Composite Fabric Blankets for Plastic Gears

Abstract

Two approaches for increasing the load capacity of plastic gears in general are proposed and investigated: modifying the conventional involute profile of the gear tooth surfaces by applying a parabolic-crowned profile, and introducing a composite fabric, which blankets the surface of the teeth. The investigation is carried out using the finite element method (IGD/ANSYS). A five-tooth model is applied for the gears, and nylon and carbon/nylon are adopted for the materials. The evolution of maximum contact and bending stresses is evaluated over two cycles of meshing for both the pure plastic (nylon) gears and the gears with the composite surface blanket (carbon/nylon) to investigate the process of transfer of load between consecutive pairs of teeth and detect possible edge contacts. The results indicate that selecting the proper parabolic-crowned profile helps to alleviate the contact stress, and more specifically, to reduce the peaks of contact stresses due to edge contacts at the tip of the teeth. The results also indicate that there are an optimum parabolic-crowned profile and an optimum thickness of the composite blanket, which render the lowest maximum level of contact stresses over the cycle of meshing and bending stresses at the fillet. However, this preliminary research work suggests that, for the case considered, the novel idea of composite blanket is inconclusive — though the blanket may protect the plastic core, it itself becomes vulnerable to failure. The idea is being explored more, and the results will be disseminated in a future work.