To ensure melting suitable for the type of metal by providing a first stage melting process for enlarging the melting range by induction heating an object to be melted, and a second stage melting process for enlarging the melting range to the entire region of a crucible by increasing the induction heating frequency thereby enhancing the efficiency and practicality of melting.
An object to be melted X inserted into a crucible 1 is brought into molten state by heating externally through action of a plasma torch 23 in a preliminary heating means 2. For the object X brought into molten state at least partially on the surface in preliminary heating process, molten range is enlarged gradually using induction heating frequencies in two bands. In a first stage melting process, an induction current of relatively low frequency is fed through a heating coil 32 in order to increase a liquid phase produced by the means 2. For the object X grown to a desired size in the first stage melting process, melting range is enlarged to the entire region of the crucible 1 in second stage melting process.
HOSOKAWA TAKAHITO
ISHIKAWA HIROTOSHI
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