16. In preheating aluminum with charcoal, what precautions are taken in setting up; in starting the fire; during the welding operation, and in cooling the piece?
17. (a) Are preheating torches played directly on aluminum work?
(b) What kind of an oven is used?
18. (a) Is it necessary to heat the whole of an aluminum crank-case if one part has to be preheated?
(b) Give reasons.
19. (a) Are clamps used to hold parts in place on preheated aluminum?
(b) Explain why.
20. When starting to weld a cold piece of aluminum, the flame is brought in contact with the work and held there much longer than on a similar size piece of steel before any apparent change occurs. How is this accounted for, knowing that aluminum has a much lower melting point that steel?
LECTURE NUMBER TWENTY
Subject—Aluminum Welding
(Part Three)
21. Explain fully why it is necessary to employ greater speed in the welding of aluminum than on any other metal?