Numerical Verification of the Performance of Double Jet Air-knife System in Avoiding the Check-mark Stain on the Zinc Coated Surface

摘要

When galvanized steel strip is produced through a con- tinuous hot-dip galvanizing process, the thickness of ad- hered zinc film is controlled by impinging plane nitrogen gas jet, hereinafter called “air-knife system”. In such a gas- jet wiping process, stain of check-mark shape appears fre- quently on the coated surface. Fig. 1 demonstrates the micro-scale view of the zinc coated surface with 3rd grade check-mark defect taken by the scanning electron micro- scope (SEM). The height from a valley to the nearby crest is about 2-3 um and the distance between nearby crests is usually 3-4mm. The check-mark stain causes many prob- lems such as irregularity in the electrical and thermal char- acteristics and diffused reflection on the coated surface.