Patent ID: 7328597

Claim:
A circumferential length correcting method for a metal ring, comprising the steps of: a circumferential length measuring step for measuring the actual circumferential length of the ring under tension while passing the metal ring around a driving roller and a driven roller that are capable of being displaced away from each other, and displacing the driving roller and the driven roller away from each other; and a circumferential length correcting step for correcting the circumferential length of the ring by holding the driving roller and the driven roller at a predetermined distance, and displacing a circumferential length correcting roller, which is positioned between the driving roller and the driven roller, in a direction intersecting the direction of displacement of the driving roller and the driven roller in which the metal ring is extended by a predetermined distance determined based on the actual circumferential length of the ring measured in the circumferential length measuring step, wherein, before said circumferential length correcting step, the method further comprises the step of an arc-shape imparting step for imparting an arc shape conforming to the shape of the circumference of the arc-shape imparting roller to the metal ring by displacing an arc-shape imparting roller, which has a circumference having an arc shape with the center protruding outward in lateral cross section, the diameter of which is smaller than those of the driving roller or the driven-roller and the circumferential length correcting roller and is positioned inside said metal ring, by a predetermined distance in a direction in which the metal ring is extended.