MANUFACTURE OF STEEL SHEET HOT-DIP-GALVANIZED WITH ZN OR ZN ALLOY INHIBITING GROWTH OF SPANGLE PATTERN

摘要

PURPOSE:To inhibit the growth of spangle pattern at the surface of a steel sheet galvanized with zinc or zinc alloy, by spraying, while regulating spraying speed and spraying quantity, a metal-oxide powder of the prescribed grain size or below on a strip which is pulled up from a plating bath and in which coating weight is regulated, before the plating layer of the strip is solidified. CONSTITUTION:In a hot dip galvanizing line by ordinary Sendzimir process or nonoxidizing furnace method, the steel sheet hot-dip-galvanized with zinc or zinc alloy which is pulled up from a plating bath and subjected to coating weight regulation is sprayed with the metal-oxide powder of =50mum grain size, such as Al2O3, etc., at =5m/sec spraying speed by =0.01g/m2 per unit area before the plating layer of the plated steel sheet is solidified. In this way, the size of the spangle at the plated surface is regulated to =1mm diameter and the occurrence of visible spangle pattern is inhibited, so that galvanized steel sheet having uniform appearance can be obtained.