GB800929A - Method of shaping a coiled rectilnear incandescent electric lamp filament - Google Patents

Abstract

800,929. Sharing filaments for electric lamps. ATELIERS DES LAMPES DE GENNEVILLIERS. Oct. 18, 1956 [Nov. 8, 1955], No. 31747/56. Class 39(2) [Also in Group XXII] Lamp filaments which are coiled into a single or multiple helix on a rectilinear axis, and from which the winding or supporting core has been removed, are shaped to an arcuate or other form by introducing a central wire or like body 9 axially into the helix, deforming the filament together with the introduced body 9 to give the filament the requisite shape, heating the filament assembly to a temperature sufficient to eliminate the stresses produced by the deformation, and finally removing the central body by chemical means. The invention is particularly applicable to helical filaments of arcuate form which are supported solely by their leading-in wires within bulbs for motor vehicle lamps. In the example, the end portion of a molybdenum wire 9 of a diameter slightly less than that of a single coiled helical filament is threaded through the helical filament 14 which has two parallel leading-in portions 3, 5 at rightangles to its axis. The wire 9 is unwound from a spool 10 by a gripping device 8 until its extremity meets a stop 1, the helix being located in a recess of arcuate section in a clamp 4. A former 16 of circular cross-section is pressed lightly against the middle of the helix. The length 13 of the wire 9 between the end stop 1 and a pair of co-operating shears 7, 12 is then severed by operation of the shears, and the protruding end portions of the severed wires are pressed downwardly by pushers 2 and 6 provided with grooved faces to receive the said ends, the pushers being moved along arcuate paths 17 and 15 respectively having their centre at the centre of the former 16. After bending the filament, together with the length of inserted wire, to the extent required the pushers and the former 16 are retracted, and the released filament is annealed at about 1250‹C. for ten minutes in a hydrogen atmosphere or in a mixture of 25 per cent hydrogen and 75 per cent nitrogen. The central body 13 may be removed by dipping the filament assembly in a hot bath of sulpho-nitric acid. The insertion of the central body into the helix and the shaping of the parts thus associated may be carried out on. separate machines.