Type a line (ball C 30.7 kN P 3 kN 1450 1/min; ball P 2 kN 1500 1/min 20000 h) or fill in the fields: the line and the fields stay in step.
Enter the bearing type, C (the basic dynamic load rating from the bearing maker’s catalogue), P (the equivalent dynamic load) and the speed in 1/min, and the calculator gives the basic rating life of ISO 281: L10 in millions of revolutions and L10h in hours. Enter a target life in place of C or P, and it gives the C needed or the P allowed. The working is shown with your numbers, the point is marked on a chart of L10h against P, and the result comes as a line you can copy or add to a request.
The basic rating life is a statistical life at 90 % reliability. The real life of a bearing also depends on lubrication and contamination, which the adjusted life methods take into account; the calculator gives no adjusted life, supplies no C values and gives no advice on which bearing to choose.
L10 = (C / P)^p in millions of revolutions: C the basic dynamic load rating from the bearing maker’s catalogue, P the equivalent dynamic load, p = 3 for ball bearings and 10/3 for roller bearings. For a ball bearing with C 30.7 kN and P 3 kN: 10.2333^3 = 1071.67 million revolutions.
L10h = 10^6 / (60 x n) x L10, with n the speed in 1/min: the shaft turns 60 x n times an hour. At 1450 1/min: 10^6 / 87000 x 1071.67 = 12,318 h. In years of continuous running: 12,318 / 8760 = 1.41.
C needed = P x L10^(1/p) and P allowed = C / L10^(1/p), with L10 = L10h x 60 x n / 10^6 for a target in hours. For a ball bearing with P 2 kN at 1500 1/min and 20,000 h: L10 = 1800, 1800^(1/3) = 12.1644, C = 24.33 kN.
| Item | Equals | Note |
|---|---|---|
| p, ball bearing | 3 | deep groove, angular contact and other ball bearings |
| p, roller bearing | 10/3 | cylindrical, tapered, spherical and needle roller bearings |
| 1 kN | 1000 N | load unit |
| 1 lbf | 4.4482216152605 N | exact, by definition |
| 1 kgf | 9.80665 N | exact, by definition |
| 1/min | one revolution a minute | also r/min; 60 x n revolutions an hour |
| 1 year of continuous running | 8760 h | 24 h x 365 days |
The basic rating life is a statistical figure: the life that 90 % of a large group of identical bearings reach or exceed under the same conditions, so one bearing in ten may fail sooner.
The formula is the basic rating life of ISO 281, L10 = (C / P)^p with p = 3 for ball bearings and 10/3 for roller bearings, and L10h = 10^6 / (60 x n) x L10 with n in 1/min; both were checked against a bearing maker’s technical page and two engineering references, and every step of the working is shown so that it can be checked. That the basic rating life is a life at 90 % reliability, and that lubrication and contamination enter the adjusted life methods, are each stated in at least two sources. No reliability factor is given: the sources found do not agree on its values. 1 lbf = 4.4482216152605 N and 1 kgf = 9.80665 N by definition.
By the basic rating life of ISO 281: L10 = (C / P)^p in millions of revolutions, with C the basic dynamic load rating, P the equivalent dynamic load, and p = 3 for ball bearings and 10/3 for roller bearings. In hours at a speed n in 1/min: L10h = 10^6 / (60 x n) x L10, as the shaft turns 60 x n times an hour. For a ball bearing with C 30.7 kN and P 3 kN at 1450 1/min: C / P = 10.2333, 10.2333^3 = 1071.67 million revolutions, and 10^6 / 87000 x 1071.67 = 12,318 h, about 1.41 years of continuous running.
It is a statistical life at 90 % reliability: the life that 90 % of a large group of identical bearings reach or exceed under the same conditions. One bearing in ten may fail sooner, so L10 is not the life of one particular bearing. The 10 in L10 stands for that 10 % of the group.
C, the basic dynamic load rating, is in the bearing maker’s catalogue for the exact designation: the load at which the basic rating life is one million revolutions. P, the equivalent dynamic load, is the load on the bearing in the application, given by you. The calculator supplies no C values and does not work out P. Both can be in kN, N, lbf (4.4482216152605 N) or kgf (9.80665 N); C and P only need to be in the same unit, or the calculator converts them to newtons first.
A great deal, because P is raised to the power p. Doubling P on a ball bearing gives (1/2)^3 = 1/8 of the life; on a roller bearing (1/2)^(10/3) = 0.0992, about one tenth. Halving P gives 8 times the life on a ball bearing and 10.08 times on a roller bearing. The speed acts in direct proportion: half the speed, twice the hours for the same L10.
Yes. The target in hours becomes revolutions, L10 = L10h x 60 x n / 10^6, and then C needed = P x L10^(1/p), or P allowed = C / L10^(1/p). For a ball bearing with P 2 kN at 1500 1/min and a target of 20,000 h: L10 = 1800 million revolutions, 1800^(1/3) = 12.1644 and C = 24.33 kN. For a roller bearing with C 50 kN at 1000 1/min and 30,000 h: L10 = 1800, 1800^(3/10) = 9.4751 and P = 5.277 kN.
The basic rating life takes only C, P and the bearing type. The real life of a bearing also depends on lubrication and contamination, which the adjusted life methods take into account. The calculator gives no adjusted life and no reliability factor: for those, the bearing maker’s method and the operating conditions are needed.
The calculator gives the basic rating life only. When a bearing is needed, send the line from the calculator with the full designation as marked on the bearing or its box, and Vessel Core checks the details before an offer goes back.
