Radial and axial loads can combine in a roller bearing. The equivalent dynamic load P represents that combination as a single radial load for use in a bearing rating-life calculation. SKF gives a piecewise rule for selected single-row cylindrical roller bearings with flanges. The threshold e and axial factor Y depend on the bearing series, so the correct series group must be identified before applying the equation.

Roller Bearing Equivalent Radial Load Factors

Choose the correct branch

Let Fr be the radial load and Fa the axial load. First calculate Fa divided by Fr using consistent units. If that ratio is at or below the series-specific e value, SKF’s rule gives P = Fr. Above e, the rule is P = 0.92Fr + YFa. For the series 10, 2, 3, and 4 groups, the cited catalog lists e = 0.2 and Y = 0.6. For series 22 and 23 it lists e = 0.3 and Y = 0.4.

As a calculation check, consider a series 22 bearing with Fr = 10 kN and Fa = 4 kN. The ratio is 0.4, which exceeds e = 0.3, so P = 0.92×10 + 0.4×4 = 10.8 kN. This arithmetic example illustrates the branch selection only; it is not a recommendation for a real bearing or a service rating.

Check the axial-load limit

The ratio Fa/Fr also has a stated maximum in the cited guidance. The SKF catalog distinguishes EC designs from other designs, with limits of 0.5 and 0.4 respectively for the relevant table. Check the exact bearing design and suffix before using the limit. A ratio within e does not mean that an unlimited axial load is acceptable, and the equivalent-load formula should not be extrapolated beyond the manufacturer’s stated range.

Axial load capacity can be influenced by flange design, lubrication, speed, and the bearing’s internal geometry. Review the current product data for the selected bearing and contact SKF or a qualified bearing engineer if the axial component is material to the application. Do not substitute factors from a different roller bearing family.

Keep load definitions and units consistent

Use the loads acting at the bearing, not loads taken from an unrelated point in the mechanism. Account for gear forces, belt tensions, coupling misalignment, shaft reactions, and dynamic or shock loads as appropriate. If Fr is zero or very small, the ratio is undefined or unstable and this simplified equation should not be used without reviewing the manufacturer’s method.

Maintain a consistent unit system throughout the calculation. P, Fr, and Fa must use the same force unit. The factors e and Y are dimensionless. Keep the load direction, operating case, and duration attached to each calculation so the worst case is not lost when multiple load combinations exist.

Equivalent load is one input to life

Equivalent dynamic load is not a bearing-life result by itself. The basic rating life also depends on the dynamic load rating and the roller-bearing life exponent; modified-life estimates add reliability, lubrication, contamination, and other factors. Verify speed, lubrication viscosity, operating temperature, cleanliness, alignment, fits, internal clearance, and load spectrum. For fluctuating loads, use an appropriate equivalent-load method for the duty cycle instead of selecting a single convenient point.

These SKF factors are taken from the 2018 catalog edition and are scoped to its specified single-row cylindrical roller designs. Before release, compare the current catalog and exact bearing designation. If the design has changed or the series is outside the table, use the manufacturer’s current calculation tool or obtain engineering review.

References

• SKF Bearings and Mounted Products catalog, 2018 edition

Use this factor table only within the stated SKF bearing scope. Confirm the current catalog, exact design, axial-load limit, operating conditions, and complete rating-life calculation.