CARB toroidal roller bearings

CARB toroidal roller bearings (fig. 1) combine the self-aligning capability of spherical roller bearings with the axial displacement ability of cylindrical roller bearings (fig. 2). CARB bearings can also have the compact cross section and high load carrying capacity normally associated with needle roller bearings.
CARB bearings are intended exclusively as non-locating bearings. They can simplify locating/non-locating bearing arrangements because thermal expansion of the shaft can be accommodated within the bearing virtually without friction. Bearing systems consisting of a spherical roller bearing in the locating position and a CARB bearing in the non-locating position (fig. 3) provide a space- and weight-saving bearing system with a low cost of ownership. CARB bearings can reduce noise and vibration levels, for example, in paper machines and fans.
CARB bearings are single row bearings with long, slightly barrel-shaped symmetrical rollers. The outer ring has a torus-shaped raceway with a profile radius extending beyond the centre of the bearing. The inner ring raceway is shaped accordingly. The rollers of CARB bearings are self-guiding, i.e. they always adopt the position where the load is favourably distributed over the roller length, irrespective of whether the bearing rings are misaligned or axially displaced. The ability to distribute loads favourably keeps the friction and frictional heat at low levels. Lower operating temperatures extend the service life of the lubricant and the bearing.

Factors that influence CARB bearing performance

Bearing performance is not only determined by load or speed ratings. There are a number of other factors that contribute to bearing performance. To a large extent, performance is influenced by the geometry of the rollers, raceways and cages, the heat treatment, as well as the surface finish of all contact surfaces. Main factors which influence CARB bearing performance include, but are not limited to:
  • Symmetrical rollers
    Symmetrical rollers self-adjust, providing optimal load distribution along the roller length. This keeps stresses low under all load conditions and extends bearing service life
  • Roller tolerances
    The rollers in a CARB bearing are manufactured to extremely tight tolerances for dimension and form. Each roller is virtually identical in size and shape to the other rollers in the set. This optimizes load distribution over the rollers to maximize bearing service life.
  • Special roller profile
    The roller profile determines the stress distribution in the roller/raceway contact area. The special profile distributes loads more evenly along the rollers and prevents stress peaks at the roller ends to extend bearing service life (fig. 4).
  • Self-guiding rollers
    Self-guiding rollers keep friction and frictional heat at low levels (fig. 5).