GB1153823A - Fluorocarbon Coated Metal Surfaces - Google Patents

Abstract

1,153,823. Fluorocarbon resin coating. WALTER KIDDE & CO. Inc. 16 Jan., 1967 [2 Feb., 1966], No. 2297/67. Heading B2K. [Also in Division C7] A method of applying and adhering a fluorocarbon resin layer to a metal base selected from the group metals consisting of iron, nickel, cobalt and aluminium and their alloys comprises spraying a melt of aluminium, an alloy of nickel and aluminium molybdenum or a hydride of titanium, hafnium, zirconium, niobium or tantalum on to the metal base, impregnating the resulting exposed porous surface with an aqueous suspension of a fluorocarbon resin, heating to dry the coated surface at a temperature less than 200‹F, heating the dried surface to a temperature of from 400‹ to 500‹F and quenching in water. The fluorocarbon resin may be polytetrafluoroethylene resin. Surfaces which are non-staining, non-sticking, having a high reflectance coefficient both for infra-red radiation and sound are produced. Metal-base alloys mentioned are nickel-bearing stainless steel, nickel-copper, nickel-plated copper or brass. The metal base may be any metal plated with a layer of iron, nickel or cobalt, preferably an electro deposited layer of nickel. The metal surface is preferably flame or plasma-sprayed with nickel aluminide to form a relatively compact layer having a porous structure on its exposed surface. After brushing or abrading the surface to remove any loose particles the surface is wetted by a spray of wetting agent in water. The surface is then coated with a priming layer of an aqueous suspension of a tetrafluoroethylene resin containing pigment, wetting agent, and chromic acid or a water soluble salt thereof. The primed surface is slowly dried at elevated temperature so that the primer is gradually drawn into the porous outer structure of the aluminium-nickel alloy and is thereafter heated to a temperature sufficient to convert some or all of the chromic acid compounds to insoluble chromates without sintering the resin. Whilst still hot the primed surface is quenched by immersion in cold water to dissolve out excess chromium compounds. During the quenching operation ultrasonic energy may be used. Whilst still moist the nickel-aluminium layer is uniformly coated with a layer of polytetrafluoroethylene resin in aqueous suspension applied by spraying in an electrostatic field. The resin is then caused to be drawn into the porous nickel-aluminium surface layer by slowly drying the coated layer at less than 200‹F. The coated metal surface is then subjected to a temperature of 400 to 500‹F followed by quenching in cold water after which the coated metal is dried, burnished, heated to 725‹ to 820‹F to sinter the resin coating. The final fluorocarbon layer may be buffed. The products may be used as non-stick cooking utensils, infra-red radiation reflectors, or sonic sectors. The metal hydrides are generally used as a powder and during the flame or plasma spraying operation decomposed to release hydrogen so that the layer of sprayed metal on the base is substantially free of metallic oxide.