- 6 December 2006 -
How to maximize bearing service life in pumps
Nominal rolling bearing life in centrifugal pumps may range from 20,000 to 80,000 hours. However, the actual service life is determined by many factors - premature bearing failures cause costly equipment downtime, sometimes even with very serious consequences. Bearing experts from NKE Austria suggest some simple yet practical tips to optimize bearing performance.
Optimal bearing life starts with the right bearing choice. Right from the very beginning, design engineers can enhance the bearing service life and hence the equipment performance by selecting the right bearings for the application. Many factors - such as loads, rigidity, bearing life expectation, operating environment, etc - need be considered.
Bearings from renowned manufacturers are produced with the latest technology and undergo stringent quality assurance procedures. Nevertheless, to guarantee the optimum bearing service life, special attention should be made in the following aspects:
Appropriate storage
In principal all bearings should be stored in their original packaging until being mounted. They should be kept in a clean, non-humid environment at a fairly stable room temperature. Rolling bearings should be stored away from dust, water and aggressive chemicals. Vibrations and shocks could permanently damage the bearings mechanically and therefore must be avoided during handling and storage.
Basically, all bearings must be stored flat. Larger, and thus heavier, bearings may be deformed by their own weights if they are left standing vertically for a long period.
Special care should be taken for the storage of pre-greased (sealed or shielded) bearings. Such grease could change in consistency over a long storage period. This could raise the running noise to a certain extent when put in operation for the first time. Therefore the shelf-life of such bearings should be controlled by a first in first out system.
Cleanliness
Cleanliness is paramount when dealing with rolling bearings. The running surfaces of bearing rings and rolling elements usually have a surface finish roughness of tenths of microns (1/10 µm or 0.0001 mm), and such smooth surfaces are very sensitive to damages by contaminants. The lubrication layer between the running surfaces has usually a thickness between 0.2 to 1 µm. Impurities with particle size larger than the lubricants could become over-rolled by the rolling elements and thus build up localised stresses in the bearing steel and eventually cause premature material fatigue. As well as this, normal environment dust has a grain size of up to 10 µm, which could already damage the bearings. Therefore, a clean, dust-free environment is extremely important for bearing storage and mounting.
Thorough preparation for mounting
Bearings should be mounted and dismounted carefully by means of appropriate tools. Industry experts estimate that 16% of all premature bearing failures are caused by improper fitting. For volume mounting (i.e. in the production assembly) the conditions are usually strictly controlled, and the suitable equipment is available for bearing installation.
However, for maintenance or replacement works, the environments could vary. Therefore, thorough preparation for bearing fitting is necessary in order to ensure the optimum bearing service life. First of all, the relevant documentation, such as drawings, maintenance manuals, specifications, etc., should be carefully studied. Next, all components of the bearing arrangement, such as shafts, distance rings, housings, cups and flanges must be thoroughly cleaned and protected from contaminants. The conditions of such adjacent components should also be checked carefully.
Pump Industry Analyst
Sealing Technology
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