GB735222A - Improvements in or relating to electrically heated glass furnaces - Google Patents

Abstract

735,222. Electrode furnace for glass. HANN, D. G. Dec. 16, 1952 [Dec. 20, 1951], No. 29813/51. Class 39 (3). In,a furnace in which glass is kept molten by current therethrough between electrodes in the glass, an electrode assembly comprises an electrode 16 mounted on a conducting stem 14 both of a metal oxidizable at furnace temperature, e.g. molybdenum or tungsten, and the stem is spaced within a tubular aperture 12 in a refractory member in the furnace; and an inert non-oxidizing medium impervious to oxygen, e.g. hydrogen or crushed glass, is placed between the refractory and the stem 14 so as to preserve the stem within the furnace from oxidation. The stem extends out through the adjacent furnace wall of either the roof, side or base and the projecting end is free from coating to receive an electric cable 30. The outer end 23 of the stem is cooled by air or water to a temperature below its oxidation temperature in the surrounding air, i.e. below 500‹ C. The whole area of the stem 14 is thus protected against oxidation. The refractory member comprises a tube 13 spaced within an aperture in the furnace and extending substantially to the bottom of the stem, or the stem is mounted in an aperture in the refractory base or side wall 11 of the furnace. Crushed glass fills the space between the lower end of the stem and the refractory; the glass 17 near the inner end of the stem is of the same composition as that in the furnace, and the glass 18 around the stem at a position further from the electrode has a lower melting-point, so that when the furnace is used, all the glass melts to form a seal around the stem impervious to oxygen. Alternatively molten glass from the furnace may flow into the open end of the tube 13. A copper sleeve 19 disposed tightly around the stem projects outwardly beyond the furnace, and the inner end 20 of the sleeve of reduced cross-section extends into the glass between the stem and the refractory. The sleeve 19 may be formed with fins 28 and with a shoulder 21 engaging directly the outer end of the refractory member to form a seal against entry of air. Nitrogen is blown through passages 26 to remove any air from between the crushed glass. An asbestos packing 24 is placed between the stem and the top of the sleeve. In Fig. 4, a ring 36 is placed between the sleeve 19 and the outer end of the refractory member, and air or liquid is circulated by pipes 38 through the space between the ring 36 and the finned end of the stem 19, to cool the outer end of the stem. An inert gas, e.g. nitrogen, may be led in at 37 or circulated between the stem and the refractory member to remove air both before and after the glass between them is fused. The stem is in thermal contact with the sleeve 19, the outer end of which is finned at 28 and cooled by an air blast from a nozzle 29. The electrode comprises three parallel adjacent strips of molybdenum attached to a cross-batten strip of molybdenum, or two flat strips 16 of molybdenum arranged at an acute angle in the same plane may be attached by a nut to the conical inner end of the stem. The furnace may be one for holding glass molten for delivery in smaller quantities, the glass being delivered by raising a vertical plunger 10 fitting a discharge aperture in the base of the furnace as disclosed in Specification 671,405. Reference has been directed by the Comptroller to Specifications 664,121 and 689,583.