PURPOSE: To easily manufacture the pipe with superior roundness, by first forming the steel sheet into a pipe blank with approximately round section, after that, by applying O-forming work separately for every specified length using O-press dies shorter than the length of product pipe.
CONSTITUTION: The flat steel bar 1 as the raw material is placed between the upper dies 21, 22, for use of C-press and the punch 23 for use of U-press, and between the lower dies 24, 25, and the knock-out 26. The upper dies 21, 22, are brought down so as to give the C-press to the flat bar 1, and then, the punch 23 forms the flat bar 1 into a pipe 11 with U-section. After that, the punch 23 is drawn away from the U-pipe 11, and the lower dies 24, 25, are closed inward so as to compress the U- pipe 11 from both sides; hereby, the opening 12 is closed and a long pipe blank 13 with approximately round section is prepared. This pipe blank 13 is sent to the separate type O-press-dies 3 and is applied with O-press froming by the upper die 31 and lower die 32, which has die faces 33, 34, of semicircular section and the length l3 shorter than the total length l1 of the pipe blank 13. According to this method, the opening 12 is tightly colsed, and the seam pipe 14 is obtained; by welding this seam portion, the steel pipe is manufactured
NAGAI NOBUYUKI
YAMAGUCHI YOSHIHIRO
HATSUTORI SHIGEO
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