Two years ago, when SKF first announced CARB™ to the pulp and paper industry, engineers wondered whether or not this new Toroidal bearing would be able to live up to its claims. According to Brian Dahmer, the SKF Engineer who has been tracking test results at customer locations, the new bearing is exceeding expectations to the point that engineers outside the pulp and paper industry are testing the new bearing with amazing results. He does caution, however, that CARB is not a panacea and that the old adage, “If one is good, two is better” does not apply to CARB.
About the CARB bearing

The CARB bearing was designed to be used as the floating or non-locating bearing in applications where there is a fixed and a floating bearing. Bearings used in the floating position could be a double-row spherical, a self-aligningdouble-row ball bearing, a deep groove ball bearing, a double row angular contact ball bearing or a needle roller bearing (see Figure 1). CARB could conceivably replace any of these typical selections.

     “In applications like that,” says Dahmer, “there is going
to be a certain amount of shaft deflection to cause misalignment; and shaft thermal
expansion, which causes
axial displacement.” He goes on to say that a self-aligning ball bearing or spherical can accommodate a certain amount of misalignment but compensating for axial
displacement has always been a compromise.

     “Axial displacement is usually compensated for between the bearing and the housing. The mechanic installing the bearing has to leave a certain amount of room in the housing so that the bearing can “float” back and forth. If there’s too much play between the bearing and
housing, it can cause excessive vibration and early bearing failure. If there’s not enough radial (or axial) play, the bearing will heat up and fail prematurely. There’s a very fine line between ‘too tight’ and ‘not tight enough,’” he says.

     One of the real benefits of the CARB bearing, according to Dahmer, is that it handles misalignment and axial displacement internally. “If you look at the design of the CARB bearing (see Figure 2) you can see that the rollers and raceways are designed to seek the position of the least load. And because CARB bearings are installed without flanges, guide rings or housings to
confine them, the rollers are free to find their own optimal position,” he says.

     In talking with maintenance engineers around the country, Dahmer has found a great deal of interest in CARB to reduce vibration in fans. “If you look at a fan,” he says, “there’s no real load to speak of. However, excessive vibration in a typical fan application can substantially reduce bearing life. When we’ve installed a CARB bearing and a spherical (or other double row bearing) in a fan, the results were outstanding and vibration was almost eliminated.”

     To explain how CARB can “fix” problems of vibration caused by uneven load distribution, Dahmer uses a three-legged stool as an example. “Think of the four rows of rollers in two double-row spherical bearings as the four legs on a chair. If one leg on that chair is longer than the others there will always be a problem with proper load distribution. Now think of a three- legged stool. If one leg is shorter or longer, it really doesn’t matter. The stool will be stable and the load will be distributed evenly. The same
is true when you substitute a CARB bearing for a spherical. The design of the CARB bearing allows it to continually search for, and adjust itself to the optimum low load position.

     Dahmer concludes by saying that CARB will eventually revolutionize specialized applications like dryers in paper mills, continuous casters and even industrial transmissions. “This bearing will not only increase service life in these applications, it will accommodate heavier loads than comparably sized ball or roller bearings — and that will enable designers to reduce the size of their housings or casings — which in turn will reduce material costs and weight.”