New process for the hot forming of the integrated socket on underground drainage pipes made of high modulus polypropylene with a compact or multilayer wall structure

In underground plastic drainage pipes the integrated socket joint technology is now used widely in PVC pipes with a compact or multilayer wall. On the other hand, in PP and HDPE pipes this form of connection, despite its well-known advantages, is still not widely used. The reason for this is basically due to the difficulty of developing a process for hot forming that can be implemented in industrial machines to be installed in extrusion lines.

Despite this, the use of high modulus underground PP drainage pipes, i.e. PP-HM, and improved material formulations, typical in the structure of multi-layered walls, have made it convenient to create pipes with a ring stiffness class of SN16 in the range of diameters up to 500 mm and over 500 mm. In these types of pipes, the creation of the integrated socket with the hot forming procedure, which is repeatable, reliable and compatible with the potentialities of the extrusion lines, is a technical imperative to ensure these pipe systems have that efficiency that is only obtainable with the integrated socket joint, just as it was for the corresponding PVC-U pipes.

In many belling processes there are numerous physical phenomena of the pipe being machined that need to be managed: the thermal state of the end of the pipe to be belled, the forming process plastic deformation the profile of the socket, the calibration of the inner dimensions of the socket in relation to the varying sizes of the extruded pipe, the stability over time of the forms and dimensions of the socket. The well-known belling procedures used in the production of PVC-U pipes cannot be applied with PP and HDPE pipes, since the physical properties of the PP and HDPE pipes are very different to those of PVC-U pipes.

This document describes a new belling process allows you to bell underground PP and HDPE drainage pipes that have a large diameter and thickness with a compact or multilayer wall.