Patent GB-354346-A (GB)
Title: Improvements relating to the manufacture of sealed evacuated envelopes containing a liquid
IPC: H01J9/38
Filed: 1930-04-29
Abstract: 354,346. Obtaining high vacua. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Walker, W. R. ; 410, 8th Street, Hoboken, New Jersey, U.S.A.) April 29, 1930, No. 13202. Convention date, April 29, 1929. [Class 8 (i).] In the manufacture of sealed envelopes or vessels containing a liquid, particularly the envelopes of mercury switches and the like, the container is evacuated and then filled with a nondeleterious gas of such density that air is substantially precluded from entering during the subsequent introduction of the liquid, after which the container may either be sealed off or subjected to a further exhausting, scouring, and filling with an' arc-suppressing gas in a second apparatus before sealing off. The container, such as that of a mercury switch 34, Fig. 9, provided with a tubular stem 33, is placed upon an automatic machine provided with an intermittently rotating watercooled head consisting of hollow arcuate segments 4, Fig. 1, provided with a series of openings 30 to establish gas-tight connection with the tubular stems. The containers are carried around through an oven 50 where thev are heated to drive off occluded gases and water vapour, and also connected to a succession of ports through which they are subjected to a rough exhaust, a final exhaust, and a flushing by hydrogen or other gas, the exhausting and flushing being repeated several times. Towards its point of removal a container is cooled by a blast of air, and at the last port is filled with nitrogen at atmospheric pressure. Since the density of nitrogen is slightly greater than that of air, the container can be removed from the machine without deleterious effects, whereupon mercury is admitted and the switch is tested while still unsealed. Subsequently it is placed in a second exhausting machine and subjected to a further series of exhausting and flushing operations, after which hydrogen or other arc-suppressing atmosphere may be admitted before sealing off in the usual manner. The hollow carrier segments 4, Fig. 1, are carried upon a spider 3 mounted above a geneva mechanism 2 on a bedplate 1, intermittent rotation being imparted by a motor 11 geared to a worm 12 which drives a gear wheel 15 on the shaft of a wheel provided with teeth on a portion only of its periphery, whereby a gear wheel 17 operates a crank arm 18 to drive the geneva wheel anticlockwise in intermittent, stages. Each opening 30 in the water-cooled segments 4 contains a short length of indiarubber tubing 31, Fig. 3, adapted at its upper end to receive and grip the tubular stem of an inverted container, the lower end of the tubes 31 being connected by tubes 35 to apertures in the revolving disc 21, Fig. 5, of a rotary valve, the co-operating stationary disc 20 being provided with a series of ports 26. The disc 21 is rotated intermittently by connecting it to the geneva wheel by vertical pins 23. The ports 26 comprise a series of three separate groups, the ports of each group being interconnected, as shown in Fig. 2, by manifolds 37, 41, 45 respectively to a prevacuum pump 39, a vacuum pump 43 which sustains and perfects the vacuum, and a source of hydrogen at approximately atmospheric pressure. The last port 26 is connected to a source 48 of nitrogen. During about half a revolution of the carrier the vessels are traversed within the arcuate oven 50 and heated to about 500 by jets burning a suitable air and gas mixture and from the end of the oven back to the starting position A the vessels are cooled by a current of cooled air directed upon them from apertures in a pipe 55. The switch bodies 34, filled with nitrogen, are withdrawn from the machine and a quantity of purified mercury is introduced through a hollow needle inserted into the stem, after which they are inserted into an apparatus substantially similar to the first one, with the exception that they are suspended below the rotary segments. Means are also provided for introducing hydrogen or other arc-suppressing gas into the container before it is sealed off. The process may be modified by introducing ammonia instead of nitrogen in the first apparatus and sealing off immediately after the introduction of the mercury. The Specification as open to inspection under Sect. 91 (3) (a) describes also an apparatus for purifying mercury and introducing it into the stems of the containers. This. subject-matter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 252,368, [Class 8 (i), Air and gases, Compressing &c.].