Modeling on the size of the pre-breaking molten droplet in plasma atomization for controlling the size of the produced powders

Abstract

In two-phase flow atomization, e.g., Electrode Induction Gas Atomization (EIGA) and Plasma Atomization (PA), the size of the produced powder is greatly affected by the size of the large droplet fed into the atomization zone, which is named the pre-breaking molten droplet (PbMD). In EIGA, the size of the PbMD can be quantitatively modeled as its generation from a rod by induction melting is relatively simple. While in PA, the generation of PbMD from a metal wire involves complex heat and mass transfer behavior, and there currently lacks of any quantitative model on the size of the PbMD in PA, resulting in unpredictable production of metal powders. Therefore, modeling on the size of the PbMD in PA was carried out in this study. Firstly, new phenomenological models were established to show the change in the state of the molten metal during the generation of PbMD in PA. Based on the phenomenological models, a theoretical equation for calculating the size of the PbMD with two unknown error variables was successfully deduced. Observation experiments were conducted using a high-speed camera to obtain the size of the PbMD in PA, which was used to determine the unknown error variables and verify the proposed calculation equation. The verification experiments showed that the error between the calculated and experimental results was within 10%. Moreover, it was found that the size of the PbMD in PA was much smaller than that in EIGA, which makes PA easier to produce fine powders. It was also observed that the average size of the PbMD and its variance increased with the increasing arc current of the plasma generator while decreasing with the increasing gas flow rate. With the proposed model, the size of the PbMD in PA can be predicted, and the size of the produced powders can be controlled.