Question 4
(a)(i) Explain the term planishing as used in sheet metalwork.
(ii) State three reasons why planishing is necessary in sheet metalwork.
(b) What is heat treatment?
(c) Explain the following heat treatment processes
(i) annealing;
(ii) normalising.
(d) Name a material for making drill bits.
Observation
This question did not pose any difficulty to the candidates. The expected responses are as given below:
4 (a)(i) Planishing is the process used in sheet metalwork to improve the surface qualities of sheet metals:
(ii) Reasons for planishing
- To make the surface of the work smooth.
- To harden the metal.
- To remove irregularities.
- To close the grains of the sheet metal.
(b) Heat treatment is the process of heating and cooling of metals within specified time to obtain desired mechanical properties.
(c)(i) Annealing is the process of heating metal to red hot and allowing it to cool slowly in the furnace or soaked in ash. It is done to soften metal.
(ii) Normalising is the process of heating metal to red hot, soaking for a period of time, then cooling in still air. Normalising refines the structure of metal.
(d)Material for making drill bits
Drill bits are made of high speed steels or carbon steel.