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Reply to "High vibration in motor"

@Registered Member posted:

"We Strengthened the structure  but not changing on vibration" What exactly was done?

It is difficult (especially without experience) to modify a structure without understanding how it is moving/deflecting. An operating deflection shape (ODS) test with two accelerometers, or an impulse-response test with instrumented hammer and accelerometer are two methods to quantify structural deflection.

I could tell stories of how this exact problem was solved several times. If you want to try an experiment to add mass to detune the structure, then here is a practical method that has worked:

Remove the two motor lift-lug eye-bolts and get two bolts with same threads of suitable length

Make two steel weights (start with about 25-lbs each and about 50-lbs maximum) from steel blocks or plates (less than 12-inches square)

Make hole in center of each weight (drill or torch-cut) for bolt

Bolt each weight tight to motor case at the two lift-lug locations

Run motor with base bolts tight with no soft foot present. Note that shims should be snug at all four base locations when base bolts are loose to minimize soft foot.

If the vibration level at 2x line frequency (100 Hz) is substantially reduced, then a natural frequency was present and controlled. Either leave weights in place, with appropriate engineering review, or remove weights and evaluate other vibration control methods.

If you try this, then please provide before and after vibration measurements.




Foundation test: We evaluated the moisture and quality of the concrete under the equipment

Strengthen structure: We added a 10 kg weight to the base with 4 bolts, to strengthen the structure and change the resonance, but the vibrations did not change at all.

My device hasn’t ODS test, If necessary, we must provide another new device

In adjusting soft food when the electromotor is discouple, we checked each bolt with the least shim, but vibrations increase when the third or fourth bolt is tightened.

Notice: At the start of the electromotor, when the motor power is star mode, the vibrations are 4 mm/s in the horizontal direction, but after 10 seconds, when power is in the triangular mode, the vibrations suddenly increase to 16-18 mm/s

I'm sure the vibration frequency with high resolution is 2XLF (100-101 Hz), The amplitude of vibrations (2X) is shorter.

I didn't understand how your experimental test was done. Please let me know a little more clearly (or in a simple photo).