×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Vibration limits of machinery on soft bases

Vibration limits of machinery on soft bases

Vibration limits of machinery on soft bases

(OP)
There are a number of vibration limits based on machinery mounted to rigid foundations. In this case I have good experience and trusted vibration limits for a new machine: 0.3 in/s peak and 3 mils pk-pk.

I have an application where we are mounting a machine on a floating platform. The mass of the rotor is a significant portion of the total structure weight, and we're finding that the normal vibration levels are a bit higher. The literature and common sense seem to indicate higher vibration is normal in this situation.

The question is: how damaging is it really? I envision that at higher levels, the deflections will generate fatigue failures and significantly reduce bearing life. Any methods or rules of thumb to estimate a safe and practical vibration limit here?

Thanks,

David

RE: Vibration limits of machinery on soft bases

If the larger vibration amplitude is causing some part of the metal structure to bend more, then I guess fatigue and cracking could result, if the resulting stresses are above the endurance limit, or there are details that cause even higher local stress due to poor geometry.

The bearing loads often are reduced by the lower resistance of the more flexible structure.
Consider the opposite. Imagine an infinitely rigid structure. A machine could have immense unbalance, exerting forces 20 times the rotor weight or normal process loads on the bearings. The rigid structure would restrain the bearing housings so well the world would have no idea the hell the bearings were having to endure.

Auxilliary Components like switch boxes, wiring and connections going along for the ride may not enjoy the increased vibration levels.

RE: Vibration limits of machinery on soft bases

geesamand,

Is the rotor causing the vibration?

Do you know the spring rate of your mounts? If you have the acceleration and the peak to peak movement, you should be able to work out the forces. If you know the mass rating and resonant frequency, you can approximately work out the spring rate.

--
JHG

RE: Vibration limits of machinery on soft bases

(OP)
The rotor is the cause of the vibration based on spectra and common sense. We have the usual contributions from imbalance and misalignment. We have another contributor at 3500cpm but it's much smaller and not appearing on the overall vibration much.

The "mounts" are not to ground - the machine floats in liquid. I can see how acceleration data might lead to reasonable estimates of internal forces. As well, I can see how looking at the attenuation of vibration as it migrates away from the source might give some idea where the vibration is applying the most load.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources