How to reduce unexpected bearing failures
Every premature bearing failure reduces plant performance and profitability. According to the technical experts at SKF Maintenance Products, more than 60 per cent of premature bearing failures can be ...
June 1, 2003 | By MRO Magazine
Every premature bearing failure reduces plant performance and profitability. According to the technical experts at SKF Maintenance Products, more than 60 per cent of premature bearing failures can be prevented. Understanding why they fail can lead to better uptime and longer life. Here’s what to look for.
#1. Lubrication: Although sealed-for-life bearings can be fitted and forgotten, some 36 per cent of premature bearing failures are caused by incorrect specification and inadequate application of the lubricant. Inevitably, any bearing deprived of proper lubrication will fail long before its normal service lifespan.
Because bearings are usually the least accessible components of machinery, neglected lubrication frequently compounds the problem. Wherever manual maintenance is not feasible, fully automatic lubrication systems can be specified for optimum lubrication. Effective lubrication, using only recommended greases for the bearings of concern, along with the use of the proper tools and techniques, helps to significantly reduce downtime.
The value and importance of using the right bearing grease for the right application should not be underestimated. For example, all-purpose greases can be inadequate for specialized bearing needs, and can cause problems, rather than be beneficial. Bearing applications have wide variations of load, speed, temperature and environment, and correct lubrication calls for matching the grease precisely to the bearing application.
One solution to ensure consistent bearing lubrication is to use manual or automatic lubricators, either on individual bearings or as part of a system that lubricates multiple bearings.
#2. Fatigue: Whenever machines are overloaded, incorrectly serviced or neglected, bearings suffer from the consequences, resulting in 34 per cent of all premature bearing failures.
Sudden or unexpected failure can be avoided, since neglected or overstressed bearings emit early warning signals that can be detected and interpreted using condition monitoring equipment.
This equipment includes hand-held instruments, hard-wired systems and data management software for periodic or continuous monitoring of key operating parameters.
It’s important to determine the condition of machinery and bearings while they are in operation using predictive maintenance or condition monitoring methods. One aspect of this is to ensure there is no shaft misalignment in the application, as this is the cause of up to 50 per cent of the breakdowns in rotating machinery.
#3. Poor fitting of bearings: The company’s research shows that about 16 per cent of all premature bearing failures are caused by poor fitting (usually brute force) and being unaware of the availability of the correct fitting tools.
Individual installations may require mechanical, hydraulic or heat application methods for correct and efficient mounting or dismounting. A complete range of tools and equipment is available to make these tasks easier, quicker and more cost effective. Professional fitting of bearings, using specialized tools and techniques, is one positive step towards achieving maximum machine uptime.
Most bearings are installed with an interference fit, SKF notes. In such cases, the use of the proper installation tools ensures that the drive-up forces are applied to the ring and not through the rolling elements of the bearing, and that they are applied evenly and effectively, avoiding raceway damage. Special fitting tools are available, as are pullers for dismounting bearings.
Another solution is to mount bearings using heat. Special induction heaters are often used for larger bearings. Note that a bearing should never be heated using an open flame, nor should its temperature be raised to more than 125C, because the material may change metallurgically and produce alterations in diameter or hardness.
It’s also important, for safe tightening and loosening of lock nuts used to secure and adjust bearings, that the exact hook spanner radius is used to reduce nut damage. A spanner that fits the nut properly enables an exact fit.
#4. Contamination: A bearing is a precision component that will not operate efficiently unless both the bearing and its lubricants are isolated from contamination. And, since sealed-for-life bearings in ready-greased variants account for only a small proportion of all bearings in use, at least 14 per cent of all premature bearing failures are attributed to contamination problems.
Consider the manufacturer’s bearing manufacturing and design capabilities and the bearing’s sealing solutions, especially for use in arduous operating environments. MRO
Adapted from SKF Maintenance and Lubrication Products. For more information, visit www.skf.ca or use the reader reply card number below.
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