Bearing Equivalent Dynamic Load Calculator

What is the equivalent dynamic load?

The dynamic load rating in a bearing catalogue is defined for a constant load in a single direction. In practice a bearing usually sees radial and axial load together. The equivalent dynamic load is the hypothetical load that would have the same effect on bearing life on its own, and it is the P used in the life equation.

The equation is P = X × Fr + Y × Fa, where Fr is the radial load, Fa the axial load, and X and Y are factors specific to the bearing.

Where do X, Y and e come from?

The factors depend on bearing type, dimension series and the size of the axial load. Bearing catalogues give a calculation factors table at the start of each type, including a limit value e. First work out Fa / Fr:

• If the ratio is less than or equal to e, the axial load is ignored for a single row bearing: X = 1, Y = 0 and P = Fr.
• If the ratio is greater than e, use X and Y from the table.

For deep groove ball bearings e and Y are not constants. The row is chosen from the ratio of axial load to static load rating (Fa / C0). That is why this tool does not offer a table and asks you to enter values from the catalogue of your own bearing.

Example

Take a radial load of 4 kN and an axial load of 2 kN, with e = 0.30, X = 0.56 and Y = 1.5 read from the catalogue. The ratio 2 / 4 = 0.5 is greater than e, so P = 0.56 × 4 + 1.5 × 2 = 5.24 kN. With an axial load of 1 kN the ratio would be 0.25 and P would be 4 kN.

Limits

Angular contact ball bearings and tapered roller bearings generate an internal axial force under radial load. In opposed pairs the axial load on each bearing has to be found including these forces, a step this tool does not perform. The P you obtain here can be used in the life calculation.