Progress in gas atomization of liquid metals by means of a De Laval nozzle

Abstract

Liquid metal atomization using a De Laval nozzle has proven its efficiency in producing fine and narrow sized powders. The modelling work of gas dynamics related to nozzle geometry has led to a better understanding of the effects of the processing parameters. When used during the empting of a crucible, the decrease in the static height of the melt acts on the metal mass flow rate. Moreover, the aspiration due to the negative overpressure formed at the melt nozzle tip depends directly on the atomization pressure. Thus, the gas to metal ratio (GMR) does not increase as fast as the atomization pressure. An experimental study on the particle size distribution in the cross-section of the spray and its evolution during the process has confirmed the unsteadiness of the process. By establishing a model to fit the gas pressure to the mass flow rate evolution, an almost steady state can be reached for the process. This has brought us to reduce the mean particle size and to improve the narrowness of the as-atomized particle size distribution.