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