ВУЗ:
Составители:
Рубрика:
53
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
every zero crossing, has been addressed with the invention of special power
units that produce a square wave pattern instead of the normal sine wave,
making rapid zero crossings possible and minimizing the effects of the
problem.
2 Consumable Electrode
Methods
One of the most common types of arc
welding is shielded metal arc welding
(SMAW), which is also known as
manual metal arc welding (MMA) or
stick welding. Electric current is used to
strike an arc between the base material
and consumable electrode rod, which is
made of steel and is covered with a flux that protects the weld area from
oxidation and contamination by producing CO
2
gas during the welding
process. The electrode core itself acts as filler material, making a separate
filler unnecessary. The process is very versatile, requiring little operator
training and inexpensive equipment. However, weld times are rather slow,
since the consumable electrodes must be frequently replaced and because
slag, the residue from the flux, must be chipped away after welding.
Furthermore, the process is generally limited to welding ferrous materials,
though special electrodes have made possible the welding of cast iron, nickel,
aluminum, copper, and other metals. The versatility of the method makes it
popular in a number of applications, including repair work and construction.
Gas metal arc welding (GMAW), also known as metal inert gas (MIG)
welding, is a semi-automatic or automatic welding process that uses a
continuous wire feed as an electrode and an inert or semi-inert gas mixture to
protect the weld from contamination. Since the electrode is continuous,
Страницы
- « первая
- ‹ предыдущая
- …
- 51
- 52
- 53
- 54
- 55
- …
- следующая ›
- последняя »
