Rolling Bearing Damage - Ε. ΣΚΑΖΙΚΗΣ

1 Rolling Bearing Damage Recognition of Damage and Bearing inspectionRolling Bearing DamageRecognition of Damage and bearinginspectionPubl. No. WL 82 102/3 EAStatus 2001 PrefaceRolling bearings are machine elements found in a wide fieldof applications. They are reliable even under the toughest con-ditions and premature failure is very first sign of Rolling Bearing Damage is primarily un-usual operating behaviour of the bearings. The examination ofdamaged bearings reveals a wide and varied range of phenome-na. Inspection of the bearings alone is normally not enough topinpoint the cause of Damage , but rather the inspection of themating parts, lubrication, and sealing as well as the operatingand environmental conditions. A set procedure for examina-tion facilitates the determination of the cause of brochure is essentially a workshop manual. It providesa survey of typical Bearing Damage , its cause and remedialmeasures. Along with the examples of Damage patterns thepossibility of recognising the Bearing Damage at an early stageare also presented at the which are not classified as damaged are also in-spected within the scope of preventive maintenance which is frequently carried out.

2 This brochure therefore contains examples of bearings with the running features common to thelife in page: What may at first appear to be a photo of sanddunes taken at a high altitude is in fact the wave-shaped defor-mation-wear-profile of a cylindrical roller thrust Bearing . There is less than just 1 micron from peak to valley. At a slowspeed mixed friction occurs in the areas stressed by slidingcontact. Rippling results from the stick-slip operating behaviourindicating Damage .. Damage recognition .. monitoring with technical devices .. Damage .. in certain spots .. of Bearing exchange remaining life ..72 Securing damaged bearings .. of operating data .. and evaluation of lubricant samples .. of Bearing environment .. of Bearing in mounted condition .. damaged Bearing .. check .. of complete Bearing .. to FAG or assessment of individual parts of Bearing ..103 Evaluation of running features and Damage to dismounted bearings.

3 To be taken .. separate parts .. taken with complete Bearing .. Bearing into separate parts .. of Bearing parts .. condition of the seats .. corrosion .. marks or sliding wear .. support of Bearing rings .. grazing tracks .. of Rolling contact .. and significance of tracks .. Normal tracks .. Unusual tracks .. in raceways androlling element surfaces .. Fractures .. Corrosion Damage .. False brinelling .. Rolling element indentations .. Craters and fluting due topassage of electric current .. Rolling element edge running .. fractures .. Fatigue fractures as a result of raceway fatigue .. Axial incipient cracks and through cracksof inner rings .. Outer ring fractures in circumferentialdirection .. scratches and smear marks on thecontact surfaces .. Wear Damage with poor lubrication .. Scratches on Rolling element outside diameters .. Slippage tracks .. Score marks.

4 Due to overheating .. of lip contact .. to lip and roller faces in roller bearings .. Scoring due to foreign particles .. Seizure in lip contact .. Wear in the lip contact area .. Lip fractures .. of cage guiding surfaces .. to seal running areas .. Worn sealing lip tracks .. Discolouration of sealing track .. Damage .. due to starved lubrication and contamination .. due to excess speed .. due to roller skewing .. in ball Bearing cages due to tilting .. of cage connections .. fracture .. due to incorrect mounting .. Damage .. of sealing lips .. due to incorrect mounting ..594 Other means of inspection at FAG .. measuring of bearings and Bearing parts .. analyses and lubricant inspections .. inspection .. micro structure analysis .. electron microscope investigations .. tests .. of load conditions ..713 FAGPagePageSymptomsSources of troubleExamplesUneven runningDamaged ringsMotor vehicles:or Rolling elementsmore and more wheel wobblingincreased tilting clearancevibration of steering systemContaminationFans:growing Excessive Bearing clearancevibrationSaw mills:more knocks and blowsin connecting rodsReducedWear due Lathe:working accuracyto contaminantsgradual developmentor insufficient lubricationof chatter marks on workpieceDamaged ringsGrinders:or Rolling elementswavy ground surfaceChange in adjustmentCold Rolling mill:(clearance or preload)Periodic surface defects on rolled materialsuch as stretcher strains,ghost lines operating clearancerunning noise.

5 Whining or squealingnoiseElectric motorsrumblingExcessive clearanceGearsor irregularDamaged contact areas(the Bearing noisenoiseContaminationis hard to identifyUnsuitable lubricantsince it is generallydrowned by the noiseof the gears)gradual changeChange in operating clearancein running noisedue to temperatureDamaged running track( due to contamination or fatigue)Unusual operating behaviour indicating damageSubjective Damage recognition Bearing monitoring with technical devicesGradual deterioration of the opera-ting behaviour is normally the first signof Bearing Damage . Spontaneous damageis rare, for example that caused by mount -ing errors or a lack of lubrication, which leads to immediate machine down-time. Depending on the operating con-ditions, a few minutes, or under somecircumstances even a few months, maypass from the time Damage begins to themoment the Bearing actually fails. Thecase of application in question and theeffects of Bearing Damage on the ma -chine operation are taken as a basis whenselecting the type of Bearing monitoringto be provided.

6 Subjective Damage recognitionIn the vast majority of Bearing appli-cations it is sufficient when machineoperators watch out for uneven runningor unusual noise in the Bearing system,see table Bearing monitoring with technical devicesBearings which could be hazardouswhen damaged or which could lead tolong production down-times require onthe other hand accurate and constantmonitoring. Two examples are jet engineturbines and paper-making monitoring to be reliable, its extentmust be based on the type of damagewhich may be expected. Wide-spread damageA sufficient supply of clean lubricantis the main precondition for trouble-freeoperation. Undesirable changes can bedetected by: FAG41 Unusual operating behaviour indicating damage1: Recognition of Damage by operating staffTemper-ature1020304050 C123451234 5 Life012h50 LifeTemper-ature10012h203040 C123451234 5 Unusual operating behaviour indicating damageBearing monitoring with technical devices Monitoring lubricant supply oil level window measuring oil pressure measuring oil flow Measuring abraded matter in lubricant at intervalsmagnetic plugspectral analysis of lubricant samplesinspection of oil samples in the lab continuouslymagnetic signal transmitterfinding amount of particles flowingthrough with an online particle counter Measuring temperature generally with thermocouples5 FAG2: March of temperature with intact main spindle bearings in a machine tool.

7 Test condition: n dm= 750 000 min 1 : March of temperature with disturbed floating bearings. Test condition: n dm= 750 000 min 1 very reliable and relatively easy way ofrecognising Damage caused by inade-quate lubrication is by measuring temperature behaviour: reaching a steady state temperature instationary operation, fig. behaviour: sudden rise in temperature caused bylack of lubricant or by the occurrenceof excessive radial or axial preload onthe bearings, fig. 3. uneven march of temperature withmaximum values tending to rise dueto general deterioration of lubrica-tion condition , with attainedgrease service life, fig. the temperature is not suitable, however, to register local Damage at an early stage, C04: March of temperature as a function oftime with failing grease condition: n dm= 200 000 min 1 operating behaviour indicating damageBearing monitoring with technical devicesFAG6406080100120140160180200 Undamaged bearingDamaged bearingVibration acceleration0,086g0,086g0 Frequency [Hz]SidebandsSidebandsHarmonicfIRnIR200n IR2fIRnIRnIR3fIRnIRnIR4fIR5: Frequency spectrum of envelope signal between 0 and 200 Hz,below: undamaged Bearing ; above: damaged bearingnIRInner ring speed [min 1]fIRFrequency of inner ring signal (cycling frequency) [Hz]6: Inner ring Damage to a spherical rol-ler Bearing in a paper making machi-ne found by means of the envelope detection procedure.

8 04812162024minOperation time80401001201401606080100300 Temperature CShock valueLubrication stopped7: March of temperature and shock value as a function of time stopping lubrication. Spindle Bearing ; P/C = ; n = 9000 min 1; Lubricating oil ISO Damage in certain spotsShould Bearing Damage be restrictedto specific locations such as indentationscaused by Rolling elements, standstillcorrosion or fractures, it can be re-cognised at the earliest with vibrationmeasurements. Shock waves which originate from the cycling of local inden-tations can be recorded by means ofpath, speed and acceleration signals can be processed further atlittle or great expense depending on theoperating conditions and the accuracy ofthe expected confidence factor. Themost common are: measuring effective value measuring shock value signal analysis by envelope has shown that the latterprocedure is particularly reliable andpractical in use. The damaged bearingcomponents can even be pinpointedwith a special type of signal processing,figs.

9 5 and 6. Please refer to our TI 80-36 > Rolling Bearing Diagnosiswith the FAG Bearing Analyser<" formore information. Unusual operating behaviour indicating damageBearing monitoring with technical devices Urgency of Bearing exchange7 FAGThe vibration measuring proceduresare very suitable for detecting fatigue Damage . It is easiest with bearings withpoint contact (ball bearings) and withmore sophisticated evaluation proce-dures such as envelope detection, for ex-ample, Damage to roller bearings is found just as reliably. They are less suit-able, however, for observing the lubrica-tion condition. A fault in the lubricantsupply can be reliably spotted by tem-perature measuring, as described is particularly well illustrated in figure 7. The shock value is far less sen-sitive than the temperature sensor. Hence, in the case of expensive technicalplants, temperature and vibration measurements complement one anotherideally. 8: Development of fatigue Damage on the inner ring raceway of an angular contactball Bearing .

10 The periodic intervals between inspections from Damage begin on,are given in percentage of the nominal life Urgency of Bearing exchange remaining lifeOnce Bearing Damage has been detec-ted, the question arises as to whether thebearing must be exchanged immediatelyor whether it is possible to leave it inoperation until the machine's next sche-duled standstill. There are several condi-tions which must be given considerationbefore making any decision. If, for ex-ample, reduced working accuracy of amachine tool is reason to suspect bearingdamage, the urgency of Bearing exchan-ge primarily depends on how long partscan continue to be produced withoutlacking in quality. Bearings which blocksuddenly at a high speed due to hot run-ning caused by an interruption in lubri-cant supply going unrecognised, must bereplaced immediately, of lots of cases a machine may remainin operation without the quality of theproduct suffering despite Damage .