PURPOSE: To improve the spot weldability of a hot-dip galvanized steel strip by spraying atomized water on the surface of a hot-dip galvanized steel sheet and forming a ZnO series oxidized film thereon.
CONSTITUTION: A steel strip 1 is passed through a hot-dip galvanizing bath 2, is galvanized, is vertically pulled up from the galvanizing bath and is sprayed with an inert gas from a wiping nozzle 3 to remove excess molten Zn, by which a galvanized layer having a certain thickness can be formed. Or, the steel band is furthermore passed through an alloying furnace 4 and is heated to alloy the galvanized layer with Fe in the steel band into an Fe-Zn alloy coating layer. Next, the above is introduced into an atmospheres of atomized water, and the atomized water is regulated to fine water droplets having 10 to 1000μm diameter by pressurized air by water and a blower 7 from a supply pipe 6 and is sprayed from nozzles 8 arranged at a distance of 10 to 2500mm from the surface of the steel band at 3 to 50m/sec rate. The hot-dip galvanized steel strip in which a ZnO film is formed on the surface of the hot dip galvanized layer and excellent in spot weldability can be obtd.
MIZUYAMA YAICHIRO
SAKABA NORIO
YOKOYAMA TATSUMI
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