KEVOS® MAKEOS · Mechanics
Rotor Balancing Check (Grade, Plane Unbalance and Corrections)
Is this rotor within its balance grade in each correction plane, and if not, what correction masses go where?
Two-plane balancing check of a rigid rotor: permissible residual unbalance from the balance quality grade, mass and speed, split equally between two correction planes (as the balance grade tool), the unbalance in each plane resolved from up to three known or measured unbalance masses (as the two-plane balance tool), the correction mass and angle in each plane at its correction radius, the rotating force the initial unbalance puts on the bearings, and whether the corrections fit within your largest practical correction mass.
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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 rotor. |
| Service speed | rpm | Highest service speed. |
| Balance quality grade (G number) | mm/s | Balance quality grade for the machine type, e.g. 6.3 or 2.5 (your value from ISO 21940-11 / ISO 1940-1). |
| Distance between correction planes A and B | mm | Axial distance between the two correction planes. |
| Correction radius in plane A | mm | Radius at which weights are added or removed in plane A. |
| Correction radius in plane B | mm | Radius at which weights are added or removed in plane B. |
| Largest practical correction mass | g | Largest single weight you can fit or remove at the correction radius. |
| Unbalance masses (from plane A) | ||
| Unbalance 1 mass | g | Mass of unbalance 1 (0 if not used). |
| Unbalance 1 radius | mm | Radius of unbalance 1. |
| Unbalance 1 angle | ° | Angular position of unbalance 1. |
| Unbalance 1 distance from plane A | mm | Axial distance of unbalance 1 from plane A towards plane B. |
| Unbalance 2 mass | g | Mass of unbalance 2 (0 if not used). |
| Unbalance 2 radius | mm | Radius of unbalance 2. |
| Unbalance 2 angle | ° | Angular position of unbalance 2. |
| Unbalance 2 distance from plane A | mm | Axial distance of unbalance 2 from plane A towards plane B. |
| Unbalance 3 mass | g | Mass of unbalance 3 (0 if not used). |
| Unbalance 3 radius | mm | Radius of unbalance 3. |
| Unbalance 3 angle | ° | Angular position of unbalance 3. |
| Unbalance 3 distance from plane A | mm | Axial distance of unbalance 3 from plane A towards plane B. |
Method and formulas
- Permissible eccentricity e = G ÷ ω; permissible unbalance U = e × mass, half to each plane (as the balance grade tool).
- Resolve each unbalance m r at angle a into the planes by moments about plane A (as the two-plane balance tool): U_B = −Σ m r z ÷ L, U_A = −Σ m r − U_B (as vectors).
- Correction mass = U ÷ correction radius, at the angle of the correcting vector.
- Rotating force = U ω² (U in kg·m).
- Example: grade G6.3 at 3000 rpm allows 250.67 g·mm per plane; plane A carries 2,704.2 g·mm and needs 27.042 g at 193.9°.
Limitations
- Rigid rotor below its first bending critical speed; flexible rotors need modal balancing.
- Equal split of the permissible unbalance; ISO allows an allocation by bearing distances.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Decide whether a rotor needs balancing for its grade
- Work out correction weights in two planes
- Estimate the bearing force from unbalance
Who it is for
- Maintenance engineers
- Balancing technicians
- Design engineers
What you get
- Permissible residual unbalance per plane
- Unbalance and corrections in each plane
- Bearing force from the initial unbalance
Interpreting the result
- Correct at the largest radius available: the correction mass falls in proportion.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 191–195. Topic reference; no source tables or recommended settings are reproduced.
- ISO 21940-11 Mechanical vibration — Rotor balancing — Procedures and tolerances for rotors with rigid behaviour
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Open the Rotor Balancing Check (Grade, Plane Unbalance and Corrections) calculator
