Trial Weight Mass Calculator

Calculation Formula:

m = [K × M × 1000] ÷ [r × (N ÷ 100)²]

Variables and Coefficients:

• m — Mass of the trial weight (g)
• K — Stiffness of Supports (1 to 5)
  • K = 1: Soft supports
  • K = 5: Rigid supports
  • Average value: K = 3 for medium stiffness supports.
  This coefficient reflects how the support stiffness affects vibration amplitude and the required trial weight mass.
• M — Mass of the rotor (kg)
• r — Radius of trial weight installation (cm)
• N — Rotational speed (RPM)

Explanation of Variables:

Mass of the rotor (M): The weight of the rotor that needs balancing. Obtain this from manufacturer specifications or by measuring.
Stiffness of Supports (K): A coefficient representing the rigidity of the rotor's supports. Soft supports allow more vibration (use K = 1), while rigid supports restrict movement (use K = 5). If unsure, use the average value K = 3.
Radius (r): The distance from the center of rotation to where the trial weight will be attached, measured in centimeters.
Rotational Speed (N): The operating speed of the rotor in revolutions per minute (RPM). Obtain this from equipment specifications or measure using a tachometer.

Safety Precautions When Selecting the Trial Weight:

• Ensure all measurements (M, r, N) are accurate to prevent calculation errors.
• Verify that the calculated trial weight does not exceed the mechanical limits of the rotor or compromise safety.
• Securely attach the trial weight to prevent it from detaching during operation.
• Always follow manufacturer guidelines and safety protocols when performing balancing procedures.

Recommendations for Selecting the Mass of the Trial Weight:

• Start with an average stiffness coefficient (K = 3) if the exact stiffness is unknown.
• Use precise instruments to measure the rotor's mass, rotational speed, and installation radius.
• If the calculated trial weight seems excessively large or small, reassess the input values and coefficients.
• Consider consulting with a vibration analysis specialist for critical applications.

Important Notes

Balancing is performed only for mechanically sound equipment that is properly secured in its designated place. Otherwise, before balancing, the mechanism must be repaired, installed in functioning bearings, and properly fastened. The rotor must be cleaned of any contaminants that could interfere with the balancing process.

The amplitude and phase of vibration in the vibration meter mode should not change by more than 10-15% during measurement (from start to start). If this occurs, it can be assumed that the mechanism is operating near resonance. In this case, the rotor speed should be adjusted, or, if this is not possible, the installation conditions of the machine on the foundation should be modified, for example, by temporarily placing it on elastic spring supports. The stiffness of the supports should be chosen so that under the weight of the mechanism, the spring compression is 10-15 mm. Placing the machine on rubber pads is highly discouraged due to the potential for installation resonance falling within the operational speed range.

It is also necessary to ensure that there are no clearances in the bearings and that there is no interference from the vibrations of other nearby mechanisms.

In any case, it is recommended to take 2-3 measurements of the initial vibration amplitude and phase, as well as when trial weights are applied, and input the average data calculated from these measurements into the program.

Trial Weight

The trial weight is installed at any convenient location on the rotor. The point of installation of the trial weight will be considered the reference point (zero degrees).

With the correct selection of the trial weight mass, after its installation, the phase should shift significantly (>20-30 degrees), and the amplitude of vibration should change by 20-30%. If the changes are too small, the error in subsequent calculations increases significantly.

It is convenient to install trial weights in the same position (at the same angle) as the reference mark.

Important!

Measurements must be carried out at the steady-state operating speed of the mechanism!

Important!

Correction weights must be installed at the same radius as the trial weights!

Important!

After each trial run, the trial weights must be removed! The correction weight should be installed at the calculated angle from the trial weight location in the direction of the rotor's rotation!

Recommendation!

Before dynamic balancing, it is recommended to ensure that there is no significant static imbalance. For horizontally mounted rotors, you can manually rotate the rotor 90 degrees from its current position. If the rotor is statically unbalanced, it will tend to return to the equilibrium position. Once the rotor is in the equilibrium position, a balancing weight should be installed at the top point, approximately in the middle of the rotor's length. The weight should be selected so that the rotor remains stationary in any position.

Such preliminary balancing will help reduce vibration during the first runs of a highly unbalanced rotor.

Conclusion

This calculator offers a method for estimating the mass of the trial weight required for rotor balancing, considering the stiffness of supports. Always prioritize safety by ensuring accurate measurements, following manufacturer guidelines, and consulting with specialists when necessary. Proper application of this calculator and adherence to the recommended practices will enhance the effectiveness of rotor balancing procedures.