GB882582A - Improvements in or relating to methods for applying coatings of substances to surfaces - Google Patents

Abstract

882,582. Coating surfaces with powdered substances. BALLARD, W. E., and DOLDER, K. T. Oct. 2, 1958 [Oct. 2, 1957], No. 30803/57. Class 93 [Also in Group II] A coating of a substance in powdered or finely-divided form (e.g. of granular, globular, or particulate form) is applied to a material to be coated by subjecting the substance to a shock wave produced by an electric discharge acting through a gas to cause the substance to impinge upon and adhere to the surface of the material. The discharge may pass through the gas without combustion of the latter and the shock wave may be directed along a defined path of travel from the seat of the discharge towards the surface of the material, the substance being fed into the path of travel. The gas may be an inert gas such as argon and may be present at low pressure. The shock wave may be transmitted along gas contained in a shock tube, and the substance may be introduced between the discharge station and the shock tube inlet, into the shock tube itself, or between the shock tube outlet and the material to be coated. The shock tube may narrow in the direction of travel of the shock wave. The electric discharge may take place repeatedly to produce a time-spaced series of shock waves, and quantities of the substance may be fed into the path of travel of the waves in timed relation with the discharges. Alternatively, the substance may be present in the wave path in a form (e.g. a partly-coherent form disrupted by the shock wave) in which the requisite quantity is conveyed into contact with the material in response to the occurrence of each discharge. As shown, the apparatus comprises a discharge chamber 10 of glass, a tubular extension of which forms the shock tube 11, and a work chamber 12 of glass. The chamber 10 is provided with an electrode rod 13 and a tubular electrode 14, both of copper or tungsten and connected to the condenser bank 15 and spark gap 16. The electrode 13 extends through a metal base plate 16 clamped against a sealing ring between it and the end of the chamber 10. The plate 16 is provided with a pipe 21 carrying a valve 22 controlling the flow of argon. The electrode 14 is sealed at opposite ends to the discharge chamber and the shock tube. The work chamber 12 is sealed to the end of the shock tube and has a removable top plate 24 having a bush 28 through which passes a support 25 for the workpiece 26, a tube 3 extending from a valved storage chamber 30 for the coating substance, and a valved pipe 33 connected to a vacuum pump and to a manometer 35. The storage chamber valve may be controlled manually or in timed relation with the electric discharges. The gas need not be inert and may have some desired chemical or physical reaction with the coating substance and/or workpiece. Cooling means may be associated with the shock tube and/or work chamber, and heating means with the discharge chamber. The coating substance may be a metal or metal alloy, a metallic oxide, silicate or carbide, or a refractory ceramic substance. The material to be coated may be a metal easily oxidized in air at high temperatures.