Thermo-Elastohydrodynamics of Coated Polymer Gears

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Climate change, the depletion of scarce resources, strict carbon emission allowances and e mobility are challenges that result in a constantly increasing demand for efficient machines and systems. Lightweight designs made from engineering polymers are one very promising approach to tackle these challenges at a minimum of costs through large-scale production possibilities. However, their capabilities in high-performance power-transmitting machine elements such as gears are mainly limited by lower material strength and thermal stability compared to common metal designs of tribological systems. The comprehension of polymer tribosystems and its mechanisms, especially related to heat management, offers great potential to extend the application limits of engineering polymers. Moreover, recent developments in surface coating technology show ways for expanding capabilities of engineering polymers that increase functional density of such machine elements tremendously. Hence, the goal of this confraternal research proposal is to explore the thermo-elastohydrodynamic lubrication (TEHL) of thermoplastics and the potentials of surface coatings in these TEHL contacts in order to improve its tribological performance. Thereby, polyamide (PA6.6) and Polyetheretherketone (PEEK), both pure and reinforced, are used in steel-thermoplastic pairings (main contact setup) and plain thermoplastic pairings (complementary contact setup). Three stages are defined that lead through the project. At first, the tribological performance and load limits of uncoated thermoplastic TEHL contacts are determined. Concurrently, innovative coating systems are designed for the needs - inter alia based on graded zirconium carbide (ZrCg) and chromium-aluminum-nitride ((Cr,Al)N). Second, the previous investigations are conducted in a similar fashion on coated setups to reveal its benefits. Comprehension of the mechanical and thermal mechanisms involved in coated and uncoated thermoplastic TEHL contacts is ensured by comprehensive tribosimulations. Finally, the gained knowledge is transferred from model contacts to gear contacts and assessed for industrial applications.The systematic approach of this project allows determination of the performance and limiting factors in uncoated thermoplastic TEHL contacts as well as the benefits of coating technology in such contacts, which is essential for improving the capability of engineering polymers for power transmitting machine elements.