Improvement of CVC roll contour for complex wave shape control in 1 800 mm CSP rolling mill

A 1 800 mm compact strip plant (CSP) rolling mill is prone to edge waves or broken edge waves during the rolling process. However, edge wave control via roll bending tends to induce edge-center composite waves or high-order waves, which seriously affects strip quality and production stability. The roll contour directly influences the roll gap shape; superimposing a local reshaping curve on the basic roll contour enables modification of the local roll shape, thereby achieving the adjustment of the local strip profile. To address local edge profile issues, this study modified the edge regions of the continuous variable crown (CVC) roll contours of the downstream F5-F7 stands, realizing local adjustment and compensation of the strip edge profile without affecting the profile control of the strip middle section. A universal edge reshaping (ER) curve design method based on piecewise quartic polynomials symmetric about the roll surface midpoint was proposed for local edge profile problems. Further, a fitted edge reshaping (FER) curve in the form of a sixth-order polynomial was obtained through fitting. A novel roll contour design method was established, which involves superimposing the FER curve on the CVC roll contour to obtain the mixed continuously variable crown (MCVC) roll contour. The designed FER curve was used to reshape the roll contour within the 500 mm edge range of the work rolls. The optimized MCVC roll contour retains the crown control range of the original CVC roll contour, and its quadratic crown varies approximately linearly with roll shifting, achieving a local quadratic crown adjustment ranging from -3 μm to -43 μm for nominal roll gap at rolling widths of 1 000-1 600 mm. Without affecting the crown control characteristics of the strip middle section, the MCVC roll contour reduces the edge reduction within the rolling width range; moreover, the compensation effect on the roll gap shape at the strip edge increases with the increase of strip width. In practical applications of the MCVC roll contour in the downstream F5-F7 stands, the generation of edge waves and complex waves during online profile adjustment is significantly alleviated.