PURPOSE:To smoothly carry out the roll forming of the disk type ring body, by assembling the vertically roll forming roll in the stationary housing, by settling the dimensional reference point for the disk type ring body, and by coping with the increase of diameter of ring body depending on the radial movement of the forming roll for rolling in the direction of thickness. CONSTITUTION:The roll forming of the disk type ring body 16 is carried out under a condition that the point M of contact between the outer diameter of the ring body 16 and the roll 35 is approximately constant from the start of rolling till the end of rolling. The ring body 16 is placed at the position of point M by moving rolls 18, 17 and 27. Then, the rolls 18, 34 and 35 are respectively started; the roll 34 is gradually screwed down, and the vertical rolling for the ring body 16 is started. When the rolling further proceeds, the outer diameter of ring body 16 increases, and the displacement of the point M is detected by the detector 42, and the roll 17 is moved near the roll 18 by the mover 24 according to this detecting signal; hereby, the rolling in the direction of thickness for the ring body 16 is performed. On the other hand, the mover 31 is actuated by the signal from the detector 30 for detecting the quantity of spread-out due to the roll 27; hereby, the rolls 17, 18 and 27 are simultaneously moved radially the same distance.
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