The starting of induction crucible furnaces varies greatly, depending on the working frequency. There is the starting of a new crucible, and a crucible that has already been in operation, also known as cold starting.
Starting of a new crucible is also referred to as sintering; this may be liquid sintering following removal of a permanent template, or with a lost template, which remains in the furnace and is also melted. After reaching the maximum filling level, the melt is brought up to approx. 50 – 100 K above the normal tapping temperature, and maintained at this temperature for up to 2 hours for acidic crucibles and for up to 4 hours for neutral and alkaline crucibles. The 1st tapping is then carried out.
When starting damp lined crucibles, the manufacturer’s instructions must be
strictly observed, in order to ensure that the damp is driven out. These crucibles
cannot be charged with molten metal.
Mains frequency furnaces without liquid filling must be started using starter
blocks. The diameter should be approx. 100 mm less than the crucible diameter.
The filling height should be about 2/3 of the coil height.
Medium-frequency furnaces without liquid filling can be started using normal steel scrap, although this should not contain any chips, any dimensions greater that 50% of the crucible diameter or any magnetic yokes.