Innovative techniques and Solutions for Controlling Flatness on Cold Strip Mills and on Downstream Continuous Lines

摘要

This paper proposes an overview of recent investigations made at different ArcelorMittal cold plants to better understand/identify all the factors that modify/degrade flatness along the different processing lines : cold strip mills and downstream Hot Dip Galvanising (HDG) and Continuous Annealing Lines (CAL). Some technical solutions to overcome or at least limit these flatness degradations are also described : transverse strip temperature profile compensation and tolerances determination for pass line roll misalignment at cold strip mill, flatness gauge for downstream continuous lines (installed before and after the furnace) to investigate flatness heredity from cold strip mill to the final stage of production and to investigate the capacity of flatness reparation of the HDG furnace. In particular, it is shown that large flatness defects, when they are visible at cold strip, have their magnitude considerably under-estimated by the mill shapemeter. When these flatness defects are very huge, they are not completely suppressed by the furnace of the downstream HDG line. While, with lower flatness defects at cold strip mill, the furnace may repair them. However, the exact threshold of flatness defect repairedot repaired by the HDG furnace still remains to be determined with the help of the flatness gauge. This threshold will be anyway specific for each HDG line since the capacity of flatness reparation of a HDG furnace depends on many process parameters (furnace length, thermal cycle, line speed …). Finally some trends for the future in flatness control are discussed.