Importance

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Abstract

Plural calibers which perform a rough rolling step include: a grooving caliber configured to perform grooving vertically with respect to end parts in a width direction of a material to be rolled; one or plural split calibers formed with projections configured to create splits vertically with respect to the end parts in the width direction of the material to be rolled after being grooved to form divided parts on the end parts of the material to be rolled; and plural bending calibers formed with projections configured to abut against the splits and sequentially bend the formed divided parts, at least the split caliber of the last stage out of the one or plural split calibers is provided with caliber side surfaces configured to abut against right and left side surfaces of the material to be rolled and restrain the material to be rolled from right and left, and in the split caliber provided with the caliber side surfaces, rolling and shaping is performed under a condition where a caliber restraining rate B becomes 0.7 or more and less than 1.0.

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First Claim