Patent GB-852070-A (GB)
Title: Glow discharge process and apparatus therefor
IPC: C23C8/36
Filed: 1956-11-22
Abstract: 852,070. Nitriding. ELEKTROPHYSIKALISCHE ANSTALT B. BERGHAUS. Nov. 22, 1956 [Nov. 22, 1955], No. 35776/56. Class 72 [Also in Groups XI and XL(b)] In heating the surfaces of solid or liquid bodies by glow discharge in a vessel under partial gas pressure especially in the nitriding or carburization of metal bodies, the surfaces are maintained at a predetermined temperature, e.g. 500‹-550 ‹C. by the gas discharge and heat is led away from the surfaces under treatment by cooling other surfaces of the bodies, whereby the treated surfaces may be subjected to a more intense heating action without increase in the surface temperature. Thus in Fig. 1 a steel tube 1 to be treated is supported in a cooled doublewalled vacuum vessel 2 by pipes 6, 7 through which cooling oil is passed under control of a valve 8 to cool the inside of the tube 1. The current supply 5, e.g. at 500 volts is connected to the tube 1 forming the cathode and to a cylindrical counter electrode 3 surrounding the tube. D.C. or A.C. at 50 cycles may be used. Gas is supplied through a pipe 14 to the vessel in which a partial vacuum is maintained by a pump 11. After a starting operation as described in Specification 805,164, the oil valve 8 is opened. The surface temperature of the tube is monitored by a radiation pyrometer 17 through an aperture 15 in the electrode 3 and a window 16 in the vessel wall 2. The pyrometer may be used to maintain the temperature of the tube surface by increasing the gas pressure or the voltage when the coolant oil passes through the tube and the coolant flow may be increased to allow a greater rate of heating. This regulation and the opening of the oil valve may be controlled automatically by the pyrometer. In Fig. 3 the inner surface of a steel tube 20 is heated, the tube being supported by elastic washers 24 in a surrounding jacket 21 through which cooling oil is circulated. The tube 20 is connected electrically at 35 to the metal jacket 21, which is connected to a current supply 34. A tubular counterelectrode 32 is mounted concentrically within the tube 20 by domed end caps 29 carrying pipes 36 by which the partial vacuum within the tube 20 is adjusted. The hollow electrode 31 is also cooled by a cooling gas or liquid, especially if A.C. is used. For small objects, e.g. a metal tube 40 (Fig. 4) cooling is effected by placing the tube in an aperture in a massive metal block 41 of good heat conductivity, e.g. of copper. The discharge vessel is formed by a metal cowling 45 supported on the metal block 41 by an insulating gas tight ring 44. An electrode bar 47 passes through the cowling into the tube 40 and is connected electrically to the metal block 41, the cowling 45 forming the counter-electrode, and being also connected to the current supply 48, e.g. at 400- 1000 volts. The gas pressure may be regulated at a few m.m., and a glow edge appears on the inside surface of the tube 40 and on the outside of the electrode 47. These glow edges and the associated cathode drop spaces can be made to touch. The block 41 cools the tube 40 by conducting heat therefrom and may be cooled by air or an additional gas or liquid cooling system. It is stated that the degree of hardness or depth of treatment of a body may be increased owing to the increase of energy supply and that the time of the treatment may thus be decreased. Specification 805,163 also is referred to.