3 foundry

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© Rohan Desai- Automobile Department - New Polytechnic, Kolhapur. Page 1
Introduction:
Foundry engineering is the process of making of castings (Metals or
Non-Metals) in moulds (Sand or other material) with the help of patterns.
The art of foundry is ancient, dating back to the dawn of civilization. In 5000
BC, metals were used to make coins, arrows, knives and household articles.
The casting process is said to have been practiced in early historic times by
the craftsman of Greek and Roman civilization. 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.
Castings have several characteristics that clearly define their role in
modern equipment used for transportation, communication, power,
agriculture, construction and in industry. The foundry process is suitable for
both small and large components. It gives high rate of production, small
dimensional tolerances and good surface finish. It can be used to produce
intricate parts.
The whole process of producing casting may be classified into five stages:
a) Pattern making
b) Moulding and core making
c) Melting and casting
d) Fettling
e) Testing and inspection
Except pattern making, all other stages to produce castings are done in
foundry shops.
Q. Classify the foundries.
According to the type and framework of the organisation, foundries can
be classified as
a) Jobbing foundry
b) Production foundry
c)Semi-production foundry
d) Captive foundry

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Depending upon the materials being produced, foundries can also be
classified under two main headings.
(i) Ferrous foundries
(ii) Non-ferrous foundries
Q. What are advantages and disadvantages of foundry process?
Advantages of foundry process:
a) It one of the most versatile manufacturing process.
b) Castings provide uniform directional properties.
c) Intricate shaped parts can be produced.
d) Very complicated parts can be cast in one piece.
Disadvantages of foundry process:
a) It is only economical for mass production.
b) Sand casting process can not produce parts in accurate sizes.
c) Special casting processes are expensive.
d) In some casting process, skilled operators are required.
e) Internal defects are not identified easily.
Q. What is Pattern?
Pattern is the principle tool during the casting process. It is a full size
model of the desired casting. Its purpose is to form a cavity of desired shape
and size in the mould which when filled with molten metal produces the
casting on solidification.
Q. Which factors are to be considered while selecting the pattern?
The selection of pattern materials depends on factors such as:
(i) service requirements, e.g. quantity, quality and intricacy of castings,
minimum thickness desired, degree of accuracy and finish required;
(ii) possibility of design changes;
(iii) type of production of castings, and type of moulding method and
equipment to be used;
(iv) Possibility of repeat orders.

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Q. Which properties are necessary for patterns?
(i) easily worked, shaped and joined;
(ii) light in weight for facility in handling and working;
(iii) strong, hard and durable ( i.e. of high strength to weight ratio);
(iv) resistant to wear and abrasion, to corrosion, and to chemical action;
(v) dimensionally stable and unaffected by variations in temperatures and
humidity;
(vi) available at low cost;
The wide variety of pattern materials in use may be classified as wood and
wood products; metals and alloys; plasters; plastics and rubbers; and waxes.
Q. What are the advantages & disadvantages of Wood as a pattern?
Generally wood used are teak, sal, shisam, pine and deodar.
Advantages:
1) It is readily available.
2) It can be easily cut and formed in a desired shape by gluing.
3) By applying preservatives like shellac, varnish etc., it can be preserved
for a long time.
4) It is light in weight.
Disadvantages:
1) It is affected by moisture when it comes in contact with damp
moulding sand.
2) Because of sand abrasion, it wears out quickly.
3) Its life is short. Therefore the wood used for forming patterns should
be well seasoned, straight grained, free from knots, strong and of
reasonable cost.
Q. What are the advantages & disadvantages of metal as a pattern?
Metal patterns are used for mass production work. Commonly metals
used for patterns are cast iron, brass, aluminium alloy, magnesium alloy and
white metal.
Advantages:
1) Long life as compared to wooden pattern.
2) No change in shape with moist sand.

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3) When stored no warping occurs.
4) Resistance to wear and very strong.
5) Better surface finish with dimensional accuracy.
Disadvantages:
1) Costlier than wooden pattern.
2) Machining is required which adds to cost.
3) Heavier than wood & inconvenient to handle during moulding.
4) Alterations in the pattern can not be easily made.
Q. Write short note on plastic and waxes as the pattern material.
Plastic:
Plastic as a pattern material has following advantages:
1) It is strong and dimensionally stable.
2) It does not absorb moisture.
3) It is light in weight & durable.
4) It has high resistance to wear.
Waxes:
1) The wax patterns are excellent for investment casting process.
2) The waxes used are paraffin, shellac, bees wax and cerasin wax.
3) Normally wax patterns are formed by injecting liquid or semi-liquid wax
into a split die (water cooled) after cooling the die parts are separated
and wax pattern is taken out.
Q. List the types of patterns and explain any one.
1. Single piece pattern 9..Skeleton pattern
2. Split pattern 10 .Segmental pattern
3. Match plate pattern 11 .Shell pattern
4. Cope and drag pattern 12. Built-up pattern
5. Gated pattern 13. Box-up pattern
6. Sweep pattern 14. Lagged-up pattern
7. Loose piece 15. Left & right hand
8. Follow board pattern
Single piece pattern: (Fig. 3.1) It is without joints, partings or any loose
pieces in its construction are called a single piece or solid pattern. It is also

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known as loose pattern. When using such patterns, a moulder has to cut his
own runners and feeding gates and risers. This operation is time consuming;
hence they are used for limited production.
E.g. Soil temper, Stuffing box and gland of steam engine.
Fig 3.1 Solid Pattern Fig 3.2 Two-piece split pattern
Split pattern: (Fig. 3.2 & 3.3) Many patterns cannot be made in a single
piece because of the difficulties encountered in moulding them. To eliminate
this difficulty, and for castings of intricate design or unusual shape, split
patterns are employed to form the mould. These patterns are usually made in
two parts, as shown in Fig. 3.2, so that one part will produce the lower half of
the mould, and the other, the upper half. The two parts, which may or may
not be of the same size and shape, are held in their proper relative positions
by means of dowel-pins fastened in one piece and fitting holes bored in the
other. The surface formed at the line of separation of the two parts, usually at
the centerline of the pattern, is called the parting surface or parting line. It
will also be the parting surface of the mould.
(a) THREE-PART PATTERN (b) THREE-PART MOULD
Fig 3.3 Three-piece split pattern
It is sometimes necessary to construct a pattern for a complicating
casting that requires three or more parts instead of two to make the

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completed pattern (Fig. 3.3). This type of pattern is known as multi-piece
pattern. A three-part pattern may necessitate the use of a flask having three
parts, although it is possible to mould some types of three-part patterns in a
two-part flask.
E.g. Spindles, cylinders, steam valve bodies, water stop cocks and taps,
bearings, small pulleys and wheels
Match plate pattern: (Fig.3.4) when split patterns are mounted with one
half on one side of a plate and the other half directly opposite on the other
side of the plate, the pattern is called a match plate pattern. A single pattern
or a number of patterns may be mounted on a match plate. The pattern is
made of metal, and the plate which makes the parting line may be either
wood or metal. Patterns for gates and runners are fastened to the drag side
of the plate in their correct positions to from the complete match plate. When
the match plate is lifted off the mould all patterns are drawn, and the cope or
upper half of the mould matches perfectly with the drag or lower half of the
mould. The gates and runners are also completed in one operation.
Fig 3.4 Match plate pattern
E.g. Piston rings of I.C. Engine.
Cope and drag pattern: In the production of large castings, the
complete moulds are too heavy to be handled by a single operator. Therefore,
cope and drag patterns are used to ease this problem to efficient operation.
The patterns are made in halves, split on a convenient joint line, and separate
cope and drag patterns are built and mounted on individual plates or boards.
This arrangement permits one operator or group of operators to prepare the

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cope half of the mould while another operator or group worked on the drag
half. This planned distribution of labour increases production appreciably.
Gated pattern: (Fig 3.5)
1. Gated patterns are usually made of metal.
2. The sections connecting different patterns serve as runner and gates.
3. A gated pattern can manufacture many castings at one time.
Gated patterns may be made of wood or metal and are used for mass
production of small castings.
Fig 3.5 Gated pattern Fig 3.6 Loose-piece pattern
Loose-piece pattern: (Fig 3.6) Some patterns are produced as assemblies
of loose component pieces. The loose-piece patterns are needed when the
part is such that the pattern cannot be removed as one piece, even though it
is split and the line is made on more than one plane. In this case, the main
pattern is usually removed first. Then the separate pieces, which may have to
be turned or moved before they can be taken out, are removed. Completed
patterns of this type usually require more maintenance and are slower to
mould.
Sweep pattern: (Fig 3.7) Symmetrical moulds and cores, particularly in
large sizes, are sometimes shaped by means of sweep patterns. The sweep
pattern consists of a board having a shape corresponding to the shape of the
desired casting and arranged to rotate about a central axis as illustrated in
the Fig. 3.7. The sand is rammed in place and the sweep board is moved
around its axis of rotation to give the moulding sand the desired shape. E.g.
Sweep patterns are employed for moulding part having circular sections.

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Fig 3.7 Sweep pattern
Skeleton pattern: (Fig 3.8) Patterns for very large castings would require a
tremendous amount of timber for a full pattern. In such cases a skeleton
pattern as in Fig. 3.8 may be employed to give the general contour and size
of the desired casting. This is a ribbed construction with a large number of
square or rectangular openings between the ribs which form a skeleton
outline of the pattern to be made. The framework is filled and rammed with
clays, sand or loam, and a strike- off board known as a strickle board is used
to scrape the excess sand out of the spaces between the ribs so that-the
surface is even with the outside of the pattern. It is usually built in two parts:
one for the cope and the other for the drag.
E.g. Pipes, pipe bends, valve bodies, and boxes are few examples of
castings which are made by making skeleton patterns.
Fig 3.8 Skeleton pattern

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Segmental pattern: (Fig 3.9) They are sections of a pattern so arranged
as to form a complete mould by being moved to form each section of the
mould. When making a mould using this pattern, a vertical spindle is firmly
fixed in the center of drag flask (Fig. 3.9).
Fig 3.9 Segmental pattern
The bottom of the mould is rammed and swept level. Then the segmental
pattern is fastened to the spindle. Moulding sand is rammed between the
outside of the pattern and the flask, and in the inside, but not at the ends of
the pattern. After ramming one section, it goes forward to the next section for
ramming; and so on, until the entire mould perimeter has been completed.
Segmental patterns or part patterns are generally applied to circular work
such as rings, wheel rims, gears, etc.
Shell pattern: (Fig. 3.10.) The pattern is usually made of metal, mounted
on a plate and parted along the centre line, the two sections being accurately
doweled together. These short bends are usually moulded and cast in pairs.
The shell pattern is a hollow construction like a shell and the outside shape is
used as a pattern to make the mould, while the inside is used as a core-box
for making cores.

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Fig 3.10 Shell pattern
Sometimes, a pattern of the entire shape of the casting is termed a
shell pattern, and a pattern that is of the required shape outside, but having
the inside cored out is termed a block pattern.
The shell pattern is used largely for drainage fittings and pipe work.
Q. What are the allowances provided on the patterns? And explain
any one.
Patterns are not made the exact same size as the desired casting for
several reasons. Such a pattern would produce castings which are undersize.
Allowance must therefore be allowed for shrinkage, draft, finish, distortion,
and rapping.
Shrinkage allowance: As metal solidifies and cools, it shrinks and
contracts in size. To compensate for this, a pattern is made larger than the
finished casting by means of a shrinkage or contraction allowance. To provide
an allowance, a patternmaker uses shrink or contraction rule which is
slightly longer than the ordinary rule of the same length. Different metals
have different shrinkages; therefore, there is a shrink rule for each type of
metal used in a casting.
Draft allowance: When a pattern is drawn from a mould, there is
always some possibility of injuring the edges of the mould. This danger is
greatly decreased if the vertical surfaces of a pattern are tapered- inward
slightly. This slight taper inward on the vertical surfaces of a pattern is known
as the draft. Draft may be expressed in millimeter per metre on a side, or in
degrees, and the amount needed in each case depends upon (1) length of the

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vertical side, (2) intricacy of the pattern, and (3) the method of moulding. Fig.
3.11 shows how a draft is provided in a pattern.
Fig 3.11 Draft allowance
Machining allowance: Rough surfaces of castings that have to be
machined are made to dimensions somewhat over those indicated on the
finished working drawings. The extra amount of metal provided on the
surfaces to be machined is called machine finish allowance and the edges of
these surfaces are indicated by a finish mark V, or F. The amount that is to be
added to the pattern depends upon (1) the kind of metal to be used, (2) the
size and shape of the casting and (3) method of moulding.
Distortion or camber allowance: Some castings, because of their size,
shape and type of metal, tend to warp or distort during the cooling period.
This is a result of uneven shrinkage and is due to uneven metal thickness or
to one surface being more exposed than another, causing it to cool more
rapidly. The shape of the pattern is thus bent in the opposite direction to
overcome this distortion. This feature is called distortion or camber allowance.
Required shape of casting Distorted casting Cambered pattern
Fig 3.12 Distortion in casting

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Q. Which colour codes are used for patterns?
The colour codes are given for identification of the parts of patterns and
core boxes.
1. Surface to be left unfinished are to be painted black
2. Surface to finished are painted by red colour.
3. Seats for loose pieces are marked by red strips on yellow background
4. Core prints are painted by yellow colour.
5. Stop-offs is marked by diagonal black strips on yellow background.
Q. What is moulding?
Moulding is a process in which a cavity of a desired casting is formed in a
mould (material like sand, gelatin and metal). Thus, the empty space
formed after withdrawing the pattern from the sand compaction forms a
mould.
Q. Write short note on foundry tools.
Foundry tools & equipments may be classified into three groups namely,
hand tools, flasks and mechanical tools.
Hand Tools:
The hand tools a moulder uses are fairly numerous. A brief description
of the most important tools is given here.
Shovel: A shovel (Fig.3.13) is used for mixing and tempering moulding
sand and for moving the sand from the pile to the flask.
Fig 3.13 Shovel Fig 3.14 Riddle

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Riddle: A riddle, sometimes called a screen, consists of a circular or
square wooden frame fitted with a standard wire mesh at the bottom as
shown in Fig. 3.14. It is used for removing foreign materials such as nails,
shot metal, splinters of wood, etc., from the moulding sand.
Rammer: A hand rammer (Fig.3.15) is a wooden tool used for packing or
ramming the sand into the mould. One end, called the peen, is wedge
shaped, and the opposite end, called the butt, has a flat surface.
Fig 3.15 Hand rammer
Trowel: A trowel consists of a metal blade fitted with a wooden handle
(Fig.3.16). Trowels are employed in order to smooth or sleek over the
surfaces of moulds. A moulder also uses them in repairing the damaged
portions of a mould.
Fig 3.16 Trowel
Sprue pin: A sprue is a tapered peg (Fig.3.17) pushed through the cope
to the joint of the mould. As the peg is withdrawn it removes the sand,
leaving an opening for the metal. This opening is called the sprue through
which the metal is poured. The sprue pin forms the riser pin.
.

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Fig. 3.17 Sprue pin Fig. 3.18 Bellow
Bellow: Bellows are used to blow loose particles of sand from the pattern
and the mould cavity. A hand blower is shown in Fig.3.18. Moulding
machines are also provided with a compressed air jet to perform this
operation.
Moulding boxes:
Sand moulds are prepared in specially constructed boxes called flasks.
The purpose of the flask is to impart the necessary rigidity and strength to
the sand in moulding. They are usually made in two parts, held in
alignment by dowel pins. The top part is called the cope and the lower
part the drag. If the flask is made in three sections, the centre is called
the cheek. These flasks can be made of either wood or metals depending
upon the size required. Two types of flasks are used in a foundry: (1) the
snap flask, and (2) the tight or box flask. A snap flask (Fig.3.19) is made
with the hinge on one corner and a lock on the opposite corner so that the
flask may be removed from the mould before it is poured. The snap flask
is of advantage in that many moulds can be made for the same pouring
from a single flask.
Fig 3.19 Snap flask Fig 3.20 Box flask

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A box flask shown in Fig. 3.20 must remain in the mould until the pouring
operation is completed. These boxes are usually made of metal and are
very suitable for small and medium sized moulding.
Mechanical tools: The mechanical tools in the foundry include the many
types of moulding machines that will ram the mould, roll it over, and draw the
pattern. Besides, there are power operated riddles, sand mixers, sand
conveyors, etc. The mould is even poured and shaken out mechanically, and
the casting is taken by machine to the cleaning department. The amount of
mechanization, however, varies considerably from one foundry to the other.
Mass-production foundries making large quantities of relatively few types of
castings are in a position to mechanize more completely than the job-shop
foundries.
Q. What are the constituents of the moulding sand?
Moulding sand contains silica sand grains, clay, moisture and
miscellaneous material as ingredients.
1. Silica sand grains: It contains 80 to 90% silicon dioxide. It is a
product of the breaking of quartz rock or decomposition of
graphite.
2. Clay: They are particles of sand having diameter less than 20
microns.
3. Moisture: When it is present in required quantity, it improves
bonding strength of clay.
4. Miscellaneous material: Iron oxide, lime stone, magnesia, soda and
potash are miscellaneous materials. These must be present below 2
%.
Q. Give classification of moulding sand on the basis of composition
and use.
Moulding sand is classified on the basis of material and use
According to composition
Natural or Green sand: It is obtained from river bed, dug from
pits, crushing & milling of rocks etc. The requirements of these
sands are satisfied by IS: 3343-1965, which has classified them

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into three grades A, B and C according to their clay content and
sintering temperature.
Grade A Grade B Grade C
Clay % 5-10 10-15 15-20
Sintering Temp. in
0
C
1350-1450 1200-1350 1100-
1200
Synthetic or high silica sand: It is obtained from crushing
quartzite sandstone and then washing to get requisite shape
and grain distribution. It is also obtained from sedimentary
origin. Bentonite and water can be added to get desired
strength and bonding properties.
Special sand: Zircon, Olivine, Chromite and Chrome-magnesite
are often used as special sands. Zircon sands are suitable for
cores of brass and bronze casting. Olivine sands are suitable for
nonferrous castings of an intricate shape. Chamotte is suitable
for heavy steel casting.
According to use
Green sand: It is a mixture of silica sand with 18 to 30 per cent clay,
having a total water of from 6 to 8 per cent. The clay and water furnish
the bond for green sand. Moulds prepared in this sand are known as
green sand moulds.
Dry sand: Green sand that has been dried or baked after the mould is
made is called dry sand. They are suitable for larger castings. Moulds
prepared in this sand are known as dry sand moulds.
Loam sand: Loam sand is high in clay, as much as 50 per cent or so,
and dries hard. This is particularly employed for loam moulding usually
for large castings.
Facing sand: Facing sand forms the face of the mould. It is used
directly next to the surface of the pattern and it comes into contact with
the molten metal when the mould is poured. It is made of silica sand
and clay, without the addition of used sand.

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Backing sand: Backing sand or floor sand is used to back up the facing
sand and to fill the whole volume of the flask. Old, repeatedly used
moulding sand is mainly employed for this purpose. The backing sand is
sometimes called black sand because of the fact that old, repeatedly
used moulding sand is black in colour due to the addition of coal dust
and burning on coming m contact with molten metal.
System sand: The used-sand is cleaned and reactivated by the
addition of water, binders and special additives. This is known as system
sand. Since the whole mould is made of this system sand the strength,
permeability and refractoriness of the sand must be higher than those of
backing sand.
Parting sand: Parting sand is used to keep the green sand from
sticking to the pattern and also to allow the sand on the parting surface
of the cope and drag to separate without clinging. This is clean clay-free
silica sand which serves the same purpose as parting dust.
Core sand: Sand used for making cores is called core sand, sometimes
called, oil sand. This is silica sand mixed with core oil which is composed
of linseed oil, resin, light mineral oil and other binding materials. Pitch or
flours and water may be used in large cores for the sake of economy.
Q. Give properties of moulding sand:
Porosity/Permeability: Molten metal always contains a certain
amount of dissolved gases, which are evolved when the metal freezes.
Also, the molten metal, coming in contact with the moist sand,
generates steam or water vapor. If these gases and water vapor
evolved by the moulding sand do not find opportunity to escape
completely through the mould they will form gas holes and pores in the
casting.
Flow ability: Flow ability of moulding sand refers to its ability to
behave like a fluid, so that, when rammed, it will flow to all portions of a
mould and pack all-around the pattern and take up the required shape.
The sand should respond to different moulding processes. High flow

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ability is required of a moulding sand to get compacted to a uniform
density and to obtain good impression of the pattern in the mould.
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.
Adhesiveness: The sand particles must be capable of adhering to
another body, i.e., they should cling to the sides of the moulding boxes.
It is due to this property that the sand mass can be successfully held in
a moulding box and it does not fall out of the box when it is removed.
Cohesiveness or strength: This is the ability of sand particles to stick
together. Insufficient strength may lead to a collapse in the mould or its
partial destruction during conveying, turning over or closing. The mould
may also be damaged during pouring by washing of the walls and core
by the molten metal. The strength of moulding sand must, therefore, be
sufficient to permit the mould to be formed to the desired shape and to
retain this shape even after the hot metal is poured in the mould.
Refractoriness: The sand must be capable of withstanding the high
temperature of the molten metal without fusing. Moulding sands with a
poor refractoriness may bum on to the casting. Refractoriness is
measured by the sinter point of the sand rather than its melting point.
Q. Classify the moulding processes.
1) According to manual or machine
a) Hand moulding: for in piece & small lot production moulds are made by
hand.
b) Machine moulding: these are employed in mass production
2) According to type of material
a) Green sand moulds
b) Dry sand moulds
c) Loam moulds
3) According to methods
a) Bench moulding

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b) Floor moulding
c) Pit d) Sweep e) Plate
Q. What is Core? Why it is used?
Cores are separate shapes of sand that are generally required to from the
hollow interior of the casting or a hole through the casting. Sometimes cores
are also used to shape those parts of the casting that are not otherwise
practical or physically obtainable by the mould produced directly from the
pattern. The core is left in the mould in casting and is removed after the
casting.
Q. Which are the requirements for the core?
Or
Which characteristics are needed for the core?
1. Cores must be strong enough to retain its shape without deforming, to
withstand handling and to resist erosion and deformation by metal during
filling of the mould.
2. Cores must be permeable to allow the core gases to escape easily.
3. Cores should be highly refractory in nature to withstand high temperature
of the molten metal.
4. Cores must be sufficiently low in residual gas-forming materials to prevent
excess gas from entering the metal.
Q. Write short note on core sand and binders.
Core sands:
The ingredients of core sands are sand and binder. Core sands are usually
silica, but zircon, olivine, carbon and chamotte sands are used. Sand that
contains more than 5 per cent clay cannot be used for cores. Excessive clay
reduces not only permeability but also collapsibility.
Core binders: Core sand has no natural bond, as almost pure sand is used
for preparing cores. Hence some other materials are added to the sand to act
as binders which cement the sand particles together before and after the
cores are baked. Various commercial binders are available in the market
which consists mainly of oils, cereals, dextrine, resins, sulphite-liquor,
molasses and protein.

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Core oils, as mentioned earlier, are more popular as they are very economical
and produce better cores. The chief ingredients of these core oils are
vegetable oil, for instance, linseed oil and corn oil.
Oil sands are very popular because:
1. They are easy to use for core making.
2. An oil-sand core is more collapsible than clay bonded core known as loam
core.
3. The green and dry strengths of the oil sand mixture can be, controlled by
quite simple variations in the proportions of dextrine and oil respectively.
4. The baked cores are very hard and not easily damaged in handling or
during closing of the moulds.
Q. Write the procedure for Core making.
Core making consists of the following operation: (1) core sand preparation,
(2) core moulding, (3) baking, and (4) core finishing.
Core sand preparation: The first consideration in making a core is to mix
and prepare the sand properly. The mixture must be homogeneous so that
the core will be of uniform strength throughout. The core sands are generally
mixed in (1) roller mills and (2) core mixers.
Core moulding: Cores are then made manually or with machines. Normally
a core box is required for the preparation of cores. Green sand cores are
made by ramming the sand mixtures into boxes, the interiors of which have
desired shapes and dimensions. The methods used to ram core are usually
done by machines. Core-making machines can be broadly classified as (1)
core blowing machines, (2) core ramming machines, e.g. jolting, squeezing,
slinging.
Fig 3.21 core box & core

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Core baking: After the cores are prepared and placed on metal plate or
core carriers, they are baked to remove the moisture and to develop the
strength of the binder in core ovens at temperature from 150 0
C to 400 0
C,
depending on the type of the binder used, the size of the cores, and the
length of baking time.
Core finishing: After the baking operation, cores are smoothed. All rough
places and unwanted fins are removed by filing some cores are made in two
or more pieces which must be assembled usually by pasting together with
dextrin or other water-soluble binders.
The last operation in the making of a core is to apply a fine refractory coating
or core wash to the surface. This coating prevents the metal from penetrating
into the core and provides a smoother surface to the casting. Some materials
used for core washes include finely ground graphite, silica, mica, zircon,
flour, and a rubber-base chemical spray. Coatings may be applied to the
core surfaces by brushing, dipping, or spraying.
Q. Explain the types of cores.
The cores used in foundries are typed according to their shape and their
position in the mould. The common types of cores, illustrated in Fig.3.22, are
described below.
Horizontal cores: The most common type is the horizontal core. The core is
usually cylindrical in form and is laid horizontally at the parting line of the
mould. The ends of the core rest in the seats provided by the core prints on
the pattern.
Vertical core: This is placed in a vertical position both in cope and drag
halves of the mould. Usually top and bottom of the core are provided with a
taper, but the amount of taper on the top is greater than that at the bottom.

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Balanced core: When the casting is to have an opening only one side and
only one core print is available on the pattern a balanced core is suitable. The
core print in such cases should be large enough to give proper bearing to the
core. In case the core is sufficiently long, it may be supported at the free end
by means of a chaplet
Hanging and cover core: If the core hangs from the cope and does not
have any support at the bottom of the drag, it is referred to as a hanging
core. In this case, it may be necessary to fasten the core with a wire or rod
that may extend through the cope. On the other hand, if it has its support on
the drag it is called cover core. In this case, the core serves as a cover for the
mould, and also as a support for hanging the main body of the core.
Q. What is Core shifting and how it is avoided?
A core must be securely fixed to withstand the upward thrust of the
molten metal. If a core does not stay in just the right place in its mould,
the walls 01 the cavity it produces will not be of proper thickness. To keep
the cores in place during casting some form of chaplets are required.
Chaplets are the supporters of cores. These are rods with flat or curved
plates riveted to them. Various types of chaplets are used in supporting

-Foundry-
different types of cores. Some of the more generally used forms are
shown in Fig. 3.23
FIG. 3.23 CHAPLETS
Q. What are Core prints? Explain their types.
Castings are often required to have holes, recesses, etc. of various sizes
and shapes. These print impressions are obtained by using sand cores
which are separately made in boxes known as core boxes. For supporting
the cores in the mould cavity, an impression in the form of a recess is
made in the mould with the help of a projection suitably placed on the
pattern. This projection on the pattern is known as the core print. A core
print is, therefore, an added projection on a pattern, and it forms a seat
which is used to support and locate the core in the mould. There are
several types of core prints, viz., horizontal or parting line core print,
vertical or cope and drag core print, balancing core print, cover or hanging
core-print, wing or drop core-print. (Fig 3.24)
Horizontal core print: This is laid horizontally in the mould and is
located at the parting line of the mould. The core print is often found on
the split or two-piece pattern.
Vertical core print: This stands vertically in the mould. This is why this
type of core is referred to as a vertical core print. The core print is located
on the cope and drag sides of a pattern and is constructed with
considerable taper especially on the cope side (about 10-15°) so that they
are easily moulded. The taper on drag print is only 1.5-3°.
Balancing core print: This is used when a horizontal core does not
extend entirely through the casting, and the core is supported at one end

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only. An important feature of this core print is that the print of the core in
the mould cavity should balance the part which rests in the core seat.
Q. What are the types of Core boxes:
A core box is essentially a type of pattern made of wood or metal into
which sand is rammed or packed to form a core. The types of core boxes,
in common use, in foundry work, are described below.
Half box: A half box, as shown in Fig. 3.25, is used to form two identical
halves of a symmetrical core. After they are shaped to form and baked,
the core halves are pasted together to form a completed core.
Dump box: A dump box, illustrated in Fig. 3.26, is designed to form a
complete core that requires no pasting. If the core thus made is in the
shape of a slab or rectangle, it is called a rectangular box. The box is
made with open one side and the sand is rammed up level with the edges
of this opening.
Fig 3.25 Half box Fig 3.26 Dump box
Split box: An example of a split core box is shown in Fig. 3.27. It consists of
two halves which are clamped together. One half of the box has two or more
dowels to hold the parts in correct alignment. It is arranged with opening at
one or both ends for filling and ramming the sand. After ramming and striking

-Foundry-
off the excess sand, the core box is unclamped and rapped. This type of core
box moulds the entire core.
Fig 3.27 Split box
A booked type core box is somewhat similar to a split core box. It consists of
two halves, hinged together, opening and closing like a book to form a
complete core.
Gang box: In instances where large number of cores is to be made, a gang
core box, in which several core cavities are rammed in a single operation, is
employed. A gang core box is illustrated in Fig. 3.28.
Fig 3.28 Gang box
Q. Explain with neat sketch the Shell moulding process.
1) Shell is a special form of sand casting. This process is relatively recent and
because of its advantages it is being increasingly used
2) Shell moulding process is applicable to production of castings ranging from
about 250 gram to about 25 kilogram in ferrous as well as non-ferrous metals
and alloys.
3) The sand used in this method is a mixture of the following ingredients:
a) Dry fine silica sand and
b) Synthetic resin binder 3 to 10 % by weight.
4) Resins used are the phenol formaldehydes, urea formaldehydes, alkyds
and polyesters in the form of fine powder. The resins must be thermosetting

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plastics because the strength must be obtained after the mould is heated &
must be retained when molten metal is poured.
5) The mould is formed from a mixture of find sand (100-150 mesh) and a
thermosetting resin binder that is placed against a heated metal pattern.
6) In actual practice, the metal pattern is heated to about 200 to 300 °C,
the melting point of resin. Then after a silicon parting agent is sprayed on
the surface, the resin & sand mixture is deposited on the pattern by
blowing or dumping. The resin starts melting and, in a few seconds, forms
together with the sand a uniform & resin-soaked layer of about 4 to12 mm in
thickness, depending on the heating period. The pattern is then turned over
to allow the unbounded sand to be removed, leaving the shell on the pattern.
The shell is then stripped mechanically and once more heated for
3 to 5 minutes in a special oven to cure the plastic material.
7) In this way, stable shell moulds are obtained which are made in two
sections. Both sections are matched and joined by guides to obtain the
casting mould. Finally, they are placed in a metal case, and surrounded by
about 37 mm of steel shot, sand, and other backup material to support them
during pouring. The gates, sprue and risers are usually a part of the mould.
8) Cylinders for air-cooled engines wit tapered fins, cams, camshafts, air-
compressor crank cases, pistons and piston rings

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Fig 3.29 Shell moulding
Advantages:
1) Floor space required per ton of castings is less compared to
conventional castings.
2) Operators can be trained easily, thus, providing more output per
operator. Skilled operators are not required.
3) The process can be highly mechanised.
Disadvantages / limitations:
1) High pattern cost.
2) High resin cost.
3) High equipment cost.
Q. Write short note on Investment casting.
1) The term investment refers to a special covering which in this case
consists of a refractory mould surrounding a refractory covered wax
pattern.
2) It consists mainly of two stages which are illustrated in fig.3.30
a) First, a master pattern is made of wood or metal around which a mould
is formed. It does not consist of mould sand but of gelatin or an alloy of

-Foundry-
low melting point which is poured over the master pattern. This master
mould consists of the usual two sections and thus can be opened. It is
used for making the “lost pattern". The second pattern to be used in
further processing.
b) The master mould is then filled with liquid wax, with a thermoplastic
material liquefied by heating or with mercury. The heated materials
become solid when they are cooled to normal room temperature. If
mercury is used, the master mould must be cooled down to about -60 °C
(freezing up) to become solid.
c) The second pattern produced in this way is used for preparing the
casting mould properly. The expandable wax pattern is coated with slurry
consisting of silica flour and small amounts of kaolin and graphite mixed
with water. This process is referred to as "investment" of the pattern.
d) However, the pattern is then used to make up moulds similar to those
used in the conventional moulding process, but the pattern within the
mould is not taken out of the mould which is not opened after this
moulding process. This is the reason why a high precision is achieved in
casting.
e) The finished mould is dried in air for 2 to 3 hours and then baked in an
oven for about 2 hours to melt out the wax. At a temperature of 100 to
120°C the wax melts and runs through a hole in the bottom plate into a
tray, thus providing a cavity of high dimensional accuracy for the casting
process.
f) After this, the mould is sintered at about 1000°C to improve its
resistivity. Finally, it cooled down to a temperature between 900 and
700°C for casting.
3) It is possible to combine several hundreds lost patterns of small work
pieces into what is called a "bunch of patterns" by one common process.
Advantages:
1) Casting possess smooth surface.
2) Machining can be largely reduced or eliminated.
3) Extremely thin section can be cast successfully.

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4) Complex & intricate shaped parts that cannot be obtained by other
process can be conveniently made.
Disadvantages:
1) Castings are produced with some size limitations and majority of
casting produced having weight less than 0.5 kg.
2) Process is relatively slow & expensive.
3) The use of core makes process more difficult.
4) Precise control is required in all stage.
Applications:
1) Hollow turbine blades
2) Impeller & other pump & valve components
Fig 3.30 Investment casting

-Foundry-
Q. What do you mean by Permanent mould casting or die casting?
While in the sand castings the moulds are destroyed after solidification of
castings, the moulds are reused repeatedly in the permanent mould castings.
This requires a mould material that has a sufficiently high melting point to
withstand erosion by the liquid metal at pouring temperature, a high enough
strength not to deform in repeated use, and high thermal fatigue resistance
to resist premature crazing (the formation of thermal fatigue cracks) that
would leave objectionable marks on the finished castings. Finally, and ideally,
it should also have low adhesion.
Q. Write short note on pressure die casting.
Die casting is the art of rapidly producing accurately dimensioned parts by
forging molten metal under pressure into split metal dies which resemble a
common type of permanent mould. Within a fraction of a second, the fluid
alloy fills the entire die, including all the minute details. Because of the low
temperature of the die (it is water-cooled), the casting solidifies quickly,
permitting the die halves to be separated and the casting ejected. If the parts
are small, several parts may be cast at one time in what is known as multiple-
cavity die.
This process is particularly suitable for lead, magnesium, tin, and zinc alloys.
The advantages of die casting practice lie in the possibility of obtaining
castings of sufficient exactness and in the facility for casting thinner sections
that can not be produced by any other casting method.
Two main types of machines are used to produce die castings (1) the hot
chamber, exemplified here by the plunger-type machine, and (2) the cold
chamber machine

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Fig 3.31 Pressure die casting
In a hot chamber submerged plunger-type machine, the plunger operates in
one end of a gooseneck casting which is submerged in the molten metal.
With the plunger in the upper position, metal flow by gravity into this casting
through holes 2 just below the plunger and the entrapped liquid metal is
forced into the die 3 through the gooseneck channel and in-gate 4. As the
plunger retracts, the channel is again filled with the right amount of molten
metal. The plunger made of refractory material may be actuated manually or
mechanically and hydraulically, that is by means of air pressure below 150
kgf/cm2
(about 15 MN/m2
). Heating 5 is continued throughout the operation
to keep the molten metal sufficiently liquid. The range of alloys that can be
handled is limited by the pump material.
In a horizontal plunger cold-chamber machine, the plunger 7 is driven by air
or hydraulic pressure to force the charge into the die 3. As soon as the ladle 2
is emptied, plunger moves to the left and forces the metal into the cavity 4.
After the metal solidified, the core 5 is withdrawn, and then the die is opened.
Ejectors 6 are employed to remove the casting automatically from the die.
Advantages of die casting are:
1. Very high rate of production is achieved.
2. Close dimensional tolerances of the order of ± 0.025 mm is possible.
3. Surface finish of 0.8 microns can be obtained.

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4. Very thin sections of the order of 0.50 mm can be cast.
Disadvantages of this process are:
1. Not economical for small runs.
2. Only economical for nonferrous alloys.
3. Heavy castings cannot be cast. In fact, the maximum size is limited by the
size of the dies and the capacity of the die casting machines available.
4. Cost of die and die casting equipment is high.
Q. What is centrifugal casting? Explain any one
In the centrifugal casting, molten metal is poured into moulds while they are
rotating. The metal falling into the centre of the mould at the axis of rotation
is thrown out by the centrifugal force under sufficient pressure towards the
periphery, and the contaminants or impurities present being lighter in weight
are also pushed towards the centre. This is often machined out any way.
Solidification progresses from the outer surface inwards, thus developing an
area of weakness in the centre of the wall. The use of gates, feeders, and
cores is eliminated, making the method less expensive and complicated.
Centrifugal casting can be classified into three general types: true centrifugal,
semi centrifugal, and centrifuged.
True centrifugal casting: This employs moulds of rotational symmetry
made of steel (with a refractory mould wash or even a green- or dry-sand
lining) or of graphite. The melt is poured while the mould rotates at its axis,
which may be horizontal, vertical or inclined at any suitable angle between 0
to 90°, although horizontal axis of rotation is a more common practice. While
rotating, the molten metal is carried to the walls of the cavity by centrifugal
force (Fig. 3.32). The metal then solidifies forming a hollow casting without
the use of a central core. The outside of the mould is water-cooled to
accelerate solidification.

-Foundry-
Fig 3.32 True centrifugal casting
The method is ideal for hollow cylindrical castings such as bushings, gun
barrels, cast iron pipes, etc.
Semi centrifugal casting: This is a means of forming symmetrical shapes
about the rotative axis, which is usually vertical in a balanced state. The
molten metal is introduced through a gate which is placed on the axis, and
flows outward to the rim by the centrifugal force. If a central bore is required
in the casting, a dry sand core is best suited. The central gate acts as a- riser
for the hub portion.
Since the speeds are low, high pouring pressures are not produced and the
impurities are not rejected towards the centre as effectively as in the true
centrifugal casting.
This method is generally employed for making large-sized castings which are
symmetrical about their own axis such as gears, disked wheels, propellers and
pulleys.
Centrifuged: In this process several identical or nearly similar moulds are
located radially about a vertically arranged central riser or sprue which feeds
the metal into the cavities through a number of radially gates. The entire
mould is rotated with the central sprue which acts as the axis of rotation.
Thus, it is not a purely centrifugal process.

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Fig 3.33 Centrifuged casting
This type of casting is suitable for small, intricate parts where feeding
problems are encountered. This method can be used to advantage for stack
moulding of six or more moulds mounted one above the other.
Q. What are the functions of Gating System?
The term gate is defined as one of the channels which actually lead into the
mould cavity, and the term gating or gating system refers to all channels by
means of which molten metal is delivered to the mould cavity. The functions
of a gating system are:
1. To provide continuous, uniform feed of molten metal, with as little
turbulence as possible to the mould cavity.
2. To supply the casting with liquid metal at best location to achieve proper
directional solidification and optimum feeding of shrinkage cavities.
3. To fill the mould cavity with molten metal in the shortest possible time to
avoid temperature gradient.
4. To provide with a minimum of excess metal in the gates and risers.
Inadequate rate of metal entry, on the other hand, will result many defects in
the casting.
5. To prevent erosion of the mould walls.
6. To prevent slag, sand and other foreign particles from entering the mould.
Q. Which are the components of the gating system?
A gating system is usually made up of (1) pouring basin, (2) sprue, (3)
runner, and (4) flow-off gate. They are shown in Fig. 3.34.

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Fig 3.34 Gating system
Pouring basin: This part of the gating system is made on or in the
top of the mould. Sometimes, a funnel-shaped opening which serves as
pouring basin is made at the top of the sprue in the cope. The main purpose
of the pouring basin is to direct the flow ct metal from ladle to the sprue, to
help maintaining the required rate of liquid metal flow, and to reduce
turbulence and vortexing at the sprue entrance.
Sprue: The vertical passage that passes through the cope and
connects the pouring basin with the runner or gate is called the sprue.
The cross-section of a sprue may be square, rectangular, or circular.
Runner: In large castings, molten metal is usually carried from the
sprue base to several gates around the cavity through a passageway called
the runner. The runner is generally preferred in the drag, but it may
sometimes be located in the cope, depending on the shape of the casting. It
should be streamlined to avoid aspiration and turbulence.
Gate: A gate is a passage through which molten metal flows from the
runner to the mould cavity. The location and size of the gates are so arranged
that they can feed liquid metal to the casting at a rate consistent with the
rate of solidification. A gate should not have sharp edges as they may break
during passage of the molten metal and consequently sand particles may pass

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with the liquid metal into the mould cavity. However, the gates should be
located where they can be easily removed without damaging the casting.
According to their position in the mould cavity, gating may be broadly
classified as (1) top gating, (2) parting-line gating, and (3) bottom gating.
Q. What is risering system?
A riser or a feeder head is a passage of sand made in the cope to
permit the molten metal to rise above the highest point in the casting after
the mould cavity is filled up. Risers serve a dual function: they compensate
for solidification shrinkage which is a very common casting defect, and are a
heat source so that they freeze last and promote directional solidification.
Risers provide thermal gradients from a remote chilled area to the riser.
Besides, they enable the pourer to see the metal as it falls into that the mould
cavity. If the metal does not appear in the riser, it indicates that the mould
cavity has not been completely filled up.
The main requisites of an effective riser are:
1. It must have such a volume that it has enough reservoir of feed-metal in
order to feed the last part of the casting to freeze.
2. The solidification time of metal in the riser should be greater than that in
the mould cavity.
3. It should derive sufficient feeding pressure either by atmospheric pressure
of by metallostatic pressure.
TYPES OF RISERS
There are two types of risers: top or open risers and side or blind risers.
Q. Write cause and remedy for defects in casting.
1. Shifts. This is an external defect in a casting.
Cause: due to core misplacement or mismatching of top and bottom
parts of the casting usually at a parting line. Misalignment of flasks is another
likely cause of shift.
Remedy: By ensuring proper alignment of the pattern or die part,
moulding boxes, correct mounting of patterns on pattern plates, and
checking of flasks, locating pins, etc. before use.

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2. Warpage. Warpage is unintentional and undesirable deformation in a
casting that occurs during or after solidification.
Cause: Due to different rates of solidification different sections of a
casting, stresses are set up in adjoining walls resulting in warpage in these
areas. Large and flat sections or intersecting sections such as ribs are
particularly prone to warpage.
Remedy: is to produce large areas with wavy, corrugated construction, or
add sufficient ribs or rib-like shapes, to provide equal cooling rates in all
areas; a proper casting design can go a long way in reducing the warpage of
the casting.
3. Swell. A swell is an enlargement of the mould cavity by metal pressure,
resulting in localised or overall enlargement of the casting.
Cause: This is caused by improper or defective ramming of the mould.
Remedy: To avoid swells, the sand should be rammed properly and
evenly.
4. Blowholes. Blow holes are smooth, round holes appearing in the form of
a cluster of a large number of small holes below the surface of a casting.
These are entrapped bubbles of gases with smooth walls.
Cause: excessive moisture in the sand, or when permeability of sand is
low, sand grains are too fine, sand is rammed too hard, or when venting is
insufficient.
Remedy: To prevent blowholes, the moisture content in sand must be
well adjusted, sand of proper grain size should be used, ramming should
not be too hard and venting should be adequate.
5. Drop. A drop occurs when the upper surface of the mould cracks, and
pieces of sand fail into the molten metal.
Cause: This is caused by low strength and soft ramming of the sand,
insufficient fluxing of molten metal and insufficient reinforcement of sand
projections in the cope.
Remedy: The above factors are eliminated to avoid drop.

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