GB843814A - Improvements in or relating to electric incandescent lamps and similar devices and method of manufacture - Google Patents

Abstract

843,814. Discharge tubes. GENERAL ELECTRIC CO. Nov. 23, 1956 [Nov. 28, 1955], No. 35898/56. Class 39(1). [Also in Group XI] An electric discharge tube is constructed with a glass stem press having an exhaust tube or passageway extending therethrough and maintained open, during the press-forming operation, by a coating on the wall of the exhaust tube or passageway of a material having a melting point above that of the glass and chemically inert with respect to the filament at the incandescent operating temperature thereof. The exhaust tube 9 which is assembled with the leading-in conductors 4 within the neck 11 of the bulb and heated in the usual manner prior to pinching between jaws 15, Fig. 3, consists generally of a soft glass having a melting point of about 650‹C, the bulb or bulb stem being made of a similar glass, so that the coating material 10 which is applied preferably to the inside wall of the bore of the tube should be of a material that is stable both physically and chemically up to at least the tipping off temperature of about 700‹C. Alternatively a coating 10<SP>1</SP> may be applied to the outside wall of the tube 9, or both inside and outside walls may be coated. The coating may consist of aluminium or silver, or the oxides of aluminium, silver, zirconium, magnesium, titanium, zinc, &c. or refractory materials such as silicates, double silicates and titanates. Coating materials which are light or white in colour are preferred for their heat-reflecting characteristics which minimize the likelihood of the softening and closing of the glass exhaust tube. The oxide and silicates of zirconium perform the additional function of producing a distinctive coloured glow within the lamp bulb during the highfrequency glow testing to determine the degree of vacuum in the lamp envelope.