All tests conducted so far and the bibliography confirm the hypothesis that standstill marks develop due to various mechanisms: (1) The lubricant is literally pushed out of the friction area by micro movement and high local pressure. This leads to a lack of lubricant and the typical wear mechanisms of abrasion and adhesion ("galling"). (2) The micro movement activate the surface energy (in particular the microcon-tacts on the surface roughness peaks). This leads to tricobchemical reactions down to a depth of several nanometres. (3) Another important factor which is often not considered and can hardly be detected on superficial inspection is the microcracks caused by tangential forces due to the load changing on the surface (Contact mechanical theory of MINDLIN). When exposed to further load, these cracks result in more extensive and deeper particle break-off. The three damage mechanisms described above cause the production of wear particles and reaction products, which are not pushed out of the friction area due to a lack of "real" relative movement and thus have a strong abrasive effect. This phenomenon correlates with the formation of fretting corrosion (tribochemical corrosion) and normally leads to damage progression and deep indentations which cover the traces of the original damage mechanism. In further damage progression and bearing rotation there are additional wear mechanisms (in particular abrasion and surface disruption), which overlap and add to the covering of the real cause of damage. Depending on the predominance of one or several of the mechanisms described above, there are different types of standstill marks. The predominance of one mechanism depends on the load conditions - and within those mainly from the oscillation angle. Another damage factor with strong influ-ence is the lubricant used. Due to their better flow properties, oils are in general more effective than greases in preventing damage due to lack of lubrication. Oils may also be more suitable when it comes to preventing tribochemical corrosion as oils achieve more reliable surface wetting and thus prevent the formation of dry friction oxides (Fe2O3), which, due to their abrasiveness, lead to quickly progressing damages. One big problem is that the term "false brinelling" covers a wide variety of dam-age symptoms, which are partly caused by different mechanisms. The wear symptoms in tests with microoscillation differ significantly from the tests with relatively wide oscillation movements in the range of above 1°, as in the normal laboratory testing methods, such as the Fafnir or SNR test (Fafnir: +/- 6°; SNR test: +/-3°). Such macro-scopic oscillation movement leads to "real" bearing processes and not to the micro movements which occur and are particularly problematic with seemingly motionless bearings. Based on contact mechanical theories it will be possible to calculate the stresses in the tribological contact. These theories can help to explain why only a few load changing cycles with loading far beyond the critical value can cause such massive damage. We will soon conduct computer simulations and FEM calculations to investigate influencing parameters. Future test bench setups will be designed to either confirm or disprove the existing hypotheses. Furthermore, the project members devel-oping lubricant formula are working on concepts for improvement. But at this point of time we do not know yet if lubricants have an influence on the wear mechanism in surface disruption. The examinations conducted so far show the complexity of wear damage due to the overlapping of all four main wear mechanisms. It is thus extremely difficult to find suitable lubricants for damage prevention.


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    Titel :

    False brinelling - standstill marks on roller bearings


    Weitere Titelangaben:

    False Brinelling - Stillstandsmarkierungen in Wälzlagern


    Beteiligte:
    Grebe, M. (Autor:in) / Feinle, P. (Autor:in) / Blaskovits, P. (Autor:in)


    Erscheinungsdatum :

    2011


    Format / Umfang :

    6 Seiten, 5 Bilder, 8 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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