In daily equipment inspection, various abnormal noises will be found in the running motor, and long-term "abnormal noise operation" will seriously threaten the safety and life of the motor. In order to eliminate the abnormal phenomenon in time, the noise source must be identified accurately and quickly.
1 Noise source
Generally, motor noise sources can be divided into electromagnetic noise and mechanical noise.
The alternating magnetic field in the air gap of the motor will cause low-frequency noise generated by the stator, rotor and mechanical structure. Electromagnetic noise is mainly caused by the periodically changing radial force generated by the magnetic field in the air gap, and the non-uniform magnetic field force will cause the stator and rotor cores to produce hysteresis contraction and vibration. The reasons are as follows:
The length of the stator and rotor is too different,
The matching between the stator and rotor slots is insufficient, and the iron core is not closely laminated.
Uneven winding spacing
The rotor core vibrates radially,
The coil in the coil winding is reversed,
There is an open branch in the parallel winding, the winding is asymmetrical or the winding is short-circuited.
The friction between the stator and rotor of the motor, the unbalanced dynamic balance, the wear of the bearing and the bearing sleeve, or the resonance of the motor body will cause mechanical noise.
The reasons are as follows:
The bearing is damaged or poorly assembled. When the motor rotates, put one end of the listening rod on the end cover of the bearing, and then put the other end on the earlobe with your fingers to hear whether the sound of the bearing rotates evenly. Insufficient assembly of motor bearings, wear of bearing sleeves and looseness of bearings will cause abnormal noise in the bearings.
The dynamic balance of the motor rotor is destroyed, the rotor is unstable or the rotating shaft is bent, which will cause the rotor to vibrate.
The uneven air gap between the stator and the rotor will cause mutual friction.
The iron core is loose and the slot teeth are damaged.
Poor bearing installation or bearing damage.
The coaxiality between the motor shaft and the load shaft is poor.
2 Noise recognition method
Power-off method: Use the characteristics of electromagnetic noise to change with the magnetic field strength, load current size and conversion level. After a period of silent operation, the power supply is suddenly disconnected. After cutting off the power, the noise will disappear immediately. This is electromagnetic noise. After the power failure, the noise generated by the motor that continues to run through inertia is mechanical noise.
How to change the voltage: When the power supply voltage drops rapidly to a certain limit, if the electromagnetic noise is the main part of the motor noise, the change with the voltage will be large, while other noises remain basically unchanged.
3 noise control
Reasonable structure design: DC motors use uneven air gaps. The use of magnetic slot wedges in AC motors can not only reduce harmonic losses and improve efficiency, but also reduce electromagnetic noise caused by harmonic magnetic fields. The stator winding adopts reasonable short torque.
Correctly control the ripples, pits, roughness and radial clearance of the bearing rolling surface.
When the motor power has a margin, the rotor diameter can be appropriately reduced, the air gap can be increased, and higher harmonic noise can be eliminated. The disadvantage is that the no-load current increases and the power factor decreases.
High assembly accuracy: use high-quality bearings. Keep proper assembly interference. Improve the accuracy of the rotor dynamic balance detection, and ensure the concentricity of the motor and the load shaft during the installation process. Ensure rotor dynamic balance
This article mainly introduces the cause analysis and
countermeasures of motor noise to improve the stability of the equipment during