| 摘要 |
An expandable tube portion (4) including slots (5; 5a to 5e) arranged in a staggered fashion is expanded. When the expandable tube portion (4) is expanded, the individual slots (5b) open to a cut end portion (3) of the expandable tube portion (4) are transformed to open in V-shape while the whole body of the expandable tube portion (4) is transformed to a lattice configuration. Hence, the tube expansion only need to apply a working force required to bend intersections of the lattice configuration, resulting in the reduction of the working force for tube expansion. As a result, the working force for tube expansion does not open a butt connection portion of a subject matter, negating the need for previously weld bonding the butt connection portion of the subject matter. |
