IMPROVEMENT OF PLASMA SPRAYING EFFICIENCY AND COATING QUALITY

A commercial torch has been modified to introduce an additional anti-v ortex and shroud gas flow to counter the detrimental effects brought a bout by the vortex plasma gas flow which is used to stabilize the cath ode are attachment and to increase the anode life. Deposition efficien cy and coating quality are used as criteria to judge the modified vers us the nonmodified torch. High-speed videography and computerized imag e analysis systems are used to determine the particle trajectories, ve locities, and the plasma jet geometry. The results show that the addit ional anti-vortex and shroud gas flow to the torch can keep the partic les closer to the torch axis and reduce the amount of entrainment of c old air into the plasma jet. The consequence is that deposition effici ency and coating quality are substantially improved.