Example Data Table
| Case |
Mass |
Radius |
Speed |
Service Factor |
Use |
| Small fan |
12 g |
35 mm |
1450 rpm |
1.10 |
Light duty check |
| Pump rotor |
25 g |
40 mm |
1800 rpm |
1.25 |
Maintenance estimate |
| High speed wheel |
8 g |
60 mm |
3600 rpm |
1.50 |
Risk review |
Formula Used
Angular speed: omega = 2 × pi × rpm / 60
Residual unbalance: U = m × r
Unbalance force: F = U × omega²
Factored force: Ff = F × service factor
Correction mass: mc = U / correction radius
Actual eccentricity: e = U / rotor mass
Balance grade eccentricity: e permissible = G / omega
Left bearing reaction: RL = Ff × (span - location) / span
Right bearing reaction: RR = Ff × location / span
How to Use This Calculator
- Enter the known unbalance mass and its unit.
- Enter the radius from shaft center to the heavy spot.
- Add the rotor speed in revolutions per minute.
- Use a service factor for added design allowance.
- Enter correction radius to estimate balancing weight.
- Add rotor mass and grade for quality comparison.
- Add bearing span and location for reaction estimates.
- Press the calculate button to view results above the form.
- Download the results as CSV or PDF when needed.
Rotor Unbalance Force Guide
Why Rotor Unbalance Matters
Rotor unbalance happens when mass is not evenly placed around a spinning shaft. The heavy spot creates a rotating centrifugal force. That force rises with the square of speed. A small error can become serious at high rpm. Bearings, seals, mounts, and frames can then receive repeated dynamic loading. The result may be noise, heat, fatigue, and premature shutdowns.
What the Calculator Estimates
This calculator converts mass, radius, and speed into unbalance force. It also estimates correction mass at a chosen correction radius. When rotor mass and balance grade are entered, it compares the actual residual unbalance with a common quality target. Bearing reaction estimates are added when span and unbalance location are supplied. These values help users study how the same unbalance force is shared by two supports.
How to Interpret Results
The force value is the rotating load caused by the unbalanced mass. It is not a static weight. The load direction changes once per revolution. Higher rpm creates a much larger force. The correction mass is the amount needed at the selected correction radius to offset the entered residual unbalance. The bearing reaction values are simplified. They assume a single transverse force and a simply supported shaft.
Practical Use Tips
Use measured values whenever possible. Enter trial weight data, measured eccentricity, or calculated residual unbalance. Keep units consistent, even though the tool converts common units. For field balancing, always follow the machine maker’s limits. Stop the machine if vibration rises sharply. Check keys, couplings, fans, pulleys, and buildup before adding weights. A clean rotor often needs less correction.
Limits and Safety
This tool supports planning and education. It does not replace a vibration analyzer. Real machines may have flexible shafts, thermal growth, resonance, and phase shifts. Those effects can change the true correction angle and weight. Use trained personnel for critical equipment. Verify every result before drilling, welding, or attaching balance weights.
Maintenance Value
Regular force estimates make vibration records easier to compare. They show how a speed increase changes load. They also help teams choose correction radii before shutdown work begins. Use the notes field to store job details. Saved records can support inspections and future balancing decisions.
FAQs
What is rotor unbalance force?
It is the rotating centrifugal force caused by uneven mass distribution. The force depends on unbalance mass, radius, and speed. Speed has a strong effect because it is squared in the formula.
Why does rpm affect force so much?
Rotor force uses angular speed squared. When rpm doubles, force can become four times larger. This is why small residual unbalance can be dangerous on fast machines.
What is residual unbalance?
Residual unbalance is the remaining mass-radius effect after balancing. It is often shown in g-mm. Lower values usually mean smoother operation, but machine limits should guide acceptance.
What does correction mass mean?
Correction mass is the estimated weight needed at a chosen radius. It offsets the entered residual unbalance. Real balancing also needs phase angle and vibration readings.
Can this calculator find the correction angle?
No. It estimates force and mass amount. Correction angle requires vibration phase data, trial runs, or balancing equipment. Use proper instruments for final field correction.
What is balance quality grade?
Balance grade is a target vibration severity level. It relates permissible eccentricity to speed. Lower grade values are stricter and often used for smoother equipment.
Are bearing reactions exact?
No. They are simplified static reactions from a rotating transverse load. Real bearings may see effects from shaft flexibility, resonance, coupling forces, and mounting stiffness.
Is this safe for critical machines?
Use it for estimates and planning only. Critical rotors need trained balancing, proper lockout, measured vibration, and manufacturer limits. Never modify a rotor without verification.