LoadContact Patterns：loadcontact模式.doc

BEARING FAILURELoad/Contact PatternsAs bearings rotate, the raceways of the inner ring and outer ring make contact with the rolling elements. This results in a Wear path on both the rolling elements and raceways. Running traces are useful, because they indicate the load conditions. They should be carefully observed when bearings are disassembled.If the running traces are clearly defined, it is possible to determine whether the bearing is carrying a radial load, axial load or moment load. Additionally running traces can help determine the accuracy of bearing roundness, confirm whether unexpected loads or large mounting errors occurred, and shed light on probable causes of bearing damage. (R1)Typical Running Traces of Deep Groove Ball Bearings(a) shows the most common running trace generated when the inner ring rotates under a radial load only. (e) through (h) show different running traces that result in a shortened life due to their adverse effect on bearings. (R2)(a)(b)(c)(d)Inner ring rotation Radial loadOuter ring rotation Radial loadInner ring or outer ring rotation Axial load in one directionInner ring rotationRadial and axial loads (e)(f)(g)(h)Inner ring rotation Axial load and misalignmentInner ring rotation Moment load (Misalignment)Inner ring rotation Housing bore is ovalInner ring rotation No radial internal clearance (Negative operating clearance)Typical Running Traces of Roller Bearings(i) Shows the outer ring running trace when a radial load is properly applied to a cylindrical roller bearing which has a load on a rotating inner ring. (j) Shows the running trace in the case of shaft bending or relative inclination between the inner and outer rings. This misalignment leads to the generation of slightly shaded (dull) bands in the width direction. Traces are diagonal at the beginning and end of the loading zone. For double-row tapered roller bearings where a single load is applied to the rotating inner ring, (k) shows the running trace on the outer ring under radial load while (I) shows the running trace on the outer ring under axial load. When misalignment exists between the inner and the outer rings, then the application of a radial load causes running traces to appear on the outer ring as shown in (m). (R3)(i)(j)(k)(l)(m)Inner ring rotation Radial loadInner ring rotation Moment load (Misalignment)Inner ring rotation Radial loadInner ring rotation Axial loadInner ring rotation Radial and moment loads (Misalignment)Damage Types & CausesIn general, if rolling bearings are used correctly, they will survive to their predicted fatigue life. Bearings, however, often fail prematurely due to avoidable mistakes. The causes of, this premature failure include improper mounting, mishandling, poor lubrication, entry of foreign matter or abnormal heat generation.For example, one cause of premature failure is rib Scoring which is due to insufficient lubrication, use of improper lubricant, faulty lubrication system, entry of foreign matter, bearing mounting error, excessive deflection of the shaft or some combination of these. If all conditions are known for the times both before and after the failure, including the application, the operating conditions, and environment, then a countermeasure can be determined by studying the nature of the failure and its probable causes. A successful countermeasure will reduce similar failures or prevent them from happening again.Examples of bearing damage and countermeasures are presented in the following sections. Please consult these sections when trying to determine the cause of bearing damage. (R4)FlakingPeelingScoringSmearingFractureCracksCage DamageDentingPittingWearFrettingFalse BrinellingCreepSeizureElectrical CorrosionRust and CorrosionMounting FlawsDiscoloration1. Flaking (R5)Damage ConditionPossible CausesCountermeasuresFlaking occurs when small pieces of bearing material are split off from the smooth surface of the raceway or rolling elements due to rolling fatigue, thereby creating regions having rough and coarse texture.Excessive load; Poor mounting (misalignment); Moment load; Entry of foreign debris, water penetration; Poor lubrication, improper lubricant; Unsuitable bearing clearance; Improper precision for shaft or housing, unevenness in housing rigidity, large shaft bending; Progression from rust, corrosion pits, Smearing, dents (brinelling) Reconfirm the bearing application and check the load conditions Improve the mounting method Improve the sealing mechanism, prevent rusting during non-running Use a lubricant with a proper viscosity, improve the lubrication method Check the precision of shaft and housing Check the bearing internal clearance Photo 1-1Part : Inner ring of an angular contact ball bearingSymptom : Flaking around half of the circumference of the raceway surface Cause : Poor lubrication due to entry of cutting coolant into bearingPhoto 1-2Part : Inner ring of an angular contact ball bearingSymptom : Flaking diagonally along raceway Cause : Poor alignment between shaft and housing during mountingPhoto 1-3Part : Inner ring of deep groove ball bearingSymptom : Flaking of raceway at ball pitchCause : Dents due to shock load during mountingPhoto 1-4Part : Inner ring of an angular contact ball bearingSymptom : Flaking of raceway at ball pitchCause : Dents due to shock load while stationaryPhoto 1-5Part : Outer ring of Photo 1-4Symptom : Flaking of raceway surface at ball pitchCause : Dents due to shock load while stationaryPhoto 1-6Part : Balls of Photo 1-4Symptom : Flaking of ball surfaceCause : Dents due to shock load while stationaryPhoto 1-7Part : Inner ring of a spherical roller bearingSymptom : Flaking of only one raceway over its entire circumference Cause : Excessive axial loadPhoto 1-8Part : Outer ring of Photo 1-7Symptom : Flaking of only one raceway over its entire circumferenceCause : Excessive axial loadPhoto 1-9Part : Inner ring of a spherical roller bearingSymptom : Flaking of only one row of racewayCause : Poor lubricationPhoto 1-10Part : Rollers of a cylindrical roller bearingSymptom : Premature Flaking occurs axially on the rolling surfacesCause : Scratches caused during improper mounting2. Peeling (R6)Damage ConditionPossible CausesCountermeasuresDull or cloudy spots appear on surface along with light Wear. From such dull spots, tiny Cracks are generated downward to a depth of 5-10 m. Small particles fall off and minor Flaking occurs widely.Unsuitable lubricantEntry of debris into lubrication Rough surface due to poor lubricationSurface roughness of mating rolling partsSelect a proper lubricant Improve the sealing mechanism Improve the surface finish of the rolling mating parts Photo 2-1Part : Inner ring of a spherical roller bearingSymptom : Rounded areas of PeelingCause : Poor lubricationPhoto 2-2Part : Enlargement of Photo 2-1Photo 2-3Part : Convex rollers of Photo 2-1Symptom : Rounded areas of Peeling on the center of the rolling surfacesCause : Poor lubricationPhoto 2-4Part : Outer ring of a spherical roller bearingSymptom : Peeling occurs near the shoulder of the raceway over the entire circumference Cause : Poor lubrication3. Scoring (R7)Damage ConditionPossible CausesCountermeasuresScoring is surface damage due to accumulated small seizures caused by sliding under improper lubrication or severe operating conditions. Linear damage appears circumferentially on the raceway and roller surfaces. Cycloidal shaped damage on the roller ends and Scoring on the rib surface contacting roller ends also occur.Excessive load, excessive preloadPoor lubricationParticles are caught in the surfaceInclination of inner and outer ringsShaft bendingPoor precision of the shaft and housingCheck the size of the load Adjust the preload Improve the lubricant and the lubrication method Check the precision of the shaft and housing Photo 3-1Part : Inner ring of a spherical roller bearingSymptom : Scoring on large rib face of inner ringCause : Roller slippage due to sudden acceleration and decelerationPhoto 3-1Part : Inner ring of a tapered roller thrust bearingSymptom : Scoring on the face of inner ring ribCause : Worn particles mixed with lubricant, and breakdown of oil film due to excessive load Photo 3-1Part : Inner ring of a spherical thrust roller bearingSymptom : Scoring on the rib face of inner ringCause : Debris caught in surface, and excessive axial loadPhoto 3-1Part : Cage of a deep groove ball bearingSymptom : Scoring on the pressed-steel cage pocketsCause : Entry of debris Photo 3-2Part : Convex rollers of Photo 3-1Symptom : Scoring on roller end facesCause : Roller slippage due to sudden acceleration and decelerationPhoto 3-2Part : Rollers of a double-row cylindrical roller bearingSymptom : Scoring. on the roller end facesCause : Poor lubrication and excessive axial load Photo 3-2Part : Convex rollers of Photo 3-5Symptom : Scoring. on the roller end facesCause : Debris caught in surface, and excessive axial load 4. Smearing (R8)Damage ConditionPossible CausesCountermeasuresSmearing is surface damage which occurs from a collection of small seizures between bearing components caused by oil film rupture and/or sliding. Surface roughening occurs along with melting.High speed and light loadSudden acceleration/decelerationImproper lubricantEntry of waterImprove the preload Improve the bearing clearance Use a lubricant with good oil film formation ability Improve the sealing mechanism Photo 4-1Part : Inner ring of a cylindrical roller bearingSymptom : Smearing around circumference of raceway surfaceCause : Roller slippage due to excessive grease quantityPhoto 4-3Part : Inner ring of a spherical roller bearingSymptom : Smearing around circumference of raceway surfaceCause : Poor lubricationPhoto 4-5Part : Inner ring of a spherical roller bearingSymptom : Partial Smearing around circumference of raceway surfaceCause : Poor lubricationPhoto 4-7Part : Convex rollers of Photo 4-5Symptom : Smearing of rolling surfacesCause : Poor lubricationPhoto 4-2Part : Outer ring of Photo 4-1Symptom : Smearing around circumference of raceway surfaceCause : Roller slippage due to excessive grease quantityPhoto 4-4Part : Outer ring of Photo 4-3Symptom : Smearing around circumference of raceway surfaceCause : Poor lubricationPhoto 4-6Part : Outer ring of Photo 4-5Symptom : Partial Smearing around circumference of raceway surfaceCause : Poor lubrication5. Fracture (R9)Damage ConditionPossible CausesCountermeasuresFracture refers to small pieces which were broken off due to excessive load or shock load acting locally on a roller corner or rib of a raceway ring.Impact during mountingExcessive loadPoor handling such as droppingImprove the mounting method (shrink fit, use of proper tools) Reconsider the load conditions Provide enough back-up and support for the bearing rib Photo 5-1Part : Inner ring of a double-row cylindrical roller bearingSymptom : Chipping of the center ribCause : Excessive load during mountingPhoto 5-3Part : Inner ring of a spherical thrust roller bearingSymptom : Fracture of the large ribCause : Repeated shock loadPhoto 5-2Part : Inner ring of a tapered roller bearingSymptom : Fracture of the cone back face ribCause : Large shock during mountingPhoto 5-4Part : Outer ring of a solid type needle roller bearingSymptom : Fracture of the outer ring ribCause : Roller inclination due to excessive loading (Needle rollers are long compared to their diameter. Under excessive or uneven loading, rollers become inclined and push against the ribs.)6. Cracks (R10)Damage ConditionPossible CausesCountermeasuresCracks in the raceway ring and rolling elements. Continued use under this condition leads to larger Cracks or Fractures.Excessive interferenceExcessive load, shock loadProgression of FlakingHeat generation and Fretting caused by contact between mounting parts and raceway ringHeat generation due to CreepPoor taper angle of tapered shaftPoor cylindricality of shaftInterference with bearing chamfer due to a large shaft corner radiusCorrect the interference Check the load conditions Improve the mounting method Use an appropriate shaft shape Photo 6-1Part : Inner ring of a spherical roller bearingSymptom : Rounded areas of PeelingCause : Poor lubricationPhoto 6-3Part : Outer ring of a double-row cylindrical roller bearingSymptoms : Cracks propagated outward in the axial and circumferential directions from the Flaking origin on the raceway surfaceCause : Flaking from a flaw due to shockPhoto 6-5Part : Raceway surface of outer ring in Photo 6-4Symptom : Outside surface crack propagating to the racewayPhoto 6-7Part : Cross section of cracked inner ring in Photo 6-6Symptom : Origin is directly beneath the raceway surfacePhoto 6-2Part : Outer ring of a double-row cylindrical roller bearingSymptom : Thermal Cracks on the outer ring side faceCause : Abnormal heat generation due to contact sliding between mating part and face of outer ringPhoto 6-4Part : Outer ring of a double-row cylindrical roller bearing used for outer ring rolling (Outer ring rotation)Symptom : Cracks on outside surfaceCause : Flat Wear and heat generation due to non-rotation of the outer ringPhoto 6-6Part : Inner ring of a spherical roller bearingSymptom : Axial Cracks on raceway surfaceCause : Large fitting stress due to temperature difference between shaft and inner ringPhoto 6-8Part : Roller of a spherical roller bearingSymptom : Axial Cracks on rolling surface7. Cage Damage (R11)Damage ConditionPossible CausesCountermeasuresCage damage includes:Cage deformation, Fracture and Wear Fracture of cage pillarsDeformation of side faceWear of pocket surfaceWear of guide surfacePoor mounting (Bearing misalignment)Poor handlingLarge moment loadShock and large vibrationExcessive rotation speed, sudden acceleration and decelerationPoor lubricationTemperature riseCheck the mounting method Check the temperature, rotation and load conditions Reduce the vibration Use an appropriate shaft shape Select a different cage type Select a different lubrication method and/or lubricant Photo 7-1Part : Cage of a deep groove ball bearingSymptom : Fracture of pressed-steel cage pocketPhoto 7-3Part : Cage of an angular contact ball bearingSymptom : Fracture of machined high-tension brass cagePhoto 7-5Part : Cage of an angular contact ball bearingSymptom : Pressed-steel cage deformationCause : Shock load due to poor handlingPhoto 7-7Part : Cage of a cylindrical roller bearingSymptom : Deformation and Wear of machined high-tension brass cagePhoto 7-2Part : Cage of an angular contact ball bearingSymptom : Pocket pillar Fractures of a cast iron machined cageCause : Abnormal load action on cage due to misaligned mounting between inner and outer ringsPhoto 7-4Part : Cage of a tapered roller bearingSymptom : Pillar Fractures of pressed-steel cagePhoto 7-6Part : Cage of a cylindrical roller bearingSymptom : Deformation of the side face of machined high-tension brass cageCause : Large shock during mountingPhoto 7-8Part : Cage of an angular contact ball bearingSymptom : Stepped Wear on the outside surface and pocket surface of machined high-tension brass cage8. Denting (R12)Damage ConditionPossible CausesCountermeasuresWhen debris such as small metallic particles are caught in the rolling contact zone, Denting occurs on the raceway surface or rolling element surface. Denting can occur at the rolling element pitch interval if there is a shock during the mounting (brinell dents).Debris such as metallic particles are caught in the surfaceExcessive loadShock during transport or mountingClean the housing Improve the sealing mechanism Filter the lubrication oil Improve the mounting and handling methods Photo 8-1Part : Inner ring of a double-row tapered roller bearingSymptom : Frosted raceway surfaceCause : Debris caught in the surfacePhoto 8-3Part : Inner ring of a tapered roller bearingSymptom : Small and large indentations occur over entire raceway surfaceCause : Debris caught in the surfacePhoto 8-2Part : Outer ring of a double-row tapered roller bearingSymptom : Indentations on raceway surfaceCause : Debris caught in the surfacePhoto 8-4Part : Tapered rollers of Photo 8-3Symptom : Small and large indentations occur over the rolling surfaceCause : Debris caught in the surface9. Pitting (R13)Damage ConditionPossible CausesCountermeasuresPitting has a dull luster and appears on the rolling element surface or raceway surface.Debris becomes caught in the lubricantExposure to moisture in Poor lubricationImprove the sealing mechanism Filter the lubrication oil thoroughly Use a proper lubricant Photo 9-1Part : Outer ring of a slewing bearingSymptom : Pitting on the raceway surfaceCause : RustPhoto 9-2Part : Ball of Photo 9-1Symptom : Pitting on the rolling element surface10. Wear (R14)Damage ConditionPossible CausesCountermeasuresWear is surface deterioration due to sliding friction at the surface of the raceway, rolling elements, roller end faces, rib face, cage pock