Introduction to manufacturing process

5/20/2016 1Hareesha N G, Dept of Aero Engg, DSCE

Unit-1: Introduction to manufacturing process
• Casting Process: Introduction : Concept of Manufacturing process, its
importance.
• Classification of Manufacturing processes. Introduction to Casting
process & steps involved.
• Varieties of components produced by casting process. Advantages &
Limitations of casting process.
• Patterns: Definition, functions, Materials used for pattern, various
pattern allowances and their importance. Classification of patterns.
• Binder: Definition, Types of binder used in moulding sand.
• Additives: Need, Types of additives used.
5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 2

Factors to be considered for selecting a
production process
a) Shape and size to be produced - For products with simple
shape, machining is best suited. But for complex and intricate
shapes, casting is preferred. The size of the product is also an
important factor. For example, 'long' products such as rails or
'thin' products such as car-body panels can be best made by
forming process compared to others.
(b) Quantity to be produced - Both machining and casting can
be used for producing large quantity products, but are not
suitable for small quantity products, as they are not
economical.
(c) Type of material - Materials possess various properties like
ductility, hardness, toughness, brittleness etc. Hard materials
cannot be machined easily. Brittle materials cannot be
mechanically worked (Forming process). In such cases,
casting is preferred.

Factors to be considered for selecting a
production process
(d) Surface finish and dimensional accuracy - Casting with expendable
moulds does not yield good surface finish. However," if casting
process is selected, it should be followed by machining process to
obtain the desired surface finish and dimensional tolerance.
(e) Quality and property requirements - A defect-free product with
specific properties serve its purpose for long life. Properties of cast
material are generally less when compared to that of mechanically
worked materials. Also, casting gives a lot of defects. Hence, a process
that gives better properties and quality should be selected.
(f) Cost of the product - Customers often demand for products with more
features and performance at reduced prices. Hence, a low cost
production process should be selected, but at the same time, see that
no compromise is made in terms of quality.

CASTING PROCESS

Terms involved in casting

Terms involved in casting process
• Mould box (flask) : It is usually a metallic
frame used for making and holding a sand
mould. The mould box has two parts: the
upper part called 'cope', and the lower
part called 'drag'.
• Parting line/parting surface: It is the zone
of separation between cope and drag
portions of the mould in sand casting.
• Sprue: It is vertical passage through which the molten metal
will enter the gate.
• Pouring basin: The enlarged portion of the sprue at its top
into which the molten metal is poured.

Terms involved in casting process
• Gate/ingate: It is a short passage way which
carries the molten metal from the runner/
sprue into the mould cavity.
• Riser: A riser or feed-head is a vertical
passage that stores the molten metal and
supplies (feed) the same to the casting as it
solidifies.
• Gate/ingate: It is a short passage way which carries the molten metal from the
runner/ sprue into the mould cavity.
• Riser: A riser or feed-head is a vertical passage that stores the molten metal
and supplies (feed) the same to the casting as it solidifies.
• Mould cavity: The space in a mould that is filled with molten metal to form the
casting upon solidification.
• Core: A core is a pre-formed (shaped) mass of sand placed in the mould cavity
to form hollow cavities in castings.
• Core print: It is a projection attached to the pattern to help for support and
correct location of core in the mould cavity.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 8

STEPS INVOLVED IN MAKING A CASTING
The basic steps in making a casting are:
(a) Pattern making
(b) Mould preparation (including gating and risering)
(c) Core making
(d) Melting and Pouring
(e) Cleaning and Inspection

a) Pattern making
• A pattern is a replica of the object to be cast.
• It is used to prepare a cavity into which the molten
metal is poured.
• A skilled pattern maker prepares the pattern using
wood, metal, plastic or other materials with the help
of machines and special tools.
• Many factors viz., durability, allowance for shrinkage
and machining etc., are considered while making a
pattern.

b) Mould preparation
• Mould preparation involves forming a cavity by packing
sand around a pattern enclosed in a supporting metallic
frame called 'flask' (mould box).
• When the pattern is removed from the mould, an exact
shaped cavity remains into which the molten metal is
poured.
• Gating and risering are provided at suitable locations in
the mould.
– Gating - Passage through which molten metal flows and enter the mould
cavity.
– Risering - A reservoir of molten metal connected to the mould cavity to
supply additional metal so as to compensate for losses due to shrinkage, as
the metal solidifies.

c) Core making
• In some cases, a hole or cavity is required in the
casting.
• This is obtained by placing a core in the mould
cavity.
• The shape of the core corresponds to the shape
of the hole required.

d) Melting and Pouring
• Metals or alloys of the required composition are
melted in a furnace and poured into the mould
cavity.
• Many factors viz., temperature of molten metal,
pouring time, turbulence etc., should be considered
while melting and pouring.

e) Cleaning and Inspection
• After the molten metal has solidified and cooled, the
rough casting is removed from the mould, cleaned
and dressed.
• This involves removing cores, adhered sand particles,
gating and risering systems, fins, blisters etc., from
the casting surface.
• then sent for inspection to check for dimensions or
any defects like blow holes, cracks etc.

Components Produced by
Casting Process
• Casting is the first step and the primary process for
shaping any material.
• All materials have to be cast before it is put to use.
• The ingots produced by casting process are used as
raw material for secondary processes like machining,
forging, rolling etc.
• More than 90 % of all manufactured goods and capital
equipment use castings for their manufacture.
• To list the components produced by casting is an
endless process. A few major components produced by
casting are given below.

Components Produced by Casting Process
• Automotive sector - Nearly 90 % of the parts in automobiles are-
manufactured by castings. A few parts include brake drum,
cylinder, cylinder linings, pistons, engine blocks, universal joints,
rocker arm, brackets etc.,
• Aircraft - Turbine blades, casing etc.
• Marine propeller blades.
• Machining - Cutting tools, machine beds, wheels and pulleys,
blocks and table for supports etc.
• Agriculture and rail road equipments.
• Pumps and compressors frame, bushings, rings, pinion etc.
• Valves, pipes and fittings for construction work.
• Camera frames, parts in washing machine, refrigerators and air-
conditioners.
• Steel utensils and a wide variety of products.

Advantages of casting process
• Large hollow and intricate shapes can be easily cast.
• Quick process, and hence suitable for mass production.
• No limit to size and shape. Parts ranging from few millimeters to
meters and few grams to tons can be cast efficiently and
economically.
• Better dimensional tolerances and surface finish can be obtained
by good casting practice.
• Castings exhibit uniform properties in all the directions -
longitudinal, lateral and diagonal.
• The casting process is usually the cheapest process.
• Unrelieved internal stresses are absent in cast components.
• Certain metals and alloys can be manufactured by means of
casting only, e.g., Phosphor-Bronze.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 17

Limitations of casting process
• Presence of defects in cast parts is a major disadvantage.
• Casting process is not economical for small number of parts.
• Properties of cast materials are generally inferior when
compared to those made by machining or forging process.
• Casting process mostly deals with elevated temperatures.
• There are limitations regarding thin sections.
• Casting process is not suitable for very small number of
components.

INTRODUCTION TO PATTERN MAKING
• A pattern is a mold forming tool in the hands of foundry men.
• A pattern is a model or the replica of the object to be cast.
• Except for the various allowances a pattern exactly
resembles the casting to be made.
• A pattern is required even if one object has to be cast.
• A pattern 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.

Difference between pattern and casting
• The main difference between a pattern and the casting is their dimensions.
• A pattern is slightly larger in size as compared to the casting, because a
pattern,
– carries Shrinkage allowance, it may be of the order of 1 to 2 mm/ 100
mm.
– is given a Machining allowance to clean and finish the required surfaces.
– carries a Draft allowance of the order of 1 and 3 degrees for external
and internal surfaces respectively
– carries core prints.
• A pattern may not have all holes and slots which a casting will have. Such
holes and slots unnecessarily complicate a pattern and therefore can be
drilled in the casting after it has been made.
• A pattern may be in two or three pieces whereas a casting is in one piece.
• A pattern and the casting also differ as regards the material out of which
they are made.

Functions of a patterns
• A pattern prepares a mold cavity for the purpose of making a casting.
• A pattern may contain projections known as core prints if the casting
requires a core and need to be made hollow.
• Runner, gates and risers (used for introducing and feeding molten
metal to the mold cavity) may form a part of the pattern.
• A pattern may help in establishing locating points on the mold and
therefore on the casting with a purpose to check the casting
dimensions.
• Patterns establish the parting line and parting surfaces in the mold.
• A pattern may help position a core (in case a part of mold cavity is
made with cores), before the molding sand is rammed.
• Patterns that are properly made and having finished and smooth
surfaces, reduce casting defects.
• Properly constructed patterns minimize overall cost of the castings.

Pattern materials
• The following factors assist in selecting proper pattern material:
The number of castings to be produced. Metal patterns are
preferred when the production quantity is large.
The desired dimensional accuracy and surface finish required
for the castings.
Nature of molding process i.e., sand casting, permanent mold
casting, shell molding, investment casting etc.
Method of molding i.e., hand or machine molding.
Shape, complexity and size of the casting.
Type of molding materials i.e., sand etc.
The high probability of changing the casting and hence the
pattern in near future.
Selection of pattern materials

Materials for making patterns
• Patterns may be constructed out of the following
materials.
(a) Wood (b) Metal
(d) Plastic (d) Plaster (POP)
(e) Wax

WOOD
• The most common materials for making patterns for sand casting is the wood.
Advantages
– Inexpensive.
– Easily available in large quantities.
– Easy to machine and to shape to different configurations and forms
– Easy to join to acquire complex and large pattern shapes
– Light in weight
– Easy to obtain good surface finish
– Wooden patterns can be preserved for quite long times with the help of
suitable wood preservatives.
Limitations
– Wooden patterns are susceptible to shrinkage and swelling.
– They possess poor wear resistance.
– They are abraded easily by sand action.
– They absorb moisture, consequently get deformed and change shape and size.
– They cannot withstand rough handling.
– They are weak as compared to metal patterns.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 24

Metal
• Metal patterns are employed where large number of
castings have to be produced from the same patterns.
• Metal patterns are cast from wooden patterns.
• The different metals and alloys used for making
patterns are,
– Aluminium and Aluminium alloys
– Steel
– Cast Iron
– Brass
– White Metal

Advantages of Metal Patterns
– Unlike wooden patterns, they do not absorb moisture. They retain their
shape.
– They are more stronger and accurate as compared to wooden patterns.
– They possess life much longer than wooden patterns.
– They can withstand rough handling.
– They do not distort
– They possess greater resistance to abrasion. They have accurate
dimensional tolerances. They are far stable under different environments.
– It is easy to obtain smooth surface finish.
– They possess excellent wear resistance and strength to weight ratio.
Limitations of Metal Patterns
– Expensive as compared to wood patterns.
– Are not easily repaired e.g. (Aluminium patterns).
– Ferrous patterns get rusted.
– They (ferrous patterns) are heavier than wooden patterns,
– They cannot be machined so easily as wooden ones.

Plastic
• Advantages
– Durable
– Provides a smooth surface.
– Moisture resistant.
– A plastic pattern does not involve any appreciable change in its size or
shape.
– Lightweight.
– Wear and corrosion resistant.
– Provides good surface finish.
– It possesses low solid shrinkage.
• Limitations
– Plastic patterns are fragile and thus light sections may need metal
reinforcements.
– Plastic patterns may not work well when subject to conditions of severe
shock as in machine moulding.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 27

PLASTER
• Advantages
– can be easily worked by using wood working tools.
– Intricate shapes can be cast without any difficulty.
– It has high compressive strength (up to 285 kg/cm2)
• Disadvantages
– Can be used for small castings only
• Plaster Patterns Material: Plaster patterns may be
made out of Plaster of Paris or Gypsum cement.
• Applications: Plaster is used for making (i) Small
and intricate patterns, and (ii) Core boxes.

WAX
• Advantages
Wax patterns provide very good surface finish
They impart high accuracy to the castings.
After being molded, the wax pattern is not taken out of
the mold like other patterns; rather the mold is
inverted and heated; the molten wax comes out and/or
is evaporated. Thus there is no chance of the mold
cavity getting damaged while removing the pattern.
• Applications
• Wax patterns find applications in Investment
casting process.

PATTERN ALLOWANCES
• A pattern is always larger in size as compared to
the final casting, because it carries certain
allowances.
• The various pattern allowances are below
(a) Shrinkage or contraction allowance.
(b) Machining or Finish allowance.
(c) Draft or Taper allowance.
(d) Distortion or camber allowance.
(e) Shake or rapping allowance.

Shrinkage Allowance
• Almost all cast metals shrink or contract volumetrically after solidification and
therefore to obtain a particular sized casting, the pattern is made oversize by
an amount equal to that of shrinkage or contraction.
• Different metals shrink at different rates because shrinkage is the property of
the cast metal or alloy.
• The metal shrinkage depends upon
• The cast metal or alloy.
• Pouring temperature of the metal or alloy.
• Casting dimensions (size).
• Casting design aspects.
• Molding conditions (i.e., mold materials and molding methods
employed).
• Cast iron poured at higher temperatures will shrink more than that poured at
lower temperature.
• Wood patterns used to make metallic patterns are given double allowance; one
for the shrinkage of the metal of the pattern and the other for that of metal to
be cast.

Machining Allowance
• A casting is given an allowance for machining, because
– Castings get oxidized in the mold and during heat treatment; scales etc., thus formed
need to be removed.
– It is intended to remove surface roughness and other imperfections from the castings.
– It is required to achieve exact casting dimensions.
• How much extra metal or how much Machining allowance should be provided,
depends upon:
• Nature of metal i.e., ferrous or non-ferrous. Ferrous metals get scaled whereas non-ferrous ones do not.
• Size and shape of the casting. Longer castings tend to warp and need more material (i.e., allowance) to
be added to ensure that after machining the casting will be alright.
• The type of machining operation (i.e., grinding, turning, milling, boring etc.) to be employed for
cleaning the' castings. Grinding removes much lesser metal as compared to turning.
• Casting conditions i.e., whether casting conditions result in a rough casting or a semi-finished one. Casting
conditions include the characteristics of mold-materials etc.
• Molding process employed. Die casting produces parts which need little machining (allowance) whereas
sand-casting, require more machining allowance.
• Number of cuts to be taken. Machining allowance is directly proportional to the number of cuts required for finishing
the casting.
• The degree of surface finish desired on the cast part.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 32

Draft or Taper Allowance
• It is given to all surfaces perpendicular to the parting
line.
• Draft allowance is given so that the pattern can be easily
removed from the molding material tightly packed
around it without damaging the mold cavity.
• The amount of Taper depends upon
– Shape and size (length) of the pattern in the depth direction in contact with
the mold cavity.
– Molding method.
– Mold materials.
• Draft allowance is imparted on internal as well as
external surfaces; of course it is more on internal
surfaces.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 33

Fig. shows two patterns — one with taper allowance and the
other without it. It can be visualized that it is easy to draw the
pattern having taper allowance, out of the mold without
damaging mold walls or edges.
Taper on external surfaces = 10 to 25 mm/metre.
Taper on internal surfaces = 40 to 65 mm/metre,

Distortion Allowance
• A Casting will distort or warp if:
– it is of irregular shape,
– all its parts do not shrink uniformly i.e., some parts shrink while others are
restricted from doing so,
– it is U or V-shaped,
– it has long, rangy arms as those of the propeller strut for the ship,
– it is a long flat casting,
– the arms possess unequal thickness,
– one portion of the casting cools at a faster rate as compared to the other,
etc.
• Distortion can be practically eliminated by providing an allowance
and constructing the pattern initially distorted i.e., outsize in the
opposite direction so that the casting after cooling neutralizes the
initial distortion given on the pattern and acquires the correct shape.
• The amount of distortion allowance may vary from 2 to 20 mm
depending upon the size, shape and material of the casting.

Shake Allowance
• A pattern is shaken by striking the same with a wooden
piece from side to side. This is done so that the pattern is
loosened a little in the mold cavity and can be easily
removed.
• In turn, therefore, shaking enlarges the mold cavity
which results in a bigger sized casting.
• Shake allowance is normally provided only to large
castings because it is negligible in case of small castings
and is thus ignored.
• The magnitude of shake allowance can be reduced by
increasing the taper.

TYPES OF PATTERNS

• For selecting a particular kind of pattern for making a casting,
one may consider the following points:
– Quantity of castings to be produced.
– The size and the complexity of the shape of the casting to be
produced.
– Type of molding method to be used (i.e., hand or machine
molding).
– Problems associated with the molding operation such as
withdrawing the pattern from the mold etc.
– Other difficulties resulting from poor casting design or pattern
design.

• The different types of patterns commonly used
are:
– One piece(Solid) pattern
– Split pattern
– Loose piece pattern
– Match plate pattern
– Cope and Drag pattern
– Sweep pattern
– Gated pattern
– Skeleton pattern
– Follow board pattern.

One Piece (solid) Pattern

One Piece (solid) Pattern
• It is the simplest type of pattern.
• As the name suggests the pattern is
made from one piece and does not
contain loose pieces or joints.
• It is inexpensive.
• It is used for making a few large size simple castings
• One piece pattern is usually made up of wood or
metal depending upon the quantity of castings to be
produced.
• For making the mold, one piece pattern is
accommodated either in the cope or in the drag.

Split Pattern
• Patterns of intricate (shaped) castings
cannot be made in one piece because of
the inherent difficulties associated with
the molding operations (e.g. withdrawing
the pattern from the mold etc.) , such
patterns are, then, made as split or two
piece patterns.
The upper and the lower parts of the split pattern are accommodated in the
cope and drag portions of the mold respectively.
Dowel pins are used for keeping the alignment between the two parts of the
pattern.
The parting (surface or) line of the pattern forms the parting (surface or) line of
the mold.
Patterns for still more intricate castings are made in more than two pieces
for facilitating their molding and withdrawing.
A pattern having three pieces will require a three piece flask for the molding
purposes

Loose Piece Pattern
• Certain patterns cannot be withdrawn
once they are embedded in the molding
sand. Such patterns are usually made
with one or more loose pieces
• Pieces for facilitating their removal
from the molding box and are known as
loose piece patterns.
Loose parts or pieces remain attached with the main body of
the pattern, with the help of dowel pins.
The main body of the pattern is drawn first from the molding
box and thereafter the loose parts are removed, the result is
the mold cavity.
Loose piece patterns involve more labour and consume more
time in the molding operation.
Loose Piece

Match Plate Pattern
• A match plate pattern consists
of a match plate, on either side
of which each half of (a number
of) split patterns is fastened.
• A number of different sized
and shaped patterns may be
mounted on one match plate.
The match plate with the help of locator holes can be
clamped with the drag.
The match plate has runner and gates also attached with it.
After the cope and drag have been rammed with the molding
sand, the match plate pattern is removed from in between the
two (i.e., cope and drag.)

Match Plate Pattern
• Cope and drag are then assembled and this completes
the mold.
• Patterns, match plate, runner and gates — all may be
made up of aluminium, because it is light and
relatively inexpensive.
• Match plate patterns are normally used in machine
molding.
• Match plate patterns are preferred for producing small
castings on mass scale.
• They produce accurate castings and at faster rates.
• Piston rings of I.C. engines are produced with the help
of match plate patterns.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 45

Sweep Pattern
• A sweep pattern is just a form
made on a wooden board
which sweeps the shape of the
casting into the sand all
around the circumference. The
sweep pattern rotates about
the post.
Once the mold is ready, sweep pattern and the post can be removed
Sweep pattern avoids the necessity of making a full, large
circular and costly three dimensional pattern.
Making sweep pattern saves a lot of time and labour as
compared to making a full pattern.
A sweep preferred for producing large castings of circular
sections and symmetrical shapes.
The manufacture of large kettles of cast iron requires a sweep pattern.
Image courtesy: METAL CASTING AND JOINING By K. C. JOHN

Gated Pattern
• Gated patterns are usually made of
metal which increases their
strength and reduces the tendency
to warp.
• The sections connecting different
patterns serve as runner and gates.
This facilitates filling of the mold
with molten metal in a better
manner at the same time
eliminates the time and labour
otherwise consumed in cutting
runners and gates.
A gated pattern can manufacture many castings at one time
and thus it is used in mass production systems.
Gated patterns are employed for producing small castings.

Skeleton Patten
• A skeleton pattern is the skeleton of a desired
shape. The skeleton frame is mounted on a
metal base.
• The skeleton is made from wooden strips and is
thus a wooden framework.
• The skeleton pattern is filled with sand and is
rammed.
A strickle (board) assists in giving the desired shape to the sand and removes extra
sand.
If the object is symmetrical like a pipe, the two halves (of the pipe) can be molded by
using the same pattern and then the two molds can be assembled before pouring the
molten metal.
Skeleton patterns are employed for producing a few large castings.
A skeleton pattern is very economical as compared to a solid pattern, because it
involves less material costs.
Castings for turbine castings, water pipes, channels, etc., are made with the help of
skeleton patterns.

Follow Board Pattern
• A follow board is a wooden board and is used for
supporting a pattern which is very thin and fragile and
which may collapse under the pressure when the sand
above the pattern is being rammed.
• With the follow board support under the weak pattern,
the drag is rammed, and then the follow board is
withdrawn.
• The rammed drag is inverted, cope is mounted on it and
rammed. During this operation pattern remains over the
inverted drag and gets support from the rammed sand of
the drag under it.
• Ultimately, the pattern is removed and the cope and
drag are assembled.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 49

MOLDING SAND BINDERS
• Binders produce cohesion between the molding sand grains in the
green or dry state (or condition).
• Binders give strength to the molding sand so that it can retain its
shape as mold cavity.
• Binders (to the molding sands) should be added as optimal
minimum.
• Increasing binder content reduces permeability of molding sand.
• Increasing binder content, increases green compression strength
up to a limit; after which green compression strength remains
practically unchanged with further increase in binder content.
• Clay binders are most commonly used for bonding molding sands.
• The best clay is one which imparts the optimum combination of
bonding properties, moisture, life and cost of producing the
required casting.5/20/2016 Hareesha N G, Dept of Aero Engg, DSCE 50

• Clay binders are most commonly used for bonding molding sands.
• Clay binders can be classified as:
– Fire clay
– Bentonite
• Sodium montmorillonite
• Calcium montmorillonite
– Illite
– Kaolinite
• Bentonite:
– The most commonly used clay binders are Bentonites as they produce
strongest bonds in foundry molding sands.
– Bentonite deposits are available in India in Rajasthan and Bihar
– Bentonites are the weathered product of volcanic ash and are soft creamy
white powders.

• Fire Clay:
– Fire clay is a refractory clay usually found in the coal measures.
– Fire clay particles are about 400 times as large as compared to those of Bentonite ;
hence the same percentages of fire clay produce lower strengths.
• Illite
– Illite is the decomposition product of micaceous materials due to weathering.
– Illite is found in natural molding sands.
– Illite has softening point of about 2500°F.
– Illite does not swell in the same way as bentonite but gives reasonable strength.
– Illite particles have thickness and width of 20 and 100-250 milli-microns respectively.
• Kaolinite
– Kaolinite is the residue of weathered granite and basalt.
– Kaolinite binder has its composition 60% kaolinite, 30% illite and 10% quartz,
– Kaolinite gets Very low swelling due to water and is non-gel forming.
– Kaolinite particles possess thickness and width of 20 and 100-250 milli-microns
respectively.

WATER
• The amount of water may vary from 1.5 to 8%.
• water is responsible for the bonding action of clays.
• Water activates the clay in the sand and the clay-sand mixture develops
strength and plasticity.
• Water added to the sand mixture, partly gets adsorbed by clay and partly
remains free and is known as Free Water.
• The absorbed water is responsible for developing proper bond and the green
strength.
• The free water acts as a lubricant,
• It increases plasticity
• It improves moldability, but It reduces strength of the sand mixture.
• For a given type of clay and its amount, there is an optimum required water
content.
• Too little water will not develop proper strength and plasticity.
• Too much water will result in excessive plasticity and dry strength.
• The amount of water required to develop the optimum properties can be
found out experimentally.

ADDITIVES
• The basic constituents of molding sand mixture are;
– Sand
– binder and
– water
• Materials other than the basic ingredients are also added to
molding sand mixtures, of course in small quantities, in order to
– enhance the existing properties.
– To develop certain other properties.
– to give special qualities like resistance to sand expansion, defects etc.
• Some of the additive materials along are given below.

• Facing materials:
– Facing materials tend to obtain smoother and cleaner surfaces of castings
and help easy peeling of sand from the casting surface during shake out.
– A few facing materials are
• Sea coal
• Graphite
• Coke
• Silica floor
• Cushion materials:
– Cushion materials burn when the molten metal is poured and thus give rise
to space for accommodating the expansion of silica sand at the surfaces of
mold cavity.
– In the absence of cushion materials, large flat surfaces of castings may
buckle due to thermal expansion of silica sand grains.
– A few cushion materials are:
• Wood floor
• Cellulose
• Other special Additives:
– Finely ground corn floor, Iron oxide, Boric acid, diethylene glycol

Disclaimer:
Contents are taken from several text books and compiled for
academic purposes only. Author doesn't hold the copyright for
the contents used in this presentation.

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