motor vibration non-repeatability
motor vibration non-repeatability
(OP)
Has anyone experienced non-repeatable motor vibration, with motor running solo? One symptom is that vibration is higher initially if the motor sits for a while. Motor is an 1800 rpm induction unit with pressurized hydrodynamic bearings.





RE: motor vibration non-repeatability
RE: motor vibration non-repeatability
RE: motor vibration non-repeatability
Therefore based on the limited information available,I would suggest that you look at soft foot, resonance, and the isolators if they are present.
RE: motor vibration non-repeatability
Next, break the investigation into two parts- (1) source vibration (changes in rotor balance, etc.), and (2) response. I assume the vibration level is rough or severe. Have you determined where vibration is strongest
(eg: drive end, opp drive end?) and direction?
(1) I recommend monitoring phase and amplitude at 1X rotation and comparing over several start-ups/coast-downs. Consider doing a balance sensitivity test with a trial weight to see if you can duplicate the changes (probably not if you have non-repeatable results to begin with).
If the phase varies significantly (with the same measurement point) between runs, then consider doing
an internal inspection (after looking at (2) below) for parts or assemblies on the rotor that can change
position and affect rotor balance. I don't know what that may be on your unit, but consider it anyhow.
(2) Investigate for structural resonance, especially if the vibration is significantly directional. The changes could be more related to changes in stiffness that affect the structural response to a steady vibration level. Depending on the arrangement and structural dynamics, small changes could have a significanteffect.
Beyond that, you could go goofy and consider conditions such as bent shaft/thermal bow combinations.
Pls let us know if you find anything.
RE: motor vibration non-repeatability
http://www.reliability-magazine.com/ubb2000/ubb/Forum2/HTML/000184.html
and if any of you guys think you overdo things, try:
http://www.reliability-magazine.com/ubb2000/ubb/Forum2/HTML/000178.html
RE: motor vibration non-repeatability
RE: motor vibration non-repeatability
If the coupling is not a constantly soft one, but may get stiffer with time (ageing rubber inserts for example) you should keep an eye open for the future. If the rubber gets stiff, the node of tragged out towards the driven machine and you might slide down towards running speed again. This is an eternal struggle with feed water pumps in a nearby power station here. They are saving money to be able to buy a better dimensioned coupling that does not age that fast. Best regards Arne