Choice and Optimization of a tecno-polymer for planet wheels: Importance of the integration between material and design for plastic gears

摘要

In the last years Varvel SpA attention to tecno-polymers has run up since the number of advantages these materials can bring to gears, less noise, restrained inertia, production flexibility, together with the promising outlook of avoiding the use of lubricants. For this particular reason the R&D department started a tribological characterization of some commercial tecno-polymer in order to identify the best scenario in terms of friction and wear, following the distinction made by B.Briscoe [1,2] between cohesive and interfacial wear. The first one strongly connected to high mechanical properties, but responsible for a strong increase of friction between gears teeth, which instead is optimized by a strong component of the interfacial one. Nowadays the high number of available fillers for plastic, such as PTFE and carbon fibers CF, gave to the R&D department the chance to define his own tribologically and mechanically optimized material trough an addition on PA46 matrix, based on a DOE experimental pattern [3]. All the combinations of PTFE and CF where tested by ball on disc tribometer and tensile test for E module. The combination selected was the one that better answer to the need of having the best presence of interfacial wear, together with mechanical properties suitable for standing the operational torque of wheels in planetary gearboxes. This experimental work and its relative interpretation are described in the paper, together with the performances of planetary gearboxes with the chosen PA46, monitored at the test bench. These tests enlightened the right choice made with the optimization of the tribology and the benefit of using a DOE, but also showed how, even with improved mechanical properties, plastic require its own design for gears.