Introduction to Pattern making

UNIT NO 1
Introduction to Pattern Making

CONTENTS
 Pattern making
 Pattern Materials
 Pattern Making Tools
 Pattern Allowances
 Types of Patterns
 Core Prints and Core Boxes
 Properties of Moulding sand
 Types of Moulding Sand
 Constituents of moulding sand
 Gating System
 Gating Ratio
Prof. P.B. Borakhede, MGI-COET, Shegaon

INTRODUCTION
Pattern Making
 Patterns are a model for the object to be cast.
 Pattern may be defined as a model cavity called as mould
cavity in which when molten metal is poured, result is the
cast object.
 When this mould is filled with molten metal, and the metal
is allowed to solidify, it forms a reproduction of the pattern
and is known as casting.
 The process of making pattern is called as pattern making.
 A properly constructed pattern minimizes overall cost of
casting.

The whole process of producing casting may be
classified into five stages:
1. Pattern making
2. Moulding and core making
3. Melting and casting
4. Fettling ( finishing)
5. Testing and inspection

Pattern Materials
The selection of pattern materials depends primarily on the
following factors.
1. Service requirements, e.g. quantity, quality and intricity
of casting ie minimum thickness desired, degree of
accuracy and finish required.
2. Type of production of casting and the type of moulding
process.
3. Possibility of design changes.
4. Number of casting to be produced. i.e. possibility of
repeat orders.

Characteristics of pattern materials.
For good casting patterns should have following
characteristics
a) Easily worked, shaped and joined.
b) Light in weight
c) Strong, hard and durable so that it may be resistant to
wear and abrasion, to corrosion, and to chemical
action.
d) Easily available at low cost
e) Repairable and reused
f) Able to take good surface finish
g) Dimensionally stable in all situations.

Types of Pattern Materials
The wide variety of pattern materials which meet these
characteristics are wood and wood products, metals
and alloys, plasters, plastics and rubbers, and waxes.
1) WOOD
 Wood is most common material for pattern as it
satisfies many requirements.
 It is easy to work and readily available.
 Wood can be cut and fabricated into numerous forms
by glueing, bending, curving.
Wood has some disadvantages also
 It is readily affected by moisture.
 It changes its shape when moisture dries out of it and
when it picks up moisture from damp mould sand.

 Because of these reasons wooden patterns are not long
lasting. They are generally used when small number of
casting are to be produced.
 The most common wood used for pattern making is teak
wood.
 This wood is straight grained, light and easy to work, has
little tendancy to break and warp and has reasonable
cost.
 Other woods are mahogany, shisam, pine, deodar etc.
Applications:
 Wooden patterns are used where the number of casting
to be produced is small and pattern size is large.

2) Metal
 Metal is used when large number of casting are
desired from a pattern.
 Metal Patterns do not changes their shapes when
subjected to moist conditions.
 They are free from warping (out of shape) in storage.
 Metal patterns are very useful in machine moulding
because of their accuracy, strength, durability.
 Metals used for pattern making are steel, brass, cast
iron, aluminium etc.
a) Cast Iron
It is strong, gives good smooth mould surface with
sharp edges and is resistance to action of sand.
They are heavy and easily broken.

b) Brass
i. It is used in patterns, particularly when metal patterns
are small.
ii. It is strong, donot rust, takes better surface finish than
cast iron.
iii. It is able to withstand the wear of mould sand.
iv. Brass patterns are heavier than castiron.
c) Aluminium
i. It is best material because it melts at low temperature.
ii. It is soft, easy to work, light in weight and resistant to
corrosion.
iii. It can be damaged by rough usage.

Limitations:
 It is expensive method.
 Metals are heavy in weight.
 They cannot be machined easily like wood.
Applications:
 Metal pattern are employed where large number of
casting have to be produced from the same pattern.

3) Plastics
 It is preferable because it donot absorb moisture.
 It is strong, and dimensionally stable, resistant to wear,
have a very smooth surface and are light weight.
 Because of glossy surface it can be withdrawn from
mould without any damage to mould.
 Plastic material has a very low shrinkage.
 Two types of plastics are thermosetting and
thermoplastic.
 Thermosetting plasting can be remoulded, while
thermoplastic can not be remoulded.

4) Plasters
 Gypsum cement known as plaster of paris is also used
for making patterns.
 It has high compressive strength.
 It can be readily worked with wood tools.
 When talc and cement are mixed with water, it forms a
plastic mass capable of being cast into a mould.
5) Rubbers
 The material like epoxy resin is available in two parts,
binder and hardner. When two parts, originally in liquid
form are mixed together and poured over master pattern
or into a die a solid shape pattern is produced.

6 WAX

PATTERN MAKING TOOLS
 Patternmaker is basically a wood worker.
 Mostly tools employed in making pattern are wood
working tools.
 Some special tools are also needed.
 The principle types of these tools are described below.
1. Planning Tools
2. Sawing tools
3. Marking and Layout tools
4. Miscellaneous Requirements.

Pattern Allowances
The pattern is always made larger than the required size
of the casting in order to allow for various factors such
as shrinkage, machining, distortion and rapping etc.
Following allowances are provided in pattern:
1. Shrinkage Allowance
2. Machining allowance
3. Draft Allowance
4. Rapping or shake allowance
5. Distortion Allowance
6. Mould –wall movement Allowance

1. Shrinkage Allowances
 Most of the metals used in casting work contract during
cooling from pouring temperature to room temperature.
 This contraction takes place in three forms ie liquid
contraction, solidifying contraction and solid
contraction.
 The liquid and solidifying contractions are
compensated by gates and risers. While Solid
contraction is compensated by providing adequate
allowances to the pattern.
 The amount of contraction varies with different metals
therefore there corresponding allowances are also
different.
 For shrinkage allowance, the pattern is formed with
some extra dimension than required dimensions.

The factors which influence metal contraction are as
follows:
1. Pouring temperature of metal
2. Design and dimensions of casting.
3. Type of mould material.
4. Moulding method.
5. Mould resistance to shrinkage of metal.
6. Metal of which the casting is to be made.

2. Machining Allowance
 A casting may require machining all over or on specific
portions depending upon assembly conditions.
 Such portions or surfaces are marked in the working
drawings.
 The corresponding portions or surfaces on the pattern
are given adequate allowance in addition to shrinkage
allowance.
 Metal thickness is increases to compensate the loss of
metal due to machining of these surfaces.
 The amount of this allowance depends upon the metal
of casting, method of machining to be employed,
method of casting used, size and shape of casting and
degree of finish required on machined portion.

 Ferrous metals need more allowance than the non
ferrous metals.
 This allowance varies from 1.5 mm to 16 mm.

3. Draft Allowance
 All patterns are given a slight taper on all vertical
surfaces ie the surfaces parallel to the direction of their
withdrawal from the mould.
 This taper is called as draft or draft allowance.
 The purpose of providing taper on draft is to facilitate
easy withdrawal of pattern from the mould without
damaging surfaces and edges of the latter.
 It is provided on both internal and external surfaces.
 Amount of draft allowance varies from 10mm to 25 mm.
 Factors influencing this amount are the design of
pattern, its vertical height and method of moulding.

4 Rapping or Shake Allowances
 When a pattern is to be withdrawn from the mould, it is
first rapped of shaken, by striking over it from side to
side, so that its surface may be free of the adjoining
sand wall of the mould.
 As a result of this the size of the mould cavity
increases .
 A little negative allowance is to be provided in the
pattern to compensate the same.
 It may be considered negligible for all practical
purposes in small and medium sized castings.

5. Distortion Allowance
 The tendency of distortion is not common in all
castings.
 Castings which have a irregular shape and some
such design in which the contraction is not uniform
throughout will distort during cooling on account of
setting up of thermal stresses in them.
 Such effect can be easily seen in some dome
shaped, U shaped or T shaped castings.
 To eliminate this effect an opposite distortion is
provided in the pattern, so that the effect is
neutralized and the correct casting is obtained.

Types of Patterns
For selection a particular kind of pattern for making a
casting, one may consider the following points.
Quantity of casting to be produced.
The size and complex of the shape of the be produced.
Type of moulding method to be used operation such as
withdrawing the pattern from the moulding etc.
Other difficulties resulting from poor casting design or
pattern design.
problem associated with the moulding.

Several used patterns are as follows:
1. Single Piece Pattern
2. Split Pattern
3. Match Plate Pattern
4. Cope and Drag Pattern
5. Gated Pattern
6. Skeleton Pattern
7. Segmental Pattern
8. Loose Piece Pattern
9. Sweep Pattern.

1. Single Piece Pattern
 This Pattern is also called solid pattern.
 It is simplest form of patterns.
 It is made in one-piece and carries no joint, partition or
loose pieces.
 Single piece pattern made of up of wood or metal
depending upon the quality of casting , to be produced.
 Single piece pattern is accommodate either in cope or in
the drag.
 Its use is limited because its moulding involves large
number of manual operations like gate cutting, providing
runners and risers.

2. Two piece Pattern/ Split Pattern
 Many times the design of castings offers difficulty in
mould making and withdrawal of pattern, if a solid
pattern is used.
 For such castings, split or two piece pattern are
employed.
 They are made in two parts which are joined at the
pattern line by means of dowels.

 Dowel pins are used for keeping the alignment
between the two part of the pattern.
 While moulding, one part of the pattern is contained by
the drag and the other by cope.
 Split patterns are typically used for parts that are
geometrically complex and are produced in moderate
quantities.

3. Multipiece Pattern
 Castings having more complicated designs requires the
pattern in more than two parts in order to facilitate an
easy moulding and withdrawal of pattern.
 These patterns may consists of 3,4 or more number of
parts, depending on their design.

4. Match Plate Pattern
 These patterns are used where a rapid production of
small and accurate castings is desired on a large scale.
 These patterns find a great favour in machine
moulding.
 Their construction cost is quite high, but it is
compensated by high rate of production, greater
dimensional accuracy and minimum requirement for
machining in the casting.
 These patterns are made in two pieces; one piece
mounted on one side and other on other side of plate
called match plate.

 The plate may carry only one pattern or, a group of
patterns mounted in the same way on its two sides.
 The plate may be of wood, steel, magnesium or
aluminium.
 The last one is preferred due to its lightness and
cheapness.
 Gates and runners are also attached to plate along with
pattern.

5. Gated Patterns
 They are used for mass production of small castings.
 For such castings, multi-cavity moulds are prepared.
 To produce good casting, it is necessary to ensure that
full apply of molten metal flows into every part of the
mould.
 Provision for easy passage of the flowing metal into the
mould is called gating.
 In mass production, a number of castings are produced
in a single multicavity mould by joining a group of
patterns.
 Gates or runners for molten metal are formed by
connecting parts between individual patterns.

 Such groups of patterns with gate formers attached to
the pattern proper are called gated patterns.
 Gated patterns may be made of wood or metal and are
used for mass production of small casting.
 By using gated patterns a mass production of parts in
less time.

6. Skeleton Pattern
 When the size of the casting is very large, but easy to
shape and only a few numbers are to be made, it is in
economical to make a large solid pattern of that size.
 In such cases pattern consisting of a wooden frame
and strips is made called skeleton pattern.
 It is a ribbed construction with a large number of
square or rectangular openings between ribs which
forms 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 ribs surface is even with outside of pattern.

 It is usually made in two parts: one for cope and other
for the drag.
 A skeleton patterns are employed for producing a few
large casting. It involves less material costs.
 Examples: soil and water pipes, pipe bends, valve
bodies and boxes are made by skeleton pattern.

7. Segmental Pattern
 It is also called as part pattern.
 These patterns are generally applied to circular work
such as rings, wheel rims, gears etc.
 They are sections of pattern so arranged as to form a
complete mould by being moved to form each section
of mould.
 When making a mould using this pattern, a vertical
spindles firmly fixed in the centre of drag flasks.
 The bottom of mould is rammed and swept level.
 Then segmental pattern is fastened to spindle.
 Moulding sand is rammed between outside of the
pattern and the flask, and in the inside, but not at the
ends of pattern.

 After ramming one section, it goes forward to the next
section of ramming and so on until the entire mould
perimeter has been completed.
 In principle they work like a sweep, but the difference is
that a sweep is given a continuous revolving motion to
generate desired shape, where as segmental pattern is
a portion of solid pattern itself and the mould is
prepared in parts by it.

8. Sweep Pattern
 Sweeps can be used for preparing moulds of large
symmetrical castings, particularly of circular cross
section.
 This effects a large saving in time, labor and material.
 The equipment consist of base, suitably placed in the
sand mass, a vertical spindle and a wooden template
called sweep.
 The outer end of sweep carries contour corresponding
to the shape of desired castings.
 The sweep is rotated about the spindle to form a cavity.

 Then the sweep and spindle are removed, leaving the
base in sand.
 The hole is made by removal of spindle is patched up
by filling the sand.
 Separately prepared core is placed in the mould, gates
cut and the mould is ready for pouring.

9. Cope and drag Pattern
 When very large castings are to be made, the complete
pattern becomes too heavy to be handled by a single
operator.
 Such a pattern is made in two parts which are
separately moulded in different moulding boxes.
 After completion of moulds, the two boxes are
assembled to form complete cavity, of which one part is
contained by the drag and other in cope.
 Thus in a way it is nothing but a two piece or split
pattern of which both the pieces are molded separately
instead of being molded in the assembled position

Core prints
 Castings are often required to have holes, recesses of
various sizes and shapes.
 These impressions are obtained by using sand cores
which are separately made in boxes known as core
boxes.
 For supporting cores in the mould cavity, an impression
in the form of recess is made in the mould with the help
of projection suitably placed on the pattern.
 This projection on the pattern is known as coreprint.
 There are several types of core prints which are as
follows

1. Horizontal core
 This is laid horizontally in the mould and is located at
parting line of the mould.
 The core print is often found on split of two piece
pattern.
 When it is important that certain core be located at a
desired angular relationship with respect to central
axis, a flat portion at one end is made to coincide with
flat portion of the core print.

2. Vertical Core
 This core print stands vertically in mould so this type is
called vertical core print.
 The core print is located on the cope and drag sides of
a pattern and is constructed with considerable taper
specially on the cope side so that they are easily
moulded.

3. Balancing Core
 This is used when a horizontal core does not extend
entirely through the casting, and the core is supported
at one end 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.
4. Hanging or cover core
 This is used when entire pattern is rammed in the drag
and the core is required to be suspended from top of the
mould.
 In this case core serves are cover for the mould and
also as a support for hanging the main body of a core.

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 describe below.
1. Half box
 A half box 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.

2. Dump Box
A dump box, 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 rectangular box.
The box is made with open one side and the sand is
rammed up level with the edges of this opening.

3. Split Box
 It consist 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 off the excess sand, the core
box is unclamped and rapped.
 This type of core box moulds the entire core.

4. Strickle Box
 A strickle box is often used when a core with an irregular
shape is required.
 In a strickle box, the shape of the core is produced by
striking off the core sand from the top of the core box with
a piece of stock called strickle board made to correspond
to the contour of the required core.

MOULD MATERIALS AND THEIR
CHARACTERISTICS
Moulding Sand
 The principal material used in foundry shop for
moulding is sand.
 This is because it posses the properties important for
foundry purposes.
 The common sources of collecting foundry sands are
rivers, lakes, sea and deserts.
 Ingredients of moulding sands are silica sand grains,
clay, moisture, miscellaneous materials.

Properties of moulding sand
Proper moulding sand must posses following properties.
1. Porosity
 Molten metals always contains certain amount of
dissolved gases and water vapor which are evolved when
the metal freezes.
 If these gases do not escapes from mould completely
through mould, they will form gas holes and pores in
castings.
 Therefore sand must be sufficient porous to allow the
gases or moisture present or generated within the mould
removed freely.
 This property of sand is called porosity or permeability.

2. Flowability
 Flow ability of 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 round pattern and take up the
required shape.
 The sand should respond to different processes.
 Good flowability is very essential where energy for
compaction during ramming is transmitted through sand
mass as in machine moulding.
 Flowability increases as clay and water content
increases.
3. Collapsibility
 It is the property due to which the sand mould
automatically collapses after solidification of the casting
to allow free contraction of the metal.

 In the absence of this property the contraction of the
metal will be difficult by the mould and this will result in
tears and cracks in the casting.
4. Adhesiveness
 It is the property of the sand due to which it is capable of
adhering to the surfaces of other materials. Ie they hold
tightly to the sides of holding 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.
5. Cohesiveness
 It is that property of the sand due to which its rammed
particles bind together firmly so that the pattern is
withdrawn from the mould without damaging the mould
surfaces and edges.

 Also due to this property the mould surface get sufficient
strength to withstand the pressure of flowing molten
metal and do not get washed under pressure.
 This property is known as green bond and is effected by
grain size, clay and moisture content.
6. Refractoriness
 It is property of moulding sand which enables it to
withstand high temperature of the molten metal without
fusing, thus facilitating a clean casting.
 Moulding sand with a poor refractoriness may burn on to
the casting.

Types of Moulding Sand
Moulding sands may be classified, according to their use
into a number of varieties.
1. Green Sand
 It is a mixture of silica sand with 18 to 30 percent clay,
having total water of from 6 to 8 percent.
 The clay and water furnish the bond for green sand.
 It is fine, soft, light, and porous.
 Bring damp, when squeezed in the hand, it retains the
shape, the impression given to it under pressure.
 Moulds prepared in this sand are called green sand
moulds.

2. Dry Sand
 The green sand that has been dried or baked after the
mould is made is called dry sand.
 The are suitable for largest castings.
 Moulds prepared in this sand are known as dry sand
moulds.
3. Loam Sand
 Loam sand is high in clay as much as 50 percent or so
and dries hard.
 This is particularly employed for loam moulding usually
for large castings.
4. Facing Sand
 This sand forms the face of the mould.

 It is used directly at the surface of the pattern and it
comes into contact with the molten metal when the
mould is poured.
 It is subjected to severest conditions and possesses high
strength and refractoriness.
 It is made of silica sand and clay without the addition of
used sand.
 Different forms of sand carbons are used prevent the
metal from burning into the sand.
 The layer of facing sand usually ranges from 20 to 30
mm.
 From 10 to 15 percent of whole sand used is facing
sand.

5. Parting Sand
 Parting sand is used to allow the sand on the parting
surface of the cope and drag to separate without any
difficulty.
 This is clean silica sand which does not contains clay.
 The burnt sand and dry silica sand are used for that
purpose.
6. 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 used for
this purpose.
 This sand is also called black sand because its color is
black because of addition of coal dust and burning.

7. Core sand
 Sand used for making core 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.

 Main Constituents of Moulding Sand
1. Silica Sand
2. Binder
3. Additives
4. Water
Binders
 Purpose of adding a binder to the moulding sand is to
impart it sufficient strength and cohesiveness so as to
enable it to retain its shape after mould has been
rammed and the pattern withdrawn
 Binders are grouped as 1. organic Binders 2.
Inorganic Binders.

 Organic binders finds their specific use in core making.
The common organic binders are 1. Dextrin 2. Molasses 3.
Linseed Oil 4. Cereal Binders 5. Pitch 6. Resins
 Inorganic binders are clay, sodium silicate and portland
cement. Out of these the clay binders are commonly
used.
 The following types of clays are commonly used
1 Bentonite 2. Kaolonite 3. Limonite 4. Ball clay 5. Fire clay
6. Fuller’s earth.
Out of these varieties Bentonite is most widely used.
In our country it is found in Bihar, Rajasthan and Jammu
Kashmir.

Additives
 Additives are added to the moulding sand to
improve upon some of its existing properties or to
impart certain new properties to it. The commonly
used additives are:
1. Coal dust
 It is used in sand used for grey iron and malleable
iron casting.
 Its main purpose is to react chemically with
oxygen present in sand pores and thus produce a
reducing atmosphere at mould metal interface
and prevent oxidation.
 It is added in the facing sand.

2. Sea coal
 It is finely ground soft coal and is vastly used in sands
used for grey iron casting.
 It improves surface finish.
3. Cereals or corn flour
 It reduces expansion defects, improves strength,
toughness and collapsibility of sand.
 Its proportion in sand varies from 0.25 to 2.0 percent.
4. Silica Floor
 It increases hot strength, decreases metal penetration
into the mould, reduces expansion defects and improves
surface finish. It may be added up to 35%.

5. Dextrin and Molasses
Their addition increases the dry strength of the sand. In
other respects they behave like cornflour.
6. Wood Flour
 It promotes mould wall movement, reduces expansion
defects, increases collapsibility, improves surface finish
and thermal stability of mould.

Gating System
 The manner in which the molten metal enters the mould
has a great impact on the quality of the casting
produced.
 Therefore the passage through which it flows should be
carefully designed and produced.
 The term gating system involves all the passage
through which molten metal enters the mould cavity ie it
includes
1. Pouring basin,
2. Gates
3. Runner
4. Riser

 Ideal gating system expected to meet following
requirements.
 Molten metal should enter the mould cavity with as low
velocity as possible, free from turbulance.
 It should be able to prevent formation oxide and other
dross in the flowing metals.
 It should be able to prevent the molten metal from
absorbing air or other gases while flowing through it.
 It should help on avoiding excessively high pouring
temperatures.
 It should facilitate complete filling of the mould cavity.
 Its making should be practicable and economical.

Pouring Basin
 Pouring basin makes easier
makes easier for crucible
Operator to direct the flow of
Metal.
 It helps maintaining the
Required rate of liquid metal flow.
 It reduces turbulence at the sprue entrance.
 Helps separating dross, slag from metal before entering
in sprue.

Gates
 A gate is a channel which connects runner with the
mould cavity and through which molten metal flows to fill
the mould cavity.
 A small gate is used for a casting which solidifies slowly
and vice versa.
 A gate should not have sharp edges as they may break
during pouring and sand pieces thus may be carried with
the molten metal in the mould cavity.
 Types
Top gate
Bottom gate
Parting line side gate

Runners
 Runners are passages that distribute molten metal
from the sprue to gates or risers around the cavity
inside a mold.
 Runners slow down and smooth out the flow of liquid
metal and are designed to provide approximate uniform
flow rates to the various parts of the mold cavity.
Risers
 A riser us a passage made in the cope through which
the molten metal rises after the mould is filled up.
 It provides many advantages as follows:
1. In the initial stages of pouring it allows air, steam and
gases to go out of the mould.

2. On seeing the rising molten metal through it, it is
ensured that mould cavity has been completely filled up.
3. It acts as a reservoir to feed the molten metal to the
casting to compensate the shrinkage during
solidification.
Types of risers
1. Open riser
2. Blind riser

GATING RATIO
 Gating ratio= a:b:c where,
• a= cross-sectional area of sprue
• b= cross-sectional area of runner
• c= total cross-sectional area of ingates.
 • Gating ratio reveals-
• Whether the total cross- section decreases towards the
mould cavity. This provides a choke effect which
pressurizes the liquid metal in the system.
• Whether the total cross-sectional area increases so that
the passages remain incompletely filled. It is an
unpressurized system.

Important Questions for Examination
1. Explain different pattern materials with relative
advantages and disadvantages.
2. What are various types of allowances are provided in
pattern? Explain
3. How Patterns are differed from casting? List out
different types of patterns and explain in brief.
4. Which are the different properties of moulding sand ?
Explain
5. What is meant by: Core Print, Core Box, Core seat?
6. Explain Sweep pattern, segmental pattern in detail.
7. What do you mean by gating ratio Explain
pressurized and non pressurized gating systems.

Introduction to Pattern making

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Introduction to Pattern making