Simulation of Motion, Heating, and Breakup of Molten Metal Droplets in the Plasma Jet at Plasma-Arc Spraying
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M.Yu. Kharlamov, I.V. Krivtsun, V.N. Korzhyk, Y.V. Ryabovolyk, and O.I. Demyanov (Submitted April 10, 2014; in revised form November 16, 2014) The mathematical model for the process of plasma-arc wire spraying is proposed, which describes behavior of molten metal droplets in the plasma jet, allowing for the processes of their deformation and gas-dynamic breakup. Numerical analysis of the processes of motion, heating, and breakup of molten metal droplets, detached from the sprayed wire at plasma-arc spraying of coatings, was performed. It is shown that during molten droplets movement in the plasma jet their multiple breakup takes place, leading to formation of sprayed particles with dimensions much smaller than dimensions of initial droplets, detached from the sprayed wire tip.
Keywords
droplet breakup, mathematical modeling, molten droplets, motion and heating of particles, plasmaarc wire spraying
1. Introduction Industry has recently shown considerable interest in plasma and plasma-arc processes associated with spraying of wires and rods. In particular, the problems of spraying wire and rod consumables are encountered in the processes of coating deposition, as well as producing superfine powders. The fact that already completely molten metal particles penetrate into the flow should be regarded as one of the features of coating spray deposition using wire consumables, unlike the processes of thermal powder spraying, in which powder particles in the solid state are injected into the flow of gas or plasma (Ref 1). Moreover, plasma-arc wire spraying opens up broad capabilities of controlling the characteristics of droplets detached from the tip of sprayed wire or rod by changing the conditions of their feeding into the plasma arc. Alongside that, it should be noted that molten metal particles moving in the high-speed plasma jet are deformed and inner motion develops in them, leading to their destruction with formation of finer fragments (Ref 2). Thermal and dynamic interaction of plasma flow with liquid particles also can differ from its respective inter-
M.Yu. Kharlamov, I.V. Krivtsun, V.N. Korzhyk, Y.V. Ryabovolyk, and O.I. Demyanov, E.O.Paton Electric Welding Institute of the NAS of Ukraine, Kyiv, Ukraine. Contact e-mail: mykharlamov@ gmail.com.
Journal of Thermal Spray Technology
action with solid particles. All this affects the final result of the spraying process. In particular, the structure and properties of coatings formed in such a spraying process are determined in many respects by the dimensions, velocity, and temperature of liquid particles at their collision with the substrate. On the other hand, in a similar process of dispersion of wire and rods to produce fine and superfine powders, it is necessary to achieve the specified fractional composition of disperse phase. Therefore, study of the processes occurring during movement of molten metal particles in the plasma flow is of great importance for further development of plasma and plasma-arc material processing technologies, associated with spraying
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