Table of Contents
1. What is the difference between static and dynamic balance?
- Non-Dynamic Balance
- Rotational Balance
2. Dynamic Shaft Balancing Instruction
- First Photo: Initial Vibration Reading
- Photo Two: Calibration Weight and Vibration Measurement
- Third Image: Relocating Calibration Weight and Vibration Re-Measurement
- Image 4: Installing Final Weights and Balance Check
3. Measuring Angles for Corrective Weights Installation
4. Calculation of the Trial Weight Mass
5. Correction Planes Relative to Installed Vibration Sensors
6. How to Perform Two-Plane Dynamic Balancing of a Fan
- Planes Determination and Sensors Installation
- Steps in Balancing
- Measuring Angles
What is the difference between static and dynamic balance?
Non-Dynamic Balance
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In the first image, the rotor shows static imbalance, where the center of gravity is offset from the axis of rotation, creating a one-sided force that pulls the rotor to position its heavier side down. This imbalance is corrected by adding or removing mass at specific points to make the center of gravity coincide with the rotation axis. When the rotor is statically imbalanced, turning it 90 degrees always makes the "heavy point" go downward.
Non-Rotational unbalance:
- Occurs while the rotor is still.
- Gravity causes the rotor's heavy point to rotate downwards.
Stationary balancing: Applied to narrow disk rotors, it removes uneven mass distribution in a single plane.
Dynamic Balancing
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In the second photograph, the rotor is dynamically imbalanced with two separate mass displacements in different planes. This not only leads to a one-sided force like static imbalance but also generates moments that create extra vibrations during rotation. In cases of dynamic imbalance, the forces in one plane balance those in another. Thus, rotating the rotor 90 degrees does not cause the "heavy point" to turn downward, unlike static imbalance. Dynamic methods with a two-plane balancing vibration analyzer are required to correct this.
Dynamic imbalance:
- Happens only while the rotor spins.
- It arises because two unbalanced masses exist in separate planes along the rotor's length. As the rotor rotates, these masses produce centrifugal forces that do not offset each other because of their distinct positions.
To correct the dynamic imbalance, two compensating weights need to be installed to generate a torque that is equal and opposite to the torque from the unbalanced masses. These compensating weights do not need to be equal in weight or directly opposite the original masses, as long as they produce the required torque to balance the rotor.
Dynamic balancing: Ideal for long double-axle rotors. It balances uneven weight in two planes, stopping rotational vibration.
Dynamic Balancing of Shafts Instructions
https://vibromera.eu/product/balanset-1/
For the dynamic balancing of shafts, the Balanset-1A balancing and vibration analyzer is used.
The Balanset-1A comes with 2 channels and is intended for dynamic balancing in two planes. This makes it apt for numerous applications, such as crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and more. Its flexibility in managing different rotor types makes it a crucial tool for many industries.
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Photo 1: Initial Vibration Measurement
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The first image illustrates the initial stage of the two-plane dynamic rotor balancing process. The rotor is mounted on the balancing machine. Vibration sensors are affixed to the rotor and connected to a computer through a measuring unit. The operator starts the rotor, and the system measures the initial vibrations, which are displayed on the computer screen. This data is used as a reference for subsequent calculations.
Photo 2: Installing the Calibration Weight and Measuring Vibration Changes
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The second image illustrates the stage of installing a calibration weight on one side of the rotor in the first plane. A weight of known mass is fixed at an arbitrary point on the rotor, on the side of sensor X1. The rotor is started again, and the system measures the vibration changes with the installed weight. This data is recorded by the vibration analyzer to determine the effect of the weight on the vibrations.
Photo Three: Re-Positioning Calibration Weight and Vibration Data
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The third photo illustrates the stage of moving the calibration weight to the other side of the rotor. The weight is removed from the initial point and attached at another point on the opposite side of the rotor. The rotor is started again, and the vibration changes with the weight in the new position are measured. This data is also recorded by the portable balancing instrument for further analysis.
Image 4: Installing Final Weights and Balance Check
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The fourth image shows the final stage of balancing. Using measurement data from both sides, the vibration analyzer determines the angle and mass required for complete rotor balancing. The weights are installed at the points indicated by the instrument on the rotor. After installation, the rotor is started again to check the results. The system shows that the vibration levels have significantly decreased, confirming a successful balance.
Angle Measurement Process for Corrective Weights
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The picture illustrates the method for measuring the angle for installing corrective weights during rotor balancing.
Rotational Direction
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The diagram depicts the rotor's rotation direction with an arrow. The angle is measured in the direction of rotation.
Trial Weight Position
The trial weight is positioned at an arbitrary point on the rotor. This point is termed the "Trial weight position".
Angle Measurement
The image shows the angle f1 (or f2), measured from the trial weight position in the direction of rotation. This angle indicates the corrective weight installation point for balancing.
Corrective Weight Position (if added)
The corrective weight is installed at the point marked with a red dot on the diagram. This point is called the "Correction weight position (if added)". The angle f1 (or f2) is used to determine the exact location of this weight.
Corrective Weight Placement (if removed)
If balancing needs weight removal, the corrective weight is taken from the point located 180° opposite the trial weight position. This point is marked with a red dot with diagonal lines on the diagram and is called the "Correction weight position (if deleted; 180° opposite)".
How to Calculate Trial Weight Mass
The trial weight mass can be calculated with the formula:
MA = Mp / (RA * (N/100)^2)
where:
- MA - mass of the test weight, in grams (g)
- Mp - rotor mass to be balanced, in grams (g)
- RA - radius for installing the trial weight, in centimeters (cm)
- N - rotor speed, in revolutions per minute (rpm)
Relation of Correction Planes to Vibration Sensors
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The following photograph displays the mulcher rotor and marks the correction planes and vibration measurement points:
Correction Planes 1 and 2:
Correction Plane (blue 1): One: Marks the first plane of rotor balancing, with sensor X1 installed closer to the right edge of the photo.
Correction Plane (blue 2): Two: Points to the second plane of rotor balancing, where sensor X2 is installed near the left edge of the photo.
Points of Installation: 1 and 2:
Installation One (red 1): The site where the mass correction for the first plane will occur.
Correction Installation Two (red 2): The place where the mass correction for the second plane will be carried out.
This image demonstrates the process of balancing a mulcher rotor and indicates the zones for installing corrective weights in two planes.
How to Perform Two-Plane Dynamic Balancing of a Fan
Sensor Installation and Plane Determination
Preparation for Sensor Installation
Clean the surfaces for sensor installation by removing dirt and oil. Sensors should fit tightly to the surface.
Installation of Vibration Sensors
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- Vibration sensors are placed on the bearing housing or directly on the bearing housing.
- Sensors are typically installed in two perpendicular radial directions – usually horizontal and vertical.
- Vibration measurements are taken at the machine mounting points to the foundation or frame.
- Sensor 1 (red): Install the sensor closer to the front of the fan, as shown in the image.
- Sensor 2 (green): Place the sensor closer to the rear of the fan.
Connecting Sensors
Hook up the sensors to the Balanset-1A vibration analyzer.
Steps to Determine Correction Planes
- Plane 1 (red zone): The correction plane is located closer to the right side of the fan.
- Plane 2 (green zone): The correction plane is located closer to the left side of the fan.
Balancing Process
Initial Vibration Data
Start the fan and measure the initial vibration data.
Trial Weight Placement
Position a trial weight of known mass on the first plane (Plane 1) at an arbitrary point. Start the fan and measure the vibrations.
Move the trial weight to the second plane (Plane 2) at another arbitrary point. Start the fan again and record the vibrations.
Vibration Data Analysis
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Using the obtained data, determine the correction weights and the points where they need to be installed to balance the fan.
Process of Measuring Angles
Measuring the Angle for Installing Correction Weights
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The picture below illustrates the method for determining the angle for installing correction weights:
- Trial weight position (blue dot): Position of the trial weight. This is the reference point, zero degrees.
- Correction weight position (red dot): Position of the correction weight.
- Angle f1 (f2): Angle measured from the trial weight position in the fan's rotation direction.
Corrective Weights Installation
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Based on the angles and masses determined by the analyzer, install the correction weights on the first and second planes.
Measure the vibrations after installing the weights and ensure that they have decreased to an acceptable level.
Original Article : https://vibromera.eu/example/dynamic-shaft-balancing-instruction/