Foundry technology note

Ethiopian Technical University
Faculty of Mechanical Technology
Manufacturing Technology
Course Title: Foundry Technology
Course Number: MAT 318
Credit Hour: 3 (2Lec & 3Lab)
Prepared By: Mr. Gezae Mebrahtu (MSc in Mechanical
Manufacturing and Automation)
April 11, 2021

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Contents
CHAPTER ONE - Introduction to Foundry Technology ............................................................. 1
1.1. Introduction................................................................................................................... 1
1.2. Design Advantages of casting ...................................................................................... 1
1.3. Advantages of Casting Process..................................................................................... 2
1.4. Metallurgical Advantages............................................................................................. 2
1.5. Questions ...................................................................................................................... 4
CHAPTER TWO - Pattern and Core Making .............................................................................. 5
2.1. Pattern........................................................................................................................... 5
2.2. Common Pattern Materials ........................................................................................... 5
2.3. Factors Effecting Selection of Pattern Material............................................................ 9
2.4. Types of Pattern............................................................................................................ 9
2.5. Pattern Allowances ..................................................................................................... 14
2.5.1. Shrinkage Allowance .......................................................................................... 14
2.5.2. Machining Allowance ......................................................................................... 15
2.5.3. Draft or Taper Allowance ................................................................................... 15
2.5.4. Rapping or Shake Allowance.............................................................................. 16
2.5.5. Distortion Allowance .......................................................................................... 16
2.5.6. Mold wall Movement Allowance........................................................................ 16
2.6. Core and Core Box ..................................................................................................... 16
2.6.1. Core Box ............................................................................................................. 18
2.7. Core Box Allowances ................................................................................................. 19
2.8. Color Codification for Patterns and Core Boxes ........................................................ 20
2.9. Core Prints .................................................................................................................. 20
2.10. Wooden Pattern & Wooden Core Box Making Tools................................................ 20
2.11. Wooden Pattern & Wooden Core Box Making Machines ......................................... 22
2.12. Design Considerations in Pattern Making .................................................................. 22
2.13. Pattern Layout............................................................................................................. 23
2.14. Pattern Construction ................................................................................................... 24
2.15. Questions .................................................................................................................... 24
CHAPTER THREE - Foundry Tools and Equipment................................................................ 26
3.1. Introduction................................................................................................................. 26
3.2. Hand Tools Used in Foundry Shop ............................................................................ 26
3.3. Flasks .......................................................................................................................... 31
3.4. Power Operated Equipment........................................................................................ 34
3.4.1. Moulding Machines............................................................................................. 34
3.4.2. Classification of Moulding Machines ................................................................. 34
3.5. Questions .................................................................................................................... 36
CHAPTER FOUR - Mold and Core Making ............................................................................. 37
4.1. Introduction................................................................................................................. 37
4.2. Molding Sand.............................................................................................................. 37

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4.3. Constituents of Molding Sand .................................................................................... 37
4.3.1. Silica sand ........................................................................................................... 37
4.3.2. Binder.................................................................................................................. 39
4.3.3. Moisture .............................................................................................................. 39
4.3.4. Additives ............................................................................................................. 39
4.4. Kinds of Moulding Sand............................................................................................. 40
4.4.1. Green sand........................................................................................................... 41
4.4.2. Dry sand .............................................................................................................. 41
4.4.3. Loam sand ........................................................................................................... 41
4.4.4. Facing sand.......................................................................................................... 41
4.4.5. Backing sand ....................................................................................................... 41
4.4.6. System sand......................................................................................................... 41
4.4.7. Parting sand......................................................................................................... 42
4.4.8. Core sand............................................................................................................. 42
4.5. Properties of Moulding Sand ...................................................................................... 42
4.5.1. Refractoriness...................................................................................................... 42
4.5.2. Permeability ........................................................................................................ 42
4.5.3. Cohesiveness ....................................................................................................... 42
4.5.4. Green strength..................................................................................................... 43
4.5.5. Dry strength......................................................................................................... 43
4.5.6. Flowability or plasticity ...................................................................................... 43
4.5.7. Adhesiveness....................................................................................................... 43
4.5.8. Collapsibility....................................................................................................... 43
4.5.9. Miscellaneous properties..................................................................................... 43
4.6. Sand Testing ............................................................................................................... 43
4.6.1. Moisture Content Test......................................................................................... 44
4.6.2. Clay Content Test................................................................................................ 44
4.6.3. Grain Fineness Test............................................................................................. 45
4.6.4. Refractoriness Test.............................................................................................. 45
4.6.5. Strength Test ....................................................................................................... 46
4.6.6. Permeability Test................................................................................................. 47
4.6.7. Flowability Test................................................................................................... 48
4.6.8. Shatter Index Test................................................................................................ 49
4.6.9. Mould Hardness Test .......................................................................................... 49
4.7. Sand Conditioning ...................................................................................................... 50
4.8. Steps Involved in Making a Sand Mold ..................................................................... 52
4.9. Venting of Molds........................................................................................................ 54
4.10. Gating System in Mold............................................................................................... 55
4.11. Factors Controlling Gating Design ............................................................................. 57
4.12. Role of Riser in Sand Casting..................................................................................... 58
4.12.1. Considerations for Desiging Riser ...................................................................... 58
4.12.2. Effect of Riser ..................................................................................................... 59

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4.13. Green Sand Molding................................................................................................... 59
4.14. Core............................................................................................................................. 59
4.15. Core Sand.................................................................................................................... 60
4.16. Core Making............................................................................................................... 61
4.16.1. Core Sand Preparation......................................................................................... 61
4.16.2. Core Making Process Using Core Making Machines ......................................... 61
4.16.3. Core baking......................................................................................................... 62
4.16.4. Core Finishing..................................................................................................... 63
4.17. Green Sand Cores ....................................................................................................... 63
4.18. Dry Sand Cores........................................................................................................... 63
4.19. Classification of Molding Processes........................................................................... 63
4.20. Molding Methods........................................................................................................ 64
4.20.1. Bench Molding.................................................................................................... 64
4.20.2. Floor Molding ..................................................................................................... 64
4.20.3. Pit Molding.......................................................................................................... 64
4.20.4. Machine Molding................................................................................................ 64
4.20.5. Loam Molding..................................................................................................... 65
4.20.6. Carbon-Dioxide Gas Molding............................................................................. 65
4.20.7. Shell Molding...................................................................................................... 66
4.20.8. Plaster Molding ................................................................................................... 68
4.20.9. Antioch Process................................................................................................... 69
4.20.10. Metallic Molding ............................................................................................. 69
4.21. Questions .................................................................................................................... 70
CHAPTER FIVE - Casting......................................................................................................... 73
5.1. Significance of Fluidity .............................................................................................. 73
5.2. Permanent Mold or Gravity Die Casting .................................................................... 73
5.3. Slush Casting .............................................................................................................. 75
5.4. Pressure Die Casting................................................................................................... 75
5.5. Advantages of Die Casting Over Sand Casting .......................................................... 78
5.6. Comparison between Permanent Mold Casting & Die Casting ................................. 78
5.7. Shell Mold Casting ..................................................................................................... 79
5.8. Centrifugal Casting..................................................................................................... 81
5.9. Continuous Casting..................................................................................................... 83
5.10. Probable Causes & Suggested Remedies Of Various Casting Defects ...................... 84
5.11. Plastics Molding Processes......................................................................................... 87
5.11.1. Injection die Molding.......................................................................................... 88
5.11.2. Extrusion Molding............................................................................................... 89
5.12. Questions .................................................................................................................... 90

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CHAPTER ONE - Introduction to Foundry Technology
1.1. Introduction
Foundry engineering deals with the processes of making castings in moulds formed in either
sand or some other material. The art of the foundry is ancient, dating back to the dawn of
civilization. Even in prehistoric times, as far back as 5000BC, metallic objects in the form of
knives, coins, arrows, and household articles were in use, as observed from the excavations of
Mohenjodaro and Harappa. One of man’s first operations with metal was melting the ore and
pouring it into suitable moulds. The casting process is said to have been practiced in early
historic times by the craftsmen of Greek and Roman civilizations. Since then, the role of metals
has acquired unique significance. Copper and bronze were common in ancient times, but
evidence indicates that iron also had been discovered and developed in the period around 2000
BC, though its use was greatly restricted.
The earliest use of the metals was mostly for the purpose of knives, arrow points, coins, and
tools. The moulds were made in stone or sand. Around 500BC started the era of religious
upheavals, and metals began to be used for statues of gods and goddesses. Bronze was still the
most popular metal. It was at this time that lost wax process made its impact. Subsequently, a
still great application of metals figured in armory, guns and war material. Even in those days, the
superior quality of metals and absence of any impurities in them emphasize the ability and
precise quality control of the refining process.
The greatest breakthrough in the application of metal for gunnery and other arms possibly took
place at the time when Alexander was contemplating victory over the entire Eurasian continent.
Since then, the whole art of metal founding has emerged as an exact science. Today, we have a
variety of moulding processes and melting equipment and a host of metals and their alloys. And
though the techniques and methods of production have changed considerably, the basic
principles still remain almost the same.
Castings have several characteristics that clearly define their role in modern equipment used for
transportation, communication, power, agriculture, construction, and in industry. Cast metals are
required in various shapes and size and in large quantities for making machines and tools, which
in turn work to provide all the necessities and comforts of life.
Other metal-shaping processes, such as hot working, forging, machining, welding, and
stamping, are of course, necessary to fulfill a tremendous range of needs. However, certain
advantages inherent in casting-design and metallurgical advantages and in the casting process
itself, endow them with superiority over other methods.
1.2. Design Advantages ofcasting
The need of designers for objects having certain structural and functional shapes that can
withstand stress and strain, fulfill other service conditions, possess a desirable appearance, and
have an acceptable cost is remarkably satisfied by castings. The metal can be shaped to almost

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any configuration and may be produced with only slight limitations in size, accuracy, and
complexity. The main design advantages are:
i) Size: Casting may weigh as much as 200 tons or be as small as a wire of 0.5 mm
diameter. In fact, casting is the only method available for producing massive objects in
one single piece.
ii) Complexity: The most simple or complex curved surfaces, inside or outside, and
complicated shapes, which would otherwise be very difficult or impossible to
machine, forge, of fabricate, can usually be cast.
iii) Weight Saving: As the metal can be placed exactly where it is required, large saving
in weight is achieved. Such weight saving leads to increased efficiency in
transportation and economy in transport charges.
iv) Production of Prototypes: The casting process is ideally suited to the production of
models or prototypes required for creating new designs.
v) Wide Range of Properties and Versatility: Casting offer the most complete range of
mechanical and physical properties available in metal and as such fulfill a large
majority of service requirements. In fact, some alloys can only be cast to shape and
cannot be worked mechanically. Almost any requirement such as mechanical strength,
wear resistance, hardness, strength-to-weight ratio, heat and corrosion resistance,
electrical and thermal conductivity, and electrical resistance, can be satisfied by cast
alloys, in many cases, the appearance of the components plays a part in enhancing its
value. The blending together of various sections through the use of angles, curves, and
streamlining can produce a pleasing appearance in castings.
1.3. Advantages of Casting Process
i) Low Cost: Casting is usually found to be the cheapest method of metal shaping.
ii) Dimensional Accuracy: Castings can be made to fairly close dimensional tolerances
by choosing the proper type of moulding and casting process. Tolerances as close as
±0.1 mm can be achieved depending on the cast metal, the casting process, and the
shape and size of the casting. The surface finish can also be controlled and may vary
from 5 micros to 50 microns.
iii) Versatility on Production: Metal casting is adaptable to all types of production. It is
as suitable for jobbing work as for mass production. For example, a large number of
parts required for the automotive industry, agricultural implements, home appliances,
construction, and transportation are all produced by the casting process.
1.4. MetallurgicalAdvantages
i) Fibrous Structure: Wrought metals have a fibrous structure, mainly due to a stringer-
like arrangement of the inclusions of non-metallic impurities. In cast metal, the
inclusions are more or less randomly distributed during the solidification process.
When wrought metals are worked, the inclusions are strung out in the direction of
working, and so the fibrous nature results in marked directional properties. Cast alloys

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do not usually exhibit any fibering or directionality of properties, except under
unfavorable conditions of solidification.
ii) Grain Size: Although mechanical working of wrought metals causes breaking up of
coarse grain, and promotes fine grain size, many castings have grain sizes not very
different from those of the former. Most non-ferrous alloys retain the grain size
attained during freezing of the casting. Subsequent heat treatment of casting can also
help in improving the grain size.
iii) Density: The density of cast alloys is usually identical to that of wrought alloys of the
same chemical composition and heat treatment, when both are fully sound.
Today, it is becoming increasingly difficult to cope with the growing demand for various type
of castings as required for automobiles, scooters, tractors, earth-moving machinery, and railways.
Sophisticated castings needed for aeronautics, atomic energy, defense, and space research pose
yet another challenge in terms of stringent requirements fo quality. The problem is more or less
similar in all developing countries. To achieve self-reliance, the foundry industry has to accept
the challenge and quickly learn the new technology, methods, and know-how already available
and in use elsewhere. It is also possible, through a sharper awareness and greater appreciation of
the need for improved materials and more efficient methods, to increase production with the
existing level of inputs in terms of equipment and manpower. Adequate means of quality control
at all levels of production, steps to keep the wastage of materials and unproductive efforts at the
minimum through proper organization and coordination, and the use of enlightened human
relations can go a long way in enhancing production and productivity in foundries.
The whole process of producing castings may be classified into five stages:
i) Patternmaking: in the patternmaking section the patterns are designed and prepared as
per the drawing of the casting received from the planning section and according to the
moulding process to be employed. The material of the pattern may be selected from a
wide range of alternatives available, the selection depending on factors such as the
number of castings required the possibility of repeat orders and the surface finish
desired in the casting. Core boxes needed for making cores and all other auxiliary
tooling items are also manufactured in the patternmaking section.
ii) Moulding and Core-making: After the patterns are prepared, they are sent to the
moulding section. The moulds are prepared in either sand or a similar material with the
help of the patterns so that a cavity of the desired shape is produced. For obtaining
hollow portions, cores are prepared separately in core boxes. The moulds and cores area
then baked to import strength and finally assembled for pouring. The moulds and course
are then baked to import strength and finally assembled for pouring. The moulding on
the output required. Proper mould design and arrangement for flow of molten metal is
very important for the production of sound casting. The last 25 years have witnessed
far-reaching developments in the molding materials and processes.
iii) Melting and Casting: The metal of correct composition is melted in a suitable furnace.
When molten, it is taken into ladles and poured into the moulds. The moulds are then
allowed to cool down so that the metal solidifies. The castings are finally extranted by
breaking the moulds and area sent to the cleaning section.

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iv) Fettling: The castings as obtained from the moulds are not fit for immediate use or for
work in the machine shop as they carry unwanted metal attached in the form of gates,
risers, etc. sand particles also tend to adhere to the surface of the castings. The castings
are therefore sent to the fettling section where the unnecessary projections are cut off,
the adhering sand removed, and the entire surface made clean and uniform. The castings
may also need heat treatment depending on the required specific properties.
v) Testing and Inspection: Finally, before the casting is dispatched from the foundry, it is
tested and inspected to ensure that it is flawless and conforms to the desired
specifications. In case any defects or shortcomings are observed during inspection
which may render the casting unfit, analysis is necessary to determine the causes of
these defects, so as to prevent their recurrence. The production process then has to be
corrected accordingly.
1.5. Questions
1. What are the main design advantages of castings? Explain with examples.
2. Explain the metallurgical advantages of castings, in comparison to other products.
3. Describe the various stages of casting production in brief.

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CHAPTER TWO - Pattern and Core Making
2.1. Pattern
A pattern is a model or the replica of the object (to be casted). It is embedded in molding sand
and suitable ramming of molding sand around the pattern is made. The pattern is then withdrawn
for generating cavity (known as mold) in molding sand. Thus it is a mould forming tool. Pattern
can be said as a model or the replica of the object to be cast except for the various al1owances a
pattern exactly resembles the casting to be made. It may be defined as a model or form around
which sand is packed to give rise to a cavity known as mold cavity in which when molten metal
is poured, the result is the cast object. When this mould/cavity is filled with molten metal, molten
metal solidifies and produces a casting (product). So the pattern is the replica of the casting.
A pattern prepares a mold cavity for the purpose of making a casting. It may also possess
projections known as core prints for producing extra recess in the mould for placement of core to
produce hol1owness in casting. It may help in establishing seat for placement of core at locating
points on the mould in form of extra recess. It establishes the parting line and parting surfaces in
the mold. It may help to position a core in case a part of mold cavity is made with cores, before
the molding sand is rammed. It should have finished and smooth surfaces for reducing casting
defects. Runner, gates and risers used for introducing and feeding molten metal to the mold
cavity may sometimes form the parts of the pattern. The first step in casting is pattern making.
The pattern is a made of suitable material and is used for making cavity called mould in molding
sand or other suitable mould materials. When this mould is filled with molten metal and it is
allowed to solidify, it forms a reproduction of the, pattern which is known as casting. There are
some objectives of a pattern which are given as under.
Objectives of a Pattern
1. Pattern prepares a mould cavity for the purpose of making a casting.
2. Pattern possesses core prints which produces seats in form of extra recess for core
placement in the mould.
3. It establishes the parting line and parting surfaces in the mould.
4. Runner, gates and riser may form a part of the pattern.
5. Properly constructed patterns minimize overall cost of the casting.
6. Pattern may help in establishing locating pins on the mould and therefore on the casting
with a purpose to check the casting dimensions.
7. Properly made pattern having finished and smooth surface reduce casting defects.
Patterns are generally made in pattern making shop. Proper construction of pattern and its
material may reduce overal1 cost of the castings.
2.2. Common Pattern Materials
The common materials used for making patterns are wood, metal, plastic, plaster, wax or
mercury. The some important pattern materials are discussed as under.

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1. Wood
Wood is the most popular and commonly used material for pattern making. It is cheap,
easily available in abundance, repairable and easily fabricated in various forms using resin and
glues. It is very light and can produce highly smooth surface. Wood can preserve its surface by
application of a shellac coating for longer life of the pattern. But, in spite of its above qualities, it
is susceptible to shrinkage and warpage and its life is short because of the reasons that it is highly
affected by moisture of the molding sand. After some use it warps and wears out quickly as it is
having less resistance to sand abrasion. It cannot withstand rough handily and is weak in
comparison to metal. In the light of above qualities, wooden patterns are preferred only when the
numbers of castings to be produced are less. The main varieties of woods used in pattern-making
are shisham, kail, deodar, teak and mahogany.
Shisham
It is dark brown in color having golden and dark brown stripes. It is very hard to work
and blunts the cutting tool very soon during cutting. It is very strong and durable. Besides
making pattern, it is also used for making good variety of furniture, tool handles, beds, cabinets,
bridge piles, plywood etc.
Kail
It has too many knots. It is available in Himalayas and yields a close grained, moderately
hard and durable wood. It can be very well painted. Besides making pattern, it is also utilized for
making wooden doors, packing case, cheap furniture etc.
Deodar
It is white in color when soft but when hard, its color turns toward light yellow. It is
strong and durable. It gives fragrance when smelled. It has some quantity of oil and therefore it is
not easily attacked by insects. It is available in Himalayas at a height from 1500 to 3000 meters.
It is used for making pattern, manufacturing of doors, furniture, patterns, railway sleepers etc. It
is a soft wood having a close grain structure unlikely to warp. It is easily workable and its cost is
also low. It is preferred for making pattern for production of small size castings in small
quantities.
Teak Wood
It is hard, very costly and available in golden yellow or dark brown color. Special stripes
on it add to its beauty. In India, it is found in M.P. It is very strong and durable and has wide
applications. It can maintain good polish. Besides making pattern, it is used for making good
quality furniture, plywood, ships etc. It is a straight-grained light wood. It is easily workable and
has little tendency to warp. Its cost is moderate.
Mahogany
This is a hard and strong wood. Patterns made of this wood are more durable than those
of above mentioned woods and they are less likely to warp. It has got a uniform straight grain
structure and it can be easily fabricated in various shapes. It is costlier than teak and pine wood,
It is generally not preferred for high accuracy for making complicated pattern. It is also preferred
for production of small size castings in small quantities. The other Indian woods which may also
be used for pattern making are deodar, walnllt, kail, maple, birch, cherry and shisham.

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Advantages of wooden patterns
1. Wood can be easily worked.
2. It is light in weight.
3. It is easily available.
4. It is very cheap.
5. It is easy to join.
6. It is easy to obtain good surface finish.
7. Wooden laminated patterns are strong.
8. It can be easily repaired.
Disadvantages
1. It is susceptible to moisture.
2. It tends to warp.
3. It wears out quickly due to sand abrasion.
4. It is weaker than metallic patterns.
2. Metal
Metallic patterns are preferred when the number of castings required is large enough to
justify their use. These patterns are not much affected by moisture as wooden pattern. The wear
and tear of this pattern is very less and hence possesses longer life. Moreover, metal is easier to
shape the pattern with good precision, surface finish and intricacy in shapes. It can withstand
against corrosion and handling for longer period. It possesses excellent strength to weight ratio.
The main disadvantages of metallic patterns are higher cost, higher weight and tendency of
rusting. It is preferred for production of castings in large quantities with same pattern. The metals
commonly used for pattern making are cast iron, brass and bronzes and aluminum alloys.
Cast Iron
It is cheaper, stronger, tough, and durable and can produce a smooth surface finish. It also
possesses good resistance to sand abrasion. The drawbacks of cast iron patterns are that they are
hard, heavy, brittle and get rusted easily in presence of moisture.
Advantages
1. It is cheap
2. It is easy to file and fit
3. It is strong
4. It has good resistance against sand abrasion
5. Good surface finish
Disadvantages
1. It is heavy
2. It is brittle and hence it can be easily broken
3. It may rust
Brasses and Bronzes
These are heavier and expensive than cast iron and hence are preferred for manufacturing
small castings. They possess good strength, machinability and resistance to corrosion and wear.

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They can produce a better surface finish. Brass and bronze pattern is finding application in
making match plate pattern
Advantages
1. Better surface finish than cast iron.
2. Very thin sections can be easily casted.
Disadvantages
1. It is costly
2. It is heavier than cast iron.
Aluminum Alloys
Aluminum alloy patterns are more popular and best among all the metallic patterns
because of their high light ness, good surface finish, low melting point and good strength. They
also possesses good resistance to corrosion and abrasion by sand and there by enhancing longer
life of pattern. These materials do not withstand against rough handling. These have poor repair
ability and are preferred for making large castings.
Advantages
1. Aluminum alloys pattern does not rust.
2. They are easy to cast.
3. They are light in weight.
4. They can be easily machined.
Disadvantages
1. They can be damaged by sharp edges.
2. They are softer than brass and cast iron.
3. Their storing and transportation needs proper care.
White Metal (Alloy of Antimony, Copper and Lead)
Advantages
1. It is best material for lining and stripping plates.
2. It has low melting point around 260°C
3. It can be cast into narrow cavities.
Disadvantages
1. It is too soft.
2. Its storing and transportation needs proper care
3. It wears away by sand or sharp edges.
3. Plastic
Plastics are getting more popularity now a days because the patterns made of these
materials are lighter, stronger, moisture and wear resistant, non sticky to molding sand, durable
and they are not affected by the moisture of the molding sand. Moreover they impart very
smooth surface finish on the pattern surface. These materials are somewhat fragile, less resistant
to sudden loading and their section may need metal reinforcement. The plastics used for this
purpose are thermosetting resins. Phenolic resin plastics are commonly used. These are originally
in liquid form and get solidified when heated to a specified temperature. To prepare a plastic
pattern, a mould in two halves is prepared in plaster of paris with the help of a wooden pattern
known as a master pattern. The phenolic resin is poured into the mould and the mould is

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subjected to heat. The resin solidifies giving the plastic pattern. Recently a new material has
stepped into the field of plastic which is known as foam plastic. Foam plastic is now being
produced in several forms and the most common is the expandable polystyrene plastic category.
It is made from benzene and ethyl benzene.
4. Plaster
This material belongs to gypsum family which can be easily cast and worked with
wooden tools and preferable for producing highly intricate casting. The main advantages of
plaster are that it has high compressive strength and is of high expansion setting type which
compensate for the shrinkage allowance of the casting metal. Plaster of paris pattern can be
prepared either by directly pouring the slurry of plaster and water in moulds prepared earlier
from a master pattern or by sweeping it into desired shape or form by the sweep and strickle
method. It is also preferred for production of small size intricate castings and making core boxes.
5. Wax
Patterns made from wax are excellent for investment casting process. The materials used
are blends of several types of waxes, and other additives which act as polymerizing agents,
stabilizers, etc. The commonly used waxes are paraffin wax, shellac wax, bees-wax, cerasin wax,
and micro-crystalline wax. The properties desired in a good wax pattern include low ash content
up to 0.05 per cent, resistant to the primary coat material used for investment, high tensile
strength and hardness, and substantial weld strength. The general practice of making wax pattern
is to inject liquid or semi-liquid wax into a split die. Solid injection is also used to avoid
shrinkage and for better strength. Waxes use helps in imparting a high degree of surface finish
and dimensional accuracy castings. Wax patterns are prepared by pouring heated wax into split
moulds or a pair of dies. The dies after having been cooled down are parted off. Now the wax
pattern is taken out and used for molding. Such patterns need not to be drawn out solid from the
mould. After the mould is ready, the wax is poured out by heating the mould and keeping it
upside down. Such patterns are generally used in the process of investment casting where
accuracy is linked with intricacy of the cast object.
2.3. Factors Effecting Selection of Pattern Material
The following factors must be taken into consideration while selecting pattern materials.
1. Number of castings to be produced. Metal pattern are preferred when castings are
required large in number.
2. Type of mould material used.
3. Kind of molding process.
4. Method of molding (hand or machine).
5. Degree of dimensional accuracy and surface finish required.
6. Minimum thickness required.
7. Shape, complexity and size of casting.
8. Cost of pattern and chances of repeat orders of the pattern
2.4. Typesof Pattern
The types of the pattern and the description of each are given as under.

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1. One piece or solid pattern
2. Two piece or split pattern
3. Cope and drag pattern
4. Three-piece or multi- piece pattern
5. Loose piece pattern
6. Match plate pattern
7. Follow board pattern
8. Gated pattern
9. Sweep pattern
10. Skeleton pattern
11. Segmental or part pattern
1. Single-piece or solid pattern
Solid pattern is made of single piece without joints, partings lines or loose pieces. It is the
simplest form of the pattern. Typical single piece pattern is shown in Fig. 2.1.
Fig. 2.1 Single-piece or Solid Pattern
2. Two-piece or split pattern
When solid pattern is difficult for withdrawal from the mold cavity, then solid pattern is splited
in two parts. Split pattern is made in two pieces which are joined at the parting line by means of
dowel pins. The splitting at the parting line is done to facilitate the withdrawal of the pattern. A
typical example is shown in Fig. 2.2.
Fig. 2.2 Two Piece Pattern

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3. Cope and drag pattern
In this case, cope and drag part of the mould are prepared separately. This is done when the
complete mould is too heavy to be handled by one operator. The pattern is made up of two
halves, which are mounted on different plates. A typical example of match plate pattern is shown
in Fig. 2.3.
Fig. 2.3 Cope and drag pattern
4. Three-piece or multi-piece pattern
Some patterns are of complicated kind in shape and hence cannot be made in one or two pieces
because of difficulty in withdrawing the pattern. Therefore these patterns are made in either three
pieces or in multi-pieces. Multi molding flasks are needed to make mold from these patterns. A
typical example of three-piece pattern is shown in Fig. 2.4.
Fig 2.4 Three-piece or Multi-piece Pattern
5. Loose-piece Pattern
Loose piece pattern (Fig. 2.5) is used when pattern is difficult for withdrawal from the mould.
Loose pieces are provided on the pattern and they are the part of pattern. The main pattern is
removed first leaving the loose piece portion of the pattern in the mould. Finally the loose piece
is withdrawal separately leaving the intricate mould.
Fig 2.5 Loose-piece Pattern

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6. Match plate pattern
This pattern is made in two halves and is on mounted on the opposite sides of a wooden or
metallic plate, known as match plate. The gates and runners are also attached to the plate. This
pattern is used in machine molding. A typical example of match plate pattern is shown in Fig.
2.6.
Fig. 2.6 Match plate pattern
7. Follow board pattern
When the use of solid or split patterns becomes difficult, a contour corresponding to the exact
shape of one half of the pattern is made in a wooden board, which is called a follow board and it
acts as a molding board for the first molding operation as shown in Fig. 2.7.
Fig. 2.7 Follow board pattern
8. Gated pattern
In the mass production of casings, multi cavity moulds are used. Such moulds are formed by
joining a number of patterns and gates and providing a common runner for the molten metal, as
shown in Fig. 2.8. These patterns are made of metals, and metallic pieces to form gates and
runners are attached to the pattern.
Fig. 2.8 Gated pattern
9. Sweep pattern
Sweep patterns are used for forming large circular moulds of symmetric kind by revolving a
sweep attached to a spindle as shown in Fig. 2.9. Actually a sweep is a template of wood or
metal and is attached to the spindle at one edge and the other edge has a contour depending upon

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the desired shape of the mould. The pivot end is attached to a stake of metal in the center of the
mould.
Fig. 2.9 Sweep pattern
10. Skeleton pattern
When only a small number of large and heavy castings are to be made, it is not economical to
make a solid pattern. In such cases, however, a skeleton pattern may be used. This is a ribbed
construction of wood which forms an outline of the pattern to be made. This frame work is filled
with loam sand and rammed. The surplus sand is removed by strickle board. For round shapes,
the pattern is made in two halves which are joined with glue or by means of screws etc. A typical
skeleton pattern is shown in Fig. 2.10.
Fig. 2.10 Skeleton pattern
11. Segmental pattern
Patterns of this type are generally used for circular castings, for example wheel rim, gear blank
etc. Such patterns are sections of a pattern so arranged as to form a complete mould by being
moved to form each section of the mould. The movement of segmental pattern is guided by the
use of a central pivot. A segment pattern for a wheel rim is shown in Fig. 2.11.

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Fig. 2.11 Segmental or part pattern
2.5. Pattern Allowances
Pattern may be made from wood or metal and its color may not be same as that of the casting.
The material of the pattern is not necessarily same as that of the casting. Pattern carries an
additional allowance to compensate for metal shrinkage. It carries additional allowance for
machining. It carries the necessary draft to enable its easy removal from the sand mass. It carries
distortions allowance also. Due to distortion allowance, the shape of casting is opposite to
pattern. Pattern may carry additional projections, called core prints to produce seats or extra
recess in mold for setting or adjustment or location for cores in mold cavity. It may be in pieces
(more than one piece) whereas casting is in one piece. Sharp changes are not provided on the
patterns. These are provided on the casting with the help of machining. Surface finish may not be
same as that of casting.
The size of a pattern is never kept the same as that of the desired casting because of the fact that
during cooling the casting is subjected to various effects and hence to compensate for these
effects, corresponding allowances are given in the pattern. These various allowances given to
pattern can be enumerated as, allowance for shrinkage, allowance for machining, allowance for
draft, allowance for rapping or shake, allowance for distortion and allowance for mould wall
movement. These allowances are discussed as under.
2.5.1. Shrinkage Allowance
In practice it is found that all common cast metals shrink a significant amount when they are
cooled from the molten state. The total contraction in volume is divided into the following parts:
1. Liquid contraction, i.e. the contraction during the period in which the temperature of the
liquid metal or alloy falls from the pouring temperature to the liquidus temperature.
2. Contraction on cooling from the liquidus to the solidus temperature, i.e. solidifying
contraction.
3. Contraction that results thereafter until the temperature reaches the room temperature.
This is known as solid contraction.
The first two of the above are taken care of by proper gating and risering. Only the last one, i.e.
the solid contraction is taken care by the pattern makers by giving a positive shrinkage
allowance. This contraction allowance is different for different metals. The contraction
allowances for different metals are listed in table 2.1 below.

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Sr.No. Metal contraction (percent)
Contraction (mm per
meter)
1 Grey Cast Iron 07 to 1.05 7 to 10.5
2 White Cast Iron 2.1 21
3 Malleable Iron 1.5 15
4 Steel 2.0 20
5 Brass 1.4 14
6 Aluminum 1.8 18
7 Aluminum Alloys 1.3 to 1.6 13 to 16
8 Bronze 1.05 to 2.1 10.5 to 21
9 Magnesium 1.8 18
10 Zinc 2.5 25
11 Manganese Steel 2.6 26
Table 2.1 Contraction (Shrinkage) for different metals and alloys
In fact, there is a special rule known as the pattern marks contraction rule in which the shrinkage
of the casting metals is added. It is similar in shape as that of a common rule but is slightly
bigger than the latter depending upon the metal for which it is intended.
2.5.2. Machining Allowance
It is a positive allowance given to compensate for the amount of material that is lost in
machining or finishing the casting. If this allowance is not given, the casting will become
undersize after machining. The amount of this allowance depends on the size of casting, methods
of machining and the degree of finish.
Dimension (mm)
Allowance (mm)
Bore (internal
diameter)
Outside Surface Cope Side
Cast Iron
Up to 200 3.0 3.0 5.5
200 to 400 4.5 4.0 6.0
400 to 700 5.0 4.5 7.0
700 to 1100 7.0 6.0 8.0
Non Ferrous
Up to 200 1.5 1.5 2.0
200 to 400 2.0 1.5 3.0
400 to 700 3.0 2.5 3.0
700 to 1100 4.0 2.5 3.5
Table 2.2 Machining Allowances recommended for different cast metals for sand castings
2.5.3. Draft or Taper Allowance
Taper allowance (Fig. 2.12) is also a positive allowance and is given on all the vertical surfaces
of pattern so that its withdrawal becomes easier. The normal amount of taper on the external

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surfaces varies from 10 mm to 20 mm/m. On interior holes and recesses which are smaller in
size, the taper should be around 60 mm/m. These values are greatly affected by the size of the
pattern and the molding method. In machine molding its, value varies from 10 mm to 50 mm/m.
Fig. 2.12 Draft allowance
2.5.4. Rapping or Shake Allowance
Before withdrawing the pattern it is rapped and thereby the size of the mould cavity increases.
Actually by rapping, the external sections move outwards increasing the size and internal
sections move inwards decreasing the size. This movement may be insignificant in the case of
small and medium size castings, but it is significant in the case of large castings. This allowance
is kept negative and hence the pattern is made slightly smaller in dimensions 0.5-1.0 mm.
2.5.5. Distortion Allowance
This allowance is applied to the castings which have the tendency to distort during cooling due to
thermal stresses developed. For example a casting in the form of U shape will contract at the
closed end on cooling, while the open end will remain fixed in position. Therefore, to avoid the
distortion, the legs of U pattern must converge slightly so that the sides will remain parallel after
cooling.
2.5.6. Mold wall Movement Allowance
Mold wall movement in sand moulds occurs as a result of heat and static pressure on the surface
layer of sand at the mold metal interface. In ferrous castings, it is also due to expansion due to
graphitization. This enlargement in the mold cavity depends upon the mold density and mould
composition. This effect becomes more pronounced with increase in moisture content and
temperature.
2.6. Core and Core Box
Cores are compact mass of core sand that when placed in mould cavity at required location with
proper alignment does not allow the molten metal to occupy space for solidification in that
portion and hence help to produce hollowness in the casting. The environment in which the core
is placed is much different from that of the mold. In fact the core has to withstand the severe
action of hot metal which completely surrounds it. Cores are classified according to shape and
position in the mold. There are various types of cores such as horizontal core (Fig. 2.13), vertical
core (Fig. 2.14), balanced core (Fig. 2.15), drop core (Fig. 2.16) and hanging core (Fig. 2.17).

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Fig. 2.13 Horizontal core
Fig. 2.14 Vertical core
Fig. 2.15 Balanced core
Fig. 2.16 Drop core

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Fig. 2.17 Hanging core
There are various functions of cores which are given below
1. Core is used to produce hollowness in castings in form of internal cavities.
2. It may form a part of green sand mold
3. It may be deployed to improve mold surface.
4. It may provide external undercut features in casting.
5. It may be used to strengthen the mold.
6. It may be used to form gating system of large size mold
7. It may be inserted to achieve deep recesses in the casting
2.6.1. Core Box
Any kind of hollowness in form of holes and recesses in castings is obtained by the use of cores.
Cores are made by means of core boxes comprising of either single or in two parts. Core boxes
are generally made of wood or metal and are of several types. The main types of core box are
half core box, dump core box, split core box, strickle core box, right and left hand core box and
loose piece core box.
1. Half core box
This is the most common type of core box. The two identical halves of a symmetrical core
prepared in the half core box are shown in Fig. 2.18. Two halves of cores are pasted or cemented
together after baking to form a complete core.
Fig. 2.18 Half core-box
2. Dump core box
Dump core box is similar in construction to half core box as shown in Fig. 2.19. The cores
produced do not require pasting, rather they are complete by themselves. If the core produced is
in the shape of a slab, then it is called as a slab box or a rectangular box. A dump core-box is
used to prepare complete core in it. Generally cylindrical and rectangular cores are prepared in
these boxes.

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Fig. 2.19 Dump core-box
3. Split core box
Split core boxes are made in two parts as shown in Fig. 2.20. They form the complete core by
only one ramming. The two parts of core boxes are held in position by means of clamps and their
alignment is maintained by means of dowel pins and thus core is produced.
Fig. 2.20 Split core-box
4. Right and left hand core box
Sometimes the cores are not symmetrical about the center line. In such cases, right and left hand
core boxes are used. The two halves of a core made in the same core box are not identical and
they cannot be pasted together.
5. Strickle core box
This type of core box is used when a core with an irregular shape is desired. The required shape
is achieved by striking oft the core sand from the top of the core box with a wooden piece, called
as strickle board. The strickle board has the same contour as that of the required core.
6. Loose piece core box
Loose piece core boxes are highly suitable for making cores where provision for bosses, hubs
etc. is required. In such cases, the loose pieces may be located by dowels, nails and dovetails etc.
In certain cases, with the help of loose pieces, a single core box can be made to generate both
halves of the right-left core.
2.7. Core Box Allowances
Materials used in making core generally swell and increase in size. This may lead to increase the
size of core. The larger cores sometimes tend to become still larger. This increase in size may not

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be significant in small cores, but it is quite significant in large cores and therefore certain amount
of allowance should be given on the core boxes to compensate for this increase the cores. It is
not possible to lay down a rule for the amount of this allowance as this will depend upon the
material used, but it is customary to give a negative allowance of 5 mm /m.
2.8. Color Codification for Patterns and Core Boxes
There is no set or accepted standard for representing of various surfaces of pattern and core
boxes by different colors. The practice of representing of various pattern surfaces by different
colors varies with from country to country and sometimes with different manufactures within the
country. Out of the various color codifications, the American practice is the most popular. In this
practice, the color identification is as follows. Surfaces to be left unfinished after casting are to
be painted as black. Surface to be machined are painted as red. Core prints are painted as yellow.
Seats for loose pieces are painted as red stripes on yellow background. Stop-offs is painted as
black stripes on yellow base.
2.9. Core Prints
When a hole blind or through is needed in the casting, a core is placed in the mould cavity to
produce the same. The core has to be properly located or positioned in the mould cavity on pre-
formed recesses or impressions in the sand. To form these recesses or impressions for generating
seat for placement of core, extra projections are added on the pattern surface at proper places.
These extra projections on the pattern (used for producing recesses in the mould for placement of
cores at that location) are known as core prints. Core prints may be of horizontal, vertical,
balanced, wing and core types. Horizontal core print produces seats for horizontal core in the
mould. Vertical core print produces seats to support a vertical core in the mould. Balanced core
print produces a single seat on one side of the mould and the core remains partly in this formed
seat and partly in the mould cavity, the two portions balancing each other. The hanging portion
of the core may be supported on chaplets. Wing core print is used to form a seat for a wing core.
Cover core print forms seat to support a cover core.
2.10. Wooden Pattern & Wooden Core Box Making Tools
The job of patternmaker is basically done by a carpenter. The tools required for making patterns,
therefore do not much differ from those used by a carpenter, excepting the special tools as per
the needs of the trade. In addition to tools used by a carpenter, there is one more tool named as
the contraction rule, which is a measuring tool of the patternmaker’s trade. All castings shrinks
during cooling from the molten state, and patterns have to be made correspondingly larger than
the required casting in order to compensate for the loss in size due to this shrinkage. Various
metals and alloys have various shrinkages. The allowance for shrinkage, therefore, varies with
various metals and also according to particular casting conditions, and hence the size of the
pattern is proportionally increased. A separate scale is available for each allowance, and it
enables the dimensions to be set out directly during laying out of the patterns. The rule usually
employed the one that has two scales on each side, the total number of scales being four for four
commonly cast metals namely, steel, cast iron, brass and aluminum. To compensate for

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contraction or shrinkage, the graduations are oversized by a proportionate amount, e.g. on 1 mm
or 1 per cent scale each 100 cm is longer by 1 cm. The general tools and equipment used in the
pattern making shop are given as under.
1. Measuring and Layout Tools
1. Wooden or steel scale or rule
2. Dividers
3. Calipers
4. Try square
5. Caliper rule
6. Flexible rule
7. Marking gauge
8. T-bevel
9. Combination square
2. Sawing Tools
1. Compass saw
2. Rip saw
3. Coping saw
4. Dovetail saw
5. Back saw
6. Panel saw
7. Miter saw
3. Planning Tools
1. Jack plane
2. Circular plane
3. Router plane
4. Rabbet plane
5. Block plane
6. Bench plane
7. Core box plane
4. Boring Tools
1. Hand operated drills
2. Machine operated drills
3. Twist drill
4. Countersunk
5. Brace
6. Auger bit
7. Bit gauge
5. Clamping Tools
1. Bench vice
2. C-clamp
3. Bar clamp
4. Hand screw

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5. Pattern maker’s vice
6. Pinch dog
6. Miscellaneous Tools
1. Screw Driver
2. Vaious types of hammers
3. Chisel
4. Rasp
5. File
6. Nail set
7. Screw driver
8. Bradawl
9. Brad pusher
10. Cornering tool
2.11. Wooden Pattern & Wooden Core Box Making Machines
Modern wooden pattern and wooden core making shop requires various wood working machines
for quick and mass production of patterns and core boxes. Some of the commonly machines used
in making patterns and core boxes of various kinds of wood are discussed as under.
1. Wood Turning Lathe. Patterns for cylindrical castings are made by this lathe.
2. Abrasive Disc Machine. It is used for shaping or finishing flat surfaces on small pieces
of wood.
3. Abrasive Belt Machine. It makes use of an endless abrasive belt. It is used in shaping
the patterns.
4. Circular Saw. It is used for ripping, cross cutting, beveling and grooving.
5. Band Saw. It is designed to cut wood by means of an endless metal saw band.
6. Jig or Scroll Saw. It is used for making intricate irregular cuts on small work.
7. Jointer. The jointer planes the wood by the action of the revolving cutter head.
8. Drill Press. It is used for drilling, boring, mortising, shaping etc.
9. Grinder. It is used for shaping and sharpening the tools.
10. Wood Trimmer. It is used for mitering the moldings accurately.
11. Wood Shaper. It is used for imparting the different shapes to the wood.
12. Wood Planer. Its purpose is similar to jointer but it is specially designed for planning
larger size.
13. Tennoner. These are used for sawing (accurate shape and size).
14. Mortiser. It is used to facilitate the cutting of mortise and tenon.
2.12. Design Considerations in Pattern Making
The following considerations should always be kept in mind while designing a pattern.
1. All Abrupt changes in section of the pattern should be avoided as far as possible.
2. Parting line should be selected carefully, so as to allow as small portion of the pattern as
far as possible in the cope area
3. The thickness and section of the pattern should be kept as uniform as possible.

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4. Sharp corners and edges should be supported by suitable fillets or otherwise rounded of.
It will facilitate easy withdrawal of pattern, smooth flow of molten metal and ensure a
sound casting.
5. Surfaces of the casting which are specifically required to be perfectly sound and clean
should be so designed that they will be molded in the drag because the possible defects
due to loose sand and inclusions will occur in the cope.
6. As far as possible, full cores should be used instead of cemented half cores for reducing
cost and for accuracy.
7. For mass production, the use of several patterns in a mould with common riser is to be
preferred.
8. The pattern should have very good surface finish as it directly affects the corresponding
finish of the casting.
9. Shape and size of the casting and that of the core should be carefully considered to decide
the size and location of the core prints.
10. Proper material should always be selected for the pattern after carefully analyzing the
factors responsible for their selection.
11. Try to employ full cores always instead of jointed half cores as far as possible. This will
reduce cost and ensure greater dimensional accuracy.
12. The use of offset parting, instead of cores as for as possible should be encouraged to the
great extent.
13. For large scale production of small castings, the use of gated or match- plate patterns
should be preferred wherever the existing facilities permit.
14. If gates, runners and risers are required to be attached with the pattern, they should be
properly located and their sudden variation in dimensions should be avoided.
15. Wherever there is a sharp corner, a fillet should be provided, and the corners may be
rounded up for easy withdrawal of patterns as well as easy flow of molten metal in the
mould.
16. Proper allowances should be provided, wherever necessary.
17. As for as possible, the pattern should have a good surface finish because the surface
finish of the casting depends totally on the surface finish of the pattern and the kind of
facing of the mold cavity.
2.13. Pattern Layout
After deciding the molding method and form of pattern, planning for the development of
complete pattern is made which may be in two different stages. The first stage is to prepare a
layout of the different parts of the pattern. The next stage is to shape them. The layout
preparation consists of measuring, marking, and setting out the dimensions on a layout board
including needed allowances. The first step in laying out is to study the working drawing
carefully and select a suitable board of wood that can accommodate at least two views of the
same on full size scale. The next step is to decide a working face of the board and plane an
adjacent edge smooth and square with the said face. Select a proper contraction scale for
measuring and marking dimensions according to the material of the casting. Further the layout is

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prepared properly and neatly using different measuring and making tools specifying the locations
of core prints and machined surfaces. Finally on completion of the layout, check carefully the
dimension and other requirements by incorporating all necessary pattern allowances before
starting construction of the pattern.
2.14. Pattern Construction
On preparing the pattern layout, the construction for making it is started by studying the layout
and deciding the location of parting surfaces. From the layout, try to visualize the shape of the
pattern and determine the number of separate pieces to be made and the process to be employed
for making them. Then the main part of pattern body is first constructed using pattern making
tools. The direction of wood grains is kept along the length of pattern as far as possible to ensure
due strength and accuracy. Further cut and shape the other different parts of pattern providing
adequate draft on them. The prepared parts are then checked by placing them over the prepared
layout. Further the different parts of the pattern are assembled with the main body in proper
position by gluing or by means of dowels as the case may be. Next the relative locations of all
the assembled parts on the pattern are adjusted carefully. Then, the completed pattern is checked
for accuracy. Next all the rough surfaces of pattern are finished and imparted with a thin coating
of shellac varnish. The wax or leather fillets are then fitted wherever necessary. Wooden fillets
should also be fitted before sanding and finishing. The pattern surface once again prepared for
good surface and give final coat of shellac. Finally different parts or surfaces of pattern are
colored with specific colors mixed in shellac or by painting as per coloring specifications.
2.15. Questions
1. Define pattern? What is the difference between pattern and casting?
2. What is Pattern? How does it differ from the actual product to be made from it?
3. What important considerations a pattern-maker has to make before planning a pattern?
4. What are the common allowances provided on patterns and why?
5. What are the factors which govern the selection of a proper material for patternmaking?
6. What are master patterns? How does their size differ from other patterns? Explain.
7. Discuss the utility of unserviceable parts as patterns.
8. What are the allowances provided to the patterns?
9. Discuss the various positive and negative allowances provided to the patterns.
10. Discuss briefly the match plate pattern with the help of suitable sketch. ?
11. Where skeleton patterns are used and what is the advantage?
12. Sketch and describe the use and advantages of a gated pattern?
13. Give common materials used for pattern making? Discuss their merits and demerits?
14. Write short notes on the following:
i. Contraction scale,
ii. Uses of fillets on patterns, and
iii. Pattern with loose pieces
iv. Uses of cores
15. Discus briefly the various types of patterns used in foundry shop?

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16. Define the following?
a. Core prints
b. Mould or cavity
c. Core boxes
d. Shrinkage allowance
e. Chaplets
f. Chills
17. Discuss briefly the various functions of a pattern?
18. Write the color coding for patterns and core boxes?

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CHAPTER THREE - Foundry Tools and Equipment
3.1. Introduction
There are large number of tools and equipment used in foundry shop for carrying out different
operations such as sand preparation, molding, melting, pouring and casting. They can be broadly
classified as hand tools, sand conditioning tool, flasks, power operated equipment, metal melting
equipment and fettling and finishing equipment. Different kinds of hand tools are used by molder
in mold making operations. Sand conditioning tools are basically used for preparing the various
types of molding sands and core sand. Flasks are commonly used for preparing sand moulds and
keeping molten metal and also for handling the same from place to place. Power operated
equipment are used for mechanizing processes in foundries. They include various types of
molding machines, power riddles, sand mixers and conveyors, grinders etc. Metal melting
equipment includes various types of melting furnaces such as cupola, pit furnace, crucible
furnaces etc. Fettling and finishing equipment are also used in foundry work for cleaning and
finishing the casting. General tools and equipment used in foundry are discussed as under.
3.2. Hand Tools Used in FoundryShop
The common hand tools used in foundry shop are fairly numerous. A brief description of the
following foundry tools (Fig. 3.1) used frequently by molder is given as under.
Hand riddle
Hand riddle is shown in Fig. 3.1(a). It consists of a screen of standard circular wire mesh
equipped with circular wooden frame. It is generally used for cleaning the sand for removing
foreign material such as nails, shot metal, splinters of wood etc. from it. Even power operated
riddles are available for riddling large volume of sand.
Fig. 3.1 (a)
Shovel
Shovel is shown in Fig. 3.1(b). It consists of a steel pan fitted with a long wooden handle. It is
used in mixing, tempering and conditioning the foundry sand by hand. It is also used for moving
and transforming the molding sand to the container and molding box or flask. It should always
be kept clean.

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Rammers
Rammers are shown in Fig. 3.1(c). These are required for striking the molding sand mass in the
molding box to pack or compact it uniformly all around the pattern. The common forms of
rammers used in ramming are hand rammer, peen rammer, floor rammer and pneumatic rammer
which are briefly described as
Fig. 3.1 (b) Fig. 3.1 (c)
(i) Hand rammer
It is generally made of wood or metal. It is small and one end of which carries a wedge type
construction, called peen and the other end possesses a solid cylindrical shape known as butt. It
is used for ramming the sand in bench molding work.
(ii) Peen rammer
It has a wedge-shaped construction formed at the bottom of a metallic rod. It is generally used in
packing the molding sand in pockets and comers.
(iii) Floor rammer
It consists of a long steel bar carrying a peen at one end and a flat portion on the other. It is a
heavier and larger in comparison to hand rammer. Its specific use is in floor molding for
ramming the sand for larger molds. Due to its large length, the molder can operate it in standing
position.
(iv) Pneumatic rammers
They save considerable time and labor and are used for making large molds.
Sprue pin
Sprue pin is shown in Fig. 3.1(d). It is a tapered rod of wood or iron which is placed or pushed in
cope to join mold cavity while the molding sand in the cope is being rammed. Later its
withdrawal from cope produce a vertical hole in molding sand, called sprue through which the
molten metal is poured into the mould using gating system. It helps to make a passage for
pouring molten metal in mold through gating system

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Fig. 3.1 (d)
Strike off bar
Strike off bar (Fig. 3.1(e)) is a flat bar having straight edge and is made of wood or iron. It is
used to strike off or remove the excess sand from the top of a molding box after completion of
ramming thereby making its surface plane and smooth. Its one edge is made beveled and the
other end is kept perfectly smooth and plane.
Fig. 3.1 (e)
Mallet
Mallet is similar to a wooden hammer and is generally as used in carpentry or sheet metal shops.
In molding shop, it is used for driving the draw spike into the pattern and then rapping it for
separation from the mould surfaces so that pattern can be easily withdrawn leaving the mold
cavity without damaging the mold surfaces.
Draw spike
Draw spike is shown Fig. 3.1(f). It is a tapered steel rod having a loop or ring at its one end and a
sharp point at the other. It may have screw threads on the end to engage metal pattern for it
withdrawal from the mold. It is used for driven into pattern which is embedded in the molding
sand and raps the pattern to get separated from the pattern and finally draws out it from the mold
cavity.
Fig. 3.1 (f) Fig. 3.1 (g)

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Vent rod
Vent rod is shown in Fig. 3.1(g). It is a thin spiked steel rod or wire carrying a pointed edge at
one end and a wooden handle or a bent loop at the other. After ramming and striking off the
excess sand it is utilized to pierce series of small holes in the molding sand in the cope portion.
The series of pierced small holes are called vents holes which allow the exit or escape of steam
and gases during pouring mold and solidifying of the molten metal for getting a sound casting.
Lifters
Lifters are shown in Fig. 3.1(h, i, j and k). They are also known as cleaners or finishing tool
which are made of thin sections of steel of various length and width with one end bent 200
Introduction to Basic Manufacturing Processes and Workshop Technology at right angle. They
are used for cleaning, repairing and finishing the bottom and sides of deep and narrow openings
in mold cavity after withdrawal of pattern. They are also used for removing loose sand from
mold cavity.
Fig. 3.1 (h) Fig. 3.1 (i)
Fig. 3.1 (j) Fig. 3.1 (k)
Trowels
Trowels are shown in Fig. 3.1(l, m and n). They are utilized for finishing flat surfaces and joints
and partings lines of the mold. They consist of metal blade made of iron and are equipped with a
wooden handle. The common metal blade shapes of trowels may be pointed or contoured or
rectangular oriented. The trowels are basically employed for smoothing or slicking the surfaces
of molds. They may also be used to cut in-gates and repair the mold surfaces.
Fig. 3.1 (l) Fig. 3.1 (m)
Fig. 3.1 (n)

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Slicks
Slicks are shown in Fig. 3.1(o, p, q, and r). They are also recognized as small double ended mold
finishing tool which are generally used for repairing and finishing the mold surfaces and their
edges after withdrawal of the pattern. The commonly used slicks are of the types of heart and
leaf, square and heart, spoon and bead and heart and spoon. The nomenclatures of the slicks are
largely due to their shapes.
Fig. 3.1 (o) Fig. 3.1 (p)
Fig. 3.1 (q) Fig. 3.1 (r)
Smoothers
Smothers are shown in Fig. 3.1(s and t). According to their use and shape they are given different
names. They are also known as finishing tools which are commonly used for repairing and
finishing flat and round surfaces, round or square corners and edges of molds.
Fig. 3.1 (s) Fig. 3.1 (t)
Swab
Swab is shown in Fig. 3.1(u). It is a small hemp fiber brush used for moistening the edges of
sand mould, which are in contact with the pattern surface before withdrawing the pattern. It is
used for sweeping away the molding sand from the mold surface and pattern. It is also used for
coating the liquid blacking on the mold faces in dry sand molds.
Spirit level
Spirit level is used by molder to check whether the sand bed or molding box is horizontal or not.
Fig. 3.1 (u)

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Gate cutter
Gate cutter (Fig. 3.1(v)) is a small shaped piece of sheet metal commonly used to cut runners and
feeding gates for connecting sprue hole with the mold cavity.
Fig 3.1 (v)
Gaggers
Gaggers are pieces of wires or rods bent at one or both ends which are used for reinforcing the
downward projecting sand mass in the cope are known as gaggers. They support hanging bodies
of sand. They possess a length varying from 2 to 50 cm. A gagger is always used in cope area
and it may reach up to 6 mm away from the pattern. It should be coated with clay wash so that
the sand adheres to it. Its surface should be rough in order to have a good grip with the molding
sand. It is made up of steel reinforcing bar.
Spray-gun
Spray gun is mainly used to spray coating of facing materials etc. on a mold or core surface.
Nails and wire pieces
They are basically used to reinforce thin projections of sand in the mold or cores.
Wire pieces, spring and nails
They are commonly used to reinforce thin projections of sand in molds or cores. They are also
used to fasten cores in molds and reinforce sand in front of an in-gate.
Bellows
Bellows gun is shown in Fig. 3.1(w). It is hand operated leather made device equipped with
compressed air jet to blow or pump air when operated. It is used to blow away the loose or
unwanted sand from the surfaces of mold cavities.
Fig. 3.1 (w)
Fig. 3.1 (a–w) Common hand tools used in foundry
Clamps, cotters and wedges
They are made of steel and are used for clamping the molding boxes firmly together during
pouring.
3.3. Flasks
The common flasks are also called as containers which are used in foundry shop as mold boxes,
crucibles and ladles.

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1. Moulding Boxes
Mold boxes are also known as molding flasks. Boxes used in sand molding are of two types:
(a) Open molding boxes. Open molding boxes are shown in Fig. 3.2. They are made with the
hinge at one corner and a lock on the opposite corner. They are also known as snap molding
boxes which are generally used for making sand molds. A snap molding is made of wood and is
hinged at one corner. It has special applications in bench molding in green sand work for small
nonferrous castings. The mold is first made in the snap flask and then it is removed and replaced
by a steel jacket. Thus, a number of molds can be prepared using the same set of boxes. As an
alternative to the wooden snap boxes the cast-aluminum tapered closed boxes are finding favor
in modern foundries. They carry a tapered inside surface which is accurately ground and
finished. A solid structure of this box gives more rigidity and strength than the open type. These
boxes are also removed after assembling the mould. Large molding boxes are equipped with
reinforcing cross bars and ribs to hold the heavy mass of sand and support gaggers. The size,
material and construction of the molding box depend upon the size of the casting.
Fig. 3.2 Open molding box
(b) Closed molding boxes. Closed molding boxes are shown in Fig. 3.3 which may be made of
wood, cast-iron or steel and consist of two or more parts. The lower part is called the drag, the
upper part the cope and all the intermediate parts, if used, cheeks. All the parts are individually
equipped with suitable means for clamping arrangements during pouring. Wooden Boxes are
generally used in green-sand molding. Dry sand moulds always require metallic boxes because
they are heated for drying. Large and heavy boxes are made from cast iron or steel and carry
handles and grips as they are manipulated by cranes or hoists, etc. Closed metallic molding
boxes may be called as a closed rectangular molding box (Fig. 3.3) or a closed round molding
box (Fig. 3.4).

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Fig. 3.3 Closed rectangular molding box
2. Crucible
Crucibles are made from graphite or steel shell lined with suitable refractory material like fire
clay. They are commonly named as metal melting pots. The raw material or charge is broken into
small pieces and placed in them. They are then placed in pit furnaces which are coke-fired. In
oilfired tilting furnaces, they form an integral part of the furnace itself and the charge is put into
them while they are in position. After melting of metals in crucibles, they are taken out and
received in crucible handle. Pouring of molten is generally done directly by them instead of
transferring the molten metal to ladles. But in the case of an oilfired furnace, the molten metal is
first received in a ladle and then poured into the molds.
Fig. 3.4 Closed round molding box
3. Ladle
It is similar in shape to the crucible which is also made from graphite or steel shell lined with
suitable refractory material like fire clay. It is commonly used to receive molten metal from the
melting furnace and pour the same into the mold cavity. Its size is designated by its capacity.
Small hand shank ladles are used by a single foundry personal and are provided with only one
handle. It may be available in different capacities up to 20 kg. Medium and large size ladles are
provided with handles on both sides to be handled by two foundry personals. They are available
in various sizes with their capacity varying from 30 kg to 150 kg. Extremely large sizes, with
capacities ranging from 250 kg to 1000 kg, are found in crane ladles. Geared crane ladles can
hold even more than 1000 kg of molten metal. The handling of ladles can be mechanized for

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good pouring control and ensuring better safety for foundry personals workers. All the ladles
consist of an outer casing made of steel or plate bent in proper shape and then welded. Inside this
casing, a refractory lining is provided. At its top, the casing is shaped to have a controlled and
well directed flow of molten metal. They are commonly used to transport molten metal from
furnace to mold
3.4. Power OperatedEquipment
Power operated foundry equipment generally used in foundries are different types of molding
machines and sand slingers, core making, core baking equipment, power riddles, mechanical
conveyors, sand mixers, material handling equipment and sand aerators etc. Few commonly used
types of such equipment are discussed as under.
3.4.1. Moulding Machines
Molding machine acts as a device by means of a large number of co-related parts and
mechanisms, transmits and directs various forces and motions in required directions so as to help
the preparation of a sand mould. The major functions of molding machines involves ramming of
molding sand, rolling over or inverting the mould, rapping the pattern and withdrawing the
pattern from the mould. Most of the molding machines perform a combination of two or more of
functions. However, ramming of sand is the basic function of most of these machines. Use of
molding machine is advisable when large number of repetitive castings is to be produced as hand
molding may be tedious, time consuming, laborious and expensive comparatively.
3.4.2. Classification of Moulding Machines
The large variety of molding machines that are available in different designs which can be
classified as squeezer machine, jolt machine, jolt-squeezer machine, slinging machines, pattern
draw machines and roll over machines. These varieties of machines are discussed as under.
3.4.2.1. Squeezer machine
These machines may be hand operated or power operated. The pattern is placed over the machine
table, followed by the molding box. In hand-operated machines, the platen is lifted by hand
operated mechanism. In power machines, it is lifted by the air pressure on a piston in the cylinder
in the same way as in jolt machine. The table is raised gradually. The sand in the molding box is
squeezed between plate and the upward rising table thus enabling a uniform pressing of sand in
the molding box. The main advantage of power operated machines in comparison hand operated
machines is that more pressure can be applied in power operated.
3.4.2.2. Jolt machine
This machine is also known as jar machine which comprises of air operated piston and cylinder.
The air is allowed to enter from the bottom side of the cylinder and acts on the bottom face of the
piston to raise it up. The platen or table of the machine is attached at the top of the piston which
carries the pattern and molding box with sand filled in it. The upward movement of piston raises
the table to a certain height and the air below the piston is suddenly released, resulting in uniform

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packing of sand around the pattern in the molding box. This process is repeated several times
rapidly. This operation is known as jolting technique.
3.4.2.3. Jolt-squeezer machine
It uses the principle of both jolt and squeezer machines in which complete mould is prepared.
The cope, match plate and drag are assembled on the machine table in a reverse position, that is,
the drag on the top and the cope below. Initially the drag is filled with sand followed by ramming
by the jolting action of the table. After leveling off the sand on the upper surface, the assembly is
turned upside down and placed over a bottom board placed on the table. Next, the cope is filled
up with sand and is rammed by squeezing between the overhead plate and the machine table. The
overhead plate is then swung aside and sand on the top leveled off, cope is next removed and the
drag is vibrated by air vibrator. This is followed by removal of match plate and closing of two
halves of the mold for pouring the molten metal. This machine is used to overcome the
drawbacks of both squeeze and jolt principles of ramming molding sand.
3.4.2.4. Slinging machines
These machines are also known as sand slingers and are used for filling and uniform ramming of
molding sand in molds. In the slinging operations, the consolidation and ramming are obtained
by impact of sand which falls at a very high velocity on pattern. These machines are generally
preferred for quick preparation of large sand moulds. These machines can also be used in
combination with other devices such as, roll over machines and pattern draw machines for
reducing manual operations to minimum. These machines can be stationary and portable types.
Stationary machines are used for mass production in bigger foundries whereas portable type
machines are mounted on wheels and travel in the foundry shop on a well-planned fixed path. A
typical sand slinger consists of a heavy base, a bin or hopper to carry sand, a bucket elevator to
which are attached a number of buckets and a swinging arm which carries a belt conveyor and
the sand impeller head. Well prepared sand is filed in a bin through the bottom of which it is fed
to the elevator buckets. These buckets discharge the molding sand to the belt conveyor which
conveys the same to the impeller head. This head can be moved at any location on the mold by
swinging the arm. The head revolves at a very high speed and, in doing so, throws stream of
molding sand into the molding box at a high velocity. This process is known as slinging. The
force of sand ejection and striking into the molding box compel the sand gets packed in the box
flask uniformly. This way the satisfactory ramming is automatically get competed on the mold. It
is a very useful machine in large foundries.
3.4.2.5. Pattern draw machines
These machines enable easy withdrawal of patterns from the molds. They can be of the kind of
stripping plate type and pin lift or push off type. Stripping plate type of pattern draw machines
consists of a stationary platen or table on which is mounted a stripping plate which carries a hole
in it. The size and shape of this hole is such that it fits accurately around the pattern. The pattern
is secured to a pattern plate and the latter to the supporting ram. The pattern is drawn through the
stripping plate either by raising the stripping plate and the mould up and keeping the pattern

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stationary or by keeping the stripping plate and mould stationary and moving the pattern
supporting ram downwards along with the pattern and pattern plate. A suitable mechanism can
be incorporated in the machine for these movements.
3.4.2.6. Roll-over machine
This machine comprises of a rigid frame carrying two vertical supports on its two sides having
bearing supports of trunnions on which the roll-over frame of the machine is mounted. The
pattern is mounted on a plate which is secured to the roll-over frame. The platen of the machine
can be moved up and down. For preparation of the mould, the roll-over frame is clamped in
position with the pattern facing upward. Molding box is placed over the pattern plate and
clamped properly. Molding sand is then filled in it and rammed by hand and the extra molding
sand is struck off and molding board placed over the box and clamped to it. After that the roll-
over frame is unclamped and rolled over through 180° to suspend the box below the frame. The
platen is then lifted up to butt against the suspending box. The box is unclamped from the pattern
plate to rest over the platen which is brought down leaving the pattern attached to the plate. The
prepared mold is now lowered. The frame is then again rolled over to the original position for
ramming another flask. Other mechanisms are always incorporated to enable the above rolling
over and platen motion. Some roll-over machines may carry a pneumatic mechanism for rolling
over. There are others mechanism also which incorporate a jolting table for ramming the sand
and an air operated rocking arm to facilitate rolling over. Some machines incorporate a
mechanically or pneumatically operated squeezing mechanism for sand ramming in addition to
the air operated rolling over mechanism. All such machines are frequently referred to as
combination machines to carry out the molding tasks automatically.
3.5. Questions
1. How do you classify the different tools and equipment used in foundries?
2. Name the different tools used in hand molding stating their use.
3. Sketch and describe the different types of molding boxes you know.
4. What are ladles and crucibles? How do they differ from each other?
5. Describe the working principles and uses of different molding machines.
6. Describe, with the help of sketches, how a mould is rammed on a diaphragm molding
machine.
7. What is a molding machine? What main functions does it perform?
8. Describe the principle of working of different pattern draw machines.
9. Describe the principle of working of a rollover machine.
10. What is sand slinger and how does it differ from other molding machines

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CHAPTER FOUR - Mold and Core Making
4.1. Introduction
A suitable and workable material possessing high refractoriness in nature can be used for mould
making. Thus, the mold making material can be metallic or non-metallic. For metallic category,
the common materials are cast iron, mild steel and alloy steels. In the non-metallic group
molding sands, plaster of paris, graphite, silicon carbide and ceramics are included. But, out of
all, the molding sand is the most common utilized non-metallic molding material because of its
certain inherent properties namely refractoriness, chemical and thermal stability at higher
temperature, high permeability and workability along with good strength. Moreover, it is also
highly cheap and easily available. This chapter discusses molding and core sand, the
constituents, properties, testing and conditioning of molding and core sands, procedure for
making molds and cores, mold and core terminology and different methods of molding.
4.2. Molding Sand
The general sources of receiving molding sands are the beds of sea, rivers, lakes, granulular
elements of rocks, and deserts.
Molding sands may be of two types namely natural or synthetic. Natural molding sands contain
sufficient binder. Whereas synthetic molding sands are prepared artificially using basic sand
molding constituents (silica sand in 88-92%, binder 6-12%, water or moisture content 3-6%) and
other additives in proper proportion by weight with perfect mixing and mulling in suitable
equipment.
4.3. Constituentsof Molding Sand
The main constituents of molding sand involve silica sand, binder, moisture content and
additives.
4.3.1. Silica sand
Silica sand in form of granular quarts is the main constituent of molding sand having enough
refractoriness which can impart strength, stability and permeability to molding and core sand.
But along with silica small amounts of iron oxide, alumina, lime stone, magnesia, soda and
potash are present as impurities. The chemical composition of silica sand gives an idea of the
impurities like lime, magnesia, alkalis etc. present. The presence of excessive amounts of iron
oxide, alkali oxides and lime can lower the fusion point to a considerable extent which is
undesirable. The silica sand can be specified according to the size (small, medium and large
silica sand grain) and the shape (angular, sub-angular and rounded).
4.3.1.1. Effect of grain shape and size of silica sand
The shape and size of sand grains has a significant effect on the different properties of molding
and core sands. The shape of the sand grains in the mold or core sand determines the possibility
of its application in various types of foundry practice. The shape of foundry sand grains varies
from round to angular. Some sands consist almost entirely of grains of one shape, whereas others

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have a mixture of various shapes. According to shape, foundry sands are classified as rounded,
sub-angular, angular and compound. Use of angular grains (obtained during crushing of rocks
hard sand stones) is avoided as these grains have a large surface area. Molding sands composed
of angular grains will need higher amount of binder and moisture content for the greater specific
surface area of sand grain. However, a higher percentage of binder is required to bring in the
desired strength in the molding sand and core sand. For good molding purposes, a smooth
surfaced sand grains are preferred. The smooth surfaced grain has a higher sinter point, and the
smooth surface secures a mixture of greater permeability and plasticity while requiring a higher
percentage of blind material. Rounded shape silica sand grain sands are best suited for making
permeable molding sand. These grains contribute to higher bond strength in comparison to
angular grain. However, rounded silica sand grains sands have higher thermal expandability than
angular silica grain sands. Silica sand with rounded silica sand grains gives much better
compactability under the same conditions than the sands with angular silica grains. This is
connected with the fact that the silica sand with rounded grains having the greatest degree of
close packing of particles while sand with angular grains the worst. The green strength increases
as the grains become more rounded. On the other hand, the grade of compactability of silica
sands with rounded sand grains is higher, and other, the contact surfaces between the individual
grains are greater on rounded grains than on angular grains. As already mentioned above, the
compactability increases with rounded grains. The permeability or porosity property of molding
sand and core sand therefore, should increase with rounded grains and decrease with angular
grains.
Thus the round silica sand grain size greatly influences the properties of molding sand. The
characteristics of sub-angular sand grains lie in between the characteristics of sand grains of
angular and rounded kind. Compound grains are cemented together such that they fail to get
separated when screened through a sieve. They may consist of round, sub-angular, or angular
sub-angular sand grains. Compound grains require higher amounts of binder and moisture
content also. These grains are least desirable in sand mixtures because they have a tendency to
disintegrate at high temperatures. Moreover the compound grains are cemented together and they
fail to separate when screened.
Grain sizes and their distribution in molding sand influence greatly the properties of the sand.
The size and shape of the silica sand grains have a large bearing upon its strength and other
general characteristics. The sand with wide range of particle size has higher compactability than
sand with narrow distribution. The broadening of the size distribution may be done either to the
fine or the coarse side of the distribution or in both directions simultaneously, and a sand of
higher density will result. Broadening to the coarse side has a greater effect on density than
broadening the distribution to the fine sand. Wide size distributions favor green strength, while
narrow grain distributions reduce it. The grain size distribution has a significant effect on
permeability. Silica sand containing finer and a wide range of particle sizes will have low
permeability as compared to those containing grains of average fineness but of the same size i.e.
narrow distribution. The compactability is expressed by the green density obtained by three ram
strokes. Finer the sand, the lower is the compactability and vice versa. This results from the fact
that the specific surface increases as the grain size decreases. As a result, the number of points of

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contact per unit of volume increases and this in turn raises the resistance to compacting. The
green strength has a certain tendency, admittedly not very pronounced, towards a maximum with
a grain size which corresponds approximately to the medium grain size. As the silica sand grains
become finer, the film of bentonite becomes thinner, although the percentage of bentonite
remains the same. Due to reducing the thickness of binder film, the green strength is reduced.
With very coarse grains, however, the number of grains and, therefore, the number of points of
contact per unit of volume decreases so sharply that the green strength is again reduced. The
sands with grains equal but coarser in size have greater void space and have, therefore greater
permeability than the finer silica sands. This is more pronounced if sand grains are equal in size.
4.3.2. Binder
In general, the binders can be either inorganic or organic substance. The inorganic group
includes clay sodium silicate and port land cement etc. In foundry shop, the clay acts as binder
which may be Kaolonite, Ball Clay, Fire Clay, Limonite, Fuller’s earth and Bentonite. Binders
included in the organic group are dextrin, molasses, cereal binders, linseed oil and resins like
phenol formaldehyde, urea formaldehyde etc. Organic binders are mostly used for core making.
Among all the above binders, the bentonite variety of clay is the most common. However, this
clay alone can not develop bonds among sand grins without the presence of moisture in molding
sand and core sand.
4.3.3. Moisture
The amount of moisture content in the molding sand varies generally between 2 to 8 percent.
This amount is added to the mixture of clay and silica sand for developing bonds. This is the
amount of water required to fill the pores between the particles of clay without separating them.
This amount of water is held rigidly by the clay and is mainly responsible for developing the
strength in the sand. The effect of clay and water decreases permeability with increasing clay and
moisture content. The green compressive strength first increases with the increase in clay
content, but after a certain value, it starts decreasing.
For increasing the molding sand characteristics some other additional materials besides basic
constituents are added which are known as additives.
4.3.4. Additives
Additives are the materials generally added to the molding and core sand mixture to develop
some special property in the sand. Some common used additives for enhancing the properties of
molding and core sands are discussed as under.
4.3.4.1. Coal dust
Coal dust is added mainly for producing a reducing atmosphere during casting. This reducing
atmosphere results in any oxygen in the poles becoming chemically bound so that it cannot
oxidize the metal. It is usually added in the molding sands for making molds for production of
grey iron and malleable cast iron castings.

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4.3.4.2. Corn flour
It belongs to the starch family of carbohydrates and is used to increase the collapsibility of the
molding and core sand. It is completely volatilized by heat in the mould, thereby leaving space
between the sand grains. This allows free movement of sand grains, which finally gives rise to
mould wall movement and decreases the mold expansion and hence defects in castings. Corn
sand if added to molding sand and core sand improves significantly strength of the mold and
core.
4.3.4.3. Dextrin
Dextrin belongs to starch family of carbohydrates that behaves also in a manner similar to that of
the corn flour. It increases dry strength of the molds.
4.3.4.4. Sea coal
Sea coal is the fine powdered bituminous coal which positions its place among the pores of the
silica sand grains in molding sand and core sand. When heated, it changes to coke which fills the
pores and is unaffected by water: Because to this, the sand grains become restricted and cannot
move into a dense packing pattern. Thus, sea coal reduces the mould wall movement and the
permeability in mold and core sand and hence makes the mold and core surface clean and
smooth.
4.3.4.5. Pitch
It is distilled form of soft coal. It can be added from 0.02 % to 2% in mold and core sand. It
enhances hot strengths, surface finish on mold surfaces and behaves exactly in a manner similar
to that of sea coal.
4.3.4.6. Wood flour
This is a fibrous material mixed with a granular material like sand; its relatively long thin fibers
prevent the sand grains from making contact with one another. It can be added from 0.05 % to
2% in mold and core sand. It volatilizes when heated, thus allowing the sand grains room to
expand. It will increase mould wall movement and decrease expansion defects. It also increases
collapsibility of both of mold and core.
4.3.4.7. Silica flour
It is called as pulverized silica and it can be easily added up to 3% which increases the hot
strength and finish on the surfaces of the molds and cores. It also reduces metal penetration in the
walls of the molds and cores.
4.4. Kinds of Moulding Sand
Molding sands can also be classified according to their use into number of varieties which are
described below.

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4.4.1. Green sand
Green sand is also known as tempered or natural sand which is a just prepared mixture of silica
sand with 18 to 30 percent clay, having moisture content from 6 to 8%. The clay and water
furnish the bond for green sand. It is fine, soft, light, and porous. Green sand is damp, when
squeezed in the hand and it retains the shape and the impression to give to it under pressure.
Molds prepared by this sand are not requiring backing and hence are known as green sand molds.
This sand is easily available and it possesses low cost. It is commonly employed for production
of ferrous and non-ferrous castings.
4.4.2. Dry sand
Green sand that has been dried or baked in suitable oven after the making mold and cores, is
called dry sand. It possesses more strength, rigidity and thermal stability. It is mainly suitable for
larger castings. Mold prepared in this sand are known as dry sand molds.
4.4.3. Loam sand
Loam is mixture of sand and clay with water to a thin plastic paste. Loam sand possesses high
clay as much as 30-50% and 18% water. Patterns are not used for loam molding and shape is
given to mold by sweeps. This is particularly employed for loam molding used for large grey
iron castings.
4.4.4. Facing sand
Facing sand is just prepared and forms the face of the mould. It is directly next to the surface of
the pattern and it comes into contact molten metal when the mould is poured. Initial coating
around the pattern and hence for mold surface is given by this sand. This sand is subjected
severest conditions and must possess, therefore, high strength refractoriness. It is made of silica
sand and clay, without the use of used sand. Different forms of carbon are used to prevent the
metal burning into the sand. A facing sand mixture for green sand of cast iron may consist of
25% fresh and specially prepared and 5% sea coal. They are sometimes mixed with 6-15 times as
much fine molding sand to make facings. The layer of facing sand in a mold usually ranges from
22-28 mm. From 10 to 15% of the whole amount of molding sand is the facing sand.
4.4.5. Backing sand
Backing sand or floor sand is used to back up the facing sand and is used to fill the whole
volume of the molding flask. Used molding sand is mainly employed for this purpose. The
backing sand is sometimes called black sand because that old, repeatedly used molding sand is
black in color due to addition of coal dust and burning on coming in contact with the molten
metal.
4.4.6. System sand
In mechanized foundries where machine molding is employed. A so-called system sand is used
to fill the whole molding flask. In mechanical sand preparation and handling units, no facing
sand is used. The used sand is cleaned and re-activated by the addition of water and special

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additives. This is known as system sand. Since the whole mold is made of this system sand, the
properties such as strength, permeability and refractoriness of the molding sand must be higher
than those of backing sand.
4.4.7. Parting sand
Parting sand without binder and moisture is used to keep the green sand not to stick to the pattern
and also to allow the sand on the parting surface the cope and drag to separate without clinging.
This is clean clay-free silica sand which serves the same purpose as parting dust.
4.4.8. Core sand
Core sand is used for making cores and it is sometimes also known as oil sand. This is highly
rich silica sand mixed with oil binders such as core oil which composed of linseed oil, resin, light
mineral oil and other bind materials. Pitch or flours and water may also be used in large cores for
the sake of economy.
4.5. Properties ofMoulding Sand
The basic properties required in molding sand and core sand are described as under.
4.5.1. Refractoriness
Refractoriness is defined as the ability of molding sand to withstand high temperatures without
breaking down or fusing thus facilitating to get sound casting. It is a highly important
characteristic of molding sands. Refractoriness can only be increased to a limited extent.
Molding sand with poor refractoriness may burn on to the casting surface and no smooth casting
surface can be obtained. The degree of refractoriness depends on the SiO2 i.e. quartz content, and
the shape and grain size of the particle. The higher the SiO2 content and the rougher the grain
volumetric composition the higher is the refractoriness of the molding sand and core sand.
Refractoriness is measured by the sinter point of the sand rather than its melting point.
4.5.2. Permeability
It is also termed as porosity of the molding sand in order to allow the escape of any air, gases or
moisture present or generated in the mould when the molten metal is poured into it. All these
gaseous generated during pouring and solidification process must escape otherwise the casting
becomes defective. Permeability is a function of grain size, grain shape, and moisture and clay
contents in the molding sand. The extent of ramming of the sand directly affects the permeability
of the mould. Permeability of mold can be further increased by venting using vent rods
4.5.3. Cohesiveness
It is property of molding sand by virtue which the sand grain particles interact and attract each
other within the molding sand. Thus, the binding capability of the molding sand gets enhanced to
increase the green, dry and hot strength property of molding and core sand.

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4.5.4. Green strength
The green sand after water has been mixed into it, must have sufficient strength and toughness to
permit the making and handling of the mould. For this, the sand grains must be adhesive, i.e.
thev must be capable of attaching themselves to another body and. therefore, and sand grains
having high adhesiveness will cling to the sides of the molding box. Also, the sand grains must
have the property known as cohesiveness i.e. ability of the sand grains to stick to one another. By
virtue of this property, the pattern can be taken out from the mould without breaking the mould
and also the erosion of mould wall surfaces does not occur during the flow of molten metal. The
green strength also depends upon the grain shape and size, amount and type of clay and the
moisture content.
4.5.5. Dry strength
As soon as the molten metal is poured into the mould, the moisture in the sand layer adjacent to
the hot metal gets evaporated and this dry sand layer must have sufficient strength to its shape in
order to avoid erosion of mould wall during the flow of molten metal. The dry strength also
prevents the enlargement of mould cavity cause by the metallostatic pressure of the liquid metal.
4.5.6. Flowability or plasticity
It is the ability of the sand to get compacted and behave like a fluid. It will flow uniformly to all
portions of pattern when rammed and distribute the ramming pressure evenly all around in all
directions. Generally sand particles resist moving around corners or projections. In general,
flowability increases with decrease in green strength, an, decrease in grain size. The flowability
also varies with moisture and clay content.
4.5.7. Adhesiveness
It is property of molding sand to get stick or adhere with foreign material such sticking of
molding sand with inner wall of molding box
4.5.8. Collapsibility
After the molten metal in the mould gets solidified, the sand mould must be collapsible so that
free contraction of the metal occurs and this would naturally avoid the tearing or cracking of the
contracting metal. In absence of this property the contraction of the metal is hindered by the
mold and thus results in tears and cracks in the casting. This property is highly desired in cores
4.5.9. Miscellaneous properties
In addition to above requirements, the molding sand should not stick to the casting and should
not chemically react with the metal. Molding sand should be cheap and easily available. It should
be reusable for economic reasons. Its coefficients of expansion should be sufficiently low.
4.6. Sand Testing
Molding sand and core sand depend upon shape, size composition and distribution of sand
grains, amount of clay, moisture and additives. The increase in demand for good surface finish
and higher accuracy in castings necessitates certainty in the quality of mold and core sands. Sand

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testing often allows the use of less expensive local sands. It also ensures reliable sand mixing and
enables a utilization of the inherent properties of molding sand. Sand testing on delivery will
immediately detect any variation from the standard quality, and adjustment of the sand mixture
to specific requirements so that the casting defects can be minimized. It allows the choice of sand
mixtures to give a desired surface finish. Thus sand testing is one of the dominating factors in
foundry and pays for itself by obtaining lower per unit cost and increased production resulting
from sound castings. Generally the following tests are performed to judge the molding and
casting characteristics of foundry sands:
1. Moisture content Test
2. Clay content Test
3. Chemical composition of sand
4. Grain shape and surface texture of sand.
5. Grain size distribution of sand
6. Specific surface of sand grains
7. Water absorption capacity of sand
8. Refractoriness of sand
9. Strength Test
10. Permeability Test
11. Flowability Test
12. Shatter index Test
13. Mould hardness Test.
Some of the important sand tests are discussed as under.
4.6.1. Moisture Content Test
The moisture content of the molding sand mixture may determined by drying a weighed amount
of 20 to 50 grams of molding sand to a constant temperature up to 100°C in a oven for about one
hour. It is then cooled to a room temperature and then reweighing the molding sand. The
moisture content in molding sand is thus evaporated. The loss in weight of molding sand due to
loss of moisture, gives the amount of moisture which can be expressed as a percentage of the
original sand sample. The percentage of moisture content in the molding sand can also be
determined in fact more speedily by an instrument known as a speedy moisture teller. This
instrument is based on the principle that when water and calcium carbide react, they form
acetylene gas which can be measured and this will be directly proportional to the moisture
content. This instrument is provided with a pressure gauge calibrated to read directly the
percentage of moisture present in the molding sand. Some moisture testing instruments are based
on principle that the electrical conductivity of sand varies with moisture content in it.
4.6.2. Clay Content Test
The amount of clay is determined by carrying out the clay content test in which clay in molding
sand of 50 grams is defined as particles which when suspended in water, fail to settle at the rate
of one inch per min. Clay consists of particles less than 20 micron, per 0.0008 inch in dia.

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4.6.3. Grain Fineness Test
For carry out grain fineness test a sample of dry silica sand weighing 50 gms free from clay is
placed on a top most sieve bearing U.S. series equivalent number 6. A set of eleven sieves
having U.S. Bureau of standard meshes 6, 12, 20, 30, 40, 50, 70, 100, 140, 200 and 270 are
mounted on a mechanical shaker (Fig. 4.1). The series are placed in order of fineness from top to
bottom. The free silica sand sample is shaked in a mechanical shaker for about 15 minutes. After
this weight of sand retained in each sieve is obtained sand and the retained sand in each sieve is
multiplied by 2 which gives % of weight retained by each sieve. The same is further multiplied
by a multiplying factor and total product is obtained. It is then divided by total % sand retained
by different sieves which will give G.F.N.
Fig. 4.1 Grain fitness testing mechanical shaker
4.6.4. Refractoriness Test
The refractoriness of the molding sand is judged by heating the American Foundry Society
(A.F.S) standard sand specimen to very high temperatures ranges depending upon the type of
sand. The heated sand test pieces are cooled to room temperature and examined under a
microscope for surface characteristics or by scratching it with a steel needle. If the silica sand

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grains remain sharply defined and easily give way to the needle. Sintering has not yet set in. In
the actual experiment the sand specimen in a porcelain boat is p1aced into an e1ectric furnace. It
is usual practice to start the test from l000°C and raise the temperature in steps of 100°C to
1300°C and in steps of 50° above 1300°C till sintering of the silica sand grains takes place. At
each temperature level, it is kept for at least three minutes and then taken out from the oven for
examination under a microscope for evaluating surface characteristics or by scratching it with a
steel needle.
4.6.5. Strength Test
Green strength and dry strength is the holding power of the various bonding materials. Generally
green compression strength test is performed on the specimen of green sand (wet condition). The
sample specimen may of green sand or dry sand which is placed in lugs and compressive force is
applied slowly by hand wheel until the specimen breaks. The reading of the needle of high
pressure and low pressure manometer indicates the compressive strength of the specimen in
kgf/cm2. The most commonly test performed is compression test which is carried out in a
compression sand testing machine (Fig. 4.2). Tensile, shear and transverse tests are also
sometimes performed. Such tests are performed in strength tester using hydraulic press. The
monometers are graduated in different scales. Generally sand mixtures are tested for their
compressive strength, shear strength, tensile strength and bending strength. For carrying out
these tests on green sand sufficient rammed samples are prepared to use. Although the shape of
the test specimen differs a lot according to the nature of the test for all types of the strength tests
can be prepared with the of a typical rammer and its accessories. To prepare cylindrical specimen
bearing 50.8 mm diameter with for testing green sand, a defined amount of sand is weighed
which will be compressed to height of 50.8 mm. by three repeated rammings. The predetermined
amount of weighed molding sand is poured into the ram tube mounted on the bottom. Weight is
lifted by means of the hand 1ever and the tube filled with sand is placed on the apparatus and the
ramming unit is allowed to come down slowly to its original position. Three blows are given on
the sample by allowing the rammer weight to fall by turning the lever. After the three blows the
mark on the ram rod should lie between the markings on the stand. The rammed specimen is
removed from the tube by means a pusher rod. The process of preparing sand specimen for
testing dry sand is similar to the process as prepared before, with the difference that a split ram
tube is used. The specimen for testing bending strength is of a square cross section. The various
tests can be performed on strength tester. The apparatus can be compared with horizontal
hydraulic press. Oil pressure is created by the hand-wheel and the pressure developed can be
measured by two pressure manometers. The hydraulic pressure pushes the plunger. The adjusting
cock serves to connect the two manometers. Deformation can be measured on the dial.

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Fig. 4.2 Strength testing machine
The compression strength of the molding sand is determined by placing standard specimen at
specified location and the load is applied on the standard sand specimen to compress it by
uniform increasing load using rotating the hand wheel of compression strength testing setup. As
soon as the sand specimen fractures for break, the compression strength is measured by the
manometer. Also, other strength tests can be conducted by adopting special types of specimen
holding accessories.
4.6.6. Permeability Test
Initially a predetermined amount of molding sand is being kept in a standard cylindrical tube,
and the molding sand is compressed using slightly tapered standard ram till the cylindrical
standard sand specimen having 50.8mm diameter with 50.8 mm height is made and it is then
extracted. This specimen is used for testing the permeability or porosity of molding and the core
sand. This test is applied for testing porosity of the standard sand specimen. The test is
performed in a permeability meter consisting of the balanced tank, water tank, nozzle, adjusting
lever, nose piece for fixing sand specimen and a manometer. A typical permeability meter is
shown in Fig. 4.3 which permits to read the permeability directly. The permeability test
apparatus comprises of a cylinder and another concentric cylinder inside the outer cylinder and
the space between the two concentric cylinders is filled with water. A bell having a diameter
larger than that of the inner cylinder but smaller than that of outer cylinder, rests on the surface
of water. Standard sand specimen of 5.08 mm diameter and 50.8 mm height together with ram
tube is placed on the tapered nose piece of the permeability meter. The bell is allowed to sink
under its own weight by the help of multi-position cock. In this way the air of the bell streams
through the nozzle of nosepiece and the permeability is directly measured.

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Permeability is volume of air (in cm3) passing through a sand specimen of 1 cm2 crosssectional
area and 1 cm height, at a pressure difference of 1 gm/cm2 in one minute. In general,
permeability is expressed as a number and can be calculated from the relation
P = vh/pat
Where, P = permeability
v = volume of air passing through the specimen in c.c.
h = height of specimen in cm
p = pressure of air in gm/cm2
a = cross-sectional area of the specimen in cm2
t = time in minutes.
For A.F S. standard permeability meter, 2000 cc of air is passed through a sand specimen (5.08
cm in height and 20.268 sq. cm. in cross-sectional area) at a pressure of 10 gms/cm2 and the total
time measured is 10 seconds = 1/6 min. Then the permeability is calculated using the relationship
as given as under.
P = (2000 × 5.08) / (10 × 20.268 × (1/6)) = 300.66 App.
4.6.7. Flowability Test
Flowability of the molding and core sand usually determined by the movement of the rammer
plunger between the fourth and fifth drops and is indicated in percentages. This reading can
directly be taken on the dial of the flow indicator. Then the stem of this indicator rests again top
of the plunger of the rammer and it records the actual movement of the plunger between the
fourth and fifth drops.

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Fig. 4.3 Permeability meter
4.6.8. Shatter Index Test
In this test, the A.F.S. standard sand specimen is rammed usually by 10 blows and then it is
allowed to fall on a half inch mesh sieve from a height of 6 ft. The weight of sand retained on the
sieve is weighed. It is then expressed as percentage of the total weight of the specimen which is a
measure of the shatter index.
4.6.9. Mould Hardness Test
This test is performed by a mold hardness tester shown in Fig. 4.4. The working of the tester is
based on the principle of Brinell hardness testing machine. In an A.F.S. standard hardness tester

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a half inch diameter steel hemi-spherical ball is loaded with a spring load of 980 gm. This ball is
made to penetrate into the mold sand or core sand surface. The penetration of the ball point into
the mould surface is indicated on a dial in thousands of an inch. The dial is calibrated to read the
hardness directly i.e. a mould surface which offers no resistance to the steel ball would have zero
hardness value and a mould which is more rigid and is capable of completely preventing the steel
ball from penetrating would have a hardness value of 100. The dial gauge of the hardness tester
may provide direct readings
Fig. 4.4 Mould harness tester
4.7. Sand Conditioning
Natural sands are generally not well suited for casting purposes. On continuous use of molding
sand, the clay coating on the sand particles gets thinned out causing decrease in its strength. Thus
proper sand conditioning accomplish uniform distribution of binder around the sand grains,
control moisture content, eliminate foreign particles and aerates the sands. Therefore, there is a
need for sand conditioning for achieving better results.
The foreign materials, like nails, gaggers, hard sand lumps and metals from the used sand are
removed. For removing the metal pieces, particularly ferrous pieces, the sand from the shake-out
station is subjected to magnetic separator, which separates out the iron pieces, nails etc. from the
used sand. Next, the sand is screened in riddles which separate out the hard sand lumps etc.
These riddles may be manual as well as mechanical. Mechanical riddles may be either
compressed air operated or electrically operated. But the electrically operated riddles are faster
and can handle large quantities of sand in a short time. The amount of fine material can be
controlled to the maximum possible extent by its removal through exhaust systems under
conditions of shake out.

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The sand constituents are then brought at required proper proportion and mixed thoroughly.
Next, the whole mixture is mulled suitably till properties are developed. After all the foreign
particles are removed from and the sand is free from the hard lumps etc., proper amount of pure
sand, clay and required additives are added to for the loss because of the burned, clay and other
corn materials. As the moisture content of the returned sand known, it is to be tested and after
knowing the moisture the required amount of water is added. Now these things are mixed
thoroughly in a mixing muller (Fig 4.5).
Fig. 4.5 Sand mixing muller
The main objectives of a mixing muller is to distribute the binders, additives and moisture or
water content uniformly all around each sand grain and helps to develop the optimum physical
properties by kneading on the sand grains. Inadequate mulling makes the sand mixture weak
which can only be compensated by adding more binder. Thus the adequate mulling economizes
the use of binders. There are two methods of adding clay and water to sand. In the first method,
first water is added to sand follow by clay, while in the other method, clay addition is followed
water. It has been suggested that the best order of adding ingredients to clay bonded sand is sand
with water followed by the binders. In this way, the clay is more quickly and uniformly spread
on to all the sand grains. An additional advantage of this mixing order is that less dust is
produced during the mulling operation. The muller usually consists of a cylindrical pan in which
two heavy rollers; carrying two ploughs, and roll in a circular path. While the rollers roll, the
ploughs scrap the sand from the sides and the bottom of the pan and place it in front of For
producing a smearing action in the sand, the rollers are set slightly off the true radius and they
move out of the rollers can be moved up and down without difficulty mounted on rocker arms.
After the mulling is completed sand can be discharged through a door. The mechanical aerators
are generally used for aerating or separating the sand grains by increasing the flowability through
whirling the sand at a high speed by an impeller towards the inner walls of the casting. Aerating
can also be done by riddling the sand mixture oil on a one fourth inch mesh screen or by
spraying the sand over the sand heap by flipping the shovels. The aeration separates the sand
grains and leaves each grain free to flow in the direction of ramming with less friction. The final
step in sand conditioning is the cooling of sand mixture because of the fact that if the molding
sand mixture is hot, it will cause molding difficulties.

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4.8. Steps Involved in Makinga Sand Mold
1. Initially a suitable size of molding box for creating suitable wall thickness is selected for a
two piece pattern. Sufficient care should also be taken in such that sense that the molding box
must adjust mold cavity, riser and the gating system (sprue, runner and gates etc.).
2. Next, place the drag portion of the pattern with the parting surface down on the bottom (ram-
up) board as shown in Fig. 4.6 (a).
3. The facing sand is then sprinkled carefully all around the pattern so that the pattern does not
stick with molding sand during withdrawn of the pattern.
4. The drag is then filled with loose prepared molding sand and ramming of the molding sand is
done uniformly in the molding box around the pattern. Fill the molding sand once again and
then perform ramming. Repeat the process three four times,
5. The excess amount of sand is then removed using strike off bar to bring molding sand at the
same level of the molding flask height to completes the drag.
6. The drag is then rolled over and the parting sand is sprinkled over on the top of the drag [Fig.
4.6(b)].
7. Now the cope pattern is placed on the drag pattern and alignment is done using dowel pins.
8. Then cope (flask) is placed over the rammed drag and the parting sand is sprinkled all around
the cope pattern.
9. Sprue and riser pins are placed in vertically position at suitable locations using support of
molding sand. It will help to form suitable sized cavities for pouring molten metal etc. [Fig.
4.6 (c)].
10. The gaggers in the cope are set at suitable locations if necessary. They should not be located
too close to the pattern or mold cavity otherwise they may chill the casting and fill the cope
with molding sand and ram uniformly.
11. Strike off the excess sand from the top of the cope.
12. Remove sprue and riser pins and create vent holes in the cope with a vent wire. The basic
purpose of vent creating vent holes in cope is to permit the escape of gases generated during
pouring and solidification of the casting.
13. Sprinkle parting sand over the top of the cope surface and roll over the cope on the bottom
board.
14. Rap and remove both the cope and drag patterns and repair the mold suitably if needed and
dressing is applied
15. The gate is then cut connecting the lower base of sprue basin with runner and then the mold
cavity.
16. Apply mold coating with a swab and bake the mold in case of a dry sand mold.
17. Set the cores in the mold, if needed and close the mold by inverting cope over drag.
18. The cope is then clamped with drag and the mold is ready for pouring, [Fig. 4.6 (d)].

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Fig. 4.6 Mold making
Example of making another mold is illustrated through Fig. 4.7

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Fig. 4.7 Example of making a mold
4.9. Venting of Molds
Vents are very small pin types holes made in the cope portion of the mold using pointed edge of
the vent wire all around the mold surface as shown in Fig. 4.8. These holes should reach just near
the pattern and hence mold cavity on withdrawal of pattern. The basic purpose of vent holes is to
permit the escape of gases generated in the mold cavity when the molten metal is poured.
Fig. 4.8 Venting of holes in mold

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Mold gases generate because of evaporation of free water or steam formation, evolution of
combined water (steam formation), decomposition of organic materials such as binders and
additives (generation of hydrocarbons, CO and CO2), expansion of air present in the pore spaces
of rammed sand. If mold gases are not permitted to escape, they may get trapped in the metal and
produce defective castings. They may raise back pressure and resist the inflow of molten metal.
They may burst the mold. It is better to make many small vent holes rather than a few large ones
to reduce the casting defects.
4.10. Gating System in Mold
Fig 4.9 shows the different elements of the gating system. Some of which are discussed as under.
Fig. 4.9 Gating System
1. Pouring basin
It is the conical hollow element or tapered hollow vertical portion of the gating system which
helps to feed the molten metal initially through the path of gating system to mold cavity. It may
be made out of core sand or it may be cut in cope portion of the sand mold. It makes easier for
the ladle operator to direct the flow of molten metal from crucible to pouring basin and sprue. It
helps in maintaining the required rate of liquid metal flow. It reduces turbulence and vertexing at
the sprue entrance. It also helps in separating dross, slag and foreign element etc. from molten
metal before it enters the sprue.
2. Sprue
It is a vertical passage made generally in the cope using tapered sprue pin. It is connected at
bottom of pouring basin. It is tapered with its bigger end at to receive the molten metal the
smaller end is connected to the runner. It helps to feed molten metal without turbulence to the
runner which in turn reaches the mold cavity through gate. It sometimes possesses skim bob at
its lower end. The main purpose of skim bob is to collect impurities from molten metal and it
does not allow them to reach the mold cavity through runner and gate.

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3. Gate
It is a small passage or channel being cut by gate cutter which connect runner with the mould
cavity and through which molten metal flows to fill the mould cavity. It feeds the liquid metal to
the casting at the rate consistent with the rate of solidification.
4. Choke
It is that part of the gating system which possesses smallest cross-section area. In choked system,
gate serves as a choke, but in free gating system sprue serves as a choke.
5. Runner
It is a channel which connects the sprue to the gate for avoiding turbulence and gas entrapment.
6. Riser
It is a passage in molding sand made in the cope portion of the mold. Molten metal rises in it
after filling the mould cavity completely. The molten metal in the riser compensates the
shrinkage during solidification of the casting thus avoiding the shrinkage defect in the casting. It
also permits the escape of air and mould gases. It promotes directional solidification too and
helps in bringing the soundness in the casting.
7. Chaplets
Chaplets are metal distance pieces inserted in a mould either to prevent shifting of mould or
locate core surfaces. The distances pieces in form of chaplets are made of parent metal of which
the casting is. These are placed in mould cavity suitably which positions core and to give extra
support to core and mould surfaces. Its main objective is to impart good alignment of mould and
core surfaces and to achieve directional solidification. When the molten metal is poured in the
mould cavity, the chaplet melts and fuses itself along with molten metal during solidification and
thus forms a part of the cast material. Various types of chaplets are shown in Fig. 4.10. The use
of the chaplets is depicted in Fig. 4.11.
Fig. 4.10 Types of chaplets

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Fig. 4.11 Use of chaplets
8. Chills
In some casting, it is required to produce a hard surface at a particular place in the casting. At
that particular position, the special mould surface for fast extraction of heat is to be made. The
fast heat extracting metallic materials known as chills will be incorporated separately along with
sand mould surface during molding. After pouring of molten metal and during solidification, the
molten metal solidifies quickly on the metallic mould surface in comparison to other mold sand
surfaces. This imparts hardness to that particular surface because of this special hardening
treatment through fast extracting heat from that particular portion. Thus, the main function of
chill is to provide a hard surface at a localized place in the casting by way of special and fast
solidification. Various types of chills used in some casting processes are shown in Fig. 4.12. The
use of a chill in the mold is depicted in Fig. 4.13.
Fig. 4.12 Types of chills
Fig. 4.13 Use of a chill
4.11. Factors ControllingGating Design
The following factors must be considered while designing gating system.
(i) Sharp corners and abrupt changes in at any section or portion in gating system should be
avoided for suppressing turbulence and gas entrapment. Suitable relationship must exist
between different cross-sectional areas of gating systems.

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(ii) The most important characteristics of gating system besides sprue are the shape, location
and dimensions of runners and type of flow. It is also important to determine the position at
which the molten metal enters the mould cavity.
(iii) Gating ratio should reveal that the total cross-section of sprue, runner and gate decreases
towards the mold cavity which provides a choke effect.
(iv) Bending of runner if any should be kept away from mold cavity.
(v) Developing the various cross sections of gating system to nullify the effect of turbulence or
momentum of molten metal.
(vi) Streamlining or removing sharp corners at any junctions by providing generous radius,
tapering the sprue, providing radius at sprue entrance and exit and providing a basin instead
pouring cup etc.
4.12. Role of Riser in Sand Casting
Metals and their alloys shrink as they cool or solidify and hence may create a partial vacuum
within the casting which leads to casting defect known as shrinkage or void. The primary
function of riser as attached with the mould is to feed molten metal to accommodate shrinkage
occurring during solidification of the casting. As shrinkage is very common casting defect in
casting and hence it should be avoided by allowing molten metal to rise in riser after filling the
mould cavity completely and supplying the molten metal to further feed the void occurred during
solidification of the casting because of shrinkage. Riser also permits the escape of evolved air
and mold gases as the mold cavity is being filled with the molten metal. It also indicates to the
foundry man whether mold cavity has been filled completely or not. The suitable design of riser
also helps to promote the directional solidification and hence helps in production of desired
sound casting.
4.12.1. Considerations for Desiging Riser
While designing risers the following considerations must always be taken into account.
(A) Freezing time
1. For producing sound casting, the molten metal must be fed to the mold till it solidifies
completely. This can be achieved when molten metal in riser should freeze at slower rate
than the casting.
2. Freezing time of molten metal should be more for risers than casting. The quantative
risering analysis developed by Caine and others can be followed while designing risers.
(B) Feeding range
1. When large castings are produced in complicated size, then more than one riser are
employed to feed molten metal depending upon the effective freezing range of each riser.
2. Casting should be divided into divided into different zones so that each zone can be feed by
a separate riser.
3. Risers should be attached to that heavy section which generally solidifies last in the casting.
4. Riser should maintain proper temperature gradients for continuous feeding throughout
freezing or solidifying.

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(C) Feed Volume Capacity
1. Riser should have sufficient volume to feed the mold cavity till the solidification of the
entire casting so as to compensate the volume shrinkage or contraction of the solidifying
metal.
2. The metal is always kept in molten state at all the times in risers during freezing of casting.
This can be achieved by using exothermic compounds and electric arc feeding arrangement.
Thus it results for small riser size and high casting yield.
3. It is very important to note that volume feed capacity riser should be based upon freezing
time and freezing demand.
Riser system is designed using full considerations on the shape, size and the position or location
of the riser in the mold.
4.12.2. Effect of Riser
Riser size affects on heat loss from top at open risers. Top risers are expressed as a percentage of
total heat lost from the rises during solidification. Risers are generally kept cylindrical. Larger
the riser, greater is the percentage of heat that flows out of top. Shape of riser may be cylindrical
or cubical or of cuboids kind. If shape is cylindrical i.e. 4" high and 4" dia, insulated so that heat
can pass only into the circumferential sand walls, with a constant K value of 13.7 min./sq.ft.
Chvorinov’s rule may be used to calculate the freezing time for cylinder as 13.7 min. The
freezing time of a 4" steel cube of same sand is 6.1 minutes and the freezing time of a 2", 8" and
8" rectangular block is also 6.1 min. Since the solidification time as calculated of the cylinder is
nearly twice as long as that of either the block of the cube. Hence cylindrical shape is always
better. Insulation and shielding of molten metal in riser also plays a good role for getting sound
casting
4.13. Green Sand Molding
Green sand molding is the most widely used molding process. The green sand used for molding
consists of silica, water and other additives. One typical green sand mixture contains 10 to 15%
clay binder, 4 to 6% water and remaining silica sand. The green sand mixture is prepared and
used in the molding procedure described in section 4.8 is used to complete the mold (cope and
drag). Cope and drag are then assembled and molten metal is poured while mould cavity is still
green. It is neither dried nor baked. Green sand molding is preferred for making small and
medium sized castings. It can also be applied for producing non-ferrous castings. It has some
advantages which are given as under.
Advantages
1. It is adaptable to machine molding
2. No mould baking and drying is required.
3. Mold distortion is comparatively less than dry sand molding.
4.14. Core
Cores are compact mass of core sand (special kind of molding sand ) prepared separately that
when placed in mould cavity at required location with proper alignment does not allow the

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molten metal to occupy space for solidification in that portion and hence help to produce
hollowness in the casting. The environment in which the core is placed is much different from
that of the mold. In fact the core has to withstand the severe action of hot metal which
completely surrounds it. They may be of the type of green sand core and dry sand core.
Therefore the core must meet the following functions or objectives which are given as under.
1. Core produces hollowness in castings in form of internal cavities.
2. It must be sufficiently permeable to allow the easy escape of gases during pouring and
solidification.
3. It may form a part of green sand mold
4. It may be deployed to improve mold surface.
5. It may provide external under cut features in casting.
6. It may be inserted to achieve deep recesses in the casting.
7. It may be used to strengthen the mold.
8. It may be used to form gating system of large size mold.
4.15. Core Sand
It is special kind of molding sand. Keeping the above mentioned objectives in view, the special
considerations should be given while selecting core sand. Those considerations involves (i) The
cores are subjected to a very high temperature and hence the core sand should be highly
refractory in nature (ii) The permeability of the core sand must be sufficiently high as compared
to that of the molding sands so as to allow the core gases to escape through the limited area of
the core recesses generated by core prints (iii) The core sand should not possess such materials
which may produce gases while they come in contact with molten metal and (iv) The core sand
should be collapsible in nature, i.e. it should disintegrate after the metal solidifies, because this
property will ease the cleaning of the casting.
The main constituents of the core sand are pure silica sand and a binder. Silica sand is preferred
because of its high refractoriness. For higher values of permeability sands with coarse grain size
distribution are used. The main purpose of the core binder is to hold the grains together, impart
strength and sufficient degree collapsibility. Beside these properties needed in the core sand, the
binder should be such that it produces minimum amount of gases when the molt metal is poured
in the mould. Although, in general the binder are inorganic as well as organic ones, but for core
making, organic binders are generally preferred because they are combustible and can be
destroyed by heat at higher temperatures thereby giving sufficient collapsibility to the core sand.
The common binders which are used in making core sand as follows:
1. Cereal binder
It develops green strength, baked strength and collapsibility in core. The amount of these binders
used varies from 0.2 to 2.2% by weight in the core sand.
2. Protein binder
It is generally used to increase collapsibility property of core.
3. Thermo setting resin
It is gaining popularity nowadays because it imparts high strength, collapsibility to core sand and
it also evolve minimum amount of mold and core gases which may produce defects in the

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casting. The most common binders under this group are phenol formaldehyde and urea
formaldehyde.
4. Sulphite binder
Sulphite binder is also sometimes used in core but along with certain amount of clay.
5. Dextrin
It is commonly added in core sand for increasing collapsibility and baked strength of core
6. Pitch
It is widely used to increase the hot strength of the core.
7. Molasses
It is generally used as a secondary binder to increase the hardness on baking. It is used in the
form of molasses liquid and is sprayed on the cores before baking.
8. Core oil
It is in liquid state when it is mixed with the core sand but forms a coherent solid film holding
the sand grains together when it is baked. Although, the core drying with certain core oils occurs
at room temperature but this can be expedited by increasing the temperature. That is why the
cores are made with core oils and are usually baked.
4.16. Core Making
Core making basically is carried out in four stages namely core sand preparation, core making,
core baking and core finishing. Each stage is explained as under.
4.16.1. Core Sand Preparation
Preparation of satisfactory and homogenous mixture of core sand is not possible by manual
means. Therefore for getting better and uniform core sand properties using proper sand
constituents and additives, the core sands are generally mixed with the help of any of the
following mechanical means namely roller mills and core sand mixer using vertical revolving
arm type and horizontal paddle type mechanisms. In the case of roller mills, the rolling action of
the mulling machine along with the turning over action caused by the ploughs gives a uniform
and homogeneous mixing. Roller mills are suitable for core sands containing cereal binders,
whereas the core sand mixer is suitable for all types of core binders. These machines perform the
mixing of core sand constituents most thoroughly.
4.16.2. Core Making Process Using Core Making Machines
The process of core making is basically mechanized using core blowing, core ramming and core
drawing machines which are broadly discussed as under.
4.16.2.1. Core blowing machines
The basic principle of core blowing machine comprises of filling the core sand into the core box
by using compressed air. The velocity of the compressed air is kept high to obtain a high velocity
of core sand particles, thus ensuring their deposit in the remote corners the core box. On entering
the core sand with high kinetic energy, the shaping and ramming of core is carried out
simultaneously in the core box. The core blowing machines can be further classified into two
groups namely small bench blowers and large floor blowers. Small bench blowers are quite

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economical for core making shops having low production. The bench blowers were first
introduced during second war. Because of the high comparative productivity and simplicity of
design, bench blowers became highly popular. The cartridge oriented sand magazine is
considered to be a part of the core box equipment. However, one cartridge may be used for
several boxes of approximately the same size. The cartridge is filled using hands. Then the core
box and cartridge are placed in the machine for blowing and the right handle of the machine
clamps the box and the left handle blows the core. In a swing type bench blower, the core sand
magazine swings from the blowing to the filling position. There is also another type of bench
blowing, which has a stationary sand magazine. It eliminates the time and effort of moving the
magazine from filling to the blowing position. The floor model blowers have the advantage
being more automation oriented. These floor model blowers possess stationary sand magazine
and automatic control. One of the major drawbacks in core blowing is the channeling of sand in
the magazine which may be prevented by agitating the sand in the sand magazine.
4.16.2.2. Core ramming machines
Cores can also be prepared by ramming core sands in the core boxes by machines based on the
principles of squeezing, jolting and slinging. Out of these three machines, jolting and slinging are
more common for core making.
4.16.2.3. Core drawing machines
The core drawing is preferred when the core boxes have deep draws. After ramming sand in it,
the core box is placed on a core plate supported on the machine bed. A rapping action on the core
box is produced by a vibrating vertical plate. This rapping action helps in drawing off the core
from the core box. After rapping, the core box, the core is pulled up thus leaving the core on the
core plate. The drawn core is then baked further before its use in mold cavity to produce
hollowness in the casting.
4.16.3. Core baking
Once the cores are prepared, they will be baked in a baking ovens or furnaces. The main purpose
of baking is to drive away the moisture and hard en the binder, thereby giving strength to the
core. The core drying equipment are usually of two kinds namely core ovens and dielectric
bakers. The core ovens are may be further of two type’s namely continuous type oven and batch
type oven. The core ovens and dielectric bakers are discussed as under.
4.16.3.1. Continuous type ovens
Continuous type ovens are preferred basically for mass production. In these types, core carrying
conveyors or chain move continuously through the oven. The baking time is controlled by the
speed of the conveyor. The continuous type ovens are generally used for baking of small cores.
4.16.3.2. Batch type ovens
Batch type ovens are mainly utilized for baking variety of cores in batches. The cores are
commonly placed either in drawers or in racks which are finally placed in the ovens. The core
ovens and dielectric bakers are usually fired with gas, oil or coal.

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4.16.3.3. Dielectric bakers
These bakers are based on dielectric heating. The core supporting plates are not used in this
baker because they interfere with the potential distribution in the electrostatic field. To avoid this
interference, cement bonded asbestos plates may be used for supporting the cores. The main
advantage of these ovens is that they are faster in operation and a good temperature control is
possible with them. After baking of cores, they are smoothened using dextrin and water soluble
binders.
4.16.4. Core Finishing
The cores are finally finished after baking and before they are finally set in the mould. The fins,
bumps or other sand projections are removed from the surface of the cores by rubbing or filing.
The dimensional inspection of the cores is very necessary to achieve sound casting. Cores are
also coated with refractory or protective materials using brushing dipping and spraying means to
improve their refractoriness and surface finish. The coating on core prevents the molten metal
from entering in to the core. Bars, wires and arbors are generally used to reinforce core from
inside as per size of core using core sand. For handling bulky cores, lifting rings are also
provided.
4.17. Green Sand Cores
Green sand cores are made by green sand containing moist condition about 5% water and 15 - 30
% clay. It imparts very good permeability to core and thus avoids defects like shrinkage or voids
in the casting. Green sand cores are not dried. They are poured in green condition and are
generally preferred for simple, small and medium castings. The process of making green sand
core consumes less time. Such cores possess less strength in comparison to dry sand cores and
hence cannot be stored for longer period.
4.18. Dry Sand Cores
Dry sand cores are produced by drying the green sand cores to about 110°C. These cores possess
high strength rigidity and also good thermal stability. These cores can be stored for long period
and are more stable than green sand core. They are used for large castings. They also produce
good surface finish in comparison to green sand cores. They can be handled more easily. They
resist metal erosion. These types of cores require more floor space, more core material, high
labor cost and extra operational equipment.
4.19. Classification ofMoldingProcesses
Molding processes can be classified in a number of ways. Broadly they are classified either on
the basis of the method used or on the basis of the mold material used.
(i) Classification based on the method used
(a) Bench molding.
(b) Floor molding,
(c) Pit molding.
(d) Machine molding.

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(ii) Classification based on the mold material used:
(a) Sand molding:
1. Green sand mould
2. Dry sand mould,
3. Skin dried mould.
4. Core sand mould.
5. loam mould
6. Cement bonded sand mould
7. Carbon-dioxide mould.
8. Shell mould.
(b) Plaster molding,
(c) Metallic molding.
(d) Loam molding
Some of the important molding methods are discussed as under.
4.20. Molding Methods
Commonly used traditional methods of molding are bench molding, floor molding, pit molding
and machine molding. These methods are discussed as under.
4.20.1. Bench Molding
This type of molding is preferred for small jobs. The whole molding operation is carried out on a
bench of convenient height. In this process, a minimum of two flasks, namely cope and drag
molding flasks are necessary. But in certain cases, the number of flasks may increase depending
upon the number of parting surfaces required.
4.20.2. Floor Molding
This type of molding is preferred for medium and large size jobs. In this method, only drag
portion of molding flask is used to make the mold and the floor itself is utilized as drag and it is
usually performed with dry sand.
4.20.3. Pit Molding
Usually large castings are made in pits instead of drag flasks because of their huge size. In pit
molding, the sand under the pattern is rammed by bedding-in process. The walls and the bottom
of the pit are usually reinforced with concrete and a layer of coke is laid on the bottom of the pit
to enable easy escape of gas. The coke bed is connected to atmosphere through vent pipes which
provide an outlet to the gases. One box is generally required to complete the mold, runner, sprue,
pouring basin and gates are cut in it.
4.20.4. Machine Molding
For mass production of the casting, the general hand molding technique proves un economical
and in efficient. The main advantage of machine molding, besides the saving of labor and
working time, is the accuracy and uniformity of the castings which can otherwise be only
obtained with much time and labor. Or even the cost of machining on the casting can be reduced

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drastically because it is possible to maintain the tolerances within narrow limits on casting using
machine molding method. Molding machines thus prepare the moulds at a faster rate and also
eliminate the need of employing skilled molders. The main operations performed by molding
machines are ramming of the molding sand, roll over the mold, form gate, rapping the pattern
and its withdrawal. Most of the mold making operations are performed using molding machines
4.20.5. Loam Molding
Loam molding uses loam sand to prepare a loam mold. It is such a molding process in which use
of pattern is avoided and hence it differs from the other molding processes. Initially the loam
sand is prepared with the mixture of molding sand and clay made in form of a paste by suitable
addition of clay water. Firstly a rough structure of cast article is made by hand using bricks and
loam sand and it is then given a desired shape by means of strickles and sweep patterns. Mould is
thus prepared. It is then baked to give strength to resist the flow of molten metal. This method of
molding is used where large castings are required in numbers. Thus it enables the reduction in
time, labor and material which would have been spent in making a pattern. But this system is not
popular for the reason that it takes lots of time in preparing mould and requires special skill. The
cope and drag part of mould are constructed separately on two different iron boxes using
different sizes of strickles and sweeps etc. and are assembled together after baking. It is
important to note that loam moulds are dried slowly and completely and used for large regular
shaped castings like chemical pans, drums etc.
4.20.6. Carbon-Dioxide Gas Molding
This process was widely used in Europe for rapid hardening the molds and cores made up of
green sand. The mold making process is similar to conventional molding procedure accept the
mould material which comprises of pure dry silica sand free from clay, 3-5% sodium silicate as
binder and moisture content generally less than 3%. A small amount of starch may be added to
improve the green compression strength and a very small quantity of coal dust, sea coal, dextrin,
wood floor, pitch, graphite and sugar can also be added to improve the collapsibility of the
molding sand. Kaolin clay is added to promote mold stability. The prepared molding sand is
rammed around the pattern in the mould box and mould is prepared by any conventional
technique. After packing, carbon dioxide gas at about 1.3-1.5 kg/cm2 pressure is then forced all-
round the mold surface to about 20 to 30 seconds using CO2 head or probe or curtain as shown in
Fig. 4.14. The special pattern can also be used to force the carbon dioxide gas all-round the mold
surfaces. Cores can be baked this way. The sodium silicate presented in the mold reacts with
CO2 and produce a very hard constituents or substance commonly called as silica gel.
Na2SiO3 +CO2 —————→ Na2CO3 + SiO2.xH2O (Silica Gel)

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Fig. 4.14 Carbon dioxide molding
This hard substance is like cement and helps in binding the sand grains. Molds and cores thus
prepared can be used for pouring molten metal for production of both ferrous and nonferrous
casting. The operation is quick, simple require semi-skilled worker. The evolution of gases is
drastically reduced after pouring the thus prepared mould. This process eliminates mold and core
baking oven. Reclamation of used sand is difficult for this process Few other special molding
methods are also discussed as under
4.20.7. Shell Molding
Shell mold casting is recent invention in molding techniques for mass production and smooth
finish. Shell molding method was invented in Germany during the Second World War. It is also
known as Carning or C process which is generally used for mass production of accurate thin
castings with close tolerance of +_ 0.02 mm and with smooth surface finish. It consists of
making a mould that has two or more thin lines shells (shell line parts, which are moderately
hard and smooth. Molding sand is prepared using thermosetting plastic dry powder and find sand
are uniformly mixed in a muller in the ratio 1: 20. In this process the pattern is placed on a metal
plate and silicon grease is then sprayed on it. The pattern is then heated to 205°C to 230°C and
covered with resin bonded sand. After 30 second a hard layer of sand is formed over the pattern.

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Pattern and shell are then heated and treated in an oven at 315°C for 60 sec. Then, the shell so
formed as the shape of the pattern is ready to strip from the pattern. The shell can be made in two
or more pieces as per the shape of pattern. Similarly core can be made by this process. Finally
shells are joined together to form the mold cavity. Then the mold is ready for pouring the molten
metal to get a casting. The shell so formed has the shape of pattern formed of cavity or projection
in the shell. In case of unsymmetrical shapes, two patterns are prepared so that two shell are
produced which are joined to form proper cavity. Internal cavity can be formed by placing a
core. Hot pattern and box is containing a mixture of sand and resin. Pattern and box inverted and
kept in this position for some time. Now box and pattern are brought to original position. A shell
of resin-bonded sand sticks to the pattern and the rest falls. Shell separates from the pattern with
the help of ejector pins. It is a suitable process for casting thin walled articles. The cast shapes
are uniform and their dimensions are within close limit of tolerance ± 0.002 mm and it is suitable
for precise duplication of exact parts.
The shells formed by this process are 0.3 to 0.6 mm thick and can be handled and stored. Shell
moulds are made so that machining parts fit together-easily, held clamps or adhesive and metal is
poured either in a vertical or horizontal position. They are supported in rocks or mass of bulky
permeable material such as sand steel shot or gravel. Thermosetting plastics, dry powder and
sand are mixed ultimately in a muller. The process of shell molding possesses various
advantages and disadvantages. Some of the main advantages and disadvantages of this process
are given as under.
Advantages
The main advantages of shell molding are:
(iii) High suitable for thin sections like petrol engine cylinder.
(iv) Excellent surface finish.
(v) Good dimensional accuracy of order of 0.002 to 0.003 mm.
(vi) Negligible machining and cleaning cost.
(vii) Occupies less floor space.
(viii) Skill-ness required is less.
(ix) Moulds formed by this process can be stored until required.
(x) Better quality of casting assured.
(xi) Mass production.
(xii) It allows for greater detail and less draft.
(xiii) Unskilled labor can be employed.
(xiv) Future of shell molding process is very bright.
Disadvantages
The main disadvantages of shell molding are:
9. Higher pattern cost.
10. Higher resin cost.
11. Not economical for small runs.
12. Dust-extraction problem.
13. Complicated jobs and jobs of various sizes cannot be easily shell molded.
14. Specialized equipment is required.

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15. Resin binder is an expensive material.
16. Limited for small size.
4.20.8. Plaster Molding
Plaster molding process is depicted through Fig. 4.15. The mould material in plaster molding is
gypsum or plaster of paris. To this plaster of paris, additives like talc, fibers, asbestos, silica flour
etc. are added in order to control the contraction characteristics of the mould as well as the
settling time. The plaster of paris is used in the form of a slurry which is made to a consistency
of 130 to 180. The consistency of the slurry is defined as the pounds of water per 100 pounds of
plaster mixture. This plaster slurry is poured over a metallic pattern confined in a flask. The
pattern is usually made of brass and it is generally in the form of half portion of job to be cast
and is attached firmly on a match plate which forms the bottom of the molding flask. Wood
pattern are not used because the water in the plaster raises the grains on them and makes them
difficult to be withdrawn. Some parting or release agent is needed for easy withdrawal of the
pattern from the mold. As the flask is filled with the slurry, it is vibrated so as to bubble out any
air entrapped in the slurry and to ensure that the mould is completely filled up. The plaster
material is allowed to set. Finally when the plaster is set properly the pattern is then withdrawn
by separating the same, from the plaster by blowing compressed air through the holes in the
patterns leading to the parting surface between the pattern and the plaster mold. The plaster mold
thus produced is dried in an oven to a temperature range between 200-700 degree centigrade and
cooled in the oven itself. In the above manner two halves of a mould are prepared and are joined
together to form the proper cavity. The necessary sprue, runner etc. are cut before joining the two
parts.
Fig. 4.15 Plaster molding
Advantages
(a) In plaster molding, very good surface finish is obtained and machining cost is also
reduced.
(b) Slow and uniform rate of cooling of the casting is achieved because of low thermal
conductivity of plaster and possibility of stress concentration is reduced.
(c) Metal shrinkage with accurate control is feasible and thereby warping and distortion of
thin sections can be avoided in the plaster molding.

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Limitations
(a) There is evolution of steam during metal pouring if the plaster mold is not dried at higher
temperatures avoid this, the plaster mold may be dehydrated at high temperatures, but the
strength of the mould decreases with dehydration.
(b) The permeability of the plaster mold is low. This may be to a certain extent but it can be
increased by removing the bubbles as the plaster slurry is mixed in a mechanical mixer.
4.20.9. Antioch Process
This is a special case of plaster molding which was developed by Morris Bean. It is very well
suited to high grade aluminum castings. The process differs from the normal plaster molding in
the fact that in this case once the plaster sets the whole thing is auto-laved in saturated steam at
about 20 psi. Then the mold is dried in air for about 10 to 12 hours and finally in an oven for 10
to 20 hours at about 250°C. The autoclaving and drying processes create a granular structure in
the mold structure which increases its permeability.
4.20.10. Metallic Molding
Metallic mold is also known as permanent mold because of their long life. The metallic mold can
be reused many times before it is discarded or rebuilt. Permanent molds are made of dense, fine
grained, heat resistant cast iron, steel, bronze, anodized aluminum, graphite or other suitable
refractoriness. The mold is made in two halves in order to facilitate the removal of casting from
the mold. Usually the metallic mould is called as dies and the metal is introduced in it under
gravity.
Some times this operation is also known as gravity die casting. When the molten metal is
introduced in the die under pressure, then this process is called as pressure die casting. It may be
designed with a vertical parting line or with a horizontal parting line as in conventional sand
molds. The mold walls of a permanent mold have thickness from 15 mm to 50 mm. The thicker
mold walls can remove greater amount of heat from the casting. This provides the desirable
chilling effect. For faster cooling, fins or projections may be provided on the outside of the
permanent mold. Although the metallic mould can be used both for ferrous and nonferrous
castings but this process is more popular for the non-ferrous castings, for examples aluminum
alloys, zinc alloys and magnesium alloys. Usually the metallic molds are made of grey iron, alloy
steels and anodized aluminum alloys. There are some advantages, dis-advantages and
applications of metallic molding process which are discussed as under.
Advantages
(ii) Fine and dense grained structure in casting is achieved using such mold.
(iii) No blow holes exist in castings produced by this method.
(iv) The process is economical.
(v) Because of rapid rate of cooling, the castings possess fine grain structure.
(vi) Close dimensional tolerance is possible.
(vii) Good surface finish and surface details are obtained.
(viii) Casting defects observed in sand castings are eliminated.
(ix) Fast rate of production can be attained.

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(x) The process requires less labor.
Disadvantages
(i) The surface of casting becomes hard due to chilling effect.
(ii) High refractoriness is needed for high melting point alloys.
(iii) The process is impractical for large castings.
Applications
1. This method is suitable for small and medium sized casting.
2. It is widely suitable for non-ferrous casting.
4.21. Questions
1. Explain briefly the main constituents of molding sand.
2. How do the grain size and shape affect the performance of molding sand?
3. How natural molding sands differ from synthetic sands? Name major sources of obtaining
natural molding sands in India?
4. How are binders classified?
5. Describe the process of molding sand preparation and conditioning.
6. Name and describe the different properties of good molding sand.
7. What are the common tests performed on molding sands?
8. Name and describe briefly the different additives commonly added to the molding sand for
improving the properties of the molding sand.
9. What are the major functions of additives in molding sands?
10. Classify and discuss the various types of molding sand. What are the main factors which
influence the selection of particular molding sand for a specific use?
11. What is meant by green strength and dry strength as applied to a molding sand?
12. What is grain fineness number? Explain how you will use a sieve shaker for determining the
grain fineness of foundry sand.
13. How will you test the moisture content and clay content in molding sand?
14. Using the neat sketches, describe procedural steps to be followed in making dry sand mold.
15. Differentiate between the process of green sand molding and dry sand molding.
16. Sketch a complete mold and indicate on it the various terms related to it and their functions.
17. Discuss briefly the various types of molds.
18. Explain the procedure of making a mold using a split pattern.
19. Write short notes of the following:
(i) Floor molding
(ii) Pit molding
(iii) Bench molding
(iv) Machine molding
(v) Loam molding.
(vi) Plaster molding.
(vii) Metallic molding.
20. Describe the following:
(i) Skin dried molds

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(ii) Air dried molds
(iii) CO2 molds
(iv) Plaster molds.
21. What do you understand by the term gating system?
22. What are chaplets and why are they used?
23. Using neat sketches, describe various types of chaplets.
24. What do you understand by the term gating system?
25. What are the main requirements expected of an ideal gating system?
26. What are different types of gates? Explain them with the help of sketches stating the relative
merits and demerits of each.
27. What is chill? Explain in brief its uses.
28. What is meant by the term ‘risering’?
29. Discuss the common objectives of risers.
30. What advantages are provided by a riser?
31. What is the best shape of a riser, and why?
32. Why is cylindrical shape risers most commonly used?
33. What are the advantages of blind riser over conventional type riser?
34. Write short notes on the following terms:
(i) Use of padding
(ii) Use of exothermic materials and
(iii) Use of chills to help proper directional solidification.
35. Describe the process of shell molding indicating:
(i) Composition of sand mixture
(ii) Steps in molding
(iii) Advantages
(iv) Limitations and
(v) Applications.
36. Describe the CO2–gas molding process in detail using suitable sketches and stat its
advantages, disadvantages and applications.
37. What is a core? What purposes are served by cores?
38. What are the characteristics of a good core?
39. Classify the types of cores? Explain them with the help of sketches specifying their common
applications.
40. What is a core binder?
41. What is core print?
42. Describe different types of core sand.
43. Describe hand core making and machine core making.
44. How are the cores finished and inspected?
45. What is the function of the core in sand molding? How are cores held in place in mold? And
how are they supported?
46. Distinguish between green sand cores and dry sand cores?
47. Name the different steps in core-making? Describe the operation of making a dry sand core?

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48. What are the different stages in core making?
49. What are the different types of machines used in core-making?
50. Describe the following terms used in core-making.
(i) Core drying,
(ii) Core finishing
(iii) Use of rods, wires, arbors and lifting rings.

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CHAPTER FIVE - Casting
5.1. Significanceof Fluidity
Fluidity of molten metal helps in producing sound casting with fewer defects. It fills not only the
mold cavity completely and rapidly but does not allow also any casting defect like “misrun” to
occur in the cast object. Pouring of molten metal properly at correct temperature plays a
significant role in producing sound castings. The gating system performs the function to
introduce clean metal into mold cavity in a manner as free of turbulence as possible. To produce
sound casting gate must also be designed to completely fill the mold cavity for preventing
casting defect such as misruns and to promote feeding for establishing proper temperature
gradients. Prevent casting defect such as misruns without use of excessively high pouring
temperatures is still largely a matter of experience. To fill the complicated castings sections
completely, flow rates must be high but not so high as to cause turbulence. It is noted that metal
temperature may affect the ability of molten alloy to fill the mold, this effect is metal fluidity. 1t
include alloy analysis and gas content, and heat-extracting power of the molding material. Often,
it is desirable to check metal fluidity before pouring using fluidity test. Fig. 5.1 illustrates a
standard fluidity spiral test widely used for cast steel. “Fluidity” of an alloy is rated as a distance,
in inches, that the metal runs in the spiral channel. Fluidity tests, in which metal from the furnace
is poured by controlled vacuum into a flow channel of suitable size, are very useful, since
temperature (super-heat) is the most significant single variable influencing the ability of molten
metal to fill mold. This test is an accurate indicator of temperature. The use of simple, spiral test,
made in green sand on a core poured by ladle from electric furnace steel melting where
temperature measurement is costly and inconvenient. The fluidity test is same times less needed
except as a research tool, for the lower melting point metals, where pyrometry is a problem. In
small casting work, pouring is done by means of ladles and crucibles. There are some special
casting methods which are discussed as under.
Fig. 5.1 Fluidity spiral test
5.2. PermanentMold or Gravity Die Casting
This process is commonly known as permanent mold casting in U.S.A and gravity die casting in
England. A permanent mold casting makes use of a mold or metallic die which is permanent. A
typical permanent mold is shown in Fig. 5.2. Molten metal is poured into the mold under

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Fig. 5.2 A typical permanent mold
gravity only and no external pressure is applied to force the liquid metal into the mold cavity.
However, the liquid metal solidifies under pressure of metal in the risers, etc. The metallic mold
can be reused many times before it is discarded or rebuilt. These molds are made of dense, fine
grained, heat resistant cast iron, steel, bronze, anodized aluminum, graphite or other suitable
refractoriness. The mold is made in two halves in order to facilitate the removal of casting from
the mold. It may be designed with a vertical parting line or with a horizontal parting line as in
conventional sand molds. The mold walls of a permanent mold have thickness from 15 mm to 50
mm. The thicker mold walls can remove greater amount of heat from the casting. For faster
cooling, fins or projections may be provided on the outside of the permanent mold. This provides
the desirable chilling effect. There are some advantages, disadvantages and application of this
process which are given as under.
Advantages
(i) Fine and dense grained structure is achieved in the casting.
(ii) No blow holes exist in castings produced by this method.
(iii) The process is economical for mass production.
(iv) Because of rapid rate of cooling, the castings possess fine grain structure.
(v) Close dimensional tolerance or job accuracy is possible to achieve on the cast
product.
(vi) Good surface finish and surface details are obtained.
(vii) Casting defects observed in sand castings are eliminated.
(viii) Fast rate of production can be attained.
(ix) The process requires less labor.
Disadvantages
(i) The cost of metallic mold is higher than the sand mold. The process is impractical for
large castings.
(ii) The surface of casting becomes hard due to chilling effect.

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(iii)Refractoriness of the high melting point alloys.
Applications
(i) This method is suitable for small and medium sized casting such as carburetor bodies,
oil pump bodies, connecting rods, pistons etc.
(ii) It is widely suitable for non-ferrous casting.
5.3. Slush Casting
Slush casting is an extension of permanent mold casting or metallic mold casting. It is used
widely for production of hollow casting without the use of core. The process is similar to
metallic mold casting only with the difference that mold is allowed to open at an early stage
(only when a predetermined amount of molten metal has solidified up to some thickness) and
some un-solidified molten metal fall down leaving hollowness in the cast object. The process
finds wide applications in production of articles namely toys, novelties, statutes, ornaments,
lighting fixtures and other articles having hollowness inside the cast product.
5.4. PressureDie Casting
Unlike permanent mold or gravity die casting, molten metal is forced into metallic mold or die
under pressure in pressure die casting. The pressure is generally created by compressed air or
hydraulically means. The pressure varies from 70 to 5000 kg/cm2 and is maintained while the
casting solidifies. The application of high pressure is associated with the high velocity with
which the liquid metal is injected into the die to provide a unique capacity for the production of
intricate components at a relatively low cost. This process is called simply die casting in USA.
The die casting machine should be properly designed to hold and operate a die under pressure
smoothly. There are two general types of molten metal ejection mechanisms adopted in die
casting set ups which are:
(i) Hot chamber type
a. Gooseneck or air injection management
b. Submerged plunger management
(ii) Cold chamber type
Die casting is widely used for mass production and is most suitable for non-ferrous metals and
al1oys of low fusion temperature. The casting process is economic and rapid. The surface
achieved in casting is so smooth that it does not require any finishing operation. The material is
dense and homogeneous and has no possibility of sand inclusions or other cast impurities.
Uniform thickness on castings can also be maintained.
The principal base metals most commonly employed in the casting are zinc, aluminum, and
copper, magnesium, lead and tin. Depending upon the melting point temperature of alloys and
their suitability for the die casting, they are classified as high melting point (above 540°C) and
low melting point (below 500°C) alloys. Under low category involves zinc, tin and lead base
alloys. Under high temperature category aluminum and copper base alloys are involved.
There are four main types of die-casting machine which are given as under.
1. Hot chamber die casting machine
2. Cold chamber die casting machine.

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3. Air blown or goose neck type machine
4. Vacuum die-casting machine
Some commonly used die casting processes are discussed as under.
Hot chamber die-casting
Hot chamber die-casting machine is the oldest of die-casting machines which is simplest to
operate. It can produce about 60 or more castings of up to 20 kg each per hour and several
hundred castings per hour for single impression castings weighing a few grams. The melting unit
of setup comprises of an integral part of the process. The molten metal possesses nominal
amount of superheat and, therefore, less pressure is needed to force the liquid metal into the die.
This process may be of gooseneck or air-injection type or submerged plunger type-air blown or
goose neck type machine is shown as in Fig. 5.3. It is capable of performing the following
functions:
(i) Holding two die halves finally together.
(ii) Closing the die.
(iii)Injecting molten metal into die.
(iv)Opening the die.
(v) Ejecting the casting out of the die.
Fig. 5.3 Air blown or goose neck type die casting setup
A die casting machine consists of four basic elements namely frame, source of molten metal and
molten metal transfer mechanism, die-casting dies, and metal injection mechanism. It is a simple
machine as regards its construction and operation. A cast iron gooseneck is so pivoted in the
setup that it can be dipped beneath the surface of the molten metal to receive the same when
needed. The molten metal fills the cylindrical portion and the curved passageways of the
gooseneck. Gooseneck is then raised and connected to an airline which supplies pressure to force
the molten metal into the closed die. Air pressure is required for injecting metal into the die is of
the order of 30 to 45 kg./cm2. The two mold halves are securely clamped together before
pouring. Simple mechanical clamps of latches and toggle kinds are adequate for small molds. On
solidification of the die cast part, the gooseneck is again dipped beneath the molten metal to

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receive the molten metal again for the next cycle. The die halves are opened out and the die cast
part is ejected and die closes in order to receive a molten metal for producing the next casting.
The cycle repeats again and again. Generally large permanent molds need pneumatic or other
power clamping devices. A permanent mold casting may range in weight from a few grams to
150 kg. for aluminum. Cores for permanent molds are made up of alloy steel or dry sand. Metal
cores are used when they can be easily extracted from the casting. A dry sand core or a shell core
is preferred when the cavity to be cored is such that a metal core cannot possibly be withdrawn
from the casting. The sprues, risers, runners, gates and vents are machined into the parting
surface for one or both mold halves. The runner channels are inclined, to minimize turbulence of
the incoming metal. Whenever possible, the runner should be at the thinnest area of the casting,
with the risers at the top of the die above the heavy sections. On heating the mold surfaces to the
required temperature, a refractory coating in the form of slurry is sprayed or brushed on to the
mold cavity, riser, and gate and runner surfaces. French chalk or calcium carbonate suspended in
sodium silicate binder is commonly used as a coating for aluminum and magnesium permanent
mold castings. Chills are pieces of copper, brass or aluminum and are inserted into the mold’s
inner surface. Water passages in the mold or cooling fins made on outside the mold surface are
blown by air otherwise water mist will create chilling effect. A chill is commonly used to
promote directional solidification.
Cold chamber die casting
Cold chamber die casting process differs from hot chamber die casting in following respects.
1. Melting unit is generally not an integral part of the cold chamber die casting machine.
Molten metal is brought and poured into die casting machine with help of ladles.
2. Molten metal poured into the cold chamber casting machine is generally at lower
temperature as compared to that poured in hot chamber die casting machine.
3. For this reasoning, a cold chamber die casting process has to be made use of pressure
much higher (of the order of 200 to 2000 kgf/cm2) than those applied in hot chamber
process.
4. High pressure tends to increase the fluidity of molten metal possessing relatively lower
temperature.
5. Lower temperature of molten metal accompanied with higher injection pressure with
produce castings of dense structure sustained dimensional accuracy and free from blow-
holes.
6. Die components experience less thermal stresses due to lower temperature of molten
metal. However, the dies are often required to be made stronger in order to bear higher
pressures.
There are some advantages, disadvantages and application of this process which are given as
under.
Advantages
1. It is very quick process
2. It is used for mass production
3. castings produced by this process are greatly improved surface finish
4. Thin section (0.5 mm Zn, 0.8 mm Al and 0.7 mm Mg) can be easily casted

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5. Good tolerances
6. Well defined and distinct surface
7. Less nos. of rejections
8. Cost of production is less
9. Process require less space
10. Very economic process
11. Life of die is long
12. All casting has same size and shape.
Disadvantages
1. Cost of die is high.
2. Only thin casting can be produced.
3. Special skill is required.
4. Unless special precautions are adopted for evaluation of air from die-cavity some air is
always entrapped in castings causing porosity.
5. It is not suitable for low production.
Applications
1. Carburetor bodies
2. Hydraulic brake cylinders
3. Refrigeration castings
4. Washing machine
5. Connecting rods and automotive pistons
6. Oil pump bodies
7. Gears and gear covers
8. Aircraft and missile castings, and
9. Typewriter segments
5.5. Advantages of Die Casting Over Sand Casting
1. Die casting requires less floor space in comparison to sand casting.
2. It helps in providing precision dimensional control with a subsequent reduction in
machining cost.
3. It provides greater improved surface finish.
4. Thin section of complex shape can be produced in die casting.
5. More true shape can be produced with close tolerance in die casting.
6. Castings produced by die casting are usually less defective.
7. It produces more sound casting than sand casting.
8. It is very quick process.
9. Its rate of production is high as much as 800 casting / hour.
5.6. Comparisonbetween PermanentMold Casting & Die Casting
The comparison between permanent mold castings and die casting given as under in Table 5.1.

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Table 5.1 Comparison between Permanent Mold Castings and Die Casting
S.No. Permanent Mold Castings Die Casting
1 Permanent mold casting are less costly Die casting dies are costly
2 It requires some more floor area in comparison
to die casting
It requires less floor area.
3 It gives good surface finishing It gives very fine surface finishing
4 It requires less skill It requires skill in maintenance of die
or mold
5 Production rate is good Production rate is very high
6 It has high dimensional accuracies It also have very high dimensional
accuracies
7 This is suitable for small medium sized non-
ferrous
There is a limited scope of non-
ferrous alloys and it is used for small
sizes of castings
8 Initial cost is high hence it is used for large
production
Initial cost is also high hence used for
large production
9 Several defects like stress, surface hardness
may be produced due to surface chilling effect
This phenomenon may also occur in
this case.
5.7. Shell Mold Casting
Shell mold casting process is recent invention in casting techniques for mass production and
smooth surface finish. It was originated in Germany during Second World War. It is also called
as Carning or C process. It consists of making a mold that possesses two or more thin shells
(shell line parts, which are moderately hard and smooth with a texture consisting of
thermosetting resin bonded sands. The shells are 0.3 to 0.6 mm thick and can be handled and
stored. Shell molds are made so that machining parts fit together-easily. They are held using
clamps or adhesive and metal is poured either in a vertical or horizontal position. They are
supported using rocks or mass of bulky permeable material. Thermosetting resin, dry powder and
sand are mixed thoroughly in a muller.
Complete shell molding casting processes is carried in four stages as shown in Fig. 5.4. In this
process a pattern is placed on a metal plate and it is then coated with a mixture of fine sand and
Phenol-resin (20:1). The pattern is heated first and silicon grease is then sprayed on the heated
metal pattern for easy separation. The pattern is heated to 205 to 230°C and covered with resin
bounded sand. After 30 seconds, a hard layer of sand is formed over pattern. Pattern and shell are
heated and treated in an oven at 315°C for 60 secs.,

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Fig. 5.4 Shell mold casting process
Phenol resin is allowed to set to a specific thickness. So the layer of about 4 to 10 mm in
thickness is stuck on the pattern and the loose material is then removed from the pattern. Then
shell is ready to strip from the pattern. A plate pattern is made in two or more pieces and
similarly core is made by same technique. The shells are clamped and usually embedded in
gravel, coarse sand or metal shot. Then mold is ready for pouring. The shell so formed has the
shape of pattern formed of cavity or projection in the shell. In case of unsymmetrical shapes, two
patterns are prepared so that two shell are produced which are joined to form proper cavity.
Internal cavity can be formed by placing a core. Hot pattern and box is containing a mixture of
sand and resin. Pattern and box inverted and kept in this position for some time. Now box and
pattern are brought to original position. A shell of resin-bonded sand sticks to the pattern and the
rest falls. Shell separates from the pattern with the help of ejector pins. It is a suitable process for
casting thin walled articles. The cast shapes are uniform and their dimensions are within close
limit of tolerance ± 0.002 mm and it is suitable for precise duplication of exact parts. It has
various advantages which are as follows. There are some advantages and disadvantages of this
process which are given as under.
Advantages
The main advantages of shell molding are:
(i) Very suitable for thin sections like petrol engine cylinder.
(ii) Excellent surface finish.
(iii) Good dimensional accuracy of order of 0.002 to 0.003 mm.
(iv) Negligible machining and cleaning cost.
(v) Occupies less floor space.
(vi) Skill-ness required is less.
(vii) Molds can be stored until required.
(viii) Better quality of casting assured.
(ix) Mass production.
Disadvantages
(i) Initial cost is high.
(ii) Specialized equipment is required.

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(iii) Resin binder is an expensive material.
(iv) Limited for small size.
(v) Future of shell molding process is very bright.
Applications
(i) Suitable for production of casting made up of alloys of Al, Cu and ferrous metals
(ii) Bushing
(iii) Valves bodies
(iv) Rocker arms
(v) Bearing caps
(vi) Brackets
(vii) Gears
5.8. CentrifugalCasting
In centrifugal casting process, molten metal is poured into a revolving mold and allowed to
solidify molten metal by pressure of centrifugal force. It is employed for mass production of
circular casting as the castings produced by this process are free from impurities. Due to
centrifugal force, the castings produced will be of high density type and of good strength. The
castings produced promote directional solidification as the colder metal (less temperature molten
metal) is thrown to outside of casting and molten metal near the axis or rotation. The cylindrical
parts and pipes for handling gases are most adoptable to this process. Centrifugal casting
processes are mainly of three types which are discussed as under.
(1) True centrifugal casting
(2) Semi-centrifugal casting and
(3) Centrifuged casting
True Centriugal Casting
In true centrifugal casting process, the axis of rotation of mold can be horizontal, vertical or
inclined. Usually it is horizontal. The most commonly articles which are produced by this
process are cast iron pipes, liners, bushes and cylinder barrels. This process does not require any
core. Also no gates and risers are used. Generally pipes are made by the method of the
centrifugal casting. The two processes namely De Lavaud casting process and Moore casting
process are commonly used in true centrifugal casting. The same are discussed as under:
De Levaud Casting Process
Fig 5.5 shows the essential components of De Levaud type true centrifugal casting process. The
article produced by this process is shown in Fig 5.6. In this process, metal molds prove to be
economical when large numbers of castings are produced. This process makes use of metal mold.
The process setup contains an accurately machined metal mold or die surrounded by cooling
water. The machine is mounted on wheels and it can be move lengthwise on a straight on a
slightly inclined track. At one end of the track there is a ladle containing proper quantities of
molten metal which flows a long pouring spout initially inserted to the extremity of the mold. As
pouring proceeds the rotating mold, in the casting machine is moved slowly down the track so
that the metal is laid progressively along the length of the mold wall flowing a helical path. The
control is being achieved by synchronizing the rate of pouring, mold travel and speed of mold

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rotation. After completion of pouring the machine will be at the lower end of its track with the
mold that rotating continuously till the molten metal has solidified in form of a pipe. The
solidified casting in form of pipe is extracted from the metal mold by inserting a pipe puller
which expands as it is pulled.
Fig. 5.5 De Levaud type true entrifugal casting process.
Moore Casting System
Moore casting system for small production of large cast iron pipes employs a ram and dried sand
lining in conjunction with end pouring. As the mold rotates, it does not move lengthwise rather
its one end can be raised up or lowered to facilitate progressive liquid metal. Initially one end of
the mold is raised as that mold axis gets inclined. As the pouring starts and continues, the end is
gradually lowered till the mold is horizontal and when the pouring stops. At this stage, the speed
of mold rotation is increased and maintained till the casting is solidified. Finally, the mold
rotation is stopped and the casting is extracted from the mold.
Fig. 5.6 Article produced by true centrifugal casting process
Semi-Centrifugal Casting
It is similar to true centrifugal casting but only with a difference that a central core is used to
form the inner surface. Semi- centrifugal casting setup is shown in Fig. 5.7. This casting process
is generally used for articles which are more complicated than those possible in true centrifugal
casting, but are axi-symmetric in nature. A particular shape of the casting is produced by mold
and core and not by centrifugal force. The centrifugal force aids proper feeding and helps in
producing the castings free from porosity. The article produced by this process is shown in Fig.
5.8. Symmetrical objects namely wheel having arms like flywheel, gears and back wheels are
produced by this process.

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Fig. 5.7 Semi-centrifugal casting setup Fig. 5.8 Article produced by semicentrifugal
casting process
Centrifuging Casting
Centrifuging casting setup is shown in Fig. 5.9. This casting process is generally used for
producing non-symmetrical small castings having intricate details. A number of such small jobs
are joined together by means of a common radial runner with a central sprue on a table which is
possible in a vertical direction of mold rotation. The sample article produced by this process is
depicted in Fig. 5.10.
5.9. Continuous Casting
In this process the molten metal is continuously poured in to a mold cavity around which a
facility for quick cooling the molten metal to the point of solidification. The solidified metal is
then continuously extracted from the mold at predetermined rate. This process is classified into
two categories namely Asarco and Reciprocating. In reciprocating process, molten metal is
poured into a holding furnace. At the bottom of this furnace, there is a valve by which the
quantity of flow can be changed. The molten metal is poured into the mold at a uniform speed.
The water cooled mold is reciprocated up and down. The solidified portion of the casting is
withdrawn by the rolls at a constant speed. The movement of the rolls and the reciprocating
motion of the rolls are fully mechanized and properly controlled by means of cams and follower
arrangements.
Advantages of Continuous Casting
(i) The process is cheaper than rolling

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Fig. 5.9 Centrifuging casting setup Fig. 5.10 Article produced by centrifugal
casting process
(ii) 100% casting yield.
(iii)The process can be easily mechanized and thus unit labor cost is less.
(iv)Casting surfaces are better.
(v) Grain size and structure of the casting can be easily controlled.
Applications of Continuous Casting
(i) It is used for casting materials such as brass, bronzes, zinc, copper, aluminium and its
alloys, magnesium, carbon and alloys etc.
(ii) Production of blooms, billets, slabs, sheets, copper bar etc.
(iii)It can produce any shape of uniform cross-section such as round, rectangular, square,
hexagonal, fluted or gear toothed etc.
5.10. Probable Causes & Suggested RemediesOf Various Casting
Defects
The probable causes and suggested remedies of various casting defects is given in Table 5.2.

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Table 5.2: Probable Causes and Suggested Remedies of Various Casting Defects
S.No.
Name of
Casting
Defect
Probable Causes Suggested Remedies
1 Blow holes 1. Excess moisture content in
molding sand
2. Rust and moisture on Chills,
chaplets and inserts
3. Cores not sufficiently baked.
4. Excessive use of organic binders.
5. Molds not adequately vented.
6. Molds not adequately vented. mold
and cores
7. Molds rammed very hard.
1. Control of moisture content.
2. Use of rust free chills, chaplet
and clean inserts.
3. Bake cores properly.
4. Ram the mold s less hard.
5. Provide adequate venting in
2 Shrinkage 1. Faulty gating and risering system.
2. Improper chilling.
1. Ensure proper directional
solidification by modifying gating,
risering and chilling
3 Porosity 1. High pouring temperature.
2. Gas dissolved in metal charge.
3. Less flux used.
4. Molten metal not properly
degassed.
5. Slow solidification of casting.
6. High moisture and low
permeability in mold.
1. Regulate pouring temperature
2. Control metal composition.
3. Increase flux proportions.
4. Ensure effective degassing.
5. Modify gating and risering.
6. Reduce moisture and increase
permeability of mold.
4 Misruns 1. Lack of fluidity ill molten metal.
2. Faulty design.
3. Faulty gating.
1. Adjust proper pouring
temperature.
2. Modify design.
3. Modify gating system.
5 Hot Tears 1. Lack of collapsibility of core.
2. Lack of collapsibility of mold
3. Faulty design.
4. Hard Ramming of mold.
1. Improve core collapsibility.
2. Improve mold collapsibility.
3. Modify casting design.
4. Provide softer ramming.
6 Metal
penetration
1. Large grain size and used.
2. Soft ramming of mold.
3. Molding sand or core has low
strength.
4. Molding sand or core has high
permeability.
1. Use sand having finer grain size.
2. Provide hard ramming.
3. Suitably adjust pouring
temperature.

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5. Pouring temperature of metal too
high.
7 Cold shuts 1. Lack of fluidity in molten metal.
2. Faulty design.
3. Faulty gating.
1. Adjust proper pouring
temperature.
2. Modify design.
3. Modify gating system
8 Cuts and
washes
1. Low strength of mold and core.
2. Lack of binders in facing and core
stand.
3. Faulty gating.
1. Improve mold and core strength.
2. Add more binders to facing and
core sand.
3. Improve gating
9 Inclusions 1. Faulty gating.
2. Faulty pouring.
3. Inferior molding or core sand.
4. Soft ramming of mold.
5. Rough handling of mold and core.
1. Modify gating system
2. Improve pouring to minimize
turbulence.
3. Use of superior sand of good
strength.
4. Provide hard, ramming.
10 Fusion 1. Low refractoriness in molding sand
2. Faulty gating.
3. Too high pouring temperature of
metal.
4. Poor facing sand.
1. Improve refractoriness of sand.
2. Modify gating system.
3. Use lower pouring temperature.
4. Improve quality of facing sand.
11 Drops 1. Low green strength in molding
sand and core.
2. Too soft ramming.
3. Inadequate reinforcement of sand
and core projections
1. Increase green strength of sand
mold.
2. Provide harder ramming.
3. Provide adequate reinforcement
to sand projections and cope by
using nails and gaggers.
12 Shot Metal 1. Too low pouring temperature.
2. Excess sulphur content in metal.
3. Faulty gating.
4. High moisture content in molding
sand.
1. Use proper pouring temperature.
2. Reduce sulphur content.
3. Modify gating of system.
13 Shift 1. Worn-out or bent clamping pins.
2. Misalignment of two halves of
pattern.
3. Improper support of core.
4. Improper location of core.
5. Faulty core boxes.
1. Repair or replace the pins, for
removing defect.
2. Repair or replace dowels which
cause misalignment.
3. Provide adequate support to core.
4. Increase strength of both mold
and core.

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6. Insufficient strength of molding
sand and core
14 Crushes 1. Defective core boxes producing
over-sized cores.
2. Worn out core prints on patterns
producing under sized seats for cores
in the mold.
3. Careless assembly of cores in the
mold
1. Repair or replace the pins, for
removing defect.
2. Repair or replace dowels which
cause misalignment.
3. Provide adequate support to core.
and core.
15 Rat-tails or
Buckles
1. Continuous large flat surfaces on
casting.
2. Excessive mold hardness.
3. Lack of combustible additives in
molding sand.
1. Break continuity of large flat
groves and depressions
2. Reduce mold hardness.
3. Add combustible additives to
sand.
16 Swells 1. Too soft ramming of mold.
2. Low strength of mold and core
3. Mold not properly supported.
1. Provide hard ramming.
and core.
17 Hard Spot 1. Faulty metal composition.
2. Faulty casting design.
1. Suitably charge metal
composition.
2. Modify casting design.
18 Run out,
Fins and
Fash
1. Faulty molding.
2. Defective molding boxes.
1. Improving molding technique.
2. Change the defective molding
boxes.
3. Keep weights on mold boxes.
19 Spongings 1. Availability of dirt and swarf held
in molten metal. metal.
2. Improper skimming.
3. Because of more impurities in
molten metal
1. Remove dirt swarf held in molten
2. Skimming should be perfect.
3. Fewer impurities in molten metal
should be there.
20 Warpage 1. Continuous large flat surfaces on
castings indicating a poor design.
2. No directional solidification of
casting.
1. Follow principle of sufficient
directional solidification
2. Make good casting design
5.11. Plastics Molding Processes
There are various methods of producing components from the plastics materials which are
supplied in the granular, powder and other forms. Various plastics molding processes are:
1. Compression Molding.

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2. Transfer Molding
3. Injection Molding.
4. Blow Molding.
5. Extrusion Molding
6. Calendaring.
7. Thermoforming.
8. Casting
Two major processes from the above are discussed as under.
5.11.1. Injection die Molding
In this process, thermoplastic materials soften when heated and re-harden when cooled. No
chemical change takes place during heating and cooling. Fig. 5.11 illustrates the injection
molding process. The process involves granular molding material is loaded into a hopper from
where it is metered out in a heating cylinder by a feeding device. The exact amount of material is
delivered to the cylinder which is required to fill the mold completely. The injection ram pushes
the material into a heating cylinder and doing so pushing bushes a small amount of heated
material out of other end of cylinder through the nozzle and screw bushing and into cavities of
the closed mold. The metal cooled in rigid state in the mold. Then mold is opened and piece is
ejected out material heating temperature is usually between 180°- 280°C. Mold is cooled in order
to cool the mold articles. Automatic devices are commercially available to maintain mold
temperature at required level. Injection molding is generally limited to forming thermoplastic
materials, but equipment is available for converting the machines for molding thermosetting
plastics and compounds of rubber.

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Fig. 5.11 Typical injection molding
5.11.2. Extrusion Molding
Generally all thermo plastic materials are highly suitable for extrusion in to various shapes such
as rods, tubes, sheets, film, pipes and ropes. Thermosetting plastic is not suitable for extrusion
molding. In this process the powder polymer or monomer is received through hopper and is fed
in to the heated chamber by a rotating screw along a cylindrical chamber. The rotating screw
carries the plastic powder forward and forces it through the heated orifice of the die. As the
thermoplastic powder reaches towards the die, it gets heated up and melts. It is then forced
through the die opening of desired shape as shown in the sectional view of the extrusion molding
process through Fig 5.12. On leaving the product from the die, it is cooled by water or
compressed air and is finally carried by a conveyor or belt. The process is continuous and
involves low initial cost.

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Fig. 5.12 Schematic extrusion molding
5.12. Questions
1. Describe in detail the terms ‘solid zone’, ‘mushy zone’ and ‘liquid zone’ used in
solidification of castings. Using figures explain the term directional solidification used in
castings.
2. What is “directional solidification”, and what is its influence on casting quality?
3. Is directional solidification is necessary in casting? How does it help in the production of
sound castings?
4. What are the controlling factors of directional solidification in casting? Name different
stages through which the metal contraction takes place during the solidification of the
casting?
5. Why do you prefer fabricating of metal parts by casting?
6. Define casting. What four basic steps are generally involved in making a casting?
7. What are the common factors which should be considered before designing a casting?
8. Sketch the cross-section through a permanent mold, incorporating all its principal parts.
Describe its construction in detail.
9. Describe the permanent mold casting process and discuss how it differs from the other
casting processes.
10. What are the common materials used for making the permanent molds?
11. Describe step by step procedure for casting using a permanent mold. What are the
advantages, dis-advantages and applications of permanent mold casting?
12. What different metals and alloys are commonly cast in permanent molds?
13. What is the difference between gravity die casting and pressure die casting?
14. How are die casting machines classified? What are the common constructional features
embodied in most of them?
15. Sketch and explain the construction and operation of a hot chamber die casting machine.
16. How does a cold chamber die casting machine differ from a hot chamber machine?
Explain the working of a cold chamber machine with the help of a diagram.

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17. Make a neat sketch to explain the principal parts of an air blown or goose neck type
machine. How does it differ from a hot chamber die casting machine. Discuss their
relative advantages, disadvantages and applications.
18. What is a vacuum die-casting machine? How is the vacuum applied to hot and cold
chamber machines to evacuate the entrapped air completely. What is the main advantage
of this type of machine?
19. Specify features required to be embodied in a successful design of a die-casting die.
20. Describe the various alloys commonly cast through pressure die-casting.
21. What are the general advantages, disadvantages applications of die casting?
22. How does a cold chamber die casting machine differ from a hot chamber die casting
machine?
23. Make neat sketch and explain the construction and operation of a hot chamber die casting
machine.
24. Make neat sketch and explain the construction and operation of a cold chamber die casting
machine.
25. Explain the various steps involved in the investment casting of metals.
26. What is investment casting? What are the main materials used for making the investment
pattern?
27. Describe the complete step by step procedure of investment casting. What are the main
advantages and disadvantages of investment casting?
28. Describe briefly the shell casting process using neat sketches. State its advantages,
disadvantages and generation applications
29. Describe continuous casting process and discuss the important metallurgical features of
the billets produced by these methods.
30. Explain with the help of a neat sketch, the process of centrifugal casting.
31. What do you understand from centrifugal casting?
32. How are the centrifugal casting methods classified?
33. With the help of a neat diagram describe the process of true centrifugal casting. How can
this method be used for production of pipes?
34. Illustrate and describe the process of semi-centrifugal casting.
35. What is centrifuging casting?. Describe the process, stating its differences with other
centrifugal casting methods.
36. What are the advantages and disadvantages of true centrifugal casting?
37. Which materials are commonly used for making the molds for centrifugal casting?
38. Explain the difference with the help of sketches between true centrifugal casting, semi-
centrifugal casting and centrifuge casting.
39. What is continuous casting? Name the various processes of continuous casting you know.
Describe in detail the reciprocating process of continuous casting.
40. How will you select the vertical and inclined axes of rotation in true centrifugal casting.
41. Write short notes on the following:

Foundry Technology
92
(i) Slush casting
(ii) Pressed casting
(iii) De Lavaud process for centrifugal casting
(iv) Moore sand spun process for centrifugal casting.
42. What are the general rules and principles to be followed in designing a casting?
43. What do you understand by foundry mechanization? Explain in brief.
44. What are the advantages of mechanization of foundry?
45. Describe the various units for which mechanization can be easily adopted.
46. What are the main factors which are responsible for producing defects in the castings?
47. Name the various defects which occur in sand castings and state their probable causes and
remedies?
48. List the defects generally occurring from the following, stating the precautions necessary
to prevent them:
(i) Improper pouring technique,
(ii) Use of defective gating system
(iii) Poor or defective cores,
(iv) High moisture content in sand.
49. Discuss briefly the causes and remedies of the following casting defects:
(i) Blow holes,
(ii) Porosity,
(iii) Hot tears
(iv) Shrinkage cavities,
(v) Scabs, and
(vi) Gas porosity
50. Write short notes on the following casting defects:
(i) Sand inclusions,
(ii) Cuts and washes,
(iii) Misrun and cold shuts,
(iv) Honey combing,
(v) Metal penetration,
(vi) Drops,
(vii) Warpage and
(viii) blow holes
51. Explain the causes and remedies of the following casting defects:
(i) Fins
(ii) Shot metal
(iii) Shifts
(iv) Hard spots
(v) Run out
(vi) Rattails or buckles
(vii) Fusion
(viii) Swells
(ix) Crushes
52. What are the various operations generally required to be performed after shake out for
cleaning the castings?
53. Explain the various methods used for removal of gates and risers etc.
54. What are the common methods used for cleaning the surface of the casting?
55. Why are the castings heat treated?
56. How do you repair the castings? Explain.
57. What do you understand from destructive and non-destructive testing methods of
inspecting castings?

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93
58. What are the various non-destructive testing methods used for inspection of castings?
State their advantages and limitations:
59. Write short notes on the following inspection methods:
(i) Visual inspection
(ii) Pressure test
(iii) Penetrate testing
(iv) Radiography
(v) Magnetic particle testing
(vi) Ultrasonic testing.

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