When the time comes to replace a rolling element bearing, the question is often asked if the capacity of the bearing in question was sufficient for the particular application. Let’s look at a few points that will help us clarify this question.

How do we measure bearing capacity?

As a rule of thumb, the rolling element bearing capacity can be determined by using the theoretical life calculation. However, the theoretical life of the rolling element bearing is intimately linked to the dynamic capacity Cr. Most rolling element bearing manufacturers include the value of Cr in their catalogues. Cr represents a statistical measure of the load a rolling element bearing can support for 1 million revolutions with 90% reliability.

Can I load a rolling element bearing to the Cr value?

Certainly, but the life of the rolling element bearing will only be one million revolutions. Take for example an application rotating at 3600 RPM with a load Cr, the life (1 million revolutions) will only be 4.6 hours!

What would be considered a typical rolling element bearing load?

There is a simple rule of thumb used to determine the magnitude of the load applied to the bearing under normal operating conditions. Although it does not replace the theoretical life calculation, the following table is a useful guide.

Let’s consider an example: a roll from a paper machine.

We must start by adding all the loads: weight of the rollers 4000 lbs/bearing, tension: 3000 lbs/bearing. If we assume these are the only radial loads, the resultant load is Pr=7000 lbs. The capacity Cr of a 22228 bearing is approximately 153000 lbs, so Pr/Cr=7000/153000=4.5%. The majority of rolling element bearings used in paper machines fall below 6% of the dynamic capacity Cr.

Rolling element bearings are moving parts of a precise and fragile nature. Many variables must be controlled to ensure the bearing’s reliability, load capacity being one of them. For more information on rolling element load capacity, please contact your local NTN Technical Support Team.