Basic knowledge of motor vibration and the causes of large motor vibration

1. What are the calculation units of motor vibration value? How to understand these units?

The commonly used measurement units of motor vibration value are speed effective value (referred to as speed), vibration amplitude value (referred to as amplitude, divided into single amplitude and double amplitude) and vibration acceleration. The first one is used more.

"Speed effective value" can be simply understood as the distance moved by the vibrating material (which can be regarded as a point) in unit time. W is the distance that the vibrating material actually swings back and forth in one place and does not move to other places. Therefore, the so-called "moved distance" can only be a description method, so the words "effective" or "equivalent" are used to further explain it. It can be imagined that the value of vibration speed is related to the distance of the vibration amplitude (the distance from the center position) of the vibration point. In addition, it is related to the frequency of vibration (the number of swings back and forth in unit time) and they are proportional; generally mm/s is used as the unit.

The vibration point is a particle that swings back and forth in two directions. When swinging, the maximum distance from the center position is called the amplitude. The maximum distance in one direction is called the single amplitude, and the distance between the farthest points in two directions is called the double amplitude - usually in mm or m.

Vibration acceleration is the increase in velocity per unit time M, usually in m/s2.

2. Which of the two values of the speed effective value and the amplitude of the vibration value is better? Is there a conversion relationship between them?

As mentioned above, the amplitude value only reflects the size of the swing amplitude, while the speed effective value reflects both the size of the swing amplitude and the speed of the swing. The degree of damage caused by vibration to the motor itself and related equipment is related to the amplitude and frequency (speed of swing). Therefore, it is more objective and more valuable to use the vibration speed to evaluate the size of the vibration value of a motor. This is also the reason why the speed effective value is generally used as the vibration measurement value in relevant international and domestic standards.

Because the conditions for generating the two quantities of speed and amplitude are not exactly the same, the speed has one more vibration frequency than the amplitude. For a running induction motor, [https://www.simomotors.net/flameproof-motor-for-underground-coal-mines-ybk3-product/] the vibration frequency is not single, and sometimes it is very complicated, with both high frequencies generated by electo-magnetics and medium and low frequencies generated by machinery.

Therefore, there is no fixed conversion relationship between the two, but generally speaking, when the amplitude is large, the vibration speed will also increase accordingly.

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3. Possible reasons for the large vibration of the motor:

(1) The purchased bearings are of poor quality and do not meet the quality standards. The assembly is not carried out according to the process requirements, causing deformation due to impact. The tolerance of the bearing chamber of the motor end cover is unreasonable, too tight or too loose. At this time, the simplest method is to use a hammer to gently knock along the axis to see if there is any improvement.

(2) Due to the high stop of the bearing cover or the wave spring is too hard, the bearings at both ends are stuck. At this time, the vibration of the three phase asynchronous motor [https://www.simomotors.net/flameproof-motor-for-underground-coal-mines-ybk3-product/] is often high, and a "buzzing" sound is often emitted.

(3) The dynamic balance of the rotor is not accurate, and the accuracy is not enough.

(4) The air gap between the stator and the rotor is uneven, and there is a local sweeping phenomenon.

(5) The rotor is broken, and the load current will swing at a certain period.

(6) The elecreic motor [https://www.simomotors.net/flameproof-motor-for-underground-coal-mines-ybk3-product/] foot is uneven, or it is not installed concentrically with the load equipment.

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