Commercial large fans are commonly used in places such as fitness centers, sports arenas, shopping malls, amusement parks, and theaters. In the hot summer, people in these commercial settings can enjoy the gentle natural breeze from the fan and benefit from the fresh outdoor air brought in when discussing temperature. However, in commercial settings, the primary issue that needs to be addressed with commercial large fans is noise. Without proper noise control, it can cause discomfort for the people below. The main source of noise in large fans is the motor, so we need to take certain measures to reduce motor noise.
To reduce motor noise, we first need to understand the reasons behind motor noise generation, and different causes require different methods to reduce the noise.
- Noise caused by rotor imbalance: The motors used in commercial large fans are brushless motors, and rotor imbalance can easily cause noise. Mechanical imbalance of the rotor can be divided into static balance, dynamic imbalance, and mixed imbalance. Vibration caused by static imbalance produces equal and in-phase vibrations on both supports, while vibration caused by dynamic imbalance produces equal and opposite-phase vibrations on both supports. These vibrations generate noise.
Therefore, here are several production techniques to improve rotor dynamic balance accuracy: (1) The machining of the rotor must ensure symmetry and concentricity. (2) The circular and flat surfaces supported by the fan and windings should be machined as much as possible to ensure their concentricity, and non-machined surfaces should be smooth. (3) Before machining the shaft material, it should be checked, and bent materials should be straightened before machining. (4) The unbalance distribution in different parts of the rotor is not the same. To reduce centrifugal force during rotation, two correction planes must be chosen. To achieve a better balance effect, the support points should be as close to the bearing seats as possible, and the radius of the location where the balance weight in the correction plane is placed should be as large as possible to reduce the weight of the balance weight. (5) Uneven thickness and large burrs of silicon steel sheets can cause imbalance. Strictly follow the process regulations and mold maintenance rules during punching and stacking processes to minimize imbalance. (6) If balance calibrating is needed, balance weights should be added to the fan, balance rings, and winding supports to ensure overall dynamic balance. (7) The operation and maintenance of the dynamic balancing machine must strictly adhere to relevant regulations.
- Noise caused by bearings: Bearings are important components in motors. Bearing noise can be divided into two categories: noise generated by the bearing itself and noise caused by the assembly accuracy between the bearing and the motor.
Most motors use rolling bearings, including ball bearings and roller bearings. Rolling bearings consist of inner rings, outer rings, and balls or rollers with a cage. During motor rotation, these components experience relative motion, resulting in irregular friction and collisions that generate noise, especially at high speeds.
The main methods to reduce bearing noise include: (1) Pay attention to bearing selection. (2) Pay attention to the size of the radial clearance. Excessive radial clearance can increase low-frequency noise, while too small clearance can lead to high-frequency noise. (3) Apply appropriate pressure to the bearing. The purpose is to eliminate axial clearance in the rotor. Waveform elastic washers or three-point elastic washers can be used, and they should be placed at the end of the shaft. (4) For motors used in commercial environments, low-noise bearings should be selected, and oil-impregnated sliding bearings can also be used.
- Noise caused by mechanical processing factors: The machining accuracy of the housing, stator, rotor, shaft, bearing housing, etc., including coaxial, roundness, dimensional tolerances, surface roughness, etc., all have an impact on the final assembly quality. These factors can lead to the accumulation of mechanical noise, resulting in increased fan noise.
Therefore, when assembling shafts, bearings, etc., they should be placed on dedicated fixtures to avoid radial impacts. Directly striking the end face of the shaft or bearing during axial impact should be avoided, and brute force assembly should be avoided. Before assembling the bearings, they should be cleaned and demagnetized, and thermal expansion methods should be used for assembly, with an appropriate amount of lubricating grease applied. The precision machining processes for the rotor, shaft bearing seats, and end cap bearing housings should establish quality control points and implement focused control. The machining accuracy should be as close as possible to the middle value of the tolerance band. At the same time, the process level, production equipment, and fixtures of the manufacturing company must ensure the precision of mechanical processing.
The motor is the heart of a commercial large fan, and when used in commercial environments, especially in settings where sound is important, strict control of motor noise is necessary to ensure that the fan functions properly and provides a pleasant experience. Therefore, in the production design of the motor, we need to develop and implement comprehensive process regulations, adopt advanced process methods and equipment, and effectively control the noise of commercial large fan motors.