RotoPrecision Miniature and Instrument Bearings

Load Ratings

Whereas fatigue life depends on the wear of a bearing based on its use over a period of time, load ratings depend on the amount of force that can be exerted on a bearing before permanent deformation becomes evident. Types of load ratings include:

1) Dynamic Load Ratings

The dynamic load rating is the constant stationary radial load in which 90% of apparently identical bearings from a sufficiently large sample will achieve a nominal life of 1 million revolutions. 

2) Static Load Ratings

The static load rating is the constant stationary load in which a total permanent deformation of 0.0001 times the ball diameter is exhibited at the most heavily stressed point of contact between the ball and race. For most applications, a measure of .0001 is tolerated without any adverse implications on the expected bearing performance and overall bearing life.  

Dynamic and Static Equivalent Load Calculations

Equivalent load calculations are designed to calculate the actual loads and life of a bearing under operating conditions. By inserting actual (or anticipated) operating data into equivalent load calculations, it is possible to estimate a reasonable assumption of expected bearing life. In applications where high smoothness or low torque is especially required, it is important to select a bearing that is well within its load capabilities in order to prevent deformation which could compromise bearing performance. Calculating equivalent loads may be achieved with the help of the following equation:

Table 1: Values of X and Y for Calculating Load Ratings.

Bearing Rating Life Calculations

Calculating the bearing rating life is an expression of the relationship between the bearing capacity, loading and expected fatigue life. The bearing rating life (L 10 ) is defined as the life in millions of revolutions that 90% of a group of apparently identical bearings will complete or exceed. For a single bearing, it also denotes the number of revolutions that a bearing will complete with 90% probability. Bearing rating life can be expressed through the formula:

Dynamic Load Ratings (Cr) are provided in the Bearing Series Tables found in the catalogue and will depend upon several variables including the material used in the bearing, the contact angle and the configuration of the internal geometry.

To view a sample calculation, please click here.

For any additional information or for immediate assistance
please contact Application Support.

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