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Chapter 29 Special Welding and Cutting Processes
The electrogas welding (EGW) process was developed as a means of welding extremely thick metal. To
make the weld, the welding arc is struck, and the consumable electrode fed in from the top melts in the
joint to form the weld. Two water-cooled copper shoes contain the molten metal in the weld area,
supply shielding gas, and cool the completed weld.
The electroslag welding (ESW) process is similar to electrogas welding. A thick layer of powdered flux
is placed in the joint before welding begins. Once welding starts, the powdered flux melts and forms a
protective, floating slag above the weld area.
In submerged arc welding (SAW), a consumable electrode is fed into the weld joint. A thick layer of a
powdered flux is deposited ahead of the electrode. The arc between the electrode and base metal
occurs beneath this thick flux layer. The flux cover prevents any spatter.
Plasma arc welding (PAW) uses superheated plasma to melt the base metal. In the transferred arc
process, an arc is struck between a nonconsumable tungsten electrode in the torch and the base metal.
In the nontransferred arc process, an arc is struck between the electrode and the restricted nozzle. In
both processes, an inert gas emitted from the torch turns into superheated plasma as it passes through
the arc. It is the plasma that melts the base metal.
Arc stud welding (SW) was developed to weld threaded studs, location pins, or nails to metal plates. In
this process, a stud is loaded into a stud welding gun. The gun and stud are placed against the base
metal. When the trigger is pulled, electricity flows through the stud to the base metal. The stud is then
automatically pulled away from the plate, and an arc is struck. Electricity flows for only a fraction of a
second. The gun then forces the molten tip of the stud into the molten base metal.
Shielded metal arc welding (SMAW) is done underwater to repair bridges, ships, and oil drilling rigs.
The process is similar to regular SMAW. However, the electrode holder for underwater welding has
especially good electrical insulation and the electrode coating is waterproof.
Solid-state welding (SSW) may be defined as a group of welding processes that produce a fusion weld
by application of pressure at a welding temperature below the melting temperature of the base metal
and filler metal.
SummaryyrammuS Summary
(continued)
Figure 29-20. An exothermic cutting rod is gouging and
removing a 3/4″ (19 mm) fillet weld. A 24″ (600 mm) long
weld bead can be removed in 20 seconds. (Oxylance, Inc.)
Figure 29-21. This exothermic burning bar is being used during
a salvaging operation to cut through 18″ (460 mm) thick steel
casting. (Oxylance, Inc.)