GB852731A - Electrode structures for kaolin melting - Google Patents

Abstract

852,731. Electric furnaces. BABCOCK & WILCOX CO. Nov. 6, 1956 [Nov. 21, 1955], No. 33874/56. Class 39(3). An electric furnace for melting refractory material e.g. kaolin by passing current therethrough between electrodes 30, Fig. 1, extending through a refractory lining of a metal casing 15 of the furnace, the electrodes comprise steel bars 25 with internal cooling passages 36, Fig. 3, for water and an end tip or plate 40 of refractory metal such as molybdenum tungsten or tantalum welded to the end of the bar 35 to conduct current into the kaolin, each plate being thinner and wider than any cross-sectional dimension of the supporting bar and in alignment with the longitudinal axis of the bar. To prevent high current densities at the edge of the end plate 40 rods 42 of the same metal but of greater diameter than the thickness of the plate are welded to its edges. The plate 40 is welded to a channel seat 43 welded to the end of the bar 35 spaced channels being closed by welded plates 37 and water inlet and outlet pipes 39 being attached where shown. The electrodes are enclosed for most of their lengths by refractory bricks 25 shaped as shown, are mounted in vertical slots in the metal casing 15 and are radially adjustable by levers 31, Fig. 1. The steel bars 35 carry at their outer ends insulating straps 45 bolted to a bar 46 bolted to a metal yoke 47 carrying a pin 33 for pivoting the lever 31. A cable is connected to the outer part of the bar 35. Kaolin is fed from a hopper 14 to well above the electrodes 30, which are moved inwardly to start the heating and moved radially outwards as a pool of molten kaolin is formed and when the pool is large, a tapping nozzle assembly 50 is pushed up through a central aperture in the base of the furnace into the pool. The nozzle is then heated by connecting it in circuit as an electrode, and the molten kaolin withdrawn therethrough is blown by an external air blast into fibres. The nozzle is of tantalium, tungsten or molybdenum and comprises a sleeve 81, Fig. 7, formed with a cone 83 having a flattened apex with a central aperture with an integral outlet opening 85. The nozzle sleeve 81 fits over guide sleeve 65 of alumina resting on an internal ledge on a steel support tube 60 carrying outer radial studs 74 extending through vertical slots 53 in a guide sleeve 55 below the aperture 18 in the furnace base so that the nozzle assembly may be moved vertically by the studs 74. The lower end of the tube 60 is welded to a flange 61 and metal is removed from the outer surface of the tube between its ends to form a circumferential recess 62 enclosed by a tube 66 forming the inner wall of a water cooling jacket 75 with a water inlet 58 and outlet 73. Helium is supplied by a pipe 56 to pass up through the circumferential recess 62 and passes through slots 64 cut in the outer side of the top end of the tube 60 into the space between the sleeve 65 and tube 81 and down through the tube 60 so as to remove air and prevent oxidation of the sleeve 80 when immersed in molten kaolin. As the kaolin is removed the electrodes are moved inwards for re-starting the process on withdrawal of the nozzle, calcined kaolin being added from the hopper. When the furnace is shut down after several days, the molten kaolin solidifies in a solid mass around the electrodes and in the furnace base. The furnace is dis-assembled and the solidified kaolin is split to expose the electrodes, the tips 40 of which are cut off and replaced. The nozzle assembly 80 is also removed by screwing it out of a ring 76 attached to the top of the cooling jacket 75 and if necessary replaced by a new assembly. The furnace casing 15 is in three vertical segments and has an inner lining of built-up refractory shapes. Specification 625,100 is referred to.