| 摘要 |
PROBLEM TO BE SOLVED: To obtain a hollow body or pipe with specified outside diameter and wall thickness while reducing reheating time and preventing the danger of the bottom being broken through by using a mandrel with a spherical end when the hollow material pipe, wherein the bottom material integrally formed at the time of boring the hollow material pipe is reduced in thickness from the edge area toward the center, is punched. SOLUTION: A steel ingot or a continuous-cast steel is heated to the plastic working temperature, and with dies and a punching mandrel 2, rolling into a hollow material pipe is done so that the bottom is shaped into a truncated cone. With the dies, the material of a bottom portion 6' is reduced in thickness from the edge area toward the center and the bus line contour of the bottom portion 6' is brought into agreement with a hyperbolic binding string through the first approximation. Then the hollow material pipe is punched into the final size with a mandrel 17 on which a spherical end area 18 formed and one or more ring dies 7, and when necessary, the material is reheated between passes so that the bottom 6" is remained on the hollow material pipe or cut from the hollow material pipe. Thus, the seamless hollow body with a bottom or a seamless pipe of 200-1,450 mm outside diameter and 20-250 mm wall thickness can be obtained.
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