| 摘要 |
PROBLEM TO BE SOLVED: To reduce a frictional force generated between a hollow product, a die and a former by providing a plurality of protrusions each having a radius of curvature in its section of a specific value or more on a side circumferential surface of the former. SOLUTION: Protrusions 10 provided on a side circumferential surface of a former 3 each has a radius of curvature in its section of 0.5mm or more, and its shape is not particularly limited. As the former with the protrusions 10, a substantially conical former 3 having a plurality of protruding strips circulated on the circumferential surface or a former 3 having protrusions 10 each of a substantially semispherical state is used. The strip of the semispherical state may be a sectional circular shape or a semicircular doughnut-like ring. These protrusions 10 may be provided integrally with a body of the former 3 or separately therefrom. A hollow product 1 is heated in an oven 4, drawn out of an apparatus through between an inner periphery of a molding hole of a die 2 and an outer periphery of the former 3 to become a tubular body 7. And, an end of the body 7 at its downstream side is grasped by a clamp 5, and moved rightward at a constant speed by a tensile unit. |
