Английский для сварщиков. Гричин С.В. - 49 стр.

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Text 3. Characteristics of the Principal Welding Processes
Welding is the process of joining together pieces of metal or metallic
parts by bringing them into intimate proximity and heating the places of
contact to a state of fusion or plasticity. This leads to interpenetration of the
atoms of the metals in the weld zone, and a strong inseparable joint is
formed after the metals have cooled.
Welding finds widespread application in almost all branches of
industry and construction. Welding is extensively employed in the
fabrication and erection of steel structures in industrial construction and civil
engineering (frames of industrial buildings, bridges, etc.), vessels of welded-
plate construction (steel reservoirs, pipelines, etc.) and concrete
reinforcement.
Welding processes may be classified according to the source of energy
employed for heating the metals and the state of the metal at the place being
welded. A master chart of the principal welding processes is shown on
the next page.
In fusion welding the welding area is heated by a concentrated source
of heat to a molten state and filler metal must be added to the weld. In
accordance with the method applied for feeding the filler metal to the weld,
welding procedures are classified as manual, semi-automatic or automatic
welding.
Pressure welding processes involve the heating of the metallic parts
only to a plastic or lightly fused state and forcing them together with
external pressure. Pressure welding processes are applied to metals which
are capable of being brought to a plastic state by heating or due to the
action of external forces. It has been established that in this process the most
weldable metals prove to be those metals which have higher thermal
conductivity. Such metals more rapidly dissipate heat from the weld zone
and do not allow an excessively high temperature to be concentrated in a
small area (the latter may lead to considerable internal stress).
The quality of the joint obtained in pressure welding depends to a great
extent upon the magnitude of the applied pressure and the temperature to
which the metal is heated at the moment of welding. The higher this
temperature, the less unit pressure will be required to produce the weld.
Proper cleaning of the surface to be joined is one of the main conditions for
obtaining high-quality welds in pressure-welding procedures.

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