To improve a production efficiency and to reduce a cost, etc., by conducting rolling control so that a pack rolling material crown ratio after/ before rolling is equal to a core plate crown ratio before rolling so as to elimi nate a shape straightening process of annealing, etc., due to the improvement of flatness of a core material.
A plate crown and a plate thickness of a core material 1 are measured from a plate thickness distribution in the core material 1 in the longitudinal direction, a core plate crown ratio before rolling is obtained. Pack rolling is conducted so that change in a pack rolling plate crown ratio before/after rolling is turned to be a plate thickness and a plate crown of a pack rolled material after rolling, which enters in a shape nonsensitive zone of the core material. Where, plate crown is difference between plate thickness at plate width center and at plate end, core material crown ratio is core material crown/ core material plate thickness, pack rolled material crown ratio is plate crown in the part except both end parts of pack rolled material where spacers 3 are inserted/plate thickness in the part except both end ports where the spacers 3 are inserted.
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