Abstract
Abstract Over-based calcium sulfonate (OBCaSul) additives in oils are considered potentially critical in driving WEC formations, this ‘driving’ effect being unclear. Rolling contact fatigue testing of 100Cr6 steel using FE8 and PCS Micro-Pitting-Rig lubricated with oils containing varying OBCaSul concentrations have been conducted, tested samples being analysed using serial sectioning, Thermal desorption analysis (TDA) to measure hydrogen diffusion, and SEM/EDX of the tribofilms formed. Results show that OBCaSul concentration appears to affect WEC formation propensity, a reversal relationship of formations being shown between test rigs. Evidence shows oils containing OBCaSul form thick Ca dominated tribofilms, potentially promoting hydrogen diffusion and WEC formations in the FE8 rollers, where thinner Zn S tribofilms on the FE8 raceways may demote hydrogen diffusion and WEC formations.
Highlights
Premature failures of wind turbine gearbox bearings (WTGBs) cause significant downtime and high repair costs causing substantial impact to the wind energy industry
One of the most noted failure modes of WTGBs is that of White Structure Flaking (WSF) due to the formation of White Etching Cracks (WECs) typically ∼ 1 mm below the contact surface, WECs being associated with a microstructural alteration known as White Etching Area (WEA)
Mild wear is observed on the ZDDP only (OBCaSul 0%) and Over-based calcium sulfonate (OBCaSul) 1.4% tests with a slight increase seen for OBCaSul 2.8% and 5.6%
Summary
Premature failures of wind turbine gearbox bearings (WTGBs) cause significant downtime and high repair costs causing substantial impact to the wind energy industry. One of the most noted failure modes of WTGBs is that of White Structure Flaking (WSF) due to the formation of White Etching Cracks (WECs) typically ∼ 1 mm below the contact surface, WECs being associated with a microstructural alteration known as White Etching Area (WEA). One specific factor is the effect of additive chemistry and in addition, the effect additive chemistry has on the generation and diffusion of hydrogen, as a prominent driver for WSF and WECs. Additives found in lubricants that have been shown to reduce RCF life and promote WSF include; greases and lubricants containing sulphur-phosphorous extreme-pressure/anti-wear (EP/AW) additives, such as zinc dithiophosphates (ZDDP/ZnDTP/ZnDDP) and detergent/rust preventatives such as calcium sulfonates [1–10]. Hydrogen poisoning sulphur can aid in hydrogen diffusion by inhibiting molecular hydrogen recombination [11], where decomposition of EP/ AW additives such as ZDDPs at nascent catalytic surfaces can generate hydrogen [12,13]
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