The document provides information on metal casting processes including definitions of key terms. It discusses the basic steps of metal casting which include making a pattern, preparing molds and cores, melting metal, pouring the molten metal into molds, solidification and cooling, removing and finishing the casting. Key sections include the foundry process, casting terms, pattern making, molding materials, melting and pouring, solidification, inspection and applications of casting.

1. - by Kishore
09331A0396

2. Introduction:
Metal Casting is one of the oldest materials
shaping methods known. Casting means
pouring molten metal into a mold with a
cavity of the shape to be made, and
allowing it to solidify. When solidified, the
desired metal object is taken out from the
mold either by breaking the mold or
taking the mold apart. The solidified
object is called the casting. By this
process, intricate parts can be given
strength and rigidity frequently not

3. Foundry:
” Foundry or casting is the process of
producing metal/alloy component parts of
desired shapes by pouring the molten
metal/alloy into a prepared mould (of that
shape) and then allowing the metal/alloy to
cool and solidify. The solidified piece of
metal/alloy is known as a CASTING”.

4. Casting Terms:
1. Flask: A metal or wood frame, without fixed
top or bottom, in which the mold is formed.
Depending upon the position of the flask in
the molding structure, it is referred to by
various names such as drag - lower molding
flask, cope - upper molding flask, cheek intermediate molding flask used in three piece
molding.
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

5. 4. 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.
5. Pouring basin: A small funnel shaped
cavity at the top of the mold into which the
molten metal is poured.
6. 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.
7. Runner: The channel through which the

6. 8. Gate: A channel through which the molten
metal enters the mold cavity.
9. Chaplets: Chaplets are used to support
the cores inside the mold cavity to take
care of its own weight and overcome the
metallostatic force.
10. Riser: A column of molten metal placed
in the mold to feed the castings as it
shrinks and solidifies. Also known as feed
head.
11. Vent: Small opening in the mold to
facilitate escape of air and gases.

7. Basic Features:
Pattern and Mould
◦ A pattern is made of wood or metal, is a replica of
the final product and is used for preparing mould
cavity.
◦ Mould material should posses refractory
characteristics and with stand the pouring
temperature.
◦ When the mold is used for single casting, it made
of sand and known as expendable mold.
◦ When the mold is used repeatedly for number of
castings and is made of metal or graphite are
called permanent mould.
◦ For making holes or hollow cavities inside a
casting, cores made of either sand or metal are

8. Melting and Pouring:
◦ Several types of furnaces are available for
melting metals and their selection depends
on the type of metal, the maximum
temperature required and the rate and the
mode of molten metal delivery.
◦ Before pouring provisions are made for the
escape of dissolved gases. The gating
system should be designed to minimize the
turbulent flow and erosion of mould
cavity.The other important factors are the
pouring temperature and the pouring rate.

9. Solidification and Cooling:
◦ The properties of the casting
significantly depends on the
solidification time cooing rate.
◦ Shrinkage of casting, during cooling of
solidified metal should not be
restrained by the mould
material, otherwise internal stresses
may develop and form cracks in
casting.
◦ Proper care should be taken at the
design stage of casting so that
shrinkage can occur without casting

10. Removal, Cleaning, Finishing and
Inspection:
◦ After the casting is removed from the
mould it is thoroughly cleaned and the
excess material usually along the parting
line and the place where the molten metal
was poured, is removed using a potable
grinder.
◦ White light inspection, pressure test,
magnetic particle inspection, radiographic
test, ultrasonic inspection etc. are used

11. Schematic diagram of casting
mould:

13. Steps involved in making a casting:
Make the pattern out of Wood , Metal or Plastic.
2. Prepare the necessary sand mixtures for mould
and core making.
3. Prepare the Mould and necessary Cores.
4. Melt the metal/alloy to be cast.
5. Pour the molten metal/alloy into mould and
remove the casting from the mould after the
metal solidifies.
6. Clean and finish the casting.
7. Test and inspect the casting.
8. Remove the defects, if any.
9. Relieve the casting stresses by Heat Treatment.
10. Again inspect the casting.
1.

14. Advantages of metal casting:
Casting is one of the most versatile
manufacturing process.
 Casting provides the greatest freedom of
design in terms of shape, size and the
product quantity.
 Casting imparts uniform directional
properties and better vibration capacity to
the cast parts.
 Casting produces machinable parts.
 Shapes difficult and uneconomic to obtain
otherwise may be achieved through casting


15. A product may be cast as one piece, there
by eliminating the need of metal joining
processes.
 Very heavy and bulky parts which are
otherwise difficult to get fabricated may be
cast.
 Metals (like cast iron) dificult to be shaped
by other manufacturing processes may be
cast.
 Casting can be designed for equal
distribution of loads and for minimum stress
concentration in order to achieve more
strength and increased service life.


16. Limitations of casting:
Dimensional accuracy and surface finish of
the castings made by sand casting
processes are a limitation to this technique.
 Many new casting processes have been
developed which can take into consideration
the aspects of dimensional accuracy and
surface finish.
 Some of these processes are die casting
process, investment casting
process, vacuum-sealed molding
process, and shell molding process.
 The metal casting process is a labor
intensive process


17. Applications of Casting:
 Transportation
 Turbine
vehicles
vanes
 Power generators
 Railway crossings
 Agricultural parts
 Aircraft jet engine parts
 Sanitary fittings
 Communication, Construction and
Atomic Energy applications, etc..

18. Different Sections in Foundry:
Pattern making
2) Sand mixing & preparation
3) Mould and core making
4) Mould assembly & handling
5) Melting
6) Pouring
7) Shaking out
8) Fettling & finishing
9) Heat treatment
10) Inspection & testing
1)

20. Raw Materials for
Foundry:
Metals and alloys.
2) Fuels (for melting
metals).
3) Fluxes.
1)

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

22. Fuels for Melting Metals:
Coal
2. Coke
3. Gas
4. Oil
5. electricity
1.

23. Fluxes:
A flux is a low melting point material.
 When heated up, it melts and combines
with ash, viscous slags, sand, metallic
oxides etc., and makes a fluid and easy
flowing slag.
 This slag being lighter comes on to the
surface of the molten metal from where it
can be easily skimmed, tapped or removed
before pouring the metal into the mould.
 Slag protects molten metal from furnace


24. Refractories:
o Refractories
are heat resistant materials.
o They can withstand high temperatures
without being fused.
o Crucibles and furnace sides and bottoms
containing molten metal are made up of
refractories.
o These are used as ladles for pouring
metal into the mould.
o Refractories constitute furnace walls and
roof and thus minimize heat losses.

25. Core and core prints:







Castings are often required to have
holes, recesses, etc. of various sizes and shapes.
These impressions can be obtained by using cores.
So where coring is required, provision should be made
to support the core inside the mold cavity.
Core prints are used to serve this purpose.
The core print is an added projection on the pattern and
it forms a seat in the mold on which the sand core rests
during pouring of the mold.
The core print must be of adequate size and shape so
that it can support the weight of the core during the
casting operation.
Depending upon the requirement a core can be placed
horizontal, vertical and can be hanged inside the mold

26. Pattern having core prints.

27. 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.

28. Functions of Patterns:




A Pattern prepares a mould cavity for
the purpose of making a casting.
A Pattern may contain projections
known as core prints if the casting
requires a core and need to be made
hollow.
Patterns properly made and having
finished and smooth surfaces reduce
casting defects.
Properly constructed patterns
minimize overall cost of the casting.

29. Selection of Pattern Materials:
The following factors assist in selecting
proper pattern material:
No. of castings to be produced.
Dimensional accuracy & surface finish.
Shape, complexity and size of casting.
Casting design parameters.
Type of molding materials.
The chance of repeat orders.
Nature of molding process.

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

31. Materials for making patterns:
a.
b.
c.
d.
e.
Wood
Metal
Plastic
Plaster
Wax.

32. 1. Wood Patterns:
Advantages:
Inexpensive
Easily available in large quantities
Easy to fabricate
Light in weight
Thay can be repaired easily
Easy to obtain good surface finish
Limitations:





Susceptible to shrinkage and swelling
Possess poor wear resistance
Abraded easily by sand action
Obsorb moisture, consequently get wraped
Cannot withstand rough handling
These are used where the no. of castings to be
produced is small and pattern size is large.

33. 2. Metal Patterns:
Advantages:
Do not absorb moisture
More stronger
Possess much longer life
Do not wrap, retain their shape
Greater resistance to abrasion
Accurate and smooth surface finish
Good machinability
Limitations:
 Expensive
 Not easily repaired
 Ferrous patterns get rusted
 Heavy weight
These are employed where large no. of
castings have to be produced from same patterns.

34. 3. Plastic Patterns:
Advantages:
 Durable
 Provides a smooth surface
 Moisture resistant
 Does not involve any appreciable change in size or
shape
 Light weight
 Good strength
 Wear and corrosion resistance
 Easy to make
 Abrasion resistance
 Good resistance to chemical attack
Limitations:
 Plastic patterns are Fragile
 These are may not work well when subject to
conditions of severe shock as in machine molding

35. 4. Plaster Patterns:
Advantages:
 It can be easily worked by using wood working
tools.
 Intricate shapes can be cast without any difficulty.
 It has high compressive strength.
 Plaster may be made out of
Plaster of paris or Gypsum
cement.

Plaster mixture is
poured into a mould made by

36. 5. Wax patterns:
Advantages:
Provide very good surface finish.
Impatr high accuracy to castings.
After being molded, the wax pattern is not
taken out of the mould like other patterns;
rather the mould is inverted and heated; the
molten wax comes out and/or is evaporated.
Thus there is no chance of the mould cavity
getting damaged while removing the pattern.

Wax patterns find
applications in Investment casting
process.

37. Types of Patterns:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Single piece pattern.
Split piece pattern.
Loose piece pattern.
Match plate pattern.
Sweep pattern.
Gated pattern.
Skeleton pattern
Follow board pattern.
Cope and Drag pattern.

38. (a)Split pattern
(b) Follow-board
(c) Match Plate
(d) Loose-piece
(e) Sweep
(f) Skeleton
pattern

40. 1. Single piece (solid) pattern:
Made from one piece and does not
contain loose pieces or joints.
 Inexpensive.
 Used for large size simple castings.
 Pattern is accommodated either in the
cope or in the drag.
 Examples:
1. Bodies of regular shapes.
2. stuffling box of steam engine.


41. Fig: Single piece pattern

42. 2. Split piece pattern:





Patterns of intricate shaped castings cannot be
made in one piece because of the inherent
difficulties associated with the molding operations
(e.g. withdrawing pattern from mould).
The upper and the lower parts of the split piece
patterns are accommodated in the cope and drag
portions of the mold respectively.
Parting line of the pattern forms the parting line of
the mould.
Dowel pins are used for keeping the alignment
between the two parts of the pattern.
Examples:
1. Hallow cylinder
2. Taps and water
stop cocks etc.,

43. Fig: split piece pattern

45. 3.Loose piece pattern:
Certain patterns cannot be withdrawn once
they are embedded in the molding sand.
Such patterns are usually made with one or
more loose pieces for facilitating from the
molding box and are known as loose piece
patterns.
 Loose parts or pieces remain attached with
the main body of the pattern, with the help of
dowel pins.
 The main body of the pattern is drawn first
from the molding box and thereafter as soon
as the loose parts are removed, the result is
the mold cavity.


46. 4. Match plate pattern:
It consists of a match plate, on either
side of which each half of split patterns is
fastened.
 A no. of different sized and shaped
patterns may be mounted on one match
plate.
 The match plate with the help of locator
holes can be clamped with the drag.
 After the cope and drag have been
rammed with the molding sand, the
match plate pattern is removed from in
between the cope and drag.
 Match plate patterns are normally used
in machine molding.


47. Fig: Match plate pattern

48. 5. Sweep pattern:





A sweep pattern is just a form made on a
wooden board which sweeps the shape of the
casting into the sand all around the
circumference. The sweep pattern rotates
about the post.
Once the mold is ready, Sweep pattern and the
post can be removed.
Sweep pattern avoids the necessity of making
a full, large circular and costly threedimensional pattern.
Making a sweep pattern saves a lot of time and
labour as compared to making a full pattern.
A sweep pattern is preferred for producing

49. 6. Gated pattern:



The sections connecting different
patterns serve as runner and gates. This
facilitates filling of the mould with molten
metal in a better manner and at the
same time eliminates the time and labour
otherwise consumed in cutting runners
and gates.
A gated pattern can manufacture many
casting at one time and thus it is used in
mass production systems.
Gated patterns are employed for
producing small castings.

50. castings
Gating system

51. 7. Skeleton pattern:






A skeleton pattern is the skeleton of a desired
shape which may be S-bend pipe or a chute or
something else. The skeleton frame is mounted
on a metal base
The skeleton is made from wooden strips, and is
thus a wooden work.
The skeleton pattern is filled with sand and is
rammed.
A strickle (board) assists in giving the desired
shape to the sand and removes extra sand.
Skeleton patterns are employed for producing a
few large castings.
A skeleton pattern is very economical, because it
involves less material costs.

52. 8. Follow board pattern:
A follow board is a wooden board and is used
for supporting a pattern which is very thin and
fragile and which may give way and collapse
under pressure when the sand above the
pattern is being rammed.
 With the follow board support under the weak
pattern, the drag is rammed, and then the
fallow board is with drawn, The rammed drag is
inverted, cope is mounted on it and rammed.
During this operation pattern remains over the
inverted drag and get support from the rammed
sand of the drag under it.
 Follow boards are also used for casting master
patterns for many applications.


53. 9. Cope and Drag patterns:





A cope and drag pattern is another form of
split pattern.
Each half of the pattern is fixed to a separate
metal/wood plate.
Each half of the pattern(along the plate) is
molded separately in a separate molding box
by an independent molder or moulders.
The two moulds of each half of the pattern
are finally assembled and the mould is ready
for pouring.
Cope and drag patterns are used for
producing big castings which as a whole
cannot be conveniently handled by one
moulder alone.

54. Fig: Cope and drag pattern

55. Pattern Allowances:
A pattern is larger in size as
compared to the final casting, because it
carries certain allowances due to
metallurgical and mechanical reasons for
example, shrinkage allowance is the result
of metallurgical phenomenon where as
machining, draft, distortion, shake and
other allowances are provided on the
patterns because of mechanical reasons.

56. Types of Pattern Allowances:
The various pattern
allowances are:
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.

57. 1.Shrinkage Allowance:
All most all cast metals shrink or contract
volumetrically on cooling.
The metal shrinkage is
of two types:
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.
2. Solid Shrinkage:
it refers to the reduction in volume caused
when metal loses temperature in solid state. To

58. 


Almost all cast metals shrink or contract
volumetrically after solidification and therefore
the pattern to obtain a particular sized casting
is made oversize by an amount equal to that of
shrinkage or contraction.
Different metals shrink at different rates
because shrinkage is the property of the cast
metal/alloy.
The metal shrinkage depends upon:
1. The cast metal or alloy.
2. Pouring temp. of the metal/alloy.
3. Casted dimensions(size).
4. Casting design aspects.
5. Molding conditions(i.e., mould

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

60. 2. Machining Allowance:
A Casting is given an
allowance for
machining, because:
i.
ii.
iii.
iv.
Castings get oxidized in the mold and during heat
treatment; scales etc., thus formed need to be
removed.
It is the intended to remove surface roughness and
other imperfections from the castings.
It is required to achieve exact casting dimensions.
Surface finish is required on the casting.
How much extra metal or how much
machining allowance should be
provided, depends on the factors
listed below:
i.
Nature of metals.

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

62. 3. Draft or Taper Allowance:

It is given to all surfaces perpendicular to
parting line.
 Draft allowance is given so that the pattern
can be easily removed from the molding
material tightly packed around it with out
damaging the mould cavity.
 The amount of taper depends upon:
i.
Shape and size of pattern in the depth
direction in contact with the mould cavity.
ii. Moulding methods.
iii. Mould materials.
iv. Draft allowance is imparted on internal as
well as external surfaces; of course it is
more on internal surfaces.

63. Table 2 : Draft Allowances of
Various Metals:
Pattern material
Height of the
given surface
(inch)
Draft angle
(External
surface)
Draft angle
(Internal
surface)
Wood
1
1 to 2
2 to 4
4 to 8
8 to 32
3.00
1.50
1.00
0.75
0.50
3.00
2.50
1.50
1.00
1.00
Metal and plastic
1
1 to 2
2 to 4
4 to 8
8 to 32
1.50
1.00
0.75
0.50
0.50
3.00
2.00
1.00
1.00
0.75

65. Fig: taper in design

66. 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,
iv. The arms possess unequal thickness,
v. It has long, rangy arms as those of propeller
strut for the ship,
vi. It is a long flat casting,
vii. One portion of the casting cools at a faster

68. 5. Shake allowance:

A patter is shaken or rapped by striking the
same with a wooden piece from side to side.
This is done so that the pattern a little is
loosened in the mold cavity and can be easily
removed.
 In turn, therefore, rapping enlarges the mould
cavity which results in a bigger sized casting.
 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.
 The magnitude of shake allowance can be
reduced by increasing the tapper.

69. Pattern Layout:
Steps involved:
 Get the working drawing of the part for
which the pattern is to be made.
 Make two views of the part drawing on a
sheet, using a shrink rule. A shrink rule
is modified form of an ordinary scale
which has already taken care of
shrinkage allowance for a particular
metal to be cast.
 Add machining allowances as per the
requirements.
 Depending upon the method of
molding, provide the draft allowance.

70. Pattern Construction:
 Study





the pattern layout carefully and establish,
a. Location of parting surface.
b. No. of parts in which the pattern will be made.
Using the various hand tools and pattern making
machines fabricate the different parts of the
pattern.
Inspect the pattern as regards the alignment of
different portions of the pattern and its
dimensional accuracy.
Fill wax in all the fillets in order to remove sharp
corners.
Give a shellac coatings(3 coats) to pattern.
impart suitable colors to the pattern for
identification purposes and for other

71. Pattern Colours:
Patterns are imparted
certain colors and
shades in order to:
i.
ii.
iii.
iv.
Identify quickly the main body of pattern
and different parts of the pattern.
Indicate the type of the metal to be cast.
Identify core prints, loose pieces, etc.,
Visualise the surfaces to be
machined, etc.

72. Moulding Materials
Major part of Moulding material in sand casting are
1. 70-85% silica sand (SiO2)
2. 10-12% bonding material e.g., clay cereal etc.
3. 3-6% water
Requirements of molding sand are:
(a) Refractoriness
(b) Cohesiveness
(c) Permeability
(d) Collapsibility
The performance of mould depends on following
factors:
(a) Permeability
(b) Green strength
(c) Dry strength

73. Molding Material and Properties:
A large variety of molding materials is
used in foundries for manufacturing
molds and cores. They include
molding sand, system sand or backing
sand, facing sand, parting sand, and
core sand. The choice of molding
materials is based on their processing
properties. The properties that are
generally required in molding
materials are:

74. 1. Refractoriness:
It is the ability of the molding material to
with stand high temperatures
(experienced during pouring) with out
1. Fusion,
2. Cracking, buckling or scabbing,
3. Experiencing any major physical
change.

Silica sand have high
refractriness.

75. 2. Permeability:





During pouring and subsequent solidification of a
casting, a large amount of gases and steam is
generated.
These gases are those that have been absorbed
by the metal during melting, air absorbed from the
atmosphere and the steam generated by the
molding and core sand.
If these gases are not allowed to escape from the
mold, they would be entrapped inside the casting
and cause casting defects.
To overcome this problem the molding material
must be porous.
Proper venting of the mold also helps in escaping
the gases that are generated inside the mold

76. 3. Green Strength:
The molding sand that contains moisture
is termed as green sand.
 The green sand particles must have the
ability to cling to each other to impart
sufficient strength to the mold.
 The green sand must have enough
strength so that the constructed mold
retains its shape.
 Green strength helps in making and
handling the moulds.


77. 4. Dry Strength:


A mould may either intentionally be dried, or
a green sand mould may lose its moisture
and get dried while waiting for getting poured
or when it comes in contact with molten
metal being poured.
The sand thus dried must have dry strength
to
1. Withstand erosive forces due to
molten metal,
2. Withstand pressure of molten metal,
3. Retain its exact shape,and
4. Withstand the metallostatic pressure
of the liquid material.

78. 5. Hot Strength:
As soon as the moisture is eliminated, the
sand would reach at a high temperature
when the metal in the mold is still in liquid
state.
 The strength of the sand that is required to
hold the shape of the cavity is called hot
strength.
 In the absence of adequate hot strength, the
mold may
1. enlarge


79. 6. Collapsibility:
Collapsibility determines the readiness
with which the molding sand,
1. Automatically gets collapsed
after the casting solidifies, and
2. Breaks down in knock out and
cleaning operations.
 If the mould or core does not
collapse, it may restrict free
contraction of solidifying metal and
cause the same to tear or crack.


80. 7. Flowability:
It is the ability of the molding sand to
get compacted to a uniform density.
 Flowability assists molding sand to
flow and pack all-around the pattern
and take up the required shape.
 Flowability increases as clay and
water contents increase.


81. 8. Adhesiveness:
It is the property of molding sand owing
to which, it
1. Sticks with the walls of molding
boxes,
2. Sticks with gaggers, and
3. Thus makes it possible to mold
cope and drag.

82. 9. Fineness:
Finer sand mould resist metal
penetration and produce smooth
casting surfaces.
 Fineness and permeability are in
conflict with each other and hence
they must be balanced for optimum
results.


83. Molding Sand Composition:
The main ingredients of any molding
sand are:
 Base sand,
 Binder, and
 Moisture

84. 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 is cheapest among all
types of base sand and it is easily
available.


85. 2. Binder:

Binders are of many types such as:
1. Clay binders,
2. Organic binders and
3. Inorganic binders

Clay binders are most commonly used binding
agents mixed with the molding sands to provide the
strength.

The most popular clay types are:
◦ Kaolinite or fire clay (Al2O3 2 SiO2 2 H2O) and
Bentonite (Al2O3 4 SiO2 nH2O)
◦ Of the two the Bentonite can absorb more water

86. 3. Moisture:
Clay acquires its bonding action only in the
presence of the required amount of
moisture.
 When water is added to clay, it penetrates
the mixture and forms a microfilm, which
coats the surface of each flake of the clay.
 The amount of water used should be
properly controlled.
 This is because a part of the water, which
coats the surface of the clay flakes, helps in
bonding, while the remainder helps in
improving the plasticity.


87. A Typical Composition of
Molding Sand:
Molding Sand Constituent
Weight Percent
Silica sand
92
Clay (Sodium Bentonite)
8
Water
4

88. Effect of moisture, grain size and shape
on mould quality

89. Classification of casting
Processes:
Casting processes can be classified into
following FOUR categories:
1. Conventional Molding Processes Green Sand Molding
a.
b.
Dry Sand Molding
Flask less Molding
2. Chemical Sand Molding Processes
a.
b.
c.
Shell Molding
Sodium Silicate Molding
No-Bake Molding
3. Permanent Mold Processes
a.
b.
Gravity Die casting
Low and High Pressure Die Casting
4. Special Casting Processes
a.
b.
c.
d.
e.
Lost Wax
Ceramics Shell Molding
Evaporative Pattern Casting
Vacuum Sealed Molding
Centrifugal Casting

90. 1.Green Sand Molding:
Green sand is the most diversified
molding method used in metal casting
operations. The process utilizes a mold
made of compressed or compacted moist
sand. The term "green" denotes the
presence of moisture in the molding sand.
The mold material consists of silica sand
mixed with a suitable bonding agent
(usually clay) and moisture.
Advantages:
 Most metals can be cast by this method.
 Pattern costs and material costs are relatively low.
 No Limitation with respect to size of casting and type
of metal or alloy used
Disadvantages:

91. 2.Dry Sand Molding:
When it is desired that the gas forming
materials are lowered in the molds, airdried molds are sometimes preferred to
green sand molds. Two types of drying of
molds are often required.
 Skin drying and
 Complete mold drying.
In skin drying a firm mold face is
produced. Shakeout of the mold is almost
as good as that obtained with green sand
molding. The most common method of

92. 3.Shell Molding Process:




It is a process in which, the sand mixed with
a thermosetting resin is allowed to come in
contact with a heated pattern plate (200
oC), this causes a skin (Shell) of about 3.5
mm of sand/plastic mixture to adhere to the
pattern..
Then the shell is removed from the pattern.
The cope and drag shells are kept in a flask
with necessary backup material and the
molten metal is poured into the mold.
This process can produce complex parts
with good surface finish 1.25 µm to 3.75
µm, and dimensional tolerance of 0.5 %.
A good surface finish and good size

94. 4.Sodium Silicate Molding
Process
In this process, the refractory material is
coated with a sodium silicate-based
binder. For molds, the sand mixture can
be compacted manually, jolted or
squeezed around the pattern in the flask.
 After compaction, CO 2 gas is passed
through the core or mold. The CO 2
chemically reacts with the sodium silicate
to cure, or harden, the binder. This cured
binder then holds the refractory in place
around the pattern. After curing, the


95. The major disadvantage of the process is
that the binder is very hygroscopic and
readily absorbs water, which causes a
porosity in the castings.. Also, because
the binder creates such a hard, rigid
mold wall, shakeout and collapsibility
characteristics can slow down
production.
 Some of the advantages of the process
are:
 A hard, rigid core and mold are typical
of the process, which gives the


96. .
.

97. Review:

98. Foundry activities

99. 2 types of moulding flask designs

100. Sand mold - opened

101. Sand mold - closed

102. Cooling curve for pure metal

104. Mixing moulding sand with binders & adhesives

105. Filling sand in moulding flasks

106. Melting furnace

107. Pouring molten liquid

108. Knock out

109. Heat treatment

110. Machining

111. final products of casting

112. Reference:
A text book of Production Technology Vol. I /
O.P. Khanna / Dhanpat Rai Publications
2. A text book of Production Technology
(Manufacturing Processes) / P. C. Sharma / S.
Chand & Company Ltd
3. Manufacturing Technology (Second Edition) / P
N Rao / Tata McGraw-Hill Publishing Company
Ltd
&
1.
http://nptel.iitm.ac.in/

113. Thank you...