Motor Noise Analysis and Noise Reduction Measures

Noise control is an important content of environmental protection, and motor noise is an important technical index to measure the quality of motor products. Therefore, the control of motor noise has become an important issue for the survival and development of domestic and foreign motor manufacturers. This paper analyzes and discusses the main causes of noise and the noise reduction measures taken.

When the motor is running, a variety of noise sources usually coexist at the same time. Different noises are generated by various parts of the motor, and the different parts of the motor that form the noise are generally unrelated to each other. Therefore, special noise reduction measures can be taken separately.

1. Electromagnetic noise

Electromagnetic noise is mainly caused by changes in time and space, and by the magnetic pull between the various parts of the motor. The magnetic field in the air gap space is a rotating force wave, and its radial force wave causes radial deformation and periodic vibration of the stator and rotor, which is the sound source of noise. Most of the sound waves are radiated to the surrounding space by the vibration of the stator and other components, becoming "airborne noise", while most of the electromagnetic noise belongs to "airborne noise".

There are also many reasons for design and failure, which will also cause the increase of electromagnetic noise, such as: imbalance of magnetic pull, influence of iron core saturation, influence of open slot, noise generated by magnetic flux oscillation, dynamic eccentricity of air gap, pulsation component in thyristor power supply, harmonic component in power grid, broken bar of asynchronous motor, short circuit between armature and main pole turn of DC motor, tight pressing of core of AC motor, uneven assembly of air gap, etc.

Therefore, appropriately reduce the air gap magnetic flux density of the motor and increase the air gap. If the armature chute is used in the design, the uneven air gap of the DC motor and the magnetic slot wedge of the AC motor are all to reduce tooth harmonics and electromagnetic noise. Effective measures. Increasing the stiffness of the machine base can reduce the vibration and noise caused by the fundamental wave rotating force in the air gap field of the stator and rotor. Improving the uniformity of air gap assembly and the stacking quality of iron core are conducive to reducing electromagnetic noise.

2. Aerodynamic noise

The aerodynamic noise of the motor has two kinds of eddy current noise and whistling noise.

The eddy current noise is mainly caused by the turbulence of the cooling air caused by the rotor and the fan, and the alternating eddy current on the rotating surface; the whistling noise is generated by compressed air or air passing over a fixed obstacle. The whistling noise in the motor is mainly caused by the radial ventilation ditch. The whistling noise increases with the decrease of the gap between the rotating parts and the fixed parts. Therefore, the use of a sealed soundproof cover to "seal" the noise in the soundproof cover, increase the gap between the rotating parts and the fixed parts, and improve The shape of the wind deflector and the use of blades with uneven distribution and unequal length are effective ways to reduce the whistling noise. In addition, reducing the peripheral speed of the rotor surface, reducing the surface area of the motor and the surface roughness of the rotor can also reduce the aerodynamic noise.

3. Commutation noise

Commutation noise, also known as brush noise.

In motors with slip rings and commutators, commutation noise is inevitable and sometimes becomes a major noise source. causes of commutation noise:

Friction noise: The sliding connection between the brush and the slip ring and the commutator will inevitably produce friction noise. The magnitude of the friction noise is related to the surface state of the slip ring and commutator, the friction coefficient of the brush, the absolute humidity of the air and the brush pressure. Therefore, the methods to reduce friction noise are: improve the smoothness and roundness of the working surface of the slip ring and commutator, ensure that the absolute humidity of the air is not less than 5 g/m, clean the surface of the brush, the hardness of the brush material cannot be too large, and appropriately reduce the diameter of the commutator.

Impact noise: This is because there is a mica groove between the commutator segments. Due to the deformation of the commutator, the undercutting and chamfering process of the mica groove is not good, so that the brush will often hit the commutator segments when the motor rotates, making the commutator segments and reducing this noise.

4. Mechanical noise

Rotary motor noise is mainly mechanical noise, large, high-speed motors are prone to produce this noise.

Poor rotor dynamic balance is one of the most common causes of mechanical vibration and mechanical noise, and improving the accuracy of rotor dynamic balance can effectively reduce this noise. When the installation and adjustment are poor, the natural frequency of the stator and rotor parts is consistent with the speed frequency, mechanical noise will also be generated. When the motor is equipped with an end cover type wind cover, the cover is often shaken by the vibration of the motor, and vibration occurs, and noise is also generated. In this case, the vibration of the motor stator is often the excitation source of the end cover or the wind cover. To reduce this vibration noise, the measure is to increase the dynamic stiffness of the end cover and the cover. The vibration amplitude of the stator can be reduced by adding a vibration-absorbing material, such as felt, at the junction of the end shield and the stator.

5. Load noise

The main reason for this noise is poor manufacturing, assembly clearance, and operation, transportation, installation process caused by the work surface damage and electric corrosion damage, will make the bearing operation imbalance and irregular impact. For example, the surface roughness of the shaft does not meet the requirements, the roundness of the bearing hole is out of tolerance (stator or end cover), the material of the bearing hole is poor, and the extended end of the armature core shaft is slightly scratched.

Noise reduction measures include: during the bearing processing and incoming inspection, the test and inspection of the smoothness, roundness and surface roughness of the inner wall of the bearing must be strengthened to confirm whether the oil hole or material of the inner wall of the bearing meets the requirements and whether the roundness of the bearing hole is out of tolerance, carefully check the shaft head and confirm whether the shaft head on the end cover side is qualified; When riveting the shaft, whether the shaft extension end is scratched.

In short, in order to effectively control and reduce motor noise pollution, in addition to the production process of good quality, but also must master the motor noise monitoring, diagnosis and identification technology, in order to take effective measures to reduce noise.