GB152157A - Improvements in and relating to induction electric furnaces - Google Patents

Abstract

152,157. British Thomson - Houston Co., (General Electric Co.).Aug. 8, 1919. Induction furnaces.-The walls of the annular crucible 8 are inclined at an angle of from 60 to 90 degrees. The magnetic circuit has a central core 2, top and bottom yokes 5, 4, and outer legs 1, 3 arranged closely about the windings and within the leakage field. The primary winding 6 is in two or more concentric sections, the connexions of which may be varied m order to vary the relation of the magnetic centre to the furnace charge. The primary winding is arranged above the crucible 8 and is carried by a housing 20 of non-magnetic material, such as brass or 25 per cent nickel steel, supported by circular angle-irons 26, 27 on the upper yoke 5. These angle-irons may also be connected to the crucible cover 12 by rods 17 so that the upper yoke, primary winding, and crucible cover may be removed as one unit. The crucible 8 is enclosed in an outer steel shell 9 lined with firebrick 10 and crystallized magnesia or other refractory material 11. The central leg 2 of the core is surrounded by a casing 12 allowing space for a blast of air, which also passes round the primary coil. Openings 24 permit some of the air to pass over the top of the cover 12. The magnetic core is so proportioned that the fluxdensity is uniform when the furnace is under load. To prevent damage due to possible breakage of the crucible, the core is provided with a metal shield covered with a layer of mica and a layer of asbestos, which latter may be impregnated with a binder such as a phenolic condensation product. The crucible is provided with a number of charging-doors and a pouring-spout.