Study of the effect of the cross profile of cold rolled strips on the occurrence of flatness defects

Abstract

The paper considers the influence of the profile of cold-rolled steel, obtained on a multi-stand continuous mill, on one of the main factors in the quality of the shape of a steel strip - the flatness index (non-flatness amplitude and type of defect). For this, the existing model of the formation of the steel strip flatness was used, which takes into account the main factors of rolling and makes it possible to determine the shape of the cross section and the amplitude of the flatness defect of finished steel strips. With the help of the mentioned model, the thickness of the cold-rolled strip along the section width is calculated, and its non-flatness is also determined. Using methods of mathematical statistics, the effect of partial reduction in the last stand of the mill and the convexity of the crosssectional profile of the finished strip on flatness indicators has been established, and limitations on the values of these factors have been determined. A cold rolling mode is proposed on a five-stand mill 1700 of PJSC Severstal, which ensures the production of a strip of a high category of flatness, due to the optimal choice of the distribution of partial reductions over the stands. Introduction of the proposed mode, as well as the modes determined using the created flatness assessment methodology, will reduce the level of rejection by flatness defects to 1–1.5% of the current level.