PLASMA ARC WELDING, Advantages of PLASMA ARC WELDING and Disadvantages of PLASMA ARC WELDING

PLASMA ARC WELDING

Plasma is the state of matter present in between electrodes in any arc. In this part, gas is ionized to make it a conductor of electric current. – PAW uses a non- consumable tungsten electrode and a shielding gas such as argon, helium or a mixture of both with hydrogen. – 

Plasma torch

 Pure argon gas is allowed through the inner orifice surrounding the tungsten electrode to form plasma gas. The constraining nozzle squeezes the gas to form a concentrated and straight arc and also increases the heat contained per unit volume of the arc (~110000C).Ionization of the arc occurs through a low current pilot arc between electrode and constricting nozzle.

This initiates the PAW arc. Due to constriction the plasma gas attains a very high temperature and also provides a low resistance path to initiate the welding arc between electrode and work piece. This is called transferred arc. Inert shielding gas is allowed to flow through outer gas nozzle which protects the weld metal.Higher ampere rating Constant current or drooper type of dc power supplies are used as power sources. Electrode is taken as negative.PAW is done by”key hole” technique. 

Due to high temperature the base metal beneath the arc melts completely forming a thin keyhole. With the advancement of the torch the metal melted ahead (down hand welding position) flows into the keyhole. Thus the keyhole travels continuously along the torch direction. 

Advantages of PLASMA ARC WELDING

 Because of arc concentration heat input can be properly controlled and the heat affected zone around the weld metal is small. – Uniform deep penetration can be obtained. – Greater distance between electrode tip and work piece makes use of filler metal rod easier without contamination of electrode. Higher metal deposit rate. 

Disadvantages of PLASMA ARC WELDING

 Expensive frequent replacement requirement of nozzle.

Leave a Comment