| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method of a circular steel pipe by which thin and thick circular steel pipes are obtained efficiently. SOLUTION: A steel plate 1 having a prescribed width is successively stepwise hot-formed from a circular-arcuate plate body 1B into a round-shaped steel pipe 1C by a plurality of stages of roll type forming means 21, 26, 31, 36, 41 after wholly heating the steel plate up to a prescribed temperature or the vicinity of it by a heating means 16 and, next, passing through a hot-forming part 20 while conveying the heated steel plate 1A in the length direction. The circular steel pipe 5 is manufactured by joining 4 the free ends of the round-shaped steel pipe 1C by welding in the state that the free ends are opposed to each other while restraining the round-shaped steel pipe 1C from the outer periphery. By performing the hot-forming by the plurality of stages of the roll type forming means while conveying the heated steel plate in the length direction, the forming from the steel plate into the round-shaped steel pipe is performed like the flow production and, by joining between the free ends of the round-shaped steel pipe by welding, the thin and thick circular steel pipes are manufactured efficiently and at a low cost. COPYRIGHT: (C)2007,JPO&INPIT |
