is held rigidly in the torch by means of a collet that
Alternating current, high-frequency (ACHF)
screws into the body of the torch. A variety of collet
welding is a combination of dc straight polarity and dc
sizes are available so different diameter electrodes can
reverse polarity. One half of the complete ac cycle is
be used. Gas is fed to the weld zone through a nozzle,
DCSP and the other half is DCRP. Unfortunately,
which consists of a ceramic cup. Gas cups are threaded
oxides, scale, and moisture on the work piece often tend
into the torch head to provide directional and
to prevent the full flow of current in the reverse polarity
distributional control of the shielding gas. The cups are
direction. If no current whatsoever flowed in the reverse
interchangeable to accommodate a variety of gas flow
polarity direction during a welding operation, the
rates. Gas cups vary in size. The size you should use
partial or complete stoppage of current flow would
depends upon the type and size of torch and the
cause the arc to be unstable and sometimes go out. To
diameter of the electrode.
prevent this, ac welding machines incorporate a
high-frequency current flow unit. The high-frequency
Pressing a control switch on the torch starts the
current is able to jump the gap between the electrode
flow of both the current and gas. On some equipment,
and the work piece, piercing the oxide film and forming
the flow of current and gas is energized by a foot
a path for the welding current to flow.
control. The advantage of the foot control is that the
variable current flow can be used as the end of the weld
Welding Equipment
is reached. By gradually decreasing the current, it is
less likely for a cavity to remain in the end of the weld
Gas tungsten-arc welding equipment is produced
puddle and less danger of cutting short the shielding
by many manufacturers. For this reason, it is very
gas.
important to remember that the equipment being
discussed in this chapter is only one of the many types
ELECTRODES.--Pure tungsten, or tungsten
that can be found throughout the Navy. However, the
alloyed with thorium or zirconium, is the best electrode
functions of similar component parts of different makes
for gas tungsten-arc welding. The addition of thorium
of machines are identical, although they may not appear
increases the current capacity and electron emission,
to be so.
keeps the tip cooler at a given level of current,
minimizes movement of the arc around the electrode
TORCHES.--Manually operated torches are
tip, permits easier arc starting, and the electrode is not
constructed to conduct both the welding current and the
as easily contaminated by accidental contact with the
inert gas to the weld zone. These torches are either air
work piece.
or water-cooled. Air-cooled torches are designed for
welding light gauge materials where low current values
The diameter of the electrode selected for a
are used. Water-cooled torches (fig. 6-44) are
welding operation is governed by the welding current to
recommended when the welding requires amperages
be used. Larger diameter tungsten electrodes are
over 200 amps. A circulating stream of water flows
required with reversed polarity than with straight
around the torch to keep it from overheating. The
polarity.
tungsten electrode, which supplies the welding current,
Figure 6-44.--Typical water-cooled GTA welding torch.
6-30
