point
metals)

Disadvantages
 Rough surface.
 Poor dimensional accuracy.
 High machining tolerances.
 Coarse Grain structure.
 Limited wall thickness: not higher
than 0.1” – 0.2” (2.5 – 5 mm).

Steps involved in Sand casting
Process
Sand Casting Steps:
Mould masking
Clamping
Pouring
Cooling
Removal
Trimming

1.3 Moulding Sands
 Most sand casting operations use silica
sand (SiO2).
 A great advantage of sand in
manufacturing applications is that sand is
inexpensive.
 Sand casting is one of the few processes
that can be used for metals with high
melting temperatures such as steels,
nickel, and titanium.
 A typical mixture by volume could be
89% sand, 4% water, 7% clay.

Uses of binders in Sand Casting
 A mould must have the physical integrity
to hold its keep its shape.
 Clay serves an essential purpose in the
sand casting manufacturing process, as a
binding agent to adhere the moulding
sand together.
 Organic resins, (such as phenolic resins),
and inorganic bonding agents (such as
phosphate and sodium silicate), may also
be used to hold the sand together.

Important ingredients of Moulding
Sand
The moulding sands are Consisting
of the following ingredients.
They are
(i) Silica sand grains
(ii) Clay
(iii) Moisture
(iv) Miscellaneous materials

 Silica is the product of the breaking up
of quartz rocks or the decomposition of
the granite.
 Silica sand contains 80 to 90% of
Silicon dioxide (Sio2) .
 Clay is the particles of sand that fail to
settle at a rate of 30 mm per minute,
when suspended in water.
 Mostly moulding sands has different
grades of work contain 5 to 20% of
clay.

 Moisture gives the good bonding action
of clay.

 The water should be 2 to 9%
 Miscellaneous materials are the
ingredients which are added to silica and
clay in moulding sand are oxide of iron,
limestone, magnesia, soda and potash.
The impurities should be below 3%.

Properties of moulding sand
Grain size and shape
Porosity (or) Permeability
Refractoriness
Cohesiveness (or) Strength
Adhesiveness
Plasticity
Collapsibility

(i) Grain size and shape
The size and shape of the grains in
the sand determine the application in
various types of foundry.
There are three different sizes of
sand grains.
• Fine
• Medium
• Coarse

• Fine:
Fine for small and intricate
casting.
• Medium:
Medium for bench work and
light floor works.
• Coarse:
Coarse for larger size
casting.

(ii) Porosity (Or) Permeability
The moulding sand must be
sufficiently porous to allow the
dissolved gases, which are evolved
When the metal freezes or
moisture present or generated with
in the moulds to be removed freely
when the moulds are poured.

(iii) Refractoriness
Refractoriness is the property of
withstanding the high
temperature.
It is the ability of the moulding
material to resist the temperature
of the liquid metal to be poured so
that it does not get fused with the
metal.

(iv) Cohesiveness (or) strength
The strength of the moulding sand
must be sufficient to permit the
mould to be formed, to the desired
shape and to retain the shape even
after the molten metal is poured in
to the mould.

 Green Strength:
The moulding sand that contains
moisture is termed as green sand.
 Dry Strength :
When the molten metal is poured in
the mould , the sand around the mould cavity is
quickly converted into dry sand, evaporates due
to the heat of the molten metal.
 Hot Strength:
As soon as the moisture is eliminated,
the sand would reach at a high temperature when
the metal in still in liquid state. The strength of
the sand that is required to hold the shape of the
cavity is called hot strength.

(v) Adhesiveness
Sticking strength of the moulding
sand to the sides of the mould
boxes.
It is defined as the sand particles
easily attach itself with the sides
of the moulding box and give
easy of lifting and turning the box
when filled with the sand.

(vi) Plasticity
It is the ability to behave like a
fluid so that, when rammed, it will
flow to all portions of a mould and
park all – round the pattern and
take up the required shape.
(vii) Collapsibility
Easy to collapse after solidified
metal is to be taken out from the
mould.

Types of moulding sands
(i) According to the properties of
moulding sand
(i) According to the usage

(i) According to the properties of
moulding sand
• Natural moulding sand
• Synthetic (or) High silica sand
• Special sand

(ii) According to the usage
• Green sand
• Dry sand
• Loam sand
• Facing sand
• Backing sand
• System sand
• Parting sand
• Core sand

(i) Green sand
 The sand which is in moist state
is known as green sand.
It is a mixture of silica sand
with 18 to 30% of clay having a
total water of from 6 to 8%.

(ii) Dry sand
After the mould is made, the
green sand has been heated then it
is called Dry sand.
This is suitable for large
casting.

(iii) Loam sand
It consists of fine silica sand, fine
refractories, clay, graphite, fiber and
water.
The clay content is very high in
loam sand.

(iv) Facing sand
It will be applied for covering
the surface of the pattern.
(v) Backing sand
 It is also called ‘floor sand’.
It is used to back up the facing
sand and to fill the whole volume of
the flask.

(vi) System sand
The used sand is cleaned and
reactivated by the addition of water
binders and special additives.
(vii) Parting sand
It is used to keep the green sand
from sticking to the pattern and also
allow the sand on the parting surface of
the cope and drag.

(viii) Core sand
These sands are used for making
core.
 It is also called as oil sand

Methods of Sand testing
(i) Moisture content test
(ii) Clay content test
(iii) Grain fitness test
(iv) Permeability test

(v)Strength test
• Green and Dry compression
• Green tensile
• Green and Dry shear
• Bending
(vi) Refractoriness test
(vii) Mould hardness test

1. Moisture content test
 Moister is defined as the amount
of water present in the moulding
sand. Low moisture content does
not develop strength properties.
 High moisture content decreases
permeability.

Moisture content test methods
 Using direct reading moisture teller, the
test reaction is:
CaC2+ 2 H2O = Ca (OH)2 C2H2
The pressure of C2H2 gives the direct
reading of the water content on the
pressure gauge.
 Using electrode probe devices
 Employing measurements of microwave
absorption in compacted sand samples.
 In using infrared heating

Procedure to find moisture
content moulding sand
Step 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.
Step 2: The moisture in the moulding
sand is thus evaporated.
Step 3 : Moulding sand is taken out of the
pan and reweighed.

Step 4: The percentage of moisture can be
calculated from the difference in the
weights, of the original moist and the
consequently dried sand samples.
Where
W1–Weight of the sand before drying
W2–Weight of the sand after drying

2. Clay content test
Clay influences strength,
permeability and other moulding
properties.

Procedure to find Clay content
Step 1 : Small quantity of prepared
moulding sand was dried.
Step 2 : Separate 50 gms of dry
moulding sand and transfer wash
bottle.
Step 3 : Add 475 cc of distilled water +
25 cc of a 3% NaOH.

Step 4 : Agitate this mixture about 10
minutes with the help of sand stirrer.
Step 5 : Fill the wash bottle with water
up to the marker.
Step 6 : After the sand has settled for
about 10 minutes, Siphon out the
water from the wash bottle.
Step 7 : Dry the settled down sand.

Step 8: The clay content can be determined
from the difference in weights of the
initial and finish sand samples.
Where
W1–Weight of the sand before drying
W2–Weight of the sand after drying

3. Grain Fitness Test
grain
The
distribution, grain finess
size,
are
determined with the help of the
fitness testing of moulding sands.

4. Permeability test
The quantity of air that
a standard
will pass
specimen
particular
through
of the
pressure
sand at a
condition is
called the permeability of the sand.

Major parts of the permeability test
equipment
An inverted bell jar, which floats in
a water.
Specimen tube, for the purpose of
hold the equipment.
A manometer (measure the Air
pressure)

5. Strength test
 Measurement of strength of
moulding sands can be carried out
on the universal sand strength
testing machine.
 The sands could be tested are
green sand, dry sand or core sand.

(a) Green Compression strength
 Green compression strength or
simply green strength generally refers
to the stress required to rupture the
sand specimen under compressive
loading.
 The green strength of sands is
generally in the range of 30 to 160
Kpa.

(b) Green Shear strength
 A different adapter is filled in the
universal machine so that the loading
now be made for the shearing of the
sand sample.
 The stress required to shear the
specimen along the axis is then
represented as the green shear
strength.
 It may vary from 10 to 50 Kpa.

(c) Dry strength
 This test uses the standard
specimens dried between 105 and
1100 C for 2 hours.
 The range of dry compression
strengths found in moulding sands
is from 140 to 1800 Kpa,
depending on the sand sample.

6. Refractoriness Test
The refractoriness test is used
to ability to withstand the moulding
sand for the higher temperature
condition.

Steps in refractoriness test:
Step 1 : Prepare a cylindrical specimen of
sand.
Step 2 :Heating the specimen at 1500oC
for two hours.
Step 3 : Observe the changes in
dimension and appearance.
Step 4 : If the sand is good, it remains
specimen share and shows very little
expansion. If the sand is poor, specimen
will shrink and distort.

7. Mould Hardness Test
Where,
P – Applied Force (N)
D – Diameter of the indentor (mm)
d –Diameter of the indentation (mm)

Moulding Sand preparation
The preparation of sand
includes the following primary process.
(i) Mixing of sand
(ii) Tempering of sand
(iii) Sand conditioning

(i) Mixing of sand
Remove the all foreign matters from
sand. (nails, fans)
 Screening of sand
Mechanical mixing of sand with
ingredients by using MULLER

(ii) Tempering of sand
 Temper the mould sand ingredients.
 Conditions mulling action given
until is a uniform distribution of the
ingredients occur.

(iii) Sand conditions
 Areation process
Check whether some highly amount
of sand grains are separates (or) not in
the areation process

Pattern and Pattern Making
A pattern is simply the duplicate of
the component which has to be
manufactured by the casting process.
The pattern are packed into sand that is
mixed with binding agents.
The pattern is purposely made larger
than the cast part to allow for shrinkage
during cooling.

Sand “cores” can be inserted in the
mould to create holes and improve the
casting’s final shape.
Vent holes are created to allow hot
gases to escape during the pour.
The selection of a pattern material
depends on the side and shape of the
casting, dimensional accuracy, the
quantity of casting required.

Pattern Materials
The most used pattern materials has
good characteristics. There are
(i) Wood and wood materials
(ii) Metals andAlloys
(iii) Plasters
(iv) Plastic and Rubbers
(v) Waxes

The most wood is straight grained,
light, easy to work.
The most common wood used for
pattern is teak wood.
Metal patterns are very useful in
machine moulding.
A metal pattern is itself cast from a
wooden pattern called “master pattern”.

 Cast iron is used for some highly
specialized types of patterns
Aluminium is probably the best all
round metal.
Plastics are now finding their place as
a modern pattern material because they
do not absorb moisture.
Gypsum cement known as plaster of
paris is also used for making patterns
are core boxes.

Types of Patterns
(i) Single piece pattern (or) Solid pattern.
(ii) Split pattern
(iii) Match plate pattern
(iv) Cope and Drag pattern
(v) Gated pattern
(vi) Loose – piece pattern
(vii) Sweep pattern
(viii) Skeleton pattern
(ix) Segmental pattern
(x) Shell pattern

(i) Single piece pattern (or) Solid
pattern.
It is are generally used for simpler
shapes and low quality production.
These type of patterns are made with
out joints, partings (or) any loose
pieces in its.
Soil temper, staffing – box and
gland of a steam engine are few
examples of casting which are made by
making solid patterns.

(ii) Split pattern
Split patterns are two – piece patterns made
such that each part forms a portion of the
cavity for the casting.
The upper and the lower parts of the split
pattern are accommodated in the cope and
drag portions of the mould.
The surface formed at the center line of the
pattern, is called the parting surface (or)
parting line.
Making of more parts instead two to make
completed pattern for a complicated this type
of pattern is called multi- piece pattern.

(iii) Match plate pattern
The match plate pattern is typically used
in high production industry runs for
casting manufacture.
A match plate pattern is a two piece
pattern representing the casting.
In the match plate pattern, however, each
of the parts are mounted on a plate.
Match plate patterns are normally used in
machine moulding.
They produce accurate castings and at
faster rates.

(iv) Cope and Drag pattern
The cope and drag pattern enables the
cope section of the mould and the
drag section of the mould to be
created separately and latter
assembled before the pouring of the
casting.
It is used to produce the big
castings.

(v) Gated pattern
In these patterns the sections are
connecting different patterns serve
as runner and gates.
 That is used for mass production
systems.
Gated patterns are usually made of
Metal which increases their strength
and reduces the tendency to wrap.

(vi) Loose – piece pattern
These loose – piece patterns are
needed, when the part is such that the
pattern cannot be removed as one
piece, even though it is split and the
line is made on more than one plane.

(vii) Sweep pattern
A sweep pattern is just a form, made
on a wooden board with sweeps the
shape of the casting into the sand all
around the circumference.
The sweep patterns are rotating about
the post. It is used for producing large
casting of circular sections.

(viii) Skeleton pattern
This is a ribbed construction with a
large number of square or rectangular
openings between the ribs which from a
skeleton outline of the pattern to be made.
The framework is filled and rammed
with clays, sand or loam and a strike-off
board known as a strickle board.

(ix) Segmental pattern
 These type patterns are also called as
Part patterns.
They are applied to circular work such
as rings, wheel of the automobile, gears.
After ramming one section, it goes
forward to the next section for ramming,
and so on, until the entire mould
perimeter has been completed.

(x) Shell pattern
These types of patterns are usually
made up of metal, mounted on plate
and parted along the center line, the
two sections being accurately dweled
together.
The shell pattern is used largely for
pipe works and drainage fittings.

Thursday, February 8, 2018 99
PATTERN ALLOWANCES
A pattern is always made somewhat larger
than the final job to be produced. This excess
in dimensions is referred to as the Pattern
allowance.
Types
1. Shrinkage or Contraction allowance
2. Draft or Taper allowance
3. Machining or Finish allowance
4. Rapping or ShakingAllowance
5. Distortion or CamberAllowance

Shrinkage or contraction allowance
 Generally metals shrink in size during
solidification and cooling in the mould.
So casting becomes smaller than the pattern.
To compensate for this, the pattern should be
made larger than the casting.
The amount of compensation for shrinkage is
called the shrinkage allowance.

Shrinkage or contraction allowance
• 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.
• 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.

Rate of Contraction of Various Metals
Material Dimension Shrinkage allowance
(inch/ft)
Grey Cast Iron Up to 2 feet 0.125
2 to 4 feet 0.105
over 4 feet 0.083
Cast Steel Up to 2 feet 0.251
2 feet to 6 feet 0.191
over 6 feet 0.155
Aluminum Up to 4 feet 0.155
4 feet to 6 feet 0.143
over 6 feet 0.125
Magnesium Up to 4 feet 0.173
Over 4 feet 0.155

Draft or taper allowance
• When a pattern is drawn from a mould, there is always a
possibility of damaging the edges of the mould.
• Draft is taper made on the vertical faces of a pattern to make
easier drawing of pattern out of the mould as shown in Fig.
• The draft is expressed in millimeters per metre on a side or
in degrees.

Draft Allowances of Various Metals
Pattern material Height of the
given surface
(inch)
Draft angle
(Externalsurface)
Draft angle
(Internalsurface)
Wood 1 3.00 3.00
1 to 2 1.50 2.50
2 to 4 1.00 1.50
4 to 8 0.75 1.00
8 to 32 0.50 1.00
Metal and Plastic 1 1.50 3.00
1 to 2 1.00 2.00
2 to 4 0.75 1.00
4 to 8 0.50 1.00
8 to 32 0.50 0.75

Machining or finish allowance
Is given due to the following reasons:
1. For removing surface roughness, Scale, slag, dirt and other
imperfections from the casting.
2. For obtaining exact dimensions on the casting.
3. To achieve desired surface finish on the casting.
The dimension of the pattern to be increased depends upon the
following factors:
1. Method of machining used (turning, grinding, boring, etc.).
2. Characteristics of metal
3. Method of casting used.
4. Size and shape of the casting.
5. Degree of finish required.

Machining Allowances of Various Metals
Metal Dimension (inch) Allowance (inch)
Cast iron Up to 12 0.12
12 to 20 0.20
20 to 40 0.25
Cast steel Up to 6 0.12
6 to 20 0.25
20 to 40 0.30
Non ferrous Up to 8 0.09
8 to 12 0.12
12 to 40 0.16

Rapping or Shaking Allowance
• When the pattern is shaken for easy withdrawal, the
mould cavity, hence the casting is slightly increased
in size. In order to compensate for this increase, the
pattern should be initially made slightly smaller.
• For small and medium sized castings, this allowance
can be ignored.
• Large sized and precision castings, however, shaking
allowance is to be considered.
• The amount of this allowance is given based on
previous experience.

Distortion or CamberAllowance
• Sometimes castings, because of their size, shape and
type of metal, tend to warp or distort during the
cooling period depending on the cooling speed.
• Expecting the amount of warpage, a pattern may be
made with allowance of warpage. It is called camber.
• For example, a U-shaped casting will be distorted
during cooling with the legs diverging, instead of
parallel as shown in fig. For compensating this
warpage, the pattern is made with the legs converged
but,as the casting cools, the legs straighten and
remain parallel.
Thursday, F
Ce
b
r
au
sa
r
ty
in8
,g
2
0
1
w
8ithout camber 109
Actual casting Pattern with camber allowance

CORES
What is core in Casting?
A core is a body made of sand which is used to
make a cavity or a hole in a casting.
Also used to make recesses, projections,
undercuts and internal cavities.

TYPES OF CORES
(a) According to the state of core
(i) Green sand core
(ii) Dry sand core
(b) According to the position of core in mould
(i) Horizontal core
(ii) Vertical core
(iii) Balanced core
(iv) Hanging core
(v) Drop core

1.Green sand core
When the pattern leaves a core as a part of
the mould, then the body of sand is called
green sand core.
It is suitable only for vertical openings.
2.Dry sand core
The cores heated to 200°C to 350°C in the core
baking ovens are called dry sand cores.
These cores are commonly used.

3. Horizontal core
 Placed horizontally
Cylindrical in shape
Supported in core seats at both the ends.

4.Vertical core
Positioned vertically
Ends of the core rest in cope and drag.
Major portion is in drag box.

5.Balacing core
Supported and balanced from its end
 Require long core seat
Used when blind holes along a horizontal axis
is needed.

6.Hanging core
Supported at top and hang into mould
Supported by seat at top portion of drag
Used when cored casting is to be completely
moulded in drag with help of single piece solid
pattern.

7.Drop core
Used when a hole is not in the parting line
Hole may be above or below the parting line
Depending upon the usage it may be called as
tail core, chair core or saddle core.

Moulding Machines
Moulding machines will do the following
operations:
1.Ramming the moulding sand
2.Rapping the pattern for easy removal
3.Removing the pattern from the sand

1.Jolting machine
Pattern is placed in the flask on the table
The table is raised to 80mm and suddenly
dropped
Table is operated pneumatically or hydraulically.
Sudden dropping of table makes the sand pack
evenly around the pattern
Mainly used for ramming horizontal surfaces on
the mould.
Operation is noisy.

2.Squeezing machine
Moulding sand in the flask is squeezed between
the machine table and a Squeezer head.
Two types
1.Top Squeezing machine
2. Bottom Squeezing machine

1.Top Squeezer machine
Mould board is clamped on the table
Flask is placed on the mould board
Pattern is placed inside the flask
Sand is filled up and levelled
Table is raise by table lift mechanism against
the sqeezer head
Patterns enters the sand frame and packs sand
tightly

2.Bottom Squeezer machine
Pattern is placed on the mould table
Mould table is clamped on the ram
Table with pattern is raised against the
Squeezer head
Flask with the pattern is squeezed between
squeezer head and the table.

3.Sand Slinger
Pattern is placed on a board
Flask is placed over it
The slinger is operated
Slinger has impeller which can be rotated with
different speeds
Impeller rotates will throw a stream of sand at
great velocity into the flask
Slinger is moved to pack sand uniformly.

Melting furnaces
Cupola furnaces:

Construction:
Cylindrical shell made of 10 mm thick steel
plate.
Lined with refractory bricks inside.
Two bottom doors.
Sand bed laid over the bottom doors.
Slag hole provided above the tap hole.
Opening called tuyeres one meter above
bottom
Wind box and blower
Charging door.

Preparation:
Previous melting cleaned
Broken bricks must be replaced
Bottom doors are closed
Sand bed sloping towards tap hole-height 200mm
Tap hole lined with clay
Slag hole is prepared
Cupola dried thoroughly

Firing
Oil and wooden piece-placed at bottom
Air- sufficient amount is supplied
Coke-charged at several portions
Blast is turned off
More coke- upto tuyeres level
Coke-level of bed charge
Coke-burn for half an hour
Charging-at the charging door

Charging and Melting
Pig iron and iron scrap-charged at charging door
Coke-charged alternatively
Limestone-remove impurities-thorough mixing
Pig iron to limestone ratio: 25:1
Pig iron to coke: 10:1
Iron soaked for 1 hour
Blast turned on
Molten metal-collected at sand bed
Clay plug-collected in ladles

Molten metal-poured into moulds
Floating slag-tapped out through slag hole
Furnace charged full-repeating same procedure
Cupola shut off-by stopping air blast
Wastes-dropped down and quenched by water
Application:
Melting Cast iron

Advantages of Cupola furnace
1.Initial cost is low
2.Simple in design
3.Requires only less floor area
4.Operations and Maintenance is simple
5.Operated continuously for many hours

PROCESS IN THE BLAST
FURNACE
1.Introduction of charge
2.Introduction of hot blast
3.Combustion of coke
4.Production of carbon monoxide
(reducing agent)
5. Reduction of haematite
6.Decomposition of limestone
7.Formation of slag

1. Introduction of charge
The charge is introduced into the
furnace through the cup and cone
arrangement.

2. Introduction of hot blast
Simultaneously a hot blast of air is
introduced into the furnace through
the tuyeres

3. Combustion of coke
Coke present in the
charge burns in the hot air producing
carbon dioxide generating more heat
C + O2 → CO2 + ∆

4. Production of carbon monoxide
(reducing agent)
The carbon dioxide formed
rises up and reacts with the incoming
coke forming carbon monoxide
CO2 + C → 2CO

5. Reduction of haematite
Carbon monoxide formed is a
powerful reducing agent.
It reduces haematite to iron
Fe2O3+ 3CO → 2Fe + 3CO2↑

6. Decomposition of limestone
limestone decomposes
Due to the heat,
forming
calcium oxide and carbon dioxide
CaCO3+ 3CO CaO + CO2↑

7. Formation of slag
The quick lime (i.e. CaO) thus
formed acts as a flux and combines with
sand (an acidic impurity) converting it
into calcium silicate, an easily fusible
mass. Thus mass is called slag.
CaO + SiO2 → CaSiO3

The iron formed is collected at the
bottom of the furnace and the slag
forms a layer on it. It protects the
molten iron from oxidation.
The iron obtained by this process is
called pig iron. It contains carbon as
an impurity.

Blast Furnace

Special moulding Processes
A. Sand moulds
1. Green sand mould
2. Dry sand mould
3. Core sand mould
4. Carbon dioxide mould (CO2 mould)
5. Shell mould
6. Investment mould
7. Sweep mould
8. Full mould
B. Metal moulds
9. Gravity die casting or Permanent mould casting
10. Pressure die casting
11. Continuous casting
12. Centrifugal casting
13. Squeeze casting
21/8/420.18Thixocastingprocess 146

5. SHELL MOULDING
.
147
• Shell moulding is an efficient and
economical method for producing steel
castings.
• The process was developed by Herr
Croning in Germany during World war-II
and is sometimes referred to as the
Croning shell process.
Procedure involved in making shell mould
a. A metallic pattern having the shape of
the desired casting is made in one half
from carbon steel material. Pouring
element is provided in the pattern itself
b. The metallic pattern is heated in an oven to a suitable temperature between
180 - 250°C. The pattern is taken out from the oven and sprayed with a
solution of a lubricating agent viz., silicone oil or spirit to prevent the shell
(formed in later stages) from sticking to the pattern.
c. The pattern is inverted and is placed over a box as shown in figure 3.3(b). The
box contains a mixture of dry silica sand or zircon sand and a resin binder (5%
2/8/2b0a18sedon sand weight).

d. The box is now inverted so that the
resin-sand mixture falls on the heated
face of the metallic pattern. The resin-
sand mixture gets heated up, softens
and sticks to the surface of the pattern.
Refer figure (c).
e. After a few seconds, the box is again
inverted to its initial position so that the
lose resin-sand mixture falls down
leaving behind a thin layer of shell on
the pattern face. Refer figure (d).
f. The pattern along with the shell is
removed from the box and placed in an
oven for a few minutes which further
hardens the shell and makes it rigid. The
shell is then stripped from the pattern
with the help of ejector pins that are
provided on the pattern. Refer figure (e).
2/8/2018 147

g. Another shell half is prepared in the
similar manner and both the shells are
assembled, together with the help of
bolts, clips or glues to form a mould.
The assembled part is then placed in a
box with suitable backing sand to
receive the molten metal. Refer figure
(f).
h. After the casting solidifies, it is
removed from the mould, cleaned and
finished to obtain the desired shape.
Advantages
Better surface finish and dimensional tolerances.
Reduced machining.
Requires less foundry space.
Semi-skilled operators can handle the process easily.
Shells can be stored for extended periods of time.
Disadvantages
 Initially the metallic pattern has to be cast to the desired shape, size and finish.
 Size and weight range of castings is limited.
 Process generates noxious fumes.
2/8/2018 148

6. INVESTMENT MOULD
• Investment mould also called as 'Precision casting' or 'Lost
wax process' is an ancient method of casting complex
shapes like impellers, turbine blades and other airplane
parts that are difficult to produce by other manufacturing
techniques.
The various steps involved in this process are:
Step 1 Die and Pattern making
• A wax pattern is prepared by injecting liquid wax into a pre-
fabricated die having the same geometry of the cavity of
the desired cast part. Refer figure.1.
• Several such patterns are produced in the similar manner
and then attached to a wax gate and sprue by means of
heated tools or melted wax to form a 'tree' as shown in
figure 2.
2/8/2018 149

a
e
o
')
Step 2 Pre-coating wax patterns
• The tree is coated by dipping into refractory slurry which is
mixture of finely ground silica flour suspended in ethyl silicat
solution (binder).
• The coated tree is sprinkled with silica sand and allowed t
dry. Refer figure 3 and 4.
Step 3 Investment
• The pre-coated tree is coated again (referred as 'investment
by dipping in a more viscous slurry made of refractory flour
(fused silica, alumina etc.) and liquid binders (colloidal silica,
sodium silicate etc.) and dusted with refractory sand.
• The process of dipping and dusting is repeated until a solid
shell of desired thickness (about 6 - 10 mm) is achieved.
Note: The first coating is composed of very fine particles
that produce a good surface finish, whereas the second
coating which is referred as 'Investment' is coarser so as
to build up the shell of desired thickness.
2/8/2018 150

Step 4 De-waxing '
• The tree is placed in an inverted position and heated in a oven to about 300°F. The wax
melts and drops down leaving a mould cavity that will be filled later by the molten metal.
Refer figure 5.
Step 5 Reheating the mould
• The mould is heated to about 1000 - 2000°F (550-1100°C) to remove any residues of wax
and at the same time to harden the binder.
Step 6 Melting and Pouring
• The mould is placed in a flask supported with a backing material and the liquid metal of
the desired composition is poured under gravity or by using air pressure depending on
the requirement. Refer figure.6.
• After the metal cools and solidifies, the investment is broken by using chisels or hammer
and then the casting is cut from the gating
systems, cleaned and finished. Refer figure.7.
2/8/2018 151

2/8/2018 152
Advantages
• Gives good surface finish and dimensional tolerances to
castings
• Eliminates machining of cast parts.
• Wax can be reused.
Disadvantages
• Process is expensive.
• Size and weight range of castings is limited
• In some cases, it is difficult to separate the refractory
(investment) from the casting.
• Requires more processing steps.

Ceramic mould casting
Ceramic slurry-refractory powders of
zircon+alumina+fused silica
Slurry applied over the pattern surfaces
Baked in less expensive fire clay
Pattern removed from mould and heated in oven
about 1000°C
Molten metal poured into mould cavity
Partial filling of mould is completely eliminated
Can be used for all materials.

2/8/2018 154
PRESSURE DIE CASTING
 Pressure die casting often called 'Die casting' is a casting
process in which the molten metal is injected into a 'die' under
high pressures.
 The metal being cast must have a low melting point than the die
material which is usually made from steel and other alloys.
 Hence, this process is best suitable for casting non-ferrous
materials, although a few ferrous materials can be cast.
 The two basic methods of die casting include:
a) Hot chamber die casting process
b) Cold chamber die casting process.

Hot chamber die casting process
 Figure shows a 'goose neck' type of hot chamber die casting machine.
 In this process, the dies are made in two halves: one half called thefixed
die or 'stationary die’ while the other half called 'movabledie’.
 The dies are aligned in positions by means of ejector pins which alsohelp
to eject the solidified casting from the dies.
Figure: Hot chamber die casting (Submerged plungertype) 155
2/8/2018

Steps involved in the process
Figure: Hot chamber die casting (Goose
neck or air injection type)
2/8/2018 157
• A pivoted cast iron goose neck is submerged in a reservoir of molten metal where
the metal enters and fills the goose neck by gravity.
• The goose neck is raised with the help of a link and then the neck part is
positioned in the sprue of the fixed part of the die.
• Compressed air is then blown from the top which forces the liquid metal into the
die cavity.
• When the solidification is about to complete, the supply of compressed air is
stopped and the goose neck is lowered back to receive the molten metal for the
next cycle. In the meantime, the movable die half opens by means of ejector pins
forcing the casting from the die cavity.
• The die halves close to receive the molten metal for the next casting.
Hot chamber process is used for casting metals
like zinc, tin, magnesium and lead based alloys.

Cold chamber Die CastingProcess
2/8/2018 Fig: cold chamber die casting machine158
• In hot chamber process, the charging unit (goose neck) rests in the melting
chamber, whereas in cold chamber process, the melting chamber is separate and
the molten metal is charged into the machine by means of ladles.
• Cold chamber process is employed for casting materials that are not possibleby
the hot chamber process.
• For example, aluminum alloys react with the steel structure of the hot chamber
machine and as a result there is a considerable iron pick-up byaluminum.
• This does not happen in cold chamber process, as the molten metal has a
momentary contact with the structure of the machine.
• Figure shows the cold chamber die casting machine
• The machine consists of a die, made
in two halves: one half called the
'fixed die' or 'stationary die’ while the
other half called 'movable die’.
• The dies are aligned in positions by
means of ejector pins which also
help to eject the solidified casting
from the dies.

Steps involved in the process
• A cylindrical shaped chamber called 'cold chamber' (so called because, it
is not a part of melting or charging unit unlike in hot chamber process) is
fitted with a freely moving piston and is operated by means of hydraulic
pressure.
• A measured quantity of molten metal is poured into the cold chamber by
means of ladles.
• The plunger of the piston is activated and progresses rapidly forcing the
molten metal into the die cavity. The pressure is maintained during the
solidification process.
• After the metal cools and solidifies, the plunger moves backward and the
movable die half opens by means of ejector pins forcing the casting from
the die cavity.
• The cold chamber process is slightly slower when compared to the hot
chamber process.
2/8/2018 158

2/8/2018 159
Advantages of Die casting process
• Process is economical for large production quantities.
• Good dimensional accuracy and surface finish.
• Thin sections can be easily cast.
• Near net shape can be achieved.
Disadvantages
• High cost of dies and equipment.
• Not economical for small production quantities.
• Process not preferable for ferrousmetals.
• Part geometry must allow easy removal from die cavity

CENTRIFUGALCASTING
• Centrifugal casting is a process in which the molten metal is
poured and allowed to solidify in a revolving mould.
• The centrifugal force due to the revolving mould holds the
molten metal against the mould wall until it solidifies.
• The material used for preparing moulds may be cast iron,
steel, sand or graphite (for non-ferrous castings).
• The process is used for making castings of hollow
cylindrical shapes.
.
2/8/2018 160

Applications
Water pipes,gears,bush bearings,fly
wheels,piston rings,brake drums,Gun barrels
Advantages:
1.Core not required for hollow components
2.Rate of production is high
3.Pattern,runner and riser not required
4.Thin castings can be made
Limitations:
Suitable only for Cylindrical castings
Cost of equipment is high

CARBON DIOXIDE (CO2)MOLDING
 Carbon dioxide moulding also known as
sodium silicate process is one of the widely
used process for preparing moulds and cores.
 In this process, sodium silicate is used as the
binder. But sodium silicate activates or tend
presence
to bind the sand particles only
of carbon dioxide gas.
in the
For this
reason, the process is commonly known as C02
process.
2/8/2018 162

2/8/2018 163
Steps involved in making carbon dioxide mould
• Suitable proportions of silica sand and sodium silicate binder (3-5% based on sand
weight) are mixed together to prepare the sand mixture.
• Additives like aluminum oxide, molasses etc., are added to impart favorable
properties and to improve collapsibility of the sand.
• The pattern is placed on a flat surface with the drag box enclosing it. Parting sand
is sprinkled on the pattern surface to avoid sand mixture sticking to thepattern.
• The drag box is filled with the sand mixture and rammed manually till its top
surface. Rest of the operations like placing sprue and riser pin and ramming the
cope box are similar to that of green sand moulding process.
• Figure (a) shows the assembled cope and drag box with vent holes. At this stage,
the carbon dioxide gas is passed through the vent holes for a few seconds. Refer
figure (b).
• Sodium silicate reacts with carbon dioxide gas to form silica gel that binds the
sand particles together. The chemical reaction is given by:
Na2Si03 + C02 -> Na2C03 + Si02
(Sodium Silicate) (silica gel)
• The sprue, riser and the pattern are withdrawn from the mould, and gates are cut
in the usual manner. The mould cavity is finished and made ready for pouring.

2/8/2018 164
Advantages
• Instantaneous strength development. The development of strength takes place
immediately after carbon dioxide gassing is completed.
• Since the process uses relatively safe carbon dioxide gas, it does not present
sand disposal problems or any odour while mixing and pouring. Hence, the
process is safe to human operators.
• Very little gas evolution during pouring of molten metal.
Disadvantages
• Poor collapsibility of moulds is a major disadvantage of this process. Although
some additives are used to improve this property for ferrous metal castings, these
additives cannot be used for non-ferrous applications.
• The sand mixture has the tendency to stick to the pattern and has relatively poor
flowability.
• There is a significant loss in the strength and hardness of moulds which have
been stored for extended periods of time.
• Over gassing and under gassing adversely affects the properties of curedsand.

Stir casting

Casting defects causes and
remedies
The following are the defects in
castings.
1. Shrinkage
2. Cold Shut
3. Mismatch
4. Blow holes
5. Pin Holes
6. Fin

7. Drop
8. Swell
9. Metal Penetration
10. Hot Tears
11. Porosity
12. Scabs
13. Hard Spots
14. BucklesRat Tails
15. Misrun

1. SHRINKAGE
Shrinkage cavity is a void on
the surface of the casting
by uncontrolled
solidification
caused
and
of the
mainly
haphazard
metal.

Causes:
• inadequate and improper gating
• poor design of casting involving
abrupt changes in thickness
• too high pouring temperature

Remedies:
Use the suitable composition
that is adjusted silicon and (1.80 to
2.10) or carbon equivalent (3.9 to
4.1) .Carry out proper ramming and
maintain optimum pouring
temperature and time.

2. COLD SHUT
When two streams of molten metal
approach each other in the mould
cavity from opposite directions but
fail to fuse properly, with the result
of discontinuity between them, it is
called a cold shut.

Causes:
• low
metal
temperature of molten
• improper gating system
• too thin casting sections
• slow and intermitted pouring
• improper alloy composition
• use of damaged pattern

Remedies:
• Smooth pouring with the help of
monorail.
• Properly transport mould during
pouring.
• Arrange proper clamping
arrangement.
• -providing appropriate pouring
temperature.

3. MISMATCH
It is a shift /misalignment
between two mating surfaces or
the top and bottom parts of the
casting at the mould joint.

Causes:
• Worn dowel in patterns made in
halves.
• Improper alignment of mould
boxes due to worn out/ill fitting
mould boxes.
Remedies:
• Properly arrange box warpage.
• Properly move boxes with pins.
• Properly clamp the boxes.

4. BLOW HOLES
Balloon-shaped gas cavities caused
by release of mould gases during
pouring are known as blow holes.

Causes:
• Ramming is too hard.
• Permeability is insufficient.
• Venting is insufficient.

Remedies:
•moisture content of moulding sand
should be controlled
•sand of appropriate grain size should
be used.
•ramming should not be too hard.
•moulds should be adequately vented.

5. PIN HOLES
•Pin holes are tiny blow holes
appearing just
•below the casting surface.

Causes:
• Sand with high moisture content.
• Absorption of hydrogen/carbon
monoxide gas in the metal.
• Alloy not being properly degassed.
• Steel is poured from wet ladles.
• Sand containing gas producing
ingredients.

Remedies:
• Reducing the moisture content of
moulding sand.
• Increasing its permeability.
• Employing good melting and
fluxing practices.
• Improving a rapid rate of
solidification.

6. FINS
Fins are excessive amounts of
metal created by solidification into the
parting line of the mold

Causes:
• Inadequately weighted sand as well
as incorrectly assembled moulds
and cores.
• Over flexible bottom boards.
• Loose plates and improper
clamping of flasks.
Remedies:
• Correct assembly of the mould and
cores used for casting.

7.DROP
Drop is an irregularly-shaped
projection on the cope surface caused
by dropping of sand.

Causes:
• Low green strength of the molding
sand.
• Low mould hardness.
• Insufficient reinforcement of sand
projections in the cope.
Remedies:
• Molding sand should have
sufficient green strength.
• Ramming should not be too soft

8. SWELL
• Swells are excessive amounts of
metal in the vicinity of gates or
beneath the sprue

Causes:
• Insufficient or soft ramming.
• Low mould strength.
• Mould not being adequately
supported.
Remedies:
• Sand should be rammed evenly and
properly.

9. METALPENETRATION
Penetration occurs when the
molten metal flows between the sand
particles in the mould. These defects
are due to inadequate strength of the
mold and high temperature of the
molten metal adds on

Causes:
• Low strength of moulding sand.
• Large size of moulding sand.
• High permeability of sand.
• Soft ramming.

Remedies:
• Use of fine grain with low
permeability.
• Appropriate ramming.

10. HOT TEARS
A hot tear is a fracture formed
during solidification because of
hindered contraction.

Causes:
• Faulty casting design leading to
excessive stresses at certain portions
in the casting.
• Very hard ramming.
• Too much shrinkage of molten metal.
• Incorrect pouring temperature.
• Improper gates and risers.
• Low flow ability of molten metal.
• High sulphur content in molten
metal.

Remedies:
• Ramming should not be too hard.
• Modification in pattern to take care
of residual stresses.

11. POROSITY
Porosity is pockets of gas
micro-
inside the metal caused by
shrinkage during solidification.

Causes:
• Dissolved hydrogen and sulphur
dioxide in molten metal.
• Excessive poring temperature.
• Slow rate of solidification.
• High moisture content of the
mould.

Remedies:
• Maintenance
temperature.
of proper melting
• Casting should be made to solidify
quickly by using proper gating and
risering.
• Permeability of the mould should
be increased
• Moisture content of mould should
be kept low.

12. SCABS
Scabs are surface slivers
caused by splashing and rapid
solidification of the metal when it is
first poured and strikes the mold wall

Causes:
• Insufficient strength of mould and
core.
• Uneven mould ramming.
• Lack of binding material in facing
as well as core sand.
• Faulty gating.
• Intense local heating due to slow
running of molten metal over sand
surface.

Remedies:
• Appropriate ramming.
• Improved gating system.
• Addition of sufficient binders in
facing and core sands.

13. HARD SPOTS
These spots are formed due to
the local chilling by moulding sand
which leads to the formation of white
cast iron at those places, rendering
them hard.

Causes:
• Faulty metal composition.
• Faulty casting design resulting in
relatively more rapid cooling of
certain spots.
Remedies:
• Modification of casting design.
• Modification of casting composition.

14. BUCKLES/RAT TAILS
Rat tail or a buckle is a long,
shallow, angular depression caused by
expansion of the sand.

Causes:
• Excessive mould hardness.
• Lack of combustible additives in the
moulding sand.
• Continuous large surfaces on the
casting.
Remedies:
• Suitable addition of combustible
additives to moulding sand.
• Reduction in mould hardness.
• Modifications in casting design.

15. Misrun
When the molten metal fails to
fill the entire mould cavity before the
metal starts solidifying , resulting in
an incomplete casting, the defect is
known as misrun.

Causes:
• Low temperature of molten metal
• Improper gating system
• Too thin casting sections
• Slow and intermitted pouring
• Improper alloy composition
• Use of damaged pattern

Remedies:
• Smooth pouring with the help of
monorail.
• Properly transport mould during
pouring.
• Arrange proper clamping
arrangement.
• Providing appropriate pouring
temperature.

Casting Processes

More Related Content

What's hot

Similar to Casting Processes

Recently uploaded

Casting Processes

Editor's Notes