Silver.......... .129 Wrought Iron..... .078
Bronze.......... .118 Cast Iron........ .068




CHAPTER VI

ELECTRIC WELDING


RESISTANCE METHOD

Two distinct forms of electric welding apparatus are in use, one producing
heat by the resistance of the metal being treated to the passage of
electric current, the other using the heat of the electric arc.

The resistance process is of the greatest use in manufacturing lines where
there is a large quantity of one kind of work to do, many thousand pieces
of one kind, for instance. The arc method may be applied in practically any
case where any other form of weld may be made. The resistance process will
be described first.

It is a well known fact that a poor conductor of electricity will offer so
much resistance to the flow of electricity that it will heat. Copper is a
good conductor, and a bar of iron, a comparatively poor conductor, when
placed between heavy copper conductors of a welder, becomes heated in
attempting to carry the large volume of current. The degree of heat depends
on the amount of current and the resistance of the conductor.