Passage:
Passage-IV The simplest method of welding two pieces of metal together is known as pressure welding. The ends of metal are heated to a white heat — for iron, the welding temperature should be about 1300°C — in a flame. At this temperature the metal becomes plastic. The ends are then pressed or hammered together, and the joint is smoothed off. Care must be taken to ensure that the surfaces are thoroughly clean first, for dirt will weaken the weld. Moreover, the heating o f iron or steel to a high temperature cause oxidation, and a film o f oxide is formed on the heated surfaces. For this reason, a flux is applied to the heated metal. At welding heat, the flux melts, and the oxide particles are dissolved in it together with any other impurities which may be present. The metal surfaces are pressed together, and the flux is squeezed out from the centre o f the weld. A number of different types of weld may be used, but for fairly thick bars o f metals, a vee-shaped weld should normally be employed. It is rather stronger than the ordinary butt weld.
hammering heated pieces
- Athe metal will not take white heat
- Bthe resulting weld will be weak
- Cthe joint will be rough
- Dthe metal will be less plastic
Explanation
The passage warns: 'Care must be taken to ensure that the surfaces are thoroughly clean first, for dirt will weaken the weld.' If the surfaces are not cleaned before the heated pieces are hammered together, the dirt remains trapped in the joint. The stated consequence is a weakened weld. Hence the resulting weld will be weak, option (B).