Influência da alteração do layout do pote de zinco no arraste de Dross no material galvanizado a quente

Abstract

The production of hot-dip galvanized steel has increasingly required in-depth knowledge of the phenomena involved in the interaction of the moving steel strip with the molten zinc bath. One of the biggest challenges is controlling the defect from dragging dross through the strip in the process. Dross is the combination of the Fe provided by the strip to the galvanizing bath and the elements of the molten metal bath composed of 99.8% Zn and 0.2% Al. Some studies involving mathematical and physical simulation have been developed to better understand the phenomena involved in this process. However, there are many different galvanizing pot layouts and dimensions and not all of these galvanizing pot configurations and geometries have been studied. In the present work, four conditions, listed below, were proposed and tested in order to verify the influence of the changing in the zinc pot layout on dross drag in hot galvanized material. These conditions, which have not yet been explored in other studies, occur inside the galvanizing pot during the production process and have effects on the formation of dross and the dragging of these particles by the steel strip in the process. The four conditions are: 1) the effect of the position of the electrical inductors for heating and maintaining the temperature of the galvanizing bath on the fate of the dross particles generated in the “v zone”, the region between the part of the strip that enters and the strip that comes out of the pot; 2) the effects of reversing the position of the stabilizing rollers also on the fate of the dross particles generated in “v zone”; 3) the effect that the snout depth within the zinc bath has on the fate of dross particles generated in the “v zone”; 4) the effect of the immersion depth of the melting zinc ingot, during pot filling, on the dross particles precipitated by local cooling during melting. The effect of changing these conditions was also evaluated through a mathematical model using the ANSYS FLUENT software, which in turn had its flow pattern validated in a cold physical model. In the results, it was seen that for condition 1, depending on the position of the inductor used, the dross particles can be adhered to the strip more easily in certain regions of the bath, in the case of inductors facing the strip, and can also be directed to the snout more intensely, in the case of lateral inductors. For condition 2, notably, the number of dross particles incident on the upper face of the strip is lower than in the original design position, when there is an inversion of the stabilizer rollers. For condition 3, it was also observed that the depth at which the snout penetrates into the bath also has important effects on the fate of dross particles precipitated in the “v zone”, the deeper it goes, the more particles are dragged by the strip. For condition 4, from the results obtained, it was evident that the immersion depth of the ingot for melting has a great influence on the fate of the dross particles precipitated during the local cooling of the bath in the melting front of the ingot, the deeper it is, the more particles spread through the zinc bath and find the strip. Conditions 3 and 4 were also tested on an industrial scale and had consistent results with those found in computer simulations. With the results obtained in this work, it is evident that the conditions of the galvanizing pot layout configuration contribute significantly to the occurrences of dross drag and that changes in these conditions can alter, reduce, or intensify these occurrences.