Experimental Investigations on Wear in Oscillating Grease-Lubricated Rolling Element Bearings of Different Size and Type

Abstract

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.

Comparison of Different Standard Test Methods for Evaluating Greases for Rolling Bearings under Vibration Load or at Small Oscillation Angles

“…Oil release, base oil viscosity and shear thinning effects (structural viscosity) play a decisive role [11,16]. WANDEL has introduced the so-called Starvation Number to describe this risk of deficient lubrication [6,19], which is suitable, for considering blade bearings of wind turbines [15,19].…”

Research on the Rheological Characteristics of Wind Power Grease Based on Rheological Parameters

“…The main shaft bearing of wind turbines, as a special bearing, generally uses grease as a lubricant [5]. For greases, the study of rheology has become an important field.…”

Research on the crack behaviors under rolling contact of oscillation applications in wind turbine bearings

“…They pointed out that the bearing in an oscillation condition behaves differently from that in rotating, and the oscillation factor aosc was introduced to consider the difference. Both [6] and [7] indicated that the sequence and amplitude of an oscillation movement play an important role in wear occurrence.…”