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

摘要

A travelling mold tunnel for forming double walled corrugated tube has a first portion for forming corrugated tube and a second belled portion for forming a cuff portion suitable for coupling with another tube. At the upstream end of the belled portion, radial small diameter passages are provided so that a pressure differential may be set up between the inside and the outside of a first parison within the belled portion. Thus, vacuum may be applied through the radial passages to allow an inner parison to laminate with the first parison over its inner surface in the belled portion. The first parison is drawn into the passages in protruding balloons. These may be ruptured. Alternatively, positive pressure may be used. In this case, the balloons may be ruptured inwardly.