In the transferred arc process, an arc is struck
between the electrode and the work. The inert gas is
turned into superheated plasma as it passes through
the arc at the orifice (hole) in the restricted nozzle. It
is the plasma that melts the base metal.
In a nontransferred arc plasma torch, the arc
occurs between the tungsten electrode and the
restricted nozzle. See Figure 29-5. When automatic
plasma arc welding (PAW) is done, the filler wire is
fed into the weld pool automatically, Figure 29-6.
Edge and flange joints may be welded without the
addition of filler metal.
Arc Stud Welding (SW)
Arc stud welding (SW) was developed to weld
threaded studs, location pins, or nails to metal plates.
The process is fast and simple. It requires little skill.
To perform the weld, the stud is loaded into a stud
welding gun, Figure 29-7. The gun and stud are
Welding Technology Fundamentals
354
AC or DC + - electrode
Ground
Solidified flux (slag)
Plate metal
Weld metal
Granulated flux
Workpiece
Weld
backing
if required
Welding flux tube
Welding electrode
Vee if required
Direction of welding
Figure 29-3. A diagram of a submerged arc weld in progress. Note the flux granules are deposited ahead of the consumable
electrode. (ESAB Welding and Cutting Products)
Figure 29-4. Two submerged arc welds being made during the
assembly of a vertical column exposed in an open atrium.
(The Lincoln Electric Co.)
Restricted
nozzle
Gas
nozzle
Tungsten
electrode
Arc
Plasma
Transferred Nontransferred
Plasma
Arc
Orifice gas
Shielding gas
Figure 29-5. Cross-sectional drawing of the transferred and
nontransferred plasma arc welding torch.