What is the reason for abnormal noise when the centrifugal fan is running?

The reasons for abnormal noise when the centrifugal fan is running may be as follows:
Blade problem: When the blade rotates, it rubs against the air or impacts. The faster the speed, the wider or thicker the blade, the sharper the noise; the blade installation angle is too large, or the fan blade bending changes too much, resulting in eddy currents during operation, which not only reduces the efficiency of the fan, but also generates noise; dirt, wear, deformation or damage on the blades may also cause abnormal noise.
Fan resonance: Resonance with the duct housing, or the fan's own parts such as the impeller, motor, etc. resonate with other structures, and the inner surface joints of the duct and the fan housing are rough and uneven, which can also cause tearing sounds.
Bearing abnormality: Bearing defects, wear, loose support, insufficient lubrication, loose shaft, misaligned seals, foreign matter, or micro-corrosion between the inner race and the shaft will all cause increased noise.
Motor problems: Poor motor design or poor quality may cause loud noise; loose anchoring, base or fan of the motor; loose lead-in cables, AC hum in the motor or relay, relay vibration, cooling fan hitting the shield and other motor faults may also cause abnormal noise.
Gas-solid coupling noise: When the impeller rotates, the velocity and pressure of the circumferential airflow at the blade outlet are unevenly distributed, which acts on the volute to form pressure pulsation and generate noise; the rotating blades are disturbed when passing through the volute tongue, causing the force of the airflow on the blade to pulsate over time and generate noise.
Other reasons: If the centrifugal fan is used for too long, it may break the frame, vibrate, or run unstably, causing the fan blades and the casing to collide or repel; when the air flows, it encounters sharp obstacles to generate turbulence; there are obstacles in the system, such as dampers, sharp elbows, sudden expansion or contraction of the pipe, pipe leakage, turning blades or fins on the coil, etc., causing abnormal airflow and noise; the pulley is not tight on the shaft, the belt hits the belt tube, the belt is too loose or too tight, the belt cross section is wrong, the belt length on the multi-belt drive does not match, the variable pitch groove wheel is not adjusted to cause the pitch diameter of each groove to be the same, the pulley is misaligned or the belt is worn; the coupling key is loose, unbalanced, misaligned, loose or lubricated incorrectly; the shaft seal is not lubricated sufficiently, the shaft is misaligned or the shaft is bent, etc.
If the centrifugal fan has abnormal noise, it is recommended to stop the machine for inspection in time, and repair or replace the relevant parts according to the specific reasons to ensure its normal operation and reduce noise. In daily use, you should also pay attention to the regular maintenance and care of the centrifugal fan.
If you want to know the reason for the abnormal noise of the centrifugal fan, you are welcome to contact JN Fan. We will do our best to help you!