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Ralph, first of all tanks for your reply. I am in contact with a Schenck salesman but I want to get some technical information to understand better our problem. - We're not the manufacturers of the rotor but we have been told that the critical speeds are over the nominal speed. However, when...

Hello all, I have a couple of problems that I would like to share with you... I am balancing a magnetic rotor that must turn to 90.000 rpm (1500 Hz). With my actual system I am facing some problems and I am thinking on getting a new one. I need to be awared about what can be determinant and...

Yes, you're right. It should be a number but if you're measuring continuously you will get a value each sample. If the value is very different from time to time may be is because your system is not stationary. (I don't know if I've understood your question).

Thanks a lot for your response electricpete. I started by balancing the rotor and left a small residual imbalance. Now it works much more better. Harmonics are smaller (almost have disappeared). Referring to sidebands they're small and appears only in a few revolutions. I will try to check...

FeX32, I know that the solution doesn not make sense but in fact what I have done is put some damping between parts. I have not killed the problem I have just smooth its effects. Ramping up further (1kHz) bands have appeared again. Now I am working to reduce imbalance of the rotor since I...

It's strange because in all literature says that loosness and gaps appears at 0.5x, 1x, 1.5x, 2x...but anyway it has worked. However when I go down I still can heard a small sound when I pass through the frequency where sidebands appeared. Refering to the measures in different planes I can...

Thanks electricpete but it seems that I've solved the problem by adding an o-ring between two components. Yes, I was talking about 1500 Hz or 90.000 rpm.

Hello all, I have a problem with an electrical motor. Two sidebands are apperaing next to syncronous peak and its harmonics (700Hz) while I am rumping up my electrical motor (1500 Hz nominal speed). A strange noise can be heard when sidebands appears. I've been looking for some information...

I use synchronous sampling. I enter the info of the tach with a NI acquisition card where I also connect the accelerometers.

Tmoose, The brand is GRW. Hybrid bearings 12-28-8. Angular contact (15º). Specially designed to be used in high speed and high temperature systems. We are working in some different protos and the arrangement varies a little bit from proto to proto. In general you can imagine a shaft with a...

Tmoose, First of all thanks for this valuable information. Although bearing preload is given by a smalley (kind of flat spring) it is true that the bearing is fixed by the axial force given by the nuts. It can be a source of error, specially for possible radial clearance, but where I think...

TPL, The external consultancy is begining in 2 weeks and this is the time I have to learn and test by myself to give them information and be ready to learn with them. It is clear that this forum will not give me the solution but I am learning important things from people that for sure knows...

TPL, You're right that I am not qualifyied to solve the problem but since the external company has not been able to finish our generator, we are looking for another company to finish or rebuilt it. At the same time I have to learn something about mechanical vibrations (3 months ago I didn't...

Greg, I will check again the frequencies of the system mounted, just in case. How could I check if we have torsional vibrations? Which could be the origin of this vibrations? Thanks

GregLocock, Does it make sense to do a hammer test with thes shaft mounted in the bearings? I did it and although we can see a slight difference it cannot explain the fault. Don't you think that if the natural frequencies are above the problems we are facing, means that the problem is mode...

TPL, What is the purpose of building it – is it a commercial undertaking or is it some sort of educational project? It is not really home-made. An external company has been developing the project but we have been required to solve the mechanical problems. They will work in the elecrics and we...

Tmoose, The first time we balance a systme we first balance the rotor by itself. From then we balance all the system mounted. Our correction planes are the two nuts of each end of the rotor. This two nuts maintain bearings, cases, smollies and some more parts fixed into the rotor(see drawing...

Btrueblood, It is a BLDC motor with permanent magnets. All testing is done by spining the generator through a range of speeds. The driver is electrical (PWM Control) so we are injecting current to the stator of the motor and controlling it with halls and the control electronics. There is no...

BobM3, The harmonics can excite them but I'm not sure both together. In any case now I'm trying to reduce mecanical looseness to minimize harmonics.

MotorVib, My hand calculations were just an approximation. In FEA simulations, Ansys added weak springs to solve the case (at least it was said in an information message). To think about a reasonable residual imbalance I've used ISO 1940. This standard does not takes into account if the rotor...