GB764779A - Improvements in or relating to rotary furnaces - Google Patents

Abstract

764,779. Coating with metals. DIFFUSION ALLOYS, Ltd. Feb. 14, 1955, No. 4331/55. Class 82(2) [Also in Group XII] A rotary retort furnace for the heat treatment of small or medium size metal objects, e.g. for cementation, white annealing, nitriding or chromizing, comprises a refractory brick chamber 1 enclosing a cylindrical rotary retort 3, and a removable chamber 7 which is slid axially into the retort, the chamber 7 being closed by a cover 11 screwed against a fluidtight packing 12 resting on a flange 10. A hollow driving strait 5 attached to the retort 3, which is seated on rollers 4, forms a housing for a temperature measuring instrument, and engages a recess 9 formed in the chamber 7. A sheath 18 formed with openings 19 is welded to the recess 9 and engages a tube 15 formed in a hollow chamber of considerable length l attached to the cover 11, the said tube being opened or closed by a valve 16. A further tube 20 for the supply of atmosphere gas, e.g. a reducing or halogenated gas, extends through the valve 16, the tube 15, and the sheath 18 having an open end near the openings 19. The removable chamber 7 is made of good heat conducting material, e.g. metal or silicon carbide, and may be positively driven from the shaft 5 which may be of polygonal cross-section. 'The chamber is removed from the furnace for cooling purposes and is replaced by another charged container. In chromizing steel articles using the aforementioned furnace and the diffusion method disclosed in Specification 646,637, the articles may be packed in a mixture of 66 parts by weight of fine ferrochromium, 66 parts of chromium, 33 parts of alumina, and 0.2 part of ammonium iodide. The articles are treated at 900‹C. for 4 hours with the retort revolving at 3 revs./min. The sheath 18 and tube 20 are not required in this instance, the valve 16 being kept open while the air in the chamber 7 is partly expelled and closed during the heating and cooling process.