Flow-forming of super-tough polypropylene pipes using a twin motor-driven rollers setup

Abstract

For decades, the flow-forming process has been well investigated and widely applied in the metal-forming industry. This research begins with the intention to apply the flow-forming process to the plastics industry. An understanding of the deformation characteristics of the polymer material related to the process is thus necessary. For this purpose, a conventional lathe machine was modified and a specially-designed setup fabricated for the flow-forming experiments. Polypropylene pipes were employed in the present study. Mechanical testing has shown remarkable improvement over the original un-flow-formed material. The tensile yield strength and ultimate tensile strength of the flow-formed pipes increased significantly with percentage thickness reduction, especially those along the direction of the helix line. The hydrostatic burst test, which is the overall test for the flow-formed pipes, shows clearly that the hoop strength increases with percentage thickness reduction. The ballooning effect observed during the hydrostatic burst test is another added advantage in piping failure detection. This is attributed to the particular way of flow-forming the pipes using twin motor-driven rollers, whereby the pipe material is rendered anisotropic in a specific manner. With a better understanding of the process on polymeric material, flow-forming may now be applied to the plastics industry in the near future to produce super-tough polymer pipes. © 1997 Elsevier Science S.A.