How to reduce WEC in Wind turbines · Texaco Meropa 320 5 % Failure free running time maximum time:...
Transcript of How to reduce WEC in Wind turbines · Texaco Meropa 320 5 % Failure free running time maximum time:...
White Etching Cracks (WEC)How to reduce WEC in Wind turbines
Summary: WEC and cause for WEC
What is White Etching Cracks (WEC)?
WEC are material changes that can occur in rolling bearingsteels and have significantly higher hardness than the originalstructure. Under mechanical load, cracks may develop betweenthe white, hard areas and the matrix that, under strain,propagate to the surface and lead to failure. These cracks occurin both through hardened and case hardened rolling bearings.
How do WEC occur?
Schaeffler has comprehensive testing facilities for assessing theinfluences and developing solution concepts for reducing the riskof WEC.
According to our current level of knowledge, WEC occur only asa result of unspecified additional loads (such as electricity,dynamics, mixed friction) that supplement the usual bearingloads and not to a root cause in the bearing itself or in thebearing design.
Influences, which could have an effect on component fatigue,such as contact pressure, an insufficient level of steel purity oroverloading, do not cause the occurrence of WEC.
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How to reduce WEC in wind turbines
Summary: Schaeffler solutions
Through hardened bearings with Durotect® B
Schaeffler recommends Durotect® B (black oxide coating)
Ø Good protection against WEC
Ø Longest and best field experience: failure rate 0,02%482.000 Bearings, < 100 Failures in the past 9 years
Ø Economical solution
Ø Durotect® B also minimizes the risk of damage caused byslippage, improves running-in behavior and providesprotection against corrosion
The WEC risk can be limited by the design of the bearingand the selection of lubricants or materials.
Lubrication advise
Ø Oil changes: keep the oil history clean and document the oilchanges
Ø Avoid water in lubricant as far as possible.
Further Schaeffler solutions
Special carbonitriding steel Mancrodur® with Durotect® BHigh chromium special steel Cronidur® 305
How to reduce WEC in wind turbines
What is White Etching Cracks (WEC)?
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How to reduce WEC in wind turbines
White BandsRelated to classic fatigue
White etching layer WEL ButterflyWhite flanks around non metallic inclusions
White Etching Cracks (WEC)Crack networks including white etching flanksA type of White Etching Area WEAà Nital etching: phase that do not corrode, appear white
Related designations:White structure flakingBrittle crack networkAxial Cracks (referring to damage appearance atmartensitic steels)
Other White Etching Areas (WEA)
What is White Etching Cracks (WEC)?
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How to reduce WEC in wind turbines
Affected Applications
WEC occurs in many sectors of Industry includingAutomotive
WEC occurs in all bearing components, except cages
Øindependent from line or point contact
Øindependent from bearing type
Øindependent from material (except Cronidur)
Øindependent from heat treatment
WEC failures are not unique to wind turbines. There aremany other applications that have experienced problemsrelated to WEC.
Martensitic
Bainitic
Case hardened
What is White Etching Cracks (WEC)?
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How to reduce WEC in wind turbines
Affected Applications in wind turbines
Rotor shaftSpherical roller bearingsTapered Roller bearings
GearboxCylindrical roller bearingsTapered Roller bearingsin Planet Gears
Intermediate speed shaftHigh speed shaft
How do White Etching Cracks occur?How to reduce WEC in wind turbines
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Electricity Mixed Friction Dynamics
Reduceelectrostaticsand current
flows
Reducemixed friction
as far aspossible
Reducevibrations
Reducetractionslippage
Preventunfavourable
bearingkinematics
WEC
A d d i t i o n a l L o a d s
P r e v e n t i v e M e a s u r e s
lead to
reduce the risk of
Lubricationin combinationwith auxiliary
loadsinfluences
How do White Etching Cracks occur?How to reduce WEC in wind turbines
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Preventive MeasuresThe risk of WEC can be reduced if variouspoints are observed in design of the bearingarrangement and the selection of lubricantsand materials.
Reduceelectrostatics andcurrent flows
Optimise groundingconcept (couplingdesign, insulatingcoatings, ...),quality/concept of drive(windings) andcontrol/inverter
Identify electrostaticsources: belt drives,rotor blades, paper rollcontact, flowing liquids.Take appropriatemeasures
Reduce mixedfriction as far aspossible
Pay attention tolubrication conditions
Prevent mixed friction(κ < 1)
Ensure low roughnessof element at risk offailure (normally innerring)
Avoid excessively highviscosities (κ > 10) athigh n · dM values
Ensure sufficient oilrelease from greases
Reduce vibrations
Avoid high axial androtationalaccelerations
Reduce highfrequency vibrations(> 100 Hz)
Reduce tractionslippage
Achieve preload/lowoperating clearance asfar as possible
Specific load (Fr/C0)not too low ordifference fromminimum load not toolarge
Keep splash losseslow (avoid high oilflows, large outletholes)
Use design withoptimised tractionslippage
Preventunfavourablebearing kinematics
Select optimum bearingtype for frictionkinematics: low pvvalue
Keep differential andspin slippage low
Pay attention toskewing(tapered roller bearings,cylindrical rollerbearings)
reduce the risk of
Recommended Schaeffler Solution: Through hardened + Durotect® B
Through hardened bearings with Durotect® BSchaeffler recommends Durotect® B (black oxide coating)
Ø Good protection against WEC
Ø Longest and best field experience: failure rate 0,02%482.000 Bearings, < 100 Failures in the past 9 years
Ø Economical solution
Ø Durotect® B also minimizes the risk of damage caused by slippage, improves running-inbehavior and provides protection against corrosion
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How to reduce WEC in wind turbines
Recommended Schaeffler Solution: Through hardened + Durotect® B
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How to reduce WEC in wind turbines
What is Durotect ® B?The coating system Durotect® B has been consistentlydeveloped from conventional black oxide finishes to giveincreased performance.
AdvantagesDurotect® B…Ø minimizes the risk of damage caused by slippageØ improves running-in behaviorØ provides protection against corrosionØ increases the level of robustness to WEC independent
from base materialSchaeffler therefore always recommends its customersto use gearbox bearing supports in Durotect® B.
FeaturesØ Coating comprising mixed iron oxidesØ Colour: dark brown to deep black
Schaeffler's Surface Technology Competence Center hasdeveloped an ideal coating system to reduce/eliminateWEC damage.
Recommended Schaeffler Solution: Through hardened + Durotect® B
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How to reduce WEC in wind turbines
Field track recordIt has been proven statistically that black oxide finishing of outer and inner rings as well asrollers significantly reduces the formation of white etching cracks.
Longest and best field experience: failure rate 0,02%482.000 Bearings, < 100 Failures in the past 9 years
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Recommended Schaeffler Solution: Through hardened + Durotect® B
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How to reduce WEC in wind turbines
Field track recordLongest and best field experience: failure rate 0,02%482.000 Bearings, < 100 Failures in the past 9 years
Statistics in relation to 482.000 bearings (delivered 2005 – 2014)Bearing locationin wind gearboxes
Planet bearings 45 %High speed shaft bearings 35 %Intermediate speed shaft bearings 20 %
Heat treatment(all bearings are through hardened)
Martensitic 55 %Bainitic 45 %
Bearing type Cylindrical roller bearings 80 %Tapered roller bearings 20 %
Lubricants(In general the 482.000 bearings areoperated in all common lubricants used inwind gearboxes. This is our experience interms of prevalence of wind oils.)
Mobil SHC XMP 320 70 %Castrol Synthetic X 320 20 %Castrol Synthetic A 320 5 %Texaco Meropa 320 5 %
Failure free running time maximum time: 9 years, average time: 4 years