Development of a centrifugal atomization process for the production of large spherical metal powders

摘要

A centrifugal atomization process was developed for the production of large spherical metal powders. The final design of the process incorporated a low speed rotating liquid bath (RLB) for the cooling of atomized molten metal droplets generated from an atomizing disk. Experiments were conducted in an open air system with pure Ag and with an alloy of Ag-15 wt % Cu. Spherical powders were obtained in the case of pure Ag where there was no oxidation of the droplets. Use of silicone oil for the RLB was found to have a spheroidizing effect or irregular oxidized droplets of Ag-15 wt % Cu. Microstructural examination of individual Ag-15 wt % Cu particles revealed evidence of partitionless solidification around the rim of the particles. These partitionless rims were attributed to undercooling of the droplets caused by the high cooling rate imparted by the RLB. The average particle size of the pure Ag powders was closely controlled in the size range of 450 to 650 (mu)m by controlling the speed of the atomizing disk. Results from particle size calculations suggested that the RLB did not cause any significant secondary disintegration of the atomized droplets. The size distributions of the powders were narrow with geometric standard deviations in the range of 1.4 to 1.6. The predominant atomization mode for these experiments was determined to be alignment disintegration. Even narrower size distributions are thought to be possible with the process if the atomization parameters could be modified to gain access to the direct drop formation regime. Specific recommendations are presented to accomplish this enhanced control of the atomization process. 32 refs., 31 figs., 5 tabs.