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Chapter 29 Special Welding and Cutting Processes
The weld area is protected from contamination by
a shielding gas. The gas may be carbon dioxide, an
inert gas, or a combination of two gases. It is supplied
from above through openings in the shoes and covers
the molten metal.
Electroslag Welding (ESW)
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 weld-
ing starts, the powdered flux melts. It forms a protec-
tive, floating slag above the weld area as shown in
Figure 29-2. Impurities in the molten metal float to the
top and mix with the flux. The molten flux protects the
weld metal from impurities in the air above the weld.
Submerged Arc Welding (SAW)
Submerged arc welding (SAW) has several advan-
tages over other welding processes. The larger elec-
trodes, higher currents, and narrower groove angles
used in SAW permit faster welding. The following is
a list of the advantages of SAW:
• Faster than manual arc welding.
• No visible arc.
• No spatter.
• High-quality weld.
• The welding groove angle may be smaller.
In SAW, as in GMAW, a consumable electrode is fed
into the weld joint. A thick layer of a powdered flux is
deposited ahead of the electrode, as shown in Figure 29-3.
The arc between the electrode and base metal occurs
beneath this thick flux layer. The flux covers the arc and
prevents any spatter. This is normally a fully automated
machine welding process, Figure 29-4. It may be done
semiautomatically, as well. In that case, the welder
guides the wire and flux-feeding mechanism.
Plasma Arc Welding (PAW)
Scientists say that there are four states (condi-
tions) of matter: solid, liquid, gas, and plasma.
Plasma is an ionized gas (a gas made up of atoms that
have lost or gained electrons). Ionized gas or plasma
is extremely hot—reaching temperatures as high as
43,000°F (24,000°C). The plasma arc is an excellent
heat source for welding or cutting. Cross sections of
the two types of arc plasma torches, transferred and
nontransferred, are shown in Figure 29-5.
An inert gas, such as helium, argon, or nitrogen, is
used to create the plasma. The gas, which flows
through the restricted nozzle, is called the orifice gas.
Inert shielding gas is passed around the restricted
nozzle to shield the weld area. A nonconsumable
tungsten electrode is used in the torch. The noise of the
plasma arc process can be harmful to one’s hearing;
therefore, industrial quality ear protection should be
worn when performing plasma arc welding.
Wire feed rolls and oscillating
mechanism mounted on carriage
that rises automatically as
weld metal builds up
Face of
plate
#1
Plates in vertical position
Water-cooled copper
slides confine molten slag
and weld metal
Completed weld
Face of
plate
#2
Thickness
of plate
Solidified
weld metal
Molten
weld metal
Molten slag
Consumable
electrodes
Figure 29-2. A schematic drawing of an electroslag weld in progress. Three consumable electrodes are used in this application.
The molten slag floating above the weld prevents oxidation.