Cylindrical article made of fiber-reinforced resin material, injection molding mold thereof, and injection molding method

An injection molding method for forming a cylindrical article, the injection molding method for the cylindrical article comprising:

• injecting a molten resin containing reinforcing fibers from a gate into a cavity to join molten resins containing the reinforcing fibers together in the cavity to form a weld line;
• installing a center pin shaping an inner peripheral surface side of the cylindrical article and an external piece shaping an outer peripheral surface side of the cylindrical article;
• forming the cavity between the center pin and the external piece;
• and
• moving the external piece with respect to the center pin to change an interval between the external piece and the center pin, to forcibly cause the molten resin containing the reinforcing fibers in the cavity to flow, and to disturb directions of the reinforcing fibers at the weld line.

A cylindrical article made of a fiber-reinforced resin material and formed by injecting a molten resin containing reinforcing fibers from a gate into a cavity of an injection molding mold having a center pin shaping an inner peripheral surface side of the cylindrical article, and an external piece shaping an outer peripheral surface side of the cylindrical article, the cavity being formed between the center pin and the external piece, and the external piece being moved with respect to the center pin to change an interval between the external piece and the center pin to forcibly cause the molten resin containing the reinforcing fibers in the cavity to flow while disturbing directions of the reinforcing fibers at the weld line, said cylindrical article comprising:

• a cylindrical portion;
• and
• a hollow circular plate at an end of said cylindrical portion;
• wherein said cylindrical portion and said hollow circular plate are made of a resin containing reinforcing fibers and have a weld line;
• and
• wherein orientations of the reinforcing fibers in the resin at the weld line are disturbed by the movement of the external piece with respect to the center pin such that the reinforcing fibers at the weld line are tangled.