Method and apparatus for elongating metal tubes by means of a mandrel mill

摘要

In a method of elongating a metal tube by means of a mandrel mill, a tapered mandrel bar is inserted into a hollow piece and the feeding speed of the mandrel bar is controlled so as to change the length by which the mandrel bar projects beyond the delivery end of the final stand of the mandrel mill at the point of time when the leading end of the hollow shell is gripped by the rolls in the final stand. As a result, the wall thickness of the hollow shell is altered to permit the rolling of hollow shells of many sizes with different wall thicknesses using a single mandrel bar.