GB750693A - Improvements in or relating to the fabrication of composite electrical conductors - Google Patents

Abstract

750,693. Coating by deposition from the vapour state. WESTERN ELECTRIC CO., Inc. Dec. 24, 1952 [Dec. 29, 1951; Nov. 14, 1952], No. 32756/52. Class 82(2). [Also in Groups XXXV and XXXVI] Apparatus for making a composite electrical conductor having alternate very thin layers of metal and insulating material, e.g. a Clogston conductor as described in Specification 715,359, [Group XXXVI], comprises one or more pressurereduced metal evaporating chambers, one or more pressure-reduced insulating material evaporating chambers, means for passing the core member of the conductor through these chambers seriatim one or more times so that alternate layers of metal and insulating material are deposited in succession, and means for controlling the thickness and rate of deposition of each of the successively applied layers. A metallic or insulating core 17 is driven, by means of reels 12, 13, 14, 15, 16 mounted in a casing 11, through a series of groups of chambers, comprising in succession metal evaporating chambers 20, metal thickness control chambers 30, insulating material evaporating chambers 40 and insulation thickness control chambers 50, the whole being maintained at a reduced pressure e.g. of 10-5 mms. of mercury, by vacuum pumps connected to pipes 18. Each group of chambers is symmetrically arranged about the cable axis as shown in Fig. 4. Each chamber 20 comprises an enclosure 21 surrounding an evaporating cup or boat 22 formed of W, Mo or Ta and holding the metal e.g. Cu, Ag or Al to be evaporated, the metal being in the form of a bar or filament fed manually or automatically into the cup or boat, heating being effected by direct or alternating current through the cup, by a heater coil or by high frequency means. Inner and outer baffles 25, 26 are provided and have apertures variable by diaphragms 27, 28 operated manually or automatically. In the chamber 30, the resistance of the deposited metal film is used to produce a voltage drop between contact members 32, 33 operating through a servo-mechanism 37, 38 to control the heating rate in the chamber 20, the apertures of the baffles 25, 26, or the rate of feed of metal or any combination of these. In the chambers 40, which are similar to the chambers 20, insulating material, e.g. manganous fluoride, magnesium fluoride, silicon monoxide or silicon dioxide, with or without cryolite or zinc sulphide, is evaporated, the thickness of this layer being similarly controlled by servo-mechanisms 55, 56 operated by photoelectric cells 54 in the chambers 50 which include light sources 51, optical systems 52 focussing light on the insulating coating and optical systems 53 focussing the light reflected from the insulating coatings on the cells 54. The cable passes one or more times through a series of such groups of chambers forming stacks of as many as 100 layers of metal and of insulating material. Such stacks of layers 60, Fig. 5, may extend to the outer shield 61 or intermediate insulation 62 may be interposed, as shown, between stacks 60, 63. The insulation 62 may be formed in the same apparatus, the chambers 20, 30 being disabled, in additional evaporating chambers or in a coating bath. In modifications, (1) the group of metal evaporating chambers 20 is replaced by a single evaporator in the form of a hollow tungsten sphere (2) the reels 12, 16 are replaced by storage reels to and from which the cable is run alternately, control chambers being provided on either side of the evaporating chambers and being brought into action to actuate the appropriate servo-mechanisms or disabled according to the direction of movement of the cable. Deposition is preferably effected at 500- 1000 Angstrom units per second, but by using very low pressures and heating the core to 150‹C., a deposition rate of 100 Angstrom units per second may be employed.