Optimisation study of roll profile for controlling high-order wave defects in an ultra-wide rolling mill

This paper investigates the issue of higher-order waviness in the rolling process of wide strip steel, focusing on the different higher-order roll shape compensation curves of Baotou steel 2250 mm hot strip mill. First, three typical higher-order waviness compensation curves are fitted and quantitatively evaluated. Second, a mathematical model of the unloaded roll gap is established to analyse the shape control characteristics of the entire roll gap. Finally, a finite element model of the roll system (work roll Φ700 × 2550 mm and support roll Φ1600 × 2250 mm) is constructed to analyse the effects of changes in the position of the shifting rolls on the cross-section of the strip steel at different widths (1400, 1600, 1800 and 2000 mm) using a controlled variable method. The study finds that the fourth-order roll shape demonstrates good performance in controlling higher-order waviness while maintaining the linear control characteristics of quadratic crown. Considering the magnitude of higher-order waviness in actual rolling processes, the compensation amount for the quartic crown is determined to be 0.05 mm. Based on this, the higher-order work roll shape is optimised, resulting in industrial applications where the flatness hit rate of 1.2–2.5 mm thick strip steel increased from 70.57% to 88.7% and the hit rate for 2.51–4 mm thick strip steel increased from 89.11% to 90.8%. Further optimisation of the roll crown setting from [−0.7 mm, 0.4 mm] to [−0.55 mm, 0.55 mm] and adjustment of the shifting roll position improved the middle waviness, ultimately increasing the flatness hit rate for 1.2–2.5 mm thick strip steel to 89.2% and for 2.51–4 mm thick strip steel to 92.1%, thus validating the effectiveness of the roll shape optimisation.