| 摘要 |
<p>The present invention provides a multi-layered corrugated cylindrical tubular structure formed from a strip (10) of material having one edge reduced in diameter by a step portion (16) and reduced in length by corrugations (18). The strip may be formed on a forming arrangement comprising confronting corrugating rollers (74, 76) having regions formed with corrugating undulations of differing height and an un-corrugated portion.</p> |
