Coil grout is applied in crucible induction furnaces direct to the coil, which is insulated with intermediate layers. This ceramic “coil insulation” is also referred to as the smooth coil plastering. This serves to even out any uneven areas of the coil at the inner coil wall, and as a sliding bearing for the crucible, which is gradually increasing in size. Between the coil plastering and the wear crucible, a separating material of micanite, Isoplan or similar materials is applied as an “insulating layer”. The crucible can slide down the wall as the wall gets colder and upwards as it heats up. If a crucible is operated continuously without any “extended interruptions”, this sliding or separating layer can be dispensed with. In the case of a 3-t furnace and 10 crucible changes per year, this can provide a saving of approx. 1,500 €, or for 20-t furnaces of approx. 5,000 €.
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