Experimental Investigation of Air-Knife Geometry in Continuous Hot-Dip Galvanizing

Abstract

<p>This thesis investigates the wall pressure distributions of the single-slot impinging jet and multiple-slot impinging jet as a function of various parameters and compares the results obtained with the computational study of Tamadonfar [2010]. The process of gas wiping is used in many industrial applications such as tempering of the plate glass, the chemical mixing process, and turbine blade cooling. One of the most important industrial applications of gas jet wiping is the production of galvanized steel strip in a continuous hot-dip galvanizing line. In this process, an impinging jet is used to remove the excess zinc alloy from the steel strip and control the final coating weight by applying wall pressure and shear stress on the moving substrate emerging from the bath of molten zinc. Changing the various operating parameters such as jet Reynolds number (<em>Re</em>), the jet to strip distance (<em>z</em>), the jet slot width (<em>d</em>), and jet inclination angles (<em>α</em>) allows manufacturers manipulate the final coating weight on the substrate. Production of high quality sheet steels, which have a very thin coating weight and high uniformity quality, is one of the goals of the automotive industry. In order to obtain thinner and more uniform coating weight, a new model of impinging jet which is comprised of one main jet with two auxiliary jets, one on each side of the main jet, called a multiple-slot impinging jet, is of considerable interest.</p> <p>For the current study, a multiple-slot impinging jet was designed and manufactured and measurements were performed for both the single-slot impinging jets, the current model used in continuous hot-dip galvanizing lines, and the multiple-slot impinging jet subjected to a wide range of gas wiping parameters which include the main jet Reynolds number (<em>Re_m</em>), the auxiliary jet Reynolds number (<em>Re_a</em>), and the plate-to-nozzle ratio (<em>z/d</em>). A comparison between the measured results obtained for the two impinging jet configurations and the numerical results by Tamadonfar [2010] has been provided. The similarities and differences between the experimental and numerical results are presented and discussed.</p>