| 摘要 |
PURPOSE:To make it possible to extrude two or more kinds of tubular bodies different in outer diameter and wall thickness with a single die by a method wherein the ratio of the length of a restrictor part to its gap size is made larger than that of the length of a parallel part near an outlet to its gap size. CONSTITUTION:A die A straightens and shapes molten resin, which is extruded from an extruder B, so as to extrude it from the outlet of a resin flow path 3 in the form of parison C. By passing through the resin flow path 3, the molten resin is subjected to elastic deformation effects at a spider part 43 and a restrictor part 31. The resultant elastic deformation memory given to the resin is relieved at a parallel part 33 near the outlet. Since the ratio l2/t2 of the length L2 of the restrictor part 31 to its gap size t2 is made to be larger than the ratio l1/t1 of the length l1 of the parallel part 33 near the outlet to its gap size t1 and consequently the relieving effect of the elastic deformation memory at the parallel part 33 near the outlet is very weak, the Barus effect is very strongly revealed at the die A. Accordingly, at the forming of a parison C with a forming device D, the outer diameter of the parison can be set with freedom within the wide range, in which the parison C is allowed to expand. Or two or more kinds of tubular bodies different in outer diameter can be extruded with a single die A. |
