Method of controlling heat input to an alloying furnace for manufacturing hot galvanized and alloyed band steel

A plate temperature and an emissivity are determined at the outlet of an insulated heated zone, and compensations are established which reduce deviations between the respective measured values and the respective target values. A heat input is compensated for in accordance with the greater one of the compensations relating to the plate temperature and the emissivity, respectively. For a U-pattern material, DELTA Q is previously added to the heat input for the leading and the trailing end portion of the material. The band steel is irradiated by laser radiation at the outlet of the heating zone in order to detect the degree of alloying on the basis of the intensity of reflected radiation. When an unalloyed surface is detected, a target value of the heat input is modified. ITV camera is used to determine the optical reflectivity of the surface of the band steel at the outlet of a cooling zone in order to detect the degree of alloying. After the process has been stabilized, the heat input is gradually decremented, and when any slight insufficiency in the degree of alloying is detected, a fixed compensation is added to the heat input under that condition, subsequently ceasing to update the heat input. A space in which a calculation formula is defined is chosen as a two dimensional or higher dimensional space, which is divided into domains, to each of which an independent calculation formula is allocated. For a boundary region between adjacent independent domains, membership functions are used to derive a contribution factor of such boundary region to each independent domain, and a heat input is obtained by calculating a weighted mean while utilizing calculation formulae for the plurality of independent domains.