Patent GB-670201-A (GB)
Title: Improvements in and relating to electric lamps and similar devices
IPC: H01J5/32
Filed: 1949-06-29
Abstract: 670,201. Electron discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. June 29, 1949 [July 2, 1948], No. 17212/49. Class 39 (i). [Also in Group XI] A sealed hollow glass envelope 1 such as an electric lamp or discharge tube is provided with a relatively thick header or end-wall 2, Fig. 8, formed with a dome-shaped re-entrant portion in its outer surface to which a glass exhausting-tube 10 is connected and tipped off closely thereto, the domeshaped re-entrant portion, and the exhausting-tube, being of materially reduced thickness compared with the remainder of the end wall. In making the lamp a combined base and mount assembly is formed as a separate unit by supporting a glass collar 15, Fig. 2, within a recess in a mould 17 provided with a pair of diametrically opposite apertures to receive contact pins 4 which rest upon a vertically reciprocable sleeve 19 with their upper ends level with the bottom of the mould cavity 16. The upper ends of the pins 4 are butt-welded to the lower ends of short lead-in wires 6 which have a coefficient of expansion approximating to that of glass, and the upper ends of these wires are butt-welded to filament supporting wires 5 which are maintained vertical by locating them within grooves 24 on opposite sides of an upper spacing member 23. A vertically reciprocable pin 20 with a domed upper end 21 extends upwardly through the sleeve 19 into the glass collar 15, its retracted position being shown in Fig. 2. The mould 17 and upper guide 25 are rotated while gas flames 22 are directed initially upon the upper regions of the glass collar until it begins to soften, whereupon the flames are shifted downwardly on to the lower regions. The glass down into the cavity 16 and around the wires, with the greater portion around the outer regions of the mould, and at this stage the spacing member 23 is replaced by a plunger 27, Fig. 4, while at the same time the centreforming pin 20 is raised in co-operation to form the glass to the shape of the face of the plunger and with a thin central domed portion. Subsequently the pin 20 is removed and the upper end of an exhausting tube placed against the underside of the domed portion, a gas flame then being directed downwardly upon the dome to soften the glass and seal the tube thereto, whereupon a puff of air is directed up through the tube to form an exhausting aperture through the dome. The filament supporting wires 5 are next bent to the required shape and a filament 9 connected across their upper ends, after which a glass envelope is placed upon the foot and the latter rotated while flames are directed upon its meeting edge with the envelope. During the sealing the glass foot is supported on a member 37, Fig. 7 (not shown), with apertures for receiving the contact pins 4 and the exhausting tube, the latter being shielded from the heat of the sealing flames by locating it in an axial aperture through a frusto-conical boss which extends upwardly inside the dome. The envelope is exhausted and, if necessary, gas-filled in the usual manner through the exhausting tube 10, and during this process the tube is located in an aperture 47, Fig. 8, in a cantilever blade spring 44 which is flexed downwardly by pressing the base end of the lamp thereon, the spring forming a baffle to.shield the lamp and upper portion of the exhausting tube from the heat of gas flames 45 directed against the latter at the underside of the spring member. As the glass of the exhausting tube softens, it is stretched and attenuated by the force of the deflected spring baffle, and thereby sealed or tipped-off.