Pattern

Pattern:-
Replica of the object to be made by the casting process with some modifications.
Modifications-
(a) Addition of pattern allowance
(b) Provision of core prints
(c) Elimination of fine details
(A) Pattern Allowances-
Pattern dimensions are different from final dimension of casting.
Shrinkage
All metals shrink when cooling except bismuth. This may be due to inter atomic vibrations amplified by increase in temperature.
Two types:-
Liquid shrinkage – Reduction in volume when metal changes from liquid to solid at solidus temperature.
Solid shrinkage – Reduction in volume when a metal loses temperature in solid state.
Actual value of shrinkage depends on
 Composition of alloy cast
 Mould materials used
 Mould design
 Complexity of pattern
 Component size
Metallic pattern casting – double shrinkage