PURPOSE:To enable accurate control of a strip annealing temp. independently of strip size and quality changes by making combined use of feedforward control and feedback control in a direct firing type gas combustion system continuously annealing furnace. CONSTITUTION:By feedforward control the flow rate of fuel gas required to maintain the desired strip temp. at the outlet side of an annealing furnace is calculated and set according to a total heat absorption rate estimating equation when a strip size or quality change point reaches the inlet side of the furnace. By feedfack control the set value of the fuel gas flow rate in feedforward control is corrected on the basis of the actual values of total heat absorption rate calculated from measured values of furnace temp., strip temp. and conveying speed every fixed time after the above-mentioned feedforward control. On the basis of the actual values of the rate the estimating equation is corrected every feedforward control, and every feedback control the flow rate of gas required is corrected according to the difference between the flow rate of gas calculated on the basis of the actual values and the flow rate of gas measured.
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