BIZOMAT MAKEOS · Engineering
Bearing L10 Life
How many hours will this rolling bearing run before 10% of a group would be expected to fail?
Calculate the basic rating life of a rolling bearing from its catalogue dynamic load rating, the equivalent dynamic load and a constant speed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bearing type | choice | Ball bearings use life exponent 3 and roller bearings 10/3, as in the basic rating life method. |
| Basic dynamic load rating C | kN | Basic dynamic load rating from the bearing manufacturer’s catalogue for the exact bearing. |
| Equivalent dynamic bearing load P | kN | Equivalent dynamic load combining radial and axial loads with the manufacturer’s X and Y factors. Enter it in the same unit as C. |
| Constant rotational speed | rpm | Inner-ring speed relative to the outer ring. Use a weighted average for a varying duty. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Bearing type
- What it is
- Whether the rolling elements are balls or rollers (cylindrical, tapered, spherical or needle). The choice sets the life exponent p used to turn the load ratio into a life.
- Units and format
- Choose one of 2 options from the list: Ball bearing · exponent 3; Roller bearing · exponent 10/3.
- Example
- The form opens with “Ball bearing · exponent 3” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Roller bearings use the larger exponent 10/3, so the same load ratio above 1 gives a longer life than with balls.
- Get it right
- Check the bearing designation in the catalogue; a spherical roller bearing is a roller bearing even though it looks round.
What this means: Basic dynamic load rating C
- What it is
- The catalogue load a bearing can carry for one million revolutions of basic rating life. It is a property of the exact bearing designation, printed in the manufacturer’s tables.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Life rises with C/P raised to the exponent, so a 10 % higher rating gives roughly 30 % or more extra life.
- Get it right
- Use the dynamic rating C, not the static rating C0, and type it in kN like the load P.
What this means: Equivalent dynamic bearing load P
- What it is
- A single constant radial (or axial, for thrust bearings) load that would give the same life as the real combination of radial and axial loads acting on the bearing.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Life falls with the load to the power of the exponent: doubling P cuts a ball bearing’s life to one eighth.
- Get it right
- Combine radial and axial loads with the manufacturer’s X and Y factors; entering only the radial load understates P when there is thrust.
What this means: Constant rotational speed
- What it is
- How fast the inner ring turns relative to the outer ring. It converts life in revolutions into life in operating hours.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.1 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Hours are inversely proportional to speed: double the speed halves the life in hours, not in revolutions.
- Get it right
- If the outer ring rotates, use the relative speed between the rings; for a varying duty use a time-weighted average speed.
Method and formulas
- L10 (million revolutions) = (C / P)^p, where p = 3 for ball bearings and 10/3 for roller bearings.
- L10h (hours) = L10 × 10⁶ / (60 × speed in rpm).
- Example: a ball bearing with C = 30 kN, P = 10 kN at 1,000 rpm gives L10 = 3³ = 27 million revolutions and L10h = 27 × 10⁶ / 60,000 = 450 h.
Limitations
- Basic rating life only: the reliability factor and the lubrication, contamination and material life-modification factors used in modified rating life are not applied.
- Assumes constant load and speed, correct mounting and lubrication, and a bearing that fails only by rolling contact fatigue.
- No certification, bearing selection or warranty life is implied.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Compare bearing sizes at the design stage
- Check whether a catalogue bearing is in a sensible life range
- Estimate how life changes with load or speed
Who it is for
- Design engineers
- Maintenance engineers
What you get
- Basic rating life L10 (million revolutions)
- Basic rating life L10h (hours)
- Load ratio C/P
Interpreting the result
- L10 means 90% of a large group of identical bearings should reach or exceed this life; individual bearings can fail sooner.
- A result shorter than the machine’s required service life means a larger bearing, lower load or a full manufacturer calculation is needed.
Before relying on the result
- Take C, and the X and Y factors used for P, from the manufacturer for the exact bearing designation.
- Run the manufacturer’s modified rating life calculation for lubrication and contamination before final selection.
References
- Budynas R. G. and Nisbett J. K., Shigley’s Mechanical Engineering Design, 10th edition (McGraw-Hill, 2015), chapter 11, Rolling-Contact Bearings. Topic reference; no source tables or recommended settings are reproduced.
- ISO 281:2007, Rolling bearings — Dynamic load ratings and rating life (cited by title; no content reproduced).
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