same time, the electrode tip is also melted, and variable-voltage, dc generator welding unit, and (2)
metal from the tip is carried across the arc into the the rectifier-type welding machine.
molten pool. The decomposition of the electrode
covering shields the molten metal from oxidation. Variable-Voltage, DC Generator
The temperature of the arc between the electrode Welding Unit
and the base metal is approximately 6500°F.
This unit consists of a dc generator driven by an
WELDING MACHINES ac electric motor or by a gasoline or diesel engine.
The voltage produced by the generator usually
The Navy has a wide variety of shielded ranges from 15 to 45 volts across the arc, and the
metal-arc welding equipment. In general, this current output varies from 40 to 400 amperes,
equipment is classified as either ac or dc; either depending on the type of unit. In most units, the
stationary or portable; and either single-operator or voltage and ampere output of the generator is
multiple-operator equipment. In addition, it may be controlled automatically by the self-regulating or
classified according to the source of power and the drooping voltage characteristics in the generator.
number of amperes delivered at certain arcvoltages. (An increase in current through the generator
results in a decrease in voltage.) In addition, the
The types of equipment available on any generator output is manually controlled by one or
particular ship or IMA will depend upon the kind of two manual adjustments.
electrical power available and the size and mission
of the ship. Since most ships are equipped with ac Welding machines of this type may have single
power, we will discuss only the welding machines or dual controls. In the usual single-control
that use an ac power supply or are diesel-driven. generator, output is adjusted by shifting the position
Small combatant-type ships, such as destroyers, may of generator brushes or by moving a portion of the
be equipped with two motor-driven, single-operator, magnetic field structure of the generator. In the
dc generator sets; whereas, cruisers and aircraft usual dual-control generator, output is adjusted by
carriers will have a larger number of these types of varying the generator shunt field strength and
welders. The motor-driven dc generator set uses an varying the strength and direction of the series field.
ac power supply to run the motor, and the generator The machine shown in figure 10-l is a dual-control
provides dc welding current. Repair ships and type fastened on an ordnance handling truck. A
tenders may also be equipped with diesel-driven, ground plate is attached to the work to be welded,
motor-generator sets as well as the electric and the electrode is clamped in the electrode
motor-generator sets. holder.
All types of arc-welding machines require a When an electric power supply is available,
source of power that will allow you to strike and welding generators are usually driven by an electric
maintain a stable arc suitable for welding. The motor connected to the generator by a flexible
principal sources of power for shipboard welding are coupling. Others are set up with the generator and
as follows: the motor on the same shaft. When an electric
power supply is not available, you must have a
A dc generator with variable voltage
characteristics may be used in a single-operator
welding system. The generator is so designed that
it delivers a voltage high enough to start the arc and
reduce the voltage as required to maintain the arc
during the welding.
A rectifier may be used to convert ac to dc
for welding.
The power from these sources is used in various
types of welding equipment to provide the necessary
current. The basic types of welding equipment used
Figure 10-1.—Variable-voltage dc generator welding unit
for shielded metal-arc welding are (1) the
(dual-control type).
10-2
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