vibration case histories presentation, 091203.pdf · 9/19/2006 3 case history#1, excessive...
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9/19/20061
Vibration Case HistoriesVibration Case HistoriesBarry T. CeaseMeadWestvaco
9/19/20062
IntroductionIntroduction
Case History#1 – ExcessiveVibration Of Motor
Case History#2 – Strange Motor &Gearbox Vibration
Case History#3 – Repeat FanBearing Failures
Case History#4 – Pump BearingCage Failure
9/19/20063
Case History#1,Case History#1,Excessive Vibration Of MotorExcessive Vibration Of Motor
EQUIPMENT: Nash 9000 seriesvacuum pump driven by a singlereduction, parallel gearbox and a700 HP synchronous motor.
The vacuum pump is one of manyused to pull water out of the paper(dry it) as it moves thru theprocess.
9/19/20064
CH#1 – Equipment LayoutCH#1 – Equipment Layout
9/19/20065
CH#1 - ProblemCH#1 - Problem
Excessive & noisy vibration atmotor.
This problem could be heard & feltclearly at the motor.
It sounded like something wasrubbing and/or loose.
9/19/20066
CH#1 – Test Data & ObservationsCH#1 – Test Data & Observations(Motor)(Motor)
Motor speed was exactly 400 rpm. Pump speed was 267 rpm. Pump vibration data showed no
abnormal patterns or levels. Motor spectra showed many
harmonics of running speed and of133 cpm (1/3 x rpm).
Motor waveform showed impactingat 400 & 133 cpm.
9/19/20067
CH#1 - Motor SpectraCH#1 - Motor Spectra
9/19/20068
CH#1 – Motor Spectra ZoomCH#1 – Motor Spectra Zoom
9/19/20069
CH#1 – Motor WaveformCH#1 – Motor Waveform
9/19/200610
CH#1 – Test Data & ObservationsCH#1 – Test Data & Observations(Gearbox)(Gearbox) Gearbox input speed was 400 rpm. Gearbox output speed was 267 rpm
(1.5:1 ratio and 56T/84T). Gearbox spectra showed many
harmonics of both input & output speedand 133 cpm (1/2 x output).
Gearbox spectra didn’t show highgearmesh frequency at 22,400 cpm.
Gearbox waveform showed heavyimpacting at 400 cpm.
Gearbox Peakvue data showed manyharmonics of 400 cpm.
9/19/200611
CH#1 – Gearbox SpectraCH#1 – Gearbox Spectra
9/19/200612
CH#1 – Gearbox Spectra ZoomCH#1 – Gearbox Spectra Zoom
9/19/200613
CH#1 – Gearbox WaveformCH#1 – Gearbox Waveform
9/19/200614
CH#1 –CH#1 – PeakvuePeakvue SpectraSpectra
9/19/200615
CH#1 –CH#1 – PeakvuePeakvue WaveformWaveform
9/19/200616
CH#1 – Maintenance HistoryCH#1 – Maintenance History
The motor was changed out in7/02 and the gearbox was changedin 8/02.
After motor change in 7/02, motorvibration levels initially dropped,but eventually resumed previouslevels.
The gearbox installed in 8/02 hadbeen used before, but was the onlyspare available at the time.
9/19/200617
CH#1 – Conclusions &CH#1 – Conclusions &RecommendationsRecommendations
It was recommended that the gearboxbe changed out when possible due to aprobable gear fault.
The gearbox was changed in 5/03. An inspection of the gearbox showed
many gear teeth broken off on thepinion gear with significant wear onboth gears.
Follow-up data on both machines afterthe gearbox change showed much lowervibration levels – the problem vanished.
9/19/200618
CH#1 – Gearbox InspectionCH#1 – Gearbox Inspection
9/19/200619
CH#1 – Motor Data, B & ACH#1 – Motor Data, B & A
9/19/200620
CH#1 – Gearbox Spectra, B & ACH#1 – Gearbox Spectra, B & A
9/19/200621
CH#1 – Gearbox Wave, B & ACH#1 – Gearbox Wave, B & A
9/19/200622
Case History#2, Strange Motor &Case History#2, Strange Motor &Gearbox VibrationGearbox Vibration
EQUIPMENT: Agitator driven thrusingle reduction, parallel gearboxby an induction motor.
This agitator helps maintain theconsistency of the stock in ourhydrapulper tank.
9/19/200623
CH#2 - ProblemCH#2 - Problem
Strange pulsing noise comingfrom motor & gearbox.
9/19/200624
CH#2 – Test Data & ObservationsCH#2 – Test Data & Observations(Motor)(Motor)
Motor speed was exactly 1192 rpm. Agitator speed was 236 rpm (5:1 ratio). Motor spectra showed many harmonics
of running speed & closer inspectionshowed 48 cpm sidebands around eachharmonic.
Motor waveform showed pulsations ormodulation at a period of approx. 1.25sec or 48 cpm.
9/19/200625
CH#2 – Motor DataCH#2 – Motor Data
9/19/200626
CH#2 – Motor ZoomCH#2 – Motor Zoom
9/19/200627
CH#2 – Test Data & ObservationsCH#2 – Test Data & Observations(Gearbox), Part 1(Gearbox), Part 1
Gearbox speed was 1192 rpm input &236 rpm output (single reduction @ 5:1ratio).
Gearbox spectra showed high gearmeshfrequency (26,200 cpm) with sidebandsat 945 cpm.
Gearmesh sidebands usually relate toone of the gear speeds, but 945 cpmdidn’t correlate to either speed (1192 or236 rpm).
9/19/200628
CH#2 – Test Data & ObservationsCH#2 – Test Data & Observations(Gearbox), Part 2(Gearbox), Part 2
Gearbox waveform showedimpacting or modulation at 945cpm.
Agitator data showed nothingabnormal.
9/19/200629
CH#2 – Gearbox DataCH#2 – Gearbox Data
9/19/200630
CH#2 – Gearbox ZoomCH#2 – Gearbox Zoom
9/19/200631
CH#2 – Conclusions &CH#2 – Conclusions &Recommendations (Motor), P1Recommendations (Motor), P1 It was concluded that the strange
vibration data on the motor was theresult of broken rotor bars.
The 48 cpm sidebands around themotor harmonics related directly to itspole pass frequency.
The classic spectral pattern of brokenrotor bars is running speed harmonicswith sidebands at pole pass frequency.
The classic waveform pattern of brokenrotor bars is pulsations at pole passfrequency.
9/19/200632
CH#2 – Conclusions &CH#2 – Conclusions &Recommendations (Motor), P2Recommendations (Motor), P2
Pole Pass Frequency =(Theoretical RPM – True RPM) * #Poles. PPF = (1200 – 1192) * 6 = 48 cpm. The recommendation was made to
changeout the motor at the next outage. Later inspection by a motor repair shop
showed many broken rotor bars.
9/19/200633
CH#2 – Conclusions &CH#2 – Conclusions &Recommendations (Gearbox)Recommendations (Gearbox) After consultation with the gearbox
vendor, it was concluded the thestrange data from the gearbox waslikely due to the 4-yoke design ofthe bull gear.
The 4-yokes in the gear hub resultin minor deviations from the gearpitch circle causing modulationeach time these teeth move in andout of the mesh.
4 * 236 rpm = 945 cpm.
9/19/200634
CH#2 - 4-Yoke GearCH#2 - 4-Yoke Gear
9/19/200635
CH#2 – Conclusions &CH#2 – Conclusions &Recommendations (Gearbox),Recommendations (Gearbox),Part 2Part 2
The vendor indicated it shouldn’tbe a problem, but recommendedan annual gear inspection &continued vibration monitoringlooking for any change incondition.
9/19/200636
Case History #3, Repeat FanCase History #3, Repeat FanBearing FailuresBearing Failures
EQUIPMENT: Overhung,centrifugal fan belt-driven by a 60HP induction motor.
This is a critical fan necessary tothe process of winding the paperinto customer-specified sizes.
9/19/200637
CH#3 – Equipment LayoutCH#3 – Equipment Layout
9/19/200638
CH#3 - ProblemCH#3 - Problem
Repeat fan bearing failures. In one instance, vibration detected
bearing faults on this fan less than amonth after changeout.
Predictive maintenance was able todetect these failures early enough toschedule repairs during outages, butafter three fan bearing changeouts in 12months, we knew something had to bedone differently.
9/19/200639
CH#3 – Test Data & Observations,CH#3 – Test Data & Observations,Part 1Part 1
Motor speed was 1786 rpm Fan speed was 1985 rpm Motor spectra showed running speed &
harmonics, fan speed & harmonics, beltfrequencies & little else.
Fan spectra was similar to motor data,but also showed fan bearing defectfrequencies (BPFO & harmonics).
9/19/200640
CH#3 – Fan SpectraCH#3 – Fan Spectra
9/19/200641
CH#3 – Test Data & Observations,CH#3 – Test Data & Observations,Part 2Part 2
Fan trend data showed initial dropwhen bearings were changed, butsoon jumped up to previous highlevels days or weeks afterchangeout.
One of the mechanics involved inthe bearing change told us, “it tookus over an hour to get the bearingsaligned to where the shaft wouldeven turn”.
9/19/200642
CH#3 – Fan Trend DataCH#3 – Fan Trend Data
9/19/200643
CH#3 – Test Data & Observations,CH#3 – Test Data & Observations,Part 3Part 3
The fan bearings were standardpillow block style housings withtapered roller bearings inside.
We assumed these were self-aligning bearings as most pillowblocks are, but this assumptionturned out to be false.
9/19/200644
CH#3 – Conclusion &CH#3 – Conclusion &Recommendations, Part 1Recommendations, Part 1 The relatively tight alignment tolerances
of the existing tapered roller bearingscombined with the poor condition of thefan base made for short bearing life.
We asked our bearing supplier for areplacement bearing type that wouldcarry the same load, but be moreforgiving for misalignment.
We also had our machine shop fabricatea new fan base that was machined flat& line bored to perfectly fit the newpillow block bolt pattern.
9/19/200645
CH#3 – Conclusions &CH#3 – Conclusions &Recommendations, Part 2Recommendations, Part 2
After installation of the new typebearings & new fan base we have nothad another bearing failure.
Our bearing life has went from anaverage of 4-months to 26 months andcounting.
Further inspection of maintenancehistory showed a fan speed increasewhich corresponded quite well to ourincreased rate of failure.
9/19/200646
CH#3 – Conclusions &CH#3 – Conclusions &Recommendations, Part 3Recommendations, Part 3
This case history is a good example ofboth predictive & proactivemaintenance.
Predictive maintenance allowed us toavoid catastrophic fan bearing failuresand perform repairs during scheduledoutages.
Proactive maintenance extended the life& reliability of the fan bearings.
9/19/200647
Case History#4, Pump OutboardCase History#4, Pump OutboardBearing Cage FailureBearing Cage Failure
Equipment: Double-suction, centrifugalpump driven by a 1250 HP synchronousmotor turning at 514 rpm.
This is the most critical pump in theprocess directly providing the product(stock) used to make paper on the papermachine.
9/19/200648
CH#4 - ProblemCH#4 - Problem
Increasing HFD vibration levels at pumpoutboard. Current levels had exceededmaximum of long term trend.
9/19/200649
CH#4 – Test Data & Observations,CH#4 – Test Data & Observations,Part 1Part 1
Since the bearing was oil lubricated, ananalysis of the outboard bearing oil wasrequested.
Oil analysis results showed very highcopper levels indicating cage wear.
Vibration data showed very high HFDlevels on outboard bearing.
9/19/200650
CH#4 – HFD TrendCH#4 – HFD Trend
9/19/200651
CH#4 – Test Data & Observations,CH#4 – Test Data & Observations,Part 2Part 2
Peakvue spectra showed harmonics offundamental train frequency (cage).
An 10/01 paper by J. Robinson & J. Berryrecommends a Peakvue fault level of 4.0g’s pk-to-pk for a 500 rpm machine.
Peakvue waveform on outboard bearingshowed levels at 11.3 g’s pk-to-pk!!!
Maintenance history showed a continuingproblem of a leaking pump outboard seal.
9/19/200652
CH#4 –CH#4 – PeakvuePeakvue Spectra, P1Spectra, P1
9/19/200653
CH#4 –CH#4 – PeakvuePeakvue Spectra, P2Spectra, P2
9/19/200654
CH#4 –CH#4 – PeakvuePeakvue WaveformWaveform
9/19/200655
CH#4 – Conclusion &CH#4 – Conclusion &Recommendations, Part 1Recommendations, Part 1
The recommendation was made tochangeout the pump outboard bearing.
Later inspection of the bearing showed thecage worn badly particularly in the areaseparating the rolling elements from oneanother.
During the bearing change, shims werefound under the bearing making up the fitwith the housing.
9/19/200656
CH#4 – Conclusion &CH#4 – Conclusion &Recommendations, Part 2Recommendations, Part 2 Failure analysis of the bearing found lube
contamination and skidding as the primarycauses of failure. Corrective actions were asfollows:
1) Replace the outboard bearing housing, 2) Repair or replace the pump outboard packing
gland, 3) Replace the pump rotor which was causing
thrust loading, and 4) Upgrade the lube from an ISO 68 to an ISO
150 weight oil (temporarily use grease untilpacking gland repaired).
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