A common application for grease-lubricated oscillating rolling element bearings is, e.g., rotor blade bearings in wind turbines. These bearings mainly operate under conditions that are prone to starvation. If the grease is unable to provide enough inlet lubricant supply for the contact between rolling element and bearing raceway, wear in the form of False Brinelling and thus premature bearing failure is possible. Bearing experiments with different lithium complex model greases, which differ mainly in their base oil viscosity and oil separation rate, were carried out to show the influence of the grease parameters on wear initiation. The results show that the ability of the grease to release a high amount of base oil with high mobility into the track of the rolling element is a crucial mechanism to prevent wear, especially at small oscillation angles. For oscillation angles larger than a critical angle, a secondary replenishment mechanism may prevent early wear initiation. The experimental results are used to validate a starvation model proposed in earlier work (Wandel et al. in Tribol Int 165:107276, 2022).
Grease-lubricated rolling element bearings can suffer from wear due to lubricant starvation under certain oscillating operating conditions. Especially for large-scale slewing bearings, such as blade bearings in wind turbines, experimental investigations are complex compared to small-scale reference testing. For an easier manner of testing, it is desirable to know whether the results of small-scale testing are applicable to larger-sized bearings. In this work, three different bearing types were tested and compared to already published results from a small-scale ACBB with a pitch diameter of 60 mm. The newly tested bearing types comprise a downscaled blade bearing (4-point contact double row ball bearing) with a pitch diameter of 673 mm, a small-scale CRTB with a pitch diameter of 77.5 mm and another ACBB with a pitch diameter of 95 mm. Qualitatively, all tested bearings show similar wear behaviour in terms of friction energy when operation parameters are varied. With higher oscillation frequency, damage becomes more severe. The oscillation amplitude shows three distinctive regimes. Within the range of small amplitudes, an increase in amplitude leads to more pronounced damage. We observe a threshold amplitude where this is no longer the case; a further increase in amplitude counteracts wear initiation until a final threshold is reached, beyond which no more wear is observed. These findings are in accordance with the reference results of the small-scale ACBB. Direct comparison between point and line contact shows that the latter is more prone to wear initiation under grease-lubricated, oscillating operating conditions. Furthermore, a previously introduced empirical number shows good performance in assessing critical operating parameters of the different bearing types. Specifically, harmful operating conditions can be classified for all studied bearing types with an accuracy of 78%. This method can be useful to assess operating conditions of greased, oscillating, rolling element bearings, e.g., to assess different pitch controllers or designs of slewing bearings.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.