I have an Alfa Laval centrifuge that is producing fairly high levels of 1x Bowl RPM on the outboard motor bearing.

The motor is flange mounted and overhung. The gearbox contains 4 bearings, 2 gears (ring gear and a beveled gear with unknown tooth counts), and a 3 piece coupling.
The gearbox was recently PM’d, but no abnormalities were noted.

I recommended inspecting the coupling. The inserts were found to be worn, and subsequently replaced. We ran the motor independent of the centrifuge and vibration levels were normal. The motor was coupled up and returned to normal operation and amplitudes returned to what they were before the coupling was replaced. The bowl was replaced several months ago and had no effect on amplitudes.

Trends are stable, but overalls on the outboard motor bearing are .40 in/sec in the horizontal and vertical directions. Waveform energy is minimal with no sign of impacting.

I am seeing harmonics of 4x RPM in the Demod spectrum with possible sidebands of 951 cpm. I suspect its Pole Pass, but I'm not certain.

The motor is running at 200 degrees F, and its current draw fluctuates between 50 and 90 amps with no change in load.

Amplitudes on the gearbox vary from below .2 in/sec to .4 in/sec.

I have an identical unit that is generating the same frequencies, but at much lower amplitudes.
I have not performed any resonance testing on the unit yet, but I am considering it.

I don't think the condition is critical at this time, but any insight on this would be helpful.

This message has been edited. Last edited by: sgierden,

Alfa_Laval_Px.doc (140 Kb, 19 downloads)

I suggest checking the mounts.

The two mounts under the coupling are in compression, however the two mounts opposite are in tension due to the overhung weight of the motor and if there is any looseness/damage in the mounts, the unit will 'rock' about the coupling giving raise to high vertical vibrations on the motor NDE at bowl 1x.

These mounts do fatigue, and there is a tensioning procedure in the operators manual.

This is a common problem in the marine industry, where they are seeing more belt driven purifiers and less direct drive units.

Regards

W

Unfortunately, there are no mounts. The motor is mounted directly to the gearbox.

Mounts under centrifuge!

W

It appears the mounts are adjustable. We are going to attempt an adjustment and hopefully we can detune the system. I will let you know if it works.

Thanks!!

WHAT PURPOSE YOU ARE USING THIS FOR? AS A PURIFIER OR ANY OTHER PURPOSE.HAVE YOU RECENTLY CHANGED BOWLS OR DISCS OR ANY ROTATING COMPONENT?
MAY BE UNBALANCE AND ALFA LAVAL RECOMMENDS BALANCING AFTER CHANGE OF ANY ROTATING COMPONENT LIKE GRAVITY DISC OR CHANGING THE NO. OF BOWLS . DUE TO THE HIGH RPM OF THE CENTRIFUGE, 1X VIBRATION MAY BE REFLECTED.
REGARDS
IRSHAD AKHTAR

I agree with AKHTAR. This is simply a matter of either excessive residual imbalance in the centrifuge or high transmissibility. Both could be assessed and corrected.

Dave

This centrifuge is used in the refining of vegetable oil. The bowl was replaced some time back and cleaned in July, but amplitudes were not effected. The levels on the centrifuge itself are not excessive, however the casing is pretty far removed from the rotating components. We will be looking at the mounts next week to determine if they are adjustable or defective. I will let you know if we find anything. Your suggestions are much appreciated.

Thanks,
Steve

Pl. also confirm that this vibration is persisting continuously or coming and going after bowls cleaning. Deposition of sludge in bowls and sludge basket also causes unbalance and may be, you have to increase your bowl cleaning frequency. Is the centrifuge driven by friction coupling? Check the condition of friction pads. Also , pl. confirm the RPM of the bowl by counting the revolutions of the revolution counter and multiplying by the multiplier. May be it is not rotating at its designated RPM due to wear of friction pads and exciting resonance. Also pl. check the flow through the bowls if it is varying and between designated range. Any malfunctioning of the flow regulator.Current variation hints towards varying flow.
Regards
Irshad Akhtar

This message has been edited. Last edited by: AKHTAR,

Akhtar,

The vibration I am seeing is consistent, it does not fluctuate. The bowl has been cleaned and replaced with no effect on vibration. The coupling was also inspected and found to be worn. We replaced the coupling inserts with no effect on vibration amplitudes. The bowl is running at its rated speed, and the flow seems to be fine.

Thanks,
Steve

This message has been edited. Last edited by: sgierden,