Powder injection molding symposium

Abstract

Although high-pressure gas atomization has been widely used for the large-scale production of fine metal powders, high operating costs remain one of its biggest issues. The key to efficiency lies in how to strengthen the gas/molten metal interaction. Despite this, most of the extensive previous studies have focused on evaluating various nozzles by flow visualization and the size measurement of the resulting powder. It is known that strong shock waves are inevitably produced by a pressure mismatch through the nozzle, however the effect of those shock waves on gas flow and breakup behavior is still unclear. The purpose of this numerical simulation study was to determine whether any efficient paths for maximizing the gas-melt interaction exist, and to elucidate possible effects of the shock waves. Two types of supersonic nozzles were employed for the simulations: an annular slit nozzle, versus an isentropic plug nozzle working in shock-free mode. Single particle analysis was performed by injecting a single coarse droplet at different locations near the nozzle exit and then monitoring the local gas velocity and breakup characteristics along its path. The same path-resolved analysis was repeated for continuous droplet injection under various gas-to-melt ratios. The results indicate that more efficient paths exist for the maximal use of gas kinetic energy, and that shock waves are detrimental to producing smaller sized powders.