| 摘要 |
PROBLEM TO BE SOLVED: To obtain a product without a molding defective and generation of burr at a tip edge of a core cylinder by disposing the tip edge of the core cylinder by being depressed more than a tip edge of a short tube body in an axial direction by a specified value, in a short tube with inside surface spiral guide path in which the core cylinder is disposed within the short tube body and the spiral guide path is provided between the core cylinder and the short tube body. SOLUTION: A mold for reaction injection molding 2 which is suitably used for molding a short tube with spiral guide path which is suitable to be used for a natural flowing down type vertical drainage conduit is formed by disposing tip edge forming parts 221, 231 of core cylinders in a pair of inner molds 22, 23 so as to be depressed more than tip edge forming parts 211, 211 of a short tube body in an outer mold 21 in an axial direction by a length L1 of 0.5 mm or more. As a result, the short tube can be molded by a reaction injection molding method without involving air bubbles at tip parts of the core cylinders and the surrounding parts and requiring burring work. Resin for molding the short tube with spiral guide path is not limited in particular and thermoplastic resin such as polyvinyl chloride or methacrylic resin is used.
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