Understanding Static Balancing (Single-Plane Balancing)

Devices

Portable balancer & Vibration analyzer Balanset-1A

€1,975.00 + VAT (if applicable)

Parts

Vibration sensor

€90.00 + VAT (if applicable)

Parts

Optical Sensor (Laser Tachometer)

€124.00 + VAT (if applicable)

Devices

Balanset-4

€6,803.00 + VAT (if applicable)

Parts

Magnetic Stand Insize-60-kgf

€46.00 + VAT (if applicable)

Parts

Reflective tape

€10.00 + VAT (if applicable)

Devices

Dynamic balancer “Balanset-1A” OEM

€1,735.00 + VAT (if applicable)

Static balancing is the simplest form of rotor balancing. It corrects static unbalance — a condition in which a rotor‘s centre of mass is offset from its axis of rotation, creating a single “heavy spot.” Because that heavy spot reveals itself under gravity alone, the correction can, in principle, be carried out with the rotor at rest: place a rotor with pure static unbalance on a frictionless surface such as knife edges, and it will roll until the heavy spot settles at the bottom. The fix is made in a single plane — one correction weight placed 180° opposite the heavy spot to bring the centre of mass back onto the centre of rotation. That single-plane simplicity is the method’s great strength and, as we will see, also its defining limitation.

1. Static Unbalance vs Dynamic Unbalance

Static unbalance is also called “force unbalance,” because it produces a centrifugal force acting radially outward from the centre of rotation. Crucially, it creates no “couple” or rocking motion. That distinguishes it from dynamic unbalance, which combines force and couple unbalance and requires corrections in at least two planes to resolve fully. A rotor can be perfectly statically balanced and still carry a significant couple unbalance that makes it vibrate severely once it spins — which is why static balance, on its own, is only ever appropriate for a particular class of rotor.

2. When is Static Balancing Sufficient?

Static balancing is appropriate only for a specific class of rotors. It is generally reserved for components that are very narrow or disc-shaped, where the axial length is small compared with the diameter. For such rotors, a significant couple unbalance is unlikely to exist in the first place, so a single-plane correction genuinely solves the problem.

Common examples where single-plane static balancing is often sufficient include:

• Grinding wheels
• Automotive wheels and tyres
• Single, narrow fan or blower wheels
• Flywheels
• Pulleys and sheaves

For any rotor of significant length — a motor armature, a multi-stage pump, or a long shaft — static balancing alone is inadequate and dynamic balancing in two planes is required. The single-plane approach itself is described further under single-plane balancing.

3. Methods of Static Balancing

1. Knife-Edge Balancing

This is the classic, non-rotating method. The rotor is placed on a pair of parallel, level, low-friction knife edges. It rolls until its heaviest point is at the bottom; a temporary weight is then added at the top (180° opposite) until the rotor will rest in any position without rolling. That weight is then made permanent. It needs no power and no electronics — only patience and a true, level pair of edges — and it remains a perfectly valid field check for a narrow disc.

2. Vertical Balancing Machine

Modern static balancing is often done on a vertical balancing machine. The rotor — a flywheel or a tyre, say — sits on a horizontal plate supported by force sensors. The machine spins it at low speed, and the sensors measure the magnitude and direction of the unbalance force, displaying the required correction on a screen. For wheels and tyres specifically, a wheel-balancing-weights calculator turns that reading into clip-on or adhesive weight sizes.

3. Single-Plane Field Balancing (Balanset-1A)

Static (single-plane) balancing can also be performed on a fully assembled machine using a portable balancing system — the essence of field balancing. With the Balanset-1A, the “Balancing in one plane (‘static’)” mode measures rotor speed (RPM) and the vector of the 1× vibration — its RMS value and phase. From the “Run #0” and “Run #1” measurements, the software automatically calculates the mass and installation angle of the corrective weight needed to reduce the rotor’s imbalance, using the influence-coefficient method.

Balancing results are saved to an archive, and on completion a balancing report can be generated, edited, and printed in the built-in report editor.

How single-plane balancing is performed in the Balanset-1A program

1. Install sensors and connect the system. Install the vibration sensor at the selected measurement point and connect it to the device. Install the phase sensor (tachometer), apply reflective tape on the rotor, and connect the device to a Windows laptop.
2. Start Single-Plane Balancing mode. In the main operating window select “Single-plane” mode and start balancing. The program opens the single-plane balancing archive window.
3. Create an archive record. Enter the rotor name, place of installation, tolerances (vibration and residual imbalance), and the date. The software creates an archive folder where charts and report files will be saved.
4. Set balancing parameters in “Balancing settings”.
   • Influence coefficient: choose “New Rotor” (two runs to calibrate) or “Saved coeff.” (one run, for the same type of machine with saved influence coefficients).
   • Trial weight mass: choose “Gramm” or “Percent”. If you plan to use “Saved coeff.” mode later, enter the trial weight mass in grams (weigh it on the scales).
   • Weight Attachment Method: choose “Circum” (any angle on the circumference) or “Fixed position” (fixed holes/blades/positions; enter the number of positions).
   • Mass mount radius: enter the radius used for mounting the trial and correction weights.
   • Leave trial weight in Plane1: enable this only if you cannot remove the trial weight during the process.
5. Run #0 (initial run, no trial weight). Bring the machine to stable speed and start “Run #0” to measure the initial vibration. The software records RPM, RMS value and phase of the 1× vibration component. The “Charts” tab shows the waveform and spectrum.
6. Install the trial weight. Stop the machine and install the trial weight at a known radius. The trial weight must change vibration amplitude or phase significantly. A common criterion is the “30/30 rule”: the trial weight should change the amplitude by about 30% (lower or higher) or the phase by about 30° or more. If you plan to use “Saved coeff.” mode later, install the trial weight at the same angle as the reflective mark.
7. Run #1 (trial weight installed). Restart the machine, wait for stable speed, and perform “Run #1”. The software calculates the corrective weight parameters.
8. Install the correction weight. Stop the machine, remove the trial weight, and install the correction weight. The installation angle is counted from the trial-weight position in the direction of rotor rotation. Install the correction weight on the same radius as the trial weight.
9. RunTrim (check balance quality). Perform “RunTrim” to verify the result. If the residual vibration and/or residual unbalance meet the tolerance, balancing can be completed. If not, the software calculates an additional corrective weight and balancing continues by successive approximations.

Result visualisation: polar graph and fixed positions

Balanset-1A can display the correction weight’s mass and angle in a polar coordinate view. If “Fixed position” is selected, the program can automatically split the corrective weight into two parts and show the position numbers where each part must be installed — a convenience mirrored by the blade-correction calculator for fans and impellers with fixed mounting points.

4. Verifying the Result Against Tolerance

A static balance is only “finished” when the residual vibration and residual unbalance fall inside an agreed tolerance, which is where the RunTrim step earns its keep. The permissible residual unbalance is normally drawn from a balance-quality G-grade under the modern ISO 21940-11 standard (which absorbed the older ISO 1940-1). Converting a G-grade and a service speed into an allowable gram-millimetre figure — and choosing a sensible first test weight — is quick with a residual-unbalance calculator (ISO 21940-11) and a trial-weight calculator. Recording both the initial and the final residual unbalance gives an honest measure of how effective the job was and forms the core of the balancing report.

5. Limitations

The primary limitation of static balancing is its inability to detect or correct couple unbalance. Applying a static balance to a rotor that actually has a dynamic unbalance can sometimes make matters worse — correcting the force component while ignoring, or even aggravating, the couple component. For this reason, for most industrial machinery, two-plane dynamic balancing is the standard and required practice, and static balancing is best reserved for the narrow, disc-shaped rotors where its single-plane assumption genuinely holds.

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