Patent GB-673104-A (GB)
Title: Improvements in and relating to methods of and apparatus for bending and exhausting tubular lamps
IPC: H01J9/38
Filed: 1949-09-02
Abstract: 673,104. Making electric discharge lamps. BRITISH THOMSON-HOUSTON, CO., Ltd. Sept. 2, 1949 [Sept. 3, 1948], No. 22814/49. Class 39(ii) In making a tubular electric discharge lamp of curvilinear configuration, a lamp assembly comprising a straight tube is operated on in a sequence of operations while mounted in a turret machine which indexes it through a series of work stations respectively provided with means for (1) heating and exhausting the assembly to remove contaminating gases &c. and render the glass workable; (2) bending the tube to the required configuration; (3) exhausting the tube before appreciable cooling takes place; (4) introducing a gas filling and permanently sealing the lamp. The turret 3, Fig. 1, is provided with a series of work-receiving heads 2 around its periphery to receive, in turn, a lamp assembly at loading stations A1 and A2. The lamp assembly comprising a straight tube 8, Figs. 2 and 3, with a flanged metal cap 6 at each end and leading-in wires to the electrodes mounted therein is suspended vertically from one end which is held in the head 2. At station A3 the lamp assembly advances through the open end of an oven 10 and into the interior thereof, and an exhaust port 5 of the head is connected to exhausting means (not shown). These operations are continued at stations A4 and A5, and at station A6 the connection to the exhaust port 5 is broken and the tube connected to a source of non-contaminating gas, e.g., nitrogen, at a pressure slightly above atmospheric in order to reduce ingress of air during succeeding intervals of operation. The lamp assembly continues to be heated by the oven 10 while at station A7, the exhaust port 5 being then open to the atmosphere. The assembly leaves the oven 10 at station A8 and is received by a longitudinally divided cylindrical oven 11 which is moved from a radially outward position and then closed to surround the lamp assembly, so that an increased and more even heating of the entire periphery of the lamp is effected by heating-resistance elements within the oven. At station A9 a positioning-arm 13 is swung around against the lower end of the lamp assembly to arrange the latter in a true vertical position in alignment with a control pin 14 directly below the head 2, whereupon the control pin is moved upwardly to. engage the lower end of the lamp, the positioning-arm 13 returns to its original position, and a longitudinally divided oven 15, similar to oven 11, is moved outwardly from a radially inward position to surround the assembly. This oven heats the glass rapidly to a workable condition, and then moves away concurrently with the movement of bending apparatus 16 towards. the lamp, a form 12 being brought against the end portion of the assembly while a heating and backing plate 17 is brought against one side of the lamp tube 8. As described, the tube is bent into substantially a complete circle, while at station A9 and is then advanced to station A10 where an exhaust connection is made through the port 5 in the head 2, and the assembly is evacuated while still at a high temperature. Further exhausting as well as cooling is effected at station A11 and is supplemented by a conditioning operation performed on the electrode subassemblies 9 by passing a current through them, this being effected by the leading-in wires 20, 21 wiping against contact sections on a stationary contact member 22. The exhaust connection is broken during passage towards station A12, and flushing is effected by connection, first to a mercury dispenser which admits mercury through the exhaust port 5 into the exhausting tube 4, and a momentary connection to a source which admits a measured quantity'of ionizable gas, e.g. argon. A considerable proportion of these flushing agents is removed at station A12, where an electrical connection between the leading-in wires and contact member 22 is again made to effect treatment of the electrodes of the lamp. The exhaust connection is continued during transit to station A13, and connection to different contacts on the member 22 produces a discharge between the electrodes of the tube. Exhaust connection continues to be made at stations A14 and A15, and is broken just before the assembly leaves the latter station, whereupon connection is made to a source of argon comprising the final filling. The exhausting and filling tube 4 is sealed off close to the lamp cap while at station A16, this being also the discharge station Turret details.-Each head 2 of the turret is provided with a holder 7, Figs. 2 and 3, which receives a shaped crown 26 on the metal cap 6 at one end of a tube assembly 1, and a vertical lug or pin 31 on the crown is received within a guiding-notch in a lateral finger on the top of the holder to facilitate the correct positioning of the exhausting tube 4, which is offset and extends into the exhausting port 5 when aligned correctly. The crown 26, Fig. 3, is gripped in the holder by clockwise rotation of a ring 28 which is seated in the holder and has a segmental projection 29 on its lower surface arranged to be positioned opposite a cooperating fixed lug 30 when the ring 28 is rotated manually by means of a vertical pin thereon. A gas-tight connection with the body of the exhaust port 5, Fig. 2, is ensured by tightening a screw-threaded cap 33 containing a compressible rubber washer 36. A considerable portion of the body 35 of the exhaust port is surrunded by a chamber 37, through which cooling-water is cir culated, and above the chamber is a pinching-clamp 39 comprising a deformable rubber tube 41 which may be closed either manually or automatically by rotation of a lever 42, thereby isolating the exhaust port when the holder 7 does not contain a lamp assembly or an assembly held therein is so defective as to allow ingress of atmospheric air. The oven 10 for heating the lamp assembly after leaving station A2 is similar to that described in Specification 543,079, [Group XL]. Loss of heat from the oven is retarded by a shield 25, Fig. 2, -mounted between the exhaust port 5 and an arcuate opening 10<SP>1</SP> in the top of the oven. The several connections of the lamp assembly to a vacuum pump and to sources of flushing gas and finally filling gas are effected by a valve 52 with a rotary upper section 51 which rotates with the turret and moves over a stationary lower section 55. The vertical cylindrical oven 11, Fig. 1, which the lamp assembly enters at station A8, on emergence from the long arcuate oven 10, comprises two half-cylinders 68; 68<SP>1</SP> which are secured by brackets 70, 70<SP>1</SP> respectively to vertical rods 69, 69<SP>1</SP> mounted between end bearings on a carriage 71 which is movable radially inward and outward relative to the turret, the two halves of the oven being swung open automatically during their inward movement towards a work holder, and then closed around it to apply a uniformly distributed heat to the entire surface of the lamp assembly by means of electrical resistance elements over the entire interior surfaces of the half-cylinders. The automatic opening and closing of these hinged halves is effected by camfollower arms 73, 73<SP>1</SP> extending radially from the vertical rods 69, 69<SP>1</SP> and each provided with a roller at its outer end in engagement with cam slots 74, 74<SP>1</SP> in a fixed horizontal table upon which the carriage 71 is reciprocated by a rack and pinion device 77, 76. The cam slots 74, 74<SP>1</SP> are so shaped that the halves of the cylinder are opened and closed rapidly to prevent undue loss of heat. The lamp assembly is next indexed towards station A9 for further heating to bring the tube to the requisite temperature for bending, the heating oven 15 being similar to the oven 11. Before reaching station A9 the tube is positioned accurately vertical by, the positioning arm 13, Fig. 5, which is pivoted at 87 in a bracket 88 on the table 72 and connected by a link 89 to a rocking-arm actuated by a cam on the main cam shaft 78, Fig. 6, which produces the indexing of the table, so that the arm 13 is swung downwardly in timed operation with the advance of the table. The end of the arm 13 is bifurcated to engage the lower end of the lamp, and one fork carries a pivoted finger 95 which is operated by a light linkage and bell-crank system 99-105 under the action of a cam on the main cam shaft, the finger 95 being moved thereby to gather the lamp assembly into the base of the fork and align the tube with the vertical control pin 14. The control pin 14 is next moved up into engagement with the metal cap 6 on the lower end of the lamp assembly, this operation being effected by mounting the pin 14 in a block 114, Fig. 6, on the upper end of a slidable vertical rod 107 guided within a bracket 110 and carrying at its lower end a block 113 connected by links 112 to a yoke 111 on one end of a balance beam 108 pivoted centrally on a fixed pivot 116. The other end of the beam carries a counterweight 109, and this end is adapted to be pulled downwardly to raise the control pin 14 when the beam is engaged by the offset upper end of a rod 122 which is pulled downwardly by a lever 119 controlled by a cam 120 on the main cam shaft 78. The vertical rod 107, thus lifted by the beam 108, is retained in the elevated position by a friction shoe 123 located in a lateral housing on the bracket 110, adjustment of the pressure being provided by a screw 125 acting on a spring 124. The oven 15, which is constructed and operated similarly to oven 11, is located radially inward of the station A9 when movement of the lamp assembly from station A8 is initiated, whereupon the rack and pinion device is operated to move the oven and close it about the assembly on arrival at station A9. The rack and pinion devices associated with the ovens 11 and 15 are driven by motors 138, 139, Fig. 6, which are connected to feeder lines wi