Providing Tight Thickness Tolerances in Manufacturing Automobile Sheet Steels

Results are presented for the studies on real variation in the thickness of cold-rolled strip, which consists in the sum of the longitudinal and transverse thickness variation that exceeded the level of ±2% throughout a length amounting up to 150 m before the operation. The reason for different thickness variation level between the rolling mills of the Severstal CherMK plant and two cold-rolling mills of other manufacturers has been determined to be connected with an error in determining the strip motion velocity inherent in the CherMK plant rolling mill being significantly higher than that inherent in the two cold-rolling mills of other manufacturers. It is revealed that the worst thickness variation in the course of obtaining cold-rolled products at CherMK plant is observed at the end sections of the strip rolls owing to a decrease in the rolling velocity upon passing welded seams. In the course of the experiments, the technology of hot and cold metal rolling with longitudinal and transverse thickness variation within the tolerance of ±2% has been mastered. The best result in longitudinal thickness variation achieved in the rolling of pilot batches, amounts to 99.56% of the length, i.e., the section lengths that did not fall within the tolerance of ±2% being no more than 20 m. The requirements for hot-rolled billets in terms of transverse thickness variation, for the modes of compression and tension upon hot rolling and profiling of working rolls have been determined, too. Necessary cold-rolling velocity modes have been established.