Types of Bearings

Mechanical bearings are devices that reduce friction and wear between moving parts by providing a smooth contact surface. Bearings can be classified into two main types: journal bearings and rolling element bearings.

Journal bearings are bearings that support a rotating shaft by allowing it to slide along a lubricated surface. The lubricant, usually oil or grease, forms a thin film that separates the shaft and the bearing, preventing metal-to-metal contact. Journal bearings can be further divided into plain bearings, which have a simple cylindrical shape, and hydrodynamic bearings, which have a curved shape that creates a pressure wedge of lubricant.

Rolling element bearings are bearings that use balls, rollers, or needles to support a rotating shaft. The rolling elements reduce friction by rolling instead of sliding along the contact surface. Rolling element bearings can be further divided into ball bearings, which use spherical balls, and roller bearings, which use cylindrical or tapered rollers. Ball bearings can handle both radial and axial loads, while roller bearings can handle higher radial loads but lower axial loads.

Watch the following CAE video to understand the type of rolling element bearings and their uses:

Questions:

Can you answer the following questions after watching the video:

1. What are the main parts of rolling element bearing?
2. What is the advantage of a roller bearing versus a ball bearing?
3. When selecting a bearing, what factors would influence you to select a roller versus a ball bearing?
4. What is the difference between axial loads and radial loads, what type of bearings are used depending on the load levels?

Bearing Selection

Bearing manufacturers provide useful tools on their website to help identify a bearing. In order to use these tools, you will first need to identify the loads that the bearings will need to support using static force analysis, the speed at which the bearing or shaft will be rotating, and the anticipated service life and desired reliability for the bearing. These parameters will help you determine the size, type, and configuration of the bearing that best suits your application.

The dynamic and static load ratings for bearings are important parameters that indicate the load-carrying capacity and durability of the bearings. The dynamic load rating is the maximum load that a bearing can support under a given speed and operating condition, while the static load rating is the maximum load that a bearing can withstand without permanent deformation. The dynamic and static load ratings are usually expressed in newtons (N) or kilonewtons (kN), and they depend on factors such as the material, geometry, design, lubrication, and cleanliness of the bearings. The dynamic and static load ratings are used to calculate the fatigue life and safety factor of the bearings, respectively.

Try it yourself!

Assume you have found the reactions forces (the radial force) that a bearing needs to support from a static analysis. Use that value to select a rolling element bearing using SKF’s selection tool and see how life, reliability and many other factors are calculated based on your loading situation.