| 摘要 |
A cylindrical billet of superconducting material is enclosed by a copper sheath circumferentially, and by a lid and nose of copper at its longitudinal ends. A short cylindrical nose piece of lesser diameter than the billet, is attached at the billet's front end. At the rear end of the billet, an annular ring of copper is positioned. The billet is enclosed in a liner leading to a convergent conical die. Longitudinal force is applied by a ram to the annular ring, which pushes against the outer periphery of the billet at the rear end in a direction toward the die orifice. The stepped nose piece deforms against the die. During an initial period wherein no extrusion takes place, the nose piece exerts an opposite reactive force on the center of the billet, moving the center material toward the ram. As a result of these two opposite actions on the billet, the central longitudinal portion of the billet is pushed back (upset) toward the ram and deforms into the opening of the annular ring. As ram force further increases, the billet breaks through the die opening and actual extrusion of superconducting rod commences. As a result of using a complementary combination of annular ring and stepped nose piece, wherein the stepped nose piece diameter approximately equals the diameter of the annular ring opening product yield is significantly increased. |
