Rules of dynamic equilibrium

Rotating components such as rotors, fans, impellers, crankshafts, and turbines play a critical role in the operation of machines in various industries. One of the main problems associated with these components is     mass imbalance,     which can cause vibration, noise, and damage to mechanical components.

Dynamic balancing is     one of the most important methods for reducing or eliminating these imbalances. This process is carried out according to international standards to ensure low-vibration operation of equipment and extend its service life. This article describes the concept of dynamic balancing,     relevant   international standards, operating methods, calculation methods, advantages, limitations, and industrial applications.

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Part One: The Basics

What’s up?

An imbalance occurs when the mass is unevenly distributed around the axis of rotation and the center of gravity deviates from the axis of rotation. This creates centrifugal forces during rotation. These forces are transferred to the bearings and the hull, causing vibration, increased noise, material stresses, and ultimately   component failure     .

Type of defect

1. Static imbalance:
   In this case, the object’s center of gravity is perpendicular to the axis of rotation, far from its center. Even at rest, the object tends to sink downward along with its heavier parts.

2. Torque imbalance:
   A torque imbalance occurs when two identical masses are in different planes but in opposite directions to the axis of rotation. In this case, the center of gravity of the group lies on the axis of rotation, but a centrifugal moment occurs.

To achieve perfect equilibrium, both imbalances must be eliminated, which  is called     dynamic equilibrium    .

The difference between static equilibrium and dynamic equilibrium

• A static counterweight     simply aligns the center of gravity with the axis of rotation and is suitable for low-speed components.

• In addition to eliminating static imbalance,     dynamic balancing can also eliminate the torque generated by joints, which is crucial for high-speed components.

In high-speed industries such as the manufacture of turbines, industrial fans, generators and electric motors, only dynamic balancing can reduce vibration to an acceptable level.

SPMmixers laboratory mixers

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Part Two: Dynamic Balance Criteria

To ensure the quality and comparability of results across sectors,      international standards     have been developed. The most important of these are     ISO     1940     and its updated version,     ISO 21940     .

ISO 1940/ISO 21940 standards

This standard specifies requirements and permissible degrees of unbalance for cast iron rotors.     Part 1 defines the quality of balancing using a characteristic     called the balance class (Class G).

The lower the G-value, the more accurate the scale and the smaller the permissible error.

The general formula for calculating the acceptable error is as follows:

Above = 9.54 × G × mnU_{\mathrm{by}} = \frac{9.54 \times G \times m}{n}      U      by      ​=     n      9.54      ×      G      ×      m 

Where:

• UperU_{\text{per}}      U      per      ​:     Permissible unbalance (g-mm)

• $G$     : Balance

• $m$     : rotor mass (kg)

• $n$     : speed (rpm)

In this case,  the specific degree of defect is     equal to:

eper=Uperme_{\mathrm{per}} = \frac{U_{\mathrm{per}}}{m}      e      per      =     m      U      per 

General G-values ​​across industries

ISO standards also define measurement methods, error correction, and acceptable tolerances.

Other relevant rules

• ISO 10816:     Standard for measuring vibration of rotating machinery

• API 617 and API 610:     Balancing requirements for industrial compressors and pumps

• VDI 2060:     German quality standard for scales

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Part Three: Steps to Implementing Dynamic Budgeting

The dynamic balancing process is usually carried out in several steps:

1. Initial preparations and measurements

The rotor is mounted on a balancing machine and rotated at a set speed. A vibration sensor (accelerometer or tachometer) records the vibration intensity in a specific direction. By analyzing the vibration amplitude and phase, the fault can be localized.

2. Add test weight.

To determine the system’s sensitivity to mass changes, weights of a specific weight are attached at specific locations. The vibration changes caused by these weights allow the position and number of correction weights to be precisely calculated.

3. Calculate the adjusted weight.

Based on the initial data, the required number and correction angle of test weights are determined after installation. In two-plane balancing, two weights are installed on either side of the rotor to eliminate unbalanced forces and moments.

4. Install the correction weight.

Correction weights are     attached to specific locations on the rotor. Depending on the component type, fastening methods include screws, adhesives, welding, and nuts.

5. Final approval

After installing the counterweights, test the rotor again at the same speed. If the residual vibration is within acceptable limits, the process was successful.

Balance present

In large machines such as turbines, industrial fans, and power plant generators, the components cannot be moved. In these cases, on-site dynamic balancing is required. Sensors are mounted on the machine body and balanced during operation.

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Part 4: Calculation examples

To better understand the concept of margin of error, let’s look at a simple numerical example.

He thinks:

• Rotor weight: 20 kg

• Speed: 3000 rpm

• Balancing quality: G=6.3

Allows you to calculate the defect:

  Top side      =        9.54   x   6.3    x    203000      =    0.40      g     –   mm 

This means that the maximum unbalance of the rotor in question is 0.4 g/mm.

A lack of quality is also synonymous with:

eper=0.4020=0.02 mm e_{\text{per}} = \frac{0.40}{20} = 0.02 \text{ mm}      e      per      ​=     200.40      ​=      0.02       mm 

In this example, the center of gravity must     be 0.02 mm away from the axis of rotation in order to comply with the standard tolerance range.

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Part five: Benefits and importance of maintaining the accounting standard

1. Reduced vibrations and noise    : By reducing imbalance,     unwanted   mechanical vibrations and noise from equipment are avoided.

2. Longer service life of bearings and shafts.
   No additional forces are transferred to the bearings, thus extending the service life of the system.

3. Improved operating efficiency:
   Balanced rotors have less rotational friction and higher efficiency.

4. Reduced maintenance costs.
   Lower vibrations mean a lower risk of breakdowns and unexpected production line downtime.

5. Compliance with quality requirements in the planning and construction of industrial plants
   and maintaining the balance specified in    contracts    or standards are requirements of quality assurance.

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Part Six: Limitations and Problems

1. Cost of precision balancing equipment: Modern  dynamic
   balancing equipment is expensive and requires a skilled operator.

2. At high speeds, the vibration behavior of a flexible rotor   differs     from that of a rigid rotor    and requires special flexible balancing procedures.

3. Differences in operating and laboratory conditions (such as temperature, pressure, or working volume)   can lead to changes in mass distribution and the equilibrium can change in real time.

4. Correction weights are not installed correctly:
   If the weights are installed at the wrong angle or in the wrong   position, not only will balance not be achieved, but vibrations will also increase.

5. Sometimes the cause of unbalanced vibration is not the presence of other vibration factors
   , but rather a bearing failure, shaft misalignment, or component misalignment.

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Section 7: Application of dynamic equilibrium

1. Fans and impellers:
   prevent strong vibrations and extend bearing life .

2. Pumps and compressors:
   Precise balancing is crucial for turbomachinery.

3. Crankshafts and car engines:
   Dynamic balancing of the crankshaft reduces engine vibration and improves fuel efficiency.

4. Turbines and generators:
   At high speeds, even a small malfunction can cause serious damage.

5. Heavy industry and power plants:
   On-site balancing of large equipment such as steam turbines, cooling fans, and large generators.

6. Aerospace:
   Engine blades and components are balanced to an accuracy of 0.4 G.

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Part 8: Implementation and Maintenance Tips

1. Choose the G-force depending on the device type
   : the faster and more sensitive the device, the lower the G-force should be.

2. The device should be calibrated under conditions that are as close as possible to the actual operating conditions
   . If possible, the device should be calibrated according to the actual operating temperature and conditions.

3. Regular checks after operation
   After a certain period of operation, deposits or corrosion can lead to new imbalances, so it is recommended to carry out the balancing process regularly.

4. Precise installation of sensors and devices.
   Precise sensor positioning is crucial for achieving accurate results.

5. Complete documentation of budget processes
   and recording of data before and after budget preparation are crucial for quality control.

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Finally

Dynamic balancing is     one of the most important processes for increasing the service life, performance, and safety of rotating machinery. Proper execution of this process and compliance with international standards such as     ISO 1940 and ISO 21940     help reduce vibration and prevent damage caused by imbalance.

Compliance with balancing standards not only ensures manufacturing and assembly quality, but also reduces maintenance costs and improves the performance of industrial equipment. Selecting the correct balancing class (G), precise work execution, and regular inspections are the three pillars for the successful implementation of dynamic balancing standards.