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Chapter 29 Special Welding and Cutting Processes
placed against the base metal, as shown in Figure 29-8.
When the trigger is pulled, electricity flows through
the stud to the base metal. The stud is then automati-
cally 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. It is held for a second or two and
the weld is completed. On nonferrous metals, a
shielding gas is used to produce good arc stud welds.
Shielded Metal Arc Welding (SMAW)
Underwater
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 weld-
ing has especially good electrical insulation. The coat-
ing on the electrode is waterproof. See Figure 29-9.
Special training, equipment, and safety procedures
are required to weld underwater.
Figure 29-6. Plasma arc welding equipment used in an auto-
mated application welding a lid to a small canister. (Process
Welding Systems, Inc.)
Collet
Trigger
Shielding
gas
chamber
Figure 29-7. An arc stud welding gun. This gun is being used
to weld aluminum. Shielding gas is fed into a chamber sur-
rounding the stud. (Nelson Stud Welding, Inc.)
Chuck
Stud
Ferrule
A–Fluxed end of stud is placed
in contact with work.
B–Stud is automatically retracted
to produce an arc.
C–Stud is plunged into pool
of molten metal.
D–Operation completed–stud
is welded to work.
Figure 29-8. The steps that take place during an arc stud weld
on a steel plate. (Nelson Stud Welding, Inc.)