Extrusion machine and method of continuous tubular extrusion

Abstract

The invention describes a machine and a process whereby a material of unlimited length is continuously extruded into a tubular shape. Two annular toruses have their inner rims connected to rotating drive shafts by leaf springs. The exterior toroidal surfaces have suitable shaped grooves on them. The toruses are squeezed against each other radially by suitable means so as to cause a maximum radial deformation in each of them of a magnitude substantially greater than 0.2 percent but less than an amount that would cause permanent set in the torus material or the leaf springs. This deformation forms a contact length between the two toruses. A further requirement of the radial deformation on the two toruses is that the contact length between them be at least twice the extrusion length necessary for the contemplated extrusion. A bridge die supported by a die stem is located substantially at the center of the contact length. A heated material of unlimited length is fed between the toruses into the chamber formed by the grooves. The toruses are rotated by rotating the drive shafts. The incoming material is pushed by the friction between the toruses and the material. The extrusion length is the minimum contact length between the toruses and the extruding rod which enables the friction drive stresses to generate a pressure at the die sufficient for the contemplated extrusion. Since the contact length between the toruses is greater than twice the necessary extrusion length, the incoming material extrudes through the bridge die. In the die the material splits into a plurality of streams and is then recombined to form a tubular product of unlimited length.