After the centrifugal fan leaves the factory and runs for a period of time, it is necessary to perform dynamic balance detection and correction on the impeller, in order to reduce the vibration of the fan and prevent possible fan failures, such as lower efficiency, impeller wear, noise, etc. How to test the dynamic balance of centrifugal fan?
1) Detection method of dynamic balance of centrifugal fan
Impeller imbalance of centrifugal fan is one of the key factors that cause equipment vibration, and it plays a particularly important role in fan characteristics and life. Therefore, wind rotor balance is an important process in fan production, and the measurement data of wind rotor balance is used to judge the balance of wind rotor and Important basis for eligibility.
Under normal circumstances, the detection of the dynamic balance of the impeller of the centrifugal fan is carried out on the dynamic balancing machine. The dynamic balancing machine is not only used as a production equipment to dynamically balance the impeller, but also used as a detection machine to detect the remaining unbalance of the impeller.
1. Detection principle of dynamic balancing machine
The transmission methods of the dynamic balancing machine include belt drive, universal coupling drive and self-drive. The detection principle is that when the rotor is rotating, according to the support vibration caused by the unbalance of the rotor, or the vibration force acting on the support, the vibration sensor installed on the support is transformed into an electrical signal and transmitted to the signal processor, which is connected with the detection system. The angle signal in the rotor speed signal is compared to detect the unbalance of the fan impeller.
2. Dynamic balance detection process
After confirming that the dynamic balancing machine is installed, turn on the centrifugal fan. After the fan reaches the normal working speed, enter the dynamic balancing function interface. After clicking the test run function, press the OK button to start to detect the initial vibration value and phase of the fan impeller. Wait for the data to stabilize Then save it and stop the fan.
2)the centrifugal fan dynamic balance detection deviation
Detection deviation is an important parameter that directly affects dynamic balance correction, and it is difficult to avoid. There are many sources of deviation in the dynamic balance detection process of centrifugal fan impeller. According to the source of deviation, it can be divided into three types: systematic deviation, random deviation and scalar deviation. .
1. System deviation
The systematic deviation is the deviation of the numerical value and phase evaluation based on the measurement and detection. The main sources include:
(1) Data deviation caused by the impeller dynamic balancing shaft or drive shaft: The fan impeller usually has no shaft, so the unbalance can be measured on the dynamic balancing machine only if it is installed on the dynamic balancing shaft, and the dynamic balancing shaft itself has unbalance.
(2) Data deviation caused by the vibration of the dynamic balance shaft and the drive shaft: The imbalance of the fan impeller is caused by the non-coincidence of the mass axis of the impeller and the rotating shaft. If the balance shaft that drives the impeller to rotate and the drive shaft have radial and axial vibrations , it will lead to the deviation of the impeller dynamic balance data.
(3) Data deviation caused by unreasonable design and assembly of the impeller bushing and the dynamic balancing shaft: the impeller is usually connected to the motor shaft or transmission shaft by a keyway. Errors are generated, which in turn cause detection deviations.
(4) Dynamic balancing machine deviation: The existence of the dynamic balancing machine itself will not cause a certain deviation to the balance detection of the fan impeller, so the rotor of the dynamic balancing machine must be corrected before each dynamic balancing.
2. Random Bias
Random deviation is the change in magnitude and phase of unpredictable deviations that occur when several measurements are carried out under the same conditions. Primary sources include:
(1) The loose parts of the impeller itself: such as random deviations caused by the loose parts of the shaft sleeve, the wheel disc, and the riveted blades on the impeller.
(2) External factors of the impeller: random deviations caused by oil pollution, coating wear, scratches, deformation, etc. on the outside or on the surface of the impeller during the manufacturing process and the transportation process.
(3) Wind resistance effect of impeller: The fan impeller is composed of multiple blades. The rotation of the impeller will cause aerodynamic effects during dynamic balance detection. If the wind resistance is large, it will affect the results of dynamic balance detection.
(4) Thermal effect: The dynamic balance correction methods of the fan impeller mainly include weighting, grinding, drilling, etc. These methods will cause greater heat and cause certain deformation of the impeller, resulting in random deviations in dynamic balance detection.
3. Scalar Deviation
Scalar deviation refers to the deviation that evaluates or calculates the larger value of the deviation but does not find its phase. The main sources include:
(1) Error limit of impeller design tolerance: When producing according to the design tolerance, the size of each impeller will not be the same, and there is always a certain limit deviation, which will affect the dynamic balance test results.
(2) There is a gap between the dynamic balance shaft and the impeller: in actual manufacturing, the dynamic balance shaft and the balance impeller generally have a clearance fit, and this gap will affect the dynamic balance test results.
(3) Different disassembly and assembly methods: During the transportation and installation of some impellers, due to different installation methods or incorrect installation, the dynamic balance test results will be inconsistent.