The goal of this article is to give you bearing preload strategies you can implement for success.
Precision bearings should have a preload established to achieve a high RPM and long application life.
Especially for angular contact bearings. These bearings require a preload to so constant contact happens between the balls and the bearing raceway.
This constant contact is the main difference between the performance of angular contact bearings and radial ball bearings. Angular contact bearings can operate at a much higher RPM and load rating vs. a common radial ball bearing.
Applying a preload to radial ball bearings will greatly increase the running characteristics, as well, although it’s not required.
Having established that a preload is almost always required, here are a few influences on the optimal preload value:
- Application RPM
- Application loads, static or dynamic and axial or radial
- Mating materials, i.e. shaft and housing
- Application operating temperature
- Required application rigidities/stiffness, axial and radial
Application Speed (RPM)
The application RPM has one of the most direct influences on the required preload. Centrifugal forces acting on the balls as they rotate around the bearing push radially out with a lot of force.
This force needs to be counteracted axially — by the preload.
This balance of loads will keep the balls riding at or near the designed bearing contact angle. A bearing designed for a 15°(C) contact angle, but running at either 5° (low) or 28° (high) contact angle will have a detrimental effect on bearing life.
Some high speed applications with interesting loads may require a 25°(E) contact angle to provide optimal running conditions. Various options and configurations are available to create a successful application. i.e. 18° bearings have become fairly common.
Both static and dynamic, as well as both axial and radial application loads can affect the optimal installed preload.
If there is a known static axial load like a heavy vertical shaft, then this needs to be taken into account for the preload strategy (and even the bearing arrangement).
A vertical application with a heavy shaft creating a static axial load can increase the load on the lower bearings and reduce or maybe eliminate the preload on the upper bearings. In this scenario, both bearings may have an equally short life but for opposite reasons – too low vs. too high of axial load / preload.
Mating materials can also play a role in effecting optimal installed preload.
If you are using an Aluminum housing, make sure to take into account this material is considered soft and the coefficient of thermal expansion is around double that of AISI 52100 bearing steel.
Aluminum may require a heavier press fit than mating steel to ensure that there is no creep of the bearing race while running.
Also, if the application temperature is quite a bit higher than the installation temperature, thermal expansion needs to be looked at closely.
Example of thermal effects: Let’s use a GMN angular contact bearing S6005 CTA A7 UL. A 20°C rise in application temperature from ambient temperature can create a differential of ~11 microns of growth between bearing steel and common aluminum.
This situation could create an issue with your target running preload. This growth differential could either decrease or increase a press fit, depending on where the materials are located and other application parameters.
Rigidity & Stiffness
There are also applications that require a large amount of rigidity like a precision grinding spindle.
One way to achieve this is to use multiple bearings and to increase the preload of the bearings to create this rigidity/stiffness.
There are many applications that will both increase the number of bearings at the front (nose) of the spindle and increase the preload to achieve a greater level of stiffness.
Note: The term ‘preload’ can have multiple definitions. Please click here for an explanation of the different definitions of preload.
More Resources & Guides
Love reading about this? Well we’ve put together a handy list of other articles for your precision bearing reading journey. Check them out:
- Precision Bearings: Everything You Need to Know
- How To Properly Secure Bearings During & After Installation
- Find the Right Bearing Tolerance for Mating Parts
Why Buy From GMN Bearing USA?
The success of our business comes from three main pillars of excellence:
- Rapid Response: 99% of inquiries are responded to within one business day and most orders ship out the same day (from Houston, Texas).
- Expert-Level Support: Our onsite mechanical engineers and technical support specialists provide answers to your most difficult questions.
- Quality 360°: Our internal quality control process is one of the highest in the industry. We make sure GMN is synonymous with quality.
Need help finding the right product for your application? Contact us today.