In order to ascertain the mechanism of the edge over-coating (EOC) developed near the edge of a galvanized steel strip, the effects of surface tension (Marangoni convection) and flow structure in the vicinity of strip edge are analyzed.
The temperature gradient of molten zinc near the strip edge is calculated and the accumulation of zinc on the strip edge region due to the surface tension difference is estimated by solving the momentum equation of free surface. About 10% of the EOC is attributed to the Marangoni convection.
The oscillation frequency of opposed impinging plane jets is measured by CTA for the range of 300<$Re_j$<13,000. The 3-D flow field with alternating vortices in the region away from the strip edge is also 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 that the alternating vortices are the main cause of EOC.
