9. In which cases is preheating absolutely necessary in order to make a satisfactory weld?
10. (a) Give a sketch showing a preheating torch for use on illuminating gas and compressed air, which can be constructed very easily.
(b) Why are preheating torches not popular for general welding?
(c) Where are they used in numbers?
LECTURE NUMBER EIGHTEEN
Subject—Aluminum Welding
(Part One)
1. (a) Is the welding of aluminum, more or less difficult than such metals as cast iron and steel?
(b) Explain why.
2. (a) Name the two methods of making aluminum welds.
(b) Can they be combined?
(c) Why?