Influence of Hydrodynamic Instability of the Jet Metal on Dispersion of Granules at Spraying

Processy litʹâ, 2020, Tom 141, №3, p.8-18

Abstract

Received 29.06.2020

UDC 621.762.2

For the production of high-quality billets and products intended for mechanical engineering and other industries, metal powders are used, including those from highly alloyed alloys. Various methods for producing powder materials are known. The leading place among the technologies for producing high-quality powders of metals and alloys belongs to the methods of spraying melts, which is primarily due to the high productivity and efficiency of this process. The most important characteristic of the sprayed powder is the particle size distribution and particle shape. It is known that the formation of particles in size and geometry is determined not only by the physical parameters of the melt (viscosity, surface tension, temperature) and energy carrier gas (temperature, flow rate, speed, etc), but also by spray parameters. The work the technological processes of producing metal powders during gas and centrifugal spraying based on the study of the laws of motion of a jet of a low-viscosity melt and establishing the dependence of the particle size distribution of powder granules on the hydrodynamic instability of the jet are investigated. Formulas for calculation and theoretical flow patterns of a low-viscosity melt jet are presented. It is shown that longitudinal instability waves arise on the surface of a liquid metal jet, but only one develops, with a maximum amplitude. Using the film and photographs of the process of atomization of the Ni - 50 % Fe alloy, it was shown that the motion of the melt jet is unstable, the jet is gradually crushed, and then decay into fragments of different configurations. Empirical models of various authors are analyzed, taking into account a large number of spraying parameters and the difference in their effect on the size of the resulting particles during gas and centrifugal spraying. It has been established that in both cases the determining parameter of the effect on the size of powders and granules is the diameter of the metal jet, which decomposes due to instability,.The results of experimental studies of the highly alloyed alloys, carried out under the conditions of the pilot production of UkrNIISpetsstal and OJSC Dneprospetsstal, proved that gas spraying of the melt by the limited-jet method allows particles to be obtained with minimal differences in their size. In centrifugal spraying, the length of the melt stream to the disk plays an important role, with a decrease in which the yield of fine fractions increases.