BIZOMAT MAKEOS · Engineering
Rolling Bearing Friction Torque and Heat
How much friction torque and heat does this rolling bearing produce?
Approximate friction torque, power loss and heat of a rolling bearing from its load, bore and a friction coefficient for the bearing type.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bearing load | N | Resultant load on one bearing. |
| Bore diameter | mm | Bearing bore diameter. |
| Friction coefficient for the bearing type | Approximate constant friction coefficient from the bearing maker for the type (deep groove ball about 0.0015, cylindrical roller about 0.0011, spherical and tapered roller about 0.0018). | |
| Speed | rpm | Shaft speed. |
| Number of bearings | bearings | Number of similar bearings. |
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 load
- What it is
- The resultant load carried by one bearing, combining radial and axial loads, from your shaft load analysis.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Friction torque and power loss rise in direct proportion to load.
- Get it right
- Enter the load on one bearing, not the total for the shaft; the number of bearings multiplies the loss separately.
What this means: Bore diameter
- What it is
- The bore diameter of the bearing, the diameter of the shaft seat, used as the lever arm for the friction force.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Friction torque and power loss rise in direct proportion to bore.
- Get it right
- Use the bore, not the outside diameter of the bearing.
What this means: Friction coefficient for the bearing type
- What it is
- An approximate constant friction coefficient for the bearing type, as given by the bearing maker, relating friction torque to load and bore.
- Units and format
- Enter a plain number with no unit. The form accepts 0.0005 to 0.05. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.0015 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Friction torque and power loss rise in direct proportion.
- Get it right
- Take it from the bearing maker’s catalogue for the type; it is a small dimensionless number, not a percentage.
What this means: Speed
- What it is
- The rotational speed of the shaft running in the bearings.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power loss rises in direct proportion to speed; friction torque does not change.
What this means: Number of bearings
- What it is
- How many similar bearings, each carrying the load entered, share in the total loss.
- Units and format
- Enter a number in bearings: bearings. The form accepts 1 bearings to 100 bearings. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 bearings as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total power loss and heat rise in proportion to the number of bearings.
- Get it right
- Count only bearings carrying a similar load; bearings with very different loads should be worked out separately.
Method and formulas
- Friction torque M = 0.5 μ P d.
- Power loss = M × 2πn ÷ 60 per bearing, times the number of bearings.
- Heat per hour = power × 3600.
- Example: 5000 N on a 50 mm bore at 1500 rpm loses about 58.905 W for 2 bearings.
Limitations
- Constant-coefficient approximation for normal loads and good lubrication; seals, churning and high speed add losses.
- Use the maker’s friction model for accurate thermal design.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate bearing losses in a drive
- Check heat input to a gearbox or spindle
- Compare bearing types
Who it is for
- Maintenance engineers
- Reliability engineers
- Maintenance technicians
What you get
- Friction torque per bearing
- Power loss
- Heat per hour
Interpreting the result
- Seal and lubricant drag often exceed load friction at light loads.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2365–2420. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Useful alongside · BIZOMAT original book
Plain or rolling, and diagnosing failures
In Plain Bearings by the Numbers
What it covers: Compare plain and rolling bearings on friction with the BIZOMAT rolling bearing friction tool and on life, damping and dirt, then diagnose wiping, fatigue, scoring, electrical damage and oil whirl.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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