| 摘要 |
PROBLEM TO BE SOLVED: To roll a taper thread for tube to a tube end part of a thin wall steel tube. SOLUTION: In rolling a taper male thread for tube to a tube end part of a thin wall steel tube, a core jig 1 inserted to the tube end end inside of the thin wall steel tube is used. A parallel male thread 1a, which has the same pitch as a taper male thread and in which a root diameter d1 is made smaller than the root diameter at a thread tip part of the taper male thread and an outer diameter (d) is made smaller than that at the thread tip part of the taper male thread, is formed on the outer circumference. A jig extended part 1c of small diameter, which is smaller than the min diameter of the thin wall steel tube after the taper male thread is rolled, is arranged in continuing to the thread forming part 1b of the parallel male thread 1a. Further, a spherical body projecting part 1d which is energized in the protruding direction, is arranged to outer circumferential six places of the jig extended part 1c so as to have a diameter larger than the inner diameter of the thin wall steel tube. A hexagonal hole shaped recessed part 1f is formed to the side face of the opposite side to the jig extended part 1c in a thread forming part 1b.
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