GB611609A - Improvements in or relating to methods of electropolishing, and the improved hollow stem valves having an electropolished internal surface - Google Patents

Abstract

611,609. Electrolytic polishing. THOMPSON PRODUCTS, Inc. March 14, 1944, No. 4720. Convention date, April 9, 1943. [Class 41] [Also in Group XXVII] The internal wall of a tubular metal member closed at one end, such as the stem of a hollow valve, is polished electrolytically to present a smooth surface free from any amorphous layer and having a high rate of heat transfer to the metal coolant such as sodium or copper, by allowing an electrolyte to flow into the member and overflow at the top, suitable electric current being passed through the electrolyte from the member as anode. A valve 13 is fixed vertically in a clamp 14 from which it is insulated at 17 and a hollow conductor 28 passes centrally down the valve stem through insulating spacers 30, 31 and clamp 29 which hold it respectively inside and outside the valve. An electrolyte, preferably a 75 per cent solution of orthophosphoric acid at 100‹ F. is passed from a reservoir (not shown) down the tube 28 and overflows, passing through apertures 33, 32 in spacers 31, 30. By positive connection 34 and negative connection 35 to valve 13 and conductor 28 these become anode and cathode respectively, a current passing between them through the electrolyte. If 2.5 to 3.5 amps. are passed for about 40 minutes with a cathode # inch diameter spaced #to # inches from the internal surface of the valve stem, the latter receives a mirror-like polish entirely free from the amorphous layer produced by reaming and abrading. Sulphuric and phosphoric acids and mixtures of the two are mentioned as possible electrolytes, while the valve may be made of alloys containing such metals as chromium, nickel, molybdenum, iron, cobalt and tungsten, such as those sold under the Registered Trade Marks " Nichrome," " Hastelloy," " Brightray " and " Stellite." The internal surface of the valve head may be polished by the use of an electrode extension such as that described in Specification 611,610.