| 摘要 |
PURPOSE:To eliminate a gap defect and to enable effective bulging of a longitudinal pleat by forming a blank material pipe while working the end part of the longitudinal pleat with a press die simultaneously with compression of said pipe. CONSTITUTION:Pressing projection parts 25, 25 in right and left press dies 24, 24 for the end part of a longitudinal pleat are inserted into the groove for the die cavity of a forming die 22 from the end part thereof. Right and left pressing rods 26, 27 are advanced toward the center to bring the top ends thereof into contact with the end face of a blank material pipe 1 thereby sealing the pipe when a liquid pressure for bulging is introduced into the pipe. A die clamping force W is acted on an upper guide die 20 and a liquid pressure P for bulging is introduced into the pipe 1 through an introducing hole 29 for the bulging liquid, then the outside surface of the blank material pipe begins to bulge. An axial compressive force F is acted on the right and left rods 26, 27 to compress the pipe 1 and at the same time the dies 24, 24 are advanced toward the center. The parts 25, 25 of the press dies for the end part of the longitudinal pleat progress bulging while pressing the respective end parts of the longitudinal pleat. The formation is completed at the die cavity length l of the longitudinal pleat. The liquid pressure P for bulging in the pipe is increased in this stage, whereby a longitudinally pleated pipe 5 having no gap defect in the central and end parts is obtd. |
