1

VIBRATION STUDIES OF CEMENT MILL

Steps for vibration measurements

Impact test was carried out at selected locations on the torsion bar to know its natural

frequency

Normal vibration signatures were recorded with motor speed being 994 rpm and pinion

speed 122 rpm

Vibration data was recorded on selected bearing locations of motor, gearbox and pinion

bearings

Data was recorded along horizontal, vertical and axial direction with 90% load on the

mill

Phase measurements were recorded to know the behavior of pinion DE with respect to

pinion NDE of pressing and lifting side

OBSERVATIONS

Vibration signatures recorded on Pinion DE and NDE of both pressing and lifting side

bearing shows predominant gear mesh frequency and its harmonics

Side bands were observed along with gear mesh frequency and its harmonics

Gear mesh frequency 60.9 Hz is appearing predominantly in all HVA direction

Time waveform recorded on pinion DE and NDE bearings clearly shows modulation

which occurs due to above phenomena

Impacting of the gear teeth was also observed. Refer time plots provided in this report

in subsequent pages

Only Side bands of pinion speed (2.03 Hz or 122 rpm) are seen, no side bands of Girth

gear was seen in the data

The phase measurements recorded on pressing pinion DE and NDE along axial and

horizontal direction shows the phase is not consistent with time suspecting looseness

due to uneven movement of pinion

Vertical vibrations recorded on pinion DE bearing lifting side shows the vibrations are

low (5 mm/sec) on one end while its high (11 mm/sec) on the other end even though

it’s a common top cover of that bearing

For any normal 2 mating gears the selection of no. of teeth on each gear should be

such that when factorizing is done no common factor should be found apart from 1

In this case pinion has 30 teeth and Girth gear has 210 teeth

o Then as per calculations

o Pinion 30 = 1 x 2 x 3 x 5 , GG 210 = 1 x 2 x 3 x 5 x 7

o So common factor are 2 x 3 x 5

2

NATURAL FREQUENCY MEASUREMENTS ON THE TORSION BAR UNDER STATIC CONDITION

Photograph showing direction of

sensor mounted on torsion bar

(Hollow member) for natural

frequency measurements near

the pinion bearing pedestal

(Pressing side)

Photograph showing direction of

sensor mounted on torsion bar

for natural frequency

measurements near the gearbox

output bearing pedestal

Can this generate a 60 Hz natural

frequency? I could not excite this

with soft hammer

3

Fig showing natural frequency spectral data recorded along horizontal direction on torsion

bar near Pressing side pinion bearing pedestal. Data shows predominant natural frequency at

32.4 Hz or 1944 rpm

Fig showing natural frequency spectral data recorded along vertical direction on torsion bar

near Pressing side pinion bearing pedestal. Data shows predominant natural frequency at

32.9 Hz or 1974 rpm and 84.1 Hz or 5046 rpm

Gear mesh frequency

4

Fig showing natural frequency spectral data recorded along horizontal direction on torsion

bar near drive gearbox output bearing pedestal (Pressing side). Data shows predominant

natural frequency at 32.1 Hz or 1974 rpm and 73.8 Hz or 5106 rpm

Fig showing natural frequency spectral data recorded along vertical direction on torsion bar

near drive gearbox output bearing pedestal (Pressing side). Data shows predominant natural

frequency at 28.5 Hz or 1710 rpm

Gear mesh frequency

Gear mesh frequency

5

Fig showing natural frequency spectral data recorded along horizontal direction on torsion

bar near drive gearbox output bearing pedestal (Pressing side). Data shows predominant

natural frequency at 28.6 Hz or 1716 rpm

Fig showing natural frequency spectral data recorded along vertical direction on torsion bar

near drive gearbox output bearing pedestal (Lifting side). Data shows predominant natural

frequency at 30.9 Hz or 1854 rpm and 83.5 Hz or 5010 rpm

Gear mesh frequency

Gear mesh frequency

6

Fig showing natural frequency spectral data recorded along horizontal direction on torsion

bar near drive pinion bearing pedestal (Lifting side). Data shows predominant natural

frequency at 28.6 Hz or 1716 rpm

Fig showing natural frequency spectral data recorded along vertical direction on torsion bar

near drive pinion bearing pedestal (Lifting side). Data shows predominant natural frequency

at 28.6 Hz or 1716 rpm

Gear mesh frequency

Gear mesh frequency

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PRESSING SIDE

LIFTING SIDE

8

Table-1 showing vibration severity levels recorded on PRESSING SIDE train, all vibrations in

mm/sec RMS, motor speed 994 rpm, pinion speed: 122 rpm

LOCATION HORIZONTAL VERTICAL AXIAL

MOTOR DE-2 1.85 0.54 0.76

MOTOR NDE-1 2.19 1.21 0.73

GEARBOX INPUT DE-3 1.66 2.59 4.51

GEARBOX INPUT NDE-4 1.90 3.28 4.37

GEARBOX OUTPUT DE-5 1.56 3.33 5.43

GEARBOX OUTPUT NDE-6 1.95 3.04 5.20

PINION DE BEARING-7 23.0 8.83 10.4

PINION NDE BEARING-8 14.5 6.83 5.62

Table-2 showing vibration severity levels recorded on LIFTING SIDE train, all vibrations in

mm/sec RMS, motor speed 994 rpm, pinion speed: 122 rpm

LOCATION HORIZONTAL VERTICAL AXIAL

MOTOR DE-2 2.34 1.08 0.80

MOTOR NDE-1 2.58 1.94 0.82

GEARBOX INPUT DE-3 2.52 2.89 2.73

GEARBOX INPUT NDE-4 4.16 3.51 3.22

GEARBOX OUTPUT DE-5 2.99 3.92 3.34

GEARBOX OUTPUT NDE-6 3.93 3.45 3.93

PINION DE BEARING-7 20.7 6.31 8.01

PINION NDE BEARING-8 11.7 6.29 2.93

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Vibration Signatures recorded on Pressing side pinion train

Fig showing frequency spectrum recorded on Pressing Pinion DE bearing DE along HVA

direction at 122 rpm

Fig showing frequency spectrum recorded on Pressing side pinion DE along horizontal

direction, data shows predominant gear mesh frequency with its harmonics and also with

side bands (Log scale)

HORIZONTAL

VERTICAL

AXIAL

1st

GMF

2nd

GMF

3rd

GMF 4th

GMF 5th

GMF

6th

GMF

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Fig showing zoomed view of the 1

st gear mesh frequency with side bands of pinion speed 2.03

Hz on both sides of Gear mesh frequency (Pressing side pinion DE)

Fig showing zoomed view of the 2

nd gear mesh frequency with side bands of pinion speed

2.03 Hz on both sides of Gear mesh frequency (Pressing side pinion DE)

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Fig showing zoomed view of the 3

rd gear mesh frequency with side bands of pinion speed 2.03

Hz on both sides of Gear mesh frequency (Pressing side pinion DE)

Fig showing time data recorded on Pinion DE bearing along horizontal direction, data shows

the phenomena of modulation

12

Fig showing individual spectrum of Pinion NDE bearing pressing side along horizontal

direction, data shows GMF along with its harmonics (2nd

, 3rd

, 4th

GMF)

13

Vibration Signatures recorded on Lifting side pinion train

Fig showing frequency spectrum recorded on Lifting side pinion DE bearing along HVA

direction at 122 rpm

HORIZONTAL

VERTICAL

AXIAL

14

Fig showing frequency spectrum recorded on Lifting side pinion NDE bearing along HVA

direction at 122 rpm

HORIZONTAL

VERTICAL

AXIAL

15

Fig showing high resolution frequency spectrum recorded on pressing side pinion DE bearing

along horizontal direction, data shows predominant gear mesh frequency with side bands of

3 times pinion speed (2.03 X 3 = 6.09)

Fig showing time waveform recorded on Pinion DE bearing (Lifting side), data clearly shows

the modulation pattern

1st

GMF with 6.09 Hz side bands

2nd

GMF 3

rd GMF

16

Fig showing time waveform recorded on Pinion DE bearing along horizontal direction (Lifting

side), data clearly shows the modulation pattern and the impacts

Fig showing time waveform recorded on Pinion DE bearing along vertical direction (Lifting

side), data clearly shows the modulation pattern and the impacts

IMPACTS

IMPACTS

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Photograph showing Left side of

one sample tooth of Gerth gear

Photograph showing Right side of

one same tooth of Gerth gear

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Phase measurements carried out on Pinion NDE bearing pressing side (122 rpm) along axial

direction

1X Phase

0.011 99 deg

0.015 50 deg

0.014 289 deg

0.013 226 deg

0.017 343 deg

Phase measurements carried out on Pinion NDE bearing pressing side (122 rpm) along

horizontal direction

1X Phase

0.142 234 deg

0.167 251 deg

0.161 247 deg

0.164 245 deg

19

Phase measurements carried out on Pinion DE bearing pressing side (122 rpm) along

horizontal direction

1X Phase

0.039 167 deg

0.021 131 deg

0.026 119 deg

0.028 113 deg

20

Phase measurements carried out on Pinion DE bearing pressing side (122 rpm) along axial

direction

1X Phase

0.029 95 deg

0.036 94 deg

0.034 87 deg

0.042 83 deg

0.029 112 deg

0.040 84 deg

Photograph showing vibration data collected on the top bolt of Pinion DE lifting bearing along

vertical direction, vibration in mm/sec

11.2 11.4

5.39 5.88

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Cracks were observed near base of pinion NDE bearing pedestal of pressing side. This may

have developed due to high vibrations