| 摘要 |
Double-walled thermoplastic tubes, with corrugated outer walls (18) and smooth inner walls (24) are formed with integral bell sections spaced along the tube. The outer, corrugated wall is formed with a bell section. One of the walls (18) is pierced between the ends of the bell section (34) to allow the escape of air, and the inner wall (24) is pressed outwards into engagement with the bell section (34) of the outer walls (18). |
