Bearing revolution – where are they now?

Three years on, is SKF’s CARB bearing fulfilling its potential?

When SKF launched the toroidal roller bearing CARB in 1995 it was heralded as a technological breakthrough SKF claimed that the compact bearing – originally targeted at the pulp and paper industry – combined the ability to accommodate misalignment and axial displacement of shafting while displaying a high radial load carrying capability with very low levels of friction. CARB was also said to enable designers to downsize bearing housings and reduce energy consumption while maintaining or improving bearing life and performance.

In the pulp and paper sector massive savings were made in both maintenance and downtime. But, such has been the interest within steel and metal industries, mining, industrial gearing, power transmission and fans, for instance, that SKF’s application engineering teams have also been heavily involved in extensive proving trials in all these areas over the last two years.

The trials are now developing into both OEM and retrofit contracts for SKF, and over the next 12 months sales of CARB are set to increase by more than 700% compared with 1997.

For example, the CARB bearing can be used in the planetary gear in a planetary gearbox. Ideally, the planetary gear adjusts itself for best possible load distribution along the gear teeth, irrespective of any bending of the planet carrier. A self-aligning bearing, such as a spherical roller bearing, serves this purpose. But the spherical surface of the inside of the outer ring limits the possible width, or demands a greater cross section than there is room for. In some cases this means that the desired load carrying capacity, which is often very high, cannot be reached. The flatter curvature of the CARB bearing rings allows the use of wider and stronger bearings, or allows the gearbox to be downsized for the same performance.

A planetary gear for a speed reducer has been running with CARB bearings. Perfect load distribution of the gear teeth was obtained, and the bearing was no longer the limiting component for gearbox life. These benefits can be used for greater reliability or to make boxes more compact and less complex. In some cases spline couplings and shimming can be dispensed with.