发电机轴承剥落机理和导电油脂选择

Select additives that protect the oxidation layer of the bearing race steel during contact slip of the rolling elements
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Active sulphur free Extremely good corrosion protection


Consequence
Hydrogen enhanced WECs Whitቤተ መጻሕፍቲ ባይዱ structure flaking (WSF)
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AWF Understanding and ELC Greases
Electrical Conductive Grease
High local stress induced around inclusion
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AWF Understanding and ELC Greases
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(a) parallel white etching cracks (WECs)
Optical image of material removal by WSF on bearing inner raceway
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Electrical Conductive Grease
(b) branching network white etching cracks (WECs)
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AWF Understanding and ELC Greases
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Bearings for automotive electrical accessories
Ball bearing
Cross section of failure bearing for automotive alternator
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AWF Understanding and ELC Greases
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WSF formation drivers
Hydrogen invading the bearing steel Tribochemical reaction of grease (EP/AW additives) Water, corrosion Contact slip and traction Static electricity generated by friction between the drive belt and pulley Impact loads, vibration, bending stress and tensile hoop stress
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Influence of hydrogen
Hydrogen ions (H+) combine with electrons (e-) at fresh steel surfaces to form atomic hydrogen (H) Recombination of H+ to H2 gas can be inhibited by e.g. sulphur, leading to more atomic hydrogen in the steel Atomic hydrogen attracts and strongly binds to crystal defects
Electrical Conductive Grease
Formation conditions
Contact pressure: ~1.5GPa Stress-cycles: ~0.01•106
Non-metallic inclusions
White etching area (WEA) butterfly wing
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AWF Understanding and ELC Greases
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Formation of WSF
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AWF Understanding and ELC Greases
AWF Understanding and ELC Greases
Electrical Conductive Grease
Initial situation: White structure flaking (WSF)
Subsurface originated flaking of unusual microstructure, related to non-metallic inclusions Generated in specific applications Occurring after 1/10th to 1/20th of the calculated bearing life time
Solution to avoid hydrogen enhanced WSF
Select base oil that minimizes hydrogen formation
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PFPE Polyphenyl ether PAO Ester oil Hydrogen formation increases