| 摘要 |
PROBLEM TO BE SOLVED: To reduce inside flaws caused when a mandrel bar is drawn with a mandrel mill. SOLUTION: With a mandrel mill having multiple roll stands, wherein each stand is provided with a pair of mutually opposing rolls, arranged along the rolling line in such a way that the rotation axis of the following roll is orthogonal to the preceding roll, the outside diameter of the material to be rolled is measured at the roll groove bottom center position on the outlet side of the final stand and at the position orthogonal to the roll groove bottom center line, and the roll clearance of the final stand is adjusted so that the outside diameter deviation rate DD will be -1.0<=DD<=1.0, provided DD=(DF-DG)/ DG×100 (DG is outside diameter of material at the roll groove bottom center position, and DF is outside diameter of a material at the position orthogonal to the roll groove bottom center line). This can prevent the inside flaws caused when the mandrel bar is drawn, thus improving the quality and yield.
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