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Technical Committee Lubricants

Calculation Method and Boundary Criteria for the Continuous Wear Behaviour of Grease Lubricated Gears with Regard to Different Material Combinations

The main goal of the research project is to develop a calculation approach in order to estimate the grease supply in the tooth contact. Further studies and experimental investigations focus on the verification and validation of the newly developed test method acc. to DGMK 725 and the creation of a basic knowledge for the wear behaviour of differently heat treated gear pairings. In addition to theoretical studies, we therefore conducted systematic experimental investigations on a FZG back-to-back test rig to test lubricating greases of different compositions over a wide range of circumferential speed and under different operating conditions. The lubrication supply mechanism has been observed and the occurring types of damage have been documented. Additionally, we have expanded the result basis of the modified test procedure for greases in systematic slow-running wear tests and investigated the wear behaviour of gear pairings with different heat treatment in further tests.

The results of the experimental investigations show that the operating and boundary conditions as well as the grease properties influence/affect the lubricant supply significantly. For example, a higher amount of grease in the gearbox and a higher lubricant temperature support the supply mechanism circulating. In contrast, a higher torque and a higher consistency of the grease support channeling. Further influences results from certain grease components such as the base oil or the type of thickener. Based on these results, we have developed a calculation approach that offers the possibility to estimate the lubricant supply mechanism of grease lubricated gears. Concerning the slow-speed wear tests, we confirmed that the modified test method acc. to DGMK 725 is appropriate for evaluation of the wear of grease lubricated gear pairings. The results are repeatable and distinguishable. Moreover, we observed a significant influence of the flowing properties of the grease on the wear resistance. The tests with the gear pairing case-hardened and through-hardened gears have shown a basic increase of the slow-speed wear. The roughness of the hard pinion, the difference in surface hardness and the components of the lubricant grease are additional influences on the amount of wear of the softer wheel. Based on the results obtained, a novel calculation approach is possible that allows to convert the amount of wear from the standardised test with the hard gears to a hard/soft gear pairing under grease lubrication.

The IGF project (19627 N) of the research association DGMK Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V., Überseering 40, 22297 Hamburg was funded by the Federal Ministry for Economic Affairs and Energy via the AiF within the framework of the programme for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag.

Dipl.-Ing. Benedikt Siewerin
Dr.-Ing. Thomas Tobie
Prof. Dr.-Ing. Karsten Stahl
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