GB369943A - Improvements in or relating to coating metals by spraying - Google Patents

Abstract

369,943. Coating with metals. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(General Electric Co. ; Schenectady, New York, U.S.A.) Dec. 24, 1930, No. 38931. [Class 82 (ii).] To provide a uniform wear-resisting hard metal coating on a foundation metal, e.g. iron or steel, a mixture of a finely divided carbide of an element of the sixth group of Mendelejeff's periodic table, e.g. tungsten carbide, and a finely divided cementing metal, e.g. iron, nickel, or cobalt, is heated and sprayed on to the foundation metal, which may also be heated, at a temperature a b o v e the melting - point of the cementing metal but below the melting- point of the carbide in a non-oxidizing and preferably non-decarbonizing atmosphere. The coating renders the foundation metal suitable for use as a metal cutting tool or die. A spray torch for carrying out the process comprises an outer metal casing 1, Fig. 1, spaced from an inner receptacle 2 within which, separated from it by insulating material 2<1>, is a heating chamber 3 which consists of a cup-shaped graphite member 4 and a concentric hollow graphite member 5 with a plurality of inclined openings 8. The member 5 surrounds an opening 6 in the bottom of the member 4, which opening communicates with ducts 7 in the side and bottom walls of the member 4. A graphite or tungsten pipe 9 which passes through the top and bottom of the casing 1 and within the member 5 has a large aperture 10 so that hot gas from the heating chamber can pass into the pipe. Insulating plugs 11, 12 are fitted on the upper ends of the members 4, 5 respectively and a graphite plug 13 fitted round the pipe 9 closes the aperture 6 below the level of the ducts 7. The pipe 9 and member 5 are connected to a source of electrical energy through leads 17, 16 respectively. The coating mixture is fed into the upper end of the pipe 9 and non-oxidizing gas, e.g. carburetted hydrogen, nitrogen, argon, or nitrogen mixed with a small percentage of hydrogen, is supplied to the casing 1 through a pipe 19, one portion of the gas passing through the ducts 7 and the opening 6 into the heating chamber and finally through the opening 10 into the pipe 9 while the remainder of the gas passes down between the casings 1, 2 and is exhausted through openings 20 in the casing 1. The powdered mixture in the tube 9 is forced out by the flow of gas entering through the opening 10 to form a coating on a foundation metal body 21 which is preferably mounted on a movable table 22. A modified form of spray torch which acts as a radiant heater to heat the foundation metal is shown in Fig. 2. A hollow graphite heater 23 is provided at its upper end with a cap 24 and at its lower end with a screw-threaded graphite plug 25, through which passes a tungsten or graphite tube 26 insulated from the cap 24 and having an aperture 28 within the heater. The side walls of the heater are coated with an insulating refractory cement comprising zirconium oxide, sodium silicate, and magnesium oxide, and the heater and the tube 26 are connected to a source of electrical energy. The whole of the gas entering the heater passes into the tube 26 and is exhausted with the coating metal, and the plug 25 radiates heat to the foundation metal. Specifications 8889/15, [Class 72, Iron &c.], and 213,524, [Class 82 (i), Metals, Extracting &c.], are referred to.