Download - Primer Bearing Failure Detection
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A PRIMER ON
USING VIBRATION ANALYSISTO DETECT ROLLING ELEMENT
BEARING FAILURES.
JOHN E. JUDD
DMC-CT Dynamic Measurement Consultants, LLc
Hamden, CT USA
07-15-08
US PATENT #6,763,312, B1 other patents pending.
Copyright 2006 Dynamic Measurement Consultants, LLC.
All rights reserved.
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General Suggestions:
Based on experience.
Acceleration is more useful than velocity.
Time & Impact analysis is more useful
than frequency spectra. Use quality, hard mounted, accelerometer.
Mount in/near load zone.
Avoid use of hand probes. Be cautious with bonding & magnets.
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Bearing failure characteristics.
For maintenance activities on motors, pumps,generators and HVAC equipment.
The paper is a primer on aspects of rolling elementbearing monitoring and failure detection.
Its content is derived from a variety of sources and ismeant as an informational piece only.
No responsibility is assumed, or implied for itsapplication.
Bearing failure characteristics are complex and bearing
manufacturers should be consulted for additionalinformation on the subject.
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Lets Review:
Some of the basics!
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FAILURE:
A general definition
An unsatisfactory condition- out of spec orcatastrophic.
Failure to meet specified performance.
Potential failure-Identifiable/quantifiablecondition that indicates failure is imminent.
Note: Routine maintenance is notconsidered as failure, but time is typicallycounted as downtime.
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Bearing Failure-Definition?
When a bearing surface spall reaches 10square mil inches. (Ref: Timken bearingmanual.)
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GENERAL-
BEARING FAILURE MODES
Contact fatique
Wear
Plastic flow
Fracture
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SOME TYPICAL BEARING FAILURE MODES
FATIQUE PROBABLE CAUSE
Spalling-subsurface fatigue excessive load
Peeling-surface fatigue lubrication
WEAR
Fretting /surface corrosion vibration/looseness
Abrasion contamination
Scoring/Abrasion defective seals
Corrosion
Brinneling excessive vibration
localized fretting/hardening excessive vibration
Smearing/pitting/fluting electric discharge
PLASTIC FLOW/FRACTURES
Brinneling/denting excessive or point load
Material failure hot/cold working/latent defect
All causeHighfrequencyimpacting.
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MEAN FAILURE DEFINITIONS
MTBF = Mean time between subsequent failures in a system
or family of similar components.
MTTF = Mean time to first failure in a family of similarcomponents. This is the preferred definition for bearings
because they are seldom repaired.
MTTR = Mean time to repair.
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Most studies have concluded that absentlubrication failures or other negligence,
operational bearing failures generallyconform to a Weibull exponential failuredistribution. The Weibull characteristic isdescribed in other tutorials available fromDMC-CT..
GENERAL CONCLUSIONS:
Failures are random!
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Interesting Question for you?
If you are running a machine with two bearings and eachhave MTTF estimates of one year. (8,760 hrs.) What are
the odds of having problems within the next month?
The estimated probability of failure = 8%Having problems within the next year?
The estimated probability of failure = 86.5%
Surprised???
Thats why it is important to track both MTTF andProbability of Failure!
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Bearing LifeGuard tm
....uses proven bearing failure diagnostictechniques with patented Multiple
Discriminant Analysis Technology.
tm
It provides immediate estimates on:*Life Expectancy*MTTF
*Failure Probability*Financial Risk.
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UPON DATA COLLECTION
Multiple Discriminant Analysis
PROBLEM DATA
IMBALANCE COUPLING
GEAR MISALIGNMENT
WARP SHAFT
ECCENTRICITY BELT
DEFECT BELT
RESONANCE PULLEY
ALIGN PULLEY BALANCE
BLADE PASS
HF ENERGY
STRESS WAVE IMPACTS
ACOUSTIC EMMISSIONCREST FACTOR
PEAK G IMPACTS
KURTOSIS
DEMOD ENVELOPE
PROC
PROC..
DYNAMIC
FORCE
NUMBER
BEARING
CONDITION
NUMBER
CONDITION
INFORMATION
MANAGEMENT INFORMATION SCREEN
US PAT 6,763,512
Other patents pending.
Copyright Dynamic Measurement
Consultants, LLC
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Bearing Condition Information
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INTEGRATED INFORMATION ON
DYNAMIC FORCE FACTOR- (DF)INTGRATES FORCING FUNCTIONS-IMBALANCE ANDMISALIGNMENT THAT INFLUENCE AND REDUCE MTTF. and your MACHINE BEARING LIFE.
DEGRADATION FACTOR (BD)INTEGRATES THE ANALYTICAL DATA THAT INDICATEDEGRADATION OR CONDITION OF A BEARING
,,,,,,and helps you see predict failure estimate.
LIFE EXPECTANCY FACTOR-(LE)INTEGRATES BC + DF TO PRODUCE A USER SELECTEDESTIMATE OF REMAINING BEARING LIFEand provides it for you directly.
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You may observe these metric trends
over timeoptimum9(Red)
BD overall bearingdegrade/condition.
LE Life Expectancyreduction due to highBD+DF.
DF Dynamic Forces.Due to imbalance,misalignment, highfrequency impacting.
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Diagnostic Discriminant Trends(All contribute to BD)
Optimum (green) 9
LF-Low Frequencybalance alignment forces.
HF-sonic/ultra sonicenergy detects surfaceroughness.
CF- shock wave impactratios detect surfacecrack spiking defects.
KF-Kurtosis detectsserious fatigue cracksand spalling defects
ED-short durationball/race impacting.
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Acceleration time waveform.
(Analyst selects Reading 1,2,N tab.)
Acceleration vs.time.
Zoom for
examination
Auto or manualtime or amplitude.
Adjustable markerwith g level readout.
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Acceleration Spectrum Display
(Analyst selects Spectrum tab.)
Zoom
X-Y axis
Auto ormanual
Markerallows
display offrequency g level.
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Low Frequency Spectrum Display.
Velocity & g level (User selects-Spectrum-LF)
Display inVelocity (in/sec-rms)
g (rms) Zoom X-Y axis
Auto or manual
Frequency-Amplitudemarker.
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Demodulated Frequency Spectrum
Showing clear ball/race impacts.
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ONE CUSTOMERS SUCCESS STORY!350 horsepower centrifugal compressor
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PRESENTATION TO MANAGEMENT:Financial risk $155, 000.
Cost of routine repair
$12,000.Bearing Probability of Failure within 90 days=63%.Easy decision!
B EARINGLIFEGUARD
POF = 63%BD FATOR = 10
BEARING SERVICE
RECOMMENDED
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PHOTO OF REMOVED BEARINGCatastrophic Failure avoided..
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Facility Managers Desired List
Trends- reliability,condition, downtime cost by facility, buildingor floor.
How do we measure reliability/ downtime cost?
Are we getting better? How do we know?
Where are the key problems, high cost areas? How can wereduce the cost/risk?
Reliable indicator of when to tear down machine.
How do we compare with other similar facilities?
Managers act on information not spectra!
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Easier to use.Easier to understand.Timely Information.
Fastest data collectionReduced Training CostsExtends Equipment Life.
Focus on Financial Impact.
Better Reporting of $ results.Better Communication.More Effective Program
Metrics Based Condition Management:
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For more Information
on the benefits of Bearing LifeGuard ina
Metrics based
Total Facility Maintenance Program
Contact:
[email protected] toll free:877-358-4437