Mathematical Modelling of Jet Finishing Process for Hot-dip Zinc Coatings on Steel Strip

A mathematical model has been developed to predict the zinc coating thickness, and hence coating weight on a steel strip after passing it through a molten zinc pot, and wiping excess zinc from the surface of the strip using a pair of air wiping jets. The developed model predicts the coating weight as a function of different operating parameters such as strip velocity, jet nozzle pressure, nozzle-to-strip distance and nozzle slit opening. The required pressure and the shear stress profile on the strip surface were calculated through numerical simulations, carried out using FLUENT, a finite volume based commercial code. These were then correlated to the plant operating parameters through statistical regression analysis. Having been incorporated the developed correlations; the model was validated with the actual coating weight measured in CGL#2 of Tata Steel and also with the experimental results of J. M. Buchlin et al. The validated model was used to carry out the sensitivity analysis to determine the favourable operating regime for the air jet wiping process. It has been proposed that favourable operating regime should be chosen such that nozzle-to-strip distance is as small as possible and the nozzle pressure is as high as possible.