Coating Weight Model for the Continuous Hot-Dip Galvanizing Process

Abstract

A coating weight model was developed to describe the pressure and wall shear stress distributions as functions of slot gap (d) and impingement distance (Z), for the air knife wiping of the liquid zinc coatings in continuous hot dip galvanizing at ratios of Z/d £ 8. This model was then used in validation studies in order to predict the coating weight as a function of the process parameters. The model was based on improved correlations for pressure and shear stress developed by a combination of experimental and computation techniques, which has resulted in more accurate predictions of coating weight validated using industrial coil average coating weight data, particularly for coating weights of up to 75 g/m 2 . For this region, the maximum deviation between the predicted and measured coating weights was 8 pct. The coating weight model was further developed by incorporating a lumped heat-transfer analysis to predict the solidification ''dry line'' of the coating. For a typical continuous galvanizing process, the model predicts an 80 pct coating solid fraction for a coating weight of 130 g/m 2 to occur at 15 m from the air knives, which agrees qualitatively with visual observations in continuous galvanizing lines.

Deformations during jet-stripping in the galvanizing process

“…In addition, we have used empirically determined shape functions [4], [7][8][9] for the pressure and shear.…”

“…In short, this suggested that there were regions in which it was possible for disturbances to grow in amplitude if a number of conditions were met. Using the empirically determined values and pressure and shear distributions from [7,8] it is possible to consider this behaviour more carefully. If we re-write (12) in the form…”

Wiping Systems: Influence of the Surface Tension in Water Film Rupture

“…The time step was set at 10 −4 and the residuals was set at 10 −5 . The choice of turbulence model has been based on numerous papers [5,6], where the RNG k-ε combined to "Non-equilibrium Wall Functions" is strongly recommended. The input thickness is set by the modification of the input conditions, more exactly with the velocity inlet.…”

Cross Coating Weight Control by Electromagnetic Strip Stabilization at the Continuous Galvanizing Line of ArcelorMittal Florange

“…Further improvement of the model of Ellen and Tu has been the subject of more recent works. [5][6][7] Whatever their refinements, the analytical expressions of the coating thickness contain at least two jet design-dependent fitting parameters, respectively, for the pressure and shear stress distributions imposed on the strip by the impinging jet, and two physical properties of the liquid metal which are the dynamic viscosity and the density. Application of these expressions to a fitting dataset has revealed three major conceptual problems: in order to have an acceptable prediction, (1) values of the fitting parameters should fall outside their respective prescribed ranges; (2) these values depend on the coating metal, whereas AlSi-and Zn-coated strips are wiped with exactly the same knives; (3) the physical properties of AlSi take inconsistent values.…”