Study of free fall gas atomisation of liquid metals to produce powder

Abstract

A free fall gas atomising unit was designed and constructed to produce metal powder. The effect of focal length, number, and diameter of nozzles and apex angle of atomisers is studied on size and size distribution of the powder, atomisation efficiency, and particle shape by disintegrating the molten stream at various plenum pressures, superheats, and free fall distances. Droplets were found to be solidified and built up around the nozzles and the liquid delivery tube whenever the atomiser was used beyond a particular value of the plenum pressure; this pressure is termed limiting plenum pressure. All the powder collectives produced under a wide range of conditions were found to obey log normal distribution function. The geometric standard deviation was shown to bear a constant value. The mass median size was correlated with the dynamic parameters characterising the atomising field and a correlation is proposed. The atomisation efficiency was correlated with the mass flowrate and velocity of gas.