Moulding

Molding (American English) or moulding (British and

Commonwealth English; see spelling differences) is the
process of manufacturing by shaping liquid or pliable raw
material using a rigid frame called a mold or matrix.This itself
may have been made using a pattern or model of the final
object.

A mold or mould is a hollowed-out block that is filled with a

liquid or pliable material such as plastic, glass, metal, or
ceramic raw material.[2] The liquid hardens or sets inside the
mold, adopting its shape. A mold is a counterpart to a cast.
The very common bi-valve molding process uses two molds,
one for each half of the object.
Moulding sand
 Moulding sands
• The principal material used in the foundry shop for moulding
is the sand.
• This is because it possesses the properties vital for foundry
purposes.
• Sources:
• All sands are formed by the braking up of rocks due to the
action of natural forces such as frost, wind, rain, heat and
water currents.
• Rocks are very complex in their composition, and sands
contain most of the elements of the rocks of which they are
fragmented.
• The moulding sand vary in different parts of the world.
• Sand obtained from places which were bottom & banks of
rivers and sand dunes.
 Principal ingredients of Moulding sands
• The principal ingredients of moulding sands are:
1. Silica sand and grains
2. Clay
3. Moisture
4. Miscellaneous materials
 Principal ingredients : 1. Silica sand and grains
• It is in the form of granular quartz.
• It contains 80 to 90% silicon dioxide & is characterized by a
high softening temperature & thermal stability.
• It is a product of breaking up of quartz rocks or
decomposition of graphite.
• They impart refractoriness, chemical resistivity, &
permeability to the sand.
 Principal ingredients : 2. Clay
• It is defined as those particles of sand (under 20µm in dia.)
that fail to settle at a rate of 25mm per min when suspended
in water.
• It consists of two ingredients: fine slit and true clay.
• Fine slit is a sort of foreign matter or mineral deposit & has
no bonding power.
• True clay imparts the necessary bonding strength to the
mould sand so that mould does not loose its shape after
ramming.
• True clay is found to be made up of extremely minute
aggregates of crystalline particles called clay minerals.
• Most moulding sands for different grades of work contain 5
to 20% clay.
 Principal ingredients : 3. Moisture
• It is require in requisite amount, furnishes the bonding action
of clay.
• When water is added to clay, it penetrates the mixture and
forms a microfilm which coats the surface of flake shaped
clay particles.
• The bonding quality of clay depends on the maximum water
film thickness it can ,maintain.
• The bonding action is considered best if the water added is
exact quantity required to form the film.
• The mould becomes weakened if excess water is added due
to which the bonding action is reduced and mould gets
weakened.
• The water should be added between 2 to 8%.
 Principal ingredients : 4. Miscellaneous materials
• In addition to silica, water and clay miscellaneous materials
like iron oxide, limestone, magnesia (is produced from the
heating of magnesite or magnesium hydroxide) , soda
and potash.
• Their addition should be less than 2%.
• Addition of iron oxide
• The shear strength and permeability of moulding sand has
reaches to its maximum value by adding iron oxide to it.
• It can be used to prevent mold cracking and metal
penetration, essentially improving refractoriness.
• It improves green strength, dry compression strength and hot
compression strength of moulding sand.
 Principal ingredients : 4. Miscellaneous materials
• Addition of limestone (Calcium carbonate)
• It improves compressive strength of moulding sand.

• Addition of soda
• It improves green strength, dry compression strength and
hot compression strength of moulding sand.
Principal ingredients : 4. Miscellaneous materials
• Addition of Mg
• The addition of 2% Mg increases tensile strength 57.9%
and hardness of 25%.
 Classification of moulding sand
• Moulding sands may be classified into three different types:
1. Natural moulding sands or Green moulding sands
2. Synthetic moulding sands
3. Special moulding sands

1. Natural moulding sands or Green moulding sands

• They are taken from river beds or are dug from pits.
• They possess appreciable amount of clay which acts as a
bond between the sand grains & use as received with water.
• The quantity & type of clay mineral present affect the
strength, toughness & refractoriness of the sand.
 Natural moulding sand
• Natural moulding sands are also obtained by crushing &
milling soft yellow sandstone, carboniferrous rocks, etc.
• Due to their ease of availability, low cost, & high flexibility
of operation, they are used for most of the ferrous &
nonferrous light castings.
• The requirements of these sands are classified by IS:3343-
1965, which has classified them into three grades A, B and
C.

Grade A Grade B Grade C

Clay % 5-10 10-15 15-20

Sintering temp. in 0C 1350-1450 1200-1350 1100-1200

 2. Synthetic moulding sands
• They are basically high silica sands constisting little (less than
2%) or no binder (clay) in natural form.
• They occur as loose or poorly consolidated deposits of
sedimentary origin, dunes blown inland from coast.
• The desired strength & bonding properties of these sands
developed by separate additions such as bentonite, water
and other materials.
• This allows greater flexibilities in the content of properties
such as green and dry strength, permeabilities, and others
that can be easily varied as per requirement.
• They are more expensive than natural sands.
 3. Special moulding sands
• They are ideal in getting special characteristics, which are not
ord.inarily obtained in other sands.
• Zircon, olivine, chamotte, chromite and chrome-magnesite
are often used as special sands.
• Zircon sands are suitable for cores of brass and bronze
castings.
• Some foundries use olivine sand for nonferrous castings of an
intricate nature.
• Chamotte is valuable for heavy steel castings.
• Chromite and chrome-magnesite sands are particularly
useful where the chilling tendency is to be increased to
control solification.
Types of moulding sands
Moulding sands may again be classified, according to
their use into a number of varieties.
1. Green sand
2. Dry sand
3. Loam sand
4. Facing sand
5. Backing sand
6. System sand
7. Parting sand
8. Core sand
 Types of moulding sands:
1. Green sand
• It is a mixture of silica sand with 18 to 30% clay, having a
total water of from 6 to 8%. The clay and water furnish the
bond of green sand.
• It is fine, soft, light, and porous.
• Being damp, when squeezed in the hands, it retains its
shape, the impression given to it under pressure.
• Moulds prepared in this sand are known as green sand
moulds.
2. Dry sand
• Green sand that has been dried or baked after the mould is
made is called dry sand. They are suitable for larger castings.
Moulds prepared in this sand are known as dry sand moulds.
 Types of moulding sands:
3. Loam sand
• It consists of very high % of clay, as much as 50% or so, &
dries hard.
• This particularly used for loam moulding usually for large
castings.
4. Facing sand
• It forms the face of mould.
• It is used directly next to the surface of the pattern & it
comes into the contact with the molten metal when the
mould is poured.
• It is subjected to severe conditions & must possess,
therefore, high strength and refractoriness.
• It is made of silica sand & clay, without addition of used
sand.
 Types of moulding sands:
4. Facing sand
• The layer of facing sand in a mould usually ranges from 20
to 30 mm.
• From 10 to 15% of the whole amount of moulding sand
used in foundry is facing sand.
• A facing sand mixture of green sand moulding of cast iron
may consists of 25% fresh & specially prepared sand, 70%
old sand, & 5% sea coal.
5. Backing sand
• Backing sand or floor sand is used to back up the facing
sand & to fill the whole volume of the flask.
• Old, repeatedly used moulding sand is mainly employed for
this purpose.
 Types of moulding sands:
6. System sand
• In mechanical foundries where machine moulding is
employed a so-called system sand is used to fill the whole
flask.
• In mechanical sand preparation & handling units, no facing
sand is sued.
• The used sand is cleaned & reactivated by the addition of
water binders & special additives.
• This is known as system sand.
• The strength, permeability & refractoriness of this sand is
much higher than backing sand.
 Types of moulding sands:
7. Parting sand
• It is used to keep the green sand from sticking to the
pattern & also allow the sand on the parting surface of
cope & drag to separate without clinging ( fitting closely to
the body) .
• This is clean clay-free silica sand which serves the same
purpose as parting dust.
8. Core sand
• Sand used for making core is known as core sand.
• This is silica sand mixed with core oil which is composed of
linseed oil & other binding materials.
• Pitch or flours & water may be used in large cores for the
sake of economy.
 Grain shape & size of sand
• The grain shape and size has a substantial effect on the
properties of moulding & core sands.
• The shape of the grains & number of similar grains in the
sand determine the possibility of its application in various
types of foundry practice.
 Grain shape & size of sand
• Shapes of sand grains vary from angular to sub-angular to
rounded & compound.
• Use of angular grains (obtained during crushing of rocks or
hard sand stones) is avoided as these grains have the large
surface area.
• Thus higher % of binders is required to bring in the desired
strength.
• Rounded shape grain are best as moulding sand.
• The grains contribute to higher bond strength in comparison
to angular grains.
• However, rounded grains sands have higher thermal
expandability than angular & rounded shape grains.
 Grain shape & size of sand
• Compound grains are cemented together such that they fail
to separate when screened.
• They may consist of round, subangular, or angular grains or
a combination of the three.
• Compound grains are least desirable in sand mixtures as
they have a tendency to disintegrate at high temperatures.
• In actual practice, however, sharp, irregular shaped grains
are usually preferred because of their ability to interlock &
add strength to the mould.
 Grain shape & size of sand
• There are three sizes of sand grains: fine, medium and
Coarse.
• For small & intricate castings the use of fine sand is
desirable, so that all the details of the mould will be brought
our sharply.
• Medium sand is used in bench work & light floor work such
as making machinery castings having sections from 1 to 50
mm.
• As the size of the casting increases, the sand particles
likewise would be coarser to permit the ready escape gases
that generated in the mould.
 Grain shape & size of sand
• Grain size is determined by passing the sand through
screens or services with certain opening sizes which are
measured in microns.
• The preferred size of sand for casting is in the range of 0.3
to 0.15 mm.
• Presently foundries preference is given to the finer sands.
• The finer grain sizes have higher to metal penetration &
erosion.
• However this type is having a higher thermal expansion
defects.
Sand additives
• Additives are the materials generally added to the sand
mixture to develop special properties in the mould &
consequently in castings.
• Facing materials
• The object of using facing materials is to provide a
smooth surface on the casting.
• The material forms a thin, smooth coating on the mould.
• Various substances may be used for this purpose
including charcoal, gas carbon, coke dust, plumbago (an
economical high quality Graphite), black lead, graphite,
or sea coal.
 Sand additives
• Facing sand
• The principal carbon facings are graphite & sea coal.
• Graphite is mineral carbon that is mined from the earth.
• Sea coal (coal dust) is a mineral that contains a high percent
of carbon but less pure than graphite & gives off much
more gas.
• These materials are either applied to or moved with the
moulding sand that comes in contact with the molten
metal.
• They may be applied to dry or wet according to nature of
the mould.
 Sand additives
• Facing sand
• In the dry state of material is dusted on from a porous bag
& applied with a soft brush.
• For use in the wet state some adhesive is employed, clay.
Gum & other substance being used in water.
 Sand additives
• Miscellaneous moulding materials
• They include fire clay, clay wash, parting materials & core
binders.
• Fire clay
• It is a mineral product consisting of hydrated aluminium silicate
sand & it comes from the same sand does.
• The purpose of fire clay is that it offers a good bond when mixed
with burn sand, in proportion of 1 to 2 for coating the inside of
cupolas & pouring ladles.
• Clay wash
• It is a mixture of fire clay & water.
• It is used in the foundry where a strong bond is required, & for
repairing ladle linings with a fresh daubing (carelessly coat)
mixture.
 Sand additives
• Miscellaneous moulding materials
• Parting materials
• They are parting sand or parting dusts which must contain
no bond.
• A non-silica parting compound made from powdered
phosphate rock is the material that is widely used as a
parting dust.
• This is applied on the moulding sand from adhering to the
moulding box or to the pattern.
• Clay wash
• It is a mixture of fire clay & water.
• It is used in the foundry where a strong bond is required, &
for repairing ladle linings with a fresh aubing mixture.
Sand additives
• Miscellaneous moulding materials
• Binders
• They can be classified as inorganic & organic.
• Inorganic binders are clays (Kaolinite, illite, bentonites),
cements, gypsum, sodium silicatel, brown coal ashes etc.
• Organic binders include carbohyderate (starch, dextrine,
dextrose), molasses, various types of oils, pitches, natural
resins (cophony, shellac) & synthetic resinsrylic alkyd,
polystyrene, melamine, urea formaldehyde, phenolic, etc.)
• The primary purpose of binders is to influence the bonding
properties of sand.
• Of all binders, dextrine is perhaps the best.
• It increases air-setting strength, toughness & collapsibility
& prevents sand from drying rapidly.
Properties of moulding sand
• Proper mould sand must possess six properties.
1. Porosity or permeability
2. Flowability
3. Collapsibility
4. Adhesiveness
5. Cohesiveness or strength
6. Refractoriness
 Properties of moulding sand: 1. Porosity or permeability
• Molten metal always contains a certain amount of dissolved
gases , which are evolved when the metal freezes.
• Also, the molten metal, coming in contact with the moist
sand, generates steam or water vapor.
• If the these water vapor and gases evolved by the moulding
sand do not find opportunity to escape completely through
the mould they will form gas holes & pores in the casting.
• The sand must, therefore, be sufficiently porous to allow
the gases or moisture present or generated within the
moulds to be removed freely when the moulds are poured.
• The property of sand is called porosity or permeability.
 Properties of moulding sand: 2. Flowability
• Flowability of moulding sand refers to its ability to behave
like a fluid so that, when rammed, it will flow to all portions
of a mould & pack all-round the patterns & take up the
required shape.
• The sand should respond to different moulding processes.
• High flowability is required of a moulding sand to get
compacted to a uniform density & to obtain good
impression of the pattern in the mould.
• Good flowability is very essential where energy for
compaction during ramming is transmitted through the
sand mass as in machine moulding.
• Flowability increases as clay & water content increase.
 Properties of moulding sand:
3. Collapsibility
• When molten metal sodifies, the volume of solid decreases.
• If mould creates resistance this contraction, cracks appear
on casting.
• So it is desirable to mould sand to have low resistance to
shrinkage of molten metal.
• This is known as collapsibility.
 Properties of moulding sand:
3. Collapsibility
• After the molten metal in the mould gets solidified, the
sand mould must be collapsible so that free contraction of
the metal occurs, & this would naturally avoid the tearing or
cracking of the contracting metal.
4. Adhesiveness
• The sand particles must be capable of adhering to the
another body, i.e., they should stick to the sides of the
moulding boxes.
• It is due to this property that sand mass can be successfully
held in a moulding box & it does not fall out of the box
when it is removed.
 Properties of moulding sand:
5. Cohesiveness or strength
• This is the ability of sand particles to stick together.
• Insufficient strength may lead to collapse in the mould or its
partial destruction during conveying, turning over or
closing.
• The mould may be also damaged during pouring by
washing of the walls & core by the molten metal.
• The strength of moulding sand must, therefore, be sufficient
to permit the mould to be performed to the desired shape
& to retain this shape even after the hot metal is poured in
the mould.
 Properties of moulding sand:
5. Cohesiveness or strength
• This property of sand in its green or moist state is known as
green strength.
• A mould having adequate green strength will retain its
shape and will not distort or collapse even after the pattern
is removed from the moulding box.
• The strength of the sand that has been dried or baked is
called dry strength.
• It must have then strength to withstand erosive forces due
to molten metal, & retain its shape.
 Properties of moulding sand:
6 . Refractoriness
• The sand must be capable of withstanding the high
temperature of the molten metal without fusing.
• Moulding sands with a poor refractoriness may burn to the
casting.
• Refractoriness is measured by the sinter point of the sand
(sintering point is the temperature at which the molding
material begins to adhere to the casting, or in a test when
the sand coheres to a platinum ribbon under controlled
conditions. Also, the temperature at which sand grains
begin to adhere to one another) rather than its melting
point.
Table shows the average demand of moulding sands
Moulding processes
• Moulding processes may be classified according to
different forms.
• They are classified as
1. hand moulding
2. machine moulding.
• In piece and small lot production, sand moulds are made
by hands; machine moulding is employed in large-lot &
mass production.
• Moulding process are classified according to (1) type of
material of which the mould is made or (2) the methods
used in making the mould.
Moulding processes
• According to mould materials
A) Sand moulding
1. Green sand moulds 2. Air dried moulds
3. Dry sand moulds 4. Skin-dried moulds
5. Loam moulds 6. Cement bonded sand moulds
7. CO2 moulds 8. Shell moulds
B) Plaster moulding
C) Metallic moulding
 Moulding processes
• According to methods used in making mould, the
moulding processes are classified as
1. Bench moulding
2. Floor moulding
3. Pit moulding
4. Sweep moulding
5. Plate moulding
Moulding processes based on material used:
1. Green sand moulds

• In this , the molten metal is poured immediately after the

mould is ready, i.e., as soon as the mould is complete
after ramming.
• No baking is performed.
• The permeability of green sand should be high enough to
allow a free escape of gases & steam formed due to the
heat of the molten metal.
• These moulds are weaker & softer than other types of
sand moulds.
• Due to this, the moulds cannot be used when intricate
castings of such metals which have a high solid shrinkage.
Moulding processes based on material used:
1. Green sand moulds
• These moulds are cheaper & takes less time to prepare.
• These are used when large numbers of castings are to be
produced but the size is small or medium, particularly in
non-ferrous metals and alloys.
Advantages:

The green sand casting process is very common, and almost all iron
foundries could produce iron castings by this process. Its mainly
because of the advantages of this process.

1. Simple production process

The production process of green sand casting is very simple
comparatively, so easily handled. The materials are simple, and
easily available.

2. Lower production costs

Since the materials are simple and its prices are lower
comparatively, the production costs of green sand casting are
lower. Therefore, the green sand castings are cheaper than resin
sand castings and shell molding castings. As for the current cast
iron prices, you could check the website of Dandong Foundry.
3. Higher production rate
The green sand casting process can achieve high production
rate. The floor molding with green sand can produce castings of
100 to 200 sand boxes each day, e.g. about 100 pieces to 2000
pieces each day. The automatic molding process with green sand
can produce castings of 20 tons each day.

Moreover, green sand casting process can produce the castings

with unit weights from hundreds of grams to several tons.
Disadvantages:

The disadvantages of green sand casting process is also inevitable.

1. More casting defects

Green sand mold is a kind of soft mold, so it is not hard enough as

the resin sand molds and shell molding. So, there are more casting
defects such as sand residuals, sand holes, air holes and shrinkages.

2. Rough surface quality

The casting surfaces by green sand casting process are very rough
and coarse. If the iron foundries use the very fine green sand, the
rough surfaces will be better. However, there are few iron foundries
who use very fine green sands.
Moulding processes based on material used:
2. Skin-dried (shell) moulds
• They are the best compromise between of green sand
moulds and dry sand moulds.
• In these moulds, their surface is dried to a depth of 12.5
mm to 25 mm by means of gas torch, hot air or an
infrared lamp.
• For these moulds a suitable binders like resin, linseed oil,
molasses or corn flour, is always added to the facing of
sand so that, on drying, it will provide a very hard surface
to the mould.
• After drying the skin, the mould is closed & then molten
metal is poured immediately into it.
Moulding processes based on material used:
2. Skin-dried moulds
• If pouring is delayed, the moisture from baking sand will
be absorbed by the dry skin & its hardness is lost.
• Another method of making such type of moulds is to
make complete green sand mould as usual & then
provide a coating on its face by means of a spray or wash
of one of the binders like resin, linseed oil, molasses or
corn flour.
Advantages :
•This process reduces surface moisture and other gas-forming
materials from mold. It can commonly be used in the
production of medium-heavy to heavy castings.

Disadvantages :
•These molds are more expensive to produce. Mold sections
must be completely dry and cool prior to assembly.
 Moulding processes based on material used:
3. Dry sand moulds
• A dry sand mould is that mould in which the molten metal is
poured after baking the sand.
• These moulds are prepared from fine grained sand mixed with
suitable binders & additives.
• They are stronger & harder than green sand & skin dried
moulds.
• Because of previous baking they evolve less steam & gases
during casting, thus requiring less permeability.
• Use of fine sand enables smoother surfaces on castings.
• These moulds are commonly used for large & small castings
which need higher accuracy & carry more details.
• Because of their higher production cost, they are preferred
only when green sand moulds are found to be unsuitable.
 Moulding processes based on material used:
4. Air-dried moulds
• These moulds are similar to skin dried moulds, but they are not
artificially heated.
• The skin hardness on the mould is attained by allowing the
usual green sand moulds to be exposed to air for a certain
period, during which the mould is hardened due to
evaporation of some moisture from it.
• It is used for preparing large pit moulds which are exposed to
air for hardening.
 Moulding processes based on material used:
5. Loam moulds
• These moulds are similar to skin dried moulds, but they are not
artificially heated.
• The skin hardness on the mould is attained by allowing the
usual green sand moulds to be exposed to air for a certain
period, during which the mould is hardened due to
evaporation of some moisture from it.
• It is used for preparing large pit moulds which are exposed to
air for hardening.
• Loam is soil, that is composed of silica sand (22%), clay
(5%), coke (10%), and moisture (18-20%) by volume.
Loams are gritty, moist, and retain water easily.
 Moulding processes based on material used:
5. Loam moulds
• Loam is applied a plaster to the rough structure of the mould
usually made of brickwork & exact shape is given by a rotating
sweep around a central spindle.
• Cast iron plates & bars are used to reinforce the brickwork
which retains the moulding material.
• Loam moulds are mainly used for making of large castings for
which it would be too expensive to use full patterns & ordinary
flask equipment.
• Objects such as large cylinders, round-bottomed kettles,
chemical pans, large gears are produced in loam moulds.
• Loam molding was formerly used for making cast iron or
bronze cannon and is still used for casting large bells.
 Moulding processes based on material used:
6. Cement bonded sand moulds
• These moulds are also preferred for large castings, although
small one can be also made through them.
• The mixture consists of silica sand, portland cement & water,
mixed thoroughly to produce strong bond.
• A typical mixture will consist of 10% cement, 4.5% water &
85% pure silica sand.
• Drying & setting of cement takes about 72 hours.
• Separate penetration of cope & drag is needed due to low
strength of cement in wet state.
• On setting, it produces a mould of very high strength &
hardness.
• Cement bonded sand requires less ramming than other
sands.
 Moulding processes based on material used:
6. Cement bonded sand moulds
• A perfect alignment of cope & drag is necessary.
• The main advantage of this mould is that the castings made
in them carry very accurate & smooth surfaces; thus
minimizing , or sometimes totally eliminating, the need of
further machining & cleaning of these surfaces.
 Moulding processes based on material used:
7. Carbon di-oxide moulds
• These moulds are made from a mixture of clean & dry silica
sand & a sodium silicate base binder varies from 3 to 7%.
• The carbon dioxide gas is used only as mould hardener.
• After preparing the mould from the mixture, in the usual
manner, then the gas is passed through it to obtain the
desired hardness.
• Cores are also prepared in the same manner.
CO2 moulding (Carbon dioxide moulding) is a unique moulding
process. This is essentially a quick moulding process. Here liquid
sodium silicate is used as a binder instead of clay in the
conventional sand moulding.

The principle behind the CO2 moulding process is that when CO2
passes through a sand mix containing liquid sodium silicates binder
for two-three minutes, it immediately gets hardened by silica gel
formation. The silica gel (SiO2.x.H2O) is formed by the chemical
reaction between sodium silicate and carbon dioxide. This silica gel
gives the strength sufficient to eliminate baking/ drying of mould.
The sand used must be dry and free from clay. The sand is
mixed with 3-5% of sodium silicate. Some other additives,
such as coal powder, wood floor, Dextrin, iron oxide,
aluminium oxide etc., are also added to obtain specific
properties.

Dextrin, coal powder and wood flour improve collapsibility.

Aluminium improves the hot strength of sand at 800°C. Iron
oxide helps to prevent the deformation of cores, and it
produces a smooth interface between mould and metal, thus
helping to get a good surface finish.
The gassing of CO2 into the mould can be carried out in different
ways (gassing with a probe, gassing with a hood) depending
essentially on the mould’s size. The flow rate, time of gassing and
pressure of CO2 gas depends on the depth of penetration required.
Usually, gassing time is within 15 to 30 seconds. The mould must be
used within 12hours; otherwise, it starts to absorb water from the
atmosphere and deteriorate.

The chemical for this reaction is given below

Na2O . mSiO2 . xH2O + CO2 —> Na2CO3 + mSiO2 . xH2O

After passing carbon dioxide, the pattern is removed, and the

mould is ready to pour molten metal immediately into it. This
eliminates the headache of foundrymen's need for greater skill and
caring during mould-making and baking.
Application of carbon dioxide moulding
•Nowadays, it is used to make cores for conventional mould
instead of complete mould.
•Production of heavy and thick-walled steel casting. There is no
weight limit.
•Production of cast iron, steel, aluminium, and copper-based alloy
casting.
•For making of larger cores of heavy ferrous casting.
•Used for making parts of valves engine, machine tools railway
casting, gear casting wheel casting
Advantages of carbon dioxide moulding

The method is versatile. It can be used in small and large foundries for
light and heavy casting and ferrous and non-ferrous foundries alike.
1.Does not require core drier or baking process. It saves time and cost for
heating and floor space.
2.Withdrawal Pattern is facilitated since the mould immediately hardened.
3.Less mould cracking and deformation. Low mould rejection.
4.Since it does not involve any distortion due to baking, better
dimensional accuracy can be achieved.
5.Machining allowance can be reduced.
6.It has high strength, so it does not require other reinforcement.
7.Semi-skilled operator is required compared to dry sand moulding
8.Process good strength and hardness.
9.The process can be mechanized for mass production.
10.Molten metal can be immediately poured in to mould and hence
reduce the production time
Disadvantages or limitation of carbon dioxide moulding

1.The mould is expensive

2.One of the main disadvantages of CO2 moulding is that used sand
mixture cannot be recovered easily. An expensive and difficult
reclamation process is necessary.
3.CO2 moulding is less suitable for non-ferrous casting and thin-
walled casting.
4.The life of the mould is short. Mould should use within 12 to 24hr.
5.Poor collapsibility.
6.CO2 cores are susceptible to moisture.
 Moulding processes based on material used:
8. Shell moulds
• These moulds are prepared by heating mixture of sand &
resin over the surface of is metallic pattern.
• This enables the production of a thin & rigid layer of uniform
thickness which, when separated from pattern surface, forms
one part of the shell.
• Two such parts are joined together to form the shell mould.
The followings are the advantages of shell molding castings:

1. Good surface quality

Because shell molding uses phenolic resin as the sand binder, so the
smooth and hard surfaces of sand molds make the castings have good
surface smoothness. The following photo could be taken as sample for the
surface quality.

Moreover, this process have less sand residue during production, so could
reduce some iron casting defects, such as sand inclusion, sand holes and
air holes.

2. High rough casting dimensional accuracy

This molding material is a type of hard mold, so there will be less swell of
sand molds, so the dimensional tolerance will be smaller. This advantage
will be very useful for producing high accuracy rough castings, and reduce
machining cost.
3. Thin wall thickness and complex castings

Less than 5mm wall thickness will be taken as very thin as for sand
castings. Only shell molding process could produce these cast products.

In addition, hot shell and core molds are made by molding machines, so it
could produce the castings with complex structures, especially complex
inside structures.

4. Less manpower and molding skill requirements

Since the main works have been completed by the molding machines, so
this process could be operated by women workers, and there is no special
skill required. This is very different with green sand casting process.
Application:
Most of industrial products like gearbox housing, connecting
rod, small size boats, truck hoods, cylindrical head, Camshaft,
valve body etc. are made by shell moulding.
 Moulding processes
• According to mould materials
B) Plaster moulding
• Metallic patterns are used in this type of moulding.
• A plaster mixture is prepared, consisting of 70 to 80%
plaster & rest is talc.
• This mixture is then mixed with water in proportion of 36 to
45% mixture & the rest water by weight.
• This forms a slurry thick which is poured in the flask around
the pattern & allowed to set.
• After it is set, the pattern is withdrawn & the mould is
dehydrated by heating to a temperature range between
2040C to 7600C for a certain period of time, depending upon
the shape & size of the mould,
 Moulding processes
• According to mould materials
B) Plaster moulding
• It is ensure that complete dehydration takes place,
otherwise even a very small amount of water present in the
mould at the time of casting will render the casting
unsound.
• The defects on this account are likely to be pronounced due
to low permeability of the mould which will not allow the
escape of steam formed inside.
 Moulding processes
• According to mould materials
C) Metallic moulding
• They are also called Permanent Moulds.
• They are mostly made in two halves, which are joined
together before pouring to form the complete mould.
• These moulds are more popularly known as Dies.
• They are used for both ferrous & non-ferrous metals, but
they are generally used for non-ferrous metals.
• The moulds are commonly made from alloy steels or gray
iron or aluminum alloys.
• The main advantages of these moulds are higher dimensional
accuracy, better surface finish, higher rate of production,
elimination of usual defects noticed in sand cast castings &
promotion of finer grain structure in metal due to rapid
cooling.
 Moulding processes
• According to mould materials
C) Metallic moulding
• But they have disadvantages such as they provide a chilling
effect on the casting surface, rendering it hard, & their own
refractoriness limits their use only up to the casting of the
metals & alloys of which melting points are lower.
Applications of die casting

The applications of die casting are most suitable for casting

medium-sized parts with complex details. The technique is often
performed on nonferrous metals like magnesium, aluminum, etc.
Die casting is one of the largest casting methods that is used to
manufacture consumer, commercial and industrial products like
automobiles, toys, parts of the sink outlet, connector housing,
gears, etc.
 Moulding processes
• According to methods used in making mould, the
moulding processes are classified as
1. Bench moulding
2. Floor moulding
3. Pit moulding
4. Sweep moulding
5. Plate moulding
 Moulding processes based on method of mould making:
1. Bench moulding
• This method is usually employed for small castings, which are
light in weight.
• It is best suited for non-ferrous castings in green sand
moulds, although ferrous castings are also produced through
this method.
• Along with green sand moulds, dry sand moulds also can be
used for this method.
• In this method the moulds are prepared by the moulder on a
Bench, in standing position &, hence the name Bench
moulding.
 Moulding processes based on method of mould making:
1. Bench moulding
• When less number of castings are needed the moulds are
prepared in two or three boxes, as required, with the use of
moulding boards & then removed from the bench for
pouring.
• When mass production of identical castings is needed, a
match plate is usually employed in conjunction with the
bench.
• Stacked moulds, if required, can also be made through this
method.
 Moulding processes based on method of mould making:
2. Floor moulding
• This method of moulding is largely employed for medium &
large size articles, which cannot be conveniently moulded
through bench moulding due to their large size & heavy
weight.
• Normally, in this method the use of one flask is avoided & the
floor itself is utilized as drag.
• Sometimes use of both flasks is avoided, depending upon the
shape of casting, & the mould is then called an open mould.
• In this type complete cavity is formed in the floor & the
molten metal poured directly into it, thus avoiding the use of
runner & gate.
• But this method is used for only rough castings in which the
upper surface has no importance.
 Moulding processes based on method of mould making:
2. Floor moulding
• For better castings a cope is usually employed which carries
runner & riser etc.
• Proper gating is done in this case.
• Figure shows a Floor mould using one flask, for casting a
tapered cast iron channel.
• Floor moulding is usually done in dry sand.
 Moulding processes based on method of mould making:
3. Pit (hole in the ground) moulding
• Castings which are so large that they cannot be
accommodate in flasks are frequently moulded in Pits.
• In this, the mould is prepared in a formed pit.
• Moulding floor is dug in a square of rectangular shape & then
lined with a brick work or concrete, particularly at the
bottom a concrete base is provided to withstand heavy
pressures during casting.
• At its bottom a leveled bed is prepared of well rammed
cinder (used coal) to allow the escape of gases. Cope is
placed over the pit & sand is rammed around the pattern &
in the cope.
• Gates are cut in the cope itself after removing it.
 Moulding processes based on method of mould making:
3. Pit (hole in the ground) moulding
• The operations of removal & rolling over are carried out with
the help of a crane since the bulk of the sand contained in the
cope is too much. The method is used only by a limited
number of foundries having a background of very long
experience.
• It is mainly used for extremely large size castings.
• Bulk molten metal is required due to large size castings.
• This results in big volume of the gases produced inside which
may burst the mould.
• To prevent this, a plate, called the Bed Plate, is provided at the
bottom of the pit.
• This plate carries upward projecting bars, called tie rods, which
are attached to the cross-bars of the cope during ramming.
 Moulding processes based on method of mould making:
3. Pit (hole in the ground) moulding
• Thus, the pit acts as the drag part of the flask.
• In order to help the escape of gases inside during casting
Vent pipes are provided to connect the cinder (used coal)
bed to the floor level.
• After the mould is ready, it is dried by means of stove placed
in it.
• After drying, the core are placed & mould is closed.
• Adequate weights are placed over the cope.
Below is the actual casting pit where the final mould is placed; bell-metal runs
in from the two furnaces in the left and right background.
 Moulding processes based on method of mould making:
4. Sweep moulding
• They are employed for moulding parts whose shape is that of
a surface of revolution.
• In this, a base and spindle are well placed in the foundry
floor.
• The sand is filled in & rammed until the excavation forms
approximately to the shape & size of required castings.
• A sweep holder is then placed in the spindle land, the sweep
is attached by bolts & nuts.
• The surface of the mould is produced by the profile of the
sweep as it is rotated about the spindle.
• After sweeping, spindle is removed & mould is patched at the
centre.
 Moulding processes based on method of mould making:
5. Plate moulding
• In this process, the pattern is divide into half across the
parting & mounted in halves on to plates with parallel sides
of the same shape as the parting as shown in figure.
• The use of plates gives the following advantages:
1. The patterns can be handled easily & rapidly.
2. The task of making the joint between the two parts of the
mould is relieved as the plate provides its won joint when
the flask is rammed up.
3. The pattern can be drawn quickly, as the plate overlaps the
side of the box & the pins which hold it in position act as
guides during the drawing operations.
Making a green-sand mould
• The general procedure used in making moulds may be
acquired by following the operations used in moulding a
split pattern.
• First, one-half of the pattern is placed with its flat surface
on a mould board, & drag section of the flask is set over
the pattern on the same board as shown in figure.
Making a green-sand mould
• After powdering the pattern on the same lycopodium,
talc, or graphite, a 15 to 20 mm layer of facing sand is
riddled over the pattern.
• The drag is then filled by layers of green sand mixture
from 70 to 100mm thick, compacting each layer by
rammer.
• The top of the mould is rammed with the butt end of a
rammer.
• The object of ramming is to consolidate it, thereby
preventing the cavity of mould from being enlarged by the
pressure of the metal.
• After the sand is rammed, a strickle is used to scrape off
the excess sand level with the top of the flask.
Making a green-sand mould
• The mould is then vented by vent wire which permit the
escape of gases generated.
• A small amount of loose sand is sprinkled over the mould,
& bottom board is placed on the top.
• The drag is rolled over, the moulding board is removed,
and the upper surface is sprinkled with parting sand.
• The parting sand is used to prevent the joints between
halves of a moulds from adhering to one another when
the two parts of the moulding box are separated.
• The remaining half of the pattern & cope section of the
flask are then assembled as shown in figure.
Making a green-sand mould
• Tapered wooden pegs to serve as sprue & riser are placed
in proper position on the pattern which is riddled over
with facing sand & then the cope is filled with green-sand.
• The operation of filling, ramming, & venting of the cope
proceed in the same manner as in the drag.
• The cope usually carries a series of cross-bars to give
support to the moulding sand, which is further supported
by lifters or gaggers.
• Following these operations the wooden pegs are
withdrawn from the cope & a funnel shaped opening is
scooped out at the top of the sprue to form the pouring
basin.
Making a green-sand mould
• Next the cope is lifted off & placed on a board with the
parting line upward.
• An iron bar is now pushed down to the pattern & rapped
sideways so as to loosen the pattern in the mould.
• This rapping facilitates the removal of the pattern &
prevents any sand from sticking to the pattern.
• Next the pattern is drawn out & the runner & gate are cut
in the drag from the pattern to the spruee.
• Also, the core must be set in the print left by the pattern
in the drag.
• Loose particles of sand are removed by a jet of air & the
surfaces of the mould are brushed or dusted with foundry
blackings so as to give smooth surface to the casting.
Making a green-sand mould
• Finally the mould is assembled, the cope being carefully
placed on the drag so that the flask pins fit into the
bushes.
• Before pouring the molten metal the cope is sufficiently
loaded to prevent it from floating up when the metal is
poured.
• The complete mould is shown in figure.
Video of green sand mould
Typical moulding techniques
• Certain types of moulding problems which arises in
different moulding methods are discussed.
• False cope
• The pattern is first bedded into the cope, & a smooth
parting surface is made.
• A drag flask is set on the cope & rammed up in the usual
manner.
• Then the complete flask is rolled over, & the false cope is
lifted off, leaving the pattern in place in the drag.
• Having served its purpose, the sand in the false cope is
knocked out.
Typical moulding techniques
• The usual reason for using a false cope is to obtain an
irregular parting surface.
• The real cope, complete with gating system, is then
rammed up in the usual manner.
Typical moulding techniques
• Coping down
Typical moulding techniques
• Coping down
• The pattern shown in figure may be moulded by coping
down & making a new pattern.
• The pattern is first supported on a moulding board by
placing a suitable piece of wood under the elevated end.
• The drag is then set on the moulding board & rammed
up.
• After the drag is rolled over an irregular parting surface is
formed to the parting line of the pattern.
• The new parting surface is sloped gradually, what is
called coping down, so that the cope may be lifted
without danger of dropping the sand, which projects
downwards.
Typical moulding techniques
• Coping down
• After ramming, rolling over, & coping down, the drag
should be appear as shown in figure.
• This mould is then completed in the usual manner.
Typical moulding techniques
• Green sand match
• If several castings are required from an irregular shaped
pattern with the parting line not in one plane as shown in
figure, the coping down may be largely eliminated by
using a green sand match.
Typical moulding techniques
• Green sand match
• Ordinarily a green sand match is made by first ramming
up a drag & coping down to parting line of a pattern as
illustrated in figure.
Typical moulding techniques
• Green sand match
• The green sand match is now rammed up extra hard on
this drag without the sprue & riser pins.
• It is now retained for supporting the pattern &
automatically forming the irregular parting surface.
• The complete green-sand match with pattern in place &
ready for use is shown in Fig.
Typical moulding techniques
• Green sand match
• Much time is saved by using a sand match since it is
necessary in cope down & form a new parting surface on
the first drag.
• Other materials which are more durable than ordinary
sand are used for making matches.
• These materials are plaster-of-paris, port land cement or
follow board.
Typical moulding techniques
• Draw-back
• When patterns must be of such a shape that they cannot
be drawn from the sand owing to projections, drawbacks
are employed to get over the difficulty.
• This is illustrated in figure.
Typical moulding problems
• Draw-back
• When patterns must be of such a shape that they cannot
be drawn from the sand owing to projections, drawbacks
are employed to get over the difficulty.
• This is illustrated in figure.
Typical moulding problems
• Draw-back
• Sketch 1 shows that the solid pattern cannot be drawn
upwards from the mould without dragging out that piece
of sand marked a.
• Sketch 2 indicates the cavity dug out of the mould, well
away from the pattern.
• The space c behind the draw-back must be greater than
the width of the projection b.
• A stiff paper is rammed up in the moulding sand as shown
to form parting surface to the flange.
• Sketch 3 shows that when the draw-back has been slide,
the pattern can be withdrawn.
• When the pattern is out of the way, the draw-back is
brought back in its correct position, & space behind it is
filled up again with sand.
Typical moulding problems
• Using a dry sand core
• The method of moulding a sheave wheel or similar type of
pattern is to use a dry sand core to form the groove in the
pulley.
• A vee-shaped dry sand core known as a false core is placed
in the mould cavity to form the groove as shown in the
figure.
• A dry sand core can also be used to form the overhanging
portions of a pattern.
Typical moulding problems
• Using a cover core
• The cover core is a flat core used to cover cavity in a
mould. This is shown in figure.
Typical moulding problems
• Using a dry sand core
• The pattern having a dovetail face at the top end is placed
upside down on a moulding board with a flat cover core
confirming the shape of the dovetail at each of the dovetail
recesses.
• The drag is set over the pattern, filled up with sand &
rammed.
• The drag is then rolled over now facing dovetail at the top.
• Cover cores are removed & the pattern is drawn vertically
upward.
• They are finally replaced in the corresponding impressions
in the mould to have the desired casting.
Machine moulding
• Moulding process may be classified as hand moulding or
machine moulding to whether the mould is prepared by
hand tools or with the aid of moulding machines.
• Hand moulding is found to be economical when only a
few castings are required.
• Hand moulding is slow & it requires considerable skill to
produce good castings.
• Machine moulding is useful when large number of
castings are to be produced within less time whereas
hand moulding is more time consuming , laborious &
becomes expensive.
• With help of machine moulding castings can be produced
to close tolerance.
Machine moulding
• Machine moulding offers higher production rates &
better quality castings in addition to lighter & cheaper
castings & no skill is required to the opearator.
• A moulding machine performs two important functions:
• - it packs the sand &
• - draws the pattern.
• Moulding machines are calssified according to
(1) The method of compacting the moulding sand, &
(2) The method of removing pattern.
Classification of moulding machines according to the
methods of compacting the sand

(1) Squeezer machine

(2) Jolt machine
(3) Jolt-squeeze machine
(4) Sand slinger
Classification of moulding machines according to the
methods of removing the pattern from the mould
(1) Straight-draw molulding machine
(2) Stripping-plate moulding machine
(3) Turn-over moulding machine
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• In the squeeze method , moulding sand in the flask is
squeezed between the machine table & the overhead
squeeze board pneumatically or hydraulically until the
mould attain the desired density.
• The principle of operation of a top squeezer machine is
illustrated in figure.
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• The pattern 2 is placed on a mould board which is
clamped on the table 1.
• The flask 3 is then placed on the mould board & the sand
frame 4 on the flask.
• The flask & frame are filled with moulding sand & leveled
off .
• Next the table is raised by the table lift mechanism
against the platen 5 on the stationary squeezer head 6.
• The platen enters the sand frame up to the dotted line &
compacts the moulding sand.
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• After the squeeze, the table returns to its original
position.
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• The principle of a bottom squeezer machine is shown in
figure.
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• The pattern is placed on the mould board which is
clamped to the table.
• The flask 3 is placed on the frame 7 & filled with sand.
• Next the squeeze head is brought against the top of the
flask & the table with the pattern is raised upon the
dotted line.
• After squeezing, the table returns to its initial position.
Classification of moulding machines according to the
methods of compacting the sand
(1) Squeezer machine
• The main limitation of the squeezer method is that, the
sand is packed more densely on the top of the mould
from which the pressure is applied, & the density
decreases uniformly with the depth.
• At the parting plane & and around the pattern, the
density is found to be the lowest.
• This variation in density affects the hardness of the
mould which varies according to the depth.
• Therefore this method is restricted to moulds not more
than 150 mm in depth.
Classification of moulding machines according to the
methods of compacting the sand
(2) Jolt machine
• In the jolting method, the flask is first filled with the
moulding sand & then the table supporting to the flask is
mechanically raised & dropped in succession.
• Due to sudden change in inertia at the end of each fall,
the sand gets packed & rammed.
• The action of raising & sudden dropping the table is
called “jolting”.
• Figure illustrates the principle of a jolt moulding
machine in which the table 1, with platen & flask 3,
filled with moulding sand, is raised to 30 to 80 mm at
short intervals by the plunger 8 when compressed air is
admitted through the opening 11 & the table drops
down & strikes the guiding cylinder 12 at its bottom.
Classification of moulding machines according to the
methods of compacting the sand
(2) Jolt machine
• The draw back in this method is that sand is rammed
hardest at the parting plane & around the pattern &
remains less dense in the top.
• This necessitates hard ramming of the mould at the back
after the jolting action is completed.
• These machines are preferred for horizontal surfaces.
 Classification of moulding machines according to the
methods of compacting the sand
(3) Jolt-squeeze machine
• In order to overcome drawbacks of both the squeeze & jolt
principles of ramming the sand, a combination of squeeze &
jolt action is often employed.
• A jolting action is used to consolidate the sand on the face
of the pattern & it is followed by a squeezing action to
impart the desired density throughout the mass of the
sand.
• The jolt-squeeze machine is so constructed that both
squeeze & jolt actions can be obtained one after the other.
• A high pressure jolt-squeeze machine is capable of
producing moulds of maximum hardness, rammed
uniformly throghout the flask.
Video of Jolt-squeeze machine
 Classification of moulding machines according to the
methods of compacting the sand
(4) Sand slinger
• In the slinging operation, the construction & ramming are
obtained by the impact of sand which falls at a very high
velocity.
• The principle of a sand slinger is illustrated in figure.
 Classification of moulding machines according to the
methods of compacting the sand
(4) Sand slinger
• The overhead impeller head consists of the housing 1 which
the blade 2 rotates at a very high speed.
• The sand is delivered to the impeller through the opening 3
by means of conveyor buckets.
• The impeller head by the rotation of the blade throws the
sand through the outlet 4 down into the flask over the
pattern at a rate ranging from 500 to 2000 kg/min.
Classification of moulding machines according to the
methods of removing pattern from mould
 Classification of moulding machines according to the
methods of removing pattern from mould
(1) Straight-draw moulding machine
• In this, the pattern 1 is fixed on the pattern plate 3 on the
table-5, & the flask or moulding box 2 is placed over it &
filled with sand.
• It is then roughly rammed round the edges of the box.
• The squeeze head is next swung over in position & it
squeezes the mould.
• The flask is then lifted from the pattern by stripping pins 6.
 Classification of moulding machines according to the
methods of removing pattern from mould
(2) Stripping plate moulding machine
 Classification of moulding machines according to the
methods of removing pattern from mould
(2) Stripping plate moulding machine
• The principle of a stripping plate moulding machine is
illustrated in figure.
• The stripping plate 4 is arranged between the flask 2 &
pattern plate 3.
• The stripping plate has a recess whose contours equal those
of the pattern 1.
• When the mould is ready the pattern is withdrawn from the
mould downwards through the stripping plate, which
supports the mould when the pattern is removed.
 Classification of moulding machines according to the
methods of removing pattern from mould
(3) Turn-over moulding machine
 Classification of moulding machines according to the
methods of removing pattern from mould
(3) Turn-over moulding machine
• This is used for large size, high moulds, having parts which
might easily break away.
• In figure, the flask 2 rests on the pattern plate 3 during the
moulding operation.
• Then the flask together with the work table 5 is rotated
1800 & pin 6 lift the table 5 together with the pattern 1 out
of the mould.
Cleaning of casting
 Cleaning of casting
• After the molten metal has been poured into the mould, it is
permitted to cool & solidify.
• When the casting has solidified, it is removed from the sand
in the moulding box.
• This operation is shake-out.
• This shake-out can be effected either manually or
mechanically but generally, mechanical shake outs are used
for very large-scale work.
• When castings are taken out of mould, they are not in the
same condition in which they are desired since they have
sprue, risers, gates, etc. attached to them.
• Besides, they are not completely free of sand particles.
• This operation of cutting off the unwanted parts, cleaning &
finishing the casting is known as fettling.
 Cleaning of casting
• This fettling includes:
1. Removal of cores from the castings.
2. Removal of gates, risers, runners, etc. from the castings.
3. Removal of fins, & other unwanted projections from the
castings.
4. Removal of adhering sand & oxide from the surfaces of the
castings (surface cleaning).
5. Repairing castings to fill up blowholes, straightening the
warped or deformed castings.
• Dry sand cores may be removed by rapping or knocking
with an iron bar.
• Pneumatic or hydraulic devices may be employed for quick
knocking.
 Cleaning of casting
• Gates, risers, sprues, and runners are removed by knocking
off or breaking with a hammer, sawing, torch cutting,
electric-arc cutting, abrasive wheel cutting etc.
• The operation of removing unwanted metal fins, projections,
etc. from the surface of the casting is called snagging.
• Besides, there is always more or less sand adhering to the
casting.
• This sand must be removed before they are sent to other
places for finishing operations.
• In small foundries this is done by wire brushes.
• In big foundries, this is done in tumbling barrels & sand-
blasting, pneumatic shot-blasting, and hydraulic shot-
blasting machines, which are known as fettling machines
 Cleaning of casting
• Sometimes pickling is done in suitable acid (sulphuric acid,
hydro-fluoric acid or nitric acid) helps in removing any
adhering sand from the casting.
• After this, the casting is also pickled in alkaline solutions &,
finally, hot water to neutralize the acid remaining on the
casting.
• Defects such as blow holes, gas holes, cracks, warping,
deformation, etc., may often occur in castings. These defect
must be removed before their actual use.
• They are repaired by suitable means such as welding,
soldering , resin impregnation, epoxy filling, metal spraying
etc.
• Deformed or warped castings can be straightened in a press
by applying pressure.