The power cable to the GTA welding torch, and
--Ac welding transformer with capacity range of
the ground cable to the work, should be connected
9 0 to 500 amperes having superimposed
according to the manufacturer's directions. The
high-frequency current
welding torch should be hung in a safe location so
that the tungsten electrode cannot touch anything
--GTA welding torch and 0.040-inch, 1/16-inch,
grounded and thus complete an electrical circuit.
l/8-inch, 3/32-inch, 5/32-inch, 3/16-inch, and 1/4-inch
The switch controlling power to the torch should
diameter tungsten electrodes, collets, and suitable
always be in the "off" position when welding is not
gas cup nozzles
being done.
-- A r g o n gas, usually a cylinder with a
The following checks should be made before
regulator-flowmeter, a solenoid control valve
starting to weld with GTA units:
interlocked with the welding circuit, or a manual
cut-off valve (called an economizer) in the gas line
1. Be sure the torch is the right type and
before the torch
capacity for the current at which most of the
welding will be done. Some manufacturers offer
--Water supply, main shut-off valve, and
different torches for different ranges of welding
solenoid control valve interlocked with the welding
current.
circuit
2. Check the size, appearance, and position of
--Steel worktable and C-clamps
the tungsten electrode in the torch. It should be
clean and silvery, and the diameter should be that
--Welding helmet, gloves, and protective
recommended for the welding current to be used.
clothing
A dirty, rough electrode surface usually means that
the inert gas was shut off before the electrode
--Stainless-steel wire brush for cleaning oxide
cooled, that there was air leakage in the gas supply
from the surfaces on which weld metal will be
system or torch proper, or that the electrode tip was
deposited
contaminated by touching metal. A dirty tungsten
electrode can sometimes be cleaned satisfactorily
NOTE: Reference to standard equipment in the
with a fine emery cloth. If severely contaminated,
following exercises will be briefly summarized, but
the electrode should be replaced or the tip broken
anticipates all previously indicated items.
off and dressed on a grinding wheel. (NOTE: The
dust produced from grinding thoriated electrodes is
Specific information on the different makes of
radioactive. However, this contamination normally
GTA welding equipment is not given in this training
d o e s not exceed the maximum permissible
We suggest the operator read the
manual.
concentrations. Even though the radioactive hazard
manufacturer's instruction pamphlets for specialized
of grinding thoriated tungsten is slight, care should
information.
be taken to grind electrodes on specially designed
and constructed grinders.) When you are welding,
Most GTA welding transformers are operated
the tip should be hemispherical in shape. The
from a 220- or 440-volt ac power source. Normally,
needlepoint tips used for stainless steel should not
an Electrician's Mate is the only one allowed to
be used for aluminum. A contaminated and a good
connect or disconnect a transformer. However, you
tungsten electrode are shown in figure 10-28. Note
should know the electrical hookup and be aware
the hemispherical tip on the good electrode. The
that high voltages, if incorrectly handled, may cause
electrode should extend beyond the end of the gas
a fatal injury.
cup a distance of l/8 to 3/16 inch. It must be
securely held in the torch both for positioning and
The high-frequency current imposed on the
for good electrical contact. Because small diameter
welding current often affects radio reception unless
electrodes are easily bent, check to see that the
the transformer is properly installed, grounded, and
electrode is straight and centered in the cup. If
adjusted. Therefore, the manufacturer's instructions
necessary, straighten or replace the electrode.
on these points should be carefully followed.
10-30
