Patent GB-730739-A (GB)
Title: Improvements in and relating to lamp sealing and exhausting machines
IPC: H01J5/24
Filed: 1953-03-24
Abstract: 730,739. Making electric lamps. BRITISH THOMSON-HOUSTON CO., Ltd. March 24, 1953 [March 28, 1952], No. 8073/53. Class 39 (2). In a turret machine provided with a series of rotatable work - holding heads each carrying a lamp bulb and a mount with a downwardly extending exhaust tube, which are indexed through flames at a plurality of stations while being sealed together and are subsequently exhausted when the exhaust tube is received in an exhausting head, means are provided which co-operate with the sealing heads to position them accurately at a pre-focusing station provided with an optical device whereby the position of a filament within a bulb is determined. In an example, illustrated diagrammatically in Fig. 1 (not shown), sixteen sealing heads are indexed successively to sixteen work stations A-P, and the same number of exhausting heads are indexed around a coaxial lower path through stations a-p. A mount comprising a glass stem with leading-in wires sealed therein and supporting a filament, and provided with an exhaust tube 7, is placed in the spindle 4 of a sealing head at station A, and at station B the spindle is raised to lift the mount into position for sealing to a bulb 1 which is loaded either manually or automatically into the chuck of the sealing-head while at stations C or D. At stations E to I the head is rotated while gas flames are directed radially upon the bulb neck, causing the neck to collapse inwardly and seal to the rim of the flare. Burners at stations J and K sever the cullet below the seal, and at station L softer flames render the seal uniformly plastic prior to the pre-focusing operation at station M. The spindle 4 is also lowered to render the exhaust tube accessible to an operator. At station M the rotation of the sealing head is stopped and the head positioned accurately with respect to the optical system while an operator grasps the exhaust tube 7 and pulls it downwardly by hand to stretch the seal slightly and relieve it from strain, at the same time observing the position of the filament through a ground glass screen 83 and working the seal manually so as to bring the filament into a predetermined focal position. The seal is allowed to cool at station N and begins to harden, the hardening being complete when the head opens at station O. At station P the bulb is transferred to an exhausting head 12 located below it at station p of the exhausting system, the transfer being effected either manually or automatically by mechanism such as that described in Specification 477,250. While on the exhausting head the bulb is subjected to preliminary vacuum at stations a and b, repeated evacuation and flushing with nitrogen or other gas through stations c-m and, if desired, filled with argon or other gas at station n, the exhaust tube 7 being tipped off at station o and the finished bulb ejected into a shoot. The sealing heads are each supported on a hollow shaft 24, Fig. 3, within a journal 25, and the associated bulb holder comprises a frame or yoke 26, Fig. 4, supported vertically above the base by a single side rod 27, thereby making the exhaust tube more accessible to an operator. The rod 27 is preferably made of a low expansion alloy, and the yoke 26, which is recessed at 28 to receive the bulb, is open at the front to provide a passage for the depending exhaust tube 7 when a bulb is inserted or removed. A hinged cover 29 which presses lightly on the bulb carries a roller 31, Fig. 3, on a pin projecting rearwardly and holding the roller upon a cam track which lifts the cover automatically at intervals. The mount is raised and lowered by the lower end of the mount spindle 4 travelling over a cam track 35, and rotation is effected by an endless belt 37, Fig. 6, engaging a pulley 36 on the sealing head unit. At station K, however, the belt is disengaged from the sealing head which is indexed thereto, by passing the belt around idler pulleys 41, 42 and at station L the head is rotated a small amount by a flange 43 on the pulley 36 engaging a friction disc 44 which is driven by' a chain 45 and sprocket system. The sealing head is thus rotated until a stop pin 47 thereon is arrested by an adjacent stop-lever 48 and, on further indexing of the turret, the pin enters between a pair of concentric guide rails 50 which extend around to the bulb loading station D. The final accurate positioning. of the yoke 26 of the bulb holder is effected by a pilot mechanism comprising a slide 52, Fig. 3, with an inverted U-shaped member 62 on its lower end, the two limbs of the member 62 providing mountings for two pairs of grooved rollers 63, 64, Fig. 4, adapted to engage pins 65, 66 respectively on the yoke 26. The pilot slide 52 is reciprocated vertically by a connecting-rod 68 linked through a bell-crank 69 to a vertical arm 72 which is actuated by a cam disc 74 during the dwell of each sealing head at the prefocusing station M. The optical apparatus comprises a pair of optical systems located within a housing 76 and each consisting of an objective lens 77, a first reflecting prism 78, a pair of reversing prisms 79 and 81, and a reflecting mirror 82, whereby two real images of the filament appear side by side on the ground glass viewing-screen 83. The images are provided by two lamps 85, 86, Fig. 5 (not shown), each in line with an objective lens of one of the systems. An inclined table 89 is provided for the operator to rest her elbows upon while pulling the exhaust tube downwardly. In addition, a heat shield 91, formed by a stack of thin laminations provided with a central slot to clear the exhaust tube, is swung inwardly below the bulb when the pilot slide 52 is reciprocated downwardly, the heat shield being secured at the lower end of a rod 92 which is pivoted centrally at 93 and provided at its upper end with a roller riding upon a cam bracket 95 at the upper end of the slide 52. A protective device interrupts the operation of the machine if the head should arrive at the focusing station with the hinged cover 29 pivoted upwardly instead of holding the bulb down on the supporting yoke, in which event the roller 31, Fig. 3, on the rear of the cover would fail to hold back a cam track 97 supported on a spring-loaded lever 98, and the lever would operate a control switch 101 to stop the machine. A further device which operates in the event of the hinged cover 29 riding too high, due to the sealing head carrying an oversize bulb or one not seated properly on the head, comprises a feeler rod 103 suspended vertically from a lateral bracket carried by the vertically slidable member 52, so that the lower end 104 of the rod comes to rest on the hinged cover when the member 52 is moved down, and operates a switch 105 if the rod is not lowered fully. Specifications 232,953, [Class 39 (ii)], 404,449, 477,250 and 524,414 are referred to.