Unlike single-

carbon arc welding 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. It was the first arc-welding process developed but is not used for many ...

, in twin-carbon arc welding (TCAW) the

arc ARC may refer to: Business * Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s * Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services * ...

is maintained between two carbon (

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

)

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

s held in a special holder. The Ac current was usually used. It was switched on by operating bringing two electrodes closer by a mechanism which also adjusted arc length. The two electrodes touch momentarily, then separate and thus an arc is established. TCAW is unshielded and no artificial pressure is applied.

History

TCAW was first proposed in 1874.

Use

The size of the arc depends upon the distance between the electrode tips, electrode diameters and the welding

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

. The heat input to the job can be varied by changing the arc size or the distance between the arc and workpiece. After striking the arc, welding can be carried out in the same way as in

TIG welding Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmo ...

process. An AC supply is recommended for TCAW. In case a DC supply is used, the positive electrode will disintegrate and consume at a much faster rate as compared to negative electrode, because two-thirds of the total heat is generated at the positive anode. This will produce an unstable arc and require frequent adjustment of the electrodes. In AC welding, because of alternate reversals of polarity, both the electrodes will be affected equally and present no problem. The electrodes employed for TCAW are approximately of the same diameter as the workpiece thickness. The magnitude of arc current required for welding depends upon both electrode diameter and plate thickness. For example, an 8 mm diameter electrode will need about 65 amps to weld a mild steel sheet of thickness 3.5 mm and 80 Amps to weld a sheet of 6 mm thickness. TCAW, though more complex than single carbon arc welding, possesses the advantage that arc is independent of the job and can be moved anywhere without getting extinguished. Moreover, the workpiece is not a part of the electrical circuit. While carbon electrodes have been replaced by tungsten and other alternatives in many places, in developing countries simple twin carbon-arc torches are a cheaper and more sustainable alternative to oxyacetylene torches. A simple version of a TCAW apparatus was designed in Ethiopia, it has reduced costs and improved the accessibility of welding services.

References

{{DEFAULTSORT:Twin-Carbon Arc Welding Arc welding