| 摘要 |
PURPOSE:To reduce man power and to improve the dimensional accuracy of a pipe for uniforming the processing degree through its whole length by processing pipe stock by specific process in obtaining an outside and inside polygonal pipe having an expanding part of polygonal outside-shape on the way of its longitudinal direction. CONSTITUTION:In a round pipe stock, the outer surfaces of small diametral forming parts L2, L2 are processed by cutting, except an expanding part L1 to be left unformed consisting of a part (l1) to be formed into an expanding part of product and the parts (l2) at both sides of the part (l1). At the same time, radially expanding parts T1, T1 are formed by cutting. Next, the whole length of the pipe is expanded into a rough hexagonal shape by using a rough polygonal plug and is heat treated for softening it. Only the part L1 is successively drawn by using a polygonal plug, and then zones corresponding to the radially expanding taper-parts T1 are formed into radially contracting taper- parts T2, T2 by round off cutting the outersurfaces of parts T1, T1. Further, the expanding part 1 of a final product is formed at the central part by cutting. Next, the pipe is finally drawn from its ends to the terminal ends of the radially contracting parts T2, T2 by the prescribed processing degree by using a polygonal die and a polygonal plug to finish it to the dimensions of a product. |
