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High Vibration at 0.25 order

  • 1.  High Vibration at 0.25 order

    Posted 02-09-2024 07:08

    Dears 

    I am currently experiencing  high vibration on an important process fan drive

    at order 0.25, I have been unable to attribute it to anything concrete and it is only appearing on the horizonatal axis ( radial)

    The peaks matches no bearing signature , and there is no obvious 2 x LF signature also on the spectrum which made me eliminate rotor problems 

    Any thoughts anyone?

    RPM 1439

    Bearing SKF 6310



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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  • 2.  RE: High Vibration at 0.25 order

    Posted 02-10-2024 01:22

    There is one thing obvious that amplitude on 0.25X is varying. can you take the high resolution data and see if there is any beat? have you feel any humming noise on site? Coinciding with process/nearby equipment? If you can share other spectrums, would be great.



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    muhammad shahbaz khan
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    Original Message


  • 3.  RE: High Vibration at 0.25 order

    Posted 02-11-2024 01:38
    Sir, if you look at the spectrum and wave form data, it is possible that there is looseness in the bearing (could be the bearing with the bearing housing or the bearing with the rotor shaft)


     When you stop, try checking whether the lifting bearing is working or not?


     That's what I think.



    Original Message


  • 4.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:31

    Thank you for the comment, however the peak isnt matching up with any bearing signature.



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 5.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:37

    I checked the bearing clearance on the fans and they are within acceptable limit , I am unable to check for lift on the motor bearings accurately



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 6.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:23

    Thank you, I would try to do that 



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 7.  RE: High Vibration at 0.25 order

    Posted 02-14-2024 03:04

    Is it a real 0.25X line or just the sampling of a low-frequency ski-slope signature?

     

    Which type of accelerometer do you use, and integrator; because the noise in low frequency very much depends on the front-end.

     

    BRgds,

    Luc Fromaigeat

    Customer Support Engineer

     

    Parker Meggitt 




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    Original Message


  • 8.  RE: High Vibration at 0.25 order

    Posted 02-10-2024 10:36

    In blowers flow turbulence often occurs due to variations in pressure or velocity of the air passing through the fan or connected line-work. In fans, duct-induced vibration due to stack length, ductwork turns, unusual fan inlet configuration and other factors may be a source of low-frequency excitation. This flow disruption causes turbulence, which will generate random, low-frequency vibrations, typically in the range of 20–2000 cpm.


    Original Message


  • 9.  RE: High Vibration at 0.25 order

    Posted 02-11-2024 18:27
    Blower fan vibration. Two things here that I must assume. Your rotor rpm and fan blade outer circle rotational diameter. Let's say your rotor rpm's are 1800 and the fan blade outer circle is twenty feet. The outer tips of your fan blades will be supersonic. This is a sustained sonic boom attached to the end of every fan blade that is striking the entrance to your duct work. This in turn creates sympathetic vibrations (fan tip energy pulses) in your duct work. That frequency could have a co-relation to the number of fan blades/shaft rpms. These sympathetic vibrations could also feedback into your blower/bearing support structures and at some rpms and or flow rates these fan tip energy pulses can become synchronized with the sympathetic vibration feedback which, on your graph, can show you a spike energy signature. Hope this helps       



    Original Message


  • 10.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:35

    Are you referring to vane pass frequency in this write up ? 



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 11.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:38

    What is the solution to this , How can I confirm this suspicion 



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 12.  RE: High Vibration at 0.25 order

    Posted 02-10-2024 10:39

    In blowers flow turbulence often occurs due to variations in pressure or velocity of the air passing through the fan or connected line-work. In fans, duct-induced vibration due to stack length, ductwork turns, unusual fan inlet configuration and other factors may be a source of low-frequency excitation. This flow disruption causes turbulence, which will generate random, low-frequency vibrations, typically in the range of 20–2000 cpm.

    AK Dhar


    Original Message


  • 13.  RE: High Vibration at 0.25 order

    Posted 02-10-2024 12:32

    Hello shittu olakunle,

    Please see the attached DOC file and the questions about the sideband frequencies.



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    Ralph Stewart
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    Original Message


  • 14.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:42

    The difference is 187 CPM



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 15.  RE: High Vibration at 0.25 order

    Posted 02-20-2024 12:11
    Edited by Ralph Stewart 02-20-2024 12:23
      |   view attached

    Thanks for the info, shittu olakunle. :)

    Can you take a new spectrum and waveform with an Fmax of 7500 cpm (125 Hz) and a vertical scale of 2.0 mm/sec and show the frequency of each major "peak"?

    See the attached picture.

    Editted: Sorry I posted the wrong image. Can not edit and remove the image. :(

    Will continue to try  and change the image, if I can.

    Thanks



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    Ralph Stewart
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    Attachment(s)

    doc
    Sideband Frequency.doc   688 KB 1 version
    Original Message


  • 16.  RE: High Vibration at 0.25 order

    Posted 02-11-2024 08:02

    it would be better to give us brief history regarding the unusual vibration peak on the motor. Is it new, is the peak appeared after overhaul...things like that?

    but generally, the low frequency peak normally related to turbulence flow or excited natural frequency specially that there is hump (small noise floor) below the peak.



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    Ayman Gamal
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    Original Message


  • 17.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 09:52

    I just joined the organization, the only major activity that has coccurred since joining is fan balancing, prior this balancing the 0,25 TS peak existed but not with the same amplitude.

    Also , the 0.25TS has more amplitude in the horizontal direction in all measurement point, I have also checked fan bearings and took clearance measurement and compared to manufacturers table , it is still within acceptable limit

     



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 18.  RE: High Vibration at 0.25 order

    Posted 02-13-2024 10:29

    Hello Shittu Olakunle,

    I agree with the previous posts, some historical information may prove helpful.

    A couple of questions:

    What location was the data collected from? (i.e, D.E. or O.D.E)

    What type of drive does the fan have? Is it a belt drive or direct drive?

    If it is a direct drive what type of coupling is used? Is it a spacer, gear coupling, cardan shaft?

    I see it is a SKF 6310 bearing, is it lubricated with grease or oil?

    Thanks,



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    Christopher Spoor
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    Original Message


  • 19.  RE: High Vibration at 0.25 order

    Posted 02-11-2024 11:55

    Hello SO

    Will you please show us the time waveform in velocity?

    Well, 0,25x TS is quite unusual to see as a dominant peak, I agree with Ayman, give us a brief history.

    As other collegues wrote, one would suspect some sort of loose part but it depends on if a loose part can cause rubbing to excit 0,25x,

    or if it just loose.

    Have a look on prev. spectrum and compare them, Do you see sidebands to the left and to the right? Probably a higher LOR must be used,? Do you have a random noise floor in the spectrum?

    In my opinion, If you come to a result that the 0,25x is coming from a rotating part and not a stationary part then one should pay more attention to follow up

    /AQ

     



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    Adnan Qadour
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    Original Message


  • 20.  RE: High Vibration at 0.25 order

    Posted 02-21-2024 10:01

    Have you inspected the following:

    At 0.5x: Structural res.

    Foundation

    Coupling (misaligned or loose)

    Gearbox

    Housing open



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    Jose Castellanos
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    Original Message


  • 21.  RE: High Vibration at 0.25 order

    Posted 02-23-2024 02:59

    Jose

    Foundation--foundation is fine

    Coupling (misaligned or loose)--Laser allignment check was carried out 

    Gearbox-it does not use a gearbox

    Housing open--I have opened up fan impeller housing and physically inspected the impeller and internals, no abnomality observed



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
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    Original Message


  • 22.  RE: High Vibration at 0.25 order

    Posted 02-21-2024 11:08
      |   view attached

    Shittu olakunle

    Here is the image I intended to attach last week but accidentally inserted the wrong one.

    Thanks



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    Ralph Stewart
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    Original Message


  • 23.  RE: High Vibration at 0.25 order

    Posted 02-22-2024 03:10

    Yes, I can do this , 

    The analyser was sent out for calibration checks , as soon as its back i would take another reading and revert



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    Shittu olakunle
    Reliability Engineer
    United Kingdom
    ------------------------------

    Original Message


  • 24.  RE: High Vibration at 0.25 order

    Posted 02-22-2024 09:54

    Message From: Ron Frend

    Dear Shittu,

     

    I need more information if am to help you.

     

    1)  What is the layout of the fan?  Is it direct coupled, geared, pulley? 

     

    2)  What is the fan speed and what is the motor speed?

     

    3)  Is the fan unit directly on the concrete plinth or is there a bedplate.  If there is a bedplate, has it been designed and fabricated to ISO standards?

     

    4)  Have you carried out a bump test on the structure?  You need to know the natural frequency.

     

    5)  Has the ground beneath the concrete plinth had a geophysical survey carried out prior to build?  I've seen several instances of ground cavities causing high vibration at odd frequencies.

     

    6)  Have you checked for acoustic frequencies in the fan ducting?  Again - seen this several times.  Can be a bear to troubleshoot.

     

    I'll be teaching a course in the Middle East next week but should still be able to get emails. 

     

     

    Ron F



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    Jose Castellanos
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    Original Message


  • 25.  RE: High Vibration at 0.25 order

    Posted 02-23-2024 00:04

    Thanks Shittu olakunle.

    Looking forward to seeing the new data.



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    Ralph Stewart
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    Original Message


  • 26.  RE: High Vibration at 0.25 order

    Posted 02-23-2024 03:35

    You don't put where it appears, if only in the motor or also in the fan bearings, or if it is greater in one or another part of the equipment. I understand that this is a horizontally arranged equipment.
    With the data you provide and being the type of machine you mention, I think you can have several possible origins:
    1. High clearances in bearings. When there are high bearing clearances, rotational speed subharmonics may appear at 1/4x, 1/3x and 1/2x. Check if the 0.25x has those harmonics to verify this possibility.
    2. Another possibility is that it is a structural weakness and if it is equipment mounted horizontally, obviously its lowest structural rigidity is horizontal and for this reason only 0.25x would appear in Horizontal. However, I recommend that you analyze on a logarithmic scale in case it exists on the vertical and axial axes and you do not see it on the linear scale.
    3. Being a fan, the 0.25x could be air turbulence as well. Always check when you measure if there is any system that restricts the air flow either at the inlet or outlet or if you have very closed elbows at 90º or close to it near the body of the fan in both suction and discharge ducts.

    You will tell me.



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    ruben gonzález
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    Original Message


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