SPACE-CHARGE IN PLASMA-ARC WELDING AND CUTTING

In transferred arc plasma arc welding, the plasma is not electrically neutral. Some simple mathematical models are constructed to demonstrat e this fact and orders of magnitude are obtained. The relevance of the se models to plasma arc welding and cutting is considered; quite long arcs can be achieved if the flow rate is sufficiently high, and an arc from a consumed tubular field emitting cathode of 75 mm length is des cribed. In keyhole welding it is found that the current earths at the surface of the workpiece, or close to the top of the keyhole.