GB364188A - A new or improved method of and apparatus for securing a metal support to an articleof fused silica - Google Patents

Abstract

364,188. Mercury vapour l a m p s . BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Buttolph, L. J. ; 1, Columbia Avenue, Grantwood, New Jersey, U.S.A.) Oct. 7, 1930, No. 30014. Convention date, Oct. 7, 1929. [Class 39 (i).] A method of attaching a metal ring, ferrule, or annular support to a hollow article of fused silica, particularly to the envelope of a mercury vapour arc lamp, consists in forming the ring of metal having a relatively high coefficient of expansion as compared with that of silica, heating part of the silica article until it is plastic, and then inserting it in the metal ring and expanding it by internal pressure into contact with the ring. The silica does not contract much on cooling, but the contraction of the metal ring is considerable and it grips the article firmly when cold. A machine for attaching rings to silica arc lamp envelopes is shown in Fig. 1 and comprises a bedplate 1, a fixed headstock 2, and a sliding headstock 3 which can be moved by a hand-wheel 9. The head 2 supports a rotatable chuck 4, while the head 3 supports a mould 5 which is coaxial and rotates in unison with the chuck. A hand-lever 10 opens the chuck, and a hose 11 connects the hollow spindle of the chuck to a source of compressed air. Gas blowpipes 12 are mounted in a slidable carriage which can be moved along the bed by a handwheel 13. The mould 5, Fig. 2, is preferably formed of graphite and is provided with a recess 15 to hold a metal ring. In use, a metal ring 16, Fig. 4, is inserted in the recess 15 in the mould, and a tube 17, Fig. 1, of fused silica, having one end closed, is placed in the chuck 4. The chuck and the mould are rotated, and part of the silica tube 17 is heated by flames from the blowpipes 12. When the silica is sufficiently soft, the mould 5 is applied to the tube by means of the hand-wheel 9, and air under pressure is admitted through the hose 11 to the interior of the tube to expand the softened part into contact with the mould. The metal ring 16 is also heated by the silica and expands, so that its subsequent contraction on cooling causes it to grip the silica tube. The mould may be so shaped that the metal ring rests in a depression in the silica tube, as shown in Fig. 4. In other cases, where a depression is inadmissible, holes are formed in the metal ring and the softened silica is forced into these holes to engage the ring and lock it in place. When the silica tube forms part of a mercury arc lamp, a tubular guard is slipped over the end of the lamp and secured to the ring 16 by screwing or by the use of silver solder.