Arc Voltage and Heat Efficiency during Plasma Arc Melting of Titanium.

Abstract

The plasma arc melting (PAM) process has attracted keen attention in melting titanium, because it has many advantages such as melting under the atmospheric pressure and refining by utilizing ultra-high temperature and plasma gas. In particular, in melting titanium alloy, the plasma arc melting process produces less evaporation loss of alloying elements, enables comparatively easy composition control, and provides less restrictions in material form. It is very important to raise the melting efficiency in plasma arc melting from the commercial point of view. So, basic investigation was carried out on arc voltage and heat efficiency when titanium-based materials were melted with plasma arc. The results are summarized as follows:(1) When argon, neon, and helium are used for plasma torch gas, the plasma arc voltage becomes higher in that order, and the same tendency is found in the fraction of heat transferred to the molten pool. By substituting helium for argon as torch gas, the melting rate can become double because of the increase of arc voltage and heat efficiency to the melting material. (2) When titanium sponge is melted, arc voltage increases and greatly fluctuates by the vapor of chlorides contained. Alkali atoms are detected in the plasma arc column by spectrometry analysis. The temperature of plasma arc column is estimated. (3) Plasma arc voltage is shown as a linear equation of the arc length. The value of the intercept of the line is greater when helium is used as torch gas than as atmosphere gas.