Pattern Allowances & Casting Dimensions

Pattern allowances are necessary in casting because the dimensions of the pattern are different from the final dimensions of the casting. This is due to shrinkage that occurs during cooling and contraction of the metal in its solid state.

Liquid shrinkage refers to the reduction in volume when the metal changes from liquid to solid state at the solidus temperature. Solid shrinkage, on the other hand, is the reduction in volume caused when metal loses temperature in its solid state.

Risers are provided in the moulds to account for liquid shrinkage during the solidification of the metal. They compensate for the reduction in volume that occurs when the metal changes from liquid to solid state.

<p>The rate of contraction with temperature is dependent on the material being used. Different materials have different rates of contraction. For example, steel contracts to a higher degree compared to aluminium.</p> Signup and view all the answers

<p>No, bismuth does not shrink when cooling. It is the only metal that does not experience shrinkage when cooling due to inter-atomic vibrations that are not amplified by an increase in temperature.</p> Signup and view all the answers

<p>Pattern allowances are necessary in casting because the dimensions of the pattern are different from the final dimensions of the casting required.</p> Signup and view all the answers

<p>Shrinkage in metals during cooling is caused by inter-atomic vibrations which are amplified by an increase in temperature.</p> Signup and view all the answers

<p>Liquid shrinkage refers to the reduction in volume when the metal changes from liquid to solid state, while solid shrinkage is the reduction in volume caused when metal loses temperature in solid state.</p> Signup and view all the answers

<p>Risers are provided in the moulds to account for the liquid shrinkage of the metal as it changes from liquid to solid state, ensuring a complete and defect-free casting.</p> Signup and view all the answers

<p>The rate of contraction with temperature varies depending on the material. For example, steel contracts to a higher degree compared to aluminium.</p> Signup and view all the answers