IT is well known that the spot welding of light alloys of inherently high electrical conductivity involves several problems necessitating the use of specialized high capacity machines giving close control of the heat‐pressure cycle, and designed to give rapid electrode follow‐up, i.e. permitting the electrodes to follow closely the cooling and contracting weld. What is not so well appreciated is the disproportionate increase in energy required to weld satisfactorily material of increasing thickness. For example, the energy for welding an included thickness of 2 x 10 S.W.G. or 2 x 8 S.W.G. sheet under production conditions is so great that it precludes the use of the conventional A.C. transformer type of welder except under very favourable supply conditions. It is estimated in fact that a maximum peak demand of at least 1,000 kVA single phase, would be imposed upon the supply mains by an A.C. machine of suitable capacity.
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