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Greetings to all ,

i am facing a problem while balancing a I.D Fan in situ .Fan Vibration signature indicating Fan bearings Looseness ( Looseness found in Motor spectrum too ) .I recommended them to verify Fan bearings tightness& Coupling after their corrections vibration decreased significantly than earlier but still there is looseness and we proceeded to fan balance after Customer said we have done all the corrections and nothing to do with that .

In every Balancing attempt Fan responding to correction weights but Vibration increasing after another run .I did Polar plot method & even four run method but no use .

Two plane balancing with Polar Plot

Plane 1

Reference Run 0.8 mm/sec @215 degrees

Trial Run 1.2 mm/sec @235 degrees ( Trial weight at 0 degrees)

Correction 257 grams @ 208 degrees

Plane 2

Reference Run 3.1 mm/sec@240 degrees

Trial Run 1.8 mm/sec @ 240 degrees ( Trial weight at 0 degrees)

Correction 330 grams @ 0 degrees

Final response after Weights addition

0.5@226 degrees at Plane 1

2.1 @ 230 degrees at Plane 2

Vibration increased again , Phase at Fan D.E bearing is Unstable since first balancing attempt  .

After tried Four run method at each plane

Plane 1

RO-2.63,  R1-3.75 , R2-1.79 , R3-3.44

Correction weight 300 grms at 130 degrees .

Plane 2

R0 -6.74 ,R1-7.65 , R2-7.54 , R3-7.83

No response to same trial weight at all

Weight added at only plane 1 to see response but no use



i have a suspicion on Fan bearings , i recommended to verify looseness again before another balance attempt .

Fan weight : 1 ton Approx

Dia : 1.5 mtr

Width : 1 mtr .

SENSOR AXISINITIAL  VIBRATION MEASUREMENT
VELOCITYACCELRATIONDISPLACEMENTENVELOPE
MOTOR N.D.E HORIZONTAL3.310.3213.810.09
MOTOR N.D.E VERTICAL2.050.288.650.11
MOTOR N.D.E AXIAL2.340.287.280.1
MOTOR D.E HORIZONTAL2.320.2713.590.1
MOTOR D.E VERTICAL1.870.3312.030.16
MOTOR D.E AXIAL1.330.188.360.07
FAN D.E HORIZONTAL4.31.2116.40.53
FAN D.E VERTICAL2.511.110.610.5
FAN D.E AXIAL4.660.6516.070.33
FAN N.D.E HORIZONTAL7.931.0547.390.66
FAN N.D.E VERTICAL1.290.649.290.23
FAN N.D.E AXIAL5.320.5516.740.35


SENSOR AXISVIBRATION MEASUREMENT AFTER CORRECTIONS
VELOCITYACCELRATIONDISPLACEMENTENVELOPE
MOTOR N.D.E HORIZONTAL1.840.2415.410.07
MOTOR N.D.E VERTICAL1.290.3213.080.09
MOTOR N.D.E AXIAL0.990.2113.890.09
MOTOR D.E HORIZONTAL1.270.32160.16
MOTOR D.E VERTICAL1.070.2314.880.1
MOTOR D.E AXIAL0.690.214.870.09
FAN D.E HORIZONTAL2.20.7218.510.29
FAN D.E VERTICAL1.860.6716.790.24
FAN D.E AXIAL3.620.5818.970.26
FAN N.D.E HORIZONTAL6.070.933.240.51
FAN N.D.E VERTICAL1.390.7416.440.39
FAN N.D.E AXIAL5.46120.060.57

Attachments

Tags: Fan, Looseness, Balancing

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I have done two plane balancing with Peak Vs Phase values because balancing software in our new purchase equipment not working well ( i don't want to mention the manufacturer ) .We have given complaint and sent for their observation but no use .

Please verify the procedure and results

PLANE 1PLANE 2
mm/sec@Phasemm/sec@Phase
REFERENCE RUN0.8@215β—¦3.1@240β—¦
RESPONSETRIAL RUN 11.2@235β—¦4@240β—¦
RESPONSETRIAL RUN 20.5@200β—¦1.8@240β—¦
RESPONSECORRECTION0.5@226β—¦2.1@230β—¦
PLANE 1-Trial 1 Weight 135 grams @ 0β—¦
PLANE 2-Trial2  Weight 135 grams @ 0β—¦
PLANE 1-Correction  Weight 257 grams @ 208β—¦
PLANE 2-Correction  Weight 333 grams @ 0β—¦
RM

Dear Sir ,

I attempt two single balances but added correction weights once .

1.Taken Reference run Vibration on both planes with phase .

2.Added trial weight on Plane 1 ,noted Vibration & Phase of both planes .

3.Remove trial weight on Plane 1.

4.Added trial weight on Plane 2 ,noted Vibration & Phase of both planes .

5.Calculated Correction weight and angle basing on each single plane response .

6.After adding correction weights , overall vibrations reduced but increased after next run .We do not added any extra weight .Customer wants to check once again .

7.Seven run method followed and added weight on plane 1 because no response on plane 2.again over all vibrations reduced some extent but not with in satisfactory limits .

8.Since the first visit, i  them to verify bearings and coupling .But no use .

9.Finally i strongly said " Verify Bearings first " .

10. I had balanced so many equipment but not this kind of response .

RM

Is this a center hung rotor? direct drive? or belt drive?

If center hung, is it double suction or single suction?

If center hung, double suction, does it have a solid center "plane" between the 2 suction ends?

Is it an overhung rotor? direct drive? or belt drive?

Is it sleeve bearings? or anti-friction bearings?

If anti-friction bearings, what holds them to the shaft? Tapered sleeve? Or straight bore interference fit?

What exactly did they do during the "inspection" you suggested?

When all trial weights and permanent weights are removed, does the phase and amplitude return to basically the same original readings?

Quote: "In every Balancing attempt Fan responding to correction weights but Vibration increasing after another run ."

What do you mean by "but Vibration increasing after another run ." Another balancing run with new trial weights? or just another start-up after the balance job was supposed to be complete and the fan restarted?

What is the sideband spacing of the data near the 20,000 to 25,000 cpm area on the Fan Drive End bearing? And on the closely spaced (less than 1x) Fan NDE bearing from 5,000 cpm out to 30,000 cpm? It looks about like 1/3 rpm.

Thanks,

Ralph

RM
Last edited by Registered Member

1. Its a center hung double suction fan with taper bore anti friction bearings .

2.I am not sure weather they inspected clearances / not .They reluctant to do so ,said every thing good with bearings and clearances .

3.No extra weight added after correction run .Just taken another run to reconfirm the results .

4.No weights are removed , their management want check bearings and clearances once again .

5.If they called , i let you know .

RM
@Registered Member posted:

1. Its a center hung double suction fan with taper bore anti friction bearings .

2.I am not sure weather they inspected clearances / not .They reluctant to do so ,said every thing good with bearings and clearances .

3.No extra weight added after correction run .Just taken another run to reconfirm the results .

4.No weights are removed , their management want check bearings and clearances once again .

5.If they called , i let you know .

Thanks Kishore,

Did you check the closely spaced peaks in the spectrums to confirm their relation to 1x rpm?

A one-third (1/3) running speed sometimes relates to an anti-friction bearing being loose on the shaft, IMO. These being tapered bore bearings, it is a possibility one of the bearings could be loose on the shaft.

Your quote: "Just taken another run to reconfirm the results ." Is this, "another run", when the vibration seems to increase for no apparent reason? Do you mean it looks good after weights are attached, and then you shutdown and restart and vibration goes up again? If so, does the phase shift also?

If you go back later and try the balance again, I know of an "easy" 2-plane setup you might could try.

Thanks,

Ralph

RM

Hello Kishore,

I am very pleased at the amount of  detail you have shared with us, I have experienced similar problems before but the cause was different in every instance.

1. Have you removed trial weights when putting in correction weights and is your system doing correction calculations based  on removing or leaving on trial weitghts?

2. Is your tacho firmly achored on the  magnetic base or whatever mounting method you use and your 0-degrees blade or mark inline with a reflector tape and your tacho for correct phase reading?Is your  accelerometer firm and in correct orientation?

3. Are you using positions  or continuous angle divisions? How many blades are on the fan? What is the RPM of the fan?

4. Have you inspected the structure for cracks?(this tend to affect your 1xTS and fools the program when doing calculations)

5. Are you balancing at operating speed?

6. Now...from the data you sent, what i do differently is, after a reference run, i look at the 1xTS amplitude magnitute and phase value of each plane, for 600-1500 RPM machines i add 90 degrees and 45 degrees on 1500 - 3000 RPM on the reference phase in a direction of rotation, that will be the location for  my trial weight, the magnitute of the weitgh will be determined by the shaft & bearing sizes, RPM, the reference run 1xTS amplitude as we as the fan rotor diameter, take your  trial run and make sure the phase shift results while capturing data is 30% or more, this is neccessary for the software to compute a more reliable correction solution.

7. Make sure whether your software needs you to remove or add on trial weight when installing the correction weights and do as required by it.

> What i noticed from the data you sent, your phase shift values after trial run are not ideal, well im no expert, but so far it works for me if the shift is more than 30% and does not work if it is less than that. Another thing is, your reference run phase and a correction phase is almost similar, that is why your balance is unsuccesful, there must be a mistake you made with phase readings or setup of your apparatus or in the software, look at your tacho location setup and accelerometer oriantation setups as well as your direction of rotation setup, and make sure you balance at operating speed.

> I highly doubt the balance is affected by mechanical faults...Good Luck.

RM
Last edited by Registered Member

Filtered vibrations levels at 1xSS were very low before balancing (highest was 4 mm/sec or 0.16 in/sec). The 1xSS was not the dominant frequency in velocity spectra, so it has minimal affect on the overall velocity levels. Why are you doing balancing? If you must do balancing, then why not do a single plane solution for only Plane 2 that had roughly 3x higher vibration level levels and similar phase to Plane 1? If amplitude and phase are changing a small amount, then averaging would help balance results. If there are large variations, then looseness in bearing or structure should be corrected first. Perhaps I am not understanding all of your numbers!

Walt

RM
@Registered Member posted:

Filtered vibrations levels at 1xSS were very low before balancing (highest was 4 mm/sec or 0.16 in/sec). The 1xSS was not the dominant frequency in velocity spectra, so it has minimal affect on the overall velocity levels. Why are you doing balancing? If you must do balancing, then why not do a single plane solution for only Plane 2 that had roughly 3x higher vibration level levels and similar phase to Plane 1? If amplitude and phase are changing a small amount, then averaging would help balance results. If there are large variations, then looseness in bearing or structure should be corrected first. Perhaps I am not understanding all of your numbers!

Walt

Walt, I'm seeing numbers in the tabulated data that are in excess of the "...very low before balancing (highest was 4 mm/sec or 0.16 in/sec)" that you mention.  In the initial run I'm seeing 7.93 mm/sec in the "FAN N.D.E HORIZONTAL".  In addition, based on the provided data, that likely is mm/sec RMS.  7.93 mm/sec = 0.31 in/sec and if we bump that up it is 0.44 in/sec peak.

The data seems very erratic as well.  I see by one of the provided spectrums the 1X (975 cpm) is about 2.45 mm/sec for the same measurement point.  The overall is 6.072 mm/sec and there is a substantial amount of higher frequency above 5 kHz.  All this makes me wonder if the transducer is a hand held device, something I personally would not use in balancing.

RM

" I see by one of the provided spectrums the 1X (975 cpm) is about 2.45 mm/sec for the same measurement point.  The overall is 6.072 mm/sec and there is a substantial amount of higher frequency above 5 kHz."

That is why I questioned the value of balancing!  Some of the OP numbers could be filtered 1xSS or overall levels. I will wait for the OP to clearify the balance numbers with 1xSS amplitude-phase and overall level for each measurement point and each configuration.

Walt

RM

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