Effect of spray torch nozzle design modifications on arc and plasma jet characteristics and coating properties

摘要

In order to identify means to improve plasma spray consistency, various modifications to the design of a commercial plasma torch nozzle have been investigated. The modifications consist of preparing anode inserts with grooves in the axial direction (spline insert), and introducing a fraction of the plasma gas through a ring of micro-nozzles surrounding the anode nozzle (micro-jet ring). Different designs for each modification have been investigated, and these modifications have also been paired with a modified upstream gas injector. For each of the modified designs, a wide range of characteristics have been measured for the arc, the plasma jet, the in-flight particles and the coating. The results show that most nozzle modifications lead to higher particle velocities and temperatures. The plasma jet is significantly elongated by using some of the modified nozzles, and the cold gas entrainment somewhat reduced. The arc voltage and the luminosity fluctuations are little affected by the nozzle modifications, however, the modification of the gas injector does change the frequencies of the fluctuations. Each of the nozzle modifications can be easily implemented offering an economical way to enhance process reliability.