Chapter One

Molds and Pattern

Making
 Introduction
Casting
A process based on the property of liquid to
take up the shape of the vessel containing it.
A cavity of desired shape is made, containe
d in a mold.
Carried out in a foundry.
 History of Casting
 Ancient process, started 5000
years ago.

 Jaivana- 50 tons cannon was

th
built in 17 century in Jaipur.

 Used for making arrows,

coins, knives etc.
World’s largest Cannon in
Jaipur, made by casting
 Why Casting?
1. A job of 5m diameter and 10m length.
2. A job with a hole of 2m diameter, made of
very hard material.
3. Parts of very complicated shapes.
 What do we control?
1. Size & shape of cavity
and mold
2. Mixture composition
3. Temperature
4. Cooling time
5. Carefully remove it
 Requirement for Casting?

1. Cavity of desired shape- Mold

2. Molten metal
3. Proper channel to fill the molten metal
Basic Casting Process
 Basic terms used in Casting

1. Pattern: Replica of the desired part

2. Mold- Container with a cavity within. Divided in two halves:
Cope and Drag.
3. Gating system- Network of channels that deliver molten metal
to the cavity.
 Basic steps in Casting
1. Pattern making
2. Mold making
3. Melting of metal and pouring
4. Cooling and solidification of metal
5. Cleaning of casting and inspection
 Pattern
 Replica of the desired product
 Has some how different dimensions than the actual p
art to be manufactured
 Used to form the mold cavity

Casting Consideration
1.Materials used
2.Types of patterns
3.Pattern Allowances
 Pattern Materials
Requirements:
1. Easily shaped, worked, machined and joined
2. Resistant to wear and corrosion
3. Resistant to chemical action
4. Dimensionally stable
5. Easily available and economical
 Pattern Materials
1. Wood:
 Easy availability, low weight and low cost

 Can be easily shaped

 More than 90% castings use wood patterns

 Absorbs moisture. So, distortions and dimensional

changes occur

 Relatively lower life, hence suitable for small quantiy

 Pattern Materials
2. Metal:
Used for large quantity production and for closer
dimensional tolerances

Longer life

Aluminum is mostly used.

Other metals: cast iron, brass etc.

 Pattern Materials
3. Plastic:

Low weight, easier formability, smooth surfaces

and durability
Do not absorb moisture. So, dimensionally stable

Corrosion resistance
 Pattern Materials
4. Polystyrene:
Changes to gaseous state on heating
Disposable Patterns. Hence, suitable for single casting.
When molten metal is poured into cavity, polystyrene tr
ansforms to gaseous state.
Used mostly for small and complicated shaped castings.
 Pattern Types
1.Single piece pattern:
Used for simple shaped & large castings.
Pattern and cavity produced by it are comp
letely in the lower flask (i.e. drag)
Causes difficulty in making the mold.
2.Split pattern:
Split pattern models the
part as two separate pieces
that meet along the parting
line of the mould
Two parts are aligned by
Dowel pin.
 3.Loose Piece pattern

1. As pre the name Pattern Contain One or more than one loose piece
2. Loose piece is used to make removal of pattern easy from mould box
3. loose pieces are attached to main body with the help of dowel pins or
wire
4. First main pattern is drawn and then carefully loose pieces
5. Moulding with this pattern is expensive and require more skill
4. Match-plate pattern:
Similar to a split pattern, except that each half of the pattern is attached to
opposite sides of a single plate.
Match plate confirms the parting line
Ensures proper alignment of the mould cavities in the cope and drag and
the runner system can be included on the match plate.
Used for larger production quantities.
Ic Engines piston rings
5. Cope-Drag pattern:
Itis similar to split pattern
Each half of the pattern is attached to a separate
plate and the mould halves are made independently.
.Pattern is made in two halves and split along parting
line
These two halves are known as cope and drag
There moulding done independently
After moulding they are assembled to form complete
mould box
Often desirable for larger castings
6. Gated pattern:
Inthis patters of gate and riser or runner are permanently attached to regular
pattern
They are used to manufacture multiple casting in on time
Each pattern is connected with common runner .
Suitable for pouring small castings and for mass production
It save labour and time
 Pattern Allowances

1. Shrinkage or contraction allowance

2. Draft or taper allowance

3. Machining or finish allowance

4. Distortion or camber allowance

5. Rapping allowance
1. Shrinkage Allowance:

 Liquid Shrinkage

 Solid Shrinkage
Pattern Allowances
 Shrinkage Allowance:
 Shrinkage means contraction of metal on solidification
 All metals shrink after solidification. (Except grey cast iron that expands
on solidification).
 It is expressed in mm/m.
 Shrinkage allowance Differs from material to material.
 Positive type of allowance.
 Pattern Allowances

 Draft / Taper Allowance:

 Taper provided by the pattern maker on all vertical surfaces of the pattern
so that it can be removed from the sand without tearing away the sides of
the sand mould.
 Inner details of the pattern require higher draft than outer surfaces.
 commonly applied draught allowance is 1°to 3°
 due to draught allowance pattern can easily removed from mould box
 Pattern Allowances
2. Draft / Taper Allowance:

 The amount of draft depends upon-

1. The length of the vertical side of the pattern to be extracted;

2. The intricacy of the pattern;

3. The method of moulding

4. Pattern material.
Pattern Allowances
3. Machining / Finishing Allowance:
 The finish and accuracy in sand casting is generally poor.
 Extra material provided on the casting to enable their machining or
finishing to the required size, accuracy and surface finish.
 So it is Added in pattern dimensions.
 allowance is provided only in machining area
 Amount of machining allowance depends upon:
1. Method of moulding and casting used
2. Size and shape of casting
3. Casting orientation
4. Metal used in casting
5. Degree of accuracy and finish required
4. Distortion / Camber Allowance:
 Due to their typical shapes (U,V,T,L shapes) , castings get distorted
during solidification.
 Distortion is observed in irregular castings so that it shrink in
uneven manner
 Distortions are caused by internal stresses which are generated on
account of unequal cooling of different sections of casting.
 To avoid this distortion allowance is provided
 It varies from 2 to 20 mm
5. Rapping / shake Allowance:
 Before the withdrawal from the sand mould, the pattern is rapped all
around the vertical faces to enlarge the mould cavity slightly, which
facilitate its removal.
 When pattern is rapped, mould cavity is enlarged.
 To account for this increase, pattern size is reduced.
 This allowance is important in large-sized castings and precision
castings.
 Amount of rapping allowance depends upon:
1. Extent of rapping
2. Degree of compaction of sand
3. Size of mould
4. Sand type
It include carpenter tools and some special tool
1. Contraction scale- It is used to measure pattern dimensions include various allowances.It
is metallic scale of 300 or 500 mm length
2. Combination set- It generally used for pattern making.It is used to measure angles,
pependicularity,locate centre on cylindrical job.
3. Callipers- They are of internal or external type.Generally used to measure internal or
external diameters of patterns.
Tools
 Colour Indication
Black Unfinished surface on casting
Red Finished surface on casting
Yellow Core prints
Black strips Parting surface
Red/yellow strips Seats for loose piece

Pattern are coloured by using shellac paints.

Colours gives protection and identifies the features of patterns.
colour scheme is given as above.
 Types of Casting Methods
Centrifugal casting.
•In this process mould is poured and allowed to solidify during
revolving.
•Due to rotation of mould the poured metal is subjected to
centrifugal force.
•Centrifugal force is allowed molten metal to flow in the mould
cavity.
•Dense metal is deposited on periphery of mould and start
sophistication.
•Lighter slag, oxides, inclusions are get separated and moves
towards cen.
 Centrifugal casting
•There is no use of gates runner and riser.
•The axis of rotation may be horizontal or
vertical.
•Applications
•Pipes , cylinder liners, bearings, bushes, gears
fly wheels, gun barrels etc.
 Shell moulding
•This process is used for smooth surface finish
•It consist of dump box which is partially filled with silica
and thermoelectric resin.
•Then dump box is sealed with metallic pattern which is
preheated about 250°c.
•When dump box is inverted mixture is get melted and
forms the shell on pattern plate.
•Shell thickness varies from 5mm to 8mm.
•These two shells joint to gather to form complete mould.
 Shell moulding
Applications.
• Small pulleys ,motor housing, fan blades, cylinders,
cylinder heads, break drums.
Investment casting
•It is also known as lost wax casting precision casting.
•This method is used for manufacturing jewelry, dental goods.
•It involves following steps.
1. Making of wax pattern sometimes mercury or plastic may be
used.
2. provide wax made gates, runners, riser to the pattern.
3. Complete wax pattern put in box and filled with liquid mould
material.
4. liquid around wax pattern solidifies and form mould
5. Then mould is heated to 150°to 800°c to remove wax
Investment casting
Applications.
• surgical instruments.
• vanes and blades for gas turbine.
• costume jewelery.
• valve bodies.
• Reciprocating slides for cloth cutting
machine.
 Casting defects

Following are the casting defects arises during

faulty processes in casting.
1. Blow holes.
2. Pin holes.
3. Shift.
4. Short runs.
5. Hot tears.
6. cold shuts.
•Blow holes are spherical, flattened or elongated cavities present in
the casting .They are formed due to following reasons.

•Reasons.
1. Rapid evolution of gas from mould.
2. Lack of porosity in mould box.
3. Excess moisture in sand.
4. Hard ramming of sand.

•Remedies
•Moulds and cores are properly vanted.
•Avoid hard ramming.
•Proper amount of moisture in sand.
•Proper grain size of sand.
Pinholes
•Pin holes are small holes of less than 2mm diameter which are on
surface or bellow the surface of casting.

•Causes.
•High pouring temperature.
•Gas dissolved in molted metal.
•gases are not removed properly from molted metal.
•Sand with higher moisture content.

•Remedies.
•Maintain pouring temperature.
•increase flux proportion.
•reducing moisture content in sand.
•Effective regarding.
 Shift
It is external defect arises due to mis allotment parts of casting.
Causes.
•Core displacement.
• Misalignment of cope and drag.
•warn out or burn out of clamping pins.
•Misalignment of two halves of pattern.
•Remedies.
•Repair or replacement of dowel pins.
•Proper alignment of pattern.
•Proper alignment of cope and drag.
•Repair clamping pins.
Short run
It is also called as Morin.
when cavity in mould is filled incompletely then short run
introduces.

Causes.
Insufficient metal supply.
lack of fluidity in molten Merkel.
Molten metal temp is low.
faulty gating system.

Remedies.
Adjust pouring temp.
Adjust rate of pouring.
Modifications in gating system.
Hot tears
It is also called as pulls or hot crack.
They may be internal or external.
They having dark blue in appearance on surface.

Causes.
Lack of compatibility of core.
high temp of casting metal.
incorrect design of batting system.
Lack of fillets and corner redii.

Remedies.
Improved design of casting.
Improved compatibility.
Proper solidification.
correct pouring temp.
Thanks for Your Attention