METHOD AND APPARATUS FOR FORMING A DOUBLE WALLED THERMOPLASTIC TUBE WITH INTEGRAL BELLS AND TUBE PRODUCED

摘要

The tube is formed by extruding a first tube into a travelling mould(10) and forming a corrugated outer wall and extruding a second tube into the first tube to form a smooth inner wall. Integral bell sections are moulded into the outer wall and one of the tubes is pierced between the ends of each outer wall bell section so as to allow the escape of air from between the walls. The inner wall is pressed into continuous contact with the outer wall along each outer wall bell section.