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I.D Fan strange Balancing response

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

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