| 摘要 |
Including: an intermediate-formed product forming process forming a shoulder part 3, a pipe part 18, a tapered part 17 and an aperture-end part 16 above a trunk part; and a screw-forming forming a screw-thread part by an inner mold 64A and an outer mold 64B in which the pipe part 18 is sandwiched therebetween, an outer diameter of the pipe part is formed to an intermediate diameter between a ridge diameter and a bottom diameter of the screw-thread part in the intermediate-formed product forming process, and in the screw-forming process, the screw-thread part is formed from the tapered part to the pipe part so as to form a screw-starting part is formed at an intermediate position of the tapered part, a height of a first step of a right-hand screw-type protrusion of the inner mold is formed to be lower than a height of a second and subsequent steps in an angle range of 90° circumferentially continuing from the screw-starting part, and rolling a screw-forming tool having the inner mold and the outer mold with revolving in a left-hand direction seeing from an aperture-end toward a bottom part of the intermediate-formed product. |
