JPS6354783B

PURPOSE:To prevent generation of spangle and zinc sag on the front and rear surfaces of a steel strip in the stage of subjecting the steel strip to alloying plating on one side to different thicknesses with a continuous galvanizing line by cooling quickly the strip after plating treatment then subjecting the strip to a heat treatment for alloying. CONSTITUTION:A steel strip 1 is passed through a galvanizing cell 2 to stick molten zinc on both surfaces. The excess molten zinc is removed by the gas blown from gas wiping nozzles 3, 3'. The molten zinc is plated at 25-40g/m on one surface of the strip 1 and at 110-190g/m on the other surface by adjusting the space between both nozzles 3, 3' and the strip 1 or the pressure of the gas from both nozzles 3, 3', by which the steel strip is plated to different thicknesses. Such strip is quickly cooled and solidified by the water, etc. sprayed from a bright minisbar device 4, etc. and is then coiled. The coil is removed from the line. The zinc of the thin plating layer is alloyed to the iron of the steel strip by oven annealing and the thick plating layer is subjected to reflow.