The effect of plasma-gas swirl flow on a highly constricted plasma cutting arc

Abstract

Swirl gas is widely used in the plasma arc cutting industry for inducing better plasma column confinement and providing a more stable constricting arc. When the inlet gas swirl number increases, the maximum pressure location moves to the plenum chamber edge due to centrifugal force, and the minimum pressure location moves much closer to the axis. The difference between the maximum and minimum pressure increases with swirl number. The large pressure difference in the radial direction constricts the arc and leads to large current density and Ohm heating near the axis. This causes much higher temperature near the cathode. It is indicated that swirl gas accelerates cathode erosion for two reasons: increasing plenum chamber pressure and changing flow patterns in the vicinity of the cathode. It is also found that the gas with large swirl number leads the swirl velocity component to be larger at the cutting location according to angular momentum conservation. It has been suggested that this causes different bevel angles for the left and right edges of the cutting kerf.