Different Types of Thrust Bearings

Bearings are built to support radial loads or thrust loads. However, there are several different types of thrust bearings that each has its own strengths and weaknesses.

Angular contact thrust ball bearings are designed to handle combined radial and single-direction axial loads. They come in single-row or back-to-back duplex configurations and have a higher internal stiffness than grease-lubricated deep groove ball bearings.

Load Capacity

Unlike radial bearings that locate rolling elements on the opposing inner and outer bearing rings, thrust bearings support loads with rolling elements machined into the faces of mating rings. Several styles of thrust bearings are available, but they all share the same basic static load rating and the ability to support axial loads parallel to the shaft axis.

Thrust bearings with deep raceways are the most common and best suited to support heavy loads and high speeds. However, shallower raceways reduce thrust capacity significantly. Thin-section thrust bearings are great for saving space, but they only support axial loads to approximately 25 per cent of the basic static radial load rating.

Spherical thrust bearings support axial loads and can also handle moderate radial loads. Their design allows them to accommodate directional misalignments and shock loads with low friction. This makes them ideal for applications that experience heavy axial and radial loads, or where it may be difficult to achieve and maintain proper alignment of the bearing.

Stiffness

The stiffness of a bearing depends on the design and load capacity. A lower stiffness means more vibrations which can damage internal components. The stiffness can also be reduced by misalignment.

Spherical thrust bearings can support heavy radial and axial loads simultaneously. The design makes them self-aligning and can accommodate misalignment. They can also handle high speeds and shocks.

Needle roller thrust bearings have minimal height, making them ideal for applications with limited space. They can support axial and thrust loads without a counter washer or shaft ring. They are often implemented with a sphered groove on the outer ring to reduce the risk of misalignment.

The stiffness of a bearing must be adequate for the application. This is determined by evaluating the load capacity and shaft washer diameter. It is important that the shaft washer withstands both static and dynamic loading. To maximize this, it should be hardened to at least 58 HRC. This allows the bearing to maintain its load capacity and prevents the formation of heaving rolling-element wear paths and widespread fatigue areas.

Rigidity

Like all bearings, radial thrust bearings support both axial and radial forces. However, they're designed primarily to support axial loads. They can tolerate a minority of radial load, but only if the shaft is aligned correctly with the bearing position.

They have raceways machined into the mating outer and inner rings, with a cage or other structure retaining rolling elements to maintain even load distribution. A ball, needle, or cylindrical roller are common choices for the rolling elements.

A back-to-back arrangement of inner ring faces provides better rigidity than face-to-face arrangements, which don't support moment loads as well (see Image 2). The design of the inner ring faces must be precise to achieve preload and to restrict internal clearance. In addition to static and dynamic loads, the bearing must resist contamination, misalignment, overloading, and vibration. These can all damage the rolling elements or the raceways, leading to failure. To avoid contamination, it's important to filter lubricant and clean work areas.

Design

Unlike radial bearings, thrust bearings support axial loads (a force along the shaft’s axis). They use different geometry to reduce friction.

Spherical roller thrust bearings support moderate radial loads and heavy axial loads with little loss of capacity. Their design allows for a steep contact angle to resist axial load deflection and shaft distortion. Internal self-alignment during operation compensates for mounting errors and shaft deflection.

This type of bearing is available with a flange on the housing washer or without it. The flange prevents axial loading from pulling on the outer ring. It can also be used in opposed pairs (duplex) or in tandem for constant axial load in one direction. Angular contact thrust ball bearings use larger contact angles to handle heavier axial loads and light radial loads. They can also be heat treated to improve their thermal tolerance.