Optimisation of the quartic CVC roll contour for an 1800 mm hot rolling mill

Abstract

This study tackles the central wave defect occurring in downstream stands during the rolling of thin-gauge strip by optimising the roll contour of the F3 and F4 stands to a quartic continuous variable crown (CVC) form. Based on the flatness dead-zone theory, the cause is identified as the excessively large crown at the F4 stand exit, resulting from the use of cubic CVC in the F3 and F4 stands under the current roll bending and shifting settings. Compared with the original cubic CVC, the quartic CVC maintains the nominal quadratic crown range. By adjusting the nominal quartic crown, the partial quadratic crown under consistent roll shifting positions is effectively reduced under different strip widths, thereby decreasing the exit crown at the F4 stand. Production results indicate that the optimised quartic CVC roll contour meets the crown control requirements and mitigates the occurrence of central waves in downstream stands. For thin-gauge strips, the percentage of the head flatness hit rate not less than 90% increases from 31.9% to 56.1%, and the percentage of flatness average value less than 20 IU increases from 29.2% to 55.4%.