Cross Coating Weight Control by Electromagnetic Strip Stabilization at the Continuous Galvanizing Line of ArcelorMittal
- PDF / 1,590,582 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 67 Downloads / 190 Views
CONTINUOUS hot dip coating is an efficient method of coating large amounts of steel with a corrosion protective layer. It involves the application of a molten metallic coating onto the surface of a steel strip in a non-stop process. The moving strip is immersed in a bath of molten coating metal, such as zinc for instance, that passes around a rotating submerged sink roll which redirects it up between two gas jet knives located just above the bath (Figure 1). By their stripping action, these knives, blowing either air or nitrogen, wipe the excess coating metal, leaving only the required thickness on the strip. Before entering the pot, the strip is cleaned, annealed, and cooled to a temperature that approximately matches that of the molten bath. Due to the chemical reaction between the molten bath and the steel (alloying), the continuous hot dip coating process provides a highly adherent coating. It is the least expensive corrosion protective coating process and is used for the most demanding, i.e., automotive applications. The objective of a continuous hot dip galvanizing line (CGL) is to apply a tightly adherent, defect-free,
NICOLAS GUELTON, Process Engineer, is with Process Automation, ArcelorMittal, 17, Avenue des Tilleuls, 57190 Florange, France. Contact e-mail: [email protected] CATHERINE LOPE`S and HENRI SORDINI, Process Engineers, are with Galvanizing, ArcelorMittal, 17, Avenue des Tilleuls, 57190 Florange, France. Manuscript submitted December 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
and uniform coating of specified thickness to both surfaces of the strip. The gas pressure, knife-to-strip distance, and line speed are the only three main parameters controlling how much liquid coating is carried out of the pot on the strip surfaces. Therefore, at steady line speed and gas pressure, the knife-to strip distance at any point on the strip should be exactly the same for the coating to be uniform. Unfortunately, the strip is subject to a lot of cumulative disturbances (pass-line shift and skew, flatness defects, vibration and fluttering) which make this distance change continuously in both the longitudinal and cross directions of the strip. The galvanizer has no other choice but to increase significantly the target coating in order to avoid undercoating. But coating metal in a continuous hot dip coating line is one of the highest operating cost items and minimizing its consumption remains one of the permanent concerns of the manufacturer. There are only two ways, or more precisely, two consecutive steps to successfully reduce zinc consumption while satisfying the customers’ requirements: first improve the effectiveness of the controls, and then reduce the magnitude of the disturbances. The CGL of ArcelorMittal Florange took the first major step in 2008 by commissioning its own coating weight control system. This enabled immediate compensation for process disturbances whose effects on coating are predictable, and fast elimination of unpredictable disturbances such as strip horizontal motion betwe
Data Loading...
