Load Ratings

The dynamic radial load rating is calculated as the radial load under which 90% of a test batch of identical parts undergo 1 million revolutions before any fatigue beings to appear. In an ISO281 document, this is characterised as the rating life of rolling bearings.

This is also linked to the L10 life, which works out how many hours 90% of a batch sample will last with specific load and speed data. To calculate this, it is assumed that the bearing is performing under optimal conditions and doesn’t account for wear, improper lubrication, shaft misalignment, contamination, or other such inconsistencies.

Our testing systems can provide much more accurate lifetime calculations by considering these additional factors.

Equivalent dynamic bearing loads work to combine both the radial and axial loads into a single variable. The radial and axial load factor (X and Y respectively) can be found within the bearing manufacturers bearing sheets and catalogue and added into the equation below.

To find out the radial and axial load factors for your applications, please contact us today.

The static load rating is calculated by the radial load at which the balls cause plastic deformation in a raceway equivalent to 1/10,000 of the ball diameter, assuming 52100 chrome steel bearing raceway systems and balls. This value is impacted when different materials are used, and the ‘rule of thumb’ adjustments are as follows:

• 440C Stainless Steel Rings and Balls – 20% reduction
• Steel Rings and Ceramic Balls – 30% reduction
• Fully Ceramic – 40% reduction

These values are design-concept only, and bearing experts should be consulted when more accurate information is required.

Similar to the radial load rating, axial load rating is determined when the orientation of the load has shifted. As a conservative estimate, a standard deep groove ball bearing can accept 40% of its static radial load rating. However, this can be significantly impacted by bearing type and geometry so we advise you to contact our experts for assistance.

For example, a full complement bearing using a filing slot will have a drastically reduced axial load capacity. Alternatively, we can offer a split outer ring design that combines the maximum radial and axial load capacity, eliminating the need for a filing slot.

As it is the load at which metal fatigue will not occur, fatigue loading is typically a fraction of the static load rating. Theoretically, this allows a bearing under this load to operate indefinitely as no wear characteristics are taking place. It is assumed that the lubricant film fully separates the raceway from the rolling elements.