PLASMA ARC WELDING AND ITS WORKING PROCESS

Plasma is high-temperature ionized (its atoms loose electrons) gas and occurs in any electric arc between two electrodes. The ionized gas plasma gets hotter by resistance heating from current passing through it. If the arc is constrained by an orifice, the proportion of ionized gas increases and plasma-arc welding is created, which causes the intense source of heat primarily due to multiple collisions of the electrons within the particles, and provided greater arc stability.

A non-consumable tungsten electrode within a water cooled nozzle is enveloped by a gas. The gas is forced past an electric arc through a constricted opening at the end of the water-cooled nozzle. As the gas passes through the arc, it is dispersed. This releases more energy and raises the temperature of the nozzle. Temperatures have been reported to be 10,000*C to 30000*C. As a comparison, oxy-acetylene welding is limited to the maximum temperature of the chemical reaction and is approximately 3600*C. The ordinary electric arc, because of its diffuseness, can attain a maximum temperature of 11000*C.

The main function of the plasma gas is shielding the body of the torch from the extreme heat of the cathode. Any gas or mixture of gases that does not attack the tungsten or the copper cathode can be used ; argon and argon mixtures are most commonly used.

In this process, the penetration is deep and through and much work can be done without filler metal. Again, filler metal may be used if an extra metal supply is needed.

Any known material can be melted, even vaporized, by the plasma-arc process and thus becomes subject to welding. Results are clean and two to five times as fast as TIG welding with same equipment cost. It requires automatic control and is not practical for short welds.

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Mechinopedia For Mechanical Engineers

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