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| ? Why Bearings Fail |
The general classifications of failures and deficiencies requiring bearing removal are overheating, vibration, turning on the shaft, binding of the shaft, noise during operation, and lubricant leakage.
Listed in the following table is a trouble-shooting guide that lists the common causes for each of these failures and deficiencies. As indicated by the causes of failure listed, bearing failures are rarely caused by the bearing itself. Many abnormal vibrations generated by actual bearing problems are the result of improper sizing of the bearing liner or improper lubrication.
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Common causes for each of these failures and their causes and deficiencies. As indicated by the causes of failure listed, bearing failures are rarely caused by the bearing itself.
The primary contributors to abnormal bearing signatures are:
(1) imbalance
(2) misalignment
(3) rotor instability
(4) excessive or abnormal loads
(5) mechanical looseness.
Defective bearings that leave the manufacturer are very rare, and it is estimated that defective bearings contribute to only 2% of total failures. The failure is invariably linked to symptoms of misalignment, imbalance, resonance, and lubrication—or the lack of it. Many of the Bearing Failures are caused from the following reasons and other reasons not stated (share what you have seen).
> Improper lubrication practices (contamination and/or too much or not enough grease) If you see grease coming out of a bearing seal which is not a purge type bearing it is a major problem, "Grease out, Contamination in"
> Lack of known lubrications specifications, defined best practices
> Lack of discipline of lubrication and bearing installation by maintenance techs
> Misalignment > Bent shaft imbalance, resonance, and soft foot
> Handling of Bearings (if you drop a bearing it should not be installed unless you do not have a spare, if this occurs write a work order to replace the bearing to specifications when it can be planned and scheduled)
> Storage of Bearing (store large bearings under vibration pads) "check the floor in your storeroom for vibration, it may surprise you"
> Poor fit resulting in installation damage
> Overloading
> Improper on-site installation
> Lack of discipline by operators and not performing to "Known Best Lubrication Practices" to specifications > Lack of specifications and repeatable lubrication procedures
> Operators not operating the equipment to specifications (operator error) or lack of effective Operator Care > Excessive operating temperature > Contaminated oil/grease supply
Please post your comments. This information came from Keith Mobley and my book: "Industrial Machinery Repair" You can purchase this book in downloadable PDF or order the book by clicking on the icon below:
The Author: Ricky Smith CMRP, CMRT, CRL
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