Plasma-Spray Coating Processes: Physico-Mathematical Characterization

Approximate characterization of the complicated dynamics of plasma-spray coating processes may be useful in obtaining optimal coatings. The usual industrial method of obtaining such a characterization by experimental trial-and-error procedures may be more time-wasting and costly than a combined procedure of analysis and trial-and-error. This paper describes such an approximate analysis and presents the results in a simple graphical form. Thus, by using a few simplified differential equations which describe the fluid dynamics, temperature and velocity distributions as well as the degree of evaporation of the injected powder in the plasma jet, we illustrate our method for the specific case of spraying molybdenum particles in argon as the carrier gas. The results indicate the various limitations associated with major operating variables such as particle size, relative mass flow rates of gas and particles, plasma temperatures, and distances from the plasma gun. Evaporation losses of the powder are given in Fig. 7.