Experimental and Numerical Analysis of a Reverse-polarity Plasma Torch for Plasma Atomization

Plasma atomization (PA) is a highly recognized method for producing spherical powders for additive manufacturing and metal injection molding. It uses multiple converging plasma jets to simultaneously melt and atomize the metal wire to spherical powders. The quality of the atomized powders is highly dependent on the plasma torch for generating the plasma jet. Although the reverse-polarity plasma torch (RPT) has been commercially applied in the PA, its working characteristics relating to the high stability, high thermal efficiency, and supersonic plasma jet with high temperature desired in the PA are unclear. Therefore, experimental and numerical investigations of a self-manufactured RPT for PA were conducted to reveal its volt-ampere, thermal and jet characteristics. Results showed that the RPT works stably with the arc voltage fluctuation within 10 V ensuring the uniform quality of the produced powders. Besides, compared with the common argon plasma torch, the RPT works at high arc voltage and low arc current leading to less erosion of electrodes and purer powders. Furthermore, the thermal efficiency of the RPT and the mean enthalpy of its plasma jet is higher than 70% and 3 × 106 J/kg respectively, making it ideal for generation of the plasma jet with high energy density. Moreover, numerical results showed that the RPT with the De-Laval nozzle can generate supersonic plasma jet with temperature high enough for melting and atomizing most of materials. Finally, the PA experiment showed the effectiveness of the RPT for the production of high quality powders with smooth surfaces, high sphericity and small particle size.