10 Questions
Explain why pattern allowances are necessary in casting.
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.
What is the difference between liquid shrinkage and solid shrinkage?
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.
Why are risers provided in the moulds?
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.
What factors determine the rate of contraction with temperature?
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.
Does bismuth shrink when cooling?
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.
What is the purpose of pattern allowances in casting?
Pattern allowances are necessary in casting because the dimensions of the pattern are different from the final dimensions of the casting required.
What causes shrinkage in metals during cooling?
Shrinkage in metals during cooling is caused by inter-atomic vibrations which are amplified by an increase in temperature.
What is the difference between liquid shrinkage and solid shrinkage?
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.
Why are risers provided in the moulds?
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.
How does the rate of contraction with temperature vary for different materials?
The rate of contraction with temperature varies depending on the material. For example, steel contracts to a higher degree compared to aluminium.
Test your knowledge on pattern allowances and the reasons why the dimensions of the pattern differ from the final dimensions of a casting. Explore topics such as shrinkage and inter-atomic vibrations in this informative quiz.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
