Power transmission vibration damping

[fastline12]

Long story short, we have a transmission system that has a vibration. Decision was made that we need to get it back in service for now until there is time to do a proper rebuild and find the cause. This trans box is Al with high low ranging and a single 3ph motor standing vertical on it.

We need to isolate and damp the vibrations from carrying into the rest of the machine. Frequency was tests to swing from 40-110hz in our operating range. We did not have good calibration to give an amplitude this is a vibration you can hear and feel but certainly nothing sends you running for the E stop.

I was playing with some steel plate and seemed to be able to get about 30-40% out by contacting the motor up top. I do not have specific experience with damping and not sure if we might try a hand in a fluid device as sort of an active damper or if mass is king here? We are a bit limited on space but can fit some Lead in there but don't have any on hand any the moment.

 

[GregLocock]

You either start measuring things, or you try suck it and see.

If you go the latter route then some sort of flex coupling or hydraulic coupling provides the best shot at first time success, although I agree a big lump of lead in the right place can work wonders.

If you want some idea of a measurement based approach then you might have more luck on

http://www.eng-tips.com/threadminder.cfm?pid=384

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Tmoose]

Is the 40 -110 Hz the frequency provided to the motor? Or do you believe that is the frequency of the vibration/sound?
Even 100 Hz is pretty low. Sounds like this -

http://www.youtube.com/watch?v=mejO0hV_w80

 

[EngineerTex]

Adding weight doesn't damp it. Adding weight only changes the resonant frequency (lower).

You might also stiffen the overall structure to raise the resonant frequency, which may solve the problem if you don't have any excitation frequencies in that range.

However, 40 - 110 hz means that you've got a heavy mass on a relatively compliant spring. Have you tried rubber isolators for how it's mounted? Or some other type of vibration-absoring material?

Engineering is not the science behind building. It is the science behind not building.

 

[fastline12]

Yes, the 40-100hz is pretty accurate but does extend slightly higher as well. The notion that this is a heavy mass hanging in the wind is accurate. This is a machine tool spindle extending out from the main casting with a gear box and motor op top. The vibes from the trans are being allowed to vibrate the rest of the column which is probably why the frequencies are so low, already reduced somewhat.

I have already used some rubber isolators and YES, they do help quite a bit but I am wondering about combining mass damping with the rubber isolators to get the most effect. Because the motor is standing up on a pedestal so to speak, unsupported other than the C face mount bolts, it is allowed to vibrate.

 

[BrianE22]

Rubber isolators? The motor/transmission being part of a machine tool spindle, do you worry about torsional movement of the motor body (assuming the control encoder is mounted to the motor body)? I'd think that you'd need a stiff load path for the torsional axis.

 

[BrianE22]

So, the output of the transmission is coupled to the machine tool's vertical spindle via a belt and a rotary spline shaft? The motor/transmission is rigidly bolted to the machine tool base?

Have you verified that it's a motor/transmission problem by removing the drive belt and running the motor speed up and down?