Manual Arc Welding; Heat Protection - STAMOS S-Multi 41 Manuel D'utilisation

Manual arc welding

Manual arc welding, briefly called MMA (Manual Metal Arc Welding), is one of the ol-
dest electric welding procedures used for metallic materials, which is still used today.
In 1891 Nikolai Gavrilovich Slawjanow replaced the carbon electrodes commonly used
in his time for arc welding by a metal rod that was both the arc carrier and filler metal.
Since the first rod electrodes were not coated, the weld itself was not protected from
oxidation. Therefore these electrodes were difficult to weld. The electric arc burning
between an electrode and the workpiece is used as the heat source for welding. The
high temperature of the arc melts the material in the welding area. The rod electrode
simultaneously melts off acting as a filler material to form the weld bead. Both AC and
DC currents can be used to power the process.
Rod electrodes are used as filler material in arc welding. For each welding type the-
re are appropriate electrodes, e.g. for build-up welding and joint welding. Information
concerning the nature, characteristics and application of an electrode is provided by
the brief label, which is printed on each electrode package. The gases produced by the
melting of the electrode coating are used to stabilise the arc and separate the liquid
metal transfer in the arc from the influences of the surrounding air and to reduce the
burning of alloy components. Apart from that the melted coating also produces slag.
This liquid is lighter than liquid steel and is washed onto the weld. This enables a slow
cooling process and thus lower shrinkage stress. The anode (positive pole) is heated
by electron bombardment and positive metal ions flow from there to the workpiece.
Therefore consumable electrodes are mostly used as anodes with the workpiece mate-
rial acting as a negative pole. In TIG welding the electrode has a negative pole in order
to keep the degree of removal low. Arc welding is used in the construction industry
(bridge supports) but also in precision engineering.
The following rule applies regardless of application: The thinner the material, the more
expensive the equipment. Due to low current levels (necessary not to burn through
materials under 1 mm wall thickness), a significantly more complex control process is
required.
Tungsten inert gas welding (deu. WIG; eng. TIG)
The tungsten inert gas welding technology (TIG welding) comes from the U.S., where it
became known in 1936 as argon welding. Only after the second World War II was it in-
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troduced in Germany. In English-speaking countries this method is called TIG, after the
English word for tungsten. The method offers several interesting advantages over other
fusion welding processes. For example, it is universally applicable: if a metallic material is
at all suitable for welding, then it can be processed with this procedure. Additionally it is
also a very „clean" process, which produces very little pollution and little splashes and,
when used correctly, guarantees a high quality welded joint. A particular advantage of
TIG welding is also the fact that compared to other methods employing a consumable
electrode, the addition of a filler material and the current are not linked.
Therefore the welder has control over the power:
• it may be optimally matched to the welding task and it is only necessary to add as
much filler as is currently required. This makes the process particularly suitable for
welding root passes and for welding in forced positions.
• due to the relatively low and small-scale heat input there is little tendency for the
workpieces to warp during welding.
• these advantages have caused the process to be particularly suitable for welding of
air planes and space vehicles, construction elements used in nuclear installations and
installation components and equipment for chemical plants.
Current regulation
The automatic current suppression circuit protects against over-voltage up to the value
indicated in the technical datasheet.

Heat protection

The thermal protection circuit takes action when the device exceeds the duty cycle.
This means stopping the machine.
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