PURPOSE: To roll a blank pipe to decrease its wall thickness toward its outer end-part and to reduce its cut-off length, by inserting a mandrel into the inside of the end part of pipe and, bringing rolling rolls into rolling contact with the outer circumference of pipe to roll the pipe by revolving the rolling rolls.
CONSTITUTION: A mandrel 13 and rolling rolls 14 are advanced in the axial direction to set the rolls 14 on a rolling position when detected that the rear end-part of a blank pipe 6 is inserted to the center of a rolling device 12 for reducing pipe-end wall-thickness. Next, the pipe is held by pinch rolls 38 while the mandrel 13 is advanced to be inserted into the pipe 6. The rolls 14 are then rotated in contact rolling while the rolls 14 are revolved in the circumferential direction of the outer surface of the pipe by actuating a driving device 21 for revolving and a driving device 28 for rotating. Then the device 12 is retreated relatively to the pipe 6 by means of wheels 37. At this time, the mandrel 13 is protruded by synchronizing the movement of the device 12 by means of a hydraulic device 40.
EJIMA AKIO
ASANO SEIICHI
NAGAI TOYOHIRO
