Bearings - 2016-11-15
The service life of roller bearings used in conveyor belt drive pulleys is an important factor in governing system availability and reliability, particularly in the mining and quarrying industry where conveyors can be several kilometres in length. The selected bearings must not only be able to withstand high loads, but resist penetration by fine grains of particulate present in the working atmosphere.
Spherical roller bearings are typically selected for such applications because they can accommodate high loads and compensate for drive shaft deflection. Until now there were two types of design from which to select. One choice was the use of open bearings with no seals, which could be installed easily and without risk of error because the bearing clearance was easy to set. However, early failure was to be expected with this type of bearing due to the penetration of foreign particles, some of which are highly abrasive.
The alternative has been to use sealed spherical roller bearings, but these have the disadvantage that bearing play cannot be measured when being fitted, which increases the risk of installation errors. What’s more, the seals require additional space to ensure their load rating potential is maximised.
With these factors in mind, NSK has developed new spherical roller bearings specifically for conveyor belt drive pulley applications in sectors such as mining and quarrying. They offer long service life, high load ratings, excellent sealing and dimensions identical to the bearings that were previously in use. In addition, bearing clearance can be measured at any time during installation.
Among the bearing’s principal features, NSK has developed special steels for the inner and outer rings, which in combination with a specific annealing process, increase load capacity and make for a very compact design. As a result, the seal can fit within the available space and ensure the new spherical roller bearings are still able to attain higher dynamic load ratings than conventional bearings.
The special steel materials perform exceptionally well, even when poorly lubricated, while the very efficient seal has proven its resistance in many other harsh environment applications. Importantly, the seal is attached by a bracket screwed to the bearing housing so that it can be removed during installation to measure the bearing radial clearance. This ensures that the clearance is not set too small when sitting tightly in the inner ring, thus preventing early damage to the bearing. NSK estimates that its new spherical roller bearings offer quadruple the service life of conventional alternatives.
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