UNIDAD II ANALISIS VIBRACIONAL DIAGNÓSTICO DE RODAMIENTOS
UNIDAD IIANALISIS VIBRACIONALDIAGNSTICO DE RODAMIENTOS
Shock pulse measurement
k (t) - Method
Spike Energy Value
BCU - Value
Kurtosis Factor
gSE - Value
SEE - Value
Acceleration - Crest Factor
BUT:Normalising Alarm Levels Gradient of trend developement is necessary for evaluation of rolling bearing condition:
Start values ?
Alarm levels ?
Trend developement ?xTIME
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?
Gradient of trend development ?XZEIT
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?
dBsv = absolute shock pulse valuedBn = normalised shock pulse value
dBi = initial value
Basic value of the normalised shock pulse values determined through RPM and diameter of the bearing
measurement location with signal dampingdBsv090-9dBiadBmdBcdBn
dBia = adjusted inital value signal damping of real measurement location influencing factors like load condition lubrication and bearing type
Freqquency range of the modulated carrier frequencies
Filter 1Filter 2
Natural frequencies of bearing piecesResonance frequency accelerometerBearing rolling noiseBroad band acceleration spectra:
Filtered broad band spectrum:AF
Envelop espectrum:FA
filtered rectifiedtime signal:TA
Filtered broad band spectrum:FA
filtered rectified time signal:TA
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envelope spectrum:FA
modulated frequency range suppressed by wrong filter setting Defect frequencies completely suppressed by the filtermodulated frequencies amplified through right filter setting good visibility of the defect frequencies
Bearing geometrie and defect frequencies:
Contact AngleDR Rolling element diameterd mBearing pitch diameterNNumber of rolling elements in one rownShaft speed in RPM
Rolling element pass outer race freq.: fRPOF = ( 1 -cos )
Rolling element pass inner race freq.:fRPIF = ( 1 +cos )
Rolling element pass freq.:fRPF = ( 1 - cos2 )
Cage rotational frequency: fCRF = ( 1 -cos )
1 - Outer race defect2 - Inner race defect3 - Rolling element defect4 - Cage defect
Example Pass frequencies:
Ball bearing SKF 6211Speed n = 2998 Rev/min
No rolling track defect:
TIME SIGNAL
Rolling track defect:
TIME SIGNALENVELOPET (seg)
F (HZ)fRPOF=1/Trpof Defect frequency
a).- Outer Race Defect:
Envelope Sectrum:a inm/sf in HzfRPOF 2xfRPOF 3xfRPOF4xfRPOF5xfRPOF 6xfRPOF
Rolling element pass outer race fRFOF and Harmonics clearly visible if only 1xfRPOF appears, then it can be also an unround deformation of the outer racein case of very big unbalance, side bands with interval fnappear because of periodic load changes(in the load zone modulation with fn as the unbalance runsperiodically through the load zone)
b).- Inner Race Defect:
Envelope Spectrum:a inm/sf in HzfRPIF 2xfRPIF
Rolling element pass inner race frequency fRPIF and many side bands with interval fn
Modulated with the fundamental frequency fn , asthe inner race defect runs periodicallythrough the load zone with fn Fundamental modulation frequency fn and harmonics are visible
c) Rolling element defect:
Envelope Spectrum:a inm/sf in Hz 0,5fRPF fRPF 1,5fRPF 2fRPF 1,5fRPF 3fRPF
Rolling element pass frequency fRPF with Harmonics andwith interval fCRF
fRPF can be also visible because of too small bearing clearance or insufficient lubricationModulation with cage rotational speed fCRF, as the rolling element runs periodically through the load zone with fCRF Subharmonics of fRPF exist always with the harmonics, because theFundamental modulation frequency fCRF and harmonics are visible
d).- Cage Defect:
Envelope Spectrum:
Cage rotational frequency fCRF and Harmonics visible
fCRF Cage rotational frequency is Cage defect frequencycoming out of the load zone: the rolling elementis accelerated and slides on the cage defector coming into the load zone: the rolling element is braked and slides on the cage defect