Observation

This question did not pose any difficulty to the candidates. The expected responses are as given below:

The blast furnace uses a double bell system where two bells are used to control the entry of raw materials into the furnace.  The purpose of the two bells is to prevent the escape of hot gases in the blast furnace.
First the raw materials are emptied into the small bell which then opens to empty the charge into the larger bell.  The small bell then closes to seal the blast furnace, while the larger bell rotates to spread the charge evenly.

Sketch to show the twisting operation     

Describing in three steps how to twist a square mild steel bar

e.g.  (i)  Mark the length to be twisted.
(ii)  Heat to red hot the portion to be twisted.
(iii) Place the bar in the vice and twist with a wrench.

Explaining the reason for using coolant in the following operations:

• Grinding a chisel – it is to prevent the chisel edge from being burnt and to soften the edge.
• Taping a thread:
• it is to prevent friction which may lead to breakage of tap

OR
it aids the removal of chips.