What Is a Thrust Bearing?

Thrust bearings are used to support axial loads in one direction only. They are not able to support any radial loads. They have a separable design that facilitates easy mounting, dismounting and bearing inspection.

When properly lubricated and maintained, thrust bearings can last for decades. This is why it's important to follow maintenance and inspection procedures to avoid any mechanical failures due to heat buildup.

Material

KML Bearing USA’s thrust ball bearings feature an inner ring, outer ring and balls manufactured from vacuum degassed 52100 bearing steel. After production, they are heat treated to produce a hard, durable surface and extend the bearing life by reducing wear.

The thrust bearings also include double direction angular contact thrust ball bearings that can accommodate axial loads in both directions. They are designed to mount in combination with cylindrical roller bearings from the NN 30 K series in the same housing bore which simplifies shaft mounting and reduces machining.

Another type of thrust bearing is a tapered roller thrust bearing that uses small tapered rollers with their axes pointing toward the thrust axis. These are used in applications with minimal or low axial loading.

Design

Like other types of bearings, thrust bearings rely on rolling elements to support axial loads. However, unlike radial bearings that have races machined into the inner and outer rings, these thrust-only bearings typically feature flat raceways on one or both of the mating components.

Thrust ball bearings consist of a shaft raceway washer, a housing raceway washer and the ball and cage. They are available in both single direction and double-direction designs. Those with spherical housing washers can prevent static misalignment.

RTDs can be installed on the thrust pads to monitor differential pressure (DP). A trend of a rising DP indicates that there may be labyrinth seal wear around the balance drum and should trigger an opening of the case for maintenance. The DP can also be fed into the DCS for real-time monitoring and trending.

Size

The size of a thrust bearing is determined by the maximum load it can handle. Its capacity is based on the combination of the bearing design and the equipment manufacturer's specifications. The bearing is typically selected to be smaller than the largest axial displacement typical of a system.

Normally, single direction thrust bearings have flat seat designs and are designed and intended to support pure axial loads only. Some have a reduced bore on one race to accommodate a stepped shaft. Others have grooved washers and can accommodate bi-directional loads.

Other types of thrust bearings include cylindrical, tapered roller, spherical roller, fluid and magnetic. Click on INFO for technical drawings and load and speed ratings.

Lubrication

The main problem with thrust bearings is inadequate lubrication. Lubrication is a critical process that must be able to balance the generation of heat in the bearing with the rate at which it can be dissipated. The heat that is generated can be harmful to the lubricant and it can cause thermal distortions on the bearing surface.

One method to lubricate the bearing is with a spray-type nozzle that is threaded into the ring and directs the oil at the friction surfaces between the collar and the pads. However, this approach can present problems including churning of the lubricant and inadequate contact of the bearing with the friction surfaces. This type of lubrication system has been shown to fail. A simulated test of the bearing was conducted to present an effective method for measuring the air film thickness and the swing motions of the tilting pads.

Maintenance

Thrust bearings are tailor-made for managing axial loads, or forces that run parallel to the shaft axis. They underpin rotational motion in industrial machinery and aerospace systems.

They work in tandem with radial bearings to distribute axial loads and minimize friction and wear on the shaft. This is particularly important in high-speed applications.

Regular maintenance is essential for thrust bearings to function properly. Common causes of failure include contamination, misalignment and overloading. Contamination can come from airborne dust, dirt and other debris that enters the bearing. Filtered lubrication and cleaning tools and workspaces can help reduce contamination risk. Overloading causes excessive heat, which degrades lubricant and increases friction and wear. Proper sizing and use of load-monitoring technology like a DP transmitter can prevent overloading.