Causes and the methods of correction of the defects “transverse ribbing” and “work-hardened bands” on the surface of cold-rolled autobody sheets

A surface defect in the form of parallel alternating dark and bright bands located across the rolling direction appear periodically upon cold rolling of thin-sheet steel intended for the face parts of cars. This defect is known as transverse ribbing and is visually observed upon rolling. The difference in the dark- and bright-band thicknesses can be determined with a micrometer. A similar but finer defect in the form of work-hardened bands has recently been detected. It is only observed after the sheet surface is processed with hones. In this case, the difference in the band thicknesses cannot be determined with a micrometer. A theory is proposed to explain the causes of the appearance of these defects, and methods for their correction are developed and tested on a commercial rolling mill.