DEVELOPMENT OF A TEST DEVICE FOR THE EVALUATION OF JOURNAL BEARINGS

Transcription

1 DEVELOPMENT OF A TEST DEVICE FOR THE EVALUATION OF JOURNAL BEARINGS K. SANDVIK 1, A. LEHTOVAARA 1 *, E. MAKKONEN 1, M. KALLIO 2, K. KUVAJA 2, V-T. KUOKKALA 3. 1 Tampr Univrsity of Tchnology, Mchanics and Dsign P.O.Box 589, FIN Tampr, Finland *Corrsponding author: arto.lhtovaara@tut.fi 2 Mtso Minrals, P.O.Box 306, FIN Tampr, Finland 3 Tampr Univrsity of Tchnology, Matrials Scinc, Tampr War Cntr, P.O.Box 589, FIN Tampr, Finland ABSTRACT Journal and thrust arings ar widly usd in havy industry. Today, thr is a growing nd for studying diffrnt kinds of nw aring matrial and coating solutions in oprating conditions whr full film lurication cannot achivd or sustaind. A tst dvic for th valuation of journal arings was dvlopd. Th dvic consists of a rotating shaft and four stationary tst arings. This schm liminats th nd for support arings, allowing an accurat masurmnt of friction. Th initial tsts wr carrid out with a varity of loads and sliding spds in mixd and full film rgims. Th friction rsults in th form of a Strick curv wr otaind and found to in lin with gnral trnds. Th rsults also indicat that th aring lift-off spd occurs whn th valu of th non-dimnsional n / p - paramtr is in th rang of Kywords: hydrodynamic lurication, journal arings, tst dvic, friction pro INTRODUCTION Journal and thrust arings ar widly usd in havy industry. Th main advantags of ths arings ar thir vry low friction cofficint and no-war conditions, whn thy oprat with full film lurication. Furthr, thy allow transint loading and thy withstand dirty oprating conditions, which maks thm vry suital, for xampl, for ston crushr applications. Howvr, challngs may appar whn full film lurication cannot achivd or sustaind. This occurs at low sliding vlocitis comind with high loading, which com incrasingly vidnt if aring start and stop actions ar introducd undr loadd conditions. Othr possil rasons ar intrruptions in th oil fd and shaft misalignmnt. Ths oprating conditions lads to mixd or oundary lurication conditions, whr th load is partially (mixd) or totally (oundary) carrid y surfac aspritis. In oundary lurication conditions, prvntion of total mtal-to-mtal adhsion twn surfacs may nhancd y vry thin (molcular lvl) raction layrs formd y luricant additivs. Th rol of ths matrials and luricant proprtis ar clarly important undr ths oprating conditions. Th lurication conditions in sliding arings can oftn rprsntd y a Strick curv, which shows that th lurication conditions strongly affct th friction cofficint and th damag risk to th sliding aring. Th thortical aspcts and main proprtis of hydrodynamic journal arings can found, for xampl, in [1-3]. Th thr-dimnsional transint modls for th hydrodynamic lurication of journal and thrust arings hav n dvlopd on th asis of th Rynolds quation. Th journal 12

2 aring modl includs faturs such as thrmal ffcts, shaft misalignmnt, axial luricant supply groov, varying aring gomtry and th non-floodd oil inlt flow [4]. Th tst dvic for th valuation of thrust arings has alrady n dvlopd and th rsults wr confirmd y comparison with th numrical thrust aring modl [5]. Th modls ar formulatd in such as way that thy can applid in common nginring practic in industris rquiring a rasonaly fast and asily applical modl. Mor complx numrical modls also xist, ut thy may not yt part of common nginring practic in industry. Howvr, xprimntal tsting is clarly ndd for vrifying th numrical modl for journal arings and for dfining ralistic input valus for th modl. Today, thr is a growing nd for study of diffrnt kinds of nw aring matrial and coating solutions in oprating conditions whr full film lurication cannot achivd or sustaind. This calls for xprimnts in mixd and oundary lurication conditions. For xampl, in th most dmanding applications, such as ston crushrs, lad is usd in a aring matrial caus of its suprior dry lurication and mdding proprtis as wll as its tolration of shaft misalignmnt. Howvr, lad is an nvironmntal and occupational hazard at all stags of th product lifspan. Th Europan Union has takn stps to an th us of lad, thus crating a nd for a sustitut. Finding lad-fr or low lad contnt aring matrials is challnging and xpnsiv and it will invitaly involv fild tsts to validat promising sustitut matrials. Bfor this stag is rachd, laoratory scal tsts will ndd for scrning purposs. Various typs of dvics for tsting journal arings on a laoratory scal hav n dvlopd, for xampl in [6-8]. In addition to a tst aring unit and fram, th othr main componnts ar normally loading, driv, lurication, control and masuring systms. Th tst aring unit typically consists of on tst aring, its housing togthr with a shaft and support arings. A comprhnsiv dscription of a laoratory tst rig and in particular th instrumntation for tsting a hydrodynamic thrust aring is givn in [9]. A survy of xprimntal data for fixd gomtry hydrodynamic journal arings is givn in [10]. In this study, th dvlopmnt of a tst dvic for th valuation of journal arings undr a varity of lurication rgims is dscrid. In addition, th initial friction rsults otaind with tst dvic ar shown in th form of a Strick curv and thn discussd. HYDRODYNAMIC JOURNAL BEARINGS In this study, a journal aring consists of a rotating shaft within a stationary aring (ushing), as shown in Fig. 1. Th circular aring includs an axial luricant supply groov. Figur 1. Illustration of hydrodynamic journal aring. In stady-stat oprating conditions, th loadinducd shaft ccntricity with th ush allows th convrging wdg-shapd gomtry of th luricant film which, togthr with th shaft rotation, producs th load supporting hydrodynamic film. Th dgr of ccntricity adjusts itslf until th load is alancd y th prssur gnratd in th convrging luricant film. Th lin of cntrs (x 1 ), whr th minimum and maximum film thicknsss ar locatd, is inclind to th load lin at th attitud angl. This angl is 13

3 dpndnt on th oprating conditions. In a transint cas, a squz film ffct may also momntarily maintain th lurication film. Fig. 1 also shows an unwrappd journal aring, lngth r and width. Th solution of th hydrodynamic lurication quations twn th shaft and aring is asd on th Rynolds quation. Allowing for sid lakag, assuming a Nwtonian luricant and nglcting fluid inrtia ffcts, th transint Rynolds quation for an incomprssil luricant is: h x 3 p h x y 3 p u y 6 h h 12 x t (1) with th condition p 0 in th domain and p = 0 at th oundaris. Film thicknss h and prssur distriution p can solvd numrically from th Rynolds quation, whr u is th sliding spd and th ffctiv viscosity. Friction forc F in th x-dirction is calculatd y intgrating th shar strss of th luricant ovr th aring ara: / 2 2 r h dp u F dxdy (2) / dx h Th corrsponding friction cofficint f and powr loss h p can xprssd as: F w f (3) p r h F u (4) Assuming that a proportion K of th total hat gnratd y friction is carrid away y th luricant, th maximum tmpratur ris of th luricant T is givn as [3]: whr q in rprsnts luricant flow to th aring. Th ffctiv tmpratur T within th luricant is approximatd y th quation: T T T / 2 (6) in Th ffctiv viscosity in th aring is dtrmind from th ffctiv tmpratur. A dtaild dscription of th govrning quations rlatd to th modling aspcts of a hydrodynamic journal aring is prsntd in rfrnc [4]. EXPERIMENTAL Tst dvic Thr is nd for tsts with diffrnt kinds of matrials, coatings and surfac topographis in mixd and oundary lurication rgim as wll as tsts to vrify th hydrodynamic modl in full film rgim. This mphasizs th following faturs of th tst dvic: a) th wid oprating rang across diffrnt lurication rgims, ) an accurat friction masurmnt to stalish th Strick curvs and rlatd aring lift-off spds c) a larg nough aring siz to simulat larg-scal arings rasonaly wll, d) a vrsatil luricant fd control and ) an advancd instrumntation. Th dvlopmnt procss culminatd in a tst configuration, whr a shaft is rotating within four stationary tst arings, as shown in Fig. 2. This schm liminats th usual nd for support arings, whos frictional ffcts must somhow caliratd out from th shaft total torqu. This may oftn difficult and always includs a margin of rror. In addition, a configuration with four tst arings in paralll givs mor statistical information into th rsults sinc ach aring can also monitord individually. T 2Kh p (5) c p q in 14

4 Figur 2. Th shaft and arings with th forcs acting on thm Th principl of th tst dvic is shown in Fig. 3. An lctric motor and a loading fram ar oltd to th rigid main fram. Th lctric motor rotats th shaft, which is supportd y four tst arings. A larg lctric motor coupld to a frquncy convrtr prmits variation of th rotation spd, and hnc allows tsting undr all lurication rgims. Th load is applid with a hydraulic cylindr, which is connctd to th loading fram. Th applid load F O affcts th two middl arings whil an qual and opposit raction forc acts on th two arings on th sids rsulting in an qual loading F N on all arings. Th housings of th tst arings ar slf-aligning liminating th dg prssurs typically causd y shaft misalignmnt and dflction. A lurication unit is usd to supply oil to ach of th four tst arings through sparat piping. Th oil is fd to th arings on th maximum claranc sid. Th angl twn th axial lurication groov and th dirction of th normal loading can adjustd from -40 to 40. Figur 3. Th tst dvic as dvlopd Th oprational paramtrs, which ar th normal load, th shaft rotation spd and th oil supply flow rat, tmpratur and prssur, ar all monitord and can adjustd continuously. Th normal loading is masurd with two paralll forc clls. Idntical forc valus in oth clls also nsur that th loading is vnly distriutd across th four tst arings. Th load cll for masuring th driving torqu, i.. total frictional momnt of th tst arings, is connctd twn th tst and motor shafts via acklash-fr couplings, which ar rigid with rspct to torsion, ut which allow som nding. Th friction cofficint f can drivd from th masurd forcs as follows: M M f (7) 4r F 2r F N O whr r is th radius of th shaft, F N th load acting on ach aring, F O th cylindr load and M th friction torqu. Th lurication circuit and th rlatd masurmnts ar shown in Fig

5 hav innr diamtrs of 60 mm and a lngth of 30 mm. Thr is an axial oil supply groov on th innr surfac of th aring. Th locations of th thrmocoupls in aring 2 ar shown in Fig. 5. In othr arings only th middl location is in us. Th shaft is 60 mm in diamtr, and lngth of th aring surfac is 229 mm, to accommodat four arings with appropriat spacing. Figur 4. Th lurication chart and th location of tmpratur T, prssur P and flow rat Q masurmnts. Th total luricant supply tmpratur, prssur, and flow rat can masurd from th output of th lurication unit. Th control of th luricant tank, and hnc th aring inlt tmpraturs, is asd on this tmpratur masurmnt. Th luricant is thn fd to th tst arings, whr ths paramtrs ar masurd individually at th inlt to ach aring. Fin tuning of th flow rats is also nald in ordr to achiv an qual flow rat in ach aring. Th tmpraturs of ach aring ack (th outr surfac of aring) can masurd at a spcifid location, so th prformanc of ach aring can monitord individually in trms of frictional nrgy. Ths masurmnts ar mad in th prssurizd zon of fluid film, typically at an angl of 20 dgrs from th dirction of normal load. On of th tst aring acks is also providd with four additional tmpratur dtctors to follow th tmpratur distriution around th aring. Th dtction of th oil outlt and th surrounding tmpraturs togthr with oil inlt tmpraturs and flow rats allow an stimation of th total hat transfrrd y th oil. All tmpraturs ar masurd with thrmocoupls. Tst arings and shaft A schmatic viw of th tst aring and th shaft is shown in Fig. 5. Th tst arings Figur 5. Th tst aring and shaft with th locations of th arings indicatd 1 4. Journal aring prformanc is known to snsitiv for aring claranc and roundnss so particular attntion was focusd on masuring ths critical aring dimnsions for th tsts. In addition, th man Ra roughnss and th man diamtrs wr masurd for ach tst aring and shaft. Th shaft surfac roughnss was masurd at 27 points and for ach aring at 16 points. Th innr diamtrs of th arings wr masurd with 3-point micromtr aftr thy had n installd in th housings. Th valu for th man diamtr of ach aring is asd on 12 masurmnts. Th variation in this diamtr valu with diffrnt coordinat angls (Fig.1) indicats th dgr of roundnss of th aring. Shaft diamtrs wr masurd with a micromtr at 12 points. Th claranc is th diffrnc twn th man valu of th innr diamtr of th aring and man valu of th diamtr of th shaft. Tst matrix Th aim of th initial tsts was to dtrmin th aility of th tst dvic to mt th varity of load conditions. Th tst dvic was first hatd y ltting th luricant 16

6 circulat through th dvic ovrnight undr tst tmpratur conditions. Th friction torqu mtr was carfully caliratd for and aftr th tsts. Thr load lvls wr usd with th projctd prssurs of 2, 6 and 12 MPa. Each loading was carrid out at ight diffrnt sliding spds, ach stp having a tmpratur stailizing intrval of 15 minuts. An avrag oil inlt prssur was kpt at aout 0.15MPa, which mans that th oil inlt flow rat varis as a function of sliding spd. Th angl twn th axial lurication groov and th dirction of normal loading was 20, i.. th lurication groov narst to th point of th maximum claranc. Th aring ack tmpraturs wr masurd at a point 180 dgrs from th lurication groov. Th luricant usd was ISO VG 150 industrial gar oil. In this initial tst, sals twn th shaft and th loading fram wr usd. In latr tsts ths sals wr rmovd, which liminats any xtrnal friction losss. RESULTS AND DISCUSSION Th tmprd shaft matrial usd in this study was 34CrNiMo6 and th arings wr mad from CuSn10P10. Th avrag aring claranc was 172 m and th avrag Ra roughnss was 0.13 m for th shaft and 0.34 m for th arings. Th oil inlt tmpratur was 50 C. Th aring ack tmpraturs and friction cofficints as a function of tim, with a loading of 6 MPa, ar shown in Fig. 6. Fig. 6 shows that at th lowst spd th friction cofficint is alrady high, which indicats that th arings ar oprating in a mixd lurication rgim. During this load stp, friction dcrass which is du to th running-in of th aring. As th sliding spd is incrasd, th minimum friction cofficint can found in a controlld way. At this stag, th aring ack tmpraturs rmaind fairly constant and nar th lvl of th oil inlt tmpratur. This indicats that frictional hat is high nough to covr th hat losss to th tst dvic and to th surroundings. Furthr incrass in sliding spd gradually rais th friction cofficint showing that a full film hydrodynamic lurication rgim has n com into opration. Similarly, th aring tmpratur incrass along with frictional powr loss as th sliding spd incrass. Outr arings 1 and 4 hav vry similar tmpraturs as do innr arings 2 and 3. This indicats a vry good match of oprating and frictional conditions in ach group. Th slight tmpratur diffrnc (lss than thr dgrs) twn ths groups is du to th mor fficint hat transfr from th outr arings, and hnc slightly rducd tmpraturs. Incrasing tmpratur trnds at th nd of th load stps at last in highr sliding spds show that th stailizing intrval of 15 minuts is not nough to achiv complt stady-stat oprating conditions. Hnc, th slight dcrasing trnd in friction can still osrvd. Howvr, th corrct lvl of th friction cofficint in th full film rgim was confirmd y th modl rsults [4]. Friction havior undr diffrnt load conditions is shown in Fig. 7. Th othr load lvls wr also masurd using a stailizing intrval of 15 minuts. Again, this is not nough to achiv complt stady-stat oprating conditions at all load stags. Fig. 7 shows that th friction cofficint incrass as th loading dcrass, which is a known fatur of hydrodynamic journal arings. Th incras in th friction cofficint as a function of sliding spd is du to th incrasing shar rat of th luricant. Howvr, this incras in friction sttls down at highr spds as th incrasing powr loss raiss tmpraturs in th arings and hnc dcrass th ffctiv viscosity. Th rsults also indicat that th minimum friction cofficint occurs at low sliding spds. 17

7 Figur 6. Friction cofficint f, sliding spd and aring ack tmpraturs as a function of tim, p pro = 6 MPa. f 2 f 2 M m/s Figur 7. Th frictional trnd havior at diffrnt load conditions as a function of sliding spd. Th aring lift-off spd, which corrsponds to th location of th minimum friction cofficint, is of intrst and mrits furthr study. In this location, th transition from mixd to full film lurication occurs so that th lattr rgim starts to dominat th friction procss. Th masurmnts wr carrid out with four load lvls nar th lift-off spd. Running-in of th surfacs was carrid out for th tst. Th sam sliding distanc was usd for ach tst point instad of having a constant running tim. Th rsults ar shown in Fig. 8 as a function of sliding spd. Figur 8. Friction cofficint at diffrnt loading conditions as a function of sliding spd. Fig.8 shows that th location of minimum friction cofficint, i.. th aring lift-off spd, incrass as th projctd prssur is incrasd. Undr th oprating conditions usd, a vry low friction cofficint can achivd with sliding spds as low as 0.1 m/s. Furthrmor, th sam friction rsults wr mappd against th paramtr n /, whr is th ffctiv viscosity, p pro m/s n is th rotational spd and p pro th projctd prssur. This is known as th Hrsy numr with th diffrnc that th rotational spd is givn hr in rvolutions pr sconds. Th rsults ar shown in Fig

8 f 2 M flxil luricant fd control and tmpratur as wll as flow rat masurmnts in ach tst aring. Dtrmination of aring claranc and roundnss was asd on conditions whr th tst arings wr alrady installd in thir housings. Figur 9. Friction cofficint against n / - paramtr. p pro Fig. 9 shows that this non-dimnsional paramtr is ffctiv in consolidating th rsults masurd with diffrnt loads, xcpt for th lowst load. It may that thr is still som ffct of running-in during this load stag. It is shown that hydrodynamic arings can opratd with a friction cofficint as low as E -8 in trms of th n / p - paramtr. This is, at last, th cas whn th aring oprating conditions ar fr from ffcts of factors such as shaft misalignmnt. It is clar that th matrials and surfac roughnss hav an ffct on th lvl of th osrvd aring lift-off spd and th minimum friction cofficint. CONCLUSIONS A tst dvic for th valuation of journal arings was dvlopd. Th dvic consists of a rotating shaft and four stationary tst arings. This schm liminats th nd for support arings, allowing an accurat friction masurmnt. Th housings of th tst arings ar slf-aligning which liminats th dg prssurs typically causd y shaft misalignmnt. Th tst dvic facilitats 10^-8 pro In th initial tsts, th friction rsults in th form of Strick curvs wr otaind using a varity of loads and sliding spds in mixd and full film rgims. Th masurd aring tmpraturs wr narly uniform, indicating that th loading and friction conditions wr fairly similar in ach tst aring. Th corrct lvl of th friction cofficint in full film rgim was initially vrifid with th modl rsults. Th rsults indicatd that th nondimnsional paramtr n / p fit wll with th friction rsults masurd at diffrnt loads and spds. Th aring lift-off spd occurs whn th valu of this paramtr is in th rang twn This is at last th cas whn th aring oprating conditions ar unaffctd y factors such as shaft misalignmnt. In this study, this mans that arings could opratd with a low friction cofficint down to sliding spd lvls of m/s. ACKNOWLEDGEMENTS Th authors ar gratful for th financial support providd y Mtso Minrals Oy and Finnish Funding Agncy for Tchnology and Innovation. pro 19

9 REFERENCES 1. Hamrock, B., Fundamntals of Fluid Film Lurication, McGraw-Hill, Inc, ISBN , 1994, 690 p. 2. Stachowiak, G.W. and Batchlor, A.W., Enginring Triology, Triology Sris, 24, Elsvir, 1993, Th Nthrlands, 872 p. 3. ESDU 66023, Calculation Mthods for Stadily Loadd Prssur Fd Hydrodynamic Journal Barings, (ESDU = Enginring Scinc Data Unit), London, 1982, 70 p. 4. Lhtovaara, A., A Numrical Modl for Hydrodynamic Lurication of Journal Barings with Axial Luricant Supply Groov and Axially Varial Gomtry Finnish Journal of Triology, 26 (2007) Pasann, A., Klmola, J. and Lhtovaara, A., Dvlopmnt of a Tst Dvic for th Evaluation of Hydrodynamic Lurication in Thrust Barings, Finnish Journal of Triology, 27 (2008) Valkonn, A., Oil Film Prssur in Hydrodynamic Journal Barings, TKK Dissrtations 196, Espoo 2009, 202 pp. 7. McCarthy, D.M.C., Glavatskih, S.B, Byhdn, Å, Influnc of Oil Typ on th Prformanc Charactristics of a Two- Axial Groov Journal Baring, Lurication Scinc 21 (2009) Bouyr, J, Fillon, M., An Exprimntal Analysis of Misalignmnt Effcts on Hydrodynamic Plain Journal Baring Prformancs, Journal of Triology 124 (2002) Glavatskih, S.B, Laoratory Rsarch Facility for Tsting Hydrodynamic Thrust Barings, Proc Instn Mch Engrs Part J: J Enginring Triology 216 (2002) Swanson, E.E., Kirk, R.G,. Survy of Exprimntal Data for Fixd Gomtry Hydrodynamic Journal Barings, Journal of Triology 119 (1997) NOMENCLATURE = width of aring c p = spcific hat of luricant = ccntricity f = friction cofficint F = friction forc, surfac F o = cylindr load F N = aring total load (= w r ) h = luricant film thicknss h o = minimum film thicknss h p = powr loss K = powr loss factor M = friction torqu 20

10 n = shaft rotating spd (rps) p = fluid film prssur p pro = projctd prssur (w r / (2r *)) P = prssur q in = inlt flow rat of luricant Q = flow rat of luricant r = shaft radius t = tim T = tmpratur T = ffctiv tmpratur T in = inlt tmpratur T = luricant tmpratur ris u = sliding spd in th x-dirction w r = aring total load x = coordinat in th dirction of sliding motion x 1 = coordinat along lin of cntrs x 2 = coordinat prpndicular to lin of cntrs y = coordinat, aring width dirction = ffctiv asolut viscosity = luricant dnsity = coordinat, (x / r ) = attitud angl = shaft rotation spd 21