When
the dynamo is a part of the welding plant it should be placed as close to
the welding machine as possible, because the length of the wire used
affects the voltage appreciably.
In order to hold the voltage constant, the Toledo Electric Welder Company
has devised connections which include a rheostat to insert a variable
resistance in the field windings of the dynamo so that the voltage may be
increased by cutting this resistance out at the proper time. An auxiliary
switch is connected to the welder switch so that both switches act
together. When the welder switch is closed in making a weld, that portion
of the rheostat resistance between two arms determining the voltage is
short circuited. This lowers the resistance and the field magnets of the
dynamo are made stronger so that additional voltage is provided to care for
the resistance in the metal being heated.
A typical machine is shown in the accompanying cut (Figure 43). On top of
the welder are two jaws for holding the ends of the pieces to be welded.
The lower part of the jaws is rigid while the top is brought down on top of
the work, acting as a clamp. These jaws carry the copper dies through which
the current enters the work being handled. After the work is clamped
between the jaws, the upper set is forced closer to the lower set by a long
compression lever. The current being turned on with the surfaces of the
work in contact, they immediately heat to the welding point when added
pressure on the lever forces them together and completes the weld.
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