GB908667A - Electric resistance furnaces - Google Patents

Abstract

908,667. Electric resistance furnaces. SPEMBLY Ltd. April 27,1961 [July 15,1960; Aug. 16, 1960], Nos. 24660/60 and 28263/60. Class 39 (3). . A gas-tight electric resistance furnace includes a heating element in the form of a slotted hollow cylinder supported on current feeders mounted in a base-plate, which heating element surrounds a hearth formed by a cap supported on a pillar, both of refractory material, and is itself enclosed by a water-jacketed inverted pot removably mounted on the baseplate. The cylindrical heating element shown for use at high vacuum is slotted longitudinally to provide a zig-zag current path 2 between the supporting legs 3 which extend down to, and are 5 cured by copper clamps 4 to the current feeders 5; the latter pass through insulating, gas-tight bushes 6 mounted in the water-cooled metal base plate 7. The charge is supported on the cap 12 of a refractory column 13 supported in a tubular, water-cooled metal socket 14. Refractory discs 16, mounted on pillar 13 and separated by spacers 17, constitute radiation shields. Parts 12, 13, 16 and 17 are made of the same material as the heating element, which may be graphite, tungsten, or tantalum. The waterjacketed inverted pot 18 has an internal flange 20 to which is bolted an annulus 21 of sheet molybdenum which supports a series of spaced concentrically arranged tantalum radiation shields 22, surrounded by further shields (not shown) of molybdenum. The steel tube 23 with a quartz window 24 provides a sighting aperture for the determination or automatic control of the furnace temperature. The furnace may be evacuated via connection 33. In a modification (Fig. 2, not shown) for use with an inert gas atmosphere, the annulus 21 is of steel, and the concentric radiation shields are replaced by an inverted graphite pot bolted to the base plate, the annular space between the two pots being filled with lampblack. The hearth, supporting pillar, and heating element are also of graphite. A refractory tube is provided to extend between tube 23 and an aperture in the inner pot. In a further modification the heating element is mounted on eight spaced graphite pillars gripped in copper bus-bars, lower and upper disc radiation shields are provided, mounted on the cylindrical radiation shields and the graphite pillars, respectively, and the pot 18 is of steel. The resistance element may be provided with three legs for three-phase operation, and slotted to provide a star or delta connected configuration ; and if the furnace is used with a crucible the slots may be arranged helically to provide stirring of the charge. According to the first Provisional Specification the cylindrical radiation shields may be of steel, and pot 18 of glass.