NO134514C

1314404 Pipes DYNAMIT NOBEL AG 2 Sept 1970 [3 Sept 1969] 42065/70 Heading F2P A pipe 11 having integral sockets is continuously made by winding a band of material 10 on a cylindrical mandrel 1, the band having on the edge a tongue, and on the other edge a bead defining a groove for the tongue, with adjacent laps overlapping, and locally increasing the inner diameter of the pipe in various places at the winding stage for the sockets by intermittently increasing and subsequently decreasing the mandrel diameter, or interposing at intervals suitable means between the band and the mandrel. A roller 12 presses adjacent laps together immediately after the material 10 is wound on to the mandrel 1, the roller being radially adjustable during operation to accommodate diameter variations of the pipe 11. The pipe diameter is varied by expandable segments in the mandrel 1, or a ring 7 with a longitudinal slit introduced over the mandrel and travelling along the mandrel with the wound pipe 11, or a winding band introduced on to the mandrel prior to the material 10. The diameter transition is by a taper, and this taper can occur at both ends of the increased diameter portion, the pipe 11 being cut halfway along this portion after removal from the mandrel 1, to form two pipes with sockets. The pipe material 10 is a thermoplastic plastics, e.g. polyethylene or polyvinylchloride.