Rolling-Bearing Dynamic Equivalent Load P (ISO 281)
The equivalent dynamic load P for a bearing.
Example
You enter
- Radial load Fr (lbf) 1000
- Thrust (axial) load Fa (lbf) 500
- Basic static load rating C0 (lbf) 5000
You get
- Equivalent dynamic load P 1304 lbf
- E ratio 0.29231
Checked against published worked examples from: McGraw-Hill (Shigley's MED 10th ed. solutions, via Oakland University).
Details, formula, and sources
ScopeCombining the actual radial load Fr and thrust Fa into the single number a rating-life calculation needs (ISO 281). For a single-row deep-groove ball bearing, P = X Fr + Y Fa, with the e-ratio and thrust factor Y interpolated from the standard ISO 281 / SKF table on Fa/C0 (C0 the basic static rating). Below e the pure radial load governs (X = 1, Y = 0, P = Fr); above it X = 0.56 and Y applies. Fr = 1,000, Fa = 500, C0 = 5,000 gives Fa/C0 = 0.10 (e = 0.29, Y = 1.49 interpolated), and since Fa/Fr = 0.5 > e, P = 0.56 x 1,000 + 1.49 x 500 = 1,304 lbf - 30% above the radial load, which by the cube law cuts L10 to about 45%. Drop the thrust and P = Fr = 1,000, exactly the P an L10 rating-life calculation takes. Deep-groove ball bearings, rotating inner ring; other types use the maker's factors. A planning estimate; ISO 281 and the bearing catalogue govern.
Formula or tableP = X Fr + Y Fa. Single-row deep-groove ball: interpolate e and Y from the ISO 281 / SKF table on Fa/C0 ([Fa/C0, e, Y]: [0.014,0.19,2.30], [0.021,0.21,2.15], [0.028,0.22,1.99], [0.042,0.24,1.85], [0.056,0.26,1.71], [0.070,0.27,1.63], [0.084,0.28,1.55], [0.110,0.30,1.45], [0.17,0.34,1.31], [0.28,0.38,1.15], [0.42,0.42,1.04], [0.56,0.44,1.00], clamped at the ends); if Fa/Fr <= e then X = 1, Y = 0 (P = Fr), else X = 0.56.
Source and editionThe ISO 281 dynamic equivalent load P = X Fr + Y Fa with the standard single-row deep-groove ball-bearing X/Y/e table vs Fa/C0 (ISO 281; SKF General Catalogue; Shigley's Mechanical Engineering Design), by name; feeds the bearing-l10-life and bearing-max-load tiles.
Free accessThe equivalent-load relation and the deep-groove ball X/Y/e table are published ISO 281 / catalogue data; the radial and thrust loads and the static rating C0 come from the application and the bearing catalog.
What governsEstimate. AHJ and licensed professional govern.
API field namesradial_load_lbf, thrust_load_lbf, static_rating_lbf, equivalent_load_lbf, e_ratio
- Equivalent load P = X Fr + Y Fa; X = 0.56 for Fa/Fr > e, else X = 1 and Y = 0ISO 281
- X/Y/e table single-row deep-groove ball, e and Y interpolated on Fa/C0 over the 12 published rows (0.014->0.56)ISO 281 / SKF catalogue
- Scope deep-groove ball, rotating inner ring V = 1; other bearing types use maker factorsscope of this tile