| 摘要 |
A revolution center line (C) of a roll (R) is made eccentric with respect to an axis (L) of an elliptic tube (1). The eccentric amount epsilon is set such that when the revolution radius of the roll (R) is gradually reduced from a state in which the roll (R) is not in contact with any part of the elliptic tube (1), the roll (R) contacts one (4) of the two protuberances (4, 4) which is located on the opposite side to the eccentric direction generally earlier than any other part of the eccentric tube (1). The roll (R) is revolved and reciprocally moved in a direction of the revolution center line (C). At least at one end portion of the reciprocal movement, the roll (R) is moved towards the revolution center line (C) side. By repeating this procedure, the roll (R) is press contacted with the first-mentioned protuberance (4) so as to crush it for elimination.
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