GB767582A - Improvements in or relating to furnaces for the heat treatment of metals - Google Patents

Abstract

767,582. Heat treatment furnaces. FUEL FURNACES, Ltd. June 22, 1953 [March 21, 1952], No. 7283/52. Classes 51 (1) and 51 (2). In a batch-type heat treatment furnace fired by burners 17 positioned at the bottom of vertical passages 18 formed in the side walls 11, flues 4 formed in hearth pillars 5 direct waste gases successively into chambers 6 extending longitudinally of the hearth, through ports 7 into ducts 8 extending transversely of the hearth, and through ports 10 into waste gas flues 9 extending longitudinally of the hearth and vertically up the back wall to a stack (not shown). Each transverse duct 8 extends into a fan chamber 12, from which a fan 13 driven by a motor 14 re-circulates the waste gases to the furnace chamber through vertical passages 15 and ports 16 to mix with fresh hot gases from the burner passages 18. The fan motors 14 are switched on and off at a predetermined critical temperature which will not damage the fans, so that, when the furnace is operating at low temperatures, e.g. for tempering, the waste gases are re-eirculated, whereas, when the furnace is operating at higher temperatures, e.g. for hardening or normalizing, the gases are not re-circulated, but pass directly out through ports 10 and flues 9. Cooling air may be drawn into the fan chambers 12 by the stack draught through dampers opening automatically when the fan motors stop.