Question 4
(a) (i) What is shrinkage in casting?
(ii) How can shrinkage be prevented in casting?
(iii) State one effect of shrinkage on casting.
(b) Explain in three steps the process of blueing a workpiece.
(c) List three forge fie tools.
Observation
Candidates performed well in this question. However, some candidates could not adequately answer questions 4(a)(ii) and 4(b). The solution of those poorly answered questions are as follows.
(a) (ii) Shrinkage can be prevented in casting by providing shrinkage allowance on the pattern thus making up for the contraction of themetal during cooling in the solid state.
(b) Explaining in three steps the process of blueing in a workpiece:
- Cleaning and polishing of the steel workpiece.
- Allowing the workpiece to be heated in water vapour in a furnace
- Causing the oxidation of the steel workpiece thus resulting in blue colour.