Carbon
Arc Welding (CAW) is a process which produces coalescence of metals by heating
them with an arc between a non-consumable carbon (graphite) electrode and the
work-piece.
Carbon
arc welding is one of the oldest welding techniques that are still in use
today. DC power supply is used in this welding process. It is essential that
the welding circuit is set-up for straight polarity. If a reversed-polarity
setting is used, the arc will not be stable and a carbon residue will be left
to become entrapped in the weld.
PRINCIPLE
In carbon arc welding, the intense of
the heat of an electric arc developed between a carbon electrode and work-piece
metal is used for welding.
The carbon electrode is connected to the
negative terminal and work-piece is connected to the positive terminal, because
the positive terminal is hotter (4000°c) than the negative terminal (3000°c)
when an arc is produced.
The process of carbon arc welding uses
low voltage, high amp electricity to heat the metal once an arc is formed
between a carbon electrode and the piece being welded; if an arc is formed
between two carbon electrodes that technique is known as a twin-carbon arc.
PROCESS
1.
In this method, an electric arc is produced between the carbon electrode and
the ‘work’. A rod of carbon is used as negative (-) pole and the ‘work’ being
welded as positive (+) pole.
2.
The carbon electrode does not melt itself. It is a non-consumable electrode.
3.
The electrodes that are used in carbon arc welding consisted of baked carbon or
pure graphite which was placed inside a copper jacket.
4.
During the welding process, the electrode is not consumed as the weld
progresses; overtime, however, the electrodes will need to be replaced due to
erosion.
5.
A filler rod is used separately at the welding joint. The arc is established between the work-piece
and a carbon electrode held in the electrode holder.
6.
A long carbon arc is often desirable in order to prevent contamination of the
weld metal with the carbon monoxide given, off by the carbon electrode under
the energy of the arc.
7.
In the carbon arc welding of light-gauge plates, the use of filler rod may not
be necessary. But in welding of heavy plates of filler rod consisting of the
same material as the base metal is generally used.
8.
The filler rod is then inserted in the pool, the arc being directed against it
just above the surface of the molten metal.
9.
The end of the rod is thus melted off and deposited in the pool. The arc is
played to and fro in the pool, thoroughly melting and mixing with the metal. No
filler rod is necessary to make a lap weld on light-gauge metal with a carbon
electrode.
10.
The amount of fusion will depend upon the speed with which the arc is moved
over the surface. For less fusion, the current should be increased and the
electrode advanced at a faster rate.
ADVANTAGES
1. Low cost of
equipment and welding operation
2. Skilled operator is
not required;
3. The process can be
easily automated
4. Low distortion of
the work-piece.
DISADVANTAGES
1.
Unstable quality of the weld produces porosity
2.
Carbon of electrode contaminates weld material with carbides.
3.
This welding process develops extremely bright light. This bright light can be dangerous for the
welder if they are not wearing the proper eye protection and clothing.
APPLICATIONS
This process is used
for welding both ferrous and non-ferrous metals like steel sheet, Brass,
Bronze, Gunmetal, M/S-sheet, carbon-steel etc.
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