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New process to make oriented PVC pipe reduces process length and energy consumption |
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A new commercially available system stretches and orients PVC pipe with air rather than water, reportedly achieving both higher stretch ratios and larger diameters than previous technologies. Compared with a conventional discontinuous process, it also has the advantage of reducing handling operations considerably, since it is no longer necessary to store the pipes between the extrusion and stretching phases. This process affords considerable efficiency in terms of energy and the environment not only at the manufacturing stage but also when the product is put into use. It also brings down costs and cuts the time needed to manufacture the pipes and install them.
The new method was introduced earlier this year by Molecor. An innovation has been patented, but the license is still being finalized. It is a discontinuous technology (stretching after extrusion), but without a gap between the two operations. The innovation resides in the second phase, in the heating and cooling of the pipe before and after the molecular orientation step. As a result, the Molecor� process reduces the length of the process by 80% and energy consumption by 85%. Other benefits include:
• Unbeatable resistance to impact
• Maximum flexibility
• Greater hydraulic capacity
• High short- and long-term hydrostatic resistance
• Excellent resistance to water hammers
• Peerless corrosion resistance
• Total water quality
• Lower costs and easier installation
Oriented PVC or PVC-O is the latest advancement in PVC pipe manufacture. By orienting the randomly arranged long chain polymer molecules significant improvements can be achieved in the mechanical properties of PVC. Orientation is achieved by controlled stretching and expansion of the PVC pipe. The result is a pipe with around twice the tensile strength as PVC-U with significantly better fatigue resistance, impact resistance and resistance to crack propagation. These improvements in mechanical properties allow the pipe wall to be thinner producing a larger bore for the same nominal diameter and pressure class. Therefore for the same DN over 10% improvement in hydraulic performance will be achieved compared to PVC-M pipe and even more so compared to PVC-U pipe. Oriented PVC pipe is well developed now. Its excellent mechanical properties (rigidity, pressure and impact resistance) make thinner walled pipes and thus save significant material. Two aspects are, however, still require being resolved. Heat sealing the layers of a double-walled pipe is not possible. The existing discontinuous bi-orientation processes are slow and expensive (labour, energy consumption) and continuous ones are complicated and unsatisfactory (warm up and parameter control).
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