PRODUCTION OF THICK-COATED HOT DIP GALVANIZED STEEL SHEET EXCELLENT IN SURFACE CHARACTERISTIC

PROBLEM TO BE SOLVED: To produce a thick-coated hot dip galvanized steel sheet excellent in surface characteristic by controlling, correspondingly to the thickness of a steel sheet, the line speed and/or the height of a gas wiping nozzle from the plating bath surface. SOLUTION: The steel sheet is immersed in a hot dip galvanizing bath and pulled up, and a wiping gas is blown without delay to regulate the coating weight at least on one side to >=100g/m . In the case of producing the thick- coated hot dip galvanized steel sheet, the line speed and/or the height of a gas wiping nozzle from the plating bath surface is controlled correspondingly to the thickness of the steel sheet. For example, corresponding to the steel sheet thickness D, line speed LS and wiping nozzle height H are regulated so that they satisfy the following: LS >=110m/min and 260>=H>=240mm in the case of D=-80D+ 150m/min and 255>=H>=235mm in the case of 0.50 < D=70m/min and 250>=H>=230mm in the case of D > 1.00mm. By this method, the occurrence of rippled surface of the hot dip galvanized steel sheet can be effectively prevented.