KEVOS® MAKEOS · Power Transmission
Rolling Bearing Selection Check
Does this bearing give the life I need at the reliability I want, and is it safe statically and at speed?
Selection check of a ball or roller bearing: dynamic equivalent load from radial and axial loads, required dynamic rating for the life at the chosen reliability (Weibull reliability factor) and life modification factor, the life of the chosen bearing, static equivalent load and safety factor, and speed against the limiting speed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bearing type | choice | Ball or roller bearing (life exponent 3 or 10/3). |
| Radial load | kN | Radial load. |
| Axial load | kN | Axial load. |
| Radial factor X | Radial load factor for the bearing type and Fa/Fr ratio (from the bearing catalogue). | |
| Axial factor Y | Axial load factor (from the catalogue; use X = 1, Y = 0 when Fa/Fr is below e). | |
| Speed | rpm | Rotational speed. |
| Required life | h | Life required in hours. |
| Reliability | % | Required reliability (90% is the basic rating). |
| Reliability factor basis | choice | ISO 281:2007 gives slightly higher factors than the older ANSI/ABMA values printed in the handbook; bearing makers now use ISO 281. |
| Life modification factor | Life modification factor for lubrication and contamination (from the bearing maker’s method; 1 for basic life). | |
| Chosen bearing | ||
| Dynamic load rating | kN | Dynamic load rating of the chosen bearing. |
| Static load rating | kN | Static load rating. |
| Static radial factor | Static radial factor. | |
| Static axial factor | Static axial factor. | |
| Required static safety factor | Static safety factor required (higher for shock and quiet running). | |
| Limiting speed | rpm | Limiting speed of the bearing with its lubrication. |
Method and formulas
- P = max(F_r, X F_r + Y F_a); life exponent p = 3 (ball) or 10/3 (roller).
- Reliability factor: ANSI/ABMA 1990 a₁ = [ln(1 ÷ R) ÷ ln(1 ÷ 0.9)]^(2/3) (handbook values 0.62 at 95%, 0.21 at 99%); ISO 281:2007 a₁ = 0.95 × that + 0.05 (0.64 at 95%, 0.25 at 99%).
- Life L_h = a₁ a_ISO (C ÷ P)^p × 10⁶ ÷ 60n; required C = P [L_h,req 60n ÷ (10⁶ a₁ a_ISO)]^(1/p).
- Static: P₀ = max(F_r, X₀ F_r + Y₀ F_a); s₀ = C₀ ÷ P₀.
- Example: 4 kN radial and 1.5 kN axial at 1500 rpm need C ≥ 65.568 kN for 20000 h at 95% reliability.
Limitations
- X, Y and the life modification factor come from the bearing maker for the exact bearing.
- Fatigue life only; wear, lubrication failure and contamination often end bearings sooner.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Pick a bearing size for a shaft load and life
- Check a bearing against a higher reliability requirement
- Confirm static safety for shock loads
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Equivalent load and required rating
- Life of the chosen bearing
- Static safety and speed checks
Interpreting the result
- Raising reliability from 90% to 99% cuts the expected life to about a fifth.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2365–2422. Topic reference; no source tables or recommended settings are reproduced.
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