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IEEIATIm S W T DISPLACEMENT AND VIBRATION MEASUREMENTS FOR THE EARLY FAULT DETECTION IN
ROLLING ELEMENT BEARINGS
LEO SING LIM
A thesis submitted in fulfilment of the requirements for the degree of
Master of Engineering
Faculty of Engineering UNIVERSITI MALAYSIA SARAWAK
2004
'Phis thesis research project could not be completed without the assistance and support of
several indivitluals to whom the author wish to express his deepest ~adi*iudc. First of
all, the author wishes to take this opportrraity to sincerely thank his supervisor, Dr. IXa
Now lJng li~r his kind supervision, guidance and motivation given to see through Ihc
success of' this projc?cd.
Apart Gom t l~at : the author also wishes do thank all mecha~~ical lab assistants for
providing full assistance in ensuring the completion of his laboratory works. A sign of
gr;ztitudc is also Ibrjvarded to the Ministry of Science, Technology and the Environment
for their financial support awarded &rough the National Science Fellowship (NSF). Last
11uC not least, the author would also like to note the motivation and support given by his
fric?ads throughout this research project.
Abstract
liloXl kmg eelerneat bearings are among the most counarxaon elements wsc?d in i,hc? operation of'
rolalirmg; anracklines. They are, however, one of the weak points inx these. machines whcrtr u
large nraa,jority trf problems associated are caused by bearings failures. As a result,
condition monituraing of the rc~Bling element bearings is important in ordor to kc?ep these
mai:bineries in their proper op~erating condition. Analysis and mainl,err;ance rd'any rolling
c:lc:nnc?rnl, bearings fail-r;rres are made wn~rch easier if any fault can be idex~tified during its
early stage. Thus, it is the aim of" this research to investigate thcr rt?llativc sk~afl,
disp1an:cmcnt and bearing housing vibratio,n nzeasuremcrats for t,hc? early ihtaX~, de~r?el,ion
in rolling a:lcment bearings. Experiments were ~:onductetl on a robor ki t that clobely
sim.rnla6es the actual behaviorxr of rotating machines. In ordc?r to sirnmlal,e the? early signs
of' fault, elcvelloping, a single localized fault was inrduced on thc? oul,cr racc? and tire iurnc:r
race 18br kjtu8il beam-ings and roller k~earings, as well as on a rolling c>Xemr?n.l of ;a roller
lacasing. Bra lhis rcsearclu, vibrations caused by the good and faulty bearing for both
r:ategorics o f kpearings were analysed, ExperimentaX data from the relative shaft
displaccmernt aneasnrerments due to dyrramic vibrations of the shaft were analyscd using
time waveforxn analysis to detect the suiitlen changes in amplitude as a fixncticm sf tinrt?.
Thc bt?aring ilbarusia~g vibration signals captured were analysed with c:nvelape analysis to
detccl Ibt: re~~c?Citive iia~pulse signals caused by the bearing fault in fsequcrrcy dornixin.
ITronn /,hc exlaerirnc?ntal results, it was found that both techniqlxc?~ car1 successfr.irlly
indicatr? the rollirrg elennent bearings condition and can also &)e used to iderrtify
partlc~~llar allnmagcd component of a bearing. The experimental results also showed that
both auonilorilrg teellniques conrlplinlerlt each other.
Gallxs ~ l e r r ~ ~ n hergulca~g nzeyr~~pakan ko/?xporzeiz yare,: palir~g biasa d t g ~ ~ n a k a n d i dalam
o~~erus t sese8jua;de mesial putasan. la merupahan sakah satu tstik Kelenzahan bargt mesin
t~rsehul herana kebanycrkan masalah yang fimbul cxdalah dtsehakihan oleh kegagalcar~
galas. OJeh sebab ttu, penguwasan Keodaaan terhadap galas eleme1-s bergulirtg adrwbaJ~
pentia~~; unlulz mernastikan mesin-mesin _ ~ a n g d1,gunahan senliasa herada dalam
izocadaatn yan,g ma~muashan. An akisis dan pen,yelenggaraan sebaralxg masa lah kega4;alaxz.
galas plemen be)-guling mer~jads lebih mudah sehtraxzyca kemswkan awal pada galas
daj~ab drkesan dan dikerealpasti. "FuJ7uan penyekidikan ini iaCah vhc.nyiasa$ tehnih
pc2r1,gukuran anjakwre relati[ awci dan juga tehr~jlk per~gukuran getarale perumwh galos
uaatuk mpngesan sebarang herosakan awai pada galas ekemen berga~lir~g. Jthspertrnen-
eks~)er~,men telajz dQalankan deaagare menggunahan sebuah rotcsr kit yang b~rupaya
aas,en,stmulr~si periiaku s e b ~ n a r sebwaiz mesin berputar. Sa tu hesosakari yar~g meaj.3rerui1ai
tando tnnda awal kerosakan galas bedah dibual pada bahagian larian kuar d m larian
dalfim untuk 8;rwlas bebola dare pengguling, Selain iku, satu kerosakan .jugs dib~sat pada
elemen ped~ggull~zg unduk galas pengguling. ISalam peqyelidikan mi, gelaran yang
dihastlhmn taleh Jzedua-dua .Jen&s galas dalam kemdaar~ baik d a n rosak telah drsanalists,
Data yartAr dipprolehi dnrtpada pengukuran ar~jakan relullif aei yang berdasarkcrn
gelaran d i n a m ~ k pcada aei te2ah dianaltsis dengan mereggunakan analisis bent~lk
g~lomhang maser untuh mengewun sehamng perubahan amplitud seeara meaadadak
ine2au~aj.n. tnasa. Ss.yarat getaran yang dipprolehi dar~pada perurnail galas teSah dislnaltscs
d ( ~ n g a i ~ m~r-~ggunakan anakisis sampul untuh mengesan seharang ssyarat dedc~r~~yut
b~ru lang yang dihasilkan oEeh kerosahan pada gaka.3 di dala~re domazn fiekuensc.
Dartl~aida ke~~uttxscuuz eks~>esimen, dtdapatr bahawcr kedua-dun tekntfi tersebut bt~rupayar,
rnengesan Zderosakan pada galas elemen berguling dan juga berjaya mengenalpasti
kornponen galas ,yang telah mengalami kerosakan. Selain itu, kedua-dun teknik
pengawasa rnenunjukkan keputusan eksperimen yang sepadan di antara satu sama
lain.
TABLE OF CONTENTS
Acknowledgc?ment
Abstract
Abstsak
Table of Contents
List, of Figures
List of 'Tables
TEIt 1: INTRODUCTION
I. 1 Background
6.2 (bb%jeetives of the Research
1.3 Thesis Organization
TER 2: LITEEtATURE REVIEW
2.1 Maintenance Methods
2.2 Types of Bearings
2.2.1 Fluid film bearings
2.2.2 Rolling element bearings
2.3 Types of' Faults in Rolling Element Bearings and Their Causes
2.4 Rolling Element Bearings Frequencies
2.5 Techniques of Fault Detection in Rolling Element Bearings
PAGE
ii
iii
iv
vi
X
xiii
2,6 Vibration Analysis in Rolling Element It3earixags
2.6, I 1Tistor.y of I";luXt detection usirrg vibration analysis
2.6.2 Vabration measureulend syste~ras
2.6.3 Gauschs of vibrations
2.6.4 '1"ypes of vibration transducers and rneasurcments
2-6.5 Vittration sigrral srnaly sis
2.6.6 NJethods of vibration rnasalitoring
2.7 Surmmary
C:EiAll)llII:TC 3; METEXLODOLCIGY EWERIMENrTAL SETUP
3-1 Yrttisiudracliorl
;%.2 IPro~ac3rtics of the Test Bearinlgs
3.3 XJe\rellopment or tkac Components
1 Shaft
3.3.2 XSearing housing
3.4 Fe:xpc*rixncntal Setup for Relative Sl.raR 1)isplacement Measurement
3.4.31 'Yest rig setup
3,4 -2 AI3RE@ for WindowsTM soRware
3.4.3 208-1) Data Acquisition Interhce ZJnlt
3.5 Rxperirnental Setup for Bearing I-lousing Vibration Mcasurernent
3.5.1 Test rig setup
3.5.2 SENrI"INEBl'rM Machine M[~nitoa.ing Software
35.3 Ilatts Collector System - 2526 Series
t3.6i 8 urn rntrry
GXI'EA1I'?'EI4: 4: EXPERLMEINFfi RESUIJTS OF ELEIAKFIW SWFT
BIXSPPAC:EMERT1' MEASUREMENT
4. I Inlr'odraclion
4.2 OX.?jieetivcs o f the Hxperiments
4.3 F:xporixnoniaX Results and 13isctassions
4 -3.1 Non-tledbctivc loezrnngs
4.3.2 '6"learings vvitln a single outer race fault
4.3.3 Bearings with a single ixnner race fault
4 . 4 Xloller beizring witla. ;I single rolling elernenl f'tmult
4.4 Xrrn~nrrary
CIIAly'rElt 6: EXPERIMENTILL RESUI,TS OF IEEARXNG HCIIJSlN6:
VII3MrIQ)N MEASUREMENT
5.1 Inlroduction
5.2 Ohjcetives of lJrc Experiments
5.3 Bil:xpi?rimenl,al Results and IJiscussions
5.3.1 Non -defc?etivc bearings
5,3.2 Bearixags with a singlc outer. race fatalt
5.3.3 Vjearings with a single inner race fault
5.3.4 Roller bearing with a single rollirlg clement fault
5.4 8ummiary
5.5 Corrc?lal,lrsn Belwii?en Relative ShaR Displacemexll and nearing XSousi ng
Vibration Measureanents
CHAPTER 6: SUMMARY AND CONCLUSIONS
REFERENCES
APPENDIX
Ctandition monitoring maintenance
Rolling e1e:ment bearings terminoloa
C utimay view of a single row deelo-g~roove ball bearings
B:uCaway view 01 a double row deep-6;rsoowc? ball ilearing
Cutaway view of an angular contact ball bearing
Clataway view of a cylindrical roller bearing
Cutziway view of a sphert~c;ll roller bearing
(~~;n.tziway view of a tapered roller bearixrg
Iluhiway view o f a needle roller bearing
Cutr"~w;~y view of a thrust, ball bearing
Schematic ciiapam of the rolling clilcmermt bearing gecsmctrg
Important stages in vibration measanrements
Test bearings
Schcrmatic diugrun~ of the sha-li,
Sc:hematic diapana of the bearing housing
"I"cst rig sc?tup for relative shaft displacemerjt measurcunenl
Bevelled faces on the bearing and probe blocks
Schematic diagram of the proximity l)robc?s mounted on prok~o
marount, (a) viewed from the drive anti Cb3 viewed from the left sidc.
Tmt rig setup for bearing housing vibration measurement
The structure of tho Plant Wirrdow and Route Wirrdow
PAGE
5
9
I I
11
12
1 :-b
13
14
15
15
18
25
35
13 8
t38
40
4 2
43
LIST OF TABLES
TABLE
3.1
3.2
3.3
3.4
Ball and roller bearings dimensions
Calculated bearing frequencies for shaft rotational speed at
2000 rpm
Approximate ratio of bearing frequencies to shaft speed frequency
RK 4 Rotor Kit specifications
PAGE
36
36
37
4 1
... X l l l
vibratiiora cI.al-nracter(isties of rolling element bearings is imp~ortant for eff~?c:tivc: ;~rr;alysis
(YBl"araciora & (Ihornelhury, 1997). Vibration signals resrmlting from the rolling clcnneat
bearilr~gs Fault present a rich contenhof pllysical information, which can lead to tho clear
itlentificatiorr abor~lt the nature of'thc fault with axa appropriate analysis.
1% Objli?cdivc?s of the Research
'I'tris r.esenre1.s. invc~lves tho investigatiox~ of techniques rrsed fior early tloteetion trf arxy
iroaring hjllts. L3all arnd roller bearings were wsc:d in the analysis of' transducer response?
l o ;a singlo loealiza2d fault on the outer race, inner race and a roljing olcmr?rat,
irespcc:tiva?lly. 'Il%erefore, the main objedives of the? currenl researellr incl ude:
1. "'0 iravcstigale tkre fc?asibility of using relative shaR displacs:meurl, for tbc?
(lctection of" rolling element bearing faults. Displacements or dyrntzrrlie
vnbrations of the shaft are measure directly by using proximiCy probes,
mountc?d elosc to the bearing llnder test.
2. 1'0 investigate the application of bearing housing vibration measnrc?m(?nL
xnet!aod for "LC detec1,ion of ball and roller bearings faarlt. A casing-mtrunli,cd
trarrstlueer is mounted on Cop sf the bearirrg ht~uxsi~rg to pick up casing
vibratiitrrx siigrlals caused by good and hulty bearings.
3, "Yo ovaluato the effectiveness of relative shaft displacelmcnt and be~nring;
krcsusing vibration measurements techniques fbr the deteetatrn and
idcntmficaation trf any rolling elemelrat bearings faull arnd its severi-V,y.
1-3 Thesis Organization
Tllis thc:sis is organized into six related ch;zpders. Below is the description for ezzeh of tho
ch;iptr?r from chaptc?rs 2 Ca 6.
Chapter 2 irlcludes the literature review about conventiorlal antl rrroderr~
maintenance methods, types of b c a ~ n g s and its properties, as well as teclzniques -ibr
rolling element hearings fault detection. In addition, vibration analysis teehniquci is also
discussed in depth.
C:lsapter 3 covers the methodology and experimental setup in this research
project. IXcre, a rJescription or the experimental approaches for both rela-iivc shaft
dispiaeemon2, ;md bearing housing vibration measurements techniques will be made,
I3oacriplion for the hardware and software used arc also includt:d.
Chapter 4 lbcuses on the experiments conducted to investigate the reladive shaft
displaccncnt measurement tecl-znique. Resides, analysis of the results ant1 discussions
arc matlo fur each of Ihc? experiment.
CllapGer 5 presents the results obtaincd from the experiments conducted under
hearing housing vibration measurement technique. The results are analysed antl
discussions ihr each ofthe experiment are included.
Final conclusions of this research are present in the last chapter, In additior~,
suggcst,ior.rs for future research arc also offered.
LJl"l'E1WFmE REVIEW
2.1 Mainterranccl? Mothods
'T'raditiornal machinery maintenance prae4,ice in industry can broadly bn cadeg;orihsc?d ixn
two mrelkaods; they are, run to fail~rre and preventive maintena~rce (lF$riic?l & l(j;jor, 1989).
l n r-t~nm to Fdi I txrc ~.an;iia ten;mce prac tised, machir~ery would not be mrrirntained until i4,
broke down. This is the simplest approach to maintmamce and the systc?m rcsyrrirtrd .120
ilmpXomcnt could be extremely simple, Run to fadure can also X>e eonsida?reri as tho
dohull main tcrxanee action, since the possibility of an urxexpeeted failure will always
c?xis.l,. qM"Fnt? tlrawloacks of this approach depencll on the consequencr? of fzilurc? and
urtc?xpc>ctod failaures are disruptive B,o existing ae1,ivities. This practiet? may halt
~~rorJrrctinn ant3 result in the loss of h ~mdreds or tho-rrsarrds of dolars. On the othcr tlimnd,
pre?verak,ivc? rwnaixrtenanet? is an organizr:d activity designed to lnrevcnt tho sutddc?xl hilrrre
of oqr r ipurnea.111 components anaor syslern, where id requires the scheduled inspection
and/or raplacement of parts a t pre-determinc?d intervals. This maintenance helps to
prol,ecI, assc!ts alrrd proloxrg the usehl lift? of producticln equipment. The dif'fieul ty wit11
this ancftXrrori lies in the fad that ofien the components in grrod working condit,ic~n arc?
rc>lrlae(:d, wl~iWt3 ira many occasions damage is done during the process of rebuilding.
"'he idoal miaintenance st rate^ is that machines are c~nlg stoppc?d if3lheir
coxnd ition dernands it. Therelbre, condition monitoring as illustraterl in ;tiqigura 2. I , has
since spread rapidly thrclu& most industries cmployjng rot,atirrg machinery. Contiitio~x
rnonid,orinl~ ranc?ans keeping careful watch of' machinery and to detect the onst?C o f claangcs
in operating conditions that carr signal a breakdom. Upon dcteef,non of" such conditions,
ttle rnairatcaaancc? pmfessional can take appropriate actions to address the problcnn and
evela determine a Lime framc? within which maintenance must be carried out f,tr avoid awry
disruption to production. In this kind of maintenarrce stratt:gy, cornponexai,~ arc only
replaced when they are as close to the end of their uselirl life as possible (Rtrsaler, 1998).
Ii~?ec?rttBy, new tc:chncllo~"y in electronics axld computer Lechnolo~y enables nlaintenanco
professionals to gather and process extensive amalumts of data, and f,o xnclrc? accurately
dr:t~:n nine macbirao condition. Rarkov and A~ovtsev (1995) rncntioned {,hat, tht? ncw
gc~~eratir~ra of condition monitoring system can reliably detect not, only Lha, if,otcm.rliailly
ilangcroers faults a t Ihc initial stage of thcir developmenl,, but also identify tho cxdct type
(sf ' fa11 P 1 unad its severity.
E'igrare 2-1: (Zonditlon monitoring maintenance (Brcel& Kjaer, 1989)
In fact, condition monitoring can provide several advantages over other
maintenance strategies (Barron, 1996). These advantages are:
Improved availability of equipment
Improvement in equipment availability can occur for several reasons. Firstly,
condition monitoring can reduce the amount of planned maintenance, since
maintenance is done only when needed. Secondly, if the total number of
unscheduled failures is reduced, there will be a corresponding reduction in
the overall time that a machine is unavailable while defects are being
repaired. Finally, condition monitoring can reduce the possibility of secondary
damage by predicting the onset of the failure, which mean that the average
repair time of an unexpected failure should also be less.
Reduced breakdown costs
As condition monitoring has the ability to predict many in-service failures,
this in turn can reduce the numbers of spares kept in stock because spares
need only be purchased when it is required. In addition, by reducing the
number of breakdowns, the staffing levels needed to cope with unexpected
breakdowns may also be lower.
Improved reliability and safety
Reliability can be improved by reducing the number of faults introduced
during scheduled maintenance. This improvement is based on the premise
that a significant number of faults develop during the early stages of a
component's life and mistakes that can lead to failures may be initiated
during any rework. By using the predictive nature of condition monitoring, it
is possible to remove or to replace a piece of equipment before serious
consequence arises.
Generally, large majorities of problems in rotating machines are caused by faulty
bearings (Neale, 1995). It is very important for the maintenance professional to
understand the bearing characteristics before any corrective actions can be taken.
Ilence, the following section discusses the types of bearings and its characteristics.
2.2 Types of Bearings
The basic purpose of a bearing is to provide a near frictionless environment to support
and guide a rotating shaft. In principle, bearings can fit into two main categories:
namely, fluid film bearings and rolling element bearings (Rothbard, 1996).
2.2.1 Fluid film hearings
Thcse bearings are the most widely used plain bearing. They rely on lubricant viscosity
to separate the bearing surfaces. The rotating shaft drags the lubricant around fbrrning
a supporting wedge and that is why these bearings usually need a lubrication system.
'J'hc continuous lubrication acts to cool the bearing, which allow fluid film bearings to
support high shaft speeds and heavy loads. Fluid film bearings are used in some
applications, such as in small electric motors, steam turbines for electric power
generation, automobile and aircraft piston engines. By properly designed and lubricated,
these bearings are very reliable and offer lives measured in decades for some
applications.
According to Jc?ffrey (19911, fluid IXlm bearings may bc: classified by t1-1: 1 1 rl,ii:rle c,r:I
function; they are, journal bearings and thrust hearings. Journal bearing is
1,i:aring in whicls two surface moves relative to each other without the benefil, :t.i Irr I I I I ~ ;
elt?rnent. Thus, there is sliding contact. For the case of a bearirlg on the rotalr'i irra; i J 7 , I " I , ,
the portion of lhc rotating shale ad the bearing is called the journal and tho (,?I,- 0 i i s s 1 1 - i y
part that support the load is the bearing. A journal bearing in its simplest
jrxsl a bushing or a reamed bole in a machine for supporting a rotating s
bearing extends compIetciy around the shaR, it is called as a full journa : I : .x~J~~ I ;
Whereas it is called a partial journal-beanjng if the angle of wrap is less than ""C'iiTcm 'll'~~ 1:'
partial journal bearing may be used when the load always acts in one dir
sirrrplest form of thrust bcaring consists of two opposed washers with some
srxppiying lubricant to the interhcc. Thrust bearings accc~mmotlate the axin
of a rottzting shaft. They arc? usually used in coqjunction with journal bear-inylc* t~ c r r l r,
Iubricated by grease, which leaks from the ends of the journal housings.
2 - 2 2 Rolling element bearings
I'reviomsly, the fluid film bearings were the prevalent style used in rnosi, r n I,.] i,11 I
rnaelrinery. Ilovvever, as metallurgy and machining techniques progressed tJI.1,
elernent hearings giiiaed greater usage. Rolling elcrnent bearings are, at pr, ? : ? r r ~ , , II,I I
most widely used of ail bearing types and first choice for gc?neral applic;itisil,r~ [ i i t i i , ' , ,
1999). 'The advantages of rolling e1eunen"iearings are its ability do support b:ri,h .* , I I ;~II
and axial loads in the same bearing? low starling friction and operating frii,, i y i r , : A ~ ~ * l l
Lower sensitivity Lo Iilibricatlon comp~lred to iluid f"rm bc?arings, Figure 2.2 ilins l1t.i ~,r,rk i, i i ,
common terminology used in descr-ibing rolling element hearings (Av,n ll~-n,? (L
13aurrreister, 1987).
* Cages
I:ugc?s also called as separator or retainer. The purposes of' cages arc usetl to
spact? the rolling elenrrcnl,~ from each other. Cages arc? i'nrnishcd in a wide
variety of' materials and construction, such as pressed-stet71 cages, riwetcd or
cli arcllcd. lilearings without cages are referred as firll-complexnenl.
Rollirag elemenlt bearir~gs fall into two main clasuifications, Lhc?*y arc? ball bcarirags
arrd r o i l ~ r . boarings, E3all bearings are classified according to the ring eonligur;btioxls,
such ;IS ~.Bc:(?p groovt?, angular contact, and thrust typos. Rollcrr k~cizrings on GExo other. BlaraaX
are a:fassifietl ;recording to the shape of the rollers, such as cylirrdsieal, nocdlc, taper and
sphcli-ict~l (Moil, 1999). Some of the nnore common rolling c?lement Inr;:arings lor kxjth ball
anrt.4 rollor hcuriings are ilustrtited below and their ch;lracteristit:s an: desc~ibed briefly.
Single row deep-poove ball bearings
Thr?st? bei~ri~ags, as showlm in Figure 2.3, are probably tho no st widely used. A
d ~ p groove? is formeti on each inner and outer rings of a dc?ep grcrtrvo X~all
bearing. These bearings can handle both radial and thrust loads and it
rssualily hunt$ in applications, where the load is relatively small. l a a ball
bt?aring, thr? load is t,ransmit,te?d fionrr the outer race l o the ball and from the
lraaXl 10 the inner race. Since the ball is a sphere, i t only coa4,aets the inner aratl
OU~,E:B" race at a very small point, which helps il spin very smoothly. Eut il also
metnras that there is not very much contact area holding that load, 60 if the
bearlaig is overloadecl the balls can dcfomm or squish, ruining the bc?aring.
Figure 2.3: G~~taway view af a single row deep-groove? ball ba:;arings (The 'l'orrington (2ornpany)
* Dou'k~Ic? raw deep-poove ball bearings
rls shown in Figure 2.4, double raw deep-groove hall bea-srillgs provide lbr
heavy radial and light thrust loads without increasing tl-~c? oertc?r diameter of'
i,hc ksearin~gs. Adding a seeoxld row of balls increases the radial load carrying
capacity eorrlpared with the single row design becausc more balls siaare tint?
load. '6he greater width of double TOW beaxbing often aalversely affects tho
misaligrl mcnt capability.
Fig~rre 2.4: Cutaway view of a double row deep-gn~ovc Gall bearing (ETctovc?r-NSK Bearing Company)