Page 188 - CITS - Welder - Trade Theory

WELDER - CITS

GTAW welding torches are designed for either automatic or manual operation and are equipped with cooling
systems using air or water. The automatic and manual torches are similar in construction, but the manual torch
has a handle while the automatic torch normally comes with a mounting rack. The angle between the centerline
of the handle and the centerline of the tungsten electrode, known as the head angle, can be varied on some
manual torches according to the preference of the operator. Air cooling systems are most often used for low-
current operations (up to about 200 A), while water cooling is required for high-current welding (up to about 600
A). The torches are connected with cables to the power supply and with hoses to the shielding gas source and
where used, the water supply.
The internal metal parts of a torch are made of hard alloys of copper or brass in order to transmit current and
heat effectively. The tungsten electrode must be held firmly in the center of the torch with appropriately sized
collets, and ports around the electrode provide a constant flow of shielding gas. Collets are sized according to the
diameter of the tungsten electrode they hold. The body of the torch is made of heat-resistant, insulating plastics
covering the metal components, providing insulation from heat and electricity to protect the welder.

The size of the welding torch nozzle depends on the amount of shielded area desired. The size of the gas nozzle
will depend upon the diameter of the electrode, the joint configuration, and the availability of access to the joint
by the welder. The inside diameter of the nozzle is preferably at least three times the diameter of the electrode,
but there are no hard rules. The welder will judge the effectiveness of the shielding and increase the nozzle size
to increase the area protected by the external gas shield as needed. The nozzle must be heat resistant and thus
is normally made of alumina or a ceramic material, but fused quartz, a glass-like substance, offers great visibility.
Devices can be inserted into the nozzle for special applications, such as gas lenses or valves to improve the
control shielding gas flow to reduce turbulence and introduction of contaminated atmosphere into the shielded
area. Hand switches to control welding current can be added to the manual GTAW torches.
a Collet Body
The collet body screws into the torch body. It is replaceable and is changed to accommodate various size tungsten
and their respective collets.
b Collets
The welding electrode is held in the torch by the collet. The collet is usually made of copper or a copper alloy. The
collet’s grip on the electrode is secured when the torch cap is tightened in place. Good electrical contact between
the collet and tungsten electrode is essential for good current transfer.
c Gas Lenses
A gas lens is a device that replaces the normal collet body. It attaches to the torch body and is used to reduce
turbulence and produce a longer undisturbed flow of shielding gas. A gas lens will allow the welder to move the
nozzle further away from the joint allowing increased visibility of the arc. A much larger diameter nozzle can be
used, which will produce a large blanket of shielding gas. This can be very useful in welding material like titanium.
The gas lens will also enable the welder to reach joints with limited access such as inside corners.

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CITS : C G & M - Welder - Lesson 49 - 60