Plasma Plume Condition Forming of Cascaded Type Plasma Guns

Abstract

Abstract In the thermal spray industry there remains a constant demand for more stable, controllable and economical processing devices. Most thermal spray applicators apply a wide range of materials especially those who are allied with the turbine markets. Each material coating specification requires a relatively specific range of velocity and temperature transferred to the powder particle to achieve the required material properties on the part. The plasma gun has become a dominant process tool in the turbine industry due to the wide range of parameters that are achievable with the basic tool. In addition, there are today a large number of individual plasma guns that are each known to provide excellent results with some, but not all coating requirements. In many cases the optimum gun running condition can never be achieved due to the interdependence of arc behavior and gas conditions. The turbine industry is currently largely populated with guns that are based on the technology as it was developed in the 1960’s. These guns are characterized by poor voltage stability with a large quasi periodic oscillation in the 3-5 kHz range as described by Bisson [1], with poor performance and life under more extreme operating conditions. A key element of any plasma gun is the nozzle geometry. The cascaded gun types as typified by the Triplex offer a unique opportunity to study and document a wide range of operational parameters, especially at extreme operating conditions.