Apparatus for hydrostatic extrusion of thermoplastic polymers

A hydrostatic extrusion press provided with means for applying extrusion pressure to extrude a generally cylindrical semi-crystalline thermoplastic polymer preform having an outer surface and a bore surface whereby the preform is forced to pass in a solid state through an annular orifice defined by the surface of a die section in spaced relationship with the surface of a mandrel-head supported by a mandrel and means for rigidly aligning the press during extrusion, the press comprising:

• (a) an outer support means having two ends
• (b) a container means aligned within one end of the outer support means and including a shell having an outer surface and an inner surface and two end surfaces, a plug and piston assemblage closing one end of the shell,
• (c) the die section being a continuous surface with respect to one end of the inner surface of the shell of the container means and including a converging first section, a first generally cylindrical land surface axially aligned with respect to the apparatus, a second generally cylindrical land surface larger in diameter than the first generally cylindrical land surface and parallel thereto and a diverging conical surface connecting the first and second generally cylindrical parallel land surfaces and forming an angle .alpha. of between 15.degree. and 45.degree. with the axis of the apparatus,
• (d) an extrudate receiving means aligned within the other end of the outer support means and including a shell having an outer surface and an inner surface and two end surfaces, a mandrel having two ends coaxially aligned within the outer shell and generally in spaced relationship to the inner surface thereof,
• (e) a generally conical mandrel-head supported on the other end of the mandrel and in spaced relation with the surfaces of the die section, having a recessed base surface, a generally cylindrical tapering upper portion which forms an angle .beta. of between 20.degree. and 50.degree. with the axis of the apparatus and a generally cylindrical nose portion,
• (f) an annular orifice formed by surfaces of the mandrel-head and the die section comprised of:
• (i) a generally converging conical entrance,
• (ii) a generally cylindrical sealing zone,
• (iii) a generally conically shaped expanding zone having a generally converging cross-sectional area and a diametrically diverging geometry,
• (iv) a generally cylindrical sizing zone parallel to the sealing zone and having a smaller cross-sectional area and a median diameter which is at least 100 percent larger than the median diameter of the sealing zone, and
• (v) transition zones of desired radii and smooth surfaces between any two of the zones whereby the billet is substantially simultaneously expanded circumferentially at least 100 percent and axially elongated at least 50 percent, and
• (g) sealing means formed by the surfaces of the mandrel-head in contact with the inner surface of the billet and the die surfaces in contact with the outer surface of the billet in the container assembly whereby leakage of fluid is prevented during loading and prior to extrusion and a film of the hydrostatic fluid is formed on the surfaces of the billet during extrusion
• (h) a first pressurizing means disposed adjacent ones of the two ends of the outer support means and contiguous with the plug and piston assembly and one end surface of the container assembly of (d) whereby pressure for extrusion is applied to the preform, and
• (i) a second pressurizing means disposed adjacent the opposite end of the outer support means and contiguous with one end of the extrudate receiving means and coacting with the first pressurizing means to rigidly align the extrusion press.