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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 research project is based on three main objectives: The newly developed test method according to DGMK 725 for the evaluation of the wear capacity of gear greases is to be verified and validated by further experimental investigations; an extended calculation approach for the estimation of the lubricating grease supply in the tooth contact is to be developed and a basic level of knowledge on the wear behaviour of gear pairs with different heat treatment is to be created. In addition to theoretical studies, extensive experimental investigations are carried out on the FZG gear stress test rig. Lubricating greases of different compositions are investigated over a wide speed range and under different operating conditions while observing the supply mechanism that occurs, and the types of damage that occur are documented. Furthermore, the test basis of the modified test method for greases is enlarged in systematic low-speed wear tests and the wear behaviour of gear pairs with different heat treatment is examined in random tests.

The results of the investigation show that the transitional area of lubricant supply between recirculation and free digging is significantly dependent on the grease properties, external boundary conditions and operating conditions. For example, a higher grease quantity in the gearbox and a higher lubricant temperature can promote recirculation. On the other hand, higher torques and a higher consistency promote the mechanism of free-lifting. Further influences can be traced back to individual grease components such as the base oil or the thickener type. On the basis of these results, a calculation approach is developed which offers the possibility of estimating the lubricant supply of a grease-lubricated gearbox. In the low-speed wear tests, the suitability of the modified test method according to DGMK 725 can be confirmed. A good repeatability and differentiability of the results for different greases are given. In addition, the observations show a significant influence of the post-flow properties of the grease on the wear resistance. The stitch tests with gear pairs of case-hardened and quenched and tempered gears basically show an increased wear compared to investigations with case-hardened gears. The wear is additionally influenced by the roughness of the hard component, the surface hardness difference and the lubricant components. With these findings, a first conversion of the wear occurrence from the standardized test with the pairing hard/hard to a toothing hard/soft for grease-lubricated gears can be derived.

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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