A ball bearing with C = 25 kN runs at 750 rpm under an equivalent load of 4 kN. How many operating hours can you expect?
L10 comes from a fatigue relation
L10 = (C/P)^p, expressed in millions of revolutions, with p = 3 for ball bearings and p = 10/3 for roller bearings. The formula describes rolling-contact fatigue of the material, not wear from contamination or poor lubrication. L10 is the life that 90% of a batch of identical bearings under the same conditions reaches at minimum.
Worked example: ball bearing, C = 25 kN, P = 4 kN
L10 = (25/4)³ = 244.1 million revolutions. At a constant speed of 750 rpm, L10h = L10 · 10⁶ / (60 · n) ≈ 5,425 operating hours. That is the basic dynamic rating life at 90% reliability — not the guaranteed life of this specific bearing.
Reliability above 90% costs life
The a1 factor scales L10 to a higher reliability: a1 = 0.62 at 95%. For this example that gives L5h ≈ 5,425 · 0.62 ≈ 3,364 hours. The bearing itself doesn't change; the reporting gets stricter. Choose the reliability level based on the consequences of a failure, not by default the highest value.
Assumptions and applicability limits
This calculation takes C and P as given; the equivalent load P normally follows from a separate X/Y calculation based on the actual radial/axial load ratio, not modelled here. Lubrication and contamination influence (a_ISO from ISO 281:2007) is not included. Also check the static safety factor S0 = C0/P0 separately — for example, C0 = 20 kN and P0 = 4 kN gives S0 = 5, to be compared with the manufacturer requirement for this bearing type, shocks, loading and required running accuracy.