Relation between jet flow energy and pulverization work in gas atomization process

Abstract

The relationship between the kinetic energy of spraying medium and pulverization work for forming powder using molten metal in gas atomization process has been experimentally studied, which intends improvements of manufacturing fine powder in atomization process. Compressed air was ejected through 1.0, 1.2, 1.5 mm diameter 6 nozzles forming a reverse conical jet whose apex angle is 30 or 40 degrees. The velocity distribution of the gas jet is measured using Pitot tube attached to a traversing equipment. The kinetic energy and momentum of the gas jet were calculated based on measurements of the gas velocity distribution. The gas jet power at the horizontal plane including the geometrical focus was about 15～25 % of the compressing power and it decreases in downstream direction. With the molten metal tube fitted into the atomizing nozzle, molten tin was poured into the gas jets and the powders were produced by gas atomization. The distribution of the particle size was measured by sieving. Median diameters of the powders decreased in accordance with the gas jet power, though they exhibited a lower limit value in higher power region. The surface energy of the powder which is regarded as the pulverization work was obtained by multiplying the powder surface and the surface tension for each particle size section. The pulverization work to form powder is as small as about 1/1000 of the jet flow energy.