VERFAHREN ZUR HERSTELLUNG VON ROHREN.

摘要

In the manufacture of tubes provided with elevations or recesses, an extrusion billet is preformed (1) and compacted (2) by isostatic pressing whereupon the extrusion billet is extruded (3) into a tube. The extrusion billet consists of at least two materials, forming material (21) and tubular material (22). The forming material is applied to or inserted into a preformed body of tubular material, or inversely, before the body is compacted into an extrusion billet. Alternatively, tubular material and forming material are supplied in powdered state to a mould and are jointly compacted into an extrusion billet. During the extrusion, the forming material forms elevations or recesses in the tubular material. After the extrusion, the forming material is removed (4), preferably by pickling.