How to eliminate engine vibration

Increased vibrations drastically reduce the reliability of the electric motor and are especially dangerous for its bearings.

Under the influence of sudden shock loads from the vibrating rotor in the bearings, the oil film can break and the babbitt melt. In some cases, cracks and chips appear in the babbit. Metal fatigue phenomena quickly develop in rolling bearings, cracks, holes appear on the movable working surfaces and separators break.

Vibration can also cause the shaft to bend or break, the rotor barrel can tear off the shaft, the stator frame or end cap can crack, and the support frame and foundation can be damaged. Insulation wear on the motor windings increases and accelerates.

Excessive engine vibration must be eliminated. But for that you need to know the reason. The causes of vibrations, which are conditionally divided into two groups, can be the following.

First group

1. Incorrect alignment of the electric motor with the mechanism.

2.Unsatisfactory clutch condition: finger wear, crackers, teeth, misalignment of pin holes in half-couplers, unbalance of half-couplers or pins.

3. Impeller rotor imbalance, which is especially common in flues and fans due to vane wear.

4. Defective drive mechanism bearings.

5. Defects of the base and foundation frame: destruction of concrete from oil, fracture of welding on the supports of the frame, poor attachment of the engine to the frame after alignment, etc.

This group of causes of vibration of the electric motor must be eliminated by the personnel repairing the drive mechanism, with the exception, perhaps, of eliminating a defect in the welding of the frame under the electric motor, if it is not at the same time the frame of the mechanism.

Second group

1. Motor rotor imbalance.

2. Crack formation and breakage of short-circuited rotor winding bars from the ring.

3. Separating the rotor barrel from the shaft.

4. Bending or buckling of the rotor shaft.

5. Weak fastening of individual parts of the electric motor (bearings, end caps).

6. Inadmissibly large clearance in sliding bearings, defects in rolling bearings.

This group of causes is eliminated by personnel repairing electric motors.

In practice, vibrations are sometimes caused by more than one cause.

If an increased vibration of the bearings of an electric motor is detected, it is recommended to measure it with a vibrometer or vibrograph to know the true value.

Without turning off the engine, check whether the vibration is caused by a weak fastening of the engine, a violation of the welding of the elements of the foundation frame, or the destruction of the concrete of the foundation. For this purpose, the vibrations of the legs of the electric motor or the seats of its bearings, the bolts holding the electric motor and the frame near the legs are determined and compared by touch.

If the bolt is undertightened, only the motor leg vibrates and the bolt does not vibrate or vibrates slightly.

The difference in vibration can best be noticed by placing a finger on the joint of two mating parts, in this case the joint of the bolt and pawl. If the tight coupling between them is broken, the vibration causes one part to move relative to the other, and the finger can easily detect this.

If the bolt also vibrates, then in this way it is checked whether there is a difference in vibration at the junction between the foot and the frame, between the upper shelf and the vertical part of the frame, between the ribs and the upper and lower shelves, between the lower shelf of the frame and the bases, etc. Sometimes a violation of a strong connection between parts is also detected by the appearance of small bubbles, and with strong vibrations - and small splashes of oil at the junction.

If a defect is found at the interface between the frame and the base, which occurs most often due to the erosion of concrete with oil, all impregnated concrete, including that which has retained its strength, must be removed and replaced with fresh. While the concrete hardens, the unit must be stopped and taken out of reserve.

If no defects are found in the base, frame, attachment of the electric motor and its end caps, attachment of the drive mechanism, disconnect the clutch between the electric motor and the mechanism and start the electric motor at idle speed.

If at the time of starting and idling the electric motor works without vibration, then the cause of the vibration should be sought in misalignment, wear of the fingers or half-couplings themselves, or the appearance of an imbalance in the drive mechanism.

If the electric motor also vibrates at idle, then the reason for the vibrations is in the electric motor itself. In this case, check whether the vibration disappears immediately after disconnecting the electric motor from the mains. The disappearance of vibrations immediately after disconnection from the mains indicates an uneven gap between the rotor and the stator. In order to eliminate vibrations caused by uneven spacing, measures must be taken to equalize it.

Strong vibration of the electric motor when starting at idle indicates an uneven gap or a broken rod in the rotor winding. If the gap is the same, the reason for the vibration is only the rotor bar tearing. In this case, vibrations are eliminated by repairing the rotor winding.

If the vibration of an electric motor disconnected from the mechanism does not disappear immediately after disconnection from the network, but decreases with a decrease in the number of revolutions, then the reason for the vibration is in the imbalance of the rotor due to the imbalance of the coupling half, bending or the appearance of a crack in the shaft, displacement of the winding, separation of the rotor barrel from the shaft. In this case, it is useful to remove half of the clutch and start the electric motor without it.

Normal operation of the electric motor indicates an imbalance in the clutch half. Such a coupling half must be mounted on a mandrel and machined over the entire outer surface on a lathe. If vibration remains after removing the coupling half, the rotor should be removed and inspected for defects on the shaft and in the attachment of the rotor cylinder to it. If there are no defects, the rotor must be dynamically balanced on the machine. Statically balancing the rotor on the blades will not help in this case and therefore should not be done.

Increased clearances in plain bearings do not cause vibration by themselves. If there are no other reasons for vibration, then even with large gaps, the electric motor, especially at idle, will work normally. But if other causes of vibration appear, then its value for large gaps will be much higher than for permissible gaps. Therefore, if the electric motor only vibrates under load and it is not possible to determine the cause of the vibrations, then measures should be taken to reduce the clearance in the bearings by filling them.

Motor vibration due to defective rolling bearings is easily detected. A defective bearing makes a lot of noise and heats up. It must be replaced, and only then continue to find the cause of the vibration if it remains.

Coupling defects that cause vibration are the imbalance of the coupling halves, the mismatch of the holes in the coupling halves by more than 1 mm, the uneven weight of the fingers, their uneven wear, or the wear of soft washers to such an extent that the fingers touch the steel holes in the coupling halves.

All fingers must be weighted. If there is a difference in weight, then any two pins of the same weight are installed in opposite holes on the coupling halves. Any worn fingers should be repaired by replacing the leather or rubber.Coupling halves with bore deviation should be replaced.