New Flame-hardening Process
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A SYSTEM of flame hardening which ri is claimed to be quicker and is attended with less distortion than is usually encountered in the carburizing or nitriding process, has been introduced into this country by Surfard,
Ltd., Abbey House, Victoria Street, London, S.W.I.
In the Peddinghaus process, as it is called, the heating medium is oxy-town gas, the heat of the component being treated being automatically controlled .h y an instrument termed a milliscope. The heating of the steel is so rapid as to make the use of ordinary pyrometers. impracticable.
T h e milliscope is. capable of responding t o extremely rapid changes of temperature and its use, in conjunction with the flame h.ardening machine, makes for precise control of the hardening ternperature.
The instrument is set to the temperature required, and when this i s reached a direct current is generated, which is
used, in some cases, to control the speed of travel ot the burner, and in others, to transfer the component from the heating to the quenching position.
One type of flame-hardening machine recently demonstrated in London was of the vertical type on which spindles and rolls up to 5 ins, diameter and 2 ft. long could be progressively hardened. On this machine, the component. is rotated between centres, the heating unit being two semi-circular burners having a narrow slit from which a ribbon of. flame at an intense heat is emitted.
The burners and the 'quenching jets . situated below them are mounted on a carrier, which is raised. hydraulically throughout the length of the part to be hardened. On this carrier is mounted the working head of the milliscope, which is sighted on the portion of the work being heated. In this way the instrument follows the heated zone throughout the travel of the burner.
The faster the burners rise, the lower the heat input to the component, but their speed is capable of fine adjustment. The burners are set slightly on the slow side, so that the tenden:y is for the temperature of the, work to exceed the figure preset on the milliscope.