| 摘要 |
A pipe in which polygonization is substantially eliminated is manufactured by a reducer with a grooved roll with a groove having a groove bottom zone including the center of the groove in the roll axial direction and flange zones adjoining both sides of the groove bottom zone. The groove surface has a friction distribution in the roll axial direction such that the frictional force with respect to a material being rolled in the groove bottom zone is larger than the frictional force with respect to a material being rolled in the flange zones. This friction distribution can be achieved by working the groove surface so that the surface roughness of the groove bottom zone becomes greater than the surface roughness of the flange zones or by applying a lubricity modifier which differs with respect to amount and/or type between the groove bottom zone and the flange zones.
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