METHOD FOR CONTROLLING SHAPE OF SHEET FOR MULTISTAGE CLUSTER ROLLING MILL

PURPOSE:To correct quarter elongation and to obtain a good sheet shape by consisting a fresh feedback circuit relating to a quartic component quantity and changing a back up roll crown pattern until the quartic component quantity coincides with a target value. CONSTITUTION:A controller makes an arithmetic processing to correct the quarter elongation and outputs a back up roll crown command 2 when the preset of the back up roll pattern is not adequate and the quarter elongation is generated. Barrel parts 3B of the back up roll 3 operated by quarter adjusting parts 18B are actuated by a back up roll crown calculating device 17 in the direction where said parts are parted from an intermediate roll 4. Edge adjusting parts 18A are further actuated at the specified ratio relative to the amt. of the actuation of the quarter adjusting parts 18B so as to move the barrel parts 3A of the back up roll 3 operated by the edge adjusting parts 18A toward the intermediate roll 4 in a manner as to avoid the fluctuation of a quadratic mode, by which the feedback control is executed to obtain the coincidence with the target value with respect to the quartic mode.