Abstract: A method of manufacturing extruded seamless hollow materials characterized in that, prior to extruding a hollow billet from container liner through extrusion dies, a process wherein a centering jig for holding the tip portion of mandrel at the center of extrusion is provided on the extruding side or in the extrusion dies on the extruding side of the container liner, a process wherein the tip portion of mandrel is inserted into the centering jig to be held and a process wherein the hollow billet is pressurized to fill up said billet in the container liner are included.

Abstract: A method and apparatus utilizing a core is located at a central portion of a molten metal storing portion in a vertical semi-continuous mold. The molten metal is poured into the molten metal storing portion, and casting takes place with the inner diameter of a solidified distal portion of the molten metal being controlled by a distal portion of the core. This approach provides a reliable method for the manufacture of high-quality hollow billets which are free from internal defects.