GB1480778A - Method of treating articles under vacuum conditions with external gas flow - Google Patents

Abstract

1480778 Heat-treating metals; nitriding R A GRAY & CO Inc 3 Oct 1974 42933/74 Headings C7N and C7U [Also in Division B3] In treating articles the articles are placed in a first chamber connected by an orifice to a second chamber, a vacuum source is connected to the second chamber, a gas is introduced under pressure into the first chamber to maintain a higher pressure therein than inthe second chamber and to cause a gas flow through the orifice, the pressure in the first chamber being 100-10,000 microns and in the second chamber being 10-6700 microns. An apparatus in which the process may be carried out comprises an insulated outer wall 21 Fig. 1 within which is arranged a shell 25 with a removable cover 26 the shell, heated by elements 35, being connected by a conduit 45 to a vacuum pump. A work chamber 28 for enclosing the article arranged within the shell 25 and has a loosely fitting cover 29 providing an orifice 31 connecting the interior of the chamber 28 with the shell 25. A conduit 37 supplies gas under pressure to the chamber 28. Another apparatus comprises a work chamber 49, Fig. 2, within which articles are enclosed, connected to an enclosure 48 by a duct 51, the enclosure 48 being connected to a vacuum source 66 and the chamber 49 being supplied with gas by a conduit from a source 70 of gas under pressure. A cover 64 allows the introduction of articles to the chamber 49 which has a work support 54, heating element 56, a fan 58, cooling elements 60 and heat shields 62. A further apparatus is similar to that of Fig. 2 but is connected, through an orifice in its long side wall, to a pipe communicating with the vacuum source. In operation cast iron and/or ductile iron and/or steel castings are heat-treated and surface prepared to be coated with glass, ceramic &c. by arranging the parts in the work chamber, evacuating both chambers to 50 microns, introducing nitrogen, argon or air into the work chamber to produce pressures of 40-60 or 80 microns in the second enclosure and 250 or 400 microns in the work chamber, and heating to 1800‹F for one hour. As outgassing progresses the gas flow is increased to maintain pressures of 400 microns in the work chamber and 50 microns in the second enclosure. The heaters are turned off and the work chamber is filled with nitrogen or argon for cooling. Parts of alloy steels are heattreated at 1800‹F using a non reactive gas as the introduced gas.