Rolling Bearing Failure Analysis - Farrell Bearings
Rolling Bearing FailureAnalysis
Contents1.1.11.21.31.41.51.61.71.82.BEARING FAILURE ANALYSISDETERMINATION OF OPERATING DATALUBRICANT SAMPLINGINSPECTION OF THE BEARING ENVIRONMENTASSESSMENT OF BEARING IN MOUNTED CONDITIONDISMOUNTING THE DAMAGED BEARINGASSESSMENT OF THE COMPLETE BEARINGASSESSMENT OF BEARING COMPONENTSROLLING BEARING DAMAGE SYMPTOMS AND THEIR CAUSESROLLING BEARING DAMAGE2.1 DAMAGE RELATING TO BEARING RINGS2.1.1 FRETTING CORROSION2.1.2 TRACKS IN THE CASE OF INADEQUATE LUBRICATION2.1.3 TRACKS IN THE CASE OF CONTAMINATION IN BEARING OR LUBRICANT2.1.4 UNUSUAL TRACKS WITH DETRIMENTAL RADIAL PRELOAD2.1.5 TRACKS WITH OVAL DEFORMATION2.1.6 DETRIMENTAL AXIAL PRE-LOAD2.1.7 TRACKS WITH MISALIGNMENT2.1.8 FATIGUE OF ROLLING BEARINGS DUE TO MISALIGNMENT2.1.9 FATIGUE AS A RESULT OF POOR LUBRICATION2.1.10 CORROSION2.1.11 FALSE BRINELLING2.1.12 PASSAGE OF ELECTRIC CURRENT2.1.13 RING FRACTURES2.1.14 SLIPPAGE TRACKS2.1.15 SCORE MARKS2.1.16 DAMAGE DUE TO OVERHEATING2.1.17 ASSESSMENT OF LIP CONTACT2.2 DAMAGE RELATING TO BEARING CAGES2.2.1 CAGE WEAR DUE TO STARVED LUBRICATION AND CONTAMINATION2.2.2 WEAR DUE TO EXCESS SPEED2.2.3 WEAR DUE TO ROLLER SKEWING2.2.4 WEAR IN BALL BEARING CAGES DUE TO TILTING2.2.5 CAGE FRACTURE2.2.6 DAMAGE DUE TO INCORRECT 62728282829303131
Rolling Bearing Failure Analysis1.Bearing Failure AnalysisThe purpose of inspecting damaged bearings and their mating parts is to determine the probable causes ofthe damage and to avoid any future failures. A systematic procedure should be implemented to assist inresolving bearing failures. The following measures should be considered:9Obtain or determine operating data. e.g. loads, speed etc.9Extract lubricant samples from inside and around the bearing9Check bearing and surrounding environment9Assess bearing in mounted position9Mark orientation of bearing in the mounting position9Dismount the bearing using the correct techniques9Mark and identify the bearings and parts9Assess the complete bearing1.1Determination of operating dataWhen inspecting damaged rolling bearings, not only the bearing itself is examined but also the surroundingconditions and the application.If possible, drawings and pictures should also be considered for theassessment process. The following details would be required:9Application: machine, bearing location, service life, how many similar machines and how many failures inthese machines9Bearing constructions: locating bearing, floating bearing arrangement, adjusted bearings (adjusted withspacers, nut, covers, springs or shims)9Speed: constant, alternating (inner ring and outer ring), acceleration or deceleration9Load: axial, radial, combined, tilting movement, constant, changing (collective), oscillating (acceleration,oscillation, amplitude), centrifugal force, point load, circumferential load (which ring is running?)9Mating parts: shaft & housing (fits), fastening parts (e.g. type of locknut, bolts etc.)9Environmental conditions: external heat, cooling, special media (e.g. oxygen, vacuum, radiation),stationary vibrations, dust, dirt, dampness, corrosive agents, electric or magnetic fields9Lubrication: lubricant, lubricant quantity, lubricant supply, re-lubrication interval, date of last lubricationinterval/ last oil change9Sealing type & design: contact, non-contact9History of damaged bearing: first mounting or replacement bearing, changes in bearing location,evaluate data and records from bearing monitoring devices, if available.3Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis1.2Lubricant samplingWhen assessing damaged bearings, the condition of the lubricants should also be evaluated as part of theassessment process. The following points relate to the evaluation of the lubricants.Grease lubrication:9Documentation of grease distribution and colour in the bearing environment9Clearly identify all samples when taken from different places in the bearing and housingOil lubrication:9Remove samples from the oil flow near the bearing or from the middle of the oil reservoir9Extract samples directly after operation to obtain the typical distribution of foreign matter9Do not remove samples from the bottom or directly before the filters (wrong concentration of particles)9Filter residue should also be kept for inspection (indicates history prior to damage)General Information:9How often has the bearing been re-lubricated or had the oil changed? When was either last carried out?9Check oil or grease for any small flakes or pieces of bearing or other components9Use clean glass sample bottles9There should be enough room left in the sample bottles for stirring the oil sample in the laboratory9The analysis of the samples may take place at the customer’s or at an external lubricant laboratory.9Points of interest are generally the degree of contamination and its type (sand, steel, soft little parts,water, cooling liquid) as well as analysis of the lubricity (e.g. ageing, consolidation, colour, share ofadditives)1.3Inspection of the bearing environment9Could have the surrounding parts made contact with the bearing parts anywhere?9Any other parts damaged near the bearing (consequential or primary damage)?9Cleanliness inside and around the bearings & seals (any foreign matter in the bearing space?)9Loose fastening devices and parts (was the bearing forced to deform? Are the bolts loose?)4Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis1.4Assessment of bearing in mounted condition9Are there any ruptured or chipped areas?9Are any of the seals damaged, particularly deformed or hardened?9Has the bearing suffered any indentations on the visible areas?9Consider the effect of the fits. Does the bearing run easily or tightly in mounted condition?1.5Dismounting the damaged bearingCare should be taken to minimise any further damage to the bearings during dismounting. Any additionaldamage could alter, change or destroy the existing damage pattern or clues.The following procedure should be observed if possible:9Prevent any further damage to the damage areas inside the bearing9Do not apply dismounting force via the rolling elements9High dismounting force could be a clue9Do not open sealed bearings9Do not use cutting torches unnecessarily9Do not destroy or damage any heat-sensitive parts, such as lubricant, seal, cage9Mark bearings (mounting location, mounted position or direction)1.6Assessment of the complete bearingWhen assessing damaged bearings the lubricant should either remain in the bearing or samples taken forpossible analysis.The following should be checked:9General condition (cleanliness of bearing and condition of fitting surfaces, i.e. traces of mounting, frettingcorrosion, ring fractures, dimensional accuracy, seizing marks, discoloration)9Condition of seals and dust shields. Photograph or describe of the extent of escaped grease9Condition of cage9Manual rotation test (indication of contamination, damage or preload)9Measure the bearing clearance (displaceability of rings in radial and axial direction), whereby bearingsare loaded equally and rotated.5Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis1.7Assessment of bearing components9Assessment of bearing seating areas (axial mating surfaces, inner ring bore, outer ring outside diameter)9Raceways9Lips9Sealing seat surface/ contact surface9Rolling elements (outside diameter and face in the case of rollers)9Cages9Seals6Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis1.8Rolling bearing damage symptoms and their causesTypical causes of rollingbearing damageRolling contact areaPoor support of ringsMisalignment of shaftdeflectionXXFit too loose, too littlepreloadXXFit too tight, to muchpreloadDirtSealingCageIncorrect mountingprocedure or toolsa) Unusualrunning behaviourUneven runningUnusual noiseDisturbedtemperaturebehaviourb) Appearance ofdismountedbearing parts1. Foreign particleindentations2. Fatigue3. Stationaryvibration marks4. Molten dentsand flutes5. Skidding6, Rolling elementindentations,scuffing7. Seizing marks8. Wear9. Corrosion10. Overheatingdamage11. Fractures12. Frettingcorrosion (falsebrinelling)Lip and roller faceareasMountingDamaged area of the bearingSeatsSymptomTable 7XCopyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure AnalysisRolling bearing damage symptoms and their causes (Continued)XXXXXXXXXXXXExcess lubricantInsufficient lubricantUnsuitable lubricantXXCurrent passageXXXExternal HeatHigh SpeedsVibrationsXXAggressive media,waterXDust, dirta) Unusual running behaviourUneven runningUnusual noiseDisturbed temperaturebehaviourb) Appearance of dismountedbearing parts1. Foreign particleindentations2. Fatigue3. Stationary vibration marks4. Molten dents and flutes5. Skidding6, Rolling elementindentations, scuffing7. Seizing marks8. Wear9. Corrosion10. Overheating damage11. Fractures12. Fretting corrosion (falsebrinelling)LubricationEnvironmental influenceTypical causes of rollingbearing damageDamaged area of the bearingLoad to high or to lowOperationalStressSymptomTable 2XXXXXXXXXXXXXXXXXXXXXXXX8Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.Rolling Bearing DamageAfter analysing the all the data and the physical damage to the bearing and surrounding parts the next stepis to determine the reason/s for the failure. In this section, examples of damaged bearings (pictures andillustrations) and their symptoms, causes and possible remedies are provided.2.1Damage relating to bearing ringsWhether the tracking patterns on either the inner or outer ring raceways are to be considered normal orunusual, would depend upon on each individual application. The tracking patterns and damage on theraceways may have been caused by various problems. The following symptoms, causes and remediesmaybe of assistance in determining the cause to the failure.9Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.1Fretting corrosionSymptoms:9Brownish-black spots on the seats9Wear at fitting surfaces9Fatigue fracture possible in the case ofrotating parts (usually the shaft)9Disturbance of floating bearing functionpossible in the case of stationary parts(usually the housing)Causes:9Micro-motion between fitted parts wherefits are too loose in relation to the actingforces, but no creeping of rings9Form disturbance of fitting surfaces9Shaft deflection, housing deformation9Incorrect fit selection andfinishes for the applicationFigure 1: Fretting corrosion in bore of a cylindricalroller bearing inner ring with seat too loosesurfacePossible remedies:9Provide the correct fit and surface finishfor each bearing ring9Use fit selections that provide the bestsupport of the bearing9Make shaft & housing designs more rigid9Surface coat bearing seatsFigure 2: Fretting corrosion reveals the size of theload zone at the stationary outer ring10Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.2Tracks in the case of inadequate lubricationSymptoms:Dull roughened tracking patterns arise from poor lubricationconditions. The thinner the lubricating film the greater theinfluence on the surface. When a specific load is high in thecontract areas, the tracks are bright, pressure-polished andfrequently shiny and are a clear contrast to the cycled part ofthe raceways.Causes:9Insufficient lubrication (type & quantity etc.)9The viscosity of the lubricant is insufficient for theoperating temperature and speedPossible Remedies:9Improve lubricant supply9Change lubricant viscosity to suit operating conditions9Use approved lubricants with suitable additivesFigure 3 Spherical roller bearing inner ring11with tracks due to inadequate lubricationCopyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.3Tracks in the case of contamination in bearing or lubricantSymptoms:Symptoms of contamination:9Indentations as a result of foreign particles beingcycled on the raceway9Fatigue resulting from the cycling of foreign particles9Evidence of liquid contamination:9Water can be taken up in small amounts by thelubricant – degrades the effect of lubrication9In case of large amounts of moisture in the bearing dulltracks arise9Pressure-polished tracks with fatigue damage resultsfrom corrosion or high loadCauses:9Inadequate sealingFigure 4 Deep groove ball bearing with9Mounting conditions not cleantracks due to contamination in bearing or9Production residues, e.g. foundry sand9Temperature differences (condensation of water)9Dirty oillubricationPossible remedies:9Improve sealing constructively9Clean mounting and well washed mating parts, coat if necessary9Clean and rinse the entire oil system before commencing operation12Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.4Unusual tracks with detrimental radial preloadSymptoms:9Circumferential tracks appear on both rings in thecase of detrimental radial preload.9Running hotCauses:9Fit interference at shaft/ housing too large9Excessive temperature difference between inner andouter ring9Bearing clearance too smallFigure 5 Deep groove ball bearing underdetrimental radial pre-loadPossible remedies:9Check fit and form accuracy of mating parts9Change clearance to suit operating conditionsFigure 6: Deep groove ball bearing with innerring tracking13Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.5Tracks with oval deformationSymptoms:9Separate tracking patterns developcircumference of the stationary ringontheCauses:9Oval housing or shaft9Poor housing rigidity and support or high interferencefits on the outer ring9Storing bearings in the vertical positionPossible remedies:Figure 7 Oval deformation of a deep9Check fit and form accuracy of mating partsgroove ball bearing due to oval shaft or9Change assembly and operating conditions9Store r’s14Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.6Detrimental axial pre-loadSymptoms:9Only the locating bearing of a locating-floating bearing arrangement may have distinctive tracks.9At the most, a slight axial load share should be detected on the floating bearing.Figure 8: Running Tracks of a similar bearing arrangement under detrimental pre-loadCauses:9Disturbed floating bearing function (wrong fit, radial-acting heat expansion, tilting, fretting corrosion)9Unexpectedly high axial-loadingPossible remedies:9Check fits and form accuracy of mating parts9Change assembly and operating conditions9Use cylindrical roller bearing N, NU, NJ to allow linear expansion of the shaft when permissible.15Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.7Tracks with misalignmentSymptoms:9Tracking pattern of the stationary ring does notran parallel with the racewayCauses:9Shaft deflection9Poorly aligned housing halves or plummer blockhousings9Out-of-square abutment surfaces9Dirt between abutment surfaces and bearingrings during mounting9Bearing clearance is too high in combination withmoment loadFigure 9: Oblique track in inner ring ofdeep groove ball bearingPossible remedies:9Observe mounting specifications regardingpermissible tilting9Ensure cleanliness during mounting9Set suitable bearing clearance16Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.8Fatigue of rolling bearings due to misalignmentSymptoms:9Material flaking (relatively deep)9Tracking asymmetric to bearing centre9Fatigue damage on the edges of raceway and/ orrolling elementsCauses:9Misalignment of the housing or shaft, bending ortilting loads9Balls running on the shoulder edgeFigure 10: Fatigue may occur at the edgeof the raceway of a misaligned taperedroller bearing due to local overload.Possible remedies:9Use self-aligning bearings9Correct misalignment9Strengthen shaft17Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.9Fatigue as a result of poor lubricationSymptoms:Diverse damage patterns arise9Tiny superficial fractures and pitting developsCauses:9Poor lubrication conditioninsufficient lubricant supply9Operating temperature too high9Water penetration9Very low or high loads on the raceways9Slippage at timesasaresultofFigure 11: Micro PittingPossible remedies:9Increase lubricant quantity9Use lubricant with a higher viscosity, if possiblewith tested Extreme Pressure (EP) additives9Cool lubricant/ bearing position9Use softer grease perhaps9Prevent water penetration18Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.10 CorrosionCorrosion in rolling bearings may occur in various forms and have different causes. The damage shows upas uneven and loud running noise. Corrosion (dark grey stains and pitting) will ultimately cause wear andspalling.Symptoms:9Brownish discoloration of the complete bearingsurface, usually unevenly distributed in theform of individual pits9Spots of rust with pits9Wear at a later stage and premature fatigueoriginating at the rust pitsFigure 12: ‘Etched’ surfaces are caused byCauses:aggressive media.9Inadequate sealing against moisture,9acid fumes,9lubricants containing acids,9condensation,9unsuitable storage of the rolling bearings in thewarehouse.Possible ons of rolling bearing manufacturer9Improvementperhaps)9Use lubricant with corrosion inhibitors9Re-lubricate frequently in the case of greaselubrication, particularly prior to standstillperiodsinseals(additionalshieldsFigure 13: Surface damage due to attack ofaggressive media. The etching pits are usuallyblack19Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.11False BrinellingSymptoms:9Shinny marks and recesses on the racewaysurface at the rolling element pitch9No raised edges as opposed to marks dueto incorrect mounting9Scratches in the axial directionFigure 14: On the inner ring of a cylindrical rollerbearing, marks due to false brinelling have developedCauses:9on the raceway at rolling element pitchVibrations in stationary machines – leads tomicro-motion in the contact areasPossible remedies:9Eliminate or absorb vibrations9Use locking devices to prevent possiblemovement during transportation9Slowly rotate bearings and shaft when not inserviceFigure 15: False brinelling marks on the inner ring of aangular contact ball bearing20Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.12 Passage of Electric CurrentElectrical FlutingSymptoms:9Brownish marks parallel to the axis on alarge part of the raceway or covering theentire raceway circumferenceCauses:9Constant passage of alternating or directcurrent, even low currents cause marksPossible remedies:99Prevent currents from flowing through thebearing (earthing, insulation)Figure 17: Fluting in the inner ring raceway of aUse current insulated bearingspassage of currenttapered roller bearing was caused by the constantFusion CraterSymptoms:9The surface in the fusion craters is partlyformed like welding beads.Causes:9Welding or poor earth contactRemedial measures:99Do not direct current through bearingduring electro weldingAttached additional earth connections.Figure 18: Fusion Crater on the inner ring racewayof a cylindrical roller bearing due to welding21Copyright 2005 FAG Australia Pty Ltd
Rolling Bearing Failure Analysis2.1.13 Ring fracturesAxial cracks and completely cracked inner ringsSymptoms:9Ring partly or completely cracked in the axialdirection9Sharp-edged crack flanks indicatefracture occurred during dismounting9In case of long term operation the edges ofthe cracks may be broken offthatCauses:9Bearing slippage9Fractures in the raceway9Rotation of outer ring on the shaft9Unsuitable lubrication9Fit too tight on the shaft9Keyway or grooves in load zone9Out-of-roundness9Grazing against surrounding partsFigure 19: Cracked inner ring of a spherical rollerbearingPossible r
contents 1. bearing failure analysis 3 1.1 determination of operating data 3 1.2 lubricant sampling 4 1.3 inspection of the bearing environment 4 1.4 assessment of bearing in mounted condition 5 1.5 dismounting the damaged bearing 5 1.6 assessment of the complete bearing 5 1.7 assessment of bearing components
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investigated. Bearing failure frequencies by vibrations analysis methods using envelope and spectrum are resear-ched. Spherical roller bearing with 23160 NTN code failure analysis for prevent catastrophic failure is analyzed, and after detecting this failure, bearing was replaced. The bearing that is analyzed is shown (Fig. 1). Bearing Failure .
The FAG rolling bearing programme The FAG rolling bearing programme The FAG rolling bearing programme offers rolling bearings within outside diameters ranging from 3 millimetres to 4.25 metres, housings and accessories. The catalogue WL 41 520 “FAG Rolling Bearings” contains excerpts from
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Cylindrical Roller Bearing for Universal Joints . LYC s standard needle roller bearing tolerance is according to GB/T307.1 Rolling Bearing, Radial Bearing, and Tolerance The clearance of LYC s needle rolling bearing with inner and outer ring is according to GB/T4604 Rolling Bearing, and
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lubrication of different machine parts, including rolling bearings. Improper lubrication of the rolling bearing leads to premature bearing degradation, which can cause unexpected machine failure. According to research published in [1], [2], and [3], 80% of bearing faults is caused by improper lubrication conditions.
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