Numerical analysis of uneven coating near steel strip edges in continuous hot-dip galvanizing

In a continuous hot-dip galvanizing process, the opposite air jets from the air knife nozzles collide with each other in the region near the steel strip edges, causing complex 3D von Karman vortices. The vortices alter the pressure gradient of wiping air jet over the steel strip edge surfaces, causing uneven coating thickness. Here, the effects of the excess air vortices on zinc coating distribution at the edges are investigated with 3D eddy structures in the region of collision using detached eddy simulation (DES). The wiping pressure and shear stresses, obtained numerically, were used as boundary conditions in an analytical model to predict the stagnation line - a bottleneck region in the zinc wiping process. In comparison with experiments, the proposed analytical model successfully computes the quantity of zinc dragged upward by wiping air and the transient variations in coating values near steel strip edges.