The process of rotor balancing, also known as balance testing, involves measuring the unbalance of an unbalanced rotor and correcting it to reduce its unbalance; It is an important process in rotor machining.
Are you familiar with the dynamic balancing process and methods of balancing machines for different rotors? Below, Huake Zhichuang will share with you our experience and methods of dynamic balancing testing on different rotor workpieces.
1、 Rotor with rolling bearings
When balancing a rotor with rolling bearings, it is best to balance it together with the rolling bearings to eliminate the imbalance caused by the eccentricity of the inner ring of the rolling bearings. The rotor with bearings is generally supported on a V-shaped support. If a semi-circular support is used, the support should be matched with the rolling shaft so that the lower part of the pad contacts the bearing, leaving a slight gap on both sides. Otherwise, it will clamp the outer ring, affecting free vibration and causing measurement angle errors.
2、 Balance of rotor without shaft neck itself
Many parts that need to be balanced, such as leather pulleys, flywheels, blower impellers, etc., do not have shaft necks themselves, and the balancing of these rotors must be carried out on the process shaft. Using this assembly method for balancing, due to errors such as radial clearance and radial runout in the fit between the process shaft and the parts, inevitable errors will occur during balancing. The imbalance caused by the above errors can be calculated through parameters such as part machining accuracy.
Methods for detecting dynamic balance of different rotors
3、 Balance of assembly components
Often, there is a situation where the rotor is composed of several components, such as the rotor of a high-speed turbocharger, which consists of two impellers and a shaft. Although overall balancing can be achieved without separately operating the impellers, such as balancing at 1-2 thousand revolutions per minute, the required balance accuracy of 1 micrometer can be achieved. However, at an actual working speed of 50000 revolutions per minute, the shaft is locally bent and cannot work due to the unbalanced force and couple effect of the impellers. If the impeller is individually balanced at a speed of 1-2 thousand revolutions per minute, assembled and then balanced to 1 micrometer, it can meet the design requirements at the working speed. Therefore, for assembled parts, it is generally necessary to balance each individual piece separately according to the specified balance accuracy requirements. The unbalance after assembly is the vector sum of the unbalance of each part.
Due to the arbitrary position of the remaining unbalance of each component, even in the most unfavorable situation, it is only the algebraic sum of the unbalance quantities. In addition, there may be imbalances caused by fitting during assembly. Therefore, if the balance accuracy requirement for assembly is high and only balancing the parts cannot meet the balance accuracy requirement for the assembly, then it is necessary to perform dynamic balance testing on the entire assembly. Well balanced assembly parts should generally not be disassembled. If the process requires disassembly, the corresponding positions of each part should be marked so that they can be restored to their original positions during reassembly to ensure overall balance accuracy.
4、 A rotor with a large amount of imbalance
When a rotor with a large amount of imbalance rotates on a balancing machine, it generates a large centrifugal force, resulting in excessive amplitude of the swing frame and collision with the support, affecting measurement and even causing the rotor to fly away from the balancing machine, endangering safety. So the following measures should be taken for this type of rotor:
1. Static balancing should be performed before dynamic balancing. If static balancing is performed on a balancing machine, roller bearings should be used. When the rotor is separated from the universal joint, the rotor can freely rotate on the wheel, so that the heavier side of the rotor will naturally stop below its centerline due to the effect of gravity. At this point, the rotor can be balanced and calibrated until it reaches random equilibrium. Static balance correction is best performed within the balance plane that passes through the center of gravity of the rotor and is perpendicular to the rotor axis. If this is difficult to achieve, it can be divided into two symmetrical planes on the left and right sides.
2. First, perform low-level balancing, reduce the normal balancing speed, and minimize centrifugal force for initial balancing and calibration. When the unbalance is reduced to the range allowed by the normal balancing speed of the balancing machine, the normal speed balancing can be carried out again.
5、 Balance of rotors with aerodynamic effects
When some rotors with blades are balanced, the wind resistance is high, which not only requires the balancing machine to have sufficient driving power, but also the interference of aerodynamic forces may cause measurement instability. Therefore, balancing such rotors is often carried out by reducing the test speed, using a hard paper shell to block the direction of air flow, or selecting a rotation direction with lower wind pressure to reduce driving power and improve measurement stability.
6、 High precision rotor balancing
The balance speed of such rotors is generally high. In order to prevent danger caused by excessive centrifugal force, low-speed balance and correction should be carried out first, followed by high-speed balance and correction. For medium to large rotors using universal joints, the balance of the universal joints should be checked and corrected before rotor balancing. For small rotors, non coupled driving methods such as belt driven balancing machines or self driven balancing machines should be used to achieve high balancing accuracy.
7、 Balance of rotors under different experimental and actual working conditions
These types of rotors, such as steam turbines, rotary jet engines, large engines, etc., although well calibrated on balancing machines, can cause new imbalances when assembled and operated under actual working conditions due to thermal expansion or electromagnetic force caused by current. Therefore, on-site balancing and calibration are also required for such rotors.
Are you familiar with the dynamic balancing process and methods of balancing machines for different rotors? Below, Huake Zhichuang will share with you our experience and methods of dynamic balancing testing on different rotor workpieces.
1、 Rotor with rolling bearings
When balancing a rotor with rolling bearings, it is best to balance it together with the rolling bearings to eliminate the imbalance caused by the eccentricity of the inner ring of the rolling bearings. The rotor with bearings is generally supported on a V-shaped support. If a semi-circular support is used, the support should be matched with the rolling shaft so that the lower part of the pad contacts the bearing, leaving a slight gap on both sides. Otherwise, it will clamp the outer ring, affecting free vibration and causing measurement angle errors.
2、 Balance of rotor without shaft neck itself
Many parts that need to be balanced, such as leather pulleys, flywheels, blower impellers, etc., do not have shaft necks themselves, and the balancing of these rotors must be carried out on the process shaft. Using this assembly method for balancing, due to errors such as radial clearance and radial runout in the fit between the process shaft and the parts, inevitable errors will occur during balancing. The imbalance caused by the above errors can be calculated through parameters such as part machining accuracy.
Methods for detecting dynamic balance of different rotors
3、 Balance of assembly components
Often, there is a situation where the rotor is composed of several components, such as the rotor of a high-speed turbocharger, which consists of two impellers and a shaft. Although overall balancing can be achieved without separately operating the impellers, such as balancing at 1-2 thousand revolutions per minute, the required balance accuracy of 1 micrometer can be achieved. However, at an actual working speed of 50000 revolutions per minute, the shaft is locally bent and cannot work due to the unbalanced force and couple effect of the impellers. If the impeller is individually balanced at a speed of 1-2 thousand revolutions per minute, assembled and then balanced to 1 micrometer, it can meet the design requirements at the working speed. Therefore, for assembled parts, it is generally necessary to balance each individual piece separately according to the specified balance accuracy requirements. The unbalance after assembly is the vector sum of the unbalance of each part.
Due to the arbitrary position of the remaining unbalance of each component, even in the most unfavorable situation, it is only the algebraic sum of the unbalance quantities. In addition, there may be imbalances caused by fitting during assembly. Therefore, if the balance accuracy requirement for assembly is high and only balancing the parts cannot meet the balance accuracy requirement for the assembly, then it is necessary to perform dynamic balance testing on the entire assembly. Well balanced assembly parts should generally not be disassembled. If the process requires disassembly, the corresponding positions of each part should be marked so that they can be restored to their original positions during reassembly to ensure overall balance accuracy.
4、 A rotor with a large amount of imbalance
When a rotor with a large amount of imbalance rotates on a balancing machine, it generates a large centrifugal force, resulting in excessive amplitude of the swing frame and collision with the support, affecting measurement and even causing the rotor to fly away from the balancing machine, endangering safety. So the following measures should be taken for this type of rotor:
1. Static balancing should be performed before dynamic balancing. If static balancing is performed on a balancing machine, roller bearings should be used. When the rotor is separated from the universal joint, the rotor can freely rotate on the wheel, so that the heavier side of the rotor will naturally stop below its centerline due to the effect of gravity. At this point, the rotor can be balanced and calibrated until it reaches random equilibrium. Static balance correction is best performed within the balance plane that passes through the center of gravity of the rotor and is perpendicular to the rotor axis. If this is difficult to achieve, it can be divided into two symmetrical planes on the left and right sides.
2. First, perform low-level balancing, reduce the normal balancing speed, and minimize centrifugal force for initial balancing and calibration. When the unbalance is reduced to the range allowed by the normal balancing speed of the balancing machine, the normal speed balancing can be carried out again.
5、 Balance of rotors with aerodynamic effects
When some rotors with blades are balanced, the wind resistance is high, which not only requires the balancing machine to have sufficient driving power, but also the interference of aerodynamic forces may cause measurement instability. Therefore, balancing such rotors is often carried out by reducing the test speed, using a hard paper shell to block the direction of air flow, or selecting a rotation direction with lower wind pressure to reduce driving power and improve measurement stability.
6、 High precision rotor balancing
The balance speed of such rotors is generally high. In order to prevent danger caused by excessive centrifugal force, low-speed balance and correction should be carried out first, followed by high-speed balance and correction. For medium to large rotors using universal joints, the balance of the universal joints should be checked and corrected before rotor balancing. For small rotors, non coupled driving methods such as belt driven balancing machines or self driven balancing machines should be used to achieve high balancing accuracy.
7、 Balance of rotors under different experimental and actual working conditions
These types of rotors, such as steam turbines, rotary jet engines, large engines, etc., although well calibrated on balancing machines, can cause new imbalances when assembled and operated under actual working conditions due to thermal expansion or electromagnetic force caused by current. Therefore, on-site balancing and calibration are also required for such rotors.
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