| 摘要 |
PCT No. PCT/GB87/00571 Sec. 371 Date Apr. 7, 1988 Sec. 102(e) Date Apr. 7, 1988 PCT Filed Aug. 13, 1987 PCT Pub. No. WO88/01207 PCT Pub. Date Feb. 25, 1988.A process for making a tube bend of a predetermined wall thickness from a length of straight tube comprises forming the straight tube to have a quasi-elliptical cross section and irregular wall thickness which has a maximum value on one side of the major axis of the quasi ellipse, expanding the quasi-elliptical tube to cause the wall thickness on the other side of the major axis to be reduced and bending the tube about an axis located on said other side of said major axis. Apparatus suitable for performing the process comprises a die (2) formed with an oblique inclined converging passage (3) of circular cross section at one end changing progressively to quasi-elliptical cross section at the other end and a curved mandrel (6) having a portion (8) which changes from quasi-elliptical cross section at the shank (7) to circular cross section at the curved portion (9).
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