Method of longitudinal rolling of seamless pipe

摘要

A method of longitudinal rolling of seamless pipes in a continuous rolling procedure on an internal tool in a multiple-stand rolling train, wherein the rolls of successive rolling stands are mounted off set relative to each other. In accordance with the present invention, in a first of only two successive rolling passes, a roll thickness reduction is produced with opened roll groove sides in the roll groove bottom which reduction corresponds to or is slightly greater than the roll thickness of the finished pipe. In the second rolling pass, the side portion of the first rolling pass is reduced in the direction of the width to the wall thickness of the finished pipe in the roll groove bottom of the second rolling pass. By simultaneously applying a controlled tensile force on the pipe between the two rolling passes, the increase of the circumference of the pipe due to spreading is reduced by stretching the pipe in the direction of its longitudinal axis without reducing the wall thickness or with only a slight reduction of the wall thickness.