polarity (electrode positive), the greatest amount of
gasoline or diesel engine to rotate the generator. In
heat is concentrated on the electrode side of the
this case, the engine is equipped with a governor to
compensate for the varying loads imposed by the
Note that the concept of polarity applies only to
dc welding circuits. In ac circuits, the direction of
All dc generator welding units deliver either
current flow is constantly reversing; therefore, an ac
straight or reverse polarity welding current. The
circuit has no polarity affecting the operation of the
correct polarity is essential in metal-arc welding, so
let's see what the term polarity really means. To
understand polarity, you must first have a clear
The polarity recommended for a particular type
understanding of the welding circuit. The welding
of electrode is specified by the manufacturer. If you
circuit consists of (1) a source of welding current,
use the wrong polarity for a given electrode, the arc
(2) a lead attached at one end to the power source
will have a hissing sound and will be very difficult to
and at the other end to the electrode holder, and
control. When the proper polarity is used, the arc
(3) a ground lead or work lead attached at one end
will have a sharp, crackling sound.
to the power source and at the other end to the
work. In any electrical circuit, current flows only
In general, reverse polarity gives a slower rate of
when the circuit is closed. When a dc welding
electrode burn-off, together with deeper and more
circuit is closed, electrons flow from the negative
certain penetration. Reverse polarity also causes
terminal, through the circuit, to the positive terminal
greater fluidity and slower solidification of the weld
of the generator. The polarity can be changed by
use of the polarity switch located on the machine.
(See fig. 10-1.) If the machine does not have a
Joints in sheet metal are usually welded with
polarity switch, simply reverse the hookup of the
straight polarity. Reverse polarity is specified for
electrode lead and the ground lead, as shown in
many other types of welds, particularly for welds
made in the vertical or overhead position.
Polarity is important because it determines the
Before placing any unit in operation, check the
location of the major portion of the welding heat.
nameplate data and the manufacturer's technical
About two-thirds of the heat of the arc is developed
manual for exact instructions on setting up the unit.
at the positive pole. In straight polarity welding
Check the following points in particular:
(electrode negative), the greatest amount of heat is
concentrated on the work side of the arc. In reverse
1. If the generator is driven by an electric
motor, be sure that the power supply agrees with
the motor requirements. Never attempt to operate
a dc motor on ac power or an ac motor on dc
2. Check the motor supply cable and the fuses.
Make sure the wiring to the motor is large enough
to carry the load, and be sure the line fuses are
adequate. If you have any reason to doubt the
adequacy of the cable or the fuses, have the
equipment checked by an Electrician's Mate.
3. On machines using an ac power supply for
the motor, ensure that the rotation of the motor is
in the indicated direction. You may reverse the
rotation of three-phase ac motors by interchanging
any two supply leads.
4. Before applying power to the motor, turn
Figure 10-2.--Reverse polarity and straight polarity.
the shaft by hand to make sure it turns freely.