Filament Wound Pipes - Machining and Finishing

During talks with personnel from Redlands Reinforced Piastics Ltd. (part of the Redland Group of Companies), the process of machining plastic reinforced pipe end-forms was discussed with a view to improving manufacturing efficiency. Traditionally Redlands manufacture 65% to 70% glass reinforced plastic pipes which are filament wound and range in diameter from 25 mm to 2.5 m. The endforms of these pipes, which enable the pipes to be correctly fitted, are generally machined by turning. Due to the extremely abrasive nature of glass fibre products, and the fact that long pipes are physically restricted to a low maximum rotational speed to avoid bending and whipping, machining end-forms by turning can be an expensive and time consuming process. As an investigatory study, it was agreed that the Grinding Research Group at Bristol University would carry out preliminar investigations into the feasibility of grinding end-forms, with the proviso that any preferred grinding process should, if be carried out "dry8'; that is without the application of any coolant.

Initial grinding experiments were undertaken using 180 mm diameter, isophthalic resin pipe sections, mounted on a specially designed rig which incorporated a continuous force measuring facility. Using this rig, a variety of both aluminium oxide and silicon carbide grinding wheels were appraised and such parameters as grinding forces, specific energy, surface finish, wheel wear and out-of-roundness were collated. Initial tests were carried out with the application of grinding fluid but, upon identifying an "optimum" wheel, "dry" grinding tests were undertaken. Following the conclusion of these initial experiments, additional "high stock removal" tests were made to identify the limiting "dry" grinding conditions. In these additional experiments, carried out on a cylindrical creep-feed grinding test rig, the conditions associated with both isophthalic and vinyl-ester type resins were investigated and the differences between these two types of pipe monitored.