Page 302 - CITS - Welder - Trade Practical

WELDER - CITS

Job Sequence

• Plasma cutting (plasma arc cutting) is a melting process in which a jet of ionized gas at temperatures above
20,000°C is used to melt and expel material from the cut.
• During the process, an electric arc is struck between an electrode (cathode) and the workpiece (anode).
• The electrode is recessed in a water- or air-cooled gas nozzle which constricts the arc causing the narrow, high
temperature, high velocity plasma jet to form.
• When the plasma jet hits the workpiece, recombination takes place and the gas reverts to its normal state,
emitting intense heat as it does so.

• This heat melts the metal and the gas flow ejects it from the cut. Plasma gases are usually argon, argon/
hydrogen or nitrogen.
• These inert gases can be replaced by air but this requires a special electrode of hafnium or zirconium.

• Use of compressed air makes this variant of the plasma process highly competitive with the oxy-fuel process
for cutting carbon-manganese and stainless steels up to 20mm thick.
• Inert gases are preferred for high quality cuts in reactive alloys.

• Plasma arc can cut a very wide range of electrically conductive alloys including plain carbon and stainless
steels, aluminum and its alloys, nickel alloys and titanium.
Note: Wear protective clothing.

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CITS : CG & M - Welder - Exercise 78