GB436792A - Improved process and apparatus for applying coatings to surfaces - Google Patents

Abstract

436,792. Silvering. WALKER, C. H., Mabrouk, Lynmouth Avenue, Flixton, Manchester, SYKES, C., 2, South Meade, Timperley, Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. April 13, 1934, No. 11220. [Class 93] [See also Groups II and XXII] Surfaces are coated with metal by distillation in a vacuum by placing the coating metal in the form of a thin uniform layer on the surface of a heater, preferably an electrically heated strip of tungsten or molybdenum, raising the temperature preferably slowly until the coating metal melts to form a thin uniform coating on the heater, and then raising the temperature to distil the coating metal on to the surface to be coated. The amount of coating metal placed on the heater is sufficiently small to ensure that any alloy which penetrates through the metal of the heater has a higher melting point than the distillation point of the coating metal. The vacuum is preferably high, the pressure being less than 10-<4> mm. of mercury. The process may be carried out in a vessel formed by securing a steel cylinder 1 in a vacuumtight manner to a plate 2 provided with an opening 3 to which is welded a tube 4 connected to a vacuum pump. In the upper part of the vessel is mounted a support 10 for the body 11 which is to be coated, which is introduced into the vessel through the top of the cylinder 1 which is then closed by a plate 6 secured to the vessel by vacuum-tight joints 9 which can be readily broken. These joints may be made of the grease or wax known under the Registered Trade Mark " Apiezon." A glass window 8 may be formed in the plate 6 or in the walls of the vessel. A heater strip 13 is held by clamps 14 secured to lead-in screws 12 passing through the bottom plate 2, and in operation a thin layer of metal powder is placed on the heater strip. The process may be used for coating glass, for example with aluminium to form astronomical and epidiascope reflectors, for coating presentation cups and other silver ware with aluminium, for coating paper, for example in the production of electrical condenser sheets or low current fuses, and for coating fibrous material such as textiles, silk, &c. Transparent surfaces with very thin coatings may be used as light filters. In coating large surfaces, two or more heaters may be used and coatings of alloys or mixtures may be obtained by using two or more heaters carrying different coating metals. In coating continuous lengths of paper, textiles, &c. a plurality of heaters may be mounted on a rotating or travelling member. The Provisional Specification describes the production of galvanometer leads in which a thick layer of silver is deposited on glass, cut into strips, and the thin strips then peeled from the glass. Specifications 346,293, [Group XXVIII], 360,826, and 407,503, [Group XXVIII], are referred to.