Apparatus for the hydrostatic extrusion of thermoplastic polymers

Claim 1

Apparatus whereby a thermoplastic polymer preform is hydrostatically extruded while in a solid state into a conduit by compressive pressure, comprising: (a) outer support means having two ends connected by load supporting members, (b) a hydraulic pressurizing means axially aligned and contiguous with one end of the outer support means, (c) a container means including a shell having an outer surface and an inner surface and two end surfaces coaxially aligned within and contiguous with the hydraulic pressurizing means, (d) a die section formed on the inner surface of the shell at the other end thereof 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 α of between 15° and 45° with the axis of the apparatus, (e) an extrudate receiving means coaxially 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, one end surface being contiguous with the end of the container assembly having the die section, (f) a base section contiguous with the other end of the end surface and supporting the extrudate receiving means and contiguous with the other end of the outer support means, (g) a mandrel coaxially aligned within the outer shell and having two ends, one end of which is fixedly attached to the base section and the other end supporting a mandrel-head in spaced relation with the surface of the die section, and having a recessed base surface, a generally conical upper portion which forms an angle β of between 20° and 50° with the axis of the apparatus and a generally cylindrical nose portion, (h) an annular orifice formed by the spaced surfaces of the mandrel-head and the die section comprised of: (i) a generally converging 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 (i) 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.