Rolling Bearings Preload
The preload of rolling bearings is the tension applied to the bearing to prevent the outer ring of the bearing from rising when the bearing is in operation.
Preload is applied to the bearing in order to obtain the specified operational characteristics. It makes it easier for the rolling elements to move with minimal lubrication and optimize the contact area between the rolling element and the raceway. This enables the bearing to have a longer service life due to reduced internal heat generation. Preload also reduces vibration, noise and improves the accuracy of the bearing.
Preloading methods vary depending on the type of bearing, application and lubrication condition. The preload of a bearing is normally given according to the force, displacement or torque.
The force preload is the most common method and the preload force is generated by the axial prestressing of the bearing. Commonly used force preload methods include axial prestressing of a cylindrical rolling bearing and axial compression of angular contact bearings.
The displacement preload is used for spherical roller bearings and is achieved by adjusting the inner and outer ring spacers.
The torque preload is used for taper roller bearings and is generated by adjusting the adjusting nut.
The required preload for a bearing depends on the bearing and the operating conditions. The preload level will be given in the bearing datasheet. For example, preload levels such as mildly preloaded, lightly preloaded and highly preloaded will be given.
It is important to have the preload level of a bearing in accordance with its application as too much preload can cause brinelling to occur. Brinelling is the permanent indentation of the rolling elements due to excessive preload. It is important to remember that the preload cannot be increased after the bearing has been fitted and it should only be adjusted with special tools to ensure accuracy.
In conclusion, preload is an essential element of any rolling bearing. It is important that the desired preload level is achieved in order to ensure the bearings work to the optimum performance. Careful consideration should be taken when adjusting the preload as too much preload can lead to brinelling and reduce the life of the bearing.
