Thrust bearings are classified into thrust ball bearings and thrust roller bearings. Thrust ball bearings are further subdivided into thrust ball bearings and thrust angular contact ball bearings. The raceway ring that mates with the shaft—comprising a washer with a raceway, balls and a cage assembly—is referred to as the shaft ring, whilst the raceway ring that mates with the housing is referred to as the housing ring. In bidirectional bearings, the intermediate ring is fitted to the shaft; unidirectional bearings can withstand axial loads in one direction, whilst bidirectional bearings can withstand axial loads in both directions. Bearings with a spherical mounting surface on the housing ring possess self-aligning properties, which can minimise the effects of mounting errors. These bearings are primarily used in automotive steering mechanisms and machine tool spindles.

Thrust roller bearings are classified into thrust cylindrical roller bearings, thrust self-aligning roller bearings, thrust tapered roller bearings and thrust needle roller bearings.

Thrust cylindrical roller bearings are primarily used in oil drilling rigs and iron and steel manufacturing machinery. Thrust self-aligning roller bearings are mainly used in hydroelectric generators, vertical electric motors, marine propeller shafts, tower cranes and extruders; thrust tapered roller bearings are primarily used as follows: in one direction, they are suitable for crane hooks and the slewing rings of oil drilling rigs; and in both directions for steel rolling mill roll necks; thrust plain bearings primarily bear axial loads within assemblies and are widely used.

Although the installation of thrust bearings is relatively straightforward, errors frequently occur during actual maintenance, namely the incorrect positioning of the bearing’s tight ring and loose ring, resulting in the bearing becoming ineffective and the journal being worn down rapidly. If the tight ring is fitted to the end face of the stationary component, this constitutes incorrect assembly. The inner ring of the tight ring has a transition fit with the journal. When the shaft rotates, it drives the tight ring, causing friction with the end face of the stationary component. When subjected to an axial force (Fx), the frictional torque will exceed the fit resistance torque of the inner diameter, causing the tight ring to rotate forcibly relative to the shaft’s mating surface and accelerating journal wear. The difference between single-direction thrust ball bearings and double-direction thrust ball bearings:

Single-direction thrust ball bearings — These consist of a shaft ring, a housing ring, and a thrust assembly comprising balls and a cage.

The bearings have a separable design, making installation straightforward as the washers and the ball-and-cage assembly can be fitted separately.

There are two types of small single-direction thrust ball bearings: those with a flat housing ring and those with a self-aligning housing ring. Bearings with self-aligning outer rings can be used in conjunction with self-aligning shims to compensate for angular misalignment between the support surface in the bearing housing and the shaft.

Double-direction thrust ball bearings — A double-direction thrust ball bearing comprises three parts: an inner ring, two outer rings and two ball-and-cage assemblies. The bearing is of a separable design, and each component can be fitted independently. The ring that mates with the shaft is called the shaft ring; it can withstand axial loads in both directions and can secure the shaft in either direction. These bearings must never be subjected to any radial load. Thrust ball bearings are also available in a housing-mounted configuration; as the mounting surface of the housing is spherical, the bearing possesses self-aligning properties, which can minimise the effects of mounting errors.

Bidirectional bearings and unidirectional bearings utilise the same shaft ring, housing ring and ball-cage assembly.

Operating conditions for thrust bearings:

Thrust bearings are hydrodynamic bearings; for the bearing to operate correctly, the following conditions must be met:

1. The lubricating oil must have a suitable viscosity;

2. There must be a certain relative velocity between the rotating and stationary components;

3. The two surfaces in relative motion must be inclined to form an oil wedge;

4. External loads must be within the specified range;

5. There must be a sufficient supply of lubricating oil.

Thrust bearings possess excellent self-lubricating and wear-resistant properties, 800 times that of polytetrafluoroethylene (PTFE), and do not damage the mating surfaces; They possess good thermal properties, with a heat distortion temperature of >275 °C, and can be used continuously under load at temperatures up to 240 °C; they are resistant to chemical corrosion, have excellent electrical properties, good sealing performance, do not stick, and are non-toxic; they also exhibit good resistance to compressive creep, which is four times higher than that of pure PTFE.