Английский для сварщиков. Гричин С.В. - 57 стр.

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57
Power supplies
To supply the electrical energy
necessary for arc welding processes, a
number of different power supplies can be
used. The most common classification is
constant current power supplies and
constant voltage power supplies. In arc
welding, the voltage is directly related to
the length of the arc, and the current is
related to the amount of heat input.
Constant current power supplies are most
often used for manual welding processes
such as gas tungsten arc welding and
shielded metal arc welding, because they maintain a relatively constant
current even as the voltage varies. This is important because in manual
welding, it can be difficult to hold the electrode perfectly steady, and as a
result, the arc length and thus voltage tend to fluctuate. Constant voltage
power supplies hold the voltage constant and vary the current, and as a result,
are most often used for automated welding processes such as gas metal arc
welding, flux cored arc welding, and submerged arc welding. In these
processes, arc length is kept constant, since any fluctuation in the distance
between the wire and the base material is quickly rectified by a large change
in current. For example, if the wire and the base material get too close, the
current will rapidly increase, which in turn causes the heat to increase and the
tip of the wire to melt, returning it to its original separation distance.
The type of current used in arc welding also plays an important role in
welding. Consumable electrode processes such as shielded metal arc welding
and gas metal arc welding generally use direct current, but the electrode can
be charged either positively or negatively. In welding, the positively charged
anode will have a greater heat concentration, and as a result, changing the
polarity of the electrode has an impact on weld properties. If the electrode is
positively charged, it will melt more quickly, increasing weld penetration and
welding speed. Alternatively, a negatively charged electrode results in more
shallow welds. Non-consumable electrode processes, such as gas tungsten arc
welding, can use either type of direct current, as well as alternating current.
However, with direct current, because the electrode only creates the arc and
does not provide filler material, a positively charged electrode causes shallow
welds, while a negatively charged electrode makes deeper welds. Alternating
current rapidly moves between these two, resulting in medium-penetration
welds. One disadvantage of AC, the fact that the arc must be re-ignited after
A constant current welding power
supply capable of AC and DC

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