CONTROLLING METHOD OF CARBURIZING ATMOSPHERE

PURPOSE:To make the quick change in a carburizing atmosphere continuous with precision control by changing over the quick introduction of gas in a manual mode and the automatic fine control of gaseous compsn. in an automatic mode in accordance with the target value for the concn. of CO2. CONSTITUTION:Conversion furnace gases RX, AIR and enriching gas C3H8 are supplied to a carburization furnace, and the supply rates of the latter two are controlled according to the measured value of an IR-CO2 meter. Shot purging of C3H8 is performed in a manual mode for the beginning of a carburization period to decrease the concn. of CO2 toward the 1st target value TV. When the concn. of CO2 attains the target value TV, the mode is changed over to an automatic mode and the automatic control of the gaseous compsn. is started. A deviation alarm is made effective when the concn. of CO2 attains a certain value approximate to a set value SV. When the time set with a timer passes by and a diffusion period begins upon ending of the carburization period, the SV is changed and the mode is again changed over to the manual mode.