Starvation and Re-lubrication in Oscillating Bearings: Influence of Grease Parameters

Abstract

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).

Wear Development in Oscillating Rolling Element Bearings

“…Parameter studies (see [6,18]) have shown that, under certain operating conditions, it is possible for grease-lubricated oscillating rolling bearings to operate without damage, at least in the short term. However, if the operating conditions result in severe starvation and solid contact between the rolling element and raceway, adhesion between the contact partners can occur due to the similarity in the materials.…”

“…Other publications have dealt with lubrication mechanisms and the effectiveness of greases in preventing wear damage. Summarized from the publications of MARUYAMA, SAATCHI, WANDEL, KITA, and SHIMA, a high oil release as well as a low grease consistency and a high mobility of the base oil are crucial to prevent wear [14][15][16][17][18]. The suitability of lubricants for oscillating bearing applications is often determined using standard tests such as the Fafnir test and the SNR-FEB2-test [19,20].…”

“…The choice of operating conditions was based on the previously described frequent x/2b ratios occurring in IPC-controllers, as well as on previously performed parameter studies with the same bearing type [6,18]. These have already shown that the conditions are particularly critical for early wear initiation.…”

Wear Development in Oscillating Rolling Element Bearings

“…Parameter studies (see [6,18]) have shown that under certain operating conditions it is possible for grease-lubricated oscillating rolling bearings to operate without damage, at least for a short term. However, if the operating conditions result in severe starvation and solid contact between the rolling element and raceway, adhesion between the contact partners can occur due to the similarity of the materials.…”

“…Other publications deal with lubrication mechanisms and the effectiveness of greases in preventing wear damage. Summarized from the publications of MARUYAMA, SAATCHI, WANDEL, KITA, and SHIMA, a high oil release as well as a low grease consistency and a high mobility of the base oil are crucial to prevent wear [14][15][16][17][18]. The suitability of lubricants for oscillating bearing applications is often determined using standard tests such as the Fafnir-test and the SNR-FEB2-test [19,20].…”