Casting unit 1 notes

Manufacturing Technology / Unit 1 / Dr.M.B / RMKCET Page 1
UNIT 1 CASTING
Aim or reason to make a casting
1. Cheapest and direct way of producing finished articles
2. Desired where products are required in low quantity as against high cost in using
other process
3. Certain metals and alloys which are difficult to be worked mechanically can be cast
4. Intricate shapes and complex sectional variations, which are difficult to be fabricated
by other process can be done easily
5. Heavy equipment parts such as machine beds, large gears, ship propellers, etc can be
easily fabricated
6. Best suited for composite sections
Classification of Foundries
1. Jobbing foundry - specialize in small orders and variety of shapes
2. Repetition foundry – Mass production and large identical shapes
3. Die casting foundry – Using permanent mold for high volume
4. Pressure Die casting foundry
5. Gravity die casting foundry
Pattern
Pattern is defined as a model of a casting, constructed in such a way that it can be used for
forming an impression in damp sand to form mold
Pattern Materials
1. Wood 2. Metal 3. Plastic 4. Wax etc
Advantages of using wood
1. Ease of availability
2. Lightness
3. Ease of obtaining flat and smooth surface
4. Ability to work on it easily
5. Ease of fabricating in to different shapes
Dis-Advantages
1. Easily affected by moisture

2. Wears out quickly
3. It cannot stand rough usage
When durability and strength are required, patterns are made of metal, usually aluminium,
brass and magnesium alloy.
Characteristics of Pattern Material
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. Should be available at low cost
Pattern Allowances
Pattern allowance is a vital feature as it affects the dimensional characteristics of the casting.
Thus, when the pattern is produced, certain allowances must be given on the sizes specified
in the finished component drawing so that a casting with the particular specification can be
made. The selection of correct allowances greatly helps to reduce machining costs and avoid
rejections. The allowances usually considered on patterns and core boxes are as follows:
1. Shrinkage or contraction allowance
2. Draft or taper allowance
3. Machining or finish allowance
4. Distortion or camber allowance
5. Rapping allowance
Shrinkage or Contraction Allowance
All most all cast metals shrink or contract volumetrically on cooling. The metal shrinkage is
of two types:
i. 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.
ii. 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.

The rate of contraction with temperature is dependent on the material. For example steel
contracts to a higher degree compared to aluminum. The various rate of contraction of
various materials are given inTable 1.
Table 1 : Rate of Contraction of Various Metals
Material Dimension Shrinkage allowance
(inch/ft)
Grey Cast Iron Up to 2 feet
2 feet to 4 feet
over 4 feet
0.125
0.105
0.083
Cast Steel Up to 2 feet
2 feet to 6 feet
over 6 feet
0.251
0.191
0.155
Aluminum Up to 4 feet
4 feet to 6 feet
over 6 feet
0.155
0.143
0.125
Magnesium Up to 4 feet
Over 4 feet
0.173
0.155
Exercise 1
The casting shown is to be made in cast iron using a wooden pattern. Assuming only
shrinkage allowance, calculate the dimension of the pattern.All Dimensions are in Inches
Solution 1
The shrinkage allowance for cast iron for size up to 2 feet is o.125 inch per feet (as per Table
1)
For dim. 18inch, allowance = 18 X 0.125 / 12 = 0.1875 inch » 0.2 inch
For dim. 14inch, allowance = 14 X 0.125 / 12 = 0.146 inch » 0.15 inch
For dim. 8 inch, allowance = 8 X 0.125 / 12 = 0.0833 inch » 0. 09 inch
For dim. 6 inch, allowance = 6 X 0.125 / 12 = 0.0625 inch » 0. 07 inch
The pattern drawing with required dimension is shown below:

Draft or Taper Allowance
By draft is meant the taper provided by the pattern maker on all vertical surfaces of the
pattern so that it can be removed from the sand without tearing away the sides of the sand
mold and without excessive rapping by the molder. A pattern having no draft allowance when
removed from the pattern, In this case, its sides will remain in contact with the walls of the
mold, thus tending to break it. A pattern having proper draft allowance, the moment the
pattern lifting commences, all of its surfaces are well away from the sand surface. Thus the
pattern can be removed without damaging the mold cavity.
Draft allowance varies with the complexity of the sand job. But in general inner details of the
pattern require higher draft than outer surfaces. The amount of draft depends upon the length
of the vertical side of the pattern to be extracted; the intricacy of the pattern; the method of
molding; and pattern material. Table 2 provides a general guide lines for the draft allowance.

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
3.00
1.50
1.00
0.75
3.00
2.50
1.50
1.00
Metal and
plastic
1
1 to 2
2 to 4
4 to 8
1.50
1.00
0.75
0.50
3.00
2.00
1.00
1.00
Machining or Finish Allowance
The finish and accuracy achieved in sand casting are generally poor and therefore when the
casting is functionally required to be of good surface finish or dimensionally accurate, it is
generally achieved by subsequent machining. Machining or finish allowances are therefore
added in the pattern dimension. The amount of machining allowance to be provided for is
affected by the method of molding and casting used viz. hand molding or machine molding,
sand casting or metal mold casting. The amount of machining allowance is also affected by
the size and shape of the casting; the casting orientation; the metal; and the degree of
accuracy and finish required. The machining allowances recommended for different metal is
given in Table 3.
Table 3 : Machining Allowances of Various Metals
Metal Dimension (inch) Allowance (inch)
Cast iron
Up to 12
12 to 20
0.12
0.20
Cast steel
Up to 6
6 to 20
0.12
0.25
Non ferrous
Up to 8
8 to 12
0.09
0.12
Distortion or Camber Allowance
Sometimes castings get distorted, during solidification, due to their typical shape. For
example, if the casting has the form of the letter U, V, T, or L etc. it will tend to contract at
the closed end causing the vertical legs to look slightly inclined. This can be prevented by
making the legs of the U, V, T, or L shaped pattern converge slightly (inward) so that the
casting after distortion will have its sides vertical ( (Figure 4). The distortion in casting may

occur due to internal stresses. These internal stresses are caused on account of unequal
cooling of different section of the casting and hindered contraction. Measures taken to
prevent the distortion in casting include:
i. Modification of casting design
ii. Providing sufficient machining allowance to cover the distortion affect
iii. Providing suitable allowance on the pattern, called camber or distortion allowance
(inverse reflection)
Figure 4: Distortions in Casting
Rapping Allowance
Before the withdrawal from the sand mold, the pattern is rapped all around the vertical faces
to enlarge the mold cavity slightly, which facilitate its removal. Since it enlarges the final
casting made, it is desirable that the original pattern dimension should be reduced to account
for this increase. There is no sure way of quantifying this allowance, since it is highly
dependent on the foundry personnel practice involved. It is a negative allowance and is to be
applied only to those dimensions that are parallel to the parting plane.
Types of Pattern
The most commonly used patterns in foundry are as follows
1) SINGLE PIECE PATTERN
2) SPLIT PATTERN OR TWO PIECE PATTERN
3)MULTIPLE PIECE PATTERN

4) GATED PATTERN
4) COPE AND DRAG PATTERN
5) MATCH PLATE PATTERN
6) LOOSE PIECE PATTERN
7) FOLLOW BOARD PATTERN
8) SWEEP PATTERN
9) SKELETON PATTERN
 A solid pattern is the most simple of all and is used to make simple shapes. As the
name itself suggests, a solid pattern is a single solid piece without any subparts or
joints.
 Split Pattern - Shapes which are more intricate are manufactured using patterns
which are made out of 2 or more pieces. These pieces are aligned together with the
help of dowel pins, and such patterns are known as split patterns

 Gated Pattern - Sometimes it is convenient to produce multiple parts in one go and a
single pattern is used to make the cavity for all the part spaces. There are runners
between these pieces, which are also known as gates. Hence these patterns go by the
name of gated patterns.
 Sweep Pattern - In several cases it could be economical to save the money and
efforts of making the full pattern because of symmetry. The cavity in such a case
could be made by sweeping the pattern (which is a part of the full shape) around a
central axis, hence these are known as sweeping patterns.
 Skeleton Pattern - When the size of the casting is very large, but easy to shape and
only a few numbers are to be made, it is not economical to make a large solid pattern
of that size. In such cases a pattern consisting of wooden frame and strips is made
called skeleton pattern. It is filled with moulding sand and rammed properly.
 Match Plate Pattern - These patterns are made in two pieces. One piece is mounted
on one side and the other on the other side of a plate called match plate. Gates and

runners are also attached to the plate along with the pattern. After moulding when the
match plate is removed a complete mould with gating is obtained by joining the cope
and drag together. The complete pattern with match plate is entirely made of metal,
usually aluminium for its light weight and machinability. These are generally used
for mass production of small castings with higher dimensional accuracy. These
patterns are mainly employed for machine moulding. Their construction cost is high
but the same is easily compensated by a high rate of production and greater
dimensional accuracy.
Follow board pattern
Follow board pattern
Some castings have certain portions which are structurally weak. If those portion of the
pattern is not supported properly they are likely to break under the force of ramming. In this
case a special type of pattern called follow board pattern is adopted. A follow board is a
wooden board used to support a pattern during moulding. It acts as a seat for the pattern.
Segmental Pattern

Those pattern are used for preparing moulds of large circular castings, avoid the use of a solid
pattern of exact size. In principle they are similar to sweep patterns. But the difference is that
while a sweep pattern is given a continuous revolving motion to generate the desired shape, a
segmental pattern is a portion of the solid pattern itself and the mould is prepared in parts by
it. It is mounted on a central pivot and after preparing the part mould in one position, the
segment is moved to the next position. The operation is repeated till the complete mould is
ready.
Pattern with Loose – Pieces
Certain single piece patterns are made to have loose pieces in order to enable their easy
withdrawal from the mould. These pieces from an integral part of the pattern during
moulding. After the mould is complete the pattern is withdrawn leaving the pieces in the

sand. These pieces are later withdrawn separately through the cavity formed by the pattern as
shown in figure. Moulding with loose piece is a highly skilled job and is generally expensive.
Pattern colour code
The pattern are normally painted with contrasting colours is that the mould maker would be
able to understand the colours clearly. The colour code used are
1. Red or Orange on surfaces not to be finished and left as cast
2. Yellow on surfaces to be machined
3. Black on core prints for un machined openings
4. Yellow stripes on black on core prints for machined openings
5. Green on seats of and for loose pieces and lose core prints
6. Diagonal black striper with clean varnish on to strengthen the weak patterns or to
shorten a casting.
Machines used in Pattern Making
1. Circular saw
2. Band saw
3. Wood turning lathe
4. Drill press
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:
Refractoriness
It is the ability of the molding material to resist the temperature of the liquid metal to be
poured so that it does not get fused with the metal. The refractoriness of the silica sand is
highest.
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
cavity.
Plasticity
It is that property of sand due to which it acquires pre-determined shape under pressure and to
retain it when the pressure is removed. The sand must have sufficient plasticity to produce a
good mould.
Adhesiveness
The sand particles must be capable of sticking to other bodies, particularly to the molding
box.
Cohesiveness
It is the property of sand due to which the sand grains stick together during ramming. It is
defined as the strength of the moulding sand. Cohesiveness depends upon grain size and
shape, bonding of material and moisture content.
Flowability
Ability to pack tightly around the pattern.
Green Strength
The molding sand that contains moisture is termed as green sand. Have the ability to support
its own weight when stripped from the pattern, and also withstand pressure of molten metal
when the mold is cast.
Dry Strength
When the molten metal is poured in the mold, the sand around the mold cavity is quickly
converted into dry sand as the moisture in the sand evaporates due to the heat of the molten
metal. At this stage the molding sand must possess the sufficient strength to retain the exact
shape of the mold cavity and at the same time it must be able to withstand the metallostatic
pressure of the liquid material.
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.

Collapsibility
The molding sand should also have collapsibility so that during the contraction of the
solidified casting it does not provide any resistance, which may result in cracks in the
castings. Besides these specific properties the molding material should be cheap, reusable and
should have good thermal conductivity.
Molding sand
Sand, which binds strongly without losing its permeability to air or gases. It is a mixture of
silica sand, clay, and moisture in appropriate proportions
Molding Sand Composition
The main ingredients of any molding sand are:
 Base sand, Additives(Binder, saw dust), and Moisture
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.
Types of Base Sand
 Silica sand
 Olivine sand
 Chromite sand
 Zircon sand
 Chamotte sand
Types of base sands
Base sand is the type used to make the mold or core without any binder. Because it does not
have a binder it will not bond together and is not usable in this state.
Silica sand
Silica (SiO2) sand is the stereotype sand (i.e. the sand found on a beach) and is also the most
commonly used sand. It is made by either crushing sandstone or taken from natural occurring
locations, such as beaches and river beds. The fusion point of pure silica is 1,760 °C,
however the sands used have a lower melting point due to impurities. For high melting point
casting, such as steels, a minimum of 98% pure silica sand must be used; however for lower
melting point metals, such as cast iron and non-ferrous metals, a lower purity sand can be
used (between 94 and 98% pure).

Olivine sand
Olivine is a mixture of orthosilicates of iron and magnesium from the mineral dunite. Its main
advantage is that it is free from silica, therefore it can be used with basic metals, such as
manganese steels. Other advantages include a low thermal expansion, high thermal
conductivity, and high fusion point. Finally, it is safer to use than silica, therefore it is popular
in Europe.
Chromite sand
Chromite sand is a solid solution of spinels. Its advantages are a low percentage of silica, a
very high fusion point (1,850 °C ), and a very high thermal conductivity. Its disadvantage is
its costliness, therefore its only used with expensive alloy steel casting and to make cores.
Zircon sand
Zircon sand is a compound of approximately two-thirds zircon oxide (Zr2O) and one-third
silica. It has the highest fusion point of all the base sands at 2,600 °C , a very low thermal
expansion, and a high thermal conductivity. Because of these good properties it is commonly
used when casting alloy steels and other expensive alloys.
Chamotte sand
Chamotte is made by calcining fire clay (Al2O3-SiO2) above 1,100 °C. Its fusion point
is 1,750 °C and has low thermal expansion. It is the second cheapest sand, however it is still
twice as expensive as silica. Its disadvantages are very coarse grains, which result in a poor
surface finish, and it is limited to dry sand molding. Mold washes are used to overcome the
surface finish problem. This sand is usually used when casting large steel workpieces.
Binders
Binders are added to base sand to bond the sand particles together (i.e. it is the glue that holds
the mold together).
Clay and water
A mixture of clay and water is the most commonly used binder. There are two types of clay
commonly used: bentonite and kaolinite, with the former being the most common.
Oil
Oils, such as linseed oil, other vegetable oils and marine oils, used to be used as a binder,
however due to their increasing cost, they have been mostly phased out. The oil also required
careful baking at 100 to 200 °C to cure (if overheated the oil becomes brittle, wasting the
mold).

Resin
Resin binders are natural or synthetic high melting point gums. The two common types used
are urea formaldehyde (UF) and phenol formaldehyde (PF) resins. PF resins have a higher
heat resistance than UF resins and cost less. There are also cold-set resins, which use a
catalyst instead of a heat to cure the binder. Resin binders are quite popular because different
properties can be achieved by mixing with various additives. Other advantages include good
collapsibility, low gassing, and they leave a good surface finish on the casting.
Sodium silicate
Sodium silicate [Na2SiO3 or (Na2O)(SiO2)] is a high strength binder used with silica molding
sand. To cure the binder carbon dioxide gas is used, which creates the following reaction:
The advantage to this binder is that it occurs at room temperature and quickly. The
disadvantage is that its high strength leads to shakeout difficulties and possibly hot tears
in the casting.
Additives
Additives are added to the molding components to improve: surface finish, dry strength,
refractoriness, and "cushioning properties".
Up to 5% of reducing agents, such as coal powder, pitch, creosote, and fuel oil, may be
added to the molding material to prevent wetting (prevention of liquid metal sticking to
sand particles, thus leaving them on the casting surface), improve surface finish, decrease
metal penetration, and burn-on defects. These additives achieve this by creating gases at
the surface of the mold cavity, which prevent the liquid metal from adhering to the sand.
Reducing agents are not used with steel casting, because they can carburize the metal
during casting.
Up to 3% of "cushioning material", such as wood flour, saw dust, powdered husks, peat,
and straw, can be added to reduce scabbing, hot tear, and hot crack casting defects when
casting high temperature metals. These materials are beneficial because burn-off when
the metal is poured creating voids in the mold, which allow it to expand. They also
increase collapsibility and reduce shakeout time.
Up to 2% of cereal binders, such as dextrin, starch, sulphite lye, and molasses, can be
used to increase dry strength (the strength of the mold after curing) and improve surface
finish. Cereal binders also improve collapsibility and reduce shakeout time because they
burn-off when the metal is poured. The disadvantage to cereal binders is that they are
expensive.
Up to 2% of iron oxide powder can be used to prevent mold cracking and metal
penetration, essentially improving refractoriness. Silica flour (fine silica) and zircon flour

also improve refractoriness, especially in ferrous castings. The disadvantages to these
additives is that they greatly reduce permeability.
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. A typical composition of
molding sand is given in (Table 4).
Table 4 : A Typical Composition of Molding Sand
Molding Sand Constituent Weight Percent
Silica sand 92
Clay (Sodium Bentonite) 4
Water 4
Greensand:
It is called green sand because of its water content. However it’s color is black. Wet sand
used for molding, contains about 20-30% clay and 8 % water by part. If we can maintain the
amount of clay, then we can easily maintain the flow-ability of sand. We can maintain its
porosity. Used for small and medium castings.
Dry sand:
If we dry the green sand mentioned above, then we get dry sand. The physical composition
remains same, except for water content. The mold prepared in green sand are dried or baked
to remove moisture. Used for large and heavy molds.
Facing sand:
This sand comes in contact with direct contact of molten metal hence it is subjected to
severest conditions. The small amount of carbonaceous material sprinkled on the inner
surface of the mold cavity to give a better surface finish to the castings. Facing materials
namely graphite and lead are used with molding sand to get facing sand. It must possess high
strength and refractoriness
Backing sand:
We can use old and repeatedly used sand for this purpose as this only contributes to support
the mold. No need to waste fresh sand for it.

System sand:
We use this sand in mechanical foundries where we do molding with the aid of machines. We
fill whole container with this sand and in this case we do not use facing sand.
Parting sand:
This is used so that the green sand will not stick to the pattern. Eg: We used Bentonite
powder during our practices
Core sand:
This is also called as oil sand. This sand is obtained by mixing normal silica sand with
Linseed oil or any other oil like mineral oil or resin etc. It is used to form the core.
CO2 Sand
The silica grains instead of coating with natural clay, are coated with sodium silicate. This
mixture is packed around the pattern and then hardened by passing Co2 through the
interstices.
Nomenclature of a Mold

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 the two molding flasks that makes up
the mold.
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 molten metal is carried from the sprue to the
gate.
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.
Goals of Gating System
The goals for the gating system are
 To minimize turbulence to avoid trapping gasses into the mold
 To get enough metal into the mold cavity before the metal starts to solidify
 To avoid shrinkage
 Establish the best possible temperature gradient in the solidifying casting so that the
shrinkage if occurs must be in the gating system not in the required cast part.
 Incorporates a system for trapping the non-metallic inclusions

The gating systems are of two types:
 Pressurized gating system
 Un-pressurized gating system
Pressurized Gating System
 The total cross sectional area decreases towards the mold cavity
 Back pressure is maintained by the restrictions in the metal flow
 Flow of liquid (volume) is almost equal from all gates
 Back pressure helps in the gating system run with full of liquid metal, since the sprue
always runs full
 Because of the restrictions the metal flows at high velocity leading to more turbulence
and chances of mold erosion
 Used for steel and iron
Un-Pressurized Gating System
 The total cross sectional area increases towards the mold cavity
 Restriction only at the bottom of sprue
 Flow of liquid (volume) is different from all gates
 aspiration in the gating system as the system never runs full
 Less turbulence
 Used for oxidizable metals like aluminium and magnesium
Fig. (A) Parting Gate (B) Top Gate (C) Bottom Gate
Top gate: Conductive to a favorable temperature gradient but erosion may be high.
Turbulence
Bottom gate: Offers smooth flow with a minimum of erosion but unfavorable temperature
gradient.
Parting Gate : Most widely used and economical

Riser
Riser is a source of extra metal which flows from riser to mold cavity to compensate for
shrinkage which takes place in the casting when it starts solidifying. Without a riser heavier
parts of the casting will have shrinkage defects, either on the surface or internally.
Risers are known by different names as metal reservoir, feeders, or headers.
Shrinkage in a mold, from the time of pouring to final casting, occurs in three stages.
1. during the liquid state
2. during the transformation from liquid to solid
3. during the solid state
First type of shrinkage is being compensated by the feeders or the gating system. For the
second type of shrinkage risers are required. Risers are normally placed at that portion of the
casting which is last to freeze. A riser must stay in liquid state at least as long as the casting
and must be able to feed the casting during this time.
Functions of Risers
 Provide extra metal to compensate for the volumetric shrinkage
 Allow mold gases to escape
 Provide extra metal pressure on the solidifying mold to reproduce mold details more
exact
Design Requirements of Risers
1. Riser size: For a sound casting riser must be last to freeze. The ratio of (volume /
surface area)2
of the riser must be greater than that of the casting. However, when
this condition does not meet the metal in the riser can be kept in liquid state by
heating it externally or using exothermic materials in the risers.
2. Riser placement: the spacing of risers in the casting must be considered by effectively
calculating the feeding distance of the risers.
3. Riser shape: cylindrical risers are recommended for most of the castings as spherical
risers, although considers as best, are difficult to cast. To increase volume/surface
area ratio the bottom of the riser can be shaped as hemisphere.
There are two types of riser
Open Riser: Top of the open riser in open, it is cylinder shape
Advantages: An open riser is easy to mold,
Air can be removed from it.
Disadvantages: It is not placed in the drag. More difficult to remove from the Casting.
Close/blind riser: Blind risers are domelike risers, found in the cope half of the flask, which
are not the complete height of the cope.

Advantages: Can be placed at any position of the mold. Can be
easily removed from the casting. Metal in the riser cools slowly than the metal in the casting
Disadvantages: Difficult to mold. May draw liquid metal from solidifying casting.
Advantages of Blind Riser
 The hottest metal remains in the riser which promotes directional solidification
 A blind riser is comparatively smaller than an open riser
 Blind riser can be placed anywhere in the mold cavity
 Blind riser can be easily removed from the casting
Cores
Cores are utilized for castings with internal cavities or passages.
A core is a body, usually made of sand, used to produce a cavity in or on a casting.
Examples: forming the water jacket in a water cooled engine block and forming the air space
between the cooling fins of an air cooled engine.

Cores are placed in the mold cavity before casting to form the interior surfaces of the casting.
Core making
Core sand is placed in a core box. It can be blown into the box, rammed or packed by hand,
or jolted into the box. The excess sand is struck off, and a drier plate is placed over the box.
The core box is then inverted, vibrated or rapped, and drawn off the core. The core is then put
in a core oven and backed.
Core prints
Recesses/projection that is added to the pattern to support the core and to provide vents for
the escape of gases.
Chaplets: serve to support cores that tend to sag or sink in inadequate core print seats.
Chaplets also serve as anchor to keep the core in place during the casting process.
A chaplet is usually made of the same metal as, and becomes part of the casting.
Types of cores
1. Green sand core
2. Dry sand core

Green sand core
A green sand core is made of the same sand from which the mold has been made i.e. the
molding sand. Relatively cheap and popular.
Dry sand core
Dry sand core unlike green sand cores are not produced as a part of the mold.
Dry sand core is made separately and independent of the mold.
Backed sand or dry sand core has a binder that must be cured with heat.
Types of Cores
1. Horizontal core
2. Vertical Core
3. Balanced Core
4. Drop Core
5. Hanging Core or cover core
Molding machines:
Serve: To pack sand firmly and uniformly into the mold.
To manipulate the flasks, mold, and pattern.
Three types of molding machines are:
Jolt-squeeze Molding Machine
Jolt-rollover Molding Machine
Sand slinger
Jolt-squeeze Molding Machines: A jolt-squeezer consists basically of a table actuated by two
pistons in air cylinders, one inside the other. The mold on the table is jolted by the action of
the inner piston that raises the table repeatedly and drops it down sharply on a bumper pad.
Jilting packs the sand in the lower parts of the flask but not at the top. The larger cylinder
pushes the table upward to squeeze the sand in the mold against the squeeze head at the top.
A vibrator may be attached to the machine to loosen the pattern to remove it easily without
damaging the mold.
Jolt-rollover Pattern-draw Machines: A flask is set over a pattern on a table and is filled with
sand and jolted. Excess sand is struck off, and a bottom board is clamped to the flask. The
machine raises the mold and rolls it over onto a table or conveyor. The flask is freed from the
machine. The pattern is vibrated, raised from the mold, and returned to loading position.

The sand slinger: The sand slinger achieves a consistent packing and ramming effect by
hurling sand into the mold at a high velocity. Sand from a hopper is fed by a belt to a high-
speed impeller in the head. A common arrangement is to suspend the slinger with counter
weights and move it about to direct the stream of sand advantageously into a mold. Sand
slinger can be deliver large quantities of sand rapidly and are specially beneficial for
ramming big molds.
TESTING SAND PROPERTIES
The moulding sand after it is prepared should be properly tested to see that the requisite
properties are achieved. These are standard tests to be done as per Indian Standards.
Sample Preparation
Tests are conducted on a sample of the standard sand. The moulding sand should be prepared
exactly as is done in the shop on the standard equipment and then carefully enclosed in a
container to safeguard its moisture content.
Moisture Content
Moisture is an important element of the moulding sand as it affects many
properties. To test the moisture of moulding sand a carefully weighed sand test sample of 50g
is dried at a temperature of 1050
c to 1100
c for 2 hours by which time all the moisture in the
sand would have been evaporated. The sample is then weighed. The weight difference in
grams when multiplied by two would give the percentage of moisture contained in the
moulding sand. Alternatively a moisture teller can also be used for measuring the moisture
content. In this sand is dried by suspending the sample on a fine metallic screen and allowing
hot air to flow through the sample. This method of drying completes the removal of moisture
in a matter of minutes compared to 2 hours as in the earlier method.
Clay Content
The clay content of the moulding sand is determined by dissolving or washing it off
the sand. To determine the clay percentage a 50 g sample is dried at 105 to 1100
C and the
dried sample is taken in a one litre glass flask and added with 475 ml of distilled water and
25ml of a one percent solution of caustic soda(NaOH25 g per litre). This sample is
thoroughly stirred.
After the stirring, for a period of five minutes, the sample is diluted with fresh
water up to a 150mm graduation mark and the sample is left undisturbed for 10 minutes to
settle. The sand settles at the bottom and the clay particles washed from the sand would be
floating in the water. 125 mm of this water is siphoned off the flask and it is again topped to

the same level and allowed to settle for five minutes. The above operation is repeated till the
water above the sand becomes clear, which is an indication that all the clay in the moulding
sand has been removed. Now, the sand removed from the flask and dried by heating. The
difference in weight of the dried sand and 50g when multiplied by two gives the clay
percentage in the moulding sand.
Sand Grain Size
To find out the sand grain size, a sand sample which is devoid of moisture and clay
such as the one obtained after the previous testing is to be used. The dried clay free sand
grains are placed on the top sieve of a sieve shaker which contains a series of sieves one upon
the other with gradually decreasing mesh sizes. The sieves are shaken continuously for a
period of 15 minutes. After this shaking operation, the sieves are taken apart and the sand left
over on each of the sieve is carefully weighed. The sand retained on each sieve expressed as a
percentage of the total mass can be plotted against sieve number. But more important is the
Grain Finesses Number (GFN) which is a quantitative indication of the grain distribution. To
calculate the GFN each sieve has been given a weightage factor as given in the Table –IV.
The amount retained on each sieve is multiplied by the respective weightage factor, summed
up and then divided by the total mass of the sample, which gives the GFN.
Permeability
The rate of flow of air passing through a standard specimen under a standard pressure is
termed as permeability number. The standard permeability test is to measure time taken by a
2000 cm3 of air at a pressure typically of 980 Pa to pass through a standard sand specimen

confined in a specimen tube. The standard specimen size is 50.8 mm in diameter and a length
of 50.8 mm. Then, the permeability number, P is obtained by
Where V = volume of air = 2000 cm3
H = height of the sand specimen = 5.08 cm
p = air pressure, g/cm2
A = cross sectional area of sand specimen= 20.268 cm2
T = time in minutes for the complete air to pass through
Inserting the above standard values into the expression, we get
Specimen Preparation
Since the permeability of sand is dependent to a great extent, on the degree of ramming, it is
necessary that the specimen be prepared under standard conditions. To get reproducible
ramming conditions, a laboratory sand rammer is used along with a specimen tube. The
measured amount of sand is filled in the specimen tube, and a fixed weight of 6.35 to 7.25 Kg
is allowed to fall on the sand three times from a height of 50.8 ±0.125 mm. The specimen
thus produced should have a height of 50.8± 0.8 mm. To produce this size of specimen
usually sand of 145 to 175 g would be required. After preparing a test sample of sand as
described, 2000 cm3 of air are passed through the sample and time taken by it to completely
pass through the specimen is noted.

Fig. Sand rammer for specimen preparation
Mould Hardness
The mould hardness is measured by a method similar to the Brinell hardness test. A spring
loaded steel ball with a mass of 0.9 Kg is indented into the standard sand specimen prepared.
The depth of indentation can be directly measured on the scale which shows units 0 to 100.
When no penetration occurs, then it is a mould hardness of 100 and when it sinks completely,
the reading is zero indicating a very soft mould. Besides these, there are other tests to
determine such properties as deformation, green tensile strength, hot strength, expansion, etc.
Strength
Measurement of strength of moulding sands can be carried out on the universal sand strength
testing machine. The strength can be measured in compression, shear and tension. The sands
that could be tested are green sand, dry sand or core sand. The compression and shear test
involve the standard cylindrical specimen that was used for the permeability test.

Fig. Universal sand strength tester
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 sand specimen is taken out of the
specimen tube and is immediately (any delay causes the drying of the sample which increases
the strength) put on the strength testing machine and the force required to cause the
compression failure is determined. The green strength of sands is generally in the range of 30
to 160 KPa.
Fig. Specimen
Green Shear Strength
With a sand sample similar to the above test, a different adapter is fitted 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.
Dry Strength
This test uses the standard specimens dried between 105 and 1100
C for 2 hours. Since the
strength increases with drying, it may be necessary to apply larger stresses than the previous
tests. The range of dry compression strengths found in moulding sands is from 140 to 1800
KPa, depending on the sand sample

(1) Vent wire for sticking vent holes through the sand of the mould.
(2) Pattern lifter.
(3) Joint trowel and (4) heart trowel for smoothing and finishing the parting and flat surfaces
of the mould.
(5) Gate cutter and pattern lifter.
(6) Slick and oval spoon for finishing mould surfaces.
(7) (8) Sand lifters and slicks.
(9) Yankee heel lifter and flat slick.
(10) Flange and bead slick. (11) Corner slick. (12) Edge slick.
(13) Bound corner slick. (14) Pipe slick.
(15) Button slick. (16) Oval Slick. (17) Hand rammer for ramming sand in flasks
(18) Spirit level for leveling open sand moulds.

Advantages and disadvantages of sand casting
Advantages of sand casting
 Low cost of mold 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 of sand casting
 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).
Melting Practices
Melting is an equally important parameter for obtaining a quality castings. A number of furnaces can be used
for melting the metal, to be used, to make a metal casting. The choice of furnace depends on the type of
metal to be melted. Some of the furnaces used in metal casting are as following:.
 Crucible furnaces
 Cupola
 Induction furnace
 Reverberatory furnace
Crucible Furnace.
Crucible furnaces are small capacity typically used for small melting applications. Crucible furnace is
suitable for the batch type foundries where the metal requirement is intermittent. The metal is placed in a
crucible which is made of clay and graphite. The energy is applied indirectly to the metal by heating the
crucible by coke, oil or gas.The heating of crucible is done by coke, oil or gas. .
Coke-Fired Furnace
 Primarily used for non-ferrous metals
 Furnace is of a cylindrical shape
 Also known as pit furnace
 Preparation involves: first to make a deep bed of coke in the furnace
 Burn the coke till it attains the state of maximum combustion
 Insert the crucible in the coke bed
 Remove the crucible when the melt reaches to desired temperature

Oil-Fired Furnace.
 Primarily used for non-ferrous metals
 Furnace is of a cylindrical shape
 Advantages include: no wastage of fuel
 Less contamination of the metal
 Absorption of water vapor is least as the metal melts inside the closed metallic furnace
CUPOLA FURNACE
For many years, the cupola was the primary method of melting used in iron foundries. The cupola
furnace has several unique characteristics which are responsible for its widespread use as a melting
unit for cast iron.
Cupola furnace is employed for melting scrap metal or pig iron for production of various cast irons.
It is also used for production of nodular and malleable cast iron. It is available in good varying sizes.
The main considerations in selection of cupolas are melting capacity, diameter of shell without lining
or with lining, spark arrester.
Shape
A typical cupola melting furnace consists of a water-cooled vertical cylinder which is lined with refractory
material.
Construction
The construction of a conventional cupola consists of a vertical steel shell which is lined with a
refractory brick.
The charge is introduced into the furnace body by means of an opening approximately half way up
the vertical shaft.
The charge consists of alternate layers of the metal to be melted, coke fuel and limestone flux.
The fuel is burnt in air which is introduced through tuyeres positioned above the hearth. The hot
gases generated in the lower part of the shaft ascend and preheat the descending charge.

Manufacturing Technology – 1 / Unit 1 / Foundry / VEC / Dr.M.B Page 32
Various Zones of Cupola Furnace
Various numbers of chemical reactions take place in different zones of cupola. The
construction and different zones of cupola are :
1. Well
The space between the bottom of the tuyeres and the sand bed inside the cylindrical shell of
the cupola is called as well of the cupola. As the melting occurs, the molten metal is get
collected in this portion before tapping out.
2. Combustion zone
The combustion zone of Cupola is also called as oxidizing zone. It is located between the
upper of the tuyeres and a theoretical level above it. The total height of this zone is normally
from 15 cm. to 30 cm. The combustion actually takes place in this zone by consuming the
free oxygen completely from the air blast and generating tremendous heat. The heat
generated in this zone is sufficient enough to meet the requirements of other zones of cupola.
The heat is further evolved also due to oxidation of silicon and manganese. A temperature of
about 1540°C to 1870°C is achieved in this zone. Few exothermic reactions takes place in
this zone these are represented as:
C + O2 → CO2 + Heat
Si + O2 → SiO2 + Heat
2Mn + O2 → 2MnO + Heat
3. Reducing zone
Reducing zone of Cupola is also known as the protective zone which is located between the
upper level of the combustion zone and the upper level of the coke bed. In this zone, CO2 is
changed to CO through an endothermic reaction, as a result of which the temperature falls
from combustion zone temperature to about 1200°C at the top of this zone. The important
chemical reaction takes place in this zone which is given as under.
CO2 + C (coke) → 2CO + Heat
Nitrogen does not participate in the chemical reaction occurring in his zone as it is also the
other main constituent of the upward moving hot gases. Because of the reducing atmosphere
in this zone, the charge is protected against oxidation.
4. Melting zone
The lower layer of metal charge above the lower layer of coke bed is termed as melting zone
of Cupola. The metal charge starts melting in this zone and trickles down through coke bed
and gets collected in the well. Sufficient carbon content picked by the molten metal in this
zone is represented by the chemical reaction given as under.
3Fe + 2CO → Fe3C + CO2
5. Preheating zone
Preheating zone starts from the upper end of the melting zone and continues up to the bottom
level of the charging door. This zone contains a number of alternate layers of coke bed, flux
and metal charge. The main objective of this zone is to preheat the charges from room
temperature to about 1090°C before entering the metal charge to the melting zone. The
preheating takes place in this zone due to the upward movement of hot gases. During the

preheating process, the metal charge in solid form picks up some sulphur content in this zone.
6. Stack
The empty portion of cupola above the preheating zone is called as stack. It provides the
passage to hot gases to go to atmosphere from the cupola furnace.
Charging of Cupola Furnace
Before the blower is started, the furnace is uniformly pre-heated and the metal and
coke charges, lying in alternate layers, are sufficiently heated up.
The cover plates are positioned suitably and the blower is started.
The height of coke charge in the cupola in each layer varies generally from 10 to 15
cms. The requirement of flux to the metal charge depends upon the quality of the
charged metal and scarp, the composition of the coke and the amount of ash content
present in the coke.
Working of Cupola Furnace
The charge, consisting of metal, alloying ingredients, limestone, and coal coke
for fuel and carbonization (8-16% of the metal charge), is fed in alternating
layers through an opening in the cylinder.
Air enters the bottom through tuyeres extending a short distance into the interior
of the cylinder. The air inflow often contains enhanced oxygen levels.
Coke is consumed. The hot exhaust gases rise up through the charge, preheating
it. This increases the energy efficiency of the furnace. The charge drops and is
melted.
Although air is fed into the furnace, the environment is a reducing one. Burning
of coke under reducing conditions raises the carbon content of the metal charge
to the casting specifications.
As the material is consumed, additional charges can be added to the furnace.
A continuous flow of iron emerges from the bottom of the furnace.
Depending on the size of the furnace, the flow rate can be as high as 100 tones per
hour. At the metal melts it is refined to some extent, which removes contaminants.
This makes this process more suitable than electric furnaces for dirty charges.
A hole higher than the tap allows slag to be drawn off.
The exhaust gases emerge from the top of the cupola. Emission control technology is
used to treat the emissions to meet environmental standards.
Hinged doors at the bottom allow the furnace to be emptied when not in use.

Type of Molten Metal
Cupola is employed for melting scrap metals or (over 90 %) of the pig iron used in the
production of iron castings.
Gray Cast iron, nodular cast iron, some malleable iron castings and some copper base
alloys can be produced by Cupola Furnace.
Advantages
It is simple and economical to operate.
A cupola is capable of accepting a wide range of materials without reducing melt
quality. Dirty, oily scrap can be melted as well as a wide range of steel and iron. They
therefore play an important role in the metal recycling industry
Cupolas can refine the metal charge, removing impurities out of the slag.
The continuous rather than batch process suits the demands of a repetition foundry.
High melt rates
Ease of operation
Adequate temperature control
Chemical composition control
Efficiency of cupola varies from 30 to 50%.
Less floor space requirements comparing with those furnaces with same capacity.
Limitations
Since molten iron and coke are in contact with each other, certain elements like si, Mn
are lost and others like sulphur are picked up. This changes the final analysis of
molten metal.
Close temperature control is difficult to maintain
Reverberatory furnace
A furnace or kiln in which the material under treatment is heated indirectly by means of a
flame deflected downward from the roof. Reverberatory furnaces are used in copper, tin, and
nickel production, in the production of certain concretes and cements, and in aluminum.
Reverberatory furnaces heat the metal to melting temperatures with direct fired wall-mounted
burners. The primary mode of heat transfer is through radiation from the refractory brick
walls to the metal, but convective heat transfer also provides additional heating from the
burner to the metal. The advantages provided by reverberatory melters is the high volume
processing rate, and low operating and maintenance costs. The disadvantages of the
reverberatory melters are the high metal oxidation rates, low efficiencies, and large floor
space requirements. A schematic of Reverberatory furnace is shown in Figure

Figure 15: Schematic of a Reverberatory Furnace
Induction furnace
Induction heating is a heating method. The heating by the induction method occurs when an
electrically conductive material is placed in a varying magnetic field. Induction heating is a
rapid form of heating in which a current is induced directly into the part being heated.
Induction heating is a non-contact form of heating.
The heating system in an induction furnace includes:
1. Induction heating power supply,
2. Induction heating coil,
3. Water-cooling source, which cools the coil and several internal components inside the
power supply.
The induction heating power supply sends alternating current through the induction coil,
which generates a magnetic field. Induction furnaces work on the principle of a transformer.
An alternative electromagnetic field induces eddy currents in the metal which converts the
electric energy to heat without any physical contact between the induction coil and the work
piece. A schematic diagram of induction furnace is shown in Figure. The furnace contains a
crucible surrounded by a water cooled copper coil. The coil is called primary coil to which a
high frequency current is supplied. By induction secondary currents, called eddy currents are
produced in the crucible. High temperature can be obtained by this method. Induction
furnaces are of two types: cored furnace and coreless furnace. Cored furnaces are used almost
exclusively as holding furnaces. In cored furnace the electromagnetic field heats the metal
between two coils. Coreless furnaces heat the metal via an external primary coil.

Advantages of Induction Furnace
 Induction heating is a clean form of heating
 High rate of melting or high melting efficiency
 Alloyed steels can be melted without any loss of alloying elements
 Controllable and localized heating
Disadvantages of Induction Furnace
 High capital cost of the equipment
 High operating cost
Fig. SAND CASTING PROCESS

Classification of casting Processes
Casting processes can be classified into following FOUR categories:
1. Conventional Molding Processes
a. Green Sand Molding
b. Dry Sand Molding
c. Flask less Molding
2. Chemical Sand Molding Processes
a. Shell Molding
b. Sodium Silicate Molding
c. No-Bake Molding
3. Permanent Mold Processes
a. Gravity Die casting
b. Low and High Pressure Die Casting
4. Special Casting Processes
a. Lost Wax
b. Ceramics Shell Molding
c. Evaporative Pattern Casting
d. Vacuum Sealed Molding
e. Centrifugal Casting
Methods
Molding processes
Bench molding: is for small work, done on a bench of a height convenient to the molder.
Floor molding: When castings increase in size, with resultant difficulty in handling, the work
is done on the foundry floor. This type of molding is used for practically all medium and
large size castings.
Pit molding: Extremely large castings are frequently molded in a pit instead of a flask. The
pit acts as the drag part of the flask and a separate cope is used above it. They sides of the pit
are brick kind, and on the bottom there
Machine molding: Machines have been developed to do a number of operations that the
molder ordinarily does by hand. Ramming the sand, rolling the mold, forming the gate and
drawing the pattern can be done by these machines.

Investment Casting Process
 The root of the investment casting process, the cire perdue or “lost wax” method dates
back to at least the fourth millennium B.C.
 The investment casting process also called lost wax process begins with the production
of wax replicas or patterns of the desired shape of the castings.
 A pattern is needed for every casting to be produced. The patterns are prepared by
injecting wax or polystyrene in a metal dies. Numbers of patterns are attached to a
central wax sprue to form an assembly.
 The mold is prepared by surrounding the pattern with refractory slurry that can set at
room temperature.
 The mold is then heated so that pattern melts and flows out, leaving a clean cavity
behind. The mould is further hardened by heating and the molten metal is poured while
it is still hot.
 When the casting is solidified, the mold is broken and the casting is taken out.
The basic steps of the investment casting process are
1. Production of heat-disposable wax, plastic, or polystyrene patterns
2. Assembly of these patterns onto a gating system
3. “Investing,” or covering the pattern assembly with refractory slurry
4. Melting the pattern assembly to remove the pattern material
5. Firing the mold to remove the last traces of the pattern material
6. Pouring
7. Knockout, cutoff and finishing.

Advantages
 Excellent accuracy and flexibility of design.
 Useful for casting alloys that are difficult to machine.
 Exceptionally fine finish.
 Suitable for large or small quantities of parts.
 Almost unlimited intricacy.
 Suitable for most ferrous / non-ferrous metals.
 No flash to be removed or parting line tolerances.
Disadvantages
 Limitations on size of casting.
 Higher casting costs make it important to take full advantage of the process to
eliminate all machining operations.

Shell Molding
 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 o
C), 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 tolerance
reduce the need for machining.
 The process overall is quite cost effective due to reduced machining and cleanup
costs.
Advantages
 Adaptable to large or medium quantities
 Most ferrous / non-ferrous metals can be used.
 Rapid production rate.
 Good dimensional casting detail and accuracy.
 Shell molds are lightweight and storage becomes easy
Disadvantages
 Since the tooling requires heat to cure the mold, pattern costs and pattern wear can be
higher.
 Energy costs are higher.

Centrifugal Casting
In this process, the mold is rotated rapidly about its central axis as the metal is poured into
it. Because of the centrifugal force, a continuous pressure will be acting on the metal as it
solidifies.
The slag, oxides and other inclusions being lighter, get separated from the metal and
segregate towards the center. This process is normally used for the making of hollow pipes,
tubes, hollow bushes, etc., which are axisymmetric with a concentric hole. Since the metal
is always pushed outward because of the centrifugal force, no core needs to be used for
making the concentric hole.
The mold can be rotated about a vertical, horizontal or an inclined axis or about its
horizontal and vertical axes simultaneously. The length and outside diameter are fixed by
the mold cavity dimensions while the inside diameter is determined by the amount of
molten metal poured into the mold.
True Centrifugal Casting
 Castings are made in a hollow, cylindrical mold rotated about an axis common to
mold and casting. The axis may be horizontal, vertical and inclined.
 Parts cast by this process are pipes, liners, bushes and barrels

Semi-Centrifugal Process
 This is similar to true centrifugal casting, the only difference is that a central core is
used to form the inner surface.
 Parts produced are symmetrical objects like wheels with arms
Centrifuged or Pressure Casting
 This process is used for non-symmetrical casting having intricate details.
 The metal is introduced at the centre down a central sprue and fed in to the molds
through radial gates.
Advantages
 Formation of hollow interiors in cylinders without cores
 Less material required for gate

 Fine grained structure at the outer surface of the casting free of gas and shrinkage
cavities and porosity
 No gates or risers are used. Hence nearly 100% yield is obtained
Disadvantages
 More segregation of alloy component during pouring under the forces of rotation
 Contamination of internal surface of castings with non-metallic inclusions
 Inaccurate internal diameter
Continuous Casting
 In this process, molten metal from the ladle is poured in to the mold.
 The mold is surround all around by cooling water or sprayed with water.
 The rolls at the bottom keep on pulling the slab to match with the cooling rate.
 Below the rolls is a saw which keeps on cutting the slab to the required length.
ASARCO PROCESS
This is also a continuous casting process. In this process, the forming die becomes an
integral part of the furnace. The metal is fed in to the mold and it is continuously
solidified and withdrawn. Upper end of the die is in molten metal and thus function as
riser.
DIE CASTING
Hot Chamber Die Casting Process

The Die-casting process is a typical example of permanent-mould casting. The molten
material is forced into the die cavity at pressures ranging from 0.7 to 700 MPa.
Typical products are carburetors, motor housings, business machine and appliance
components, hand tools and toys. The weight of most castings ranges from less than 90 g to
about 25 kg.
The Hot-chamber process involves the use of a piston, which traps a certain volume of melt
and forces it into the die cavity through a gooseneck and nozzle.
The pressures range up to 35 MPa. The melt is held under pressure until it solidifies. To
improve die life and to aid in rapid heat transfer, thus reducing the cycle time, dies are cooled
by circulating water or oil through passageways in the die block.
Cycle times usually range up to 900 shots per hour for zinc, (very small components such as
zipper teeth can be cast at 18,000 shots per hour).
This process commonly casts low-melting-point alloys of metals such as zinc, tin, and lead.
Cold Chamber Die Casting Process

In the Cold-chamber process molten metal is poured into the injection cylinder with a ladle.
The shot chamber is not heated. The melt is forced into the die cavity at pressures ranging
from 20 MPa to 70 MPa, (in extremes 150 MPa). The machines may be horizontal or vertical.
Die-casting can compete favourably in some products with other manufacturing methods,
such as metallic-sheet stamping or forging.
Because the molten material chills rapidly at the die walls, the casting has a fine-grain, hard
skin with higher strength than in the centre. The strength-to-weight ratio of die-cast parts
increases with decreasing wall thickness. With good surface finish and dimensional accuracy,
die-casting can produce bearing surfaces that would normally be machined.
The cost of dies is somewhat high, but die-casting is economical for large production runs.
Casting Defects
The following are the major defects, which are likely to occur in sand castings
 Gas defects
 Shrinkage cavities
 Molding material defects
 Pouring metal defects
 Mold shift
 Honey Combing

Figure 19 : Casting Defects
Sl.No. Defect Cause Remedy
1 Mismatch or core
shift
Mismatch of the section Proper alignment of flask, pattern
and core
2 Misrun Particular section
solidifies before filling
Proper casting design
3 Swell Enlargement of the mold
cavity
Avoid rapid pouring, sufficient
ramming
4 Coldshut Two streams of molten
metal which are too cold
to meet each other and
fuse, this occurs
Proper casting design
5 Porosity Entrapped gases Provide sufficient permeability,
vent holes, use of dry sand molds
or no-bake molds
6 Metal penetration Molten metal penetrates in
to sand grains
Good optimum mold hardness
7 Hot tear Mold rigid, restrains
solidification, leading to
cracks
Avoid excessive ramming
8 Shrinkage cavity Depression in the casting Provide adequate riser

VACUUM CASTING
In this case, the material is sucked upwards into the mold by a vacuum pump. The mold in an
inverted position from the usual casting process, is lowered into the flask with the molten
metal.
One advantage of vacuum casting is that by releasing the pressure a short time after the mold
is filled, we can release the un-solidified metal back into the flask. This allows us to create
hollow castings. Since most of the heat is conducted away from the surface between the
mold and the metal, therefore the portion of the metal closest to the mold surface always
solidifies first; the solid front travels inwards into the cavity. Thus, if the liquid is drained a
very short time after the filling, then we get a very thin walled hollow o
Squeeze Casting CLA and CLV Process

In SQUEEZE CASTING, a pre-measured quantity of molten metal is poured into a preheated
die. The mould is then closed and pressure is applied until solidification is complete. Because
of the precise metal metering, quiescent die filling, and high pressure, shrinkage and gas
porosity are eliminated. The process has the advantage that it can produce fully shaped
components, of precise dimensions, excellent surface finish and with metallurgical integrity
equivalent to forgings, in one step. The process combines the principles of casting and
forging and is therefore also known as "liquid metal forging" or "squeeze forming". The dies
should be sufficiently rigid to withstand the pressures applied. Dies are made from high
quality die steels, therefore, expensive.
CLA and CLV Process
Conventional investment casting shell building techniques are used in which wax patterns are
mounted on a tree and invested in a ceramic shell. When the shell hardens, the wax is melted
out and the shell fired. In the CLA process (counter-gravity low-pressure casting of
air-melted alloys), the shell is secured in a chamber with its sprue protruding downwards
through the base of the chamber. The chamber is lowered towards the furnace. Vacuum
suction is applied causing the metal to be drawn into the chamber. In the CLV process (
counter-gravity low-pressure casting of vacuum-melted alloys), the chamber containing
the mould is positioned above a vacuum melting furnace. When the molten metal is ready for
casting, both chambers are filled with argon. The crucible is elevated until the sprue
penetrates below the metal surface. Vacuum suction is then applied to the chamber containing
the mould causing the metal to be drawn into the mould.
TESTING OF CASTING
Destructive Testing
Non-Destructive Testing
Destructive
 Bend Test
 Tensile Test
 Impact Test
 Hardness Test
Non-Destructive Test
 Visual
 Liquid Penetrant
 Magnetic
 Ultrasonic
 Eddy Current
 X-ray
LPT
• A liquid with high surface wetting characteristics is applied to the surface of the
part and allowed time to seep into surface breaking defects.
The excess liquid is removed from the surface of the part

• A developer (powder) is applied to pull the trapped penetrant out the defect and
spread it on the surface where it can be seen.
• Visual inspection is the final step in the process. The penetrant used is often
loaded with a fluorescent dye and the inspection is done under UV light to
increase test sensitivity.
Magnetic Particle Inspection
The part is magnetized. Finely milled iron particles coated with a dye pigment are then
applied to the specimen. These particles are attracted to magnetic flux leakage fields
and will cluster to form an indication directly over the discontinuity. This indication
can be visually detected under proper lighting conditions.
Radiography
The film darkness (density) will vary with the amount of radiation reaching the film
through the test object.

Foundry
Process
Process Pros / Cons
Green Sand
Molding
The green sand process utilizes a mold
made of compressed or compacted moist
sand packed around a wood or metal
pattern. A metal frame or flask is placed
over the pattern to produce a cavity
representing one half of the casting. The
sand is compacted by either jolting or
squeezing the mold.
The other half of the mold is produced in
like manner and the two flasks are
positioned together to form the complete
mold. If the casting has hollow sections,
cores consisting of hardened sand (baked or
chemically hardened) are used.
High-Density Molding (High Squeeze
Pressure / Impact) Large air cylinders,
hydraulics, and innovative explosive
methods have improved the sand
compaction around the pattern, improving
the standards of accuracy and finish which
can be achieved with certain types of
castings.
Advantages
 Most ferrous / non-ferrous
metals can be used.
 Low Pattern & Material costs.
 Almost no limit on size, shape
or weight of part.
 Adaptable to large or small
quantities
 Used best for light, bench
molding for medium-sized
castings or for use with
production molding machines.
Disadvantages
 Low design complexity.
 Lower dimensional accuracy.
Dry Sand
Molding
When it is desired that the gas forming
materials are lowered in the molds, air-dried
molds are sometimes preferred to green
sand molds. Two types of drying of molds
are often required.
1. Skin drying and
2. 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 drying the
refractory mold coating uses hot air, gas or
oil flame. Skin drying of the mold can be
accomplished with the aid of torches,
directed at the mold surface.

No-Bake
Molding
Chemical binders (furan or urethane) are
mixed with sand and placed in mold boxes
surrounding the pattern halves. At room
temperature, the molds become rigid with
the help of catalysts. The pattern halves are
removed and the mold is assembled with or
without cores.
Advantages
metals can be used.
 Adaptable to large or small
quantities
 High strength mold
 Better as-cast surfaces.
 Improved dimensional
repeatability
 Less skill and labor required
then in conventional sand
molding.
 Better dimensional control.
Disadvantages
 Sand temperatures critical.
 Patterns require additional
maintenance.
Permanent
Mold
Permanent molds consist of mold cavities
machined into metal die blocks and
designed for repetitive use. Currently,
molds are usually made of cast iron or steel,
although graphite, copper and aluminum
have been used.
Permanent mold castings can be produced
from all of the metals including iron and
copper alloys, but are usually light metals
such as zinc-base, magnesium and
aluminum.
Gravity Permanent Mold -The flow of
metal into a permanent mold using gravity
only is referred to as a gravity permanent
mold. There are two techniques in use:
static pouring, where metal is introduced
into the top of the mold through downsprues
similar to sand casting; and tilt pouring,
where metal is poured into a basin while the
mold is in a horizontal position and flows
into the cavity as the mold is gradually tilted
to a vertical position.
Normally, gravity molding is used because
it is more accurate than shell molding. It is
Advantages
 Superior mechanical properties.
 Produces dense, uniform
castings with high dimensional
accuracy.
 Excellent surface finish and
grain structure.
 The process lends itself very
well to the use of expendable
cores and makes possible the
production of parts that are not
suitable for the pressure
diecasting process.
 Repeated use of molds.
 Rapid production rate with low
scrap loss.
Disadvantages
 Higher cost of tooling requires
a higher volume of castings.
 The process is generally limited
to the production of somewhat
small castings of simple
exterior design, although
complex castings such as

preferred almost exclusively to shell
molding for light alloy components.
Low-Pressure Permanent Mold - Low-
pressure permanent mold is a method of
producing a casting by using a minimal
amount of pressure (usually 5-15 lb/sq in.)
to fill the die. It is a casting process that
helps to further bridge the gap between sand
and pressure diecasting.
aluminum engine blocks and
heads are now commonplace.
Die Casting
This process is used for producing large
volumes of zinc, aluminum and magnesium
castings of intricate shapes. The essential
feature of diecasting is the use of permanent
metal dies into which the molten metal is
injected under high pressure (normally 5000
psi or more).
The rate of production of diecasting
depends largely on the complexity of
design, the section thickness of the casting,
and the properties of the cast metal. Great
care must be taken with the design and
gating of the mold to avoid high-pressure
porosity to which this process is prone.
Advantages
 Cost of castings is relatively
low with high volumes.
 High degree of design
complexity and accuracy.
 Excellent smooth surface
finish.
 Suitable for relatively low
melting point metals
(1600F/871C) like lead, zinc,
aluminum, magnesium and
some copper alloys.
 High production rates.
Disadvantages
 Limits on the size of castings -
most suitable for small castings
up to about 75 lb.
 Equipment and die costs are
high.
Expandable
Pattern
Casting
(Lost Foam)
Also known as Expanded Polystyrene
Molding or Full Mold Process, the EPC or
Lost Foam process is an economical method
for producing complex, close-tolerance
castings using an expandable polystyrene
pattern and unbonded sand.
The EPC process involves attaching
expandable polystyrene patterns to an
expandable polystyrene gating system and
applying a refractory coating to the entire
assembly. After the coating has dried, the
foam pattern assembly is positioned on
several inches of loose dry sand in a vented
flask. Additional sand is then added while
the flask is vibrated until the pattern
Advantages
 No cores are required.
 Reduction in capital investment
and operating costs.
 Closer tolerances and walls as
thin as 0.120 in.
 No binders or other additives
are required for the sand, which
is reusable.
 Flasks for containing the mold
assembly are inexpensive, and
shakeout of the castings in
unbonded sand is simplified
and do not require the heavy
shakeout machinery required

assembly is completely embedded in sand.
A suitable downsprue is located above the
gating system and sand is again added until
it is level to the top of the sprue. Molten
metal is poured into the sprue, vaporizing
the foam polystyrene, perfectly reproducing
the pattern. Gases formed from the
vaporized pattern permeate through the
coating on the pattern, the sand and finally
through the flask vents.
In this process, a pattern refers to the
expandable polystyrene or foamed
polystyrene part that is vaporized by the
molten metal. A pattern is required for each
casting.
for other sand casting methods.
 Need for skilled labor is greatly
reduced.
 Casting cleaning is minimized
since there are no parting lines
or core fins.
Disadvantages
 The pattern coating process is
time-consuming, and pattern
handling requires great care.
 Good process control is
required as a scrapped casting
means replacement not only of
the mold but the pattern as well.
Vacuum
("V")
Process
Molding
This adaptation of vacuum forming permits
molds to be made out of free-flowing, dry,
unbonded sand without using high-pressure
squeezing, jolting, slinging or blowing as a
means of compaction. The V-process is
dimensionally consistent, economical,
environmentally and ecologically
acceptable, energy thrifty, versatile and
clean.
The molding medium is clean, dry,
unbonded silica sand, which is consolidated
through application of a vacuum or negative
pressure to the body of the sand. The
patterns must be mounted on plates or
boards and each board is perforated with
vent holes connected to a vacuum chamber
behind the board. A preheated sheet of
highly flexible plastic material is draped
over the pattern and board. When the
vacuum is applied, the sheet clings closely
to the pattern contours. Each part of the
molding box is furnished with its own
vacuum chamber connected to a series of
hollow perforated flask bars. The pattern is
stripped from the mold and the two halves
assembled and cast with the vacuum on.
Advantages
 Superb finishes.
 Good dimensional accuracy.
 No defects from gas holes.
 All sizes and shapes of castings
are possible
metals can be used.
Disadvantages
 The V-process requires plated
pattern equipment.
CO2 Process
(or)
Sodium
silicate
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 pattern is withdrawn from the
mold.
The sodium silicate process is one of the
most environmentally acceptable of the
chemical processes available. 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 casting good dimensional
tolerances;
 good casting surface finishes are
readily obtainable;

Balanced Core
(core print should be large to support the weight of
the core)
Horizontal Core
Hanging Core Vertical Core
Drop Core
Types of core boxes
1. half core box - Two halves prepared seperately
2. dump core box - Complete Core
3. split core box - Two boxes are used
4. left and right core box- Used for unsymmetrical objects
5. gang core box - Multiple cores
6. strickle core box - Irregular shape core. Strickle board is used,
which has the same contour of the required core

7. loose piece core box - Loose pieces are used for giving provision to hubs, etc
Half Core Box
Split Core Box
Dump Core Box

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