TY - JOUR

T1 - Starvation and Relubrication Mechanisms in Grease Lubricated Oscillating Bearings

AU - Wandel, Sebastian

AU - Bader, Norbert Fritz

AU - Schwack, Fabian

AU - Glodowski, Jakob

AU - Lehnhardt, Bela

AU - Poll, Gerhard

N1 - Funding Information: This document is the result of the research project - Highly loaded slewing bearings (HBDV 0324303A) - partly funded by the Federal Ministry for Economic Affairs and Energy (Germany).

PY - 2022/1

Y1 - 2022/1

N2 - Oscillating rolling element bearings can be found in various industrial applications. A popular example are the rotor blade bearings of wind turbines, which allow the rotor blades to turn around their longitudinal axis. These bearings are predominantly grease lubricated and expected to be running in a state of low velocity starvation. Elastohydrodynamic Lubrication (EHL) films in starved contacts are susceptible to the conditions of inlet lubricant supply. If the bearings are running under moderate starvation no early failure due to wear is expected. If the inlet conditions increasingly lead to a drying out of the contact, resulting in a heavily starved contact, metal-to-metal contact can lead to false brinelling and subsequent bearing failure. Using two different greases bearing experiments are used to gain an understanding of the mechanism of wear initiation. It is found that starvation seems to be a major contribution to wear appearing in the investigated operating conditions (2°-45° osc. angle, 0,2–5 Hz osc. frequency). The degree of starvation in the contact depends on the balance between lubricant displacement by the rolling element and the replenishment of lubricant during operation. The following conclusions could be drawn: Replenishment is highly dependent on the operating conditions such as the oscillation frequency, the oscillation amplitude, and lubricant rheology. For small oscillation angles the ability of the grease to release base oil with high mobility into the contact seams to be essential. For greater oscillation angles, after crossing a limiting angle, a secondary replenishment mechanism seems to become active. This prevents early wear initiation. At critical operating parameters, which mainly include high oscillation frequencies and medium oscillation angles, severe wear is initiated after just a few hundred oscillation cycles. By modifying an existing starvation factor the influences could be visualised and compared to the experimental results.

AB - Oscillating rolling element bearings can be found in various industrial applications. A popular example are the rotor blade bearings of wind turbines, which allow the rotor blades to turn around their longitudinal axis. These bearings are predominantly grease lubricated and expected to be running in a state of low velocity starvation. Elastohydrodynamic Lubrication (EHL) films in starved contacts are susceptible to the conditions of inlet lubricant supply. If the bearings are running under moderate starvation no early failure due to wear is expected. If the inlet conditions increasingly lead to a drying out of the contact, resulting in a heavily starved contact, metal-to-metal contact can lead to false brinelling and subsequent bearing failure. Using two different greases bearing experiments are used to gain an understanding of the mechanism of wear initiation. It is found that starvation seems to be a major contribution to wear appearing in the investigated operating conditions (2°-45° osc. angle, 0,2–5 Hz osc. frequency). The degree of starvation in the contact depends on the balance between lubricant displacement by the rolling element and the replenishment of lubricant during operation. The following conclusions could be drawn: Replenishment is highly dependent on the operating conditions such as the oscillation frequency, the oscillation amplitude, and lubricant rheology. For small oscillation angles the ability of the grease to release base oil with high mobility into the contact seams to be essential. For greater oscillation angles, after crossing a limiting angle, a secondary replenishment mechanism seems to become active. This prevents early wear initiation. At critical operating parameters, which mainly include high oscillation frequencies and medium oscillation angles, severe wear is initiated after just a few hundred oscillation cycles. By modifying an existing starvation factor the influences could be visualised and compared to the experimental results.

KW - False brinelling

KW - Oscillating bearings

KW - Relubrication

KW - Starvation

KW - Wear

UR - http://www.scopus.com/inward/record.url?scp=85115160570&partnerID=8YFLogxK

U2 - 10.1016/j.triboint.2021.107276

DO - 10.1016/j.triboint.2021.107276

M3 - Article

VL - 165

JO - Tribology international

JF - Tribology international

SN - 0301-679X

M1 - 107276

ER -