Effect of Torch Hardware on Oxy-Acetylene Powder Flame Spray Performance

Abstract

Abstract The effect of hardware on operating parameters and the resultant coating are qualitatively known; however, the quantitative effects have not been well defined. This study quantitatively characterizes particle temperature and velocity for the Sulzer-Metco 6P oxy-acetylene torch with 3 different nozzles and 3 air caps and also, the Alamo PG-550 then relates those data to particle diagnostics, deposition efficiency and coating microstructure. Both torches were evaluated using statistically designed experiments where the process inputs of oxy-fuel ratio, total combustible gas flow, and standoff distance were varied. Both torches can access similar regions of particle temperature - particle velocity space. Increasing total combustible gas flow increased particle velocity with little effect on particle temperature. Increasing oxy-fuel ratio decreased particle temperature with little effect on particle velocity. Higher particle velocity and particle temperature conditions yielded denser, less porous coatings. Flame cooling air caps increase the particle speed while decreasing particle temperature. Nozzles which inject powder directly into the flame jets significantly increase particle temperature as compared to nozzles which do not. Deposition efficiency is shown to not only be affected by particle temperature and particle velocity where hotter and faster usually increase efficiency, but is also dependent on the distribution of particles within the plume.