Preload is a predetermined amount of axial force that’s applied to a bearing to align the bearing raceways.
Preloading a bearing is important because it improves the performance of the bearing in the machine. Specifically it :
- Optimizes the ball spin to roll ratio
- Increases the rigidity of an application
- Enhances the synergy between the ball and bearing raceway.
Here are three ways a bearing preload is applied:
- Factory: The manufacturer designs the bearing with a preload that is activated when installed and is usually labeled as Light, Medium, Heavy
- Spring: Placing a separate external load, like a spring, on the bearing
- Application: A rotating application creates a force on the bearing when in use.
In this article, we’ll discuss the different types of preload and their benefits.
Preload for Angular Contact Bearings
First, it’s important to know that a preload is required for angular contact bearings because these bearings need constant contact to happen between the balls and raceway. This is achieved through a preload.
Radial ball bearings don’t need nonstop contact between the balls and raceway; therefore, a preload is usually not required. However, sometimes a preload on a radial bearing is a better option than switching to a “preload required” angular contact bearing.
For example, a preloaded radial bearing would be beneficial in a centrifuge with tricky mounting requirements and where precision is required while spinning, but reverse load could occur during filling or emptying the centrifuge. Adding a preload using a wavy washer, Belleville spring, or something similar would be helpful in preventing a reverse load from occurring.
Benefits of Preloading a Bearing
As mentioned earlier, preloaded bearings improve machine performance. Here are a few other benefits of preload:
- Protects from excessive ball skidding
- Decreases application vibration and sliding friction
- Increases rigidity
- High running accuracy (even if load conditions keep changing)
- Increases bearing load capacity
Types of Bearing Preload
Factory Preload
Most bearings, like our GMN angular contact bearings, have a factory preload already designed into the bearing that activates when installed. This factory preload helps to axially align the bearing raceways.
Factory preload is calculated by the manufacturer using the axial offset value between the inner and outer ring and is usually labeled as light, medium, and heavy (or strong).
Using our GMN S6005 C angular contact bearing as an example, it has an axial offset increase of 5 microns from a light to a medium preload. Going from a light to a heavy preload on this bearing increases the axial offset by 10 microns. Why is this important? Because 130 Newtons of axial force is needed to push those extra microns from light to medium and axially align the bearing raceways. Preload is that extra force that will align these raceways correctly.
When installed, the bearing should be aligned axially and generate the proper preload.
Note: It’s a common practice to optimize the factory preload of a bearing for your specific application. Using spacers on the inner and outer ring of the bearing will make this possible. Our resources and downloads page has an entire section on calculations for changing factory preloads.
Sometimes this can be challenging, so make sure to reach out to our engineers if you’d like help with this.
Spring Preload
Most bearings, like our GMN angular contact bearings, have a factory preload already designed into the bearing that activates when installed. This factory preload helps to axially align the bearing raceways.
A spring preload is a common way to easily change the factory preload values.
A spring preload is a bearing that “springs” or allows force to bump against it while in use but still has controlled movement. This is usually achieved by adding a wave spring or group of coil springs to the bearing arrangement.
These springs produce a constant axial force against the outer ring of the bearing, and has some added advantages:
- The mating parts for a spring preloaded bearing are produced at a lower cost because they don’t need to be ground to tight axial tolerances; the spring will make up the few microns of difference.
- A spring preload is very adaptable. It can allow a little flexibility in axial movement, which some applications prefer. But, if needed, it can be very rigid, almost like a rigid installation with no spring.
Application Preload
Application preload is about finding the right axial load for a bearing when the application is in its static state.
A static state means when the application is still or not rotating and before any loads are applied to the application. This static value is commonly referred to as application preload.
This type of preload is found by calculating the amount of force that will be applied to the bearing and correcting for that force to ensure the rings stay axially aligned.
Bearing Preload Summary
We hope this article provided you with a better understanding of a bearing preload and why it’s important. The three types of preload, factory, spring, and application are all different in how they apply preload but all affect machine performance.
Check out our resources and downloads page, we have an entire section on calculations for changing preload values for angular contact bearings. If you have any questions reach out to our engineers they’d love to help.
If you’d like more advanced knowledge on bearing preload, then read our article “3 Ways to Change Your Preload.”
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