REDUCED THICKNESS ROLLING METHOD BY REDUCED THICKNESS ROLLING DEVICE FOR PIPE END IN INSTALLATION FOR PRODUCING SEAMLESS STEEL PIPE

摘要

PURPOSE:To obtain a seamless steel pipe which is smoothly reduced in thickness at the end of a hollow blank pipe by adjusting relatively the revolving speed and rotating speed of rolling rolls to prevent the roling rolls from exterting rotating torque on the end of the hollow pipe. CONSTITUTION:The rear end of a hollow blank pipe 6 is fed by feed rolls 39 into the working center of a reduced thickness rolling device 12 for rear end. A mandrel 13 and rolling rolls 14 are advanced respectively in the axial direction by a set distance and thereafter the rolls 14 are set in rolling down positions. A driving device 21 for revolution and a driving device 28 for rotation are operated to bring the rolls 14 into contact with the outside peripheral part at the end of the pipe 6 in the state of revolution and rotation. The revolving speed and rotating speed of the rolls 14 are relatively adjusted to prevent the rolls 14 from exerting rotating torque on the end of the pipe 6. The pipe 6 is made movable axially in a non-rotating state. The rolls 14 roll the end of the blank pipe to reduce its thickness at a preset ratio of thickness reduction, that is, the ratio of the thickness reduction at which the increased thickness to be added to the end of the pipe 6 by reducing with a succeeding stretch reducer 8 can be offset.