KEVOS® MAKEOS · Mechanics
Single-Plane Balance Correction Check (Unbalance, Correction Mass, Residual, Grade)
From the known out-of-balance masses on this disc-shaped rotor, what correction mass do I add and where, and will the residual after rounding the mass and placing it be within the balance grade?
Single-plane balancing of a narrow rotor: the resultant unbalance and its angle from the known masses, the correction mass at your correction radius and its angle opposite, and the centrifugal force of the unbalance (as the plane balancing tool); the permissible residual unbalance for the rotor’s mass, speed and balance grade (as the balance grade tool); and the residual left when the correction mass is rounded to your weight steps and placed with an angle error.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Known unbalance masses (mass 0 = unused) | ||
| Mass 1 | g | Known unbalance mass 1 (or the trial-run equivalent). |
| Radius 1 | mm | Radius of mass 1. |
| Angle 1 | ° | Angle of mass 1. |
| Mass 2 | g | Mass 2. |
| Radius 2 | mm | Radius of mass 2. |
| Angle 2 | ° | Angle of mass 2. |
| Mass 3 | g | Mass 3. |
| Radius 3 | mm | Radius of mass 3. |
| Angle 3 | ° | Angle of mass 3. |
| Mass 4 | g | Mass 4 (0 if unused). |
| Radius 4 | mm | Radius of mass 4. |
| Angle 4 | ° | Angle of mass 4. |
| Correction | ||
| Correction radius | mm | Radius at which the correction mass is fitted. |
| Weight step available | g | Smallest step of the balance weights you have. |
| Angle placement error | ° | Likely error in placing the weight at the correct angle. |
| Rotor | ||
| Rotor mass | kg | Mass of the rotor. |
| Maximum service speed | rpm | Highest speed the rotor runs at. |
| Balance quality grade | choice | Balance quality grade required. |
Method and formulas
- Unbalance U = |Σ mᵢ rᵢ ∠aᵢ|; correction mass = U ÷ r_c at the opposite angle; force = U ω² (as the plane balancing tool).
- Permissible residual U_per = G × 1000 ÷ ω × rotor mass (g·mm) (as the balance grade tool).
- Residual = |U − m_rounded r_c ∠(angle error)| by the law of cosines.
- Example: add 32 g at 209.91° and 100 mm; the residual 116.02 g·mm is within 802.14 g·mm.
Limitations
- Single plane for narrow rotors; long rotors need two-plane balancing.
- Known masses or a trial-weight result; measurement error is not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Balance a fan, pulley or flywheel in one plane
- Check that the weights available can reach the grade
- Show the effect of placement error
Who it is for
- Maintenance technicians
- Vibration analysts
- Machinists
What you get
- Resultant unbalance and correction mass and angle
- Permissible residual for the grade
- Residual after rounding and placement error
Interpreting the result
- Angle error matters more than mass rounding: 10° error leaves about 17% of the original unbalance.
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
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