Английский для сварщиков. Гричин С.В. - 65 стр.

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65
is not applied. A major difference between EGW and its cousin electroslag
welding is that the arc in EGW is not extinguished, instead remaining struck
throughout the welding process. It is used to make square-groove welds for
butt and welding, especially in the shipbuilding industry and in the
construction of storage tanks. In EGW, the heat of the welding arc causes the
electrode and workpieces to melt and flow into the cavity between the parts
being welded. This molten metal solidifies from the bottom up, joining the
parts being welded together. The weld area is protected from atmospheric
contamination by a separate shielding gas, or by the gas produced by the
disintegration of a flux-cored electrode wire. The electrode is guided into the
weld area by either a consumable electrode guide tube, like the one used in
electroslag welding, or a moving head. When the consumable guide tube is
used, the weld pool is composed of molten metal coming from the parts being
welded, the electrode, and the guide tube. The moving head variation uses an
assembly of an electrode guide tube which travels upwards as the weld is
laid, keeping it from melting. Electrogas welding can be applied to most
steels, including low and medium carbon steels, low alloy high strength
steels, and some stainless steels. Quenched and tempered steels may also be
welded by the process, provided that the proper amount of heat is applied.
Welds must be vertical, varying to either side by a maximum of 15 degrees.
Like other arc welding processes, EGW requires that the operator wear a
welding helmet and proper attire to prevent exposure to molten metal and the
bright welding arc. Compared to other processes, a large amount of molten
metal is present during welding, and this poses an additional safety and fire
hazard. Since the process is often performed at great heights, the work and
equipment must be properly secured, and the operator should wear a safety
harness to prevent injury in the event of a fall. EGW uses a constant voltage,
direct current welding power supply, and the electrode has positive polarity.
A wire feeder is used to supply the electrode, which is selected based on the
material being welded. The electrode can be flux-cored to provide the weld
with protection from atmospheric contamination, or a shielding gas can be
used with a solid wire electrode. The welding head is attached to an apparatus
that elevates during the welding process. Also attached to the apparatus are
backing shoes which restrain the weld to the width of the workpieces. To
prevent them from melting, they are made of copper and are water-cooled.
They must be fit tightly against the joint to prevent leaks.
Stud welding is a form of spot welding where a bolt or specially formed nut
is welded on to another metal part. The bolts may be automatically fed into
the spot welder. Weld nuts generally have a flange with small nubs that melt
to form the weld. Studs have a necked down, unthreaded area for the same
purpose.

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