GB523322A - Improvements in and relating to methods of and apparatus for coating stainless steelsurfaces - Google Patents

Abstract

523,322. Electrolytic deposition of copper. REVERE COPPER & BRASS, Inc. Dec. 30, 1938, Nos. 37906, 37907 and 37908. Convention dates, Dec. 30, 1937, Nov. 12, 1938, and Nov. 12, 1938. [Class 41] In coating stainless steel surfaces, particularly the exterior surfaces of the bottoms of cooking vessels, with copper, the surface is first prepared to receive the coating, a thin coating is applied by using an electrolyte of low copper concentration and a low density plating current and a thick coating by an acid bath of high copper concentration and a highdensity plating current. A final coating of nickel, chromium or other corrosion-resistant metal may be applied. The preparatory treatment may be with an acid to generate hydrogen at the surface or the surface may be made a cathode or alternately an anode and a cathode in a sulphuric acid bath which may contain also sodium sulphate and chloride. The treatment is effected by supporting the vessel V by resilient prongs' 69 attached to the shaft of an electric motor 35 so that its base is immersed in an electrolyte in a bath 1 and is surrounded by a perforated lead electrode 11. The vessel is rotated during the electrolysis, and current is supplied through connections 25, 45 so that the vessel forms first the anode and then the cathode, a resistance being switched into the circuit to cut down the current when the vessel forms the cathode. To form the thin coating of copper, the vessel without being dried is treated in a bath of acid copper sulphate at about 80‹ F. or a copper cyanide bath at 110-130‹ F. An apparatus similar to that used for the preparatory treatment is made use of, the lead electrode being replaced by the flat copper electrode, and provision being made to discharge air below the centre of the vessel to agitate the electrolyte : or to pump the electrolyte against the electrodes. The thick coating of copper is applied in a similar apparatus using a stronger acid copper sulphate bath which may also contain aluminium sulphate and current densities up to 500 amps. per square foot and temperatures up to 150‹ F. To obtain even deposition, a shield consisting of a steel plate covered with indiarubber and having a central opening may be interposed between the electrode and the base of the vessel.