[Illustration: Figure 43--Operating Parts of a Toledo Spot Welder]
[Illustration: Figure 43a.--Method of Testing Electric Welder]
[Illustration: Figure 44.--Detail of Water-Cooled Spot Welding Head]
The transformer is carried in the base of the machine and on the left-hand
side is a regulator for controlling the voltage for various kinds of work.
The clamps are applied by treadles convenient to the foot of the operator.
A treadle is provided which instantly releases both jaws upon the
completion of the weld. One or both of the copper dies may be cooled by a
stream of water circulating through it from the city water mains
(Figure 44). The regulator and switch give the operator control of the
heat, anything from a dull red to the melting point being easily obtained
by movement of the lever (figure 45).
[Illustration: Figure 45.--Welding Head of a Water-Cooled Welder]
_Welding._--It is not necessary to give the metal to be welded any
special preparation, although when very rusty or covered with scale, the
rust and scale should be removed sufficiently to allow good contact of
clean metal on the copper dies. The cleaner and better the stock, the less
current it takes, and there is less wear on the dies. The dies should be
kept firm and tight in their holders to make a good contact. All bolts and
nuts fastening the electrical contacts should be clean and tight at all
times.
The scale may be removed from forgings by immersing them in a pickling
solution in a wood, stone or lead-lined tank.
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