Hi,

Here are the full details on the high axial vibs on the kiln main drive cement mill.

I had been there for the 2nd time and please find attached the complete vib data report with spectrums, plots, vib severity levels and pictures.

1. It's clear that the vibs went up by 3-4 times on the gearbox input and output bearings when the motor speed went up from 1350 to 1400 rpm
2. Bump test on the coupling, motor DE bearing indicates no resonance at or near operating speeds
3. Motor vibs in solo condition is well within permissible limits
4. Shaft runouts checked well within 0.02 mm
5. Alignment was redone between motor and gearbox
6. Unable to perform bump test on the gear internals as the inspection cover provided was too small and unable to access the gears.
7. 1X frequency was seen in all spectrums in all directions

Questions:

1. Does one of the gear internals have a resonance band close to 1400 rpm or above?
2. Does the gearbox internals is highly sensitive to axial vibs?

Let me know your inputs,

Madhu

kiln_main_drive.pdf (121 KB, 46 downloads)

Here are the pictures

KILN_DRIVE_PIC.pdf (246 KB, 67 downloads)

Is this problem new or been there a while or gradualy increased over time?

I can not see the gearbox side coupling half clearly but the motor half looks like it is rigid. Is the motor half rigid also? If so, this is bad business. If not, is it safe to guess that the coupling has been taken apart and inspected closely for wear that might could cause it to "lock" into the worn area under operating conditions and not really be flexiable? If it is a gear type coupling.

Sorry if all this has been answered elsewhere and I missed it.

This message has been edited. Last edited by: Ralph Stewart,

Madhu,

Did you consider torsional resonance at 1xRPM?
I suggest running a waterfall test from 1200 RPM to 1500 RPM with the full power transmission train. Take phase readings as well.

Dave

This machine is 1.5 years old now. The client says they went upto 1400 rpm and indeed ran the unit at the above speed for a couple of months in 2009. But unfortunately no one had collected the vib data. Otherwise we could have had some good history details.

The coupling is pin and bush type coupling and not a gear coupling. both coupling and gear internals were checked and no damage/wear found. The whole machine looks very rigid and all the mounting bolts were tightened before taking vib data.

I guess that there are some design issues in this machine particularly suspecting on the gearbox. 1XRPM torsional resonance... David can you eloborate on this... do you want me to do order tracking with phase...??

Thanks,

Madhu

Don't forget to check the foundation. Being only a couple of years old that wouldn't be likely but if your not solid in the mounting or the concrete has voids or cracks it can get dicey.

Madhu,

Run a regular coast-down/run-up test with phase measurement at 1x or only a cascade plot test.

You have done bump tests in various points. They all came back negative. A torsional resonance will also result in radial and axial directions vibration increase in a gear box. This is one way to detect it. Possibly it is around 1450 CPM.

It also would be interesting to see the TWF at resonance. Make sure the sampling rate/Fmax in the TWF/spectrum covers at least 3 orders of the highest GMF.

Dave

I've come accross this kind of machine in coal fired power plant with motor and gear box driving the Force Draft fan. All the symptom of you mention fit perfectly to my previous problem, the only different is our main culprit was gear coupling lock that give high excitation to the gearbox and causing it base to crack. The first thing we found is not the locked coupling but rather the crack base. With ODS plot you will be able to see it clearly were to focus.

Highly unlikely the gearbox would have any critical close to 1400 rpm. Depending on the gear design (spur, helical, bevel), each style comes with it's own character/typical vibration patterns but very very unlikely resonance issues at that low of frequency.
The vibration data clearly shows looseness present in the motor, both DE and NDE horiz readings show turning speed harmonics. I see NO harmonics on the gearbox data you provided. This would point toward a motor bearing/shaft/housing issue.
A quick check would be to shut down and perform a shaft lift check. Use dial indicator and long bar and "lift" the shaft to see how much total clearance is present, value should be less than .003"
As for the high 1x as speed increases, it has to be a critical being excited/base movement. Take a closer look at the pics you posted, 2nd page. Notice the framework under the motor, there is a pipe lying on the base next to the NDE of motor. Notice how clean the clay is, now go to DE of the motor, note the "rusty" looking area, then look to the right of the stand, it too is "rusty". This is a sign of mechanical looseness.
Someone needs to thoroughly clean the whole base around the motor and gearbox to find what is tight and what is not tight. This could be the clue to your resonance issue, and a loose base under the motor could also be the cause of your turning speed harmonics in the motor...
Dave