KEVOS® MAKEOS · Power Transmission
Ball Screw Rating Life
How long will this ball screw last at its mean load and speed?
Rating life of a ball screw in revolutions, travel distance and hours from its dynamic load rating, mean axial load, lead and speed, against a required life.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Dynamic load rating Ca | kN | Basic dynamic load rating from the ball screw catalogue. |
| Mean axial load (including preload effect) | kN | Mean axial load over the duty cycle (cubic mean of loads, with preload included per the maker). |
| Load factor fw | Load (operating condition) factor for shock and vibration (about 1.0–1.2 smooth, 1.2–1.5 normal, up to 2–3 with impact). | |
| Lead | mm | Screw lead. |
| Mean speed | rpm | Mean screw speed. |
| Required life | h | Required service life. |
Method and formulas
- L = (Ca ÷ (fw Fm))³ × 10⁶ revolutions.
- Travel life = L × lead.
- Hours = L ÷ (60 × mean speed).
- Example: Ca 15 kN at 2 kN mean load lasts 4,069 h, about 2,441.4 km of travel.
Limitations
- Basic rating life (90% reliability); the maker’s reliability and hardness factors may apply.
- Critical speed and buckling are separate checks (ball screw limits tool).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a ball screw for a machine’s service life
- Compare screw sizes and preloads
- Estimate travel life in kilometres
Who it is for
- Automation engineers
- Machine designers
What you get
- Life in revolutions
- Travel life
- Life in hours
Interpreting the result
- Life falls with the cube of load: reducing the mean load by 20% roughly doubles life.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2561–2568. Topic reference; no source tables or recommended settings are reproduced.
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