Preload of Rolling Bearings
Preloading is an adjustment method of rolling bearings that is used in many applications and it is attained by introducing a controlled force to the assembly while maintaining an accurate bearing setting. Proper preloading enhances the bearing stiffness and improves performance, including reducing rotational speed variation, transmits torque, improved fatigue life and others.
Preloading not only provides users with the opportunity to improve rolling bearing’s performance but also compensates for the effects of the environmental conditions on which the application will be used. The preload’s initial value is designed for ideal operating conditions and later it can be adjusted to fit the specific application’s needs.
When rolling bearings are preloaded their internal load distribution is no longer the same as during the design phase, which can have some consequences such as an initial increase in noise, an increase in the deformation of the components and a decrease in rolling fatigue life. When rolling bearings are correctly preloaded, the effects of external loads are counteracted and improved bearing performance is observed.
Preload magnitude of rolling bearings is determined by application’s loads that influence bearing’s internal load distribution, so when there is no external load the preload magnitude is known beforehand. For the manufacturing engineering preloads magnitude can be obtained by theoretically calculating the forces that act on the parts and measuring them in a test apparatus, where the radial forces and thrust forces of the bearing can be measured separately.
Rolling bearings preloading techniques are divided into two ranges:
1. Static preloading
2. Dynamic preloading
The static preloading method is the most common but dynamic preloading can be more precise and can be used in applications that require exact accuracy.
1. Static Preloading:
Static preload is used by applying an external force to the assembly and measuring only the axle’s movement, in this way the amount of preload is determined. This method is used for the correct adjustment of preload.
2. Dynamic Preloading:
Dynamic preloading requires the shaft and bearing temperature to be monitored to detect temperature related changes in the bearing’s preload. This method is more reliable and accurate than the static preloading method and the result it provides is more accurate than the static method.
Preloading of rolling bearings is critical for the success of any application, and it must be done properly in order to obtain maximum performance from the application. Preloading allows for greater tolerances, rigidity and accuracy and can also improve fatigue life. Preloading also helps to compensate for environmental changes in the application and can lead to an improved performance in terms of noise and vibration.
