GB484569A - Improvements in and relating to the heat treatment of metals - Google Patents

Abstract

484,569. Furnace atmospheres. PEARSON. J. L., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Nov. 3, 1936, No. 29942. [Class 51 (ii)] In the heat treatment of metals in a protective atmosphere in batch-type furnaces, e.g. furnaces of the bell type, the purging gas, which is supplied after charging and before discharging for clearing the furnace chamber of air and protective gas respectively, is collected and recirculated for use after regeneration. In the apparatus shown diagrammatically in the Figure, three furnaces 12, 13, 14 are in communication through valve-controlled pipes 10, 11 with supply and exhaust mains 17, 18 for protective gas, and can also be connected to atmosphere through the valves 16a, 16b, 16c and the conduits 25a, 25b, 25c. The exhaust main 18 leads to a large capacity flow-equalizing vessel 26, which in turn is connected to the supply main through a fan 19 and regenerating chamber 20. Flow of gas through the regenerating chamber is maintained, irrespective of fluctuations in gas flow from the furnaces, by an automatic valve 21 in a cross connection between two flow-equalizing vessels 22, 23. During purging after charging the protective gas is first allowed to escape to atmosphere for a short time, and is subsequently collected in the vessel 26 for re-use after regeneration. At the end of the heating operation gas may be driven from the furnace by air supplied through an inlet connection, and in this case only the gas from the early stages of the purging operation would be collected. Gas supplied to the furnace during the heating operation is also recirculated for re-use. Regeneration of the gas is effected by burning the oxygen content with a reducing constituent of the protective gas, or with ammonia or other fuel gas from which the protective gas is produced. In a modification. Fig. 2 (not shown), the vessel 26 is arranged on the furnace side of the regenerating chamber 20, and is in valved commumcation with each of the furnaces. In other forms, Figs. 4 and 5 (not shown), two vessels 26 are connected in parallel in the circuit, and one of them is used for collecting gas with a high oxygen concentration. Three collecting-vessels may be used, one for the gas from the early stages of purging after charging, another for gas from the later stages, and gas used during the heating-operation, and the third for gas from the purging before discharging. Specification 429,940 is referred to.