Continuous pipe rolling process

Abstract

A tubular blank is continuously rolled into a pipe through a mill which has a plurality of roll sets each comprising grooved driven rolls providing substantially circular passes of progressively reduced diameters. While the blank is passing through the roll sets, its interior is supported by a mandrel. The tail end of the mandrel is held by a pushing device when rolling is started. Namely, rolling is started by pushing the mandrel into the blank. The pushing of the mandrel is stopped between the time when the front end of the blank has passed the last roll center line in the first half roll set group and the time when it has reached before the roll center line of the last roll set. The tail end of the mandrel remains unreleased while rolling is continued. Then, the mandrel is released between the time when the tail end of the workpiece has passed the roll center line of the second last roll stand in the first half roll stand group and the time when it has reached before the roll center line of the last roll stand. After the mandrel has been released, too, the workpiece is continuously rolled through at least one stand. When the mandrel and workpiece have cleared the rolling mill, the mandrel is withdrawn from the workpiece.