Numerical analysis of edge over-coating in continuous hot-dip galvanizing

Abstract

The edge over-coating (EOC) developed near the edge of a galvanized steel strip is numerically analyzed. The 3-D flow field with alternating vortices in the region away from the strip edge is investigated and the distributions of mean impinging pressure and shear stress on the strip surface are obtained by using a commercial 3-D flow analysis code, STAR-CD. It was found that the appearance of alternating vortices causes the surface pressure to decrease gradually approaching the strip edge. The coating thickness is calculated by one integral analysis method of the boundary layer momentum equation. A sample calculation of a benchmark experiment on EOC problem shows that the present analysis method yields a reasonably accurate prediction of EOC for a given plant operating condition. And the result demonstrates theoretically that EOC can be effectively remedied by adjusting the distance of the 2-D air-knife nozzle and by installing a baffle plate parallel to the end of the steel strip.