GB774187A - Improvements in or relating to furnaces for heat treatment of articles - Google Patents

Abstract

774,187. Heat treatment furnaces. GREENE, B. May 3, 1955 [May 3, 1954; May 6, 1954], Nos. 12856/54 and 13299/54. Class 51 (2). A heat-treatment furnace of the bell type comprises an outer steel shell 10 enclosing a porous alumina-based refractory lining 11 having a pore capacity of the order of 60-75 per cent and a thickness sufficient to give a temperature gradient of approximately 1000‹ C. when the furnace is operating at approximately 1300‹ C., electric heating elements 17 mounted on the side walls and top of the furnace, a valve controlled pipe 15 for the introduction of a reducing gas such as hydrogen, and a gas outlet pipe 16 in the hearth 14. The furnace also has an oil or water-seal 9, a spy hole 18 and a thermo-couple 19. The volume of the refractory lining should not exceed approximately 40 per cent of the free space within the furnace. In a modification, Fig. 2 (not shown), the seal 9 is replaced by a gasket joint, and another modification, Fig. 3 (not shown), is a batch-type furnace with an upwardly-sliding end door. A further modification, Fig. 4 (not shown), has a removable roof unit, and this is modified, Fig. 7, by the provision of a water-jacketed wall 27 and by a water-cooled roof 31 having flanges depending into a sealing trough 25. The invention is also applied to a tunnel kiln, Fig. 8 (not shown), and to a bell type furnace having its outer walls formed with upwardly-directed cooling fins holding a coolant such as water or dry ice, Fig. 9 (not shown). Other inert gases, such as argon, may be used in the furnaces.