Hydraulic Removal Coupling Hubs-keyed Keyless

8/2/2019 Hydraulic Removal Coupling Hubs-keyed Keyless

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HYDRAULIC REM OVA L OF COUPLING HUBS-KEYED AND KEYLESSby

Michael M . CalistratO w n e r

M i c h a e l C a l i s t r a t a n d A s so c ia t esMissour i C i ty , Te xasJames R. Morris

M a i n t e n a n c e S u p e r v i s o rand

Robert ParkerMain tenance Spec ia l i st

E. I. d u P o n t d e N e m o u r s a n d C o., I n c.O r a n g e , T e x a s

Michael M. Calistrat has outstanding ex- Robert W. Parker is a Maintenance Spe-perience in the field of power transmiss ion cialist with E.I. duP ont deN emo urs & Co.,equipment, which he has accumulated work- Inc., in Ora nge, Texas.ing wirh oil drilling equipmen t, gearing, and He hus been with DuPont for the last 27flexible couplings. He also has a solid back - years, with resp onsib ilib for maintenan ce,g r o ~ i t ~ c lt1 it~ du str ial as rurhitles. reliabilir),, and troubleshootirlg of rotatingHe is acrive in engineering societies and equipmenr in rhe Ethylene Unit at Sabinemanufactur ing associations. He chaired River Works.many technicalcommittees orASM E, ASTM , Mr. Parker attended Lamar University.andASL E, and wasChairman o f the Interna-tional Conference on Power Transmission/.ing. He wa s associate editor of the AS ME Jour nal o fhinc, Ucs ign .been a coaurhor on rhree engineering manuals and hasN I U I Z ~echnical papers an d articles in the Unite s Srales,

Culisrrat was Mana ger of Research and D evelopment or theTrunsmission Division of Koppers C ompan y, where he wa sn the development of many products. Presently, hering compa ny which specializes in rotaring machin-

ABSTRACTIn rotating machinery, torque is transmitted from shafts tocoupling hubs (or vice versa) through keys, friction, or a combina-tion of the two. As a rule, coupling hubs must be installed on shaftswith a certain amount of interference. This interference has twopurposes: to prevent rocking of the hu b on the shaft, and to help inthe tora ue transmiss ion. With sufficient interferenc e all the toraue

Cu,isrriir e c e i v e d h i s ~ , ~egree n ~ ~ ~ h ~ ~ i ~ ~ l~ ~ i ~ ~ ~ ~an be iransmitted by friction, and keys can be eliminated.a

rest an d holds 17patent.7. Interference has tw o disadvantages: it make s installation diffi-cult, and hub removal even more difficult. Hydraulic methods ofhub removal are discussed. These methods are sound, make forJames R. (Bo b) Morris is a MaintenanceSupervisor with E. I. duPont deNemours &Cor r~p atly, trcorporateri. He 11u.s bee n withDuPonr for rhe past 24 years an d currentlyhas responsibil i ty or maintenance and reli-ability or turbomachinery and other equip-ment in the amm onia comp lex at Beaumont,

Texas.Before joining DuPo nt, he wa s with Fire-stone Rubber, and with Tenneco Chemicals.Mr. Morris attended Lamar University.

easy and quick hub removal, and are safe.Som e engineers are reluctant to use hydraulic removal for tworeasons: it requiresspecialized toolsand bettertraining of mechan-ics, and it was luiown to be potentially dangerous. As any new andsophisticated procedure, it also received a bad name fr om earlyfailures, all caused by misuse.The following topics are discussed:Torque transmission through keysInstallation of keyed hubs using interferenceTor que transmission through frictionInstallation of keyless hubs, heat-assisted installation, hy-draulic assisted installationHydraulic removal of hubs, dismounting keyed hubs, dis-mounting keyless hubsFailure cases


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154 PROCIZI:L>INGS OI'T HE TWENTY -SECOND TUKBOMAC'HINEKY SYMPOSIUMHydraulic m ethods for hub removal wcre disclrsscd in previous I N S T A LL A T I O N O F K E Y E D H U B S USINGpapers 11.21. The purpose hcrein is to cornpile and up date prcvious I N T E R F E R E N C Einformation, and to describe good practices. All coup lings resist being mis aligned; misalignm ent cT O R O U E T R A N S M I SS I O N T H R O U G H K E Y S types of couplings to tend to rock on their shaf ts . Tl ~ c- for th n ~o t io n so f s rn a l l m p l i tu d c i~n t l ligl~ rcql~ cncy i ~uKcy s a r c su ch an o ld ~n n ch in c ar t t h ;~ t h e au lh o r s co u ld n o t wear to occu r on bore and shaft surfaces; fretting inducetrace the i r o r ig in . There are m a n y of a n d a' 1 are in shafts, with catastrophic consequences, as shown i nstandardized. Ultimately, all keys transmit torque through shear-ing of a rectangular cross section . Three completely d if fere nt

shape sof keys are shown in Figure I , a ll having the sam e shear ingsection: a rectangle of width, W , and a length, L,.

S q u a r e K e y C y l l n d r l c a l K eyFigure, I. 'l?irr,c~ :,7/1~.~~/'SItc~/i'c.,y.v. Nol r: 7'11t~ tr.ric tlit trc ~ti .v~ or~ .v(widfh und lengrh) rem uin the strr~~c,$)r11 rypes.

Key d imensio ns were s tandard ized about 150 years ago: thewidth to be 114 of shaf t d iameter , and the length to be 1.5 t imesshaf t d iameter . A s im ple shear s tress calcu lat ion wil l demonstratewhy these particular ditncnsiorls were chosen.The shear stress generatetl by lorque in a cylindrical shaft is:

whered = sh af t d iamete rT = lo rqucNote: i f (1 is i l l ill, i 1 r 1 ~ 1T 111 i11/10, T is Il)/i11~.The shear s tress gcncratcd by torque i n the rectangular crosssection of the key is:

In trot lucing the s~i~ ntlar t l izct ley t l in ~ cn s io n s W = tl/J antl L = 1 .5cl) t he f o l l o w i l ~ gs o b t a i ~ ~ c d :

It can be seen that th e shear stres ses in the shaft and in the keyar e practically identical; it goe s without saying that the strength ofth e two mate r ial s mu s t a l so b e th e sam e. Amazin g ly , th i s s imp leru le was forgotten over the years , today , almost all engineer inghand books include table after table of various key dimen sions, 11utnot a word about key material.The autho rs have seen a numbe r of costly machine fai lures thatwere caused by the use of low carbon s teel keys in applicat ionswere both shaf ts and hubs were ma de of heat- trcated al loy s teels .A n i ~ l l p o r ~ ; ~ n tu le to r e~n cn lh c rs 111i1t {h ek c y ttrtrrc~t.itr1, n dr lr t~ r ~h u rdn ess, sh o u ld be s imi lu r ro /ha1 o f t t~e h u j o r h u b.

Th e only way to avoid fretting i s to use interference attion. Interference is created when the bore dianlete r isma ller that the shaft diam eter. How rnuch interferen ce isfor preventing fretting occurrence? First define interferI n r ~ r j e r e n c es /he d~f lere nce etween the bore an d sherers , d iv ided by the shaf i d iameter . Therefore, interfdimensionless : i t is customary to refer lo i t as in/in, or nExample A :

A cylindrical shaft has a diam eter of 4.00 0 in, and itshas a d iameter of 3.996 in. Th e resulting interfercncl: is

Example B:A tapered shaft has a nominal d iam eter of 3.00 0 in, anof 314 in/ft. The hub bore large end has a diameter of 2 .9insl;lllaliorl, thc 1l11hs ;l tlvancct l ( d r ; l wn )o ~~l~csll ;~l ' t. 0 4resullirlg inrcrt'erence IS:

i = taper x ad v an ce -- - 10'75 x 0 .0 4 8 x- 0shaf t d iameter 1 2 3 . 0 0 0Note that the bore d iameter does not en ter in the calch o wev er , i t must be sm aller than the shaft by at least:

Go ing back to the question of how much interference isto prevent fretting: experience has shown that a mini0.0005 (in per in) at operating condi tions will prevent thrcncc of fretting. Ro ta tin g sp ccd c r ca tcs cc n l r i f ~~ g i ~ l~ccwllicll in 1ur.11 ;~ ~ r s c shc hub bore to gro w, 1'0 crls~ rrchc nin ler fererlce at operat ing spee d , the au thors rec ornn~ er~


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TUTORIAL ON HYDRAU121C REMOVA L OF (OUPLING HUBS-KEY ED AND KEYLESSAt spceds up to 3,600 rpnl the mounting interferenc e should0.00075,

a1 \peecis between 3,60 0and 8,00 0rpr n the mounting intcrfer-e hho~rld e 0.0 01, ancla t speeds above 8,000 rpm the coupl ing or machine manufac-

o~ nes function of the type and diameter of coupl ings.

TRANS MIS SION THRO UGH F RICTIONInterference creates a contact pressu re at the hub-to-shaft inter-

sion of torque. Th e torque that can be transmitted by

= sIi,~l't ominal di:ilnctt.~= I ~ u h~utaidt. lianlclcr

, A Ihutl cl'fcctivc length

t' all the dime nsions are in in ches (in), T is in in/lb, and k =. 8 Ib/in-'- I ' u o assunlption s were rnade: that the hu b arid shaft are mad e ofis 0.12 (note : torque i srcctl> proportion al lo thc friction corfficierlt) . For detail5 about

I O I I I I I I ~ ; I \ ~ , 1 '< : i ~ l i h l ~ . i l l 11.' 1 ' 1 1 ~ l ' l'cctivc Iluh I c~ ~g tl is tlic I c n g t h o f c o ~ ~ t a c t~etwccnhe Ilubha f t; it deternlines the area of contact between the two. Thea lost through key \ \ays or O -r ing groovesshou ld be discounted,I \ t 1 5 ~ ~ r r ~ p e n s a t e d! a proportional increase in contac t pressure .

l j> i l i g l l C d . ~ t i ~'ron~ vritriplc 5, and assunllllp all et'f'ecti\c h11L)t4 .O il l and a l lub outs ide diameter of 4.5 in, the followingob ta~l i ed :

I ~ ~ ~ c ~ e \ t i n g l y ,his is about the rated torque of a genera l -purposeor a 3. 0 in sha ft . Although all t l le torque of thec o ~ ~ l de transnilt ted through friction, uo margin exists fortluctuations, and particularly for peak torques. Th e abov ethat, during norma l operating conditions, a 0 0 0 1nce relieves most of the stresses in keys used in general-rposc coupling \.

F S I 'E L D O N I N T E R F E I I E N C L !M O I I I I I ~ I I ~l ~ t c ~ l ' c r c ~ ~ c cs rctlucetl by 111s11~11)ss c c ~ ~ t r i f u g a l

11 At speed, the actual interference is:

' I ' I I I \ Iortliula slio~~,:,hat the reduct io ~ln ~no unt in g nterferenceg~.c i r l>nfluenced by the hu b's o utside diam eter, and by theralirlg b p t ~ t l . or h ubs with large flang es, sue11 as the o ne sllownFiyurc I, he actual i~l te rfere~lces not unit 'orm acros s the hubt ib 5nlallest just under the flange.

Example D :A flanged coupl ing hub is installed on a 3.5 in shaf t, rotating at6,0 00 rprn. Th e outside dianicter of the hu b body is 5.5 in, and thetlange outside diam eter is 8. 0 in. The moun ting interference is0 .00075 ( int in).Th e actual interference, at operating speed, varies as follows:Under the flang e

is = 0 .00075 - 0 . 0 5 5 x 60002 x 5 . 5 2x 10-l2 0 .00069or 92 percent of mount ingUnder the hub

i, = 0.00075 - 0 .055 x 6000' x 8 l x 10." = 0 .00062or 8 3 percent of mount ingAverage interference, to be used in the calculation of torquetransniission a bili ty:

is = (0 .00069 + 0 .00062) /2 = 0.00065or 87 percent mount ing

INS TALLATION O F KEYLES S HUBSWithout keys,aII the torque ( i~lc lud i~i gomentary peak torques)must be transnlitted through friction between the hub bore andsll;lft. Tlle fr ict io~ l e~lcratc*cly a 0.00 intcrl'crcncc can Ira~isrl111osto l 't ll c g c ~ ~ c r a l - l ) u r p o xo u p l i ~ ~ gorqucs. However, keylesshubs are mostly (but not exclusively) used with special-purposecouplings, w hich are made of alloy steels, operate at high speeds,and can transmit larger torques than general-purpose couplings.Therefore, in keyless cou plings the effective interference mustbc much larger. It is cmto rnar y to u.\c 0 . 0 0 2 to (1.U025 (intin)

interference. All the fo rm ula e prei.iclusl!- giv en appl!Keyless hubs ;Ire irsed nlnlost exclusibcly on tapered shat'ls.Manufacturers se ldom give recolnnle~ldat ionson how muchinterference should be used w ith their keyed-hub coupling s; theyalwa ys give detailed instructions in the case of keyless hubs. Oneparticular reason to follow manufacture rs instructions is the factthat interference cau ses high stresse s in hubs. A 0.0 03 interferencewill create stre sses a s lligll as the yield strength of alloy ed, heattreated steels . Ther efor e, sucll a high interference s houl d not beused. How ever, even a low er interference could create problems inhubs w ith a thin shell , or hub s that have oil injection holes dril ledin their bodies. In such cases stresses can be very high, and thecoupling manufacturer instructions must be closely followed.The authors know of one case where a replacement hub wasmad e by an independent machin e shop, of incorrect material . Th ehub split open at installation, which was fortunate; i t could havef;~iIcd fter rile n l i ~ c l ~ i n cas stilrtc(l!'l 'llerc are t wo w ays to insrall keyless Ilubs: tllrougll heat expall-sio n, or tllrougll Ilytlraulic exl)ansiori.Hrut-Assisted lnstallafion

Th e biggest advantag e of heat installation is that the resultingfriction coefficien t is larger than when oil dilation is used. Exper-inlcn ts have show11 hat thc tlry friction coefficient ca n be as highas0 .20 , ascornpared wi th 0 .12 in th ecas e of hydraul ic insta l la t ion.'Tl~crefore, i ther a larger torqu e can be transmitted, or a smallerinterference can be used . On the other I~a nd , eat expansionprecludes the use ofs eal sat thc hub-to-shaft interface,and requiresan oven onsi te .


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156 PROCEEDINGS OF THE TWENTY-SEC( ND TURBOMACHINERY SYMPOSIUMThermal expansion ca lc l~la t io ns how tha t for every 0 .001interference about 160F differen ce between the hub and shaft isrcqt~ir ctl . hcrcfor c, For :I 0.0025 intcrferrn cc, ant1 ;I sli;~l't t 80F,t l l c ~ n i n i r n t l l ~ ~lub telrlpcrilturc !nus1 be 500F. I I ' a ~ n a r g i n 'ol.errors is provided, hubs must be heated close to steel temperingtemperatures, which could cause degradation of material strength.The lack of seals can cause two prob lems at remo val: first ,sufficient pressure for dilation might rlot be achieved ; second,scor ing of the shaft and bore might occur . The deformat ion of asealless hub under pressure is show n in Figure 3. I t is evident thatin order toseal the oil , a high contact pressure must exist at the boreedges . Rounded corne rs are used in order to minimize the possibil-ity of scoring.The fol lowing steps should be fol lowed fo r the hub insta l la t ion:U Cle an contact.surfaces of shafts and couplings very careful-ly. If rubbing is required to remov e preservatives, use a non abra-sive njaterial , and do nclt use axial motions. Some coupling~nanufac tu rc r s se a dry prcscrvativc that can be renlovetl onlyrhrough lapping . It is very importar11 to rem ove all prcs ervativc s.because if left on, they will significantly reduce the frictioncoefficient.O Measure the shaf t and the bore and ensure that the dimen-sions are as speci fied by the manufacturer . Tapered surfacesshould bec hecked with tapered giluges; cylintlrical surfacess houltlbe ct~cckcclwi rh ~n i c ro l l i c~c r s .il C he ck f i ~ r roper c.ontac t (I'or tapered sh afts only ). After thcshaft and hub bore are thoroughly cleaned, spread a thin layer ofmechanic ' s b lue on the shaf t and push the hub snugly. Whi leapplying a l ight axial pressure, rotate the coupling hub a smallamount , and ba cku p to the or igina l posi tion. Careful ly remove thehub and check the bore for con tac t , by the amount of colored area .At least 80 percent, and preferably 9 0 percent of thc bore shouldshow contac t .i3 Find the p roh lem. If less than 8 0 percent contact i s found,check the accuracy of the surfaces using tapered gauges. It isimportant to find the problem before corrective measures aretaken.U Improve the contact. I f problems are found, e i ther the shaf t ,the bore, or both, must bc corrcctctl through lapping. The follow-ing rules should be followed:

Figure 3 . Hub D i la t i o n w i th Hydra u l i c Pressure . No te : The bar re l -type dis tor t ion is typical ofseal les.~hubs.

Hu bs arc rnore often at fault for lack o f cnnt:~ ct han 5serious defects ar e found it is advisable to first send the pIiub to ;I gr ind ing s l~opo hc " s pi ~r kc tl I I I . "I I I ~ I I ~ I I I I I I ~I I I~ n a t c r i i ~ lhoultl be rclnovetl to rccstahlisll gootl C O I I I ; I ~Use a ring and plug lapping tool set; never lap a hubshaft . Lapping tools ar e made of soft materials, usually caUsing hard tools (such as gauges) wi ll reduce the eff ec t ivlapping, and the tools might b ec on ~e amaged quickly.Lapping will cha nge the hub axial posit ion or) the sha

general rule, hubs move axially 30 t imes more than the thremoved through lapping. For example, if one mill (0.00remo ved, the hub standoff will be reduced by 0. 03 0 in. Exlapping might require machine realignment, of use of smetal flexible element couplings.To exped i te the lapping process, s ta r t wi th a coarspound, and ch ange to a progressively finer grit a s thc dcfcorrectctl .

0 Clean the l a p p ~ d u rfaces . Rernovc ill1 traces ofcomp ound, using a solverlt and lint-free towels. Rechcck tto-shaft contact.O Prote ct surfaces, by spreading thin oil on the shaft abore (to prevent rusting).

Using ;I dcp l l~ n i c ron i c t c r ,iicasurc I'l.oni tlic I'acc olto the end of the shaft , and record the "start" reading. Areading shou ld b etaken, ifposs ible, either fro ma fixed poinmachine, or from a spli t collar attached on the shaft , behub. Use parallel bars, sna p gauges, or feeler gauge s, as rCalcu late the hub overha ng after installation, by subthe intended draw from the "start" dimen sion. It is possibnegative value nlay be obtained, meaning that the slprotrude out of the hub. Although an undesirable contii toften encoun tered in cases where many correctio ns were mproper contact. If the shaft protrudes, a special retainiincorporating a counterhore, must be made.

0 Clea n sur faces. Just before installation clean the shthe bore of all lubricants, using a solvcnt a nd, iSncccss;lryfree cloth.U Hear the huh to the recommended ternperaturc. Usove n or induction heater. If the temperature to which the hbe heated is not specified, use the following rule: 160F ( ibetween h ub and sh aft , for every 0.001 in/in interference, tan additional number of degrees should be added as amargin.O Remove the huh from the oven and place i t quicklyshaft . A posit ive stop m ust be provided in front of, or behub, othcrwisc the advance could be wrong.U Measure ugain t he hub d raw (adv i l~~cc ) .tic hubadvanced on the shaft exactly the arnount specified. T

advance could result in the hub spinning on the shaft; roadvanc e could rcsult in the hub split t ing at or shortly aftelation.Hydraul ic-Assisted Insta l la t ion

Hu bs with tapered bores car1 also bc cxparlded hydraThe advance (draw) can beei ther mechanica l , using a specnut, or hydraulic, using an annu lar cylindc r (hytlraulic narrangement is shown in Figure 4.Hydraul ic advance has two advantages over the mecadvance: i t does nor require a tool to prevent the sharotating, and the hydraulic nut can also be used at remov


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T U T O R IA L O N H Y D R A U L IC R E M O V A L O F C O U P L IN G H U BS -K E YE D A N D K E Y L ES S

t--~gut.r . I t ~ . s t t r l l t r / i o~ t /Ro~ i~o~~a lyclraulic. 7'001. Not e: Th is tooli / / o ~ \\,/i~r I ~ U / - / I ~ , Y . Yt ~ , s t t ~ / / c ~ ~ i o n ,~ n t l / ) ~ t -s t!/(, r o t r ~ o ~ ~ t r / ,

Tli ' ~'e qu irc d rcssure for exp an din g tlic bore is high, usually11r.luer.1120,000 and 3 5,000 ps i .Three special tools are needed for hydraul ic advance: an in-htnllation tool (hy draul ic nut) , a high -pressure (50 ,000 ps i) oi l/ ) I I I I I I ) wit11 p r e s s ~ ~ r cauge , ;~ nd low-l ) rcs surc (10 ,000 psi ) o il~ L I I I I I ) with prcbxtrre gauge.

7'~ )nstrrc a successful ins talla t ion, the fo l lowing p rocedure isI c ~ w r ~ i ~ i l e n ( l e d :J C ' leu t~ on ~ uc r u r fucr s of shaft and coupl ing very careful ly.

I t rubbing is required to rem ove preserv at ives , use a nonab ras ivematerial, and do not use axial motions . So me coupl ing ma nufac-turers use a dry preservat ive that can be removed only throughlapping. Rem ovin g al l preservat ives is very important , because ifc f t on, they wil l s ignif icant ly reduce the fr ic t ion coefficient .2 Meu.sure the shaf t a nd the bo re and ensure that the dimen-ions are as specif ied by the manufacturer . Tapered surfacesi io ul d e checked wi th t apered gages .L) Che ck for burs on shaft ends, O-ring grooves and oi l inletIxlssagcs. Sharp etlgcs can nick the seals a n d cause diff icul t ies atr c ~ n o v a l .Check coupl ing bore for s imilar condi t ions . Burs and

rag marks can be removed us ing a f ine "Indian" grade hone.Never hone axial ly.LI C heck fo r p r op r r contuct . After the shaft and hub bore areho roug hly l eaned, spread a th in l ayer of ~ne ch ani c ' s lue on thet and push the l ~ u b nugly . Wh i le apply ing a l ight ax ia l)rcssilrc, sliglitly rotat e the coup ling hub, and back up to thel . areful ly remove the hub and check the bore foract, by ttic ariiount of colore d area. At least 8 0 percen t, andpret 'crably 0 percent , of the bore should show contact .J F i n d t he p r o b l e m . If less than 80 percent contact is found,

111portanL o finti the problenr before corr ective mea sures are3 I tnprove the conracr . If probletns are found, e i ther the shaft ,e bore, or both, must be corrected through lapping . Th e fol low-rig rules should be fol lowed:

Hub s are more often at fault for lack of contact than shafts . If~ is advisable to f i rst send ~ l i c robletni~rbo ;I grititling sliop to be "spa rke do ut. " A tirinin lu~n rrlount of~ i ;~ tc r - i ;~ ll ~ o u l t l e r c n ~ o v c d o rccs labl i s l~ ood contac t .

Use a r ing and plug lapping tool set ; never lap a hub on i tse of soft materials , usual ly cast i ron.Jsing hard tools (such as ga uges ) wil l reduce the effect iveness ofapping . and the tool s might become damag ed quickly .T.ar) l ) i~~gi ll change the hub axia l po s i ~ i o~ i11t h e s l i a f ~ . s aule, lile I I ~ I I ~iloves axially 30 l i n ~ e s n o re ~ l r i i t ~11

Excess ive lapping might require machine real ignment , br usshi ms in metal f lexible element coupl ing s .T o expedi te the lapping process , s tart with a coarse cpound, and cl ia t igc to a proprcssivcly finer grit as tlrc tlefcctcorrected.

U Clean the luppecl surfuc,es. Remove all traces of lappcom pou nd, us ing a solvent and l int-free towels . Recheck the hto-shaft contact .3 Protect the surfaces, by spreading thin oil on the shaft h u b b or e ( t o p r ev e nt r u s t i ~ ~ g ) .

W i th ou t a n y 0 - r i ~ i g s o r acktrl)rings, install IIle huh sn~ rgthe shaft. This is the start position.Using a depth m icrometer , m easure from the face of theto the en d of the shaft , and record the "s tart" reading. A secread ing shou ld be taken , if possible, eith er from a fixed point onmachine, or I'ror11 a s p l i ~ ol lar a l lachet l on ttic shaft, behindhuh. Use ~xiral lc l ars , snap g auges , or feeler gauges , as requiObtain the h ub ovcrl iung after i tis ta lla t ion, by su btr ac~ in

intended draw frotn the "start" dimension. It is possiblc thnegative value will be obtained, meaning that the shaft protrude out of the hub. Althou gh an und esirable condit ion, often encountered in case s where many correct ions were madeproper contact. If the shaft protrudes, a special retaining incorporat ing a counterbore, must be made.3 C h e c k i f pr o pe r 0 - r i n g s u t ~ t l u ck u p ri n g s u r e u v u i la b l e .cotnbi t la t ion should f i t in the groo ve without too much effortrings will protrude slightly out of the groove. Backup ringsavai lable as ei ther nol ispl i t hard rubber, or spl i t whi te nylon.split rings must be individually adjusted to fit their groovescut t ing off ' some material . Nei ther overlapping, nor gapsacce ptabl e. Back -up rings slioultl not protrude out of the groo3 In.s/cill O-rings a11d backup r ings in shaft and h ub grooOil is pump ed between the huband shaft through ashal low circgroove machined e i ther in the h ub or in the shaft . Ins tal l therings toward this groove, the backup r ings away t 'roni this groAfter they a re ins tal led, look agair l! Th e O-rings musl b e betwt l l c b a c k u p r i ~ i g s a n t l t l ~ c o i lroov es! Sp rcatla little bit ol 'hytlraoi l on al l rubber surfaces .U M o u n t " o t h e r " coniponents. Read the coupling installaprocedure aga in . Mus t o the r component s ( such as a s l eevemoun led on the shaft before the hub? If so, now is the t ime tit .Ll A pply u th in l ayer o fhydmu l ic o i l on the shu j f. This oil prevent the ro l l ing or twis t ing of the seals . Th e high pressures uduring removal will not be contain ed by defect ive seals .O Mo unr the hub on the shaft . Avoid pining the O-rings dumoun ting. Th e o-rings , being tal ler than the grooves in w hich are installed, will prevent the hub from advancing to the "stposi t ion. Tl iis is ~lornia l .!iou111 he i~ i .s~ul l t r r i ono o l . W ~ Ihe tlireatls with thin o il,rotate the tool until i t bu tts again st the sha ft sllould er. 'l 'lie lastturns wil l require the use of a spanner wren ch.O Conne ct [he hydraul ic l ines. Connect the col lapsed instt ion tool to the low-pressure oi l pump (5 ,000 psi minimuConnect the high-pressure oi l pump (40,0 00 ps i minimum) toholc provided cilher in tlic ccntcr of the shaft or or1 the outtlianic [er of tlic Iiub , tlcperidinp 011 lcsigri. Loose11 l ~ c cnf pluthe installation 1001 and putrip all the air out; retighten the p


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158 PROCEEDINGS OF THE TWENTY-SEU N D TURBOMACl+INERY SYMPOSIUMNote: Oseonly hydraulic oil ir , tI\c high-~)rcssul-eurnl). The useof lubricating oils could cause the installed hub to slide off theshaft.0 Advance the hub to the stan position by pumping the low-pressureoil pump. Continue pumpinguntil the hubadvances0.005to 0.010 in beyond the start position.Ll Expand the huh. Pump the high-pressure pump u n t i l thegauge reads between 15.000 and 17,000 psi. As the pressure

increases, the hub will tend to move off the shaft. Correct thismovement by occasionally increasing the pressure at the installa-tion tool.O Chrckfor oil leaks. The pressure at the high-pressure oilpump will droprapidly at first because the air i n thesysteni escapes

I);ISI the 0- rings. Corltilluc p~~ rnping111ti l thc prcssrlrc stirbilizcs.The hub should not be advanccd on the shaft i t' leaks are observed!A rna~irnum ressure loss of 1,000 psi/n~inute sacceptable. If thepressure drops faster than that, remove the hub and replace the 0 -rings. However, before removing the hub, make sure that the leaksdo not occur at the hydraulic connections.

U Advancethehub. Increase the pressureat the installation tooland the hub will advance on tile shaft. If a l l the previous steps wereobserved, the pressure at the high-pressure gauge will graduallyincrease (by itself!) as the hub advances. I f the pressure does notincrease, then stop! Remove the hub ant1 check the o-rings. I f thcpressure increases, keepadvancing the hub until i t touches the splitcollar or until the specified advance is reached. Do not allow thepressure to exceed 30,000 psi. If i t does, open the pump's valveslowly and release some oil. If in doing this, the pressure dropsbelow 25,000 psi, pump the high pressure pump to 25,000 psi, andcontinue the hub advance.

U Sear the hub. After ensuring that the hub is in the desiredposition, slowly release all the pressure at the high-pressure pumponly. The oil present in the space between hub and shaft must begiven time to return to the pump, less the hub slides off. Therefore,do not workon that hub for ahoutone-half hour,orone hour in coldweather. f t e r this waiting period, release all the pressure at theinstallation tool and remove it from the shaft.

U Verify the advance. Measure and then record the new over-hang of the hub over the shaft. Subtract from the overhangmeasured i n the "start" position, and the result must be the same asthe specified advance, within the given tolerances. Record theactual advance for future reference.3 Secure the hub. Remove the split collar from the shaft andinstall the retaining nut, but do not overtighten. Secure the nut withthe setscrews provided. Note: set screws should have a "cup"point, and the point shouldimbedin theshaft surface,not in the hubface. If the nut is secured to the hub, and the hub spins on the shaft,the n u t could becomc loose and act~i~llyall off the shaft.

H Y D R A U L IC R E M O V A L O F H U B SDismounting Keyed Hubs

Hubs that have been installed for a long time have a tendency tostick to theirshafts. This sticking, in addition to the friction forcesgenerated by interference, makes for difficult removal.To help i n thc renloval of kcyctl hubs, i t is rcco~iimcndctl osmear the shalt, at installation, with an antiseizing conlpound.Many such compounds are commercially available. The authorsrecommend the use of compounds blended with chromium oxides,which are easy to recognize by their silvery-gray color. An eco-nomical alternative is the use of greases containing zinc oxides,which are white-gray in color. The use of antiseizing compounds

~ ( ~ ( I I I c ~ s)y ir srllall cxlcn~lic I 'ric ~io ~~ocl'ficien~, ~ r ~ t lliglltly Icss

torqire can be trans~nittcd hrough Friction. Ar,tiscizpounds are a mixture of solids (such as chrorniu~n xideand greases. At the moment a hot hub is installed on a shoil from the compound is eliminated, and only the solidTherefore, the friction coefficient is reduced, but only bamount.Thcreare many mechanical methodsavailable for huhhowever, only Iiub renioval methods that use hydraulfor the dilation of the hub are discussed here. The advahydraulic removal arc: on one hand, dilation r ed~~ceshe interference, and on the olher hand the grease (or hydrlubricates the mating surfaces. Use ol' the hydraulic method greatly simplifies hub removal,:lrld conlplelcly cthe use of open flames on coupling cornponrrits.Hyclrir~~liccn\ov;~l(xl~~iresi sligll~ ~io(liI'ici~tii)rllhubs, but the cost ol'sucli modifications arc proh;lbl> rccthe downtime saved at the first use.Two methods are available, one which uses a plain gr[3], and another that uses two oil pumps 121.Two hubs are shown in Figure 5 modified for removagrease gun. Automotive-type guns can deliver a pressure10,000 psi. Considering that 0.001 interfercrlcc crc;\tcspressure of 8,300 psi (for D/d = IS), grease guns caovercome the contact pressure generated hy interferenc

Figure 5. Hyc/rtrulic (Grc,a.ve) Rrmovtrl Mr,/lroc/.v,f21r r wNo/(,: Meihod A o/)p l ios to geurrcl hubs: ~t~oihoi l trflanged hubsfor (111 rypcAs f couplings.

The groove that distributes grease around the boremachined so that i t does not break into the keyway. Thereways to machine such a groove: either through milling, orinstallation of thc hub in a lathe's chuck. Either way, a lol ' t/4 ir i shoultl ('xist hctwccn lllc end ol' tl,c> grtrovckeyway. Two independent grooves Inust be nlachirlcdwith two keyways.Connecting the grooves to the outside of a gear-couprequires more skill than in the case of flanged hubs. In eia small grease fitting is installed at the outside of the hgrease fitting can he left in place during coupling opcra tioit in1crfcrt.s will1 olllcr couplillg conlponcrlls. ]:or 11c1l


7/8

TUTORIAL ON HYDRAULIC REMOVAL OF COUPLING HUBS-KEYED AND KEYLESS 159cy ways hubs nus st either have two grease f i t t ings (and two g reasels inust be used at rem oval) , or the two groo ves can be con nect-

;I .sniall (118 in) hole tlr illed through the sh ah , perpen dicularthc plane of thc keyways (Figure 5) .To r emove a hub so equipped , s imply p u ~ n p r ease in the hub

a p u l l i ~ ~ gorce isapplic d. For tapered hubs , i t is possible thatg force is needed; actual ly, i t is safe to keep the s haf t nutplace (but slightly loos e) durin g remov al. For cylindrical bores,t tool t o use is one s imilar to the autom otive s teer ing-wh eelat tached with high-s trength b olts to the puller h oles of theri a ir in~p acr rench will ensurecontinuou s movem ent of t hewliilc hytlraulic pressure is main tained.1 ' 1 1 ~ . 11 1 i ~ ~ j t % c tori ~ncrl ioil sdi scu sse d by Mu11 o n a n d Zilhcrnian

1 . ; I I I C I i h I I I I I ~ I I . ; I ~ ~ ( Il l I:igirrv 6. 11 is bi~s ic ;~ l lyl ~ c alllc 21s lhc~ ~ c t l ~ c ~ c l ,xcept i l uses t wo oil p u ~ ~ ~ p s ,ne for di la t ingh c ub, the other for a ll oi l ram. Th e autho rs bel ieve that the usea steering wheel puller is as efficient, but simpler.

. H! .druul ic , 011 )Kcmovul method.^ or Keved Hubs. Note:l r \ d r u u l l ~ .cltn cut7 be replaced with a s~rering-\r,heel-rypeul ler .

11 i4 i f n p o r t a ~ ~ tU rccog ~lize hat hydraulical ly removing a hubo l v r ~ o m e d a n ge r , a n d sa fe t y p r e c a u t i o ~ ~ sust be carefullynded at ins tal la t ion, they s tore aust l ike a s tretchedsp r ing.remo ved , this potential energy is abruptly releasedd transformed into kinet ic energy , i .e . , the hub is acceleratedPumping oi l between the hub and shaf t provides theon which the hub s l ides .Another force that helps in removing hubs is the diametralr e ~ l c e e tw e e n th e t w o e n d s o f t h e b o re ( o 9 e tw e en t h e t w o 0 -in gs), ~ h i c h reates an annular hydraulic pis ton.

$41.0n shaft with 314 i~i/ f t aper an d a three-ill axial dista nce> -rin gs l,eco~ncrs n an nu lar piston wit11 il l area o f 1 .2 in'.rhe l~y dra uli c ressure is 25,000 psi, the resultant axial force istons .

11 is obvious that hubs must be stopped, or they will f ly off the~ d a m a ge themselves and anything they encounter . One~d or stop ping a hu b is illustrated in Figure 7 . The retainingi h I>i~ckecl ff sufficiently to allow the huh to tno ve slightly

I I ~ I I llc distanc e i l was advanced at ins tal la t ion. Tw o s tepse taken ro safely dissipate the kinetic energy:

washer

/. 'tgurr 7.M ~ ~ c l r c ~ r ~ r c t r l~ o j ~ j o rydruulrc. Hu h Retnoval. Nulc, T l ~ ed lsror r~on Ja lead r ing absorbs the k inet ic energy of hubs.

Firs t , a lead washer (minim um 118 in thick) should b e ins tal ledbetween the hub and the nut .Second, the gap should be m ade only 0.01 0 in to 0.02 0 in widertl1i111 the originill ; I ( I V ; I I I C ~ . A larger gap wil l i~ l lo w 11~:h i ~ b0 i ~ l l i ~ i ta loo-high velocity. The lead w asher will absorb (h e energythrough deformation . The authors know of one case where, with-out a lead washer and with a wide gap, the threaded por t ion of theshaf t was snapped of f !Eve n with al l these precautions , personnel should never s tand inl ine with the shaf t when hub s are being removed.Af ter a s top is provided, hydraulic pressure should be appliedslo wl y. A too-quic k in crease in pressure will not give time for theoil to wet the i~ t ter fac e ompletely, ant1 local ized scor ing couldoccu r. It is even possible that i t will take the hub a few minutes top o p o u t .If the mach ine is very c old, chan ces are the oi l (which b ecomesmore viscous at low temperatures) wil l not completely penetratebetween the hub and thes haf t , and the hubcanno t be removed. Onesolut ion to this problem is to apply so me heat to the hub. However ,hea ting the hub above 250 Fcan b ede t r i~ r ~en ta l .irst, because oilswill lose much of their lubricating properties, and seco nd, becauseO-r in gs can be sc orched and will no longer seal . Therefore, heat isbest used in moderation, and as a last resort.In orde r to el imin ate all r isks related to hydraulic h ub removal ,a procedure w hich requ ires the use of the installation tool (Figu re4 ) during disassemb ly was tlevelopcd many y ears ago by Calistral.T l ~ i s rocedur e cons i s t s o f thc I 'ol lowil~g teps :

Remove the shaft nut.2 Mounr the collapsed in.stul lat ion tool. Wet the shaft threadswith thin oil and rotate the tool until i t butts against the shaftshoulder. Verify that a gap exists between the tool and the hub,equal to or larger than the amount of advance used when the hubwas installed (check the record s). If the ga p is less than required,the wrong installation tool was probably selected for removal.O Connect the hydrau lic l ines. Conne ct the installation tool tothe low-p ressureoil pump(5,OOOpsi minimum ). Connect the high-pressure oi l pum p (40,000 ps i ~ ni ni mu m) o the hole providedeith er in the cent er of the shtif t or O II the outs ide diam eter of thehub, depending on the des ign. Both purnps must be equipped withpressure ga uges . Loosen the vent plug of the ins!allation tool andpump all air out; retighten rhc plug.Ll Pum p oil into the instal larion 1001.The pis ton wil l advanceunti l i t contacts the h ub. Contin ue pumping until the pressure isbe tween I 00 to 200 ps i . Check f or l eaks .J Expa nd the hub. Pu ~i ip i l between the hub and the shaf t byusing the high-pressure pump. While pum ping, watch hoth pres-s t lre gauges . When the high-pressure gauge reaches i i b o ~ ~t0 ,000psi , the pressure at the low-pressure g auge should s tan increas ing


8/8

16 0 PROCEEDINGS OF THE TWENTY-SECOND TURBO MACHINEKY SYMPOSIUMrapidly. This pressure incr ease is caused by the force that the huhexerts on the installation tool, and is an indication that the hub isfree to move. Note: depending on the interference used and onother condi t ions, the di la t ion pressure could reach 35,0 00 ps i ,before the hub will start moving.3 Waita whi le . In case the low pressure at the installation tooldoes not increase even if the high pressure rea ches 30 ,000 psi, waitahout one-half hour while maintaining the pressure. It takes timefor the oil to penetrate in the very narrow spa ce between th e huhand thesha ft. Usually, there should he no need toexceed30,OOO psiunless a very high interference was used at installation.II3 A l l o w ih o h u h 10 move. After tlrc presstrrc at 1hC ins tall atio ~itool increases, slowly open the valve at the low-pressure pump(not e: this valve could b ecom e hot, as the energy stored in the huhis dissipated there; wear protective g loves ). Th e oil from theins talla t ion tool wil l f low back in to the pump and al low the hub tomove. The pressure at the high-presslrre gauge will drop. Do notallow it to fall below 5,00 0 psi. If i t does , c lose the low-pressurevalve and pump more oi l a t the high-pressure pump . Continue theprocess until the valve at the low-pressure pump is cornplctelyopen and the pressure at the installation tool becomes zero.3 Remove the hu h. Release the high pressure and back off the

installation tool until only two or three threads are still engaged.Pum p the high-pressure pum p, and the Iiub will slide off the shaft.When the huh con tacts the installation tool , release all the pressureand remov e the tool . The hub should now com e off thc shaft hyhand. Do not remove the installation tool unless thc pressure iszero!3 Inspect the O-r ings. Reusing even s l ight ly damaged r ingsinvites t rouble. Thesafes t procedure is toalwa ys u se new seals anddiscard the old ones.

FAILURES CASESAs with any new de vic eo r nietl iod, fai lures are bound to happenin the beginning, either due to poor training, or to negligence.Although the risk of sudden release of stored energy can bedangerou s, the auth ors know of no injuries related to hydraulic hu bremoval .

In a chemica l p lan t, a g ii s cor ~~ prc s so r;rs rctrofittcd with newkeyless shafts. New c oup lings were pu rchased an d iristallcd. A fewdays after s tartup, one of the coupl ings spun on the shaft , whichbecame severely damage d. A new shaft was made and a new hubwas purchased. It was noticed durin g the installation that the forcenecessary for hub advance was much larger thanexp ected . Th e hubwas immediately rem oved, and a sheet of rubber was found on theshaft . What happened? T hc person who purchased the O-rin gseals. unaware of the need for backup r ings , ordered O-ring s thatwere as widea s thegro oves . Evident ly, the seals were too large andexceeded the cross sectional area of the grooves . They becameextruded between the bore and the shaft. Installation of correctseals solved the problem.

Sand was trapped b etween the hore and the shafgranules prevented a go od contact, but providetl sufficientfor torque transmittal.Th e backup r ings were ins tal led at the face (rather thaof the O-rings. Comb ined with the gap at the interface crethe sand, the O-rings were blown off the groov es , and pcould no longer be built .

Case 3Seven out of e ight coupl ing hubs in two compressos l ipped on their shafts during operat ion. The I iuhs hec i~rnonto the shafts , ant1 ~ l ic rains operatctl suc ccssl'r~ lly ntil s cheduled main tenance shutdown. The coupl ing h~ rbs ad toff for removal . Observat ion of the bores revealed that tpling manufacturer applied a dry coating on all couplsurfa ces, including the bores, as protection against rust osion. T his coatin g acted as a dry lubricant at the hore, praeliminating any friction. The problem w ould not ha ve occeither the bores wcre not coated. or if the huhs had h ccr( they wcre not ) . To e li rn in ir re such occur rences , ~ l i c a r i rdiscontinued the dry co ating meth od, ant1 the user m ade mandatory at installation. As a point of interest, the coapling hubs were installed by the compre ssor nlanufacturerthe user .CONCLUSIONS

Hy dra uli c remo val of c ciuplings can he useil eithe r wit1or keyless hubs .The method has (app arent) disadvantages :Couplings cos t m ore (but the addi t ional cos ts arc recovered by shortening the removal t ime)Mechanics require hetter training.Spccia li zct l ~ o o l srrc required.

The method has many advantages :- It is faster than bru te force, and consistently succ essIt eliminates the need of open flamesIt eliminates the possibility of shaft and hore damag

* In kcyli%s h~rlis,f c l i ~ i ~ i ~ i i ~ l c s l ~ ~ c ~ l r c , ~ , ioncvr~rri rr iohy keyways.REFERENCES1. Calistrat, M. M., "Hydraulically Fitted Hubs, TheoP r a c t i c e , " P r o c e e d i n g s of t he N ~ n r hT u r h o r n aSymposium,TheTurbomachinery aboratory. TheTexaUnivers i ty System, College Stat ion, Texas pp. 1-10 (12. Munyon, R . E. ant1 Zilberman, J . , "Hydraulic RemKeyetl H ubs," International P owe r Trirns~nissioli nd Conference , pp. 807-8 I3 (1989) .3. Calistrat, M. M .,"F lex ~b le Coupling Installation," NConference on Pow er Transmis s ion , pp . 2 1-35 (198 1 )

A keyless hub could not be renioved, because riot enoughpressure could he created to dilate i t . The huh had to be cut forremoval. Observation of the hore revealed that:

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Hydraulic Removal Coupling Hubs-keyed Keyless