Patent GB-334470-A (GB)
Title: Improvements in and relating to methods of and apparatus for working fused silica
IPC: C03B23/07
Filed: 1929-12-17
Abstract: 334,470. British Thomson-Houston Co., Ltd., (Assignees of Millar, G. A.). Dec. 20, 1928, [Convention date]. Forming silica glass articles.- A method of forming hollow vessels of fused silica consists in mechanically rotating a closed silica tube and heating a portion of the closed end, inserting the softened portion of the rotating tube in a suitable synchronously rotating mould, and applying air pressure to the interior of the tube to distend the softened portion in the mould. The softened portion may also be offset from the body of the tube during the blowing operation. The method may be used for shaping a tube 41, Fig. 13, forming part of a, mercury arc apparatus, in which a closed end 140 is offset from the body. A machine for shaping the tube comprises a bedplate 3, Fig. 1, supporting a pair of parallel bars 8, 9, Figs. 1 and 6. A block 12 is free to slide on the bars and it can be moved by a pinion rotated by a handwheel 16. The block carries a train of gears 20 -22, and a similar train, 17-19, is carried by a block 6 secured to the bedplate. The two gear trains are rotated in unison with one another by a telescopic shaft 24 driven by a motor 96. The gear wheel 19 carries a chuck 25 which is closed by a spring 35 and is opened by a bell-crank lever 30. The spindle of the chuck is hollow and is connected by a flexible pipe 37 with an air valve 38, Fig. 6, carried by the block 12. The gear wheel 22 carries a shaft 26 in alignment with the chuck 25. The shaft 26 carries at one end a block 44, Figs. 1 and 4, on which another block 46, slides in guides 45 at right-angles to the axis of the shaft. A graphite mould 47 is attached to the block 46 which can be moved along its guides 45 by levers 54 and a conical collar 59 loosely mounted in shaft, 26. The collar is moved by bell-crank levers 61, 62, Figs. 1 and 6, pivoted on the block 12, and an arm 67 on the lever 61 is adapted to engage a stop 68 adjustably mounted on the rod 8. The air valve 38, Fig. 6, is kept closed by a spring 69, and it is opened by a hand lever 72 which is engaged by a latch 73 but is released when the belt-cranks. 61, 62 are actuated by the stop 68. A collar mould 75, Fig. 4, co-operates with the mould 47, and is carried by means of arms 77 pivoted to a collar 78, Fig. 1, free to slide along the shank 79 of the chuck 25. The collar 78 is attached to a block 81 which slides along the bars 8, 9, and a spring urges the block and the mould 75 towards the mould 47 when a trip is released by the block 12. A carriage 103 which slides on the rods 8, 9 carries oxy-gas blowpipe burners 112, the supply of gas being controlled by a pedal 123. In use, a tube of silica with one end closed is inserted in the chuck 25 through the collar mould 75, and the motor 96 is started. The closed end of the tube 41, which projects beyond the collar mould, is heated by the flames from the burners 112 until it is softened. The flames are then cut off and the mould 47 is moved to enclose the softened part. As the mould approaches the tube, the stop 68 engages the arm 67 on the lever 61 and opens the air valve 38 to admit compressed air to the interior of the tube. At the same time, the mould is forced to the end of the guides 45, thus offsetting the end of the tube as shown in Fig. 4. As soon as the silica, has cooled and set, the rotation of the mould 47 and the chuck 25 is stopped, the chuck is opened, and the 'finished tube is removed.