Bearings and Gearbox Diagnostics

8/6/2019 Bearings and Gearbox Diagnostics

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Review of Techniques forBearings & Gearbox Diagnostics

Suri Ganeriwala, PhdSpectraQuest, Inc.Richmond, Virginia 23228, [email protected]

IMAC Conference - Feb. 3, 2010Jacksonville FL

Rolling Element BearingFaults


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Rolling Element Bearing Faults

Ball damageInner race defectOuter race defectCage damage

Rolling Element Bearing Faults cos1

2 Dd nf

BPFO r

cos12 D

d nf BPFI r

cos12 D

d f FTF r

2cos1

2

D

d

d

D BSF

ball passing frequency outer race

ball passing frequency inner race

Ball spin frequency

fundamental train frequency

D = pitch dia; d = ball dia; = contact angle;n = no. of balls


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5

1. All balls/rollers are equal in diameter2. There in pure rolling contact between balls, inner race and outer

race.

3. There is no slipping between the shaft and the bearing

4. Outer race is stationary and inner race rotates

In practice there is always some sliding and slippage specially when abearing is under load and after some wear

Approximate formulas:

BPFI = 0.55-0.6 x No. of balls x RPM

BPFO=0.45 x No. of balls x RPM

BSF = 3.5 x RPM

Assumptions Made in Bearing Fault Frequencies Equations

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Bearing Defects

BSF

BPFI

BPFO


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Time Domain Impact Response

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Illustration of Sidebands


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How do we analyze vibration signature of bearing faults?How do we analyze vibration signature of bearing faults?& Issues& Issues

Observe the time waveform and the spectrum to see differencesbetween the good and bad bearing data

Compare the observed frequencies with the calculated frequencies.Are the peaks present ?

Signals are often masked by large amplitude periodic components

Direct Spectral analysis may not give sufficient information

Bearing faults create a series of impacts witch are amplified byresonances: bearing, sensors, structure etc

This creates envelopes of specific faults at high frequencies

Fault signals are not periodic; appear more like random

Some cases can be treated as cyclostationary

New techniques are still being developed

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Techniques Currently used in Industrial ProductsTechniques Currently used in Industrial Products

Time Waveform Analysis

Frequency Spectral Analysis

High Frequency Detection (HFD)

Stress Wave Analysis or Spike Energy

PeakView

Enveloping


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Typical Bearing Outer race Fault Waveform

Typical Bearing Outer race Fault Spectra


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Typical Bearing Outer race Fault Spectra

Bearing FaultBearing Fault

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Right-sideBearing onthe MFS

BearingLoader

BearingLoader

Left-side Bearingon the MFS


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Bearing Outer Race Faults

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Outer Race Fault Signal Example

The harmonics of BPFO show up clearly


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MB ER-10K bearing parameters:Number of rolling element: 8Rolling element diameter: 0.3125 InchesPitch diameter: 1.319 inchContact angle: 0 degree

)cos*1(*2

Pd

Bd Nb BPFO

Bearing Faults for MB ER-10K bearing at the Running Speed of 2,004 RPM

Notation FaultFrequencyMultiplier

FaultFrequency (Hz)

Harmonics of the RunningSpeed

HarmonicFrequencies(Hz)

DeltaFrequencies(Hz)

Resolution to Detectthe Fault Frequencies= Delta Frequencies/4(Hz)

BPFI 4.9480 165.3176 5 167.0570 1.7394 0.4349

BFPO 3.0520 101.9704 3 100.2340 1.7364 0.4341

BSF 1.9920 66.5547 2 66.8230 0.2683 0.0671

1 2 3 4 5 6 7 8

33.411 66.823 100.234 133.646 167.057 200.469 233. 880 267.291

1.674E-5 1.966E-5 1.014E-5 4.219E-5 1.309E-4 7.179E-5 9.206E-5 7.807E-5

RPM Harmonics


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Spectral Lines Resolution, Hz Resolution, RPM

100 50.0000 3,000.0000

200 25.0000 1,500.0000

400 12.5000 750.0000

800 6.2500 375.0000

1,600 3.1250 187.5000

3,200 1.5625 93.7500

6,400 0.7813 46.8750

12,800 0.3906 23.4375

25,600 0.1953 11.7188

51,200 0.0977 5.8594

102,400 0.0488 2.9297

Spectral Resolution for 5,000 Hz Maximum Frequency Setting

Resolution: 6400 FFT Lines using a Hanning Window


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Resolution: 25600 FFT Lines using a Hanning Window

Acceleration signals acquired from an outer race faulted bearingBPFO which is roughly 71 Hz (=1/0.014)


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Acceleration signals acquired from an outer race faulted bearingBPFO which is roughly 71 Hz (=1/0.014)

Envelope Spectra

Envelope spectrum of the faulted bearing (outer race) showing theBPFO demodulated in the frequency band of 2000Hz-4000Hz


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Effect of demodulation band

Envelope spectrum of the faulted bearing (outer race) not showing theBPFO demodulated in 10k-12k Hz band

Inner race Fault Time Waveform


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Inner Race Fault Spectra

Envelope Spectrum

Envelope spectrum of the inner race faulted bearing with a shaftspeed of 20 Hz showing the BPFI and sidebands with a 750 psi load


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Effect of load

Envelope spectrum of the inner race faulted bearing not showingthe BPFI under no load

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New Techniques under ResearchNew Techniques under Research

Adaptive Noise Cancellation (ANC)

Self-adaptive Noise Cancellation (SANC)

Spectral Kurtosis

Discrete Random Separation

Cyclostationary Signal Analysis

Julian

Hilbert-Huang Transform

Entropy


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Adaptive Noise Cancellation (ANC)Removes the random components from the periodic componentsRequires reference input along with primary inputSANC uses the delayed primary signal as reference signalIt uses the fact that bearing signals has a short correlation length

Ref: Prof. Bob Randall

Fault bearing signal with gear signal (b) Gear signal discrete components(c) Bearing components- random components

Spectral KurtosisCalculates Kurtosis for each frequency lineIdentifies the impulsiveness in the dataUses short time Fourier transformDetermines optimum band for demodulation


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Spectral Kurtosis showing the maximum excited frequency bands(fc=8800hz, bw=1600hz) using outer race faulted bearing

(a) Envelope spectrum showing the BPFO(34.4Hz) in freq. range 8000-9400 hz(b) Envelope spectrum showing harmonics of BPFO much clearly in 4000-5000hz band


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Gearbox Diagnostics

Techniques for Gearbox Vibration Analysis

Time Waveform AnalysisSpectral AnalysisOrder AnalysisTime synchronous averagingCepstrum Analysis

Amplitude and Phase DemodulationTransmission Error Analysis


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Gearbox Vibration

Transmission ratio: 1.5:1, (27 and 18 teeth)


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Gearbox Vibration

Missing of tooth

Gearbox Vibration


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Gearbox Vibration

of pinion

sidebands of gear

Baseline data

Spectrum of Fault Level 1 Data

Compared with baseline, more pinion sidebands emerge


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Compared with baseline, the amplitudes of pinion sidebandsIncrease significantly.


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The amplitudes of pinion sidebands continually Increase.


The amplitudes of pinion sidebands exceed that of the mesh frequencyFor the missing of a tooth.


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Gear vibration order analysisSpeed variation captured using encoder

Intact gear(small spikes arecaused by gearmeshing)

Fault level 5(impacts causedby missed tooth)

1 revolution

Speed Variation Order Spectrum - baseline

The number of teeth on gearbox output shaft is 27. The 27 th, 54 thand 81th orders have high amplitude. They correspond to themesh frequency and its 2 nd and 3 rd harmonics.

Gear vibration order analysis


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Gear vibration order analysis

Pinion sidebands emerge clearly for the missing of a tooth

Speed Variation Order Spectrum fault level 5

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Worn Gearbox Vertical, RMS Ave.

0.00

20.00

40.00

60.00

80.00

100.00

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00

Frequency, Hz

M i n / s e c ^ 2

Time Synchronous Averaging


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0.00E+00

5.00E+00

1.00E+01

1.50E+01

2.00E+01

2.50E+01

3.00E+01

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0

Time Synchronous Averaging

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0.00E+00

5.00E+00

1.00E+011.50E+01

2.00E+01

2.50E+01

3.00E+01

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0

0.00E+00

5.00E+01

1.00E+02

1.50E+02

2.00E+02

2.50E+02

3.00E+02

0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1400.00 1600.00 1800.00 2000.00

Worn Gearbox data comparison, two Types of Averaging


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Worn Gearbox T ime SynchronousAveraging

0.0E+00

2.0E+01

4.0E+01

6.0E+01

8.0E+01

1.0E+02

1.2E+02

0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0Frequency, Hz

M i n / s e c ^ 2

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Worn Gearbox Syn. Ave. on Gear

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.0 200.0 400.0 600.0 800.0

Frequency

M i n / s e c ^ 2


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Worn Gearbox data comparison, TSA at Two Shafts

Worn Gearbox Syn. Ave. on Gear

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.0 200.0 400.0 600.0 800.0

Frequency

M i n / s e c ^ 2

Worn Gearbox Time SynchronousAveraging

0.0E+00

2.0E+01

4.0E+016.0E+01

8.0E+01

1.0E+02

1.2E+02

0 .0 5 00 .0 1 00 0.0 1 50 0.0 20 00 .0 2 50 0.0 3 00 0.0 3 50 0.0Frequency, Hz

M i n / s e c ^ 2


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Speed =

Side bands = 59.37, 23.7, 17.8 Hz


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Baseline Data

Chipped Tooth Data


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Chipped Tooth Data

Chipped Tooth Data


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Missing Tooth Data

Cepstrum AnalysisInverse Fourier transform of logarithmicspectrumUseful for detecting changes in sidebandfamiliesEcho, Transmission path, etcQuefrency, Rahmonic, Gamnitude, Lifter,Saphe

Where X(f) is the Fourier transform of x(t)


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Cepstrum Analysis


Signal Separation with Cepstrum

Use of cepstrum to remove sideband patternsRef: Prof. Bob Randall


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Amplitude & Phase Demodulation

Amplitude and Phase Demodulation of raw acceleration signalsfrom a gearbox with chipped tooth ; note both phase and amplitude demodulation work


Amplitude and Phase Demodulation of raw acceleration signals from aparallel shaft gearbox with chipped tooth (where phase demodulation did not work)


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Transmission Error

Amplitude & Phase Demodulation onTransmission Error Signal

Note that amplitude demodulation workedbut phase demodulation did not work


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Torsional Vibration Signals obtained from TVCwith zero degree deflection

Torsional Vibration Signals obtained from TVCwith 12.5 degree deflection

Bearings and Gearbox Diagnostics

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