Mg-comprising hot-dip galvanized steel sheet manufacturing method and manufacturing apparatus
The present invention relates to an apparatus and a method of manufacturing a hot dipped galvanized steel sheet that is excellent in corrosion resistance and has no linear defects, thereby being available for automobile bodies, household appliances, construction materials, and the like which need aesthetic surfaces. The apparatus for manufacturing a hot dipped galvanized steel sheet includes: a plating pot filled with a galvanizing bath for coating of a steel sheet; a sink roll; a wiping device adjusting the thickness of the coating on the steel sheet; a top roll; an oxidation process chamber; and an air cooling device. According to the present invention, after an excess molten coating solution attached to the steel sheet is evenly removed, an oxide film is made to be 0.1 μm to 0.3 μm thick before a coating layer starts to solidify. Thus, linear defects can be prevented.
1. A method of manufacturing a hot dipped galvanized steel sheet containing Mg, the method comprising:
adjusting a coating amount by an air knife after a steel sheet is immersed in and removed from a galvanizing bath of a plating pot to form a galvanized steel sheet by passing a sink roll;
forming an oxide film by oxidizing the galvanized steel sheet air-cooling the galvanized steel sheet having the oxide film; and
passing the galvanized steel sheet over a top roll after the air-cooling;
wherein the forming of the oxide film is performed by using a corona discharge ozone generator.
2. The method of claim 1 , wherein the forming of the oxide film is performed by using an ozone generator spraying an aqueous solution containing hydrogen peroxide.
3. The method of claim 2 , wherein the aqueous solution contains 0.01% to 1% hydrogen peroxide.
4. The method of claim 2 , wherein the forming of the oxide film is performed for 0.5 seconds to 1.5 seconds in a chamber,
wherein the steel sheet is inserted in the chamber at a temperature from 385° C. to 410° C. and the steel sheet is taken out from the chamber at a temperature from 380° C. to 400° C., and
wherein an ozone concentration in the chamber is 1 ppm to 100 ppm.
5. The method of claim 1 , wherein the forming of the oxide film is performed for 0.5 seconds to 1.5 seconds in a chamber,
wherein the steel sheet is inserted in the chamber at a temperature from 385° C. to 410° C. and the steel sheet is taken out from the chamber at a temperature from 380° C. to 400° C., and
wherein an ozone concentration in the chamber is 1 ppm to 100 ppm.
6. The method of claim 1 , wherein the oxide film is 0.1 μm to 0.3 μm thick.
7. The method of claim 1 , wherein the forming of the oxide film is performed for 0.5 seconds to 1.5 seconds in a chamber,
wherein the steel sheet is inserted in the chamber at a temperature from 385° C. to 410° C. and the steel sheet is taken out from the chamber at a temperature from 380° C. to 400° C., and
wherein an ozone concentration in the chamber is 1 ppm to 100 ppm.