Feature Maintenance management Where repair beats replacement


Bearing repair is not a new concept, but it is increasingly popular with heavy industrial customers, providing a tangible value. Advancements in bearing design, steel cleanliness, bearing maintenance and repair processes have greatly improved the potential benefits for bearing repair, according to Jay Alexander, Timken Industrial Service Centre plant manager


nance work schedules, unnecessary downtime and extended on-time delivery to final customers. In most heavy industrial applications, bearings are removed from service before they have reached their full useful and economic life. Bearing repair can be an effective way to extend the life of the bearing further along its theoretical bearing life, making it an economical alternative to purchasing new.


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A case for repair Advancements in technology, materi- als, condition monitoring and reliabil- ity centered maintenance programs combined with economic pressures contribute to an increased potential for successful bearing repair programs. A quality repair program can often return a bearing to like-new specifica- tions in about one third of the time it takes to procure a new bearing. Depending on the scope of work, a repaired bearing can save up to 60 per cent off the cost of buying new. Some bearing repair sources will also offer a warranty on their service. When compared to the manufacture


of a new bearing, bearing repair is con- sidered a more environmentally friendly procedure, requiring less energy input and reducing raw mater- ial consumption and waste. In addi- tion to cost and time savings, bearing repair maximises the opportunity to achieve the theoretical bearing lifecy- cle. A common question is whether a repaired bearing will last as long as a new one. Studies performed by bear- ing manufacturers and independent researchers have shown that a prop- erly repaired bearing will run a second service cycle comparable to that of the first. Repaired bearings often reuse materials that have already proved reliable in the application, therefore reducing the risk of bearing failure.


Repair – what’s eligible? Although it offers many benefits, repair is not always the best option for a dam- aged bearing. The challenge of prop-


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hen a bearing is damaged, the entire operation will suffer, resulting in additional costs, lengthened mainte-


shims would be provided. These levels of repair have traditionally been suited for bearings with a 12-inch I.D. and greater. However, reclamation service cares for bearings as small as three inches in I.D. Smaller bearings that were often thrown away can now be handled, if received in large quantities, and returned to service. Cleaning, inspection and the application of a polishing finish can return these used bearings to like-new condition for a fraction of the cost of replacement. It is good practice to have a service techni- cian review product before it is returned to a repair centre to make sure it is feasible to repair.


erly utilising bearing repair services is determining if and when bearings need to be repaired and deciding which option is the best economical and long- term decision. A critical step in any bearing repair program is to recognise potential problems through regular monitoring and inspection. Properly trained and experienced personnel involved in routine inspections serve as the first line in deciding if a bearing needs repair. Early detection of a prob- lem through routine checks, preventive and predictive maintenance, and vibra- tion analysis can reduce unnecessary downtime and expense, and help to capitalise on capabilities and benefits of bearing repair.


Repair options/methods Various industries and applications may demand different scopes of repair service, but generally, repair service tends to fall into three types. A Type I service generally describes the recerti- fication or clean and inspection repair process. Type 2 generally applies to the reconditioning or polishing repair process. Bearings with more extensive damage require a Type 3 level of ser- vice, referred to as the remanufacturing process. This level involves extensive processes, such as regrinding of races, replacement of rollers or cage compo- nents and may even include replace- ment of a bearing race. Often, the regrinding of raceways will require the manufacture of oversize rollers to maintain bearing geometry and clear- ance in bearings where radial internal clearance is critically held. In cases where lateral clearance is held – over- size rollers, new spacers or additional


The outer race of a large spherical roller bearing before (left) and after (right) remanufacture


Limitations/expectations Although bearing repair has proven to be a cost-effective solution, it is subject to limitations. Bearings can be repaired, often more than once, but not indefinitely. A general rule of thumb is that bearings should not have more than three regrinds. Regrinding removes surface material, so needs to be done carefully. The Timken Company suggests the maximum stock removal on any race should be .025in. of the diameter and the roller size should not exceed .015in. in diameter from the original equipment manufac- turer standard size. If done correctly, repaired bearings


offer like-new performance. However, it is important to recognise and under- stand how repair options address damage modes. For example, polishing can address a variety of damage modes but is not effective for the removal of debris indentations or wear. In such cases, do not expect like-new perfor- mance if the bearing is only polished. It is recommended to consult with a


A quality bearing repair program can result in significant savings compared to discarding and purchasing new bearings


Timken Industrial Service Centre www.timken.co.uk Enter 322


bearing manufacturer representative and/or application engineer to deter- mine the cause, extent and suggested repair of the damage. It also is critical to have any bearing repair performed by properly trained and experienced personnel. In addition to expertise, proper equipment is required to fix the problem and ensure damage has been reviewed and properly removed.


Conclusion The growing popularity of bearing repair demonstrates the increased understanding of the benefits and value it offers. A quality bearing repair program can result in significant savings compared with discarding and purchasing new bearings. In addition, the lead time for repair is substantially less than that of a new bearing.


SEPTEMBER 2013 Factory Equipment


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