GB621465A - Improvements relating to vitreous tubular envelopes - Google Patents

Abstract

621,465. Electric incandescent lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 19, 1944, No. 20268. Convention date, Oct. 21, 1943. Drawings to Specification. [Class 39(ii)] [Also in Group XL (a)] A method of rendering a substantially flat vitreous envelope tube, such as for an incandescent lamp, resistant to collapse by unbalanced external atmospheric pressure when the tube is evacuated, consists in chilling the longitudinal tube edges from a temperature above the strainpoint of the material to below that temperature in advance of the cooling of its wide longitudinal walls. It is stated that the longitudinal edges are put in a state of permanent preconpression or bending strain. The heating of the tube above its strainpoint may be merely incidental to drawing out and forming the glass into a flat tube, or may be a subsequent heating for the purpose of flattening an initially round-formed tube, or may be a special heating for the main purpose of imposing strain at the edges. The prechilling of the tube edges in advance of the cooling of its wide walls may be effected by blowing air on the edges, or by heating the wide walls to keep them above the strainpoint while the edges are exposed to the circumambient air and then allowing the wide walls to cool, or by merely lagging the wide walls to retain their heat. The wide walls of the tube may be perfectly flat or slightly convex outwards. As described with reference to a fluorescent discharge lamp, the tube may be flattened substantially throughout its length between round ends, or flattened right out to its very ends. Specification 486,325, (Group XL), is referred to.