KEVOS® MAKEOS · Mechanics
Centrifugal Load on a Bolted Attachment (Overspeed and Bolt Stress)
What pull does centrifugal force put on the bolts holding this mass to a rotor, does it stay within the bolt allowable at overspeed, and at what speed would it reach the limit?
Check of a mass bolted to a rotating arm, hub or drum: centrifugal force at the running speed (as the centrifugal force tool), the force at your overspeed factor, the tension per bolt for bolts loaded radially, the bolt stress on the thread stress area, the safety factor against the allowable, and the speed at which the bolts would reach the allowable.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Attached mass | kg | Mass of the part held by the bolts. |
| Radius to its centre of gravity | mm | Radius from the axis to the part’s centre of gravity. |
| Running speed | rpm | Normal running speed. |
| Overspeed factor | Highest speed the rotor can reach as a multiple of running speed (governor or trip setting). | |
| Bolts carrying the pull | Number of bolts sharing the outward pull. | |
| Bolt diameter | mm | Bolt diameter. |
| Thread pitch | mm | Thread pitch. |
| Allowable bolt tensile stress | MPa | Allowable tensile stress in the bolts (your value; allow for preload and fatigue). |
Method and formulas
- F = m ω² r (as the centrifugal force tool); at overspeed F × factor².
- Load per bolt = F ÷ bolts; stress = load ÷ A_s with A_s = π ÷ 4 (d − 0.9382P)².
- Speed at the allowable = running speed × √(allowable ÷ running stress).
- Example: 2 kg at 150 mm pulls 7,402.2 N at 1500 rpm and 10,659 N at overspeed, 72.792 MPa in each bolt.
Limitations
- Bolts loaded in pure tension; shear and bending from acceleration need separate checks.
- The rotor itself must be checked for the overspeed too.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the bolts on a counterweight, beater or blade
- Set an overspeed trip for a rotating attachment
- Choose bolt size for a rotor fitting
Who it is for
- Design engineers
- Maintenance engineers
- Safety engineers
What you get
- Centrifugal force at running and overspeed
- Load and stress per bolt
- Safety factor and limiting speed
Interpreting the result
- Force rises with the square of speed: a 20% overspeed gives 44% more pull.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 187–190, 1521–1535. Topic reference; no source tables or recommended settings are reproduced.
WORKOS 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.
Open the Centrifugal Load on a Bolted Attachment (Overspeed and Bolt Stress) calculator
