Method of and apparatus for indirect extrusion

Claim 1

An indirect extrusion press of the double-stem type for forming a tubular product by extrusion, said indirect extrusion press comprising: (a) a billet accommodating container; (b) a press stem and a die stem arranged in opposed relation to each other on the center line of extrusion on opposite sides of said billet accommodating container so that, during use of said indirect extrusion press, a billet placed onto said billet accommodating container is upset by said press and die stems and thereafter extruded through a die on the forward end of said die stem by moving said billet accommodating container and said press stem together toward said die stem, said press stem having a longitudinally extending hole extending along its longitudinal axis, the surface of said longitudinally extending hole being parallel to the press direction, said press stem having at its container end a large-diameter portion larger than the opening in said billet accommodating container such that, during use of said indirect extrusion press, said large-diameter portion of said press stem abuts the adjacent end face of said billet accommodating container; (c) a mandrel inserted in said longitudinally extending hole in said press stem and movable in the press direction, a gap being formed between the outer surface of said mandrel and the surface of said longitudinally extending hole; (d) means for moving said mandrel axially into and out of said billet accommodating container so as to pierce a billet located in said billet accommodating container; and (e) a blister preventing closure means which comprises said large-diameter portion of said press stem and a dummy block mountable on said large-diameter portion of said press stem, said dummy block having a center hole sized, shaped, and positioned to allow said mandrel to extend therethrough with little clearance, said blister preventing closure means comprising a distal cylindrical portion and a proximal cylindrical portion, said proximal and distal cylindrical portions being concentric to one another and being joined by a planar annular shoulder the entirety of which is flat and perpendicular to the center line of extrusion, said proximal cylindrical portion having an outer diameter that is not fittable in the openign in said billet accommodating container and said distal cylindrical portion having an outer diameter that is fittable in the opening in said billet accommodating container and having a working surface that comes into contact with the billet during use of said indirect extrusion press, the entirety of said working surface being perpendicular to the center line of extrusion.