Characterization of an Axial-Injection Plasma Spray Torch

Abstract

AbstractThe Axial III™ torch is a multiple-arc plasma generator with a set of three single cathode–anode units, which is still of significant importance, especially in the field of suspension plasma spraying. The division of the plasma generator into three spatially separated systems allows for central feedstock injection with improved deposition rates and efficiencies. In this work, several diagnostic methods were applied to characterize the plasma jet of an Axial III™ spray torch to further the understanding of this spray system. One important result was that the plasma temperature in the jet exhibits a triple distribution with three straight lobes arranged around the jet axis. As with every plasma torch, the total plasma power is subject to fast temporal variations. Power variations were clearly seen in the plasma jet even though it could have been anticipated that the triple jet characteristics and the natural fluctuations of the arcs generated by the three single cathode–anode units would be less pronounced after merging the three plasma streams. Unaffected by this it is nevertheless likely that the axially injected feedstock particles are caged effectively in the core of the plasma jet. Hence, the total electrical torch power and the uniformity of the single unit’s powers must be monitored to realize possible degradation and asymmetries in the plasma temperature distribution, which may influence deposition parameters.