| 摘要 |
PURPOSE:To obtain a synthetic resin tube always accurately wherein a spiral rib is formed on its inner surface by a method wherein an auxiliary core supporting a parison from an inner side of the tube is freely rotatably provided following rotation in a peripheral direction of the parison the outer peripheral surface of which is extruded. CONSTITUTION:An extrusion molding metal mold 1 is equipped with a metal mold body 2 and an auxiliary core 3. The metal mold body 2 is equipped with a land 21 and a fixed core 22, and a spiral groove 24 having a specific slant angle to an axis 23 is provided on an outer peripheral surface of the fixed core 22. The auxiliary core 3 is so arranged that an auxiliary core body 34 is put between thrust ball bearings 32, 33 fitted to a supporting shaft (a ring supporter) extending from the fixed core 22 along the axis 23. Then, the auxiliary core 34 is freely rotatably supported around the supporting shaft 31 with the thrust ball bearings 32, 33. Thereby, frictional resistance in a rotating direction between an auxiliary core outer peripheral part and a parison inner peripheral surface is decreased. |
