Analyze the causes of motor noise and noise reduction measures

Noise control is an important element of environmental protection, and motor noise is an important technical indicator of motor product quality. Therefore, the control of motor noise has become an important issue for the survival and development of motor manufacturing enterprises at home and abroad. Today I will lead you to analyze the main causes of noise and noise reduction measures that can be taken.

Motor operation usually has a variety of noise sources co-existing at the same time, different noise is generated by the various parts of the motor, and the formation of motor noise in different parts, generally unrelated to each other, and therefore can be studied separately, respectively, to take special noise reduction measures.

1. Electromagnetic noise

Electromagnetic noise is mainly caused by changes in time and space, and by the role of magnetic tension 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 makes the stator and rotor undergo radial deformation and periodic vibration, which is the sound source of noise formation. Most of the sound waves are radiated from the stator and other parts of the vibration to the surrounding space, becoming "airborne noise", and most of the electromagnetic noise belongs to "airborne noise".

There are many design and failure reasons, that will also cause an increase in electromagnetic noise, such as: magnetic tension imbalance, the effect of open slot, flux oscillation noise, asynchronous motor broken bars, DC motor armature and main pole short circuit between turns, AC motor core pressure mounting is not tight, the assembly air gap is not uniform and so on. Therefore, the appropriate reduction of motor air gap flux density, increase the air gap, design, such as the use of armature slant slot, DC motor uneven air gap and AC motor magnetic slot wedge, are effective measures to reduce tooth harmonics and electromagnetic noise. Increasing the rigidity of the seat can reduce the vibration and noise generated by the fundamental wave rotational force in the stator and rotor air gap field. Improve the uniformity of the air gap assembly and the stacking quality of the core, are conducive to reducing electromagnetic noise.

2. Aerodynamic noise

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

Eddy current noise is mainly caused by the rotor and fan cooling air turbulence, alternating eddy currents on the rotating surface caused by; flute noise is generated by compressed air, or air in the fixed obstacles and rubbed. Flute noise in the motor is mainly caused by radial ventilation grooves. Flute noise is with the rotating parts and fixed parts of the gap between the reduction and enhancement, so the use of sealed noise enclosure, the noise "sealed" in the noise enclosure, increase the gap between the rotating parts and fixed parts, improve the shape of the air guide cover, the use of uneven distribution and length of unequal spacing of the airfoil is to reduce the effective way of noise flute.

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 source of noise. Causes of commutation noise: Friction noise: Brushes and slip rings and commutator sliding connection, inevitably produce friction noise. The size 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 pressure of the brush. Therefore, the methods to reduce friction noise include: improving the smoothness and roundness of the working surface of the slip ring and commutator, ensuring that the absolute humidity of the air is not less than 5g/m³, cleaning the surface of the brushes, the hardness of the brush material should not be too large, and appropriately reducing the diameter of the commutator.

4. Mechanical noise

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

Poor rotor dynamic balance is one of the most common causes of mechanical vibration and mechanical noise, improving rotor dynamic balance accuracy can effectively reduce this noise. Installation, poor adjustment, stator, rotor parts of the intrinsic frequency and speed frequency is consistent, will also produce mechanical noise. When the motor is equipped with an end hood type windshield, the hood is often shaken by the vibration of the motor, and vibration will also produce noise. In this case, the vibration of the motor stator is often the source of excitation of the end cowl or windshield, to reduce this vibration noise, the measure is to increase the dynamic stiffness of the end cover and cowl. Adding vibration-absorbing materials, such as felt, at the combination of the end cover and stator can reduce the vibration amplitude of the stator.

5. Load noise

The main reason for this noise is poor manufacturing, assembly clearance and operation, transportation, and installation process caused by work surface damage and electrical corrosion damage, which will make the bearing run unbalanced and have irregular impact. For example, the shaft surface roughness does not meet the requirements, bearing hole roundness is not good (stator or end cap), bearing hole material is poor, armature core shaft extension end of the slight scratches and so on.

Noise reduction countermeasures are: bearing processing and incoming inspection, must strengthen the bearing wall smoothness, roundness, surface roughness test inspection, to confirm that the bearing wall oil holes or material is in line with the requirements of the bearing hole roundness is not exceeded, a careful inspection of the head of the shaft, to confirm that the end cap side of the head of the axle is qualified; series of shafts stacked riveted, the axle extension end of the scratches.

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