Thin Section Bearing Selection

Thin section bearings can help reduce the weight and space requirements of an application. It’s therefore essential that the correct bearing type, alignments, recommended fits and shaft and housing geometry are considered during selection.

Silverthin radial ball-type thin section bearings are well-suited to radial loads. However, they can also handle modest axial and reversing loads.

Radial Ball-Type

The majority of bearings used in industry are radial ball-types. These bearings can take a large radial load and small thrust load in one direction (see Figure 2). They have a limited ability to carry axial loads in the opposite direction.

Bearing speed capabilities depend on size, load, cage/retainer material, and lubrication. Heavier loads decrease speed capability. Speed capability increases with smaller diameters. Small bearings are capable of higher speeds because they experience less torque. Plastic retainers and phenolic materials are most capable of high speeds.

Bearings generate heat energy from the mechanical rubbing of the balls and raceways, and this causes friction that can increase temperature. The proper selection of a bearing and its operating conditions can reduce the amount of friction and prevent thermal damage to the bearings.

Angular Contact

Angular Contact bearings are designed to carry combined radial and axial loads. These are often used in demanding applications like pumps and machine tool spindles. Angular Contact bearings can be single-direction or double-direction depending on the load direction and the contact angle between the inner and outer raceways.

Unlike radial bearings that run with grooves, angular contact bearings have asymmetrical outer raceways and spherical rolling elements to reduce friction. A cage separates the rolling elements to keep them apart, allowing for low-friction load transmission.

To support heavy axial loads, Angular Contact Bearings are typically preloaded during installation. This allows them to accommodate a heavy axial load in one direction with little or no loss of capacity or service life.

Four-Point Contact

RBC Thin Section Bearings can handle many different types of load conditions. For example, an airborne radar system required a bearing to take radial, axial and moment loading for an aircraft gun turret azimuth drive assembly. To support the combined load conditions and meet temperature compatibility requirements, a duplex pair of angular contact Thin Section Bearings was chosen.

The X type design of these bearings uses a 'gothic archway' raceway that creates four points of contact between the balls and inner and outer rings, making them ideal for reversing axial loads and moment loads. However, unless they're used in conjunction with a C-type or A-type bearing, Angular Contact Bearings are not recommended for use under radial loads.

The speed suitability of a thin section bearing can be significantly influenced by lubrication, temperature and alignment. For more information on the factors that affect speed ratings, refer to the ABMA Thin Section Bearings Speed Ratings Table. In addition, the radial play tolerances and axial internal clearances for each bearing are shown in the Tolerance Tables.

Full Complement

Double row full complement cylindrical roller bearings incorporate a maximum number of rolling elements and therefore offer particularly high radial rigidity. They also tolerate a higher degree of shaft misalignment than bearings with cage.

NNCF and NNCL type bearings are self-locking: the outer ring has a single rib on one side and a snap ring, preventing it from moving axially during operation. This makes these bearings suitable for high loads and low speeds.

The filler notch design offers increased load capacity. By removing the retainer additional balls can be fitted, increasing the ball complement in both the inner and outer rings.

This increases the radial bearing capacity and allows higher load ratings to be achieved. However, a minimum radial load must be applied to ensure reliable operation (C/P > 25). This value can be determined from the bearing charts. In order to achieve the rated life of the bearing, the contact surfaces of the outer and inner rings must be supported over their entire flange heights without interruption (Figure 1). For this reason, the seating surface must not be interrupted by grooves or holes.