Vibration TroubleShooting Guide

8/13/2019 Vibration TroubleShooting Guide

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Reprinted from Reliabilityweb.com at http://www.reliabilityweb.com

Vibration Trouble-shooting Field Guideby Sam Pickens of PDM Engineering

What is vibration ? There are three basic types; Linear, Bending and Torsion. Three basic typesof transducers for machinery vibration study; acceleration, velocity and displacement. Three basicparameters; acceleration, velocity and displacement. So we need to be able to observe these

phenomena in an easily understood way via data acquisition instrumentation. We can then apply200-year-old math to decipher the meaning of the data represented on the instrument.

Shown is a typical modern day vibration acquisition system. There are several good ones on themarket.

It has certainly changed since I bought one of the first ADRE systems in 1981. That was back inthe days of HP-9000 (300) used as controllers for real time analyzers.

Fast Fourier Transform (FFT) is modern technology applying Jean Baptiste Fouriers (1768-1830 AD) formula into electronic format displaying time wave form data into frequency spectra.

This really makes time wave form data from machinery vibrations meaningful and somewhat easyto interpret.

Disclaimer (to make the lawyers happy): This information is supplied by third parties and is not warranted for anypurpose. The reader is responsible for ensuring accuracy and compliance with all policies, regulations and laws.

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Mr. Ray Dodd is held in esteem as the guy that fathered the modern day predictive maintenance(PdM) programs. In the 1970s we were basically carrying a portable instrument and collectingvibration data via a velocity transducer and recording that data onto a chart with pen in hand. Ifoverall level vibrations above a certain magnitude were encountered, then we would pick out thepredominate frequencies and log them as well. A long process, but one that proved its worth.

This writing is to serve as a help and guide to assist in diagnostics of vibration problems. Firstwell make sure that certain terms are defined to avoid confusion.

FUNDAMENTAL : This is running speed or 1X; referred to as the machines fundamental orfundamental component. Also component fundamental is sometimes used; i.e. the bearings ballpass frequency fundamental is expressed as component fundamental to distinguish it fromharmonics in a ball pass problem within the spectra. Always make sure it is defined if used foranything other than running speed.

FIRST HARMONIC : Some confuse this with the symbols 2X and 1X; the first harmonic (primarilyan acoustical term) is also referred to as two times RPM (2X). So, be careful. One shouldvisualize this as a bell. The bell is the center of concentric circles circles or harmonics arenumbered from the center. The bell is the center and the first circle encountered is the firstharmonic. But in machinery terms, that would be the 2X component. [The bell, itself being thefundamental or 1X component].

BEARING COMPONENT: BPFI (Ball Pass Frequency Inner Race)

BPFO (outer race frequency)

BSF (Ball Spin Frequency)

FTF (Fundamental Train Frequency) cage problem

Heres the so-called classic bearing equation

w = shaft speed in RPM h = contact angle Pd = Pitch diameter Bd = Ball diameter

BPOR = w N/2Bd/Pd (1

Bd /Pd cosh) BPIR = w N/2 (1 +

Bd/Pd cosh)

BSF = w Pd /2Bd (1 (Bd/Pd )

2 cos

2h) FTF = w/2(1 Bd/Pd cosh)


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And then theres the easy way: The rule of thumb method.

BPOR rot ~ 0.4wn BPIR rot ~ 0.6wn FTF rot ~ 0.4w

Theres no substitute for experience; again use acceleration, you cant analyze what you cantsee you cant trend what you cant see or your instrumentation doesnt see. Integration can

often drive signals into the dirt or noise floor where theyll be hidden or camouflaged to death. Thenoise floor masks or covers them up, and a small acceleration signal 0.05 gs 0-P (the beginningof trending) at 600 Hz wouldnt be noticed.

Always check the limitations of your system. Transducer selection for a paper machine should beof very high resolution with as low a frequency response, as temperature will allow. There are anumber of good transducers out there. Always make sure your acquisition system is within limitsof your interest.

Ive seen so-called consultants gather vibration data when the machine of interest was outside ofthe limitations of their instrumentation. Naturally, the sub sequential report that follows is a realgem. This writing is only a field book and to inform you of certain things that should be of concernto you in your environment. Question your transducer supplier but make certain they have theproduct you need or find one who does.

Bearings Natural Frequency: Lack of lubrication excites this frequency and creates a broadvibration pattern around this frequency region casing this phenomenon to display in the vibrationspectra.

Special Note: A broadened spike or spectral peak (from the peak on top, the shape of the peakwill broaden toward the noise floor) will denote mechanical deterioration. If you see mechanicaldeterioration and the bearings natural frequency you may want to inject grease lubricant veryslowly as not to shock the bearing. If theres only a small magnitude of vibration then you maywant to only note it in the report. If its severe and a determination must be made the addition oflube may give insight as to time of failure or assist in analysis.

LINE FREQUENCY : 60 Hertz (Hz) USA Power Turbine RPM (3600)/60=60. In Europe the poweris 50 Hertz so the generators are larger and operate at 3000 RPM.

LINE SYNC FREQ : 120 Hz (120 / # poles X 60 = RPM of a given machine) Look for especially inDC motors. In AC & DC this frequency phenomenon is generally found at upper harmonics ofhigh frequency problems associated with electrical problems or the beginning of potentialproblems.

The electrical frequency is also displayed in fluorescence light bulbs and is used to calibrate aphoto tachometer Ive also used it for a trigger.

Field balancing using a tachometer for a trigger device to sync at once per rev.

Overall or Overall level (OA): A term I use often, but not really sure if all are versed in itsmeaning. Normally an analyzer has 200, 400, 800 and 1600 lines of resolution. Imagine a


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spreadsheet of 400 columns, as thats normal for most PdM programs. The height is normally 1Volt with a resolution of 0.005 and automatic scaling. Time waveform data are broken down intofrequency spectra. So, each of the 400 windows has amplitude: that amplitude for each window issquared. Overall level (OA) is the square root of the sum of the squares. It is the sixth band in myPdM software. Or in a 200 line analyzer it would be line 201.

New subject: In the US we use g's 0-P but in Europe they use mm rms or g's rms which is totallyforeign to us. I did not mention it at all. In addition, CSI boxes used a notation of rms on their boxbut the output was really 0-P - not rms. It was a flaw in their box, but better not go there.

In this world, people in vibration should realize that integration from g's to IPS (in/sec) isn'tabsolute but only retaliative. The universal language is IPS but the analytical world is better if keptin tune with the type of transducer one is using. Acceleration - work in g's. Velocity transducer -work in IPS. Eddy current probes - work in mils. But, translate to common terms when reporting.

MEASUREMENT PARAMETERS : Acceleration, Velocity, Displacement and Acoustics (dB).

There are contact type and non-contact type. Which is best? That may be impossible todetermine. Large turbo machinery both. The contact type are cheaper and easier as a rule butare affected by the machines dampening effect caused by bearing type and mass. Massdetermines resonance so the sensors mass should be so that the frequencies of interest arebelow its natural frequency. The non-contact sensor (eddy current probe) provides rotor dynamicsand good down to DC. We are not getting into all systems, laser, all non-contacting as this is onlya field reference book.

Bearing cap data are now taken almost exclusively in acceleration. Ive used that approach since1980 exclusively. A velocity transducer is sometimes useful for balancing, apart from that I wontuse a velocity transducer and dont integrate an acceleration spectrum into velocity or doubleintegrate to a displacement spectrum. Those integrations are only relative, not absolute. I will anddo present digitized data in all three parameters for some. I do not believe in producing a velocityspectrum because it is so limited as compared to an acceleration spectrum. Velocity (IPS) is agood language to translate into words and is a common language as it is irrespective of

frequency. So, you can iterate an amplitude and one can understand its magnitude or severity.


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.

A picture is worth a thousand words. You cant analyze what you cant see. Why waste yourtime with a velocity spectrum when it isnt even a true integration from acceleration to velocity.Integration is relative, not absolute. Work in acceleration and get used to it; its the right thing todo now and the way of doing in the future. It took some transition period to get from displacementto velocity. Machines fitted with anti-friction bearings should always be monitored in acceleration,and use acceleration spectra for diagnostics: 3600 RPM to 5 kHz. Likewise, if Im using a velocitytransducer or an eddy current probe I monitor IPS and mils respectively never integrating thespectra only displaying digitized data in all three parameters.

Both displacement and acceleration are respective of frequency, therefore velocity is thelanguage to speak in for clarity and ease of understanding. But in the analysis stage whengathering acceleration data use acceleration for analysis. Discipline yourself and youll find overtime your PdM program will evolve into planned scheduled maintenance and youll get maximumlife from the machine and eliminate overtime. I have successfully implemented such programs.Youll tear into a machine and realize that you have gotten maximum life: no need to pull themagnifying glass out and look for scratches. Ive seen people do that it stands out that its anexcuse for inability or a poor program.

Relationships of sinusoidal velocity, acceleration, & displacement

ENGLISH METRIC

V=(Pi)fD V=(Pi)fD

V=61.44 g/f V=1.56 g/f

g=0.0511f 2D g=2.013 f 2D

g=0.016 2Vf g=0.64 Vf


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D=0.3183 V/f D=0.3183 V/f

D=18.57 g/f 2 D=0.4968 g/f 2

NOTE: D= inches pk to pk or meters pk to pk

V= inches per second (IPS) meters per second

f= frequency in Hertz (Hz) or cycles per second (RPM/60)

g= 386.1 IPS 2

Constants for true sine waves only

rms value = 0.707 X peak value avg rms

rms value = 1.11 X avg value

peak value = 1.414 X rms value

peak value = 1.57 X avg value

average value = 0.637 X pk value P-P

pk to pk value = 2.0 X pk value

Microphones (acoustics) are not usually associated with machines except for OSHA sound levelmeasurements.

But, if you have a machine high and away and dont have transducers mounted, then a highlydirectional microphone can assist for frequency analysis.

This will sometimes produces good results and always is better than no approach or program atall.


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Sound isnt our topic although sound is vibration and vibration is sound. We wont be getting intomedia that has so many variables and dampening factors and background noise etc. But, heresa chart nonetheless.


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In a PdM program we normally are concerned with bearing cap data and sometimes withpermanently installed transducers. However, one must know that the transducer is in calibration.

An outside consultant may choose to use known transducers such as his or her ownaccelerometers for bearing cap data. Normally, (for example) I will go into a control room andacquire data directly from the panel by plugging in to an existing system such as a BentleyNevada 3300; this gives me rotor dynamics. But, I also acquire bearing cap data.

NOTE: A normally good machinery analyses instrument system will cover 20 kHz to 0 Hz or DCand have transducers covering 0.05 Hz to 20 kHz.


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They may be phased matched having phase measuring capabilities down 30 RPM within 2%.Phase gathering triggering devices either photo tachs, laser, eddy current probes or strobes. Settransducers side by side to confirm amplitude/phase integrity as a field check.

High quality tachometer may be necessary when phase readings arent stable using conventionalphase gathering instruments.

OUT OF BALANCE CONDITION : Imbalance occurs at running speed and produces a cleansharp spike at 1X. Running speed vibration is very often misunderstood and gives manytechnicians problems. Ive seen technicians attempt to balance rotors with high 1X and almostnothing else - no 2X or 3X and relatively smooth the rest of the base band. Misalignment (gross)will totally manifest itself in 1X and youll play havoc attempting to balance that problem. Bearingproblems and faulty machine parts will manifest themselves into running speed vibration at somepercentage as the machine deteriorates. That percentage may be very small but a bearing flaw(for example) will produce drag and contribute some magnitude into running speed though itssource may not be determined. Analyze the spectra, different data points, and different positionswith phase data. Correct faults then balance. All too often I see technicians balance andamplitude at running speed will become acceptable and itll be called good. However, thatbalance job didnt magically cure the machine component that also has a fault.

Never just balance a machine to an acceptable vibration level and walk off with out some analysisto determine machine condition. Imbalance in vertical machines is usually highest transverse tothe flow or in the most flexible direction. Bottom mounted machines usually reveal higher 1Xvibration in the horizontal direction.

Once imbalance has been determined to be the fault, balance the number of planes necessary toachieve smooth machine operation.


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When field balancing one may want to use eddy current probes or existing transducers. Mostlarge turbo-machinery will have a permanent monitoring system installed that you can plug into ina control room or local panel.

On paper machine dryer cans where you balance two planes and still have excessive amplitude:does the phase match - yes, then whip is the problem and requires third plane balance or further

testing. The third plane is the center of the roll. 1X vibration problems . These are imbalance, resonance, bent shaft, external mechanical run-outs (coupling hub, pulley, etc., machine part, electrical, eccentrics) internal run-outs.

Phase measurements (see photos below) are very useful in determining misalignment and bentshaft but one of the easiest methods of detective work is to simply shut down the machine whenyou can and if practical. This enables you to monitor power off cascading to a complete stop. Usea good analyzer with capturing capabilities or a tape recorder when you can.

Often the vibration disappears upon power off if electrical in nature. By monitoring coast downone may record via instrument tape recorder, or internal capture in a real time analyzer,information that can identify resonance. Once the machine is shut down, physical measurementscan be taken; such as shaft run outs, coupling run outs, alignment, etc. On electric motors youmay find a chipped blade on its fan. A problem can be simple too.

St robe for phase and /or mot ion s tudy.

Photo tachometer fo r once per sync ort r igger.


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VIBRATION GUIDELINE CHART

Frequency Probable Cause Other Possible Causes

Running Speed (1X) Imbalance

MisalignmentBent ShaftResonance

Eccentric journals, gears or pulleysReciprocating forces

Electrical

Two Times orFirst Harmonic

(2X) MechanicalLooseness

Misalignment; high in the axial directionReciprocating forces

ResonanceLoose bearing or part

Second Harmonic(3X)

Misalignment(shaft to shaft)

Excessive axial clearanceElectrical; air gap

Internal misalignmentMachine part

Fourth 4X Coupling Problem This phenomenon occurs with coupling problem, but can also be bearing

loosenessResonance possibility in slower machines

Machine part Fifth 5X Machine Part Vane pass in pumpExcessive clearance

NOTE: Single volute pumps usually 3 or 5 vanes. Double volute pumps have even number of vanes. Non-clog pumps normallyhave two vane impellers. Pumps should have 12% cut water clearance so cavitation can be avoided.

Sixth 6X Machine Part Vane passing

Rotor slippage on shaft(usually found with 4X)

Sub-rotative43% typical

can occur @39%-48%

Oil Whirl Lubrication

Oil WhipFTF Fundamental Train Frequency

Half Running

Speed 1/2X Rub

In a sleeve bearing - rub (0.01 IPS)Resonance Drive Belts

Drive BeltsDefective machine parts

Line Frequency60 Hz Electrical

Rotor Bar ProblemEccentric rotor

Unequal air gapUnbalanced phases

Insulation Breakdown Line Sync Frequency

120 Hz Rotor Problem Rotor resonance

Torque pulses

Upper HarmonicFrequencies Gears

Gear wear, look for side bands of defective shaft speedFan speed x # blades (Aerodynamic)

Cavitation, impeller x # vanes (Hydraulic)Machine part

Upper Frequenciesnot Harmonic

Bearing DefectsLubrication

Inner race - BPIROuter race - BPOR

Ball Spin - BSFCage - FTF

Synchronous 2 pole motors operate @ 60 Hz (3600 RPM): A good real time analyzer may have a resolution of 0.0039 Hz orbetter with a dynamic range of 120 dB - good for analysis when a fault is detected: A must for third party consulting. Traceable to

the NIST is a requirement.


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OK, how do we check and solve for these problems?

Lets go to misalignment; it is usually associated with a 2X component along with 3X in the axialdirection. However, gross radial misalignment will manifest itself in 1X and not even show 2X or3X. Angular misalignment is usually found at 2X in the axial direction. Using phase as a toolmeasure both ends and across the coupling. When searching for an unknown source, dont forman opinion before youve gathered sufficient data. Ive seen people try fruitlessly to balance amisaligned machine. It happens too often. Of course a good maintenance program will havealignment records. And those alignment records should be truthful and exact so they can be usedfor an analysis tool. If physical measurements must be taken one may do so if the situationpermits.

Use good field proven techniques and procedures to gather alignment data and/or correctalignment.

Bent ley Nevada Al ignment ins t rument FixturLas er/Vibral ign Dual Beam

The procedures that follow are for all types of alignment. These are field proven and work. Theywill enable you to align in the shortest period of time. The types of alignment are: IndicatorReverse, Long Spacer Coupling and Rim & Face. The methods for these types are: Laser (singleand dual beam), dial indicators, parallels and micrometers.


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Of course this one with the big picture is my personal kit (shims are extra): PdMK-2.

Visit http://www.pdm-engineering.com


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ALIGNMENT PROCEDURES

SAFETY; lockout and tag. Rack out fuses and chain valves when necessary

! Ensure driven machine has no stress from piping or soft foot and that the anchor bolts are tight

! Inspect the feet and base of the machine to be aligned for burrs, roughness, dirt

! Evaluate if a temporary spacer is need or useful for this alignment process; note

! Inspect coupling and check for run outs

! Coupling halves must if possible rotate together for dynamic alignment

! Evaluate method of alignment to be used

! Which is best suited for this job

! Is axial thrusting a factor

! Collect SAG data and record

! Install brackets on machines and record machine dimensions

! Check for soft foot; correct as necessary

! Rough align within 1/16 inch

! Record alignment readings

! Are they valid?

! Mathematically correct and repeat?s thrust a consideration?

! Calculate shim and lateral shift change

! Via computer? Print and file.

! Calculator? Record, plot and file.

! Make changes and verify & PLOT

! If spacer was used, remove it at this time


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! PLOT THE FINAL ALIGNMENT DATA

! UNLOCK AND REMOVE TAGS; NOTIFY OPERATIONS

! PLACE RECORD AND PLOTS IN MAINTENANCE FILE

2X running speed - mechanical looseness is a prime factor when this type of vibration occurs. It isradial in nature and usually predominate in the vertical direction. It sometimes pays to acquiredata at the foot or split of a bearing cap. Reciprocating forces; are you analyzing a compressor?

If you are fortunate enough to have a good vibration lab, you can duplicate most vibrationsituations or create experiments for further study. Bentley Nevada markets a good lab kitcomplete with eddy current probes and oil whirl attachment.

Measurement techniques are important as well as applying common sense. Approach themachine like a crime scene. Notice everything; does the foundation appear correct and properlyisolated? Are there cracks on the Floor; stand on each side of the crack - is there a difference -measure? Can you feel or hear a beat? Use a stopwatch, count the beats over a five minuteperiod. Ive uncover the source of vibration using this technique. Peck on a sole plate, is therethud? Are there splits in the case or bearing housings - measure both sides. Eddy current probesgive rotor dynamics, but also take cap readings.

Cap readings make up machine and rotor movements. Is there a difference from machine tobase? What about phase end to end, radically? Phase axially: measure every ninety degrees.

In low frequency problems, resonance is usually a consideration. Can you alter speed or otherfactors? A coast down provides good information. While the unit is down, perform ring testing -this will give you natural frequency. One problem can excite another.


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Another consideration in taking low frequency measurements; low pass filters. Theyre availablein a variety of ranges. Low pass filters can let you blow up low frequency signals. This works wellespecially with an analyzer having a 90 dB range or better. Also real time zooming is a good tool.

This can give a resolution of 0.0156 Hz or better; very good to separate frequency components.Sixty Hertz from running speed; side bands around 60 Hz such as around 1.2 Hz delta freq andso on.

While were in low frequency stuff, lets consider half running speed. A rub in a sleeve bearing willshow up at and may be very severe at 0.03 IPS (inches per second).

What is a machines mass, dampening factor? A rub at 0.05 IPS is trouble. Also look for sub-harmonics. In reality; you never want to see a rub.

Sleeve bearings: rubs, excessive clearance, misalignment, lubrication and looseness are mainconcerns. Since these bearings ride on a film of oil and the hydraulic pressure provides certainlift, clearance is an important function. Excessive clearance will cause harmonic content. Oil whirlis - a riding up and slipping back on the journal; when it becomes violent it is called whip. Oilviscosity is an important factor and one must consider the type of oil system.

We have oil bath, oil circulation, ring oiled, mist lubed; etc. Lubrication usually isnt a big problemanymore. I once encountered an oil whirl in a machine with five tilting pad bearings. If a sleevebearing is loose in its housing it can produce a 4X component; make sure the 4X isnt beingproduced from another source. Again, always consider a phase study.

The fifth and sixth harmonic (5X & 6X); machine parts and looseness are main contributors but,the 6X can be generated by a loose rotor and is usually accompanied by 4X. You may havenever seen this in print before, but this comes from practical experience. Just like themisalignment condition manifesting itself exclusive in 1X. Physically setup that condition in amachine and let it prove itself.

I made this statement in 1983 about acceleration; within ten years everyone will work inacceleration. Velocity will only be used as the universal language and rightly so. However, youcant argue with success; if youre using velocity successfully and almost only worked in velocity:give acceleration a try. Back in 1980 velocity was the new kid on the block for most. I think youllbe glad you switched. Id rather fight than switch back. There was also a transition periodbetween displacement and velocity. Who works in mils today for a PdM program? Remember,acceleration is the right thing to do: integrating to velocity is not absolute only relative. There is no

pure integration and you cant analyze what you cant see.


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Anti-friction bearings: use both time waveform and frequency spectra. These bearings transmitforces more readily than sleeve bearings and the stiffest direction usually reveals a highermagnitude of vibration. Banding analysis and overall level diagnostics work well.

On 3600 RPM machines use a base band of 5 kHz. For purposes of resolution I normally view 2kHz as my primary base band. But, never limit anything when troubleshooting. Defective anti-

friction bearings are a product of mechanical deterioration. When this occurs, a sharp spike willbroaden: study spectral shape and use shape as a diagnostic tool. Overall analysis is also usefulbut always with the frequency spectra. Windowing as in different base bands is also a tool.

Theres more than just the Hanning window too. Explore! Technical Associates of Charlotte havea good section on A-F bearings; R-0792-3, page 2. A good analyzer is a very valuable too. Justany ole black box wont do. Theres more than shown.

This has been the common analytical approach since the late 70s. A word of warning; spikeenergy is not a good evaluation parameter, never rely on it for a tool. And, it isnt good at all onlow frequency machines; i.e.. paper machine dryer cans. On high RPM machines note theharmonics of bearing fundamentals. Another factor of detrimental high frequency vibrationsrelated to A-F bearings - shaft currents. This can be measured (shaft currents) with a good DMM.You can also have a buildup of static current that discharges through the bearing. Again, use 5kHz base band on 3600 & 1800 RPM machines in conjunction with your normal observancefrequencies. If magnitudes of vibration are observed near the end of the spectra (high frequencyregion), then you may want to look at the next higher base band on your analyzer.

With the absence of machine defects, bearing defects having a magnitude of 4-7 gs 0-P over 5kHz are nearing failure. This is a broad statement, mass & dampening must be taken into

account. Example: 5 gs 0-P over 5 kHz @ 3600 RPM usually will fail within a month; maybe alittle less, maybe a little more.

But, the same machine situation @ 1800 RPM may take two months to fail plus or minus a little.Please, this is an illustration, so dont hold me to exact numbers although the scenario is close. InPdM program mode use trending, if the program is old enough. Continuous monitoring systemsprovide good trending information much better than a monthly or quarterly route program.Monthly or quarterly monitoring programs require a good chief analysis. Trending is valuable oncontinuous monitoring programs but has short comings on anything less.


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Lastly, lubrication or lack of it. Check schedules, quantity per time interval, type, etc. A bearingsnatural frequency will be excited in the absence of lubrication. Lubrication makes the wheels goaround. Alignment makes them run longer, PdM makes them cost efficient.

Got a lube program? Your grease guns should be labeled one shot equals so many grams!Each grease lubed bearing should be given and exact quantity over a given time interval (i.e. 28

grams per month; 14 grams per two weeks). Classify machines as to speed and environment todetermine frequency of lubrication. Lubrication is your single most important program; notalignment or balancing or PdM. I have papers Ive written on grease lubed bearings andquantities per given time interval. I like to calculate that time/time interval as accurately aspossible. If I have a good PdM program it will fine tune those numbers. Therefore, when a goodPdM program is in place one can know when the lube is lacking. With this in mind; calculationsand estimations can be backed off slightly and fined tuned over time through frequency analysis.

Gearboxes: These can be very complicated; I dont consider any to be categorizes as simple.Correct gearbox set up is essential. It sometimes becomes necessary to stress a gearbox toachieve internal alignment. I was call on a very high H.P. unit operating at 12.0 gs 0-P @ gearmesh. Upon shut down I inspected and measured clearances. There was originally internalmisalignment. But, it had already worn a pattern. I recommended to continue operation as

distorting the case to correct internal misalignment would only cause an increase in vibrationlevel. They opted to distort the case. Vibration increased. I again recommended no action as itwould now wear a new pattern and reduce in magnitude. It was left there and monitored regularly.

At 18.0 g it was inspected and then put back in service to 20.0 gs. This is unusual but not odd. Always use time waveform as an analytical tool. The defective gear will be modulated or side-banded by the defective gears shaft speed. Also, look for a small `side spike on the side ofdefect peak in time waveform if a gear is cracked or chipped.

A voith coupling (high H.P.) may give you a bit of diagnostic problem as they can have anamplitude/frequency display in an axial position that appears excessive. But, Its a characteristicof that box.

Some of these things are only obtained from experience or being around someone withexperience. In troubleshooting always draw on all natural resources available to you.

I believe thats a good philosophy in most all aspects of everything you do. Gear mesh frequencyin most cases is in trouble at or around 10.0 gs (high frequency). Also, look for half gear mesh.How is the fundamental affected? Use phase.

Sometimes you are put in a position of doing diagnostics above your head. If you gotta, you gotta:get your feet wet. But, a critical, costly machine?

Maybe its time to call the outside consultant, who? Again, these are guidelines to help youtroubleshoot and solve your problem. Know when its time to call in help. I have developed these


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Disclaimer (to make the lawyers happy): This information is supplied by third parties and is not warranted for any 19

standards with and through others: The chief analyst must have at least ten years experience asan analyst with five years spent as an outside consultant. It shouldnt insult him if you ask for aresume and sample report as well as references. Is it warranty work; then the work must betraceable to the NIST, formerly The National Bureau of Standards, now, National Institute ofStandards and Technology.

I have developed standards for acceptance of pumps & motors, plus specifications for motorrebuild shops.

On a last note; dont over look the simple. Calibrate using a level, check calibration. Alignment check calibration before every job: Indicator Reverse, Long Spacer Coupling, Rim & Face andespecially Laser. Using a micrometer check against a standard before using.

The materials in this field guide were supplied by:SAM PICKENS ; PdM Engineering PO Box 23494 Macon, GA 31212-3494Phone 678-772-3166 Fax 386-684-4068
mailto:[email protected]://www.pdm-engineering.com/http://www.pdm-engineering.com/mailto:[email protected]

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Vibration TroubleShooting Guide