Motor vibration causes and treatment methods


Harm of motor vibration

The vibration of the motor will shorten the insulation of the winding and the bearing life, affecting the normal lubrication of the sliding bearing. The vibration force will expand the insulation gap, and the external dust and moisture will invade it, causing the insulation resistance to decrease and the leakage current to increase, even forming insulation breakdown. Waiting for an accident. In addition, the motor generates vibration, and it is easy to cause the cooler water pipe to crack and the welding point to vibrate. At the same time, it will cause damage to the load machinery, reduce the accuracy of the workpiece, cause fatigue of all mechanical parts subjected to vibration, loosen or break the anchor screw, and the motor will cause abnormal wear of the carbon brush and the slip ring, and even serious Brushing the fire and burning the collector ring insulation, the motor will generate a lot of noise, which is usually the case in DC motors.

Cause of vibration

There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; mechanical and electrical mixing reasons.

First, the electromagnetic reasons

1. Power supply: Three-phase voltage is unbalanced, and three-phase motor is out of phase.

2. Stator aspect: the stator core becomes elliptical, eccentric, loose; the stator winding is broken, grounded, short-circuited, incorrectly connected, and the stator three-phase current is unbalanced.

3. Rotor failure: The rotor core becomes elliptical, eccentric, and loose. The rotor cage strip is welded to the end ring, the rotor cage strip is broken, the winding is wrong, and the brush is in poor contact.

Second, mechanical reasons

Motor itself

The rotor is unbalanced, the shaft is bent, the slip ring is deformed, the stator and rotor air gaps are uneven, the stator and rotor magnetic centers are inconsistent, the bearing is faulty, the basic installation is poor, the mechanical mechanism is not strong enough, the resonance is loose, the ground screw is loose, and the motor fan is damaged.

2. Cooperating with the coupling

The coupling is damaged, the coupling is poorly connected, the coupling is not centered, the load is mechanically unbalanced, and the system is resonant. The linkage part of the shaft system is misaligned, the center line does not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during the installation process. There is also a case where some of the center lines of the interlocking parts are coincident in the cold state, but after a period of operation, the center line is broken due to the deformation of the rotor fulcrum and the foundation, thereby generating vibration.

Third, the reason for motor mixing

1. Motor vibration is often caused by uneven air gap, causing single-sided electromagnetic pulling force, and the single-sided electromagnetic pulling force further increases the air gap. This electromechanical mixing acts as motor vibration.

2. The axial movement of the motor is caused by the gravity of the rotor itself or the installation level and the magnetic center is not correct. The electromagnetic tension caused by the motor causes the axial movement of the motor to cause the motor vibration to increase. In severe cases, the shaft is ground and the temperature of the bearing is increased. Rapidly rises.

3. The gears and couplings associated with the motor are faulty. This kind of failure mainly manifests as poor gear occlusion, serious tooth wear, poor lubrication of the wheel, skewing and misalignment of the coupling, tooth profile of the gear coupling, incorrect tooth pitch, excessive clearance or serious wear, which will cause certain vibration.

4. Defects in the structure of the motor itself and installation problems. This kind of failure mainly manifests as the ellipse of the journal, the bending of the shaft, the gap between the shaft and the bearing bush is too large or too small, and the rigidity of the bearing seat, the foundation plate, a part of the foundation and even the entire motor installation base is insufficient, and the motor and the base plate are fixed. Not secure, the foot bolts are loose, and the bearing housing and the base plate are loose. The excessive or too small gap between the shaft and the bearing bush can not only cause vibration but also cause abnormal lubrication and temperature of the bearing bush.

5. The load dragged by the motor conducts vibration.

How to find the cause of vibration

In order to eliminate the vibration of the motor, we must first find out the cause of the vibration. Only by finding the cause of the vibration can we take targeted measures to eliminate the vibration of the motor.

1. Before the motor is not stopped, check the vibration of each part with the vibration meter. For the vibration part, test the vibration value in three directions of vertical horizontal axis. If the ground screw is loose or the bearing end cover screw is loose, Directly tighten, measure the vibration size after tightening, observe whether there is elimination or lightening, secondly check whether the three-phase voltage of the power supply is balanced, whether the three-phase fuse is blown, and the single-phase operation of the motor can not only cause vibration, It will also cause the temperature of the motor to rise rapidly, observe whether the current meter pointer swings back and forth, and the current swing phenomenon occurs when the rotor breaks. Finally, check whether the three-phase current of the motor is balanced. If problems are found, contact the operating personnel to stop the motor running in time to avoid burning the motor. damage.

2. If the motor vibration is not resolved after the surface phenomenon is processed, continue to disconnect the power supply, uncoupling the coupling, and separate the load connected to the motor. Single-turn motor, if the motor itself does not vibrate, the vibration source If the coupling is not looking for a positive or load machine, if the motor vibrates, it means that the motor itself has a problem. In addition, the power-off method can be used to distinguish whether it is an electrical cause or a mechanical cause. When the power is cut off, the motor will not vibrate immediately. Vibration reduction, it is an electrical cause, otherwise it is a mechanical failure.

Overhaul for the cause of the failure

1. Inspection of electrical causes

The first is to determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that the welding part of the stator is welded, and the winding is separated to find the phase. In addition, whether there is a turn-to-turn short circuit in the winding, if the fault is obvious, the burnt trace can be seen from the insulating surface, or the stator winding is measured with an instrument, and after confirming the short circuit between the turns, the motor winding is re-routed.

2. Maintenance of mechanical reasons

Check that the air gap is uniform. If the measured value is exceeded, re-adjust the air gap. Check the bearing and measure the bearing clearance. If it is not qualified, replace the new bearing. Check the deformation and looseness of the core. The loose iron core can be bonded and filled with epoxy resin. Check the rotating shaft, repair the reaming of the curved shaft or directly straighten the shaft, and then perform the balance test on the rotor.

3. The load mechanical part is checked normally, and the motor itself has no problem. The cause of the malfunction is caused by the connection part. At this time, check the basic level of the motor, whether the inclination, strength, center is correct, whether the coupling is damaged, and whether the motor shaft extension is in compliance with the requirements.

Steps to handle motor vibration

1. Disconnect the motor from the load, test the motor blank, and check the vibration value.

2. Check the vibration value of the motor foot. According to the national standard GB10068-2006, the vibration value at the foot plate should not be greater than 25% of the corresponding position of the bearing. If the value exceeds this value, the motor foundation is not a rigid foundation.

3. If there is only one or four diagonal vibrations of the four feet, the loosening of the anchor bolts will cause the vibration to pass, indicating that the underfoot is not properly ground, and the anchor bolts are tightened to cause vibration of the base. Put the foot on the ground, realign the centering and tighten the anchor bolts.

4. Tighten the four anchor bolts on the foundation, and the vibration value of the motor still exceeds the standard. At this time, check whether the coupling on the shaft body is level with the shoulder. If it is not flat, the exciting force generated by the excess keys on the shaft will cause the horizontal vibration of the motor to exceed the standard. Need to remove the extra keys.

5. If the vibration test of the motor is not exceeded, the vibration of the load exceeds the standard. There are two reasons: one is that the deviation is large; the other is the residual unbalance of the rotating part (rotor) of the main engine and the residual of the rotor of the motor. The phase of the unbalanced quantity overlaps, and the residual unbalance of the entire shaft system at the same position after the docking is large, and the generated exciting vibration force causes vibration. At this time, the coupling can be disengaged, and any one of the two couplings can be rotated by 180 ° C, and then the vibration of the test machine can be lowered.

6. The vibration vibration speed (intensity) does not exceed the standard, the vibration acceleration exceeds the standard, and only the bearing can be replaced.

7. Due to the poor rigidity of the rotor of the secondary high-power motor, it will be deformed without using the rotor for a long time, and it may vibrate when it is rotated. This is the reason for the poor storage of the motor. Under normal circumstances, every 15 days during storage of the secondary motor For the motor car, drive at least 8 turns or more each time.

8. The motor vibration of the sliding bearing is related to the assembly quality of the bearing bush. Check whether the bearing bush has a high point, whether the bearing oil of the bearing bush is sufficient, the bearing bushing force, the bearing bush clearance, and the magnetic center line are suitable.

9. Under normal circumstances, the vibration of the motor can be easily judged from the vibration value in three directions. The horizontal vibration is large, the rotor is unbalanced; the vertical vibration is large, the installation foundation is not flat; the axial vibration is large, the bearing assembly low quality. This is just a simple judgment. According to the situation on the spot, combined with the factors mentioned above, comprehensive consideration should be made to find the real cause of the vibration.

10. The vibration of Y series box type motor should pay special attention to axial vibration. For example, the axial vibration is greater than the radial vibration, which is extremely harmful to the motor bearing and will cause the axle accident. Pay attention to the bearing temperature. If the positioning bearing is faster than the non-locating bearing, stop it immediately.

11. After the rotor is dynamically balanced, the residual unbalance of the rotor has solidified on the rotor and will not change. The vibration of the motor itself will not change with the change of location and working conditions. It can handle the vibration problem at the user site. of. Under normal circumstances, the maintenance motor does not need to perform dynamic balance check on the motor. Except for the special case, such as flexible foundation and rotor deformation, it must be dynamically balanced or returned to the factory for processing.