VISUALIZATION OF ENHANCED PRIMARY ATOMIZATION FOR POWDER SIZE CONTROL

摘要

The grand challenges for the production of metal and alloy powders by inert gas atomization include the ability to control the resulting powder size distribution, especially the mean size and standard deviation. Recent high-speed spray movies indicated that improved melt distribution was promoted by use of a contoured and slotted pour tube within a discrete-jet close-coupled gas atomization (DJ-CCA) nozzle and by expansion of the inner bore of the nozzle. These process modifications are part of efforts to achieve gas velocity-based control of powder size based on an acceleration wave breakup mechanism. The scope of past experiments on Cu atomization with N_2 gas were expanded to include Al, with a reduced surface tension, viscosity, and density, Results were characterized by visualization of atomization spray formation and by measurement of the resulting powder size distribution, especially standard deviation (d84/d50). The results indicate that the improved coupling of melt and gas is promoted by the new nozzle/pour tube designs, reducing the achievable standard deviation from 1.9-2.0 to 1.6-1.7, while operating at a high pour rate and low gas/metal ratios.