GB380428A - Improvements in or relating to the preparation of gaseous enveloping atmospheres foruse in metallurgical operations - Google Patents

Abstract

380,428. Annealing; cementation. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Wilson, F. P. ; 1100, Union Street, Schenectady, New York, U.S.A.) March 5, 1931, No. 6917. Convention date, March 6, 1930. [Class 72.] A gaseous atmosphere for a metallurgical and like furnace is prepared by passing a fuel gas such as towns gas, through a heated zone, the temperature of which is so controlled that the fuel gas is rendered carburizing, neutral, or decarburizing with respect to the metal. Steam is preferably mixed with the gas in such proportions that the carbon freed in the heated zone will be completely reacted upon by the steam to form hydrogen and carbon monoxide. and in the apparatus shown the supply of steam to a mixing chamber 2 is automaticafly controlled by a temperature-responsive device 5. The mixture passes through a heat-interchanger 7a to header 11, from which tubes 15 depend into a firebrick-lined chamber having nickelchromium heating-resisters 14. The gas passes from the chamber to the furnace 17 through the pipe 16. The temperature maintained within the reaction chamber will vary according to the temperature and other conditions in the furnace, and may be between 700-1100‹ C. The gas supplied to the furnace will preferably contain a preponderant proportion of hydrogen, a smaller proportion of carbon monoxide, a minor content of nitrogen or carbon dioxide, and a small content of methane, ethane, propane or butane. Carbon monoxide is present in such proportion that it will be in chemical equilibrium with the carbon dioxide in the furnace. When the gas is to be used in a brazing furnace such as that described in Specification 265,950, [Class 51 (ii), Furnaces and kilns for applying &c.], the hydrogen and methane should be in chemical equilibrium, and the mixture should be in equilibrium with the carbon content of the steel at the operating temperature. A slightly decarbonizing atmosphere is produced by increasing the steam content or the reaction temperature, and the carbonizing effect can be increased by reducing the temperature, until at 700‹ C. the methane content may be 15 per cent. At high temperatures the hydrocarbon content of the gas may be completely cracked. When it is desired that the atmosphere should contain a substantial proportion of inactive gas such as nitrogen, some of the fuel gas may be incompletely burnt with air, and in this case a combustion chamber is fitted in the fuel gas supply line. When operating at high temperatures a combustion chamber may be used instead of the reaction chamber shown.