Revolvo manufactures split roller bearing for undersize shaft

Continuing its recent success in providing large split roller bearings (SRBs) for use in ball mills, Revolvo has won an order from a cement plant in Thailand to supply two large split roller bearings. One is a standard 850mm bore unit and the other is a special 849mm bore bearing to cope with an undersize shaft. Revolvo won the 40,000 order because of its willingness to manufacture the special size bearing, as well as for the overall design of its SRB unit, with a brass instead of aluminium cage, which was considered more durable in the demanding conditions.

The SRBs are being used in a ball mill to crush limestone; the rock actually being fed through the bore of the bearings. The two SRB are replacement units for aluminium-caged split roller bearings that have been failing for some time. The problem with replacing these units has been the issue of an undersized shaft. Both bearing shafts should be 850mm but, due to wear and tear, one shaft is now 1mm undersize. This fact meant that the user either had to replace the shaft completely, which would have been a mammoth and costly undertaking, or find a supplier willing to manufacture a special replacement bearing. The company searched widely for such a supplier, but found Revolvo only through a chance visit to the company's website.

In addition to its standard sizes, Revolvo manufactures larger, non-catalogue bearings in sizes up to 1500mm. These specials are used extensively in process and extraction industries worldwide. Revolvo is able to produce these bearings due its turning capacity of up to 1.8m and its new grinding capability to 1.5m.

Benefits of brass bearing cages

In common with all Revolvo's SRB bearings the Thailand units are being supplied with machined brass cages. Revolvo's cage design has CNC bored pockets that are optimised to give very accurate roller guidance, which prevents skewing, a condition that can lead to edge loading on the bearing and reduced bearing life.

In addition to providing excellent roller guidance, the brass cage also allows operation at higher temperatures up to 140degC without problems, and operating speeds up to 25 per cent higher, as long as thrust loads are within design limits. Overall, brass is one the best cage materials, as it has good frictional properties and performs well in aggressive environments where lubrication is marginal.

The ability of split roller bearings to perform reliably in aggressive cement applications is enhanced by the performance of the sealing systems available to protect the cartridge bearing units. Revolvo has developed a special labyrinth seal to exclude the fine, abrasive and hygroscopic cement dust, which is such a problem for equipment such as screw conveyors in cement plants. This sealing provides much improved bearing reliability and longer life, with greatly reduced levels of maintenance.