METHOD OF COLORING HOT DIP GALVANIZED STEEL SHEET IN CGL(CONTINUOUS GALVANIZING LINE)

摘要

PURPOSE: A method of coloring hot dip galvanized steel sheets in CGL(continuous galvanizing line) by adjusting the thickness of TiO2 coating after galvanizing operation. CONSTITUTION: In one embodiment, the method of coloring hot dip galvanized steel sheets in CGL(continuous galvanizing line) includes: (i) dipping a steel sheet to be galvanized in a plating bath containing 0.1-0.5wt.% of Ti, 0.004wt.% or less of Al, a balance Zn and other unavoidable impurities at a temperature range of 475 to 570deg.C for 1-3 seconds, wherein the steel sheet to be galvanized is in advance heated to the same temperature as the plating bath; (ii) heating the surface of a galvanized steel sheet at 500deg.C for 1-2 seconds. In the other embodiment, the method of coloring hot dip galvanized steel sheets in CGL(Continuous Galvanizing Line) includes: (i) dipping a steel sheet to be galvanized in a plating bath containing 0.1-0.5wt.% of Ti, 0.004wt.% or less of Al, a balance Zn and other unavoidable impurities at a temperature range of 475 to 570deg.C for 1-3 seconds, wherein the steel sheet to be galvanized is in advance heated to the same temperature as the plating bath; (ii) quenching the surface of a galvanized steel sheet by spraying coolant under the conditions of a liquid pressure of 1 to 2kg/cm¬2 and an air pressure of 3kg/cm¬2.