MODELING THE PROCESS OF SPHEROIDIZATION POWDER PARTICLES BY THE PLASMA-ARC METHOD
DOI:
https://doi.org/10.32782/KNTU2618-0340/2021.4.2.2.2Keywords:
spheroidization, plasma-arc method, plasma flow, heat balance, heat equationAbstract
Many modern technological processes require the use of metallic, ceramic and metal-ceramic powders, the particles of which have an ideal spherical shape. Consequently, the task arises of effective spheroidization of the powders used. The most effective way of spheroidization is powder treatment in a low-temperature plasma flow. In order to obtain perfect spherical particles, it is necessary that by the end of the distance the particle has minimal velocity and temperature in order to avoid deformation upon impact with the surface to collect the powder. In addition, during the flight, the particle must completely melt, but not reach the evaporation temperature, and then solidify. The problem of modeling the process of spheroidization of powder particles using the plasma-arc method is reduced to determination of the particle velocity and temperature in the low-temperature plasma flow considering changes in its aggregate state. Determination of the particle velocity is carried out considering the fact that the only force acting on it is the force of aerodynamic resistance. The plasma flow velocity is approximated by an exponential function. As a result, we obtain an implicit solution of the differential equation for determining the velocity of the particle along the distance. To investigate the temperature mode, we consider five sections of the distance. On the first of them (heating the particle to the melting temperature), we use the heat balance equation to determine the temperature. The second section is the process of particle melting. Here we determine the melting time of the particle, based on the heat balance equation, provided there is no heat flow at the phase transition boundary. The third section is the flight of the particle in the molten state. To model the process, we solve the boundary problem for the one-dimensional heat equation for spherical solid by approximating the plasma temperature with cubic splines. For the fourth section (solidification of the particle) the same model as for the second one is used. And for the fifth (cooling of the particle), the same approach as for the third. Finally, the results for titanium particles with a diameter of 10 μm are presented.
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