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识别和纠正引起轴承故障的原因

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Identifying andcorrecting the causes of bearing failure

Identifying andanalysing the root cause of a bearing failure is critical in order to preventsimilar failures from occuring again. Brian Williams, Quality Director at TheBarden Corporation, urges companies to introduce a regime that enables thesymptoms of bearing damage to be recognised early, as well as putting asystematic procedure in place for securing damaged bearings.

Many bearings that fail are removed andreplaced too quickly without sufficient levels of analysis into what causedtheir failure. This means that similar failures could occur again, resulting infurther damage and costly unscheduled downtime.

Examination of the failure mode oftenreveals the true cause of bearing failure, but this procedure is complicated bythe fact that one failure mode may initiate another. For example, corrosion ina ball raceway leaves rust (an abrasive), which can cause wear, resulting inloss of preload or an increase in radial clearance. The wear debris can, in agrease-lubricated bearing, impede lubrication, resulting in lubrication failureand subsequent overheating.

Companies can address these issues bydeveloping a systematic procedure for securing and inspecting bearings oncethey become damaged. Engineers should not wait until the bearing failurebecomes catastrophic, as this makes root cause analysis difficult. Instead,engineers need to perform regular monitoring and inspection of the bearings.

When precision ball bearings or rollingbearings fail, the results can be costly in terms of machine downtime and‘lost’ production. Fortunately, catastrophic failures of bearings are rare.Usually there are distinct symptoms that indicate the type of damage incurredlong before the bearings actually fail. It is therefore important for companiesto have a regime in place that enables the symptoms of bearing damage to berecognised early in their development. Once this has been acheived there mustalso be a system in place that preserves the condition of the bearings whenthey are removed from the machine in their damaged state. This is critical inassisting the bearing manufacturer to analyse the causes of failure and toavoid similar issues in the future.

Operating behaviour indicates damage

Experience shows that damge to, andsubsequent failure of, bearings is seldom due to faults in the bearingsthemselves, but more often due to the treatment they have received or the useto which they have been put. Often, the first sign of damage is indicated byunusual operating behaviour of the bearings. This can take the form of unevenrunning, reduced working accuracy, unusual running noises or any combination ofthe three. It is critical for these early indicators to be logged, asinformation gained in this early period of degradation can be very useful inidentifying te root cause of a problem. Often, as a bearing becomes moredamaged, root cause analysis becomes increasingly difficult.


The key to detecting the early signs ofa problem is effective bearing monitoring. This can take many forms, but forthe vast majority of bearing applications the monitoring supplied by themachine operator is usually sufficient to detect unusual noises at an earlystage. In situations where downtime is critical or hazardous, then moreformalised monitoring is required. A number of methods are available includingmonitoring lubricant cleanliness, measuring bearing temperature and vibrationanalysis.

The type of condition monitoringemployed is as much a factor of the experience of previous failures as theproduction environment in which the bearings are used. Bearing damage cangenerally be classified into two groups – localised or widespread. Localised damageis usually restricted to specific locations on the bearing. This can take theform of indentations caused by rolling elements, corrosion or fractures. It canbe recognised most easily using a combination of vibration and lubricantmonitoring. Vibration methods will also reliably detect fatigue damage at anyearly stage, but are not suitable for detecting lubrication problems.

Widespread damage is often the result ofan insufficient supply of clean lubricant. Failures of this type can bedetected by monitoring the lubricant suppply. Oil flow can be monitored forpressure, flow and cleanliness. A magnetic plug gives a crude indicaton oflubricant condition, whilst a spectral analysis can be used to provide a moreprecise check.

Temperature can be monitored usingthermocouples and gives a very reliable indicator of impending bearingproblems. Normally a system should reach a steady state temperature and willshow a sudden rise when there is a lack of lubricant. Typically, with grease,the temperature will rise unevenly over time if there is a generaldeterioration in the grease condition.

Securing damaged bearings

When a bearing has to be removed from amachine due to damage, the cause must be established to avoid future failures.Inspection of the bearings alone is not normally enough to pinpoint the exactcause of the damage, but rather the inspection of the mating parts, lubricationand sealing, as well as the operating and environmental conditons.

A systematic procedure for removalshould be followed to securing and inspecting the bearing. The recommendedsequence of measures is shown below:

1. Determineoperating data

2. Evaluate recordsand charts from any bearing monitoring devices

3. Extractlubricant samples

4. Check bearingenvironment for external influences and other damage

5. Assess thebearing in its mounted condition

6. Mark themounting position

7. Dismount thebearing

8. Mark bearingsand parts

9. Check beatingseats

10. Assess completebearing

The above methodology is a comprehensive one for carryingout damage assessment. However, its usefulness will decline if the level ofdamge in allowed to become excessive. The earlier a bearing can be dismounted,the more effective the assessment process will be.