1996 Volume 82 Issue 8 Pages 665-670
Gas flow characteristics in the gas atomization have been studied to design atomization nozzles for fine powder production preventing blockage. A conical jet flow is formed for the confined-type atomization nozzle that has a melt delivery tube protruding into center portion and discharges discrete gas jets toward the geometrical focus. Converging around the geometrical focus, the gas jet flows vertically downward with making vortices and reverse gas flow beneath the melt orifice. The stability of atomization is determined by the pressure at the melt orifice and vortices' size, which vary with protrusion length of melt delivery tube. Molten metal fed out of the melt delivery tube spreads into the conical gas flow region, and is pulverized near the geometrical focus. When the protrusion of the melt delivery tube is insufficient, horizontal flow of molten metal along the end of melt delivery tube is formed, resulting in the blockage of the nozzle. In case the atomization nozzle has larger apex angle, upward gas flow along the outer surface of the tube is observed in spite of suction pressure at melt orifice, leading to an unstable gas flow due to the adhesion and growth of molten metal droplets. The suction pressure at melt orifice can be explained in terms of Bernoulli's equation.
