day2 sessioniii 2 geartech errichello
DESCRIPTION
Fallas caja reductorasTRANSCRIPT
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1
Wind Turbine Gearbox Failures
Robert Errichello GEARTECH
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WIND TURBINE TYPICAL GEAR FAILURES
BENDING FATIGUE
HERTZIAN FATIGUE
WEAR
SCUFFING
CRACKING
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BENDING FATIGUE OCCURS IN 3 STAGES
Load
Crack Initiation Ratchet Marks
Crack Propagation Beach Marks
Fracture Ductile / Brittle
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4 Bending Fatigue/High-Cycle/Root Fillet Cracks
Classic bending fatigue with crack initiation at critical point of maximum bending stress. Curved trajectory of crack growth is typical as shown by adjacent fracture. Failure was caused by incomplete flame hardening.
Copyright 2000 by GEARTECH, Townsend, MT 59644 All rights are reserved.
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5 Bending Fatigue/High-Cycle/Tooth End Cracks
Bending fatigue cracks initiated in root fillets at left ends of teeth due to incomplete hardening on tooth ends.
Copyright 2000 by GEARTECH, Townsend, MT 59644 All rights are reserved.
Scuffing in slide direction
Crack origins
Beach marks
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FATIGUE SURFACE MORPHOLOGY RATCHET MARK
ORIGIN
BEACH MARK FRETTING CORROSION
ORIGIN
FRACTURE
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DEPTH BELOW SURFACE
TENSILE STRESS NEAR CASE/CORE BOUNDARY
CASE/CORE BOUNDARY IS CRITICAL
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8
Case History of Bending Fatigue Failure of INT Pinion
Courtesy of Rainer Eckert, NW Labs
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9
A
B C
D D
E
F
Bending Fatigue on INT Pinion
B
MnS inclusions
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10
A
B C
D D
E
F
Inclusion Origin on Tooth Fragment
B
MnS inclusions
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11
A
B C
D D
E
F
Close-up of Origin
B
MnS inclusions
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12
A
B C
D D
E
F
SEM Close-up of Inclusion 100X
B
MnS inclusions
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13
A
B C
D D
E
F
SEM Close-up of Inclusion 550X
B
MnS inclusions
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14
A
B C
D D
E
F
SEM Close-up of Inclusion 35X
B
MnS inclusions
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15
A
B C
D D
E
F
SEM/BSE Close-up of Inclusion 50X
B
MnS inclusions
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16
A
B C
D D
E
F
SEM/BSE Close-up of Inclusion 100X
B
MnS inclusions
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17
A
B C
D D
E
F
EDS Analysis (fingerprint) of Inclusion (SEM microscope)
B
MnS inclusions
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18
A
B C
D D
E
F
EDS Analysis (fingerprint) of Matrix (SEM microscope)
B
MnS inclusions
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19
A
B C
D D
E
F
Conclusions
B
MnS inclusions
1. Bending fatigue is primary failure mode 2. No surface defects were found at tooth surface 3. No material defects due to heat treatment were found 4. Fatigue crack initiated subsurface 5. Alumina inclusion was found at the crack origin 6. Root cause of bending fatigue is inadequate material cleanliness
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HOW TO PREVENT BENDING FATIGUE
USE STEEL THAT IS: CLEAN, HARDENABLE CARBURIZED SHOT PEENED FINE GRAINED REDUCE: BAINITE, PEARLITE NETWORK CARBIDES MICROCRACKS FLAWS BENDING STRESS
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HERTZIAN FATIGUE
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HERTZIAN FATIGUE - 3 GENERAL MODES
MACROPITTING
MICROPITTING
SUBCASE FATIGUE
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23 Hertzian Fatigue/Macropitting
Macropitting on a wind turbine pinion caused by misalignment due to excessive bearing clearance. Micropitting surrounding macropits is secondary failure. Note similar damage on each tooth including wear step at end of contact.
Copyright 2000 by GEARTECH, Townsend, MT 59644 All rights are reserved.
Macropitting
Micropitting
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HOW TO PREVENT MACROPITTING
Reduce contact stress
Use clean steel
Use carburized steel
Grind / hone gear teeth
Keep lube cool, clean, dry
Use high viscosity lube
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MICROPITTING
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26 Hertzian Fatigue/Micropitting
Micropitted gear teeth appear dull, etched, or stained with patches of gray. It attacks high points on gear tooth surfaces such as crests of undulations, peaks of cutter scallops, and ridges of grinding lay.
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
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HOW TO PREVENT MICROPITTING
Grind / hone / polish gear teeth Avoid shot-peened flanks Make hardest gear as smooth as possible Make pinion 2 HRC points harder than gear Use oil with high micropitting resistance Keep lube cool, clean, dry Use high viscosity lube Use high speeds Coat teeth with phosphate, Cu, or Ag Run-in with special lube and controlled loads
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SUBCASE FATIGUE
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29 Hertzian Fatigue/Subcase Fatigue
Subcase fatigue may be caused by inadequate case depth, inclusions near case/core boundary, or grind temper. In the helical gear shown, it was caused by grind temper. Fine, longitudinal cracks and sharp edged craters are typical.
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
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HOW TO PREVENT SUBCASE FATIGUE
Reduce contact stress
Use hardenable steel
Use optimum case / core properties
Avoid overheating & grind temper
Keep subsurface stress < subsurface strength
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31
WEAR
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32
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33 Wear/Adhesion
Adhesion is due to microwelding and tearing of asperities. Typically, mild adhesion occurs during running-in and subsides after it removes local asperities. The photo shows some local scuffs (severe adhesion).
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
Scuffing
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HOW TO PREVENT ADHESIVE WEAR
Use smooth tooth surfaces
Run-in new gearsets at reduced loads
Keep lube cool, clean, dry
Use high speeds
If low speed, use nitrided gears & high-viscosity lube
If very low speed, avoid S-P additives
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FRETTING CORROSION
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36 Wear/Fretting Corrosion
Fretting corrosion on teeth of a wind turbine pinion. It occurred because the turbine was parked for three months and the drive train vibrated when wind buffeted the rotor.
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
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SCUFFING
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38 Scuffing (severe adhesion)
Scuffing on teeth of a wind turbine pinion. It occurred because the oil supply was interrupted. Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
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SPECIFIC FILM THICKNESS DEFINES LUBE REGIME
hmin 1
2 = (12 + 22)1/2 = hmin /
Lube Regime< 1 Boundary
1 2 Mixed Film> 2 Full EHD
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GEAR LIFE DEPENDS ON
Gear Life
Micropitting Adhesion Scuffing
Macropitting
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HOW TO PREVENT SCUFFING
OPTIMIZE GEAR GEOMETRY / ACCURACY
USE NITRIDED STEEL
GRIND / HONE GEAR TEETH
COAT GEAR TEETH w/ PHOSPHATE, Cu, Ag
USE HIGH-VISC, ANTISCUFF LUBE
COOL GEAR TEETH WITH LUBE
RUN-IN NEW GEARSETS AT REDUCED LOADS
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GRINDING CRACKS
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43 Cracking/Grinding Cracks
Grinding cracks occur on ground flanks usually perpendicular to the grind direction. They are relatively shallow and parallel or in a crazed pattern. Nital etch may show grind temper as in the above photo.
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
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HOW TO PREVENT GRINDING CRACKS
Use proper wheel, feed, speed, & coolant
Keep retained austenite < 20%
Keep case free of carbide networks
Keep surface hardness < 60 HRC
Inspect for temper w/ acid etch
Inspect for cracks w/ magnetic particle
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CASE / CORE SEPARATION
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46 Cracking/Case-Core Separation
Case-Core separation is brittle fracture that usually occurs because case depth is too deep. Chevron marks on the fracture surface point to the crack origin.
Copyright 2000 by GEARTECH, Townsend, MT 59644. All rights are reserved.
Chevron marks
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HOW TO PREVENT CASE / CORE SEPARATION
Control case depth at tooth tips
Avoid narrow toplands
Mask toplands to restrict carbon penetration
Chamfer all edges of teeth
Use clean steel with high fracture toughness
Do not refrigerate
Temper immediately after quenching
Do not shot peen flanks
Wind Turbine Gearbox FailuresWIND TURBINE TYPICAL GEAR FAILURESBENDING FATIGUE OCCURS IN 3 STAGESBending Fatigue/High-Cycle/Root Fillet CracksBending Fatigue/High-Cycle/Tooth End CracksFATIGUE SURFACE MORPHOLOGYCASE/CORE BOUNDARY IS CRITICALCase History of Bending Fatigue Failure of INT PinionBending Fatigue on INT PinionInclusion Origin on Tooth FragmentClose-up of OriginSEM Close-up of Inclusion 100XSEM Close-up of Inclusion 550XSEM Close-up of Inclusion 35XSEM/BSE Close-up of Inclusion 50XSEM/BSE Close-up of Inclusion 100XEDS Analysis (fingerprint) of Inclusion (SEM microscope)EDS Analysis (fingerprint) of Matrix (SEM microscope)Slide Number 19HOW TO PREVENT BENDING FATIGUEHERTZIAN FATIGUEHERTZIAN FATIGUE - 3 GENERAL MODESHertzian Fatigue/MacropittingHOW TO PREVENT MACROPITTINGMICROPITTINGHertzian Fatigue/MicropittingHOW TO PREVENT MICROPITTINGSUBCASE FATIGUEHertzian Fatigue/Subcase FatigueHOW TO PREVENT SUBCASE FATIGUEWEARSlide Number 32Wear/AdhesionHOW TO PREVENT ADHESIVE WEARFRETTING CORROSIONWear/Fretting CorrosionSCUFFINGScuffing (severe adhesion)SPECIFIC FILM THICKNESS DEFINES LUBE REGIMEGEAR LIFE DEPENDS ON HOW TO PREVENT SCUFFINGGRINDING CRACKSCracking/Grinding CracksHOW TO PREVENT GRINDING CRACKSCASE / CORE SEPARATIONCracking/Case-Core SeparationHOW TO PREVENT CASE / CORE SEPARATION