KEVOS® MAKEOS · Mechanics
Permissible Residual Unbalance (Balance Grade)
How much residual unbalance is allowed for this rotor and balance grade?
Permissible residual unbalance and specific unbalance for a rigid rotor from its mass, maximum service speed and balance quality grade G, compared with a measured value.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Rotor mass | kg | Mass of the rotating assembly being balanced. |
| Maximum service speed | rpm | Highest speed the rotor runs in service. |
| Balance quality grade | choice | Grade from the equipment standard, purchase specification or ISO 21940-11 guidance for the machine type. |
| Correction planes | choice | One plane for narrow discs; two planes for longer rotors. Unequal plane positions need the standard’s allocation rules. |
| Measured residual unbalance per plane (0 = not measured) | g·mm | Residual unbalance per plane from the balancing machine report. |
Method and formulas
- Permissible specific unbalance e = G × 1000 ÷ ω (µm, = g·mm/kg), ω = 2πn ÷ 60.
- Permissible residual unbalance U = e × M = 9549 × G × M ÷ n (g·mm).
- With two planes and the centre of mass midway, each plane receives half of U.
- Example: a 25 kg rotor at 3000 rpm in G 6.3 may have 501.34 g·mm residual unbalance (20.054 µm).
Limitations
- Rigid rotors only; flexible rotors need ISO 21940-12 methods.
- Equal allocation to two planes applies only when the centre of mass lies midway between them.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set the balancing tolerance on a drawing or work order
- Accept or reject a balancing report
- Compare grades for a fan, pulley or spindle part
Who it is for
- Maintenance engineers
- Machinists
- Quality inspectors
What you get
- Permissible residual unbalance (total and per plane)
- Permissible specific unbalance (eccentricity)
- Measured result against the limit
Interpreting the result
- Convert the limit into a correction mass at a radius: mass (g) = U (g·mm) ÷ radius (mm).
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 191–196. Topic reference; no source tables or recommended settings are reproduced.
- ISO 21940-11:2016 Mechanical vibration — Rotor balancing — Part 11: Procedures and tolerances for rotors with rigid behaviour — https://www.iso.org/standard/54074.html
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.
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