Model Experiment and Theoretical Analysis on Direct Induction Skull Melting

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A direct induction skull melting method, in which a water-cooled induction coil is directly used as a crucible, enjoys an advantage of non-contamination from the crucible together with high energy efficiency. However, the applications of this method are limited to the materials with electrical insulating property in solid state. The aim of this study is to extend the applicable materials of the process and to melt and hold the materials with electrical conducting property in solid state such as metals and semiconductors by coating an insulating film on the coil surface. In order to clarify a theoretical base of the process, electric and magnetic field and a temperature one are simultaneously analyzed by taking account of the differences of electrical and thermal conductivities in solid and liquid states. Experiments demonstrate the feasibility of the process for a stainless steel and a silicon which indicate the electrical conducting property in solid state and clarify the validity of … More the theoretical results. It is found that the conditions of the smaller thermal conductivity, the higher heat transfer coefficient and the lower magnetic frequency, can provide the wider range of the magnetic field to form the stable skull.A new method of melting and holding of a material with low thermal and electrical conductivities is proposed to overcome the problems of long heating period and localized overheat in a charge. In this melting method, a water cooled induction coil is directly used as a crucible, and the elements heated by a high frequency magnetic field are submerged into the charge. Experiments have been conducted on glass under various operating conditions, i.e.the coil current, the frequency and the radius of the heating elements. A mathematical model is developed to calculate the process variables such as the heat generation rates in the coil and the heating elements, and the temperature distribution in the charge. The calculated process variables are compared with the observed ones. The considerably good agreement between the theoretical and experimental results indicates the validity of the model. The heat generation rate in the heating elements is determined by the ratio of the radius of the heating element to the electromagnetic penetration depth and has the maximum value at the ratio of 1.8. Less