COOLING METHOD OF HOT STEEL SHEET

PURPOSE:To obtain a shapely steel sheet by tracking and controlling the position of a hot steel sheet in a cooler, and controlling the cooling injection liquid reaching the front and the rear end with said information by a cutoff valve to make the temp. of the steel sheet uniform in the lengthwise direction. CONSTITUTION:When the rear end of a preceding steel sheet leaves a cooler 6, the amt. of a cooling liquid to be supplied to a succeeding steel sheet 1 and the number of cooling liquid supply headers are determined by a cooling control mechanism 13, and the amt. of the cooling liquid to be supplied to each header 7 is regulated by a flow control valve 11 and a flowmeter 12 while a cutoff valve 10 is kept closed. The control valve 11 is then locked. When the succeeding steel sheet 1 enters the cooler 6, the temp. distribution at the inlet side in the lengthwise direction is measured by a thermometer 9a, and the traveling speed of the steel sheet, the timing of opening and closing of the cutoff valve 11 which performs the opening and closing, and the requisite time of closing and opening are determined. Consequently, the cutoff valves 11 of the header 7 in the cooler 6 are successively closed and opened or appropriately opened and closed, and the steel sheet 1 is uniformly cooled throughout the whole length.