small production shops, body shops, home or farm
shops, or school shops. These special welding and
cutting processes are, however, being found in ever-
increasing numbers in large manufacturing and
repair businesses. The terms and abbreviations used
in this chapter to describe these processes are those
approved by the American Welding Society in AWS
A3.0, Standard Welding Terms and Definitions.
Special Arc Welding Processes
There are many welding situations that require
development of a special form of welding. Welding
on metal over 1′ (300 mm) thick is very difficult to do
using SMAW, GMAW, or GTAW. Electrogas arc weld-
ing and electroslag welding were developed to meet
this need.
When scientists created plasmas experimentally,
they discovered that extremely high temperatures
and heat outputs were also created. Welding engi-
neers developed the plasma arc welding and cutting
processes to take advantage of this new heat source.
Arc stud welding makes it possible to attach fastening
devices to steel structures very easily. Specially
designed equipment makes it possible to arc weld
under water.
Electrogas Welding (EGW)
The electrogas welding (EGW) process was devel-
oped as a means of welding extremely thick metal.
Thick metal sections are hard to weld, since the weld
area must be must be kept near the melting point at all
times. This is difficult with regular welding equipment.
Metal of almost any thickness can be welded with
the electrogas process. See Figure 29-1. The weld is
always made in a vertical position. One or more con-
sumable electrodes are fed into the joint from above.
To make the weld, the welding arc is struck, and the
consumable electrode melts in the joint to form the
weld. Solid electrode wire or flux-cored wire may be
used. Two water-cooled copper shoes act as dams.
They contain the molten metal in the weld area and
cool the completed weld. As the copper shoes and
electrode move up, the welding continues to the top
of the joint.
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352
Water
circulation
Water
connections
Gas shielding
Completed weld
Plate 1
Plate 2
Wire guide
Flux-cored electrode
Guide rollers
Molten slag
Molten weld metal
Solidifying weld metal
Solidified metal
Figure 29-1. A schematic drawing of the electrogas welding process. The shoes are water-cooled and move up along with the weld.
A shielding gas protects the weld and molten metal.