| Abstract: | Arc plasma torch is an effective tool for spheroidization of metallic powders. However, as most
conventional plasma torches were not specifically designed for plasma spheroidization, they may
exhibit the disadvantages of the radial injection of powders, large fluctuations in the arc voltage,
large gas flow rate, and disequilibrium between multiple plasma jets during the spheroidization
process. Therefore, this paper presents a triple-cathode cascade plasma torch (TCCPT) for
plasma spheroidization. Its structural design, including three cathodes, a common anode, and
three sets of inter-electrodes, are detailed to ensure that powders can be inserted into the plasma
jet by axial injection, the arc voltage fluctuations are easily maintained at a low level, and the
plasma torches can work at a relatively small gas flow rate. Experimental results showed that the
proposed TCCPT exhibits the following characteristics: (1) a relatively small arc voltage
fluctuation within 5.3%; (2) a relatively high arc voltage of 75 V and low gas flow rate range of
10–30 SLM; (3) easy to be maintained at the equilibrium state with the equilibrium index of the
three plasma jets within 3.5 V. Furthermore, plasma spheroidization experiments of SUS304
stainless steel powers were carried out using the proposed TCCPT. Results verified that the
proposed TCCPT is applicable and effective for the spheroidization of metallic powders with
wide size distribution. |
