UNIT 1 MOULDING MATERIALS

INTRODUCTION
In casting process the molten metal is poured into a mould cavity. Therefore suitability of
a casting operation depends on the selection of an appropriate moulding process and
mould material.
Suitability of a moulding material depends upon the type of material being poured, number
of castings being made, the type of casting, quality requirement by the customer and finally
on the mould and core making equipment owned by the foundry.
Objectives
After reading this unit you, should be able to learn

 about the main features of various moulding materials used in the foundry industry,
and
 about the applicability of these moulding materials in various casting processes.
Moulds can be made of number of moulding materials like sand, metal, waxes etc. Even the
properties of the above mentioned few basic materials and other moulding materials can
be altered by adding different types of additives. In the sections to follow we shall discuss
about the important characteristics of moulding materials.

MOULDING SANDS
Foundry sand consists primarily of clean, uniformly sized, high-quality silica sand or lake
sand that is bonded to form moulds for ferrous (iron and steel) and non-ferrous (copper,
aluminum, brass) metal castings. Although these sands are clean prior to use. The
automotive industry and its parts suppliers are the major generators of foundry sand.
The most common casting process used in the foundry industry is the sand cast system.
Virtually all sand cast moulds for ferrous castings are of the green sand type. Green sand
consists of high-quality silica sand, about 10 percent bentonite clay (as the binder), 2 to 5
percent water and about 5 percent sea coal (a carbonaceous mould additive to improve
casting finish). The type of metal being cast determines which additive and what gradation
of sand is used. The green sand used in the process constitutes 90 percent of the moulding
materials used.
In addition to green sand moulds, chemically bonded sand cast systems are also used.
These systems involve the use of one or more organic binders (usually proprietary) in
conjunction with catalysts and different hardening/setting procedures. Foundry sand
makes up about 97 percent of this mixture. Chemically bonded systems are most often used

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for “cores” (used to produce cavities that are not practical to produce by normal moulding
operations) and for moulds for non-ferrous castings.
The sand used for green sand moulding must fulfill a number of requirements :
(i) It must pack tightly around the pattern, which means that it must have flowability.
(ii) It should be capable of being deformed slightly without cracking, so that the pattern
can be withdrawn. In other words, it must exhibit plastic deformation.
(iii) It must have sufficient strength to strip from the pattern and support its own weight
without deforming, and to withstand the pressure of molten metal when the mould is
cast. It must therefore have green strength.
(iv) It must be permeable, so that gases and steam can escape from the mould during
casting.
(v) It must have dry strength, to prevent erosion of the mould surface by liquid metal
during pouring as the surface of the mould cavity dries out.
(vi) It must have refractoriness, to withstand the high temperature involved in pouring
without melting or fusing to the casting.
(vii) With the exception of refractoriness, all of these requirements are dependent on the
amount of active clay present and on the water content of the mixture. For the
abovesaid qualities, moulding sand must have some of the properties. It is not essential
for the sand to have all these properties at the same time rather it depends on the
application for which sand is going to be used. According to the application these
properties can be obtained at the same time economics can be worked out.
Properties of a Good Moulding Sand
To provide satisfactory and uniform results, the sand used to make moulds must be
carefully prepared. Ordinary silica sands are compounded with additives to meet following
four requirements which are essential to a moulding sand.
(i) Refractoriness : It is defined as the ability to withstand high temperatures. Therefore
higher the pouring temperature higher will be the required refractoriness. For lower
pouring temperatures even the lower value will work. Refractoriness is provided by the
basic nature of the sand.
(ii) Cohesiveness (also referred to as bond) : It is defined as the ability to retain a given
shape. Cohesiveness of sand is ascertained by amount of bonding materials present
such as clay in presence of moisture.
(iii) Permeability : It is the ability to permit gases to escape through it. The rate in
millimeter per minute at which air will pass through the sand under a standard
condition of pressure is used as index of permeability. It is dependent on the size of the
sand particles, the amount and type of clay or bonding agent, the moisture content,
and the compacting pressure. The mould must be enough porous to permit the gases
to escape and avoid defects due to entrapped gases.

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(iv) Collapsibility : It is the ability of disintegration of the cohesive mould as a result of
metal shrinkage. Collapsibility is generally obtained by adding organic material, such
as cellulose, cereals etc., that burn out when these are exposed to hot metal. The
combustion reduces both the volume and strength of the restraining sand.
(v) Green Strength : Property which tells strength and plasticity of the sand once the water
has been mixed to it.
(vi) Dry Strength : Once the metal is poured inside the cavity, sand adjacent to the hot metal
losses its water. Dry strength is the strength of dry sand to resist erosion and pressure
of the molten metal.
(vii) Thermal Stability : It is the property of the sand to remain stable dimensionally under
high temperature or heating condition. If the mould surface due to lack of thermal
stability crack, buckle or flake off, it will lead to defective casting.
(viii) Resusability : It is preferred to use the moulding sand which can be reused for the
number of operations.
Good moulding sand always represents a compromise between conflicting factors. To
obtain an acceptable compromise of the four basic requirements the size of the sand
particles, the amount of bonding agent (such as clay), the moisture content, and the
percentage of organic matter are all selected. The composition is carefully controlled to
assure satisfactory and consistent results. (A typical green-sand mixture contains about
85% silica sand, 9% clay, and 3% water and 3% organic additives.) Since moulding material
is often reclaimed and recycled, the organic material has to be added again as a portion of
it will burn during the pour. Some of the mould material may have to be discarded and
replaced with new.
It is also important for each grain of the sand to be coated uniformly with the additive
agents. This is achieved by putting the ingredients through a muller, a device that kneads,
rolls, and stirs the sand. All such devices along with testing equipment are discussed in
Appendix-A to this unit.
Principal Ingredients of Moulding Sands The principal ingredients of moulding sands are :
(i) Silica sand grains, (ii) Clay (bond), (iii) Moisture, and (iv) Organic additives.
Silica Sand Grains
Silica sand grains impart refractoriness, chemical resistivity, and permeability to the sand.
They are specified according to their average size and shape. The finer grains would lead to
more intimate contact and lower the permeability. However, fine grains tend to fortify the
mould and lessen its tendency to get distorted. The shapes of the grain may vary from
round to angular. The grains are classified according to their shape as below :
(i) Rounded Grains
(ii) Subangular Grains
(iii) Angular Grains

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(iv) Compounded Grains
In practice, sand grains contain mixed grain shapes. A sub-angular-to-rounded grain
mixture would be the best combination.
Clay
Clay imparts the necessary tensile strength to the moulding sand so that after ramming,
the mould does not lose its shape. However, as the quantity of the clay is increased, the
permeability of the mould is reduced.
Clay is defined by the American Foundrymen’s Society (A.F.S.), as those particles of sand
(under 20 microns in diameter) that fail to settle at a rate of 25 mm per minute, when
suspended in water. Clay consists of two ingredients: fine silt and true clay. Fine silt is a
sort of foreign matter of mineral deposit and has no bonding power. True clay supplies the
necessary bond. Under high magnification, true clay is found to be made up of extremely
minute aggregates of crystalline particles, called clay minerals. These clay minerals are
further composed of flake-shaped particles, about 2 microns in diameter, which are seen to
lie flat on one another.
Moisture
Clay acquires its bonding action only in the presence of the requisite amount of moisture.
When water is added to clay, it penetrates the mixture and forms a microfilm which coats
the surface of each flake. The molecules of water forming this film are not in the original
fluid state but in a fixed and definite position. As more water is added, the thickness of the
film increases up to a certain limit after which the excess water remains in the fluid state.
The thickness of this water film varies with the clay mineral. The bonding quality of clay
depends on the maximum thickness of water film it can maintain.
When sand is rammed in a mould, the sand grains are forced together. The clay coating on
each grain acts in such a way that it not only locks the grains in position but also makes
them retain that position. If the water added is the exact quantity required to form the film,
the bonding action is best. If the water is in excess, strength is reduced and the mould gets
weakened. Thus, moisture content is one of the most important parameters affecting
mould and core characteristics and consequently, the quality of the sand produced.
Other Additives to Moulding Sands
Additives are mixed during sand preparation according to the requirement of molten metal
and base sand to obtain specific characteristics in the sand. This helps in improving certain
property of the base sand like high temperature plasticity, metal penetration property,
surface finish etc. The commonly used additives are given below.
Iron Oxide
It is used for both moulding and core making sand to improve high temperature plasticity
and deep metal penetration and hot strength. In core sand it prevents cracking of cores.

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Good quality iron oxide should have iron oxide content not less than 93% and iron content
not less than 65%.
Molasses
It is commonly used in moulding of iron castings. It is obtained as a by-product during
sugar refining. It is added to achieve high dry strength and collapsibility. This also increases
green strength. However, due to the high hygroscopicity of the mix prepared with molasses,
its use is not much favoured for good quality casting.
Cold Dust
It is used in green strength and dry strength moulding for protecting mould surfaces
against the action of molten metal and improving surface finish of cast iron castings. This
also reduces expansion and metal penetration. When the molten metal comes in contact
with mould surfaces containing cold dust, a gaseous envelope is formed which resists the
fusion of sand to metal.
Sodium Silicate
This is most commonly used binder in air setting or self hardening process. Many processes
make use of sodium silicate as a binder along with a solid or gaseous hardener like CO2.
Fibrous Materials
Used to improve collapsibility, prevent scabbing and expansion defects. The commonly
used materials are wood flour, straw, asbestos, sawdust, dried glass and manure.
Dextrin
It is a binder which increases air setting strength, toughness and collapsibility and prevents
sand from quickly drying. During pouring it gasif ies producing voids between sand grains
and allowing their expansion without distortion. Dextrin is commonly used with core sand
to increase dry strength and as a binder for mould and core washes.
Sulphite Lye
It is a by-product of cellulose industry and is used for imparting better dry strength, hot
strength and collapsibility to moulds. Its use is more favoured in the production of large
and heavy iron castings.
Specifications and Testing of Moulding Sand
Moulding sand is specified in terms of the size and shape of the silica grains it contains, the
clay content, and the moisture content. These are determined as follows :
Maintaining consistent sand quality is of little concern to the casting designer, but it is a
significant matter to the foundry worker, who is expected to deliver consistent, highquality
products. Standard tests and procedures have been developed to evaluate grain size,
moisture content, clay content, and compactability, as well as mould hardness,
permeability, and strength. These test procedures have been explained in Appendix-A of
this block in detail.

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Grain size is determined by shaking a known amount of clean, dry sand downward through
a set of 11 standard sieves of decreasing mesh size. After shaking for 15 minutes, the amount
remaining on each sieve is weighed, and the weights are converted into an AFS (American
Foundrymen’s Society) grain fineness number.
Moisture content is usually determined by a special device that measures the electrical
conductivity of a small sample of sand that is compressed between two prongs. Another
method is to measure the weight lost from a 50-g sample after it has been subjected to a
temperature of about 230ºF (110ºC) for sufficient time to drive off all the water.
Clay content can be determined by washing the clay from a 50-g sample of moulding sand
in water that contains sufficient sodium hydroxide to make it alkaline. Several cycles of
agitation and washing may be required to fully remove the clay. The remaining sand is then
dried and weighed to determine the amount of clay in the original sample.

Permeability and strength tests are conducted on a standard rammed specimen. A

sufficient amount of sand is placed into a 2-inch-diameter steel tube so that after a 14-1b
weight is dropped three times from a height of 2 inch, the final height of the specimen is
within 1/32 of 2 inch.
Permeability is a measure of how easily gases can pass through the narrow voids between
the sand grains. Air in the mould before pouring (plus the steam that is produced when the
hot metal contacts the moisture in the sand) must be allowed to escape, rather than be
trapped in the casting as porosity or blow holes. During the permeability test, the sample
tube containing the rammed specimen is placed on a device and subjected to an air
pressure of 10g/cm2. By means of either a flow rate determination or measurement of the
pressure between the orifice and the sand, an AFS permeability number is determined.
Most test devices are calibrated to provide a direct readout of the permeability number.
The compressive strength of the sand is determined by removing the rammed specimen
from the tube and placing it in a mechanical testing device. A compressive load is then
applied until the specimen breaks, usually in the range of 10 to 30 psi (0.07 to 0.2 MPa).
When there is too little moisture in the sand, the grains are poorly bonded and strength is
poor. When there is excess moisture, the extra water acts as a lubricant and strength is
again poor. Thus there is a maximum strength and an optimum water content will vary
with the content of other materials in the mix. A similar optimum also applies to
permeability. Sand coated with a uniform thin film of moist clay provides the best
moulding properties. A ratio of 1 part water to 3 parts clay (by weight) is often a good
starting point.
The hardness of the compacted sand can provide a quick indication of mould strength and
give additional insight into the strength-permeability characteristics. It can be measured
by an instrument, which determines the resistance of the sand to penetration by a 0.2-inch
(5.08-mm)-diameter spring-loaded steel ball.

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Compactability is determined by sifting sand into a steel cylinder, leveling off the column,
striking it three times with a standard weight (as in the permeability test), and then
measuring the final height. The percent compactability is the change in height divided by
the original height, times 100%. The value can often be correlated with the moisture
content of the sand, with a compactability around 45% indicating a proper level of
moisture. A low compactability correlates with too little moisture.
Moulds with Different Types of Sand
Sands are classified as natural or synthetic type based on the presence of clay bonding
material. Naturally bonded sand contains clay. Synthetic sand is composed of various base
sands with bonding agents added to produce desired moulding characteristics. Silica is the
major base sand with some use being made of zircon, olivine and chromite.
Green-Sand, Dry-Sand, and Skin-Dried Moulds
In green-sand moulding, the mould material is composed of sand with a binder of clay,
water, and additives. Tooling costs are low, and the entire process is quite inexpensive.
Almost any metal can be cast, and there are few limits on the size, shape, weight, and
complexity of the products. Design limitations are usually related to the rough surface
finish, poor dimensional accuracy, and the need for subsequent machining. Still other
problems can be attributed to the low strength of the mould material and the moisture that
is present in the binder.
Because some intricate large parts are difficult to cast to required size and dimensions by
green sand techniques, dry sand is often used as the mould material for casting such parts.
The dry sand mix includes a base sand that is coarser than that used in green sand moulding
to facilitate natural venting and mould drying. Pitch is added as a carbon material along
with the cereal, molasses, dextrine, glutrin and resin. These additives thermoset at the
dryin g temperature of 149 to 316ºC (300 to 600ºF) to produce high strength and rigid mould
walls. Dry sand moulding consists of the green sand modified by baking the mould at 204
to 316ºC (400 to 600ºF). Moulds generally are dried in large mould ovens; alternatively,
large heaters may be used.

Large or medium-size castings of complex configurations (such as frames, engine cylinders,

large gears, and housings) are often made by dry sand techniques. Both ferrous and non-
ferrous metals are cast in this type of mould. Dry sand moulding is more expensive than
green sand, however, it has the advantages of producing castings with increased strength,
more exact dimensions, and smoother finishes.

These dry-sand moulds are not very popular, however, because of the long tim e required
for drying, the added cost of that operation, and the availability of practical alternatives.
An attractive compromise is to produce a skin-dried mould, drying only the sand that is
adjacent to the mould cavity. Torches are often used to perform the drying, and the water
is usually removed to a depth of about one-half inch.

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Moulds used for the casting of steel are almost always skin-dried, because the pouring
temperatures are significantly higher than those for cast iron. These moulds may also be
given a high-silica treatment prior to drying to increase the refractoriness of the surface, or
the more-stable zircon sand can be used as a facing. Additional binders, such as molasses,
lin-seed oil, or corn flour, may be added to the facing sand to provide additional strength
to the skin-dried segment.
Sodium Silicate-CO2 Moulding Material
Moulds (and cores) can also be made from a sand that receives its strength from the
addition of 3 to 4% sodium silicate, a liquid inorganic binder that is also known as water
glass. The sand can be mixed with the liquid sodium silicate in a standard muller and can
be packed into flasks by any of the methods. It remains soft and mouldable until it is
exposed to a flow of CO2 gas, after which it hardens in a matter of seconds by the reaction.
Na2SiO3 + CO2 Na2CO3 + SiO 2 (colloidal)
The CO2 gas is nontoxic and odourless, and no heating is required to drive the reaction.
The hardened sands, however, have poor collapsibility, making shakeout and core removal
difficult. Unlike most other sands, the heating that occurs as a result of the pour makes the
mould even stronger (a phenomenon similar to the firing of a ceramic material). In
addition, care must be taken to prevent the carbon dioxide in the air from hardening the
sand before the mould-making process is complete.
A modification of the CO2 process can be used when certain portions of a mould require
higher strength, better accuracy, thinner sections, or deeper draws than can be achieved
with ordinary moulding sand. Sand mixed with sodium silicate is packed around a metal
pattern to a depth of about 1 inch, followed by regular moulding sand as a backing material.
After the mould is fully rammed, CO2 is introduced through vents in the metal pattern.
This hardens the adjacent sand, and the pattern can now be withdrawn with less possibility
of damaging the mould.
No-Bake, Air-Set or Chemically Bonded Sands
An alternative to the sodium silicate process involves the use of organic resin binders that
cure by chemical reactions that occur at room temperature. Two or more binder
components are mixed with the sand just prior to the moulding operation, and the curing
reactions begin immediately. Because the mix is workable for only a short period of time,
the moulds (or cores) must be made in a reasonably rapid fashion. After a few minutes to
a few hours (depending on the specific binder and curing agent), the sands harden enough
to be removed from the pattern and are ready to pour.

Various no-bake sand systems are available, with selection being based on the metal being
poured and the specific sand performance characteristics that are desired. Each system is
based on organic resin binders, curing agents or catalysts, and various additives and

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modifiers. Like the sodium silicate moulds, no-bake offers high dimensional accuracy, good
hot strength, and high resistance to mouldrelated casting defects. Patterns can incorporate
thinner sections and deeper draws. In contrast to the sodium silicate material, however,
the no-bake moulds decompose readily after the metal has solidified, providing excellent
shakeout characteristics.
Other Sand-based Moulding Methods
Over the years, various processes have been proposed to overcome some of the limitations
of the more traditional methods. While few have become commercially significant, several
are included here to illustrate the nature of these efforts.
In one method, known as the V-process or vacuum moulding, a vacuum is used in place of
a sand binder. A vacuum flask is then placed over the pattern, the flask is filled with sand,
a sprue and pouring cup are formed, and a second sheet of plastic is placed over the mould.
A second vacuum is then drawn on the flask itself, compacting the sand and providing the
necessary strength and hardness. The pattern vacuum is released, the pattern is withdrawn,
and the mould halves are assembled. The mould is poured while maintaining a vacuum in
both the cope and drag segments of the flask.

Advantages of the vacuum process include the total absence of moisture-related defects.
Since no binder is used, binder cost is eliminated and the sand is completely reusable. No
fumes (binders burning up) are generated during the pouring operation. Shakeout
characteristics are exceptional; the mould virtually collapses when the vacuum is released.
Unfortunately, the process is relatively slow because of the additional steps and the time
required to pull a sufficient vacuum.
In another process, sand with a small amount of clay and quite a bit of water is first packed
around a pattern. The pattern is removed and liquid nitrogen is sprayed onto the mould
surface. The ice that forms becomes the binder, and the mould is then poured while it is in
its frozen condition. As with the V-process, binder cost is low and shakeout is excellent.

MATERIALS FOR CORE MAKING

Casting processes are unique in their ability to incorporate internal cavities or reentrant
sections with relative ease. To produce these features, however, it is often necessary to use
cores as part of the mould. While these cores constitute an added cost, they do much to
expand the capabilities of the process, and good design practice can often facilitate and
simplify their use.
For cores natural sand containing small percentages of clay can be used but synthetic sand
is preferred. Green sand cores in dried condition can also be used, with the bonding agents
like linseed oil and cereals. The basic advantage of organic binders as compared to clay is
that they break down under the effect of the heat and can easily be removed from the
castings at shakeout. It is extremely important that proper baking times and temperatures
be established for the various binders and for variation in core size. A properly baked core

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does not produce harmful gases, has adequate strength and collapse at the right time after
metal is poured around it.
Recently, plastics have started to supplement linseed oil as core binder. Urea formaldehyde
and phenol formaldehyde are the two most widely used. Urea formaldehyde breaks down
at very low temperature as compared to phenol or linseed oil, so it is used in the low melting
metals.
A still more recent development in core making is sodium silicate-CO2 moulding, which
has already been discussed in the earlier sections of this unit.
QUESTIONS
(a) What are the basic requirements of a proper moulding sand?
(b) Explain how green strength and permeability are affected by :
(i) Grain shape of the sand
(ii) Grain size of the sand
(iii) Grain size distribution
(c) Distinguish between pore water and free water. Explain their effects on the green
strength of the sand.
(d) Name the various additives used in moulding sand and explain how they affect its
properties.
(e) What are the basic requirements of a core sand? In what respect does it differ from
the moulding sand?
(f) Give the mechanism of hardening in carbon-dioxide moulding and explain the factors
on which it depends.

SHELL MOULDING MATERIAL

Many moulds are now being made by the shell-moulding process, which offers better
surface finish than can be obtained with ordinary sand moulding, better dimensional
accuracy, and a higher production rate with reduced labour requirements. In many cases,
the process can be completely mechanized and adapted for mass production. The full shell
moulding process has been described in the next unit.
The sand used for shell moulding consists of a mixture of the following ingredients :
(i) Dry sand grains, AFS fineness 60 to 140 distributed over 4 to 5 screens.
(ii) Synthetic resin binder, 3 to 10 per cent by weight. Resins which may be used are the
phenolformaldehydes, urea formaldehydes, alkyds, and polyesters. The resin must be a
thermosetting plastic, and is used as a powder in dry mixtures. It may also be applied as a
liquid and then dried on the sand grains. For moulding, the mixture must be dry and free
flowing.

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The shell is cured in two stages. When the sand mixture drops onto a pattern heated to
about 350 to 700 oF, the plastic partially thermosets and builds up a coherent sand shell
next to the pattern. The thickness of this shell is about ¼ to ¾ inch and is dependent on
the pattern temperature, dwell time on the pattern, and the sand mixture. The shell, still
on the pattern, can then be cured by heating it to 450 to 650oF for 3 to 1 min. Stripping the
shell from the mould presents a problem since the shell is very strong and grips the mould
tightly. A mould release agent, or parting agent, is used to obtain clean stripping when the
ejector pins push the shell off the pattern. Silicone parting solutions, sprayed on the
pattern, have been found satisfactory.
Shell moulding is probably used more for making cores than moulds. A variant of the
process, known as the hot-box process, employs a heated core box. The moulding mixture
again contains 1.5 to 4.0 per cent resin of the furane or furfuraldehyde type. Heat from the
core box causes the catalysts to start an exothermic polymerization process. As the sand
temperature rises, the resin polymerizes and the mass hardness. Moulds are made by
assembling the hot-box cores.

Fillers and Binders

The investment materials used to produce a slurry for coating the pattern are generally
separated into two categories. Fillers are the materials used to hold the refractory particles
together as a fluid-like slurry. Binders provide the basic mould refractory material. Slurries
are prepared by adding the refractory powder or flour filler to a binder liquid and then
using sufficient agitation to break up agglomerates and to thoroughly wet and disperse the
powder. Mixing is continued until the viscosity of the slurry reaches the proper level for
coating the pattern. Continued stirring is required in production to keep the powder from
settling out of suspension. Either rotating tanks or propeller mixers are used for this
purpose.
As a general rule, ethyl silicate is not used as a binder for the first and second coats of the
ceramic shell process, because the drying rate is too fast and shell surface cracking results
from the stress caused by thermal expansion of the refractory. When mixing the slurries,
the refractory flour is added to the binder to ensure good dispersion of solids. To obtain
good coverage of the patterns, a wetting agent should be used for the first ceramic shell
coat.

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CORE AND CORE MAKING PROCESS

Cores are used in our foundry casting process to create cavities as well as internal and
external features which cannot be generated by our patterns. These cores are made
from sand with three main techniques:

 shell core making

 the cold box process
 hand-rammed core making

Cores which are rammed and hardened in situ by standing in air have the core material
composed of silica sand and a group of resins which form highly cross-linked polymers
upon the action of acids. The resin binders are made by mixing various proportions of
urea, formaldehyde and furfuryl alcohol (C4H3O—CH2OH).

What is the process of cold core making?

Core-Making: Fundamental Concepts and Processes

COLD-BOX CORE PROCESS

This process utilizes a two-part binder system, typically consisting of phenolic urethane (a
resin) and a catalyst (such as an amine gas). The sand mixture is blown into the core
box, and the catalyst is introduced to the resin-coated sand, leading to rapid curing and
hardening of the core.

The process of core making

1. Selection of Sand
Properties of core sand are highly crucial and are required to have characteristics like
permeability, green strength, refractoriness, flowability, collapsibility, adhesiveness,
cohesiveness, and fry strength.
2. Mixing of sand with additives
After an initial thorough mix of sand to ensure proper distribution of sand granules,
binder is added to the silica sand with moisture content and other additives like coal
dust, dextrin, or silica flour and together they create a mixture. This mixture should be
uniform to create standardized sand cores with high production efficiency.
3. Blowing or Shooting
After the mixture is ready, next step includes blowing this flowable mixture into the core
box, and depending on the type of process used, either the core box is heated, or the
already heated sand mixture is blown into the core box and left to settle for a few
seconds. This process is also referred to as core shooting process and modern foundries
use dedicated core blowing/shooting machines for optimal production efficiency.

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4. Venting
In the casting process, the core will be surrounded by molten metal which will stimulate
gases inside the mold, and it is essential to provide a venting passage for these gases as
if remain entrapped inside the mold, these gases can result in casting defects. Therefore,
to obtain good permeability additional venting holes are made in the cores.
5. Reinforcement of Cores
Some cores, heavy & large cores in particular, might need additional reinforcement
material like cast iron grids or low-carbon steel wires to maintain coherence.
6. Baking of Cores
Depending on the type of process used, baking of sand cores is done in convention oven
with temperature between 200° C to 250° C (392° F and 482° F), the heat causes the
binder to polymerize.
7. Cleaning & Finishing
After baking, cores are ready for cleaning & finishing. Following methods are used as per
requirement:
1. Trimming of cores involve removing loose pieces and other unwanted projections
2. Brushing is used to remove loose sand off the core with fine wire brush
3. Coating is crucial step for finishing and involves coating of cores with refractory material
to improve heat resistance.
8. Inspection
This step includes either manual or machine inspection of the cores for dimensional
accuracy.
9. Assembling
This includes assembling of multiple cores together with core glue in case of small and
medium size cores and bolts in case of large cores.

Introduction

1) A core is essentially a body of materials which forms components of the mold. Itpossesses
sufficient strength to be handled as an independent unit.
2)Core is an obstruction which when positioned in the mold, naturally does not permitthe
molten metal to fill up the space occupied by the core. In this way a coreproduces hollow
casting
3)Cores are required to create the recesses, undercuts and interior cavities that areoften
apart of castings.
4)Cores are employed as inserts in moulds to form design features that
are otherwiseextremely difficult to produce by simple molding.
5) A core may be defined as a sand shape or form which makes the contour of acasting for
which no provision has been made in the pattern for molding.
6)Cores are made up of sand, metal, plaster or ceramics.

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7)Cores are used to:
a.Form the air-space between the cooling fins of an air cooled engine cylinder
b.Make the water cooling chamber in internal combustion engine.

Different functions, purpose of cores:

1.For hollow casting, core provides the means of forming the maininternal cavities.
2.Cores may form a part of green sand mould.
3.Cores may provide external undercut feature
4.Cores may be employed to improve the mould surface.
5.Cores may be inserted to achieve deep recesses in the castings
6.Cores may be used to strengthen the mould.
7.Some times the mould may be completed simply by assembling the core pieces or core.
8.Cores may be used to form the gating systems of large sizemoulds

Essential characteristics of (dry sand) cores:

Cores may possess:

1.Sufficient strength to support itself and to get handled withoutbreaking.
2.High permeability to let the mould gases escape through themould walls.
3.Smooth surface to ensure a smooth casting.
4.High refractoriness to withstand the action of hot moltenmetal(metal penetration).
5.High collapsibility in order to assess the free contractor of thesolidifying metal.
6.Those ingredients which do not generate mold gases.

Core making procedures:

1.Core sand preparation
2.Making core
3.Baking core
4.Finishing core
5.Setting core

Making the core:

1.Small cores can be made manually in hand rammed core boxes.
2.Cores on mass scale are rapidly produced on a variety of coremaking machines, to name
a few,
a.Jolt machine.
b.Core roll over machine
c.Sand slinger
d.Core extrusion machine
e.Core blower
f.Shell core machine

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Core box:
1. A core box is basically a pattern for making cores
2.Core boxes are employed for ramming cores in them
3.Core boxes impart the desired shape to the core sand.
4.Core boxes range from simple wooden structures to precisionmetal assemblies which
possess long life under extracting condition.

Types of core boxes:

a.Half core box
b.Slab or dump core box
c.Split core box
d.Left and right hand core box
e.Strickle core box
f.Loose piece core box.
g.Gang core box.

Finishing of cores:
1.Baked cores are finished before they can be set in the mald.
2.Core finishing consists of
a.Cleaning
i.Trimming
ii.Brushing
iii.Coating
iv.Mudding
b.Sizing
c.Core assembly

Setting of cores:
1.Core setting means placing cores in the mold
2.In order to obtain correct cavities in the castings the cores shouldbe accurately
positioned in the molds.
3.Cores in the moulds should be firmly secured so that they canwithstand the buoyancy
effect of the being poured molten metal.
4.Small cores are set in the moulds by hand whereas big coresmay required a crane for the
purpose.

Types of cores
A.The state or condition of core
a.Green sand core

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 b.Dry sand core

B.The nature of core materials employed

a.Oil bonded cores
b.Resin bonded cores
c.Shell cores
d.Sodium silicate cores

C.The type of core hardening process employed

a.Co2 process
b.The hot-box process
c.The cold set process
d.Fluid or castable sand process
e.Nishiyama process
f.Furan no-bake system
g.Oil no-bake system
D.The shape and position of the core
a.Horizontal core
b.Vertical core
c.Hanging or cover core
d.Balanced core
e.Drop core or stop off core
f.Ram up core
g.Kiss core

1.Green sand core:

a.Green sand cores are formed by pattern itself.
b. A green sand core is a part of the mold.
c. A green sand core is made out of the same sand fromwhich the rest of mold has been
made i.e molding steel.

2.Dry Sand cores

a.Dry sand cores, unlike green sand cores are not producedas a part of the sand.
b.Dry sand cores are made separately and independent of that mold.
c. A dry sand core is made up of core sand which differsvery much from the sand out of
which the mold is constructed.
d. A dry sand core is made in a core box and it is baked after ramming.
e. A dry sand core is positioned in the mold on core seatsformed by core print on the patten.
f. A dry sand core is inserted in the mold before closing thesame.

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What do you mean by break-even analysis?
A break-even analysis is an economic tool that is used to determine the cost structure of a
company or the number of units that need to be sold to cover the cost. Break-even is a
circumstance where a company neither makes a profit nor loss but recovers all the money
spent.

What Is Break-Even Analysis?

Break-even analysis compares income from sales to the fixed costs of doing business. Five
components of break-even analysis include fixed costs, variable costs, revenue,
contribution margin, and break-even point (BEP). When companies calculate the BEP, they
identify the amount of sales required to cover all fixed costs to begin generating a profit.
The break-even point formula can help find the BEP in units or sales

 Using the break-even point formula, businesses can determine how many units or
rupees of sales cover the fixed and variable production costs.
 The break-even point (BEP) is considered a measure of the margin of safety.
 Break-even analysis is used broadly, from stock and options trading to corporate
budgeting for various projects.

Why Break-Even Analysis Matters

 Pricing: Businesses get a comprehensible perspective on their cost structure with a
break-even analysis, setting prices for their products that cover their fixed and variable
costs and provide a reasonable profit margin.
 Decision-Making: When it comes to new products and services, operational
expansion, or increased production, businesses can chart their profit to sales
volume and use break-even analysis to help them make informed decisions
surrounding those activities.
 Cost Reduction: Break-even analysis helps businesses find areas to reduce costs to
increase profitability.
 Performance Metric: Break-even analysis is a financial performance tool that helps
businesses ascertain where they are in achieving their goals.

What is the Break-Even Analysis Formula?

The formula for break-even analysis is as follows:
Break-Even Quantity = Fixed Costs / (Sales Price per Unit – Variable Cost Per Unit)
where:
 Fixed Costs are costs that do not change with varying output (e.g., salary, rent,
building machinery)
 Sales Price per Unit is the selling price per unit
 Variable Cost per Unit is the variable cost incurred to create a unit

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It is also helpful to note that the sales price per unit minus variable cost per unit is
the contribution margin per unit. For example, if a book’s selling price is Rs. 100 and its
variable costs are Rs. 5 to make the book, Rs. 95 is the contribution margin per unit and
contributes to offsetting the fixed costs.

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