Patent ID: 8402909

Claim:
A production facility of hot dip galvannealed steel plate dipping steel plate in a plating bath, then alloying it, said production facility of hot dip galvannealed steel plate comprising: a rapid heating furnace set above a plating bath tank and having a heating capability of a 30° C./sec or higher heating rate and a 500° C. or higher peak temperature, and a soaking/cooling furnace set above said rapid heating furnace and treating the steel plate leaving said rapid heating furnace by at least one of soaking and cooling, said soaking/cooling furnace being comprised of a soaking region having a radiant heat source or a hot-air heat source for soaking the steel plate to 500° C. to 650° C. and a cooling region having spray nozzles for cooling the steel plate by a 5° C./sec or more average cooling rate, pairs of radiant heat sources or hot-air heat sources and pairs of spray nozzles being provided along a vertical or line direction arranged facing two surfaces of the steel plate as it is running, the pairs of the radiant heat sources or the hot-air heat sources and the pairs of the spray nozzles being arranged in alternating pairs of spray nozzles and either the radiant heat sources or the hot-air heat sources at predetermined intervals along the vertical or line direction, a ratio of lengths of the two regions in the furnace being freely settable, a layout of said soaking region and cooling region being freely settable, and having an air curtain in said soaking/cooling furnace wherein said spray nozzles are configured with ejection ports able to rotate about an axis parallel to a width direction of the steel plate and said spray nozzles at the boundary of said soaking region and said cooling region can spray cooling gas vertical to the steel plate and form a barrier to the flow of gas.