The importance of gases

Plasma Arc welding (PAW) takes advantage of the properties of a particular state of matter known as “Plasma”. 

Plasma is generated from gas or gas mixtures, the atoms of which have become highly ionized as they pass through an electric arc and are, therefore, capable of absorbing and conducting electrical energy. 

Well focused jets of plasma of greatly reduced dimensions and high power density are obtained thanks to “squeezing” the plasma through special nozzles with specially calibrated and opportunely cooled holes. 

The arc can occur between an infusible electrode and the weld piece (transferred arc) or between the electrode and nozzle (non-transferred arc). 

Protection of the weld pool is guaranteed by a coaxial flow of a shielding gas or gas mixture from the Stargas range. 

Plasma arc welding can be applied with or without a filler metal. 

A variation of the plasma process is the “keyhole technique”. This involves instantaneous vaporisation of the material thereby creating a passing hole and, thanks to the pressure of the metal vapour, the weld pool moves to the sides and then closes back; the balance between these two factors and the choice of the most appropriate gas mixture determines the depth reached by the jet and, therefore, the level of penetration enabling high productivity.

The “keyhole” procedure has two types of execution: none penetrating and complete penetration.