A mandrel mill is provided which can perform elongation rolling with a markedly increased working ratio and dimensional accuracy on a material which is inherently difficult to roll such as a hollow shell made of stainless steel or a thin-walled material. A mandrel mill for manufacturing a mother tube by performing elongation rolling of a hollow shell comprises a plurality of roll stands, having at least one 4-roll stand for wall thickness reduction of a hollow shell and at least one 2-roll stand including the final stand downstream of the 4-roll stand.

Continuous mandrel rolling mills consist of between 7 and 9 closely arranged in-line rolling stands which are offset by 90° to their adjacent neighbours and inclined at 45° to the horizontal.  The circumferential speeds of the rolls are adjusted to one another in accordance with the reductions in cross-sectional area, so as to ensure that there are no appreciable tensile or compressive forces acting on the stock between the stands.

There is a certain clearance between the mandrel bar and the pipe material in the region of the flanks of the oval pass formed by the two-high rolls . In the last round pass, this clearance is evenly distributed around the entire circumference in order to enable the tube to be stripped from the mandrel bar.