Vibration Analysis

49
Efft Efft ek ek Diagnostic Diagnostic Engineers Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866 Kingdom. +44(0)1768362866 SIGNATURE ANALYSIS SIGNATURE ANALYSIS Which frequencies exist and what are the relationships to the fundamental exciting frequencies. What are the amplitudes of each peak How do the peaks relate to each other If there are significant peaks, what are their source

Transcript of Vibration Analysis

Page 1: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

SIGNATURE ANALYSISSIGNATURE ANALYSISSIGNATURE ANALYSISSIGNATURE ANALYSIS

Which frequencies exist and what are the relationships to the fundamental exciting frequencies.

What are the amplitudes of each peak How do the peaks relate to each other If there are significant peaks, what are their source

Page 2: Vibration Analysis

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COUPLE UNBALANCECOUPLE UNBALANCECOUPLE UNBALANCECOUPLE UNBALANCE

1800 out of phase on the same shaft 1X RPM always present and normally dominates Amplitude varies with square of increasing speed Can cause high axial as well as radial amplitudes Balancing requires Correction in two planes at 180o

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OVERHUNG ROTOR UNBALANCEOVERHUNG ROTOR UNBALANCEOVERHUNG ROTOR UNBALANCEOVERHUNG ROTOR UNBALANCE

1X RPM present in radial and axial directions Axial readings tend to be in-phase but radial readings might be

unsteady Overhung rotors often have both force and couple unbalance each of

which may require correction

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Diagnosing UnbalanceDiagnosing Unbalance Diagnosing UnbalanceDiagnosing Unbalance

Vibration frequency equals rotor speed.

Vibration predominantly RADIAL in direction.

Stable vibration phase measurement.

Vibration increases as square of speed.

Vibration phase shifts in direct proportion to measurement direction.

900

900

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ECCENTRIC ROTORECCENTRIC ROTORECCENTRIC ROTORECCENTRIC ROTOR

Largest vibration at 1X RPM in the direction of the centerline of the rotors

Comparative phase readings differ by 00 or 1800

Attempts to balance will cause a decrease in amplitude in one direction but an increase may occur in the other direction

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ANGULAR MISALIGNMENTANGULAR MISALIGNMENT ANGULAR MISALIGNMENTANGULAR MISALIGNMENT

Characterized by high axial vibration 1800 phase change across the coupling Typically high 1 and 2 times axial vibration Not unusual for 1, 2 or 3X RPM to dominate Symptoms could indicate coupling problems

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PARALLEL MISALIGNMENTPARALLEL MISALIGNMENT PARALLEL MISALIGNMENTPARALLEL MISALIGNMENT

High radial vibration 1800 out of phase Severe conditions give higher harmonics 2X RPM often larger than 1X RPM Similar symptoms to angular misalignment Coupling design can influence spectrum shape and amplitude

RadialRadial

1x1x 2x2x4x4x

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BENT SHAFTBENT SHAFTBENT SHAFTBENT SHAFT

Bent shaft problems cause high axial vibration 1X RPM dominant if bend is near shaft center 2X RPM dominant if bend is near shaft ends Phase difference in the axial direction will tend towards 1800

difference

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MISALIGNED BEARINGMISALIGNED BEARINGMISALIGNED BEARINGMISALIGNED BEARING

Vibration symptoms similar to angular misalignment Attempts to realign coupling or balance the rotor will not alleviate the

problem. Will cause a twisting motion with approximately 1800 phase shift side to

side or top to bottom

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OTHER SOURCES OF HIGH AXIAL OTHER SOURCES OF HIGH AXIAL VIBRATIONVIBRATION

OTHER SOURCES OF HIGH AXIAL OTHER SOURCES OF HIGH AXIAL VIBRATIONVIBRATION

a. Bent Shafts

b. Shafts in Resonant Whirl

c. Bearings Cocked on the Shaft

d. Resonance of Some Component in the Axial Direction

e. Worn Thrust Bearings

f. Worn Helical or Bevel Gears

g. A Sleeve Bearing Motor Hunting for its Magnetic Center

h. Couple Component of a Dynamic Unbalance

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MECHANICAL LOOSENESS (A)MECHANICAL LOOSENESS (A)MECHANICAL LOOSENESS (A)MECHANICAL LOOSENESS (A)

Caused by structural looseness of machine feet Distortion of the base will cause “soft foot” problems Phase analysis will reveal aprox 1800 phase shift in the vertical

direction between the baseplate components of the machine

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MECHANICAL LOOSENESS (B)MECHANICAL LOOSENESS (B)MECHANICAL LOOSENESS (B)MECHANICAL LOOSENESS (B)

Caused by loose pillowblock bolts Can cause 0.5, 1, 2 and 3X RPM Sometimes caused by cracked frame structure or bearing block

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SLEEVE BEARINGSLEEVE BEARINGWEAR / CLEARANCE PROBLEMSWEAR / CLEARANCE PROBLEMS

SLEEVE BEARINGSLEEVE BEARINGWEAR / CLEARANCE PROBLEMSWEAR / CLEARANCE PROBLEMS

Later stages of sleeve bearing wear will give a large family of harmonics of running speed

A minor unbalance or misalignment will cause high amplitudes when excessive bearing clearances are present

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COMPONENT FREQUENCIES OF A SQUARE COMPONENT FREQUENCIES OF A SQUARE WAVE FORM.WAVE FORM.

COMPONENT FREQUENCIES OF A SQUARE COMPONENT FREQUENCIES OF A SQUARE WAVE FORM.WAVE FORM.

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COMPONENT FREQUENCIES OF A SQUARECOMPONENT FREQUENCIES OF A SQUARE WAVE FORM. WAVE FORM.

COMPONENT FREQUENCIES OF A SQUARECOMPONENT FREQUENCIES OF A SQUARE WAVE FORM. WAVE FORM.

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MECHANICAL LOOSENESS (C)MECHANICAL LOOSENESS (C)MECHANICAL LOOSENESS (C)MECHANICAL LOOSENESS (C)

Phase is often unstable Will have many harmonics Can be caused by a loose bearing liner, excessive bearing clearance

or a loose impeller on a shaft

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ROTOR RUBROTOR RUBROTOR RUBROTOR RUB

Similar spectrum to mechanical looseness Usually generates a series of frequencies which may excite natural

frequencies Subharmonic frequencies may be present Rub may be partial or through a complete revolution.

Truncated waveform

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RESONANCERESONANCERESONANCERESONANCE

Resonance occurs when the Forcing Frequency coincides with a Natural Frequency

1800 phase change occurs when shaft speed passes through resonance

High amplitudes of vibration will be present when a system is in resonance

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BELT PROBLEMS (D)BELT PROBLEMS (D)BELT PROBLEMS (D)BELT PROBLEMS (D)

High amplitudes can be present if the belt natural frequency coincides with driver or driven RPM

Belt natural frequency can be changed by altering the belt tension

High amplitudes can be present if the belt natural frequency coincides with driver or driven RPM

Belt natural frequency can be changed by altering the belt tension

BELT RESONANCEBELT RESONANCE

RADIAL

1X RPM

BELT RESONANCE

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BELT PROBLEMS (A)BELT PROBLEMS (A)BELT PROBLEMS (A)BELT PROBLEMS (A)

Often 2X RPM is dominant Amplitudes are normally unsteady, sometimes pulsing with either driver or

driven RPM Wear or misalignment in timing belt drives will give high amplitudes at the

timing belt frequency Belt frequencies are below the RPM of either the driver or the driven

Often 2X RPM is dominant Amplitudes are normally unsteady, sometimes pulsing with either driver or

driven RPM Wear or misalignment in timing belt drives will give high amplitudes at the

timing belt frequency Belt frequencies are below the RPM of either the driver or the driven

WORN, LOOSE OR MISMATCHED BELTSWORN, LOOSE OR MISMATCHED BELTS

BELT FREQUENCYHARMONICS

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BELT PROBLEMS (C)BELT PROBLEMS (C)BELT PROBLEMS (C)BELT PROBLEMS (C)

Eccentric or unbalanced pulleys will give a high 1X RPM of the pulley

The amplitude will be highest in line with the belts Beware of trying to balance eccentric pulleys

Eccentric or unbalanced pulleys will give a high 1X RPM of the pulley

The amplitude will be highest in line with the belts Beware of trying to balance eccentric pulleys

RADIAL1X RPM OFECCENTRICPULLEY

ECCENTRIC PULLEYSECCENTRIC PULLEYS

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BELT PROBLEMS (B)BELT PROBLEMS (B)BELT PROBLEMS (B)BELT PROBLEMS (B)

Pulley misalignment will produce high axial vibration at 1X RPM Often the highest amplitude on the motor will be at the fan RPM

Pulley misalignment will produce high axial vibration at 1X RPM Often the highest amplitude on the motor will be at the fan RPM

1X DRIVEROR DRIVEN

BELT / PULLEY MISALIGNMENTBELT / PULLEY MISALIGNMENT

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HYDRAULIC AND HYDRAULIC AND AERODYNAMIC FORCESAERODYNAMIC FORCES

HYDRAULIC AND HYDRAULIC AND AERODYNAMIC FORCESAERODYNAMIC FORCES

If gap between vanes and casing is not equal, Blade Pass Frequency may have high amplitude

High BPF may be present if impeller wear ring seizes on shaft Eccentric rotor can cause amplitude at BPF to be excessive

If gap between vanes and casing is not equal, Blade Pass Frequency may have high amplitude

High BPF may be present if impeller wear ring seizes on shaft Eccentric rotor can cause amplitude at BPF to be excessive

BPF = BLADE PASS FREQUENCY

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HYDRAULIC AND HYDRAULIC AND AERODYNAMIC FORCESAERODYNAMIC FORCES

HYDRAULIC AND HYDRAULIC AND AERODYNAMIC FORCESAERODYNAMIC FORCES

Flow turbulence often occurs in blowers due to variations in pressure or velocity of air in ducts

Random low frequency vibration will be generated, possibly in the 50 - 2000 CPM range

Flow turbulence often occurs in blowers due to variations in pressure or velocity of air in ducts

Random low frequency vibration will be generated, possibly in the 50 - 2000 CPM range

FLOW TURBULENCEFLOW TURBULENCE

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HYDRAULIC AND AERODYNAMIC HYDRAULIC AND AERODYNAMIC FORCES FORCES

HYDRAULIC AND AERODYNAMIC HYDRAULIC AND AERODYNAMIC FORCES FORCES

Cavitation will generate random, high frequency broadband energy superimposed with BPF harmonics

Normally indicates inadequate suction pressure Erosion of impeller vanes and pump casings may occur if left unchecked Sounds like gravel passing through pump

Cavitation will generate random, high frequency broadband energy superimposed with BPF harmonics

Normally indicates inadequate suction pressure Erosion of impeller vanes and pump casings may occur if left unchecked Sounds like gravel passing through pump

CAVITATIONCAVITATION

Page 26: Vibration Analysis

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BEAT VIBRATIONBEAT VIBRATIONBEAT VIBRATIONBEAT VIBRATION

A beat is the result of two closely spaced frequencies going into and out of phase

The wideband spectrum will show one peak pulsating up and down The difference between the peaks is the beat frequency which itself will be

present in the wideband spectrum

A beat is the result of two closely spaced frequencies going into and out of phase

The wideband spectrum will show one peak pulsating up and down The difference between the peaks is the beat frequency which itself will be

present in the wideband spectrum

WIDEBAND SPECTRUM

ZOOMSPECTRUM

F1 F2

Page 27: Vibration Analysis

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

Stator problems generate high amplitudes at 2FL (2X line frequency )

Stator eccentricity produces uneven stationary air gap, vibration is very directional

Soft foot can produce an eccentric stator

STATOR ECCENTRICITYSTATOR ECCENTRICITYSHORTED LAMINATIONSSHORTED LAMINATIONSAND LOOSE IRONAND LOOSE IRON

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• Electrical line frequency.(Electrical line frequency.(FLFL) = ) = 50Hz = 3000 cpm.50Hz = 3000 cpm. 60HZ = 3600 cpm60HZ = 3600 cpm• No of poles.No of poles. ((PP) )

• Rotor Bar Pass Frequency (Rotor Bar Pass Frequency (FbFb) = ) = No of rotor bars x No of rotor bars x Rotor rpm. Rotor rpm.

• Synchronous speed (Synchronous speed (NsNs)) = = 2xFL2xFL PP• Slip frequency ( Slip frequency ( FFS S )= )= Synchronous speed - Rotor rpm.Synchronous speed - Rotor rpm.

• Pole pass frequency (Pole pass frequency (FFPP )= )= Slip Frequency x No of Poles. Slip Frequency x No of Poles.

• Electrical line frequency.(Electrical line frequency.(FLFL) = ) = 50Hz = 3000 cpm.50Hz = 3000 cpm. 60HZ = 3600 cpm60HZ = 3600 cpm• No of poles.No of poles. ((PP) )

• Rotor Bar Pass Frequency (Rotor Bar Pass Frequency (FbFb) = ) = No of rotor bars x No of rotor bars x Rotor rpm. Rotor rpm.

• Synchronous speed (Synchronous speed (NsNs)) = = 2xFL2xFL PP• Slip frequency ( Slip frequency ( FFS S )= )= Synchronous speed - Rotor rpm.Synchronous speed - Rotor rpm.

• Pole pass frequency (Pole pass frequency (FFPP )= )= Slip Frequency x No of Poles. Slip Frequency x No of Poles.

FREQUENCIES PRODUCED BY ELECTRICAL FREQUENCIES PRODUCED BY ELECTRICAL MOTORS.MOTORS.

FREQUENCIES PRODUCED BY ELECTRICAL FREQUENCIES PRODUCED BY ELECTRICAL MOTORS.MOTORS.

Page 29: Vibration Analysis

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

Loose stator coils in synchronous motors generate high amplitude at Coil Pass Frequency

The coil pass frequency will be surrounded by 1X RPM sidebands

SYNCHRONOUS MOTORSYNCHRONOUS MOTOR(Loose Stator Coils)(Loose Stator Coils)

Page 30: Vibration Analysis

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

Phasing problems can cause excessive vibration at 2FL with 1/3 FL sidebands

Levels at 2FL can exceed 25 mm/sec if left uncorrected Particular problem if the defective connector is only occasionally

making contact

POWER SUPPLYPOWER SUPPLYPHASE PROBLEMSPHASE PROBLEMS(Loose Connector)(Loose Connector)

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

Eccentric rotors produce a rotating variable air gap, this induces pulsating vibration

Often requires zoom spectrum to separate 2FL and running speed harmonic Common values of FP range from 20 - 120 CPM

ECCENTRIC ROTORECCENTRIC ROTOR((Variable Air GapVariable Air Gap))

ECCENTRIC ROTORECCENTRIC ROTOR((Variable Air GapVariable Air Gap))

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

DC motor problems can be detected by the higher than normal amplitudes at SCR firing rate

These problems include broken field windings Fuse and control card problems can cause high amplitude peaks at

frequencies of 1X to 5X Line Frequency

DC MOTOR PROBLEMSDC MOTOR PROBLEMS

Page 33: Vibration Analysis

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ELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMSELECTRICAL PROBLEMS

1X, 2X, 3X, RPM with pole pass frequency sidebands indicates rotor bar problems. 2X line frequency sidebands on rotor bar pass frequency (RBPF) indicates loose rotor

bars. Often high levels at 2X & 3X rotor bar pass frequency and only low level at 1X rotor

bar pass frequency.

ROTOR PROBLEMSROTOR PROBLEMS

Page 34: Vibration Analysis

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ROTOR BAR FREQUENCIES ROTOR BAR FREQUENCIES (SLOT NOISE)(SLOT NOISE)

ROTOR BAR FREQUENCIES ROTOR BAR FREQUENCIES (SLOT NOISE)(SLOT NOISE)

POLEPOLE

MINIMUMMINIMUM

POLEPOLE

MAXIMUMMAXIMUM

MAXMAX

MINMIN

Page 35: Vibration Analysis

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CALCULATION OF GEAR MESH CALCULATION OF GEAR MESH FREQUENCIESFREQUENCIES

CALCULATION OF GEAR MESH CALCULATION OF GEAR MESH FREQUENCIESFREQUENCIES

20 TEETH20 TEETH

51 TEETH51 TEETH

1700 RPM1700 RPM

31 TEETH31 TEETH

8959 RPM -- HOW MANY TEETH ON THIS GEAR?8959 RPM -- HOW MANY TEETH ON THIS GEAR?

Page 36: Vibration Analysis

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GEARSGEARSNORMAL SPECTRUMNORMAL SPECTRUM

GEARSGEARSNORMAL SPECTRUMNORMAL SPECTRUM

Normal spectrum shows 1X and 2X and gear mesh frequency GMF GMF commonly will have sidebands of running speed All peaks are of low amplitude and no natural frequencies are present

14 teeth

8 teeth GMF= 21k CPM

2625 rpm

1500 rpm

Page 37: Vibration Analysis

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GEARSGEARSTOOTH LOADTOOTH LOAD

GEARSGEARSTOOTH LOADTOOTH LOAD

Gear Mesh Frequencies are often sensitive to load High GMF amplitudes do not necessarily indicate a problem Each analysis should be performed with the system at maximum load

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GEARSGEARSTOOTH WEARTOOTH WEAR

GEARSGEARSTOOTH WEARTOOTH WEAR

Wear is indicated by excitation of natural frequencies along with sidebands of 1X RPM of the bad gear

Sidebands are a better wear indicator than the GMF GMF may not change in amplitude when wear occurs

14 teeth1500 rpm

8 teeth2625 rpm

GMF = 21k CPM

Page 39: Vibration Analysis

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GEARSGEARSGEAR ECCENTRICITY AND BACKLASHGEAR ECCENTRICITY AND BACKLASH

GEARSGEARSGEAR ECCENTRICITY AND BACKLASHGEAR ECCENTRICITY AND BACKLASH

Fairly high amplitude sidebands around GMF suggest eccentricity, backlash or non parallel shafts

The problem gear will modulate the sidebands Incorrect backlash normally excites gear natural frequency

Page 40: Vibration Analysis

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GEARSGEARSGEAR MISALIGNMENTGEAR MISALIGNMENT

GEARSGEARSGEAR MISALIGNMENTGEAR MISALIGNMENT

Gear misalignment almost always excites second order or higher harmonics with sidebands of running speed

Small amplitude at 1X GMF but higher levels at 2Xand 3X GMF

Important to set Fmax high enough to capture at least2X GMF

Page 41: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

GEARSGEARSCRACKED / BROKEN TOOTHCRACKED / BROKEN TOOTH

GEARSGEARSCRACKED / BROKEN TOOTHCRACKED / BROKEN TOOTH

A cracked or broken tooth will generate a high amplitude at 1X RPM of the gear

It will excite the gear natural frequency which will be sidebanded by the running speed fundamental

Best detected using the time waveform Time interval between impacts will be the reciprocal of the 1X RPM

TIME WAVEFORM

Page 42: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

D0

D1DB

Note : shaft turning outer race fixed

F = frequency in cpmN = number of balls

BPFI =

BPFO =

BSF =

FTF =

Nb

2

Pd

2Bd

12 (

(

Bd

Pd

COS

RPM(

(

1-

1 + COS X

Nb

2 ( 1 - Bd

Pd

COS

(

X RPM

((

1 -Bd

Pd( COS2 (

XRPM

Bd

PdX RPM

Page 43: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 1 FAILURE MODESTAGE 1 FAILURE MODE

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 1 FAILURE MODESTAGE 1 FAILURE MODE

Earliest indications in the ultrasonic range These frequencies evaluated by Spike EnergyTM gSE, HFD(g)

and Shock Pulse Spike Energy may first appear at about 0.25 gSE for this first

stage

gSE

ZONE BZONE A ZONE C ZONE D

Page 44: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 2 FAILURE MODESTAGE 2 FAILURE MODE

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 2 FAILURE MODESTAGE 2 FAILURE MODE

Slight defects begin to ring bearing component natural frequencies These frequencies occur in the range of 30k-120k CPM At the end of Stage 2, sideband frequencies appear above and below natural

frequency Spike Energy grows e.g. 0.25-0.50gSE

ZONE A ZONE B ZONE C ZONE D

gSE

Page 45: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 3 FAILURE MODESTAGE 3 FAILURE MODE

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 3 FAILURE MODESTAGE 3 FAILURE MODE

Bearing defect frequencies and harmonics appear Many defect frequency harmonics appear with wear the number of sidebands grow Wear is now visible and may extend around the periphery of the bearing Spike Energy increases to between 0.5 -1.0 gSE

ZONE A ZONE B ZONE C ZONE D

gSE

Page 46: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 4 FAILURE MODESTAGE 4 FAILURE MODE

ROLLING ELEMENT BEARINGS ROLLING ELEMENT BEARINGS STAGE 4 FAILURE MODESTAGE 4 FAILURE MODE

Discreet bearing defect frequencies disappear and are replaced by random broad band vibration in the form of a noise floor

Towards the end, even the amplitude at 1 X RPM is effected High frequency noise floor amplitudes and Spike Energy may in fact decrease Just prior to failure gSE may rise to high levels

gSE

ZONE A ZONE B ZONE C

High just priorto failure

Page 47: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

GEARSGEARSHUNTING TOOTHHUNTING TOOTH

GEARSGEARSHUNTING TOOTHHUNTING TOOTH

Vibration is at low frequency and due to this can often be missed Synonymous with a growling sound The effect occurs when the faulty pinion and gear teeth both enter

mesh at the same time Faults may be due to faulty manufacture or mishandling

fHt = (GMF)Na(TGEAR)(TPINION)

Page 48: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

OIL WHIP INSTABILITYOIL WHIP INSTABILITYOIL WHIP INSTABILITYOIL WHIP INSTABILITY

Oil whip may occur if a machine is operated at 2X the rotor critical frequency. When the rotor drives up to 2X critical, whirl is close to critical and excessive

vibration will stop the oil film from supporting the shaft. Whirl speed will lock onto rotor critical. If the speed is increased the whip

frequency will not increase.

oil whirl

oil whip

Page 49: Vibration Analysis

EfftekEfftekDiagnostic EngineersDiagnostic Engineers St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866St. James House, Temple Sowerby, Cumbria, CA10 1RS, United Kingdom. +44(0)1768362866

OIL WHIRL INSTABILITYOIL WHIRL INSTABILITYOIL WHIRL INSTABILITYOIL WHIRL INSTABILITY

Usually occurs at 42 - 48 % of running speed Vibration amplitudes are sometimes severe Whirl is inherently unstable, since it increases centrifugal forces

therefore increasing whirl forces