Gearbox issues

Sounds like your getting started....
It ends up being the same as for oil analysis....there are 3 rules Trend....Trend...Trend....
Yes ISO tells you that there are certain "general" guidelines for overall equipment amplitude based on the type and the RPM etc. These charts are in all of the Level 1 training materials. What you will find is not all equipment acts the same. Some may operate at significently higher overall amplitudes and last for a long time. Other identical equipment runs at a much lower overall amplitude by fails due to a small defect. If you trend and monitor the rate of change watch the bearings go through the 4 stages (and amplitudes) of failure. There is no easy set of criteria to base you first set of calls, your credability is at stake. Document the rate of change and eventually you will be able to reasonably determine the severity and hence the most optimal time to provide MAintenance time to plan and schedule the repairs. Just remember the decision still has to be made if they are going to run to failure even knowing the failure is emminent. It depends on the cost and consequences. Sometimed run to failure is a cost effictive way to perform maintenance.

regards......

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Originally posted by jreamer:
When do you tell the operations department to stop gear driven drive-trains? Do you stop the machine based on gear mesh frequency amplitude or reliable spectral envelope alarms? How much is too much g's? Is there a standard relating to this?

Thanks.

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I don´t know if Walter whants tell us something, if so please re enter your reply.
I am completlly agree with Alan, trending is the best way to support and equipment stop desition, no mather whitch technic are you using.

We have been doing this type of work for awhile and there is no good answer. It depends on several factors such as what the monitored parameters are telling you, how critical the machinery is to production, and how expensive the machinery is to repair and replace. You have to do what is right for your company, not what is right for the machinery. There is a tendency by Maintenance people to want to overhaul a piece of equipment as soon as it begins to trend upward. This has to be balanced by the production needs of your company. The goal is not to have perfectly running equipment - the goal is to have perfect production. This latter goal can often be achieved with a subpar machine.

I am monitoring a very diverse fleet including dragline gearboxes and have seen components with very high overalls running for extended periods, because production could not stop them, but if the time waveform show impacts you better make waves.

Trending is the one of the most important tools in for anyone in the Condition Monitoring field and it's value should not be underestimated. There are however certain other parameters that need to be considered when monitoring gear drives.
Time waveform is critical, especially with regard to gear drives, as the defect will not always manifest clearly in a FFT but if time waveform data is disregarded you are missing crucial information. Amplitudes in the time waveform will often be >10x higher than FFT spectra.
The spacing and amplitude of your sidebands is also an important parameter to bear in mind.
In short TREND but if you see impacting in the time waveform very expensive noises are likely to follow shortly afterwards.

Often the best way is to get the person you need to convince to stand by the machine with you and if it's making a huge noise and vibrating badly, and he feels a bit scared he will agree it's time to stop it.

Now the interesting thing is that trend is important, if it's getting worse by the week or day or hour, common sense tells you to act ever more quickly.

Having strong management resistance to stopping a piece of equipment can be a wonderful learning experience because someone else is taking the responsibility of letting it go, and you get to see just how it turns out, which is a real jewel not to be missed.

Acceleration of high speed gear meshing vibration can often be quite high, like 15 g rms, but if you intergrate the spectrum to Velocity and then look at the tmf peaks you may find they are quite small, like 3 mm/s. Depending on the mass and stiffness of the gear case the levels can be very different.

Impulse demodulation is very useful, especially the CSI Peak Vue which does trap the true peaks and if you look at the waveform from a spectrum of say 100x shaft speed and 3200 lines you will see a pattern of metal to metal contact of some or all of the teeth for many turns of the shaft. This is bad as gears should not be impacting but they often do.

Hey you are on steep learning curve, just make sure you don't put yourself in a position beyond your ability and start making definite predictions when just starting out.

Cheers

John