1. Field of the Invention
In the case of induction melting furnaces and holding furnaces for liquid metal, almost exclusively crucible furnaces and core-type induction furnaces dominate. The crucible furnace is predominantly used for melting, with a cooled coil surrounding the hollow, cylindrical refractory crucible. The useful heat is produced by induced currents developing in the melting charge itself. The core-type induction furnace is preferably used for the holding or maintenance of the heat and for the overheating of an already liquid melting charge. This furnace has at least one core-type inductor which is essentially a closed-core transformer where the secondary winding is formed by at least one winding of liquid metal. The metal surrounding the iron core is then enveloped by correspondingly formed refractory material and kept away from the iron core and primary winding. The inductor or coil is mostly arranged below or laterally on the outside of the furnace crucible in the area below the bath level. Solutions are also known where the coil of the core-type inductor is arranged in a tunnel-like opening in the furnace crucible whereby this opening is accessible from two sides of the furnace crucible and is surrounded by refractory material.
2. Description of the Prior Art
Two examples are shown in the brochure "Induction Smelting and Holding Furnaces" of the firm of Brown, Boveri & Cie, Aktiengesellschaft, Mannheim, undated, on Page 3, whereby the first one shows an induction crucible furnace and the second one an induction core-type furnace.
Both the induction crucible furnace as well as the induction core-type furnace have the problem that the life of the refractory lining is reduced in the area of the coils and inductors and the furnace must be emptied for repairs and also in case of deficiencies of the coils or the inductors. This is particularly, then, a disadvantage when the furnace must suddenly be emptied because of an unexpected failure of the refractory lining. The core-type furnaces are used as storages so that such an emptying means in their case a serious operation disadvantage or an expensive damage. According to experience, such damages occur comparatively often. They are caused by the fact that the refractory linings are relatively thin-walled in the area of the inductor in the case of both mentioned types of induction furnaces for economic reasons (for example, 10 to 20 cm).
The refractory lining is subjected to extreme stress owing to the intensely flowing hot metal, to temperature changes and to chemical attacks. In the case of the core-type furnace, the refractory lining has, additionally, a very unfavorable shape where it is difficult to avoid the formation of cracks.