24th International Colloquium Tribology - January 2024 123 Wear Optimization of Roller Chain Drives with Triboactive Transfer Coatings Martin Rank 1* , Manuel Oehler 1 , Oliver Koch 1 1 RPTU Kaiserslautern-Landau, Chair of Machine Elements, Gears and Tribology (MEGT), 67663 Kaiserslautern, Germany * Corresponding author: martin.rank@rptu.de 1. Introduction The resource-saving use of machine elements is becoming increasingly important in the context of social, but also legal requirements. Above all, the optimization of tribological contacts is of great relevance. Studies show that approx. 23% of global CO 2 emissions are due to friction losses and to the replacement of worn components in such contacts [1]. Increasing wear resistance is therefore of particular interest for elements such as roller chains, whose service life is determined by wear. One promising approach is the use of surface coatings. This is already being used in series products. Coatings are usually produced by physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes [2]. However, their in-sight characteristics limit the use of such methods. Economical coating of concealed surfaces such as bores or internal sleeve geometries like chain bushings is hardly feasible. Therefore, usually only the pins of chain joints are coated. The use of triboactive transfer coatings could be one approach to realize wearand friction-reduction in chain bushings. Chemical reactions of lubricant additives with elements of suitable coatings under tribological load results in the deposition of wear and friction reducing transfer layers on the contact partner of the coated component. The use of CrAlMoN coatings and greases additivated with sulfur has already been shown to reduce friction in chain joints-[3]. Pin-on-Disc (PoD) Tribometer tests confirmed these findings and showed also reduced wear with such coating systems [4]. 2. Methods All experiments were performed with a single joint on a Chain Joint Tribometer (CJT) developed at the Chair of Machine Elements, Gears and Tribology (Figure 1). Figure 1: Chain Joint Tribometer (CJT) for wear analysis of single chain joints The CJT allows friction and wear analysis on individual chain joints, but also the bush-roller contact of roller chains. Since only individual joints are analyzed here, parameter and material investigations can be carried out cost-effectively. The test on the CJT promise a significantly higher conformity with real chain drives than model tribometer tests. The load on the joints corresponds to the real loads acting in the chain drive. Multi-body simulations (MBS) are used to calculate the link forces and deflections that are applied as a load spectrum in the CJT. In this work, tests were carried out on 10B1 roller chains with a pitch of P-=-15.875-mm according to DIN-ISO-606. Single prototype chain joints are built from series bushings and three pin variants. In addition to an uncoated series pin, a CrAlN and a CrAlMoN PVD coating of the pins are used (Table 1). Table 1: chemical metallic properties of the used pin coatings Coating Cr / At -% Al / At -% Mo / At -% Coating thickness / µm CrAlN 59 41 - 1.92 ± 0.1 CrAlMoN 17 13 70 1.79 ± 0.04 Two variants of a model grease with different additive packages are used as lubricant. The base grease consists of an ultra-high viscosity mineral oil and an inorganic thickener with antioxidants (AO). One variant is additionally additivated with 6600 ppm sulfur (S), the other with 350 ppm phosphorus (P). The load spectrum used corresponds to a twowheel drive with 120 links at numbers of teeth of z 1 = 17 and z 2 = 45, operated with a braking torque of M 2 = 125 Nm and a drive speed of n 1 = 1000-1/ min. The contact force acting in the joint in this configuration is F z = 1100 N. Wear is analyzed by real-time measurement of the joint elongation on the CJT. In addition, tactile shape measurements and surface topology investigations using a confocal microscope are performed. 3. Results The measurement of the joint elongation on the CJT show differences in wear of the various joint configurations. While the uncoated systems show the significantly highest wear, the CrAlN +P and CrAlMoN +S systems exhibit the most favorable behavior (Figure 2). Both variants show almost no running-in wear and an initially flat wear rate. The rate only increases noticeably at a sliding distance of approx. s = 500 m or a load duration of t-=-46-h. The CrAlMoN +P joint shows 124 24th International Colloquium Tribology - January 2024 Wear Optimization of Roller Chain Drives with Triboactive Transfer Coatings a quite significant run-in of the surfaces but exhibits a similarly low wear rate after. Also, an increase of the wear rate and scatter is exhibited after approx. s = 600 m or t-=-55-h. Figure 2: joint elongation Δl of the different joint configurations over sliding distance s, measured with CJT The wear is also reflected in the surfaces of the specimens. While the as-new specimens show no surface structure, the various combinations show scoring of varying intensity (Figure 3). Figure 3: Surface topology of the new joints and the different worn joint combinations The extent of the surface damage of the different specimen, especially in the bushings, appears to be analogous to the joint elongation. Only the CrAlMoN +S and CrAlN-+P systems show no structures on the surfaces. However, local coating failure and chipping of the pin coating occurs in all the joints. The wear rates, which show an increase towards the end of the runtime for the CrAlN and CrAlMoN systems, support the observation of coating failure. 4. Conclusion The investigations show that the use of suitable coatings with the appropriate greases can realize wear reduction in chain joints. Wear protection of the bushes was achieved by coating the pins. This indicates that transfer coating formation takes place. Investigations of system friction and chemical surface analysis support this impression. The observed wear was high in all specimens. Despite a load selection according to DIN ISO 10823, all coatings seem to have failed. In addition, the use of a model grease with low additive contents could be a further explanation for the generally severe wear. Accordingly, further investigations at other loads will provide further insight into the wear behavior of the chain joints. A detailed chemical analysis of the worn but intact coatings will then be possible. In addition, a single joint test rig was used for the investigations carried out here. For transfer to the real system, further investigations must be carried out on real chain drives. The setup may be supported by using the findings obtained here. 5. Acknowledgment The authors thank the Deutsche Forschungsgemeinschaft (DFG) for funding “Analysis of transfer layer formation in initially lubricated, coated drive chains” SA 898/ 31-1. References [1] K. Holmberg, P. Kivikytö-Reponen, P. Härkisaari, K. Valtonen, A. Erdemir, Global energy consumption due to friction and wear in the mining industry. Tribology International, 115: 116-139, 2017. ISSN 0301-679X. https: / / doi.org/ 10.1016/ j.triboint.2017.05.010 [2] A. Becker, Entwicklung einer Prüfmethodik für Verschleißuntersuchungen an Kettengelenken von Antriebs- und Steuerketten. PhD thesis, TU Kaiserslautern, Kaiserslautern, Germany, 2020. [3] K. Bobzin, C. Kalscheuer, M. P. Möbius, M. Rank, M. Oehler, and O. Koch, Triboactive Coatings for Wear and Friction Reduction in Chain Drives. Tribology International, page 108562, 2023. ISSN 0301-679X. https: / / doi.org/ 10.1016/ j.triboint.2023.108562 [4] M. Rank, M. Oehler, O. Koch, K. Bobzin, C. Kalscheuer, M. P. Möbius, Investigation of the Influence of Triboactive CrAlMoN Coating on the Joint Wear of Grease-lubricated Roller Chains. Tribology Transactions, 2023, https: / / doi.org/ 10.1080/ 10402004.2023.2264908