GB569685A - Improvements in and relating to electrodes - Google Patents

Abstract

569,685. Fluorescent lamps. BRITISH THOMSON-HOUSTON CO., Ltd. April 19, 1943, No. 6243. Convention date, April 22, ,1942. [Class 39 (i)] [Also in Group XXII] An electrode for fluorescent lamps of the low - pressure positive column discharge type &c. is made by winding a fine electrode wire 22 on a compositecore M of circular, oval or like section, which comprises a main wire 20 substantially covered with a metallic or non- metallic filler 23, and then removing the filler. The wires may be made of tungsten, molybdenum, tantalum, platinum, nickel, iron or alloys thereof. The filler may comprise lacquer, varnish, bitumen solution, a thermo-plastic material or a vulcanizable rubber composition and be applied by a bath, excess being removed by a die. Before removing the filler the composite body may be wound on a mandrel and this, if desired, on another mandrel. In this case the filler may be a metal applied by electrolysis, or in a molten state, or by rolling, swaging, or drawing a tube of filler metal 23 on a bar of the metal 20. A metal or refractory filler may be used if the wire 22 requires to be set by heat, e.g. at 1500‹ C. in hydrogen for tungsten. In a modification the filler may comprise a wire 23a, Fig. 6, which is wound, twisted, or braded about the main wire 20. The fine wire 22 may be wound in the groove formed between the coils of a round wire 23b, Fig. 7, or wires. The filler may be removed by disintegrating, melting, vapourizing, burning, or chemical action. This may also be used for removing any mandrels employed, the solvent selected being inactive as regards the wires 20 and 22. These may be spot welded and are finally activated. Details of construction are given for cathode for a 40-watt fluorescent tube, 1¢" diameter and 48" long. Specification 561,177 is referred to.