Coupling Hubs

8/10/2019 Coupling Hubs

1/8

bih istt

Owner

Michael Calistrat and Associates

Missouri City, Txas

Jms R oisMaintenance Supervisor

obt k

Maintenance Speciaist

E I duPont de Nmours and o., Inc.

Orang, Texas

Michael M Calistrat has outstandig ex

periece i te el of power trasmissioequipme, which he hs accumuated orki wit oil drillig equipmet, eari, exible couligs. He ao s a solid ackgrud i idustrial gas turies.

He s active i egieerig societies maufacturig associatios. e chairedmay tecical committees forASME, ASTM,dL, ad was Chairma of the Iteratoal Coferece o Power rasmissio

ad Geig. was asociate eitor of the ASME Joural ofMachie Desig.

e ha ee a coauthor o tree egieerig mal ad hsritte may techicl papers a artices i te Uites States,Japa, Frac, Caa, Hola Italy, ad aiwa.

Mr. Calistrat as aager of Researc ad Deelopmet for thePower rasmissio Divisio of Koppers Compay, where he wasistrumetal i the deveopmet of my products. Presetly, hehe a cosultig comay which specializes i rotatig macie.

Mr. Calistrat received his M.S. deree i echaical Egieerigo the Uiversi of Bucharest ad hol 17patets.

James R. (o) Mrris is a MaiteaceSuperisor with E. duPot deNemours &Compay, Icorpated. e has ee withDuPot for the past 24yers ad currtlyhas resposiili for aiteace ad reliaili for turomachie ad other quipmet i the ammoia complex at eaumot,exas.

efore joiig uPot, he was with Firestoe Ruer, ad with eeco Chemica.Mr. Morris atteded amar Uiversi.

153

ABTAT

Roert Parker is a Maiteace Spe

cialis with / uPot deNemours & Co.,Ic., i Orge, exs.

H has ee with DuPot for the ast 27years, with resposiili for aiteace,reliabili, ad trulesooti of rotatigquipmet i the thylee it at SieRiver Wor.

Mr. Prker attedd mar iversi.

In rotating mhinery torque is transmitte om shas topling hus (or vi versa though keys fritin or a mbination of the two s a rul oupling hub must be installe on saswith a ertain amount of interfrne This interrene as twourposes to prevet roking of the hu on the sha an to elp inthe torue transmission it suffiient intefrene all the toruean be transmitte by ition nd kys e eliminate

Interferene has two isavantages it akes installatin ifiult an hub removal even more iffiult Hyrauli methos ofhub removal are isusse Tee methos are soun make foreasy an quik hu removal and are saf

Some engineers are relutant to use hyrauli removal for tworeasons it requires speialize tools an better training of mehanis an it was known to be potentially angerous s any new ansophistiated proeure t also reeived a ba name from earlyfailures all aused y misuse

The following topis are isusse

Torque transmission through keys

Installation of keye hubs using interferene

Torque transmission through frition

Installation of keyless hubs heat-assiste installation hyrauli assiste installation

Hyrauli removal of hubs ismounting keye hubs ismounting keyless hubs

Failure ases


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154 PROCEEDINGS OF THE TWENTY-SECOND TURBOMACHINERY SYMPOSIM

yrauli methos for hub removal were isusse in pr viospapers 1, 2. The purpose herein is to ompile an pdat previousinformation an to esribe goo praties.

TOQUE TANMION THOUG EYKeys are suh an ol mahine part that the authors oul not

trae their origin. There are many shapes of keys an all arestanarize. Ultimat ly, all keys transmit torque trough shearing of a retangular ross setion. Three ompletely ifferent

shapes of keys are shown in Figr 1, all having the same shearingsetion a r ctangl of with W an a length L

Square Key Cylndrcal Ke

Figure I hree pes of Sh eys Note: he asic dimesios(width ad legth) remai the same r all pes

Key imensions were standardiz d about 150 years ago thewith to be 1/4 of sha iameter an the l ngt to be 1.5 timesshaft iameter. A simple shear stress calculation will emonstratewhy these partiular imensions were cos n.

The sh ar stress g n rat d by torqu in a ylinial shaft is

w r

=shat iameterT =torq

2 T 5.3 X T = =--

' 1 r d3

Note if is in in an T in in/lb, is lb/in1.The

s ar stress generate by torqu in the r ctanglar rosssetion of the key is

2T =

W L

Introducing

the stanarize key dim nsions (W =/4 an L =1.5 the following is obtaine

5.1 X T = _

d

_

It an be seen that the sear stresses in the sha and in the keyare pratially iential; it goes without saying that the strength ofth two materials must also be the sam . Amazingly, this simplrule was forgotten over the years; toay almost all engineeringhanbooks inlue table aer table of various key imensions butnot a wor about key material.

The authors have seen a number of ostly mahine failur s thatwere ause by the use of low arbon steel keys in appliationswere both shafts an hubs were mae of heat-treate alloy steels.An important rule to remember is that the key material, ad the keyhardess, should e similar to that of the sha or hu

INTALLATION OF EYED HUB UNGINTEFEENE

All uplings resist being misalige; misaligment auses alltypes of

couplings to ten to rok on their shas. Th bak-anforth motions of small amlitue an high frequeny ause frettingwear to our on bore and shaft surfac s; fretting inues fatiguein shafts with atastrophi onsequenes as shon in Figure 2

Figure 2 Frettig-Iduced Sh Failure Note: Frettig wascaused y the rockig the hu o its sh motio possileecause of istallatio without sciet iterferece

The only way to avoi fretting is to s interferene at installation. Interferene is reate wh n the bore iameter is slight ysmall that the shaft diam t r. ow much int rf r nc is r qir dfor pr v nting r tting occurr nc ? First d fin int rf r nc :

nterference is the drece etwee the ore ad sha diameters, divided y the sh diameter Therefore interferene isdim nsionl ss: it is cstomary to refer to it as in/in or mm/.

Example A

A cylindrical saft has a iameter of 4.000 in an its hb borehas a iameter of 3.996 in. T r sulting int rf r nc is

Example

i = 4.000- 3.996 =0.0014.000

A tapere sat has a nominal iameter of 3.000 in an a taperof 3/4 in/t. The hub bore large en has a iameter of 2.995 in. tinstallation, th hub is avane (rawn on the shaft 0.048 in. Ther slting interferene is

. tap r x avane1 = -

-

shat diam t r

075 X 0.048 X =0.00112 3.000

Note that the bore iameter oes not enter in the alulations;however it must be smaller than the shaft by at least

i X =0.001 X 3.000 =0.003 in

Going bak to the qu stion of how muh interferene is reqeo prevent fretting experiene has shown that a minimu of0.0005 (in per in at operating onitions will prevent the urrene of fretting. Rotating spee reates entriugal aeletonwhih in turn auses the hub bore to grow. To ensure

th

miiuminterferene at operating spee the authors reommen th


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TUTORIAL ON HYDRAULIC REMOVAL OF COUPLING HUBSKEYED AND KEYLESS 155

At speeds up to 3,600 rpm the mounting interference shouldbe 0.00075,

at speeds between 3,600 and 8,000 rpm the mounting interference should be 0.001, and

at speeds above 8,000 rpm the coupling or machine manufacturer should be consulted, as the amount of interference alsobecomes a functio of the type ad diameter of coupligs.

TOQUE TNMIION THOUGH FITIONInterference creates a contact pressre at the hub-to-shat inter

face, a this pressure, combied with frictio, helps in thetransission of torque. The torque that can be transmitted byfriction can be calculated using the formula:

where:d =shaft nominal diameterD =hub outside dimeterL =hub effective lengthi = nterferencec = D/d

Note: If all te dimensons are n inches (in), T is in nlb, and k =2.8 lb/in

Two assumptons were made: that te hub and sha are made ofsteel, and tat the ction coecient is 0.12 (note: torque sdirectly proportonal to the ction coecient). For details aboutthis rmua see Calistrat [1].

The effective hub length is the length of contact between the uband shaft; it determines the area of contact between the two. Thearea lost through keyways or -ring grooves should be iscounted,as it is compensated by a proportional increase in ontact pressure.

xamle C

Using the data from xamle B, and assuming an effective hub

length of 4.0 in and a hb outside diameter of .5 in, te followingis obtaied:

T =2.8 X 10 X 3 X (1 (5

r) X 4.5 X 0.001 =62,940 inlbsInterestingly, this s about the rated torque of a general-purpose

gear-type coupling for a 3.0 shaft. Although all the torque of thesha could be transmitted through iction, no margin exists fortorque uctuations, and particularly for peak torques. The aboveexample shows that, durig ormal oeratig coditios a 0.001interference relieves most of the stresses in keys used in generalpurpose couplings.

INFLUENE OF PEE ON INTEFEENEMounting interference s reduced by the hbs is centrifugal

growth. At speed, the actual interference s:

i = 0.055 rpm D 10

This formula shows that the reduction in mounting interferences greatly inuenced by the hb's outside diameter, and by therotating speed. For hubs with large flanges, such as the one shownin Figure 1 , the actual interference is not uniform across the hublength; it is smallest just under the flange.

xamle :

A flanged couplig hub is installe o a .5 in haft, rotating at6,000 rpm. The otsd diameter of the hub body is 5.5 i, an theange outside diameter is 8.0 in. The ounting nterference is0.00075 (in/n).

he actual interference, at operating speed, varies as follows:

Uder the age

=0.00075 0.055 X 6000 X 5.5 X Q =0.00069or 92 perent of mountng

Uder the hu

i =0.00075 0.055 X 6000 X 8 X 10 =0.00062s

or 83 percent of mounting

Average interference, to be used in the calculation of torquetransmission ablity:

i = (0.00069 + 0.00062)/2 =0.00065or 87 percent mounting

INTLLTION OF EYLE HUBWithout keys, al the torque (icluding momentary peak torques)

mst be transmitted through iction between the hub bore andshaft. The ictio generated by a 0.001 interrence ca transmitmost of the general-purpose coupling torques. However, keylesshubs are mostl (but not exclusively) used with specal-purposecouplings, which are made of alloy steels, operate at high speeds,and can transmt larger torques than general-purpose couplings.

Therefore, in keyless couplings the effective intererence mustbe much larger. t is customary to use 0.002 to 0.0025 (ini)interference. All the formulae previousl given apply.

Keyless hubs are used almost exlusvely on tapere shas.Manufacturers seldom give reomendatons on how much

interfrence should be used with their keyed-hub couplings; theyalways give detailed instructions in the case of keless hubs. Oneparticular reason to follow manufactrers instructions is the factthat interference causes high stresses i hubs. A 0.003 iterferenewill create stresses as high as th yiel stregh of alloyed, heattreated steels. Therefore, such a high iterference should not beused. However, even a lower interferene could create problems inhubs wth a thin shell, or hbs that have oil injection holes drlledin their bodies. In such cases stresses can be very high, and thecoupling manufaturer instructos must be closely followed.

The authos ow of one case where a replacement hub wasmade by an independent machine shop, of incorrect material. Thehub split open at installaton, which was fortnate; it could havefailed after the machine was startd!

There are two ways to install keyless hubs: through heat expan

son, or through hydralic expanson.HeatAssisted Istallatio

The biggest advantage of heat installation is that the resultingfrction coeficient s lager t e oi dilatons used. Experiments have shown that the dry frition coeficien can be as highas 0.20, as compared with 0.1 t case ofydrali installation.Therefore, either a larger torue e trasmitted, or a smallerinterference can be used. On the other hand, heat expansionprecludes the use of seals at the hub-to-sha interfce, ad requiresan oven onsite.


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156 PROCEEDIGS OF THE TWENTY-SECND UBOACHINERY SYMPSIUM

Therml expsion cultions show tt for every 0.001interference out 160F difference betwen the hub nd shft isrequird. herefore, for 0.0025 interference, d sh t 80F,t iimum ub temperture ust be 500. If mrin foreors is prvided, hubs must be heted close to steel temperingtepertures, which could cuse degrdtion of mteril strength.

Te lc of sels cn cuse two problems t removl: rst,sufcient pressure for diltion might not be chieved; second,scorig of the sft nd bore migt ocur. Te deformtion f

seless hub uder ressur is shown i Figure 3. It is evdent thin orr to sel the oil, high contct pressure must exist t the boreedges. ouned coers re use in order to inimize the possibility of scring.

The following stes should be followed for the hub instlltio:

Clea cotct urfaces of shs nd couplings very crefully. If rubbing is requird t remove peservtives, us nonbrsiv mteril, nd do not use xil motions. Some couplingmufcturers use d preservtive tht cn be removed onlythrouh lpping. It is very importn to remove ll preservtives,bcuse if le on, they will siificntly reduce the frictincoeficient.

Measure the sha ad the ore nd nsure tht the dimensions re s specified by the mnufcturer. Tpered surfcesshould b checed with tpered guges; cylindricl surfces shuld

e ced with micrometes. Check for proper cotact (for tpered shfts only). After the

shft nd hub bore re thoroughly clened, spred thin lye ofmechnics blue on the shft nd push the hub snugly. Whilepplying light xil pessure, rotte the coupling hub smllmount, nd bc up to the origin position. Crelly remove thehub nd chec the bore fo contct, by the mount of colord re.A lest 80 percnt, nd preferbly 90 percent of the bore shouldshow ontct.

Fi the prolem If less thn 80 percet ontct is found,chec the ccurcy of the sufces using tpered guges. It isimportnt to nd the problem before corrective mesues reten.

0 Improve the cotact If problems re found, either the shft,

the bore, or bot, mst be corrected through lppng. The following rules should be followed:

Fiure 3 Hu ilatio wih Hydraulic Pressue Not: he arelype distortio i yical of sealless hus

Hubs re more oten t fult for lc of contct hn ss. Ifserious defects re found it is dvisle to first send the problemhub to a grinding shop to be "sprd out. A minimum mount ofmteril should be removed t reestblish god contct.

Use ring nd plug lpping tool set never lp hu on itss. Lppng tools re mde of so mterils, usully cst iro.Using hrd tools (such s guges) will reduce the effectiveness oflpping, nd the tools might become dmged uicly.

pping will chnge the hub xil position on the shft. A generl rule, hubs move illy 30 times more thn the thicnessemoved through lpping. Fo exmple, if one mill 0.001 in) isremoved, t hub stndoff will be reuced b 0.030 in. Excessivelpping might require mchine relignment, of use of shims inmetl exible element couplings.

To expedite the lping pocess, strt with corse cmpound, nd chnge to progressively finer git s the defects recorrected.

Clea the lapped surfaces Remove ll trces of lppingcompound, using solvent nd lint-free towels. Rechec the hubtoshft contct.

\ Protect surfaces by spreding thin oil on the sh nd hubbore (to prevent rusting).

Measure the hu draw (dvnce). Using depth micrometer, mesure from the fce of the hub

to the end of the sh, nd record the "stt reding. A seondreding should be ten, if possible, ihe from fixed point on themchine, or from split collr ttched on the sh, behind thehub. Use pllel brs, snp guges, or feeler guges, s required.

Clulte the hub overhng fter instlltion, by subtrctingthe intended drw om the "strt dimension. It is possile tht negtie vle my be obtined, mening tht the sht willprotrude out of the hub. Although n undesirble condition, it isoen encountered in cses where mny corrections were mde forproper contct. If the shft protruds, specil retining nut,incorporting counterbore, must b mde

\ Clea surfaces Just efore instlltion clen the sht nd

the bore of ll luricnts, using solvent nd, if necessry, lintfree clth.

Heat the hu to the recommended teperture. Use n iroven or induction heter. If the temerture to which the hub mustbe heted is not specied, use the following rule: 160F derecebeteen hub nd shft, fo every .001 iin interference, to whicn dditionl number of deees should be dded s sfetymrgin.

Remove the hu from the oven nd plce it quicly on theshft. A positive stp must be provided in front of, or behind thehub, otherwise the dvnce could be wrong.

Measure agai the hub drw (dvnce). The hub must edvnced on the shft exctly the mount specified. Too littledvnce could result in the hub spinning on the shft; too much

dvnce could reslt in the ub splitting t or shortly ter instlltion.

ydraulic-Assisted Istallatio

Hubs wth tpered bores cn lso be expnded hydruliclly.The dvnce (drw) n be either mehnicl, using specil shtnut, or hydulic, using n nnulr cylinder (hydrulic nut). Therrngement is shown in Figure 4.

Hydrulic dvnce hs two dvntges over the mechnicldvnce: i does nor rquire tool to prevent the sht fromrotting, nd the hdrulic nut cn lso be used t removl.


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TUTORIAL ON HYDRAULIC REMOVAL OF COUPLING HUBSKEYED AND KEYLESS 157

Figure 4 IstallatiRemval Hydraulic l. Nte his tlallws fr heatless istallati, ad fr safe remval.

The required pressure for expanding the bore is high, usuallybetween 20,000 and 35,000 psi.

Three special tools are needed for hydraulic advance: an installation tool (hydraulic nut), a high-pressure (50,000 psi) oilpump with pressure gauge, and a low-pressure (10,000 psi) oilpump with pressure gauge.

To ensure a sucessful installation, te following procedure isrecommended:

D Clea ctact surfaces of sha and coupling very carefully.

If rubbing is required to remove preservatives, use a nonabrasivematerial, and do not use axial motions. Some coupling manufacturers use a dry preservative that can be removed only throughlapping. Removing all preservatives is very important, because ifleft on, they will significantly reduce the fiction coecient.

D Measure the sha ad the re and ensure that the dimensions are as specied by the manufacturer. Tapered surfacesshould be checked with tapered gages.

D Check fr urs sha eds -ring grooves and oil inletpassages. Sharp edges can nick the seals and cause dificulties atremoval. Check coupling bore for similar conditions. Burs anddrag mar can be removed using a ne "Indian grade hone.Never hone axialy.

D Check fr rer cact. Aer the sha and hu bore are

thoroughly cleaned, spread a thin layer of mecanic's blue on theshaft nd push the hub snugly. While applying a light axialpressure, slightly rotate the coupling hub, and back up to theoriginal position. Carefully remove the hub and check the bore forcontact, by the amount of colored area. At least 80 percent, andpreferably 90 percent, of the bore should show contact.

D Fid the rlem. If less than 80 percent contact is found,check the acuracy of the surfaces using tapered gauges. It isimportant to find the problem before corrective measues aretaken

D Imrve the ctact. If problems are found, either te shaft,the bore, or both, must be corrected through lapping. The following rules should e followed:

Hubs are more often at fault for lack of contact than shafts. Ifserious defects are found it is advisable to rst send the prolemhub to a grinding shop to be "sparked out. A minmum amount ofmaterial should be removed to reestablish good contact.

Use a ring and plug lapping tool set; never lap a hub on itsshaft. Lapping tools are made of soft materials, usually cast iron.Using hard tools (such as gauges) will reduce the efectiveness oflapping, and the tools might become damaged quickly.

Lapping will change the hub axial position on the shaft. As ageneral rule, the hub moves axially 30 times more than thethickness removed through lapping. For example, if one mill(0.001 in) is removed, the hub standoff will be reduced by 0.030 in.

Excessive lapping might require machine realignment, or use ofshims in metal flexible element couplings.

To expedite the lapping process, start with a coarse compoud, and change to a progressively ner grit as the defects arecorrected.

D Clea the laed surfaces. Remove all traces of lppingcompound, using a solvent and lint-free towels. Recheck the hubto-shaft contact.

D rtect the surfaces by spreading thin oil on the sha andhub bore (to prevent rusting).

D Measure the hu draw (dvance).

Without any -rings or backup rings, install the hub snugly onthe sha. This is the start position.

Using a depth micrometer, measure from the face of the hubto the end f the sha, and recor the "start reading. A secondreading should be taken, if possible, either from a xed point on themachine, or from a split collar attached on the sha, behind thehub. Use parallel bars, snap gauges, or feeler gauges, as required.

Obtain the hub overhung aer instalation, by subtracting theintended draw from the "stat dimension. It is possible that anegative value will be obtaied, meaning that the sha wilprotrude out of the hub. Although an undesirable condition, it isoten encountere in cases where many corrections were made rproper contact If the sha protrudes, a special retaining nut,incorporaing a counterbore, must be made.

D Check rer 0-rigs ad acku rigs are availale. Thecombination should in the groove without too much efort. -rings will protrude slightly out of the groove. Backup rings areavailable as either nonsplit hard rubber, or split white nylon. Thesplit rings must be individually adjusted to fit their grooves, bycutting o some material. Neither overlapping, nor gaps areacceptable. Back-up rings should not protrude out of the grooves.

D Istall 0-rigs ad acku rigs in shft and hub grooves.Oil is pumped between the hub and shaft through a shallow circulargroove machined either in the hub or in the shaft. Install the -rings toward this groove, the backup rings away om this groove.

Ater they are installed, look again! The -rings must be betweenthe backup rings and the oil grooves! Spread a little bit of hydaulicoil on al rubber surfaces.

D Mut "ther cets. Read the coupling installationprocedure again. Must other components (such as a sleev) bemounted on the sha before the hub? If so, now is th tim o doit.

D Aly a thi layer f hdraulic il the sha. This oil willprevent the rolling or twisting of the seals. The hih pressures usedduring removal will not e contained by defective seals.

D Mut the hu the sha. Avoid pining the -rings duringmounting. The o-rings, being taller than the grooves in which theyare installed, will prevent the hub from advancing to the "startposition. This is normal.

D Mut the istallati tl. Wet the threads with thin ol, androtate the tool until it butts against the shaft shoulder. The last fewturns will require the use of a spanner wrench.

D Cect the hydraulic lies. Connect te cllased installation tool to the low-ressure oil pump (5,000 psi minium).Connect the high-pressure oil pump (40,000 psi minimu) to thehole provided either in the center of the shaft or n the outsidediameter of the hub, depending on design. Loosen the vent plug ofthe installation tool and pump all the air out; retighten the plug.Both pmps must be equipped wih pressure gauges.


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15 PROEEDIGS OF THE TWENTY-SECOND TURB MACHINERY SYMPOSIUM

Note: e nly hydraulic oil in the highpreure pump The ueof lubricating oil culd caue the italled hub to lide off thehaft

dace the h to the tart poition by pumping the lowpreure oil pump Continue pumping until the hub advance 0.005to 0.010 in beyond the tart poition

xad the h ump the highpreure pump until thegauge read between 15,000 and 17,000 pi A the preure

icreae, the hub will tend to move off the haft Correct thimovement by occaionally increaing the preure at the intallation tool

Check for oil lea The preure at the highpreure oilpump will drop rapidly at rt becaue the air in the ytem ecapepat the ring Continue pumping until the preure tabilizeThe hub hould not be advanced on the haft if leak are oberved!A maximum preure lo of 1,000 pi/minute i acceptable If thepreure drop fater than that, remove the hub and replace the ring However, before removing the hub, make ure that the leakdo not occur at the hydraulic connection

dvace the h Increae the preure at the intallation tooland the hub will advance on the haft If all the previou tep wereoberved, the preure at the highpreure gauge will graduallyincreae (by itelf!) a the hub advance If the preure doe not

icreae then top! Rmove the hub nd check the oring If theprure increae, keep advancing the hub until it touche the plitcollar or until the pecified advance i reached Do not allow thepreure to exceed 30,000 pi If it doe, open the pump' valvelowly and rleae ome oil If in doing thi, the preure dropbelow 25,000 pi, pump the high preure pump to 25,000 pi, andcontinue the hub advace

Seat the h After enuring that the hub i in the deiredpoition, lowly releae all the preur at the highpreur pumpnly The oil preent in the pace between hub and haft mut beiven tim to return to the pump, le the hub lide off Therere,d not work on that hub for about onehalf hour, or one hour in coldather Aer thi waiting period, releae all the preure at theintallation tool and remove it from the haft

Ver the advace Meaure and then record the new overhang of te hub over the haft Subtract from the overhangmeaured in th "tart poition, and the reult mut be the ame athe pecied advance, within the given tolerance Record theactual advance for future reference

Secre the h Remove the plit collar from the ha andintall the retaining nut, but do not overtighten Secure the nut withthe etcrew provided Note: et crew hould have a "cuppoint, and the point hould imbed in the haft urface, ot in the hubface If the nut i ecured to the hub, and the hub pin on the haft,the nut could become looe and actually fall off the haft

HYDAULI EMOVAL OF HUB

ismotig Keyed Hs

Hub that have been intalled for a long time have a tendency totick to their haft Thi tickin, in addition to the friction forcegenrated by interference, mae for difficult removal

T help in the remval of eyed hb, it i recommended tomer he haft, at intallation, with an antieizing compoudMay ch compound re comercially availale The autorecommend the ue of compound blended with chromium oxide,wch are eay to recogize by their ilverygray color A n ecoomical alternative i the ue of greae containing zinc oxide,which are whitegray in color The ue of antieizing compoundreduce by a mall extet the friction coecient, and lightl le

torque can be tranmitted tough friction Atieizing compound are a mixture of olid (uch a chromium oxide powder)and greae At the moment a hot hub i intalled on a haft, all thoil from the compound i eliminate and only the olid remainTherefore, the iction coeciet i reduced, but only by a mallamount

There are many mechaical method available for hub removalhowever, only hub removal method that ue hydraulic preurefor the dilation of the hub are dicued here The advantage of

hydraulic removal are: on one had, dilatio reduce the mountinginterference, and on the other hand the greae (or hydraulic oil)lubricate the mating urface e of the hydraulic removalmethod greatly implie hub removal, and completely eliminatethe ue of open ame on coupling component

Hydraulic removal require a light modificatio of the exitinghub, but the cot of uch modification are probably recovered bythe downtime aved at the rt ue

Two method are available, one whic ue a plain greae gun[3], and another that ue two oil pump [2].

Two hub are hown in Figure 5 modied for removal uing agreae gun Automotivetype gun can deliver a preure of about10,000 pi Conidering that 0.001 interfrence crate a contactpreure of 8,300 pi (for D/d = 1.5), greae gun can eailyovrcome the contact preure generated by interference

BFigre 5 Hydralic (Grease) Removal Metho for Keyed HsNote: Method alies to geared hs; method B alies toaged hs for all es of coligs

The groove that ditribute greae around the bore mut bemachined o that it doe not break into the keyway There are twoway to machine uch a groove: either through milling, or by offetintallation of the hub in a lathe' chuck Either way, a minimumf 1/4 in hold eit beteen the end of the groo and thekyay Two ndependent roov ut be machined for hubith wo keway

Connecting the groove to the outide of a gearcoupling hubrequire more kill than in the cae of anged hub In either cae,a mall greae fitting i intalled at the outide of the hub Thigreae fitting can be le in place durig coupling operation, unleit interfere with other coupling componet For hub with two


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TUTIA N HYDRAULIC REMVAL F CUPING HUBSEYED AND EYLESS 159

keyways hus must either have two grease ttings (and two greaseguns must be used at removal), or the two grooves can be connected by a small (1/8 in) hole drilled through the shaft, perpendicularto the plane of the keyways (Figure 5).

To remove a hub so equiped, siply pump grease in the hubwhile a pulling force is applied. For tapered hubs, t is possible thatno pulling force is needed actuall, it is safe to keep the shaft nutin place (but slightly loose) uring removal. For cylindrical bores,the best tool to use is one similar to the automotive steering-wheel

puller, attached with high-strength bolts to the puller holes of thehu. An air impact wrench will ensure continuous movement of thehub while hydraulic pressure is maintained.

The oil injection method is discussed by Munyon and Zilberman[2], and is illustrated in Figure 6. It is basically the same as thegrease-gun method, except it uses to oil pumps, one for dilatingthe hub, the other fr an oil ram. The authors believe that the useof a steering wheel puller is as ecient, but simpler.

Figure 6 Hydraulic (Oil) Removal Metho for Keyed Hus. Notehe hydraulic ram ca e replaced with a steerig-wheel-ypemechaical puller.

Dismoutig Keyless Hus

It is important to recognize that hydraulically removing a hubinvolves some danger, and safety precautions must be carefullyobserved. Because hubs are expanded at installation, they store asubstantial amount of potetial energy, just like a stretched spring.hen a hub is removed, this potenti energy is abruptly releasedand transformed into kinetic energy, i.e., the hub is acceleratedaxially. umping oil between the hub and shaft provides thelubricant on which the hub slides.

Another force that helps in removing hbs is the diametraldifference between the two ends of the bore (o etween the two -rings), which cretes n nnulr hydraulic piston.

Example EA 4.0 in sha with 3/4 ift taper and a three-in axial distance

between o -rings becomes an annular piston with an area of 1.2 inIf the hydraulic pressure is 25,000 psi, the resultant axial force is15 tons.

It is obvious that hubs must be stopped, or they will fly off thesha and damage themselves and anything they encounter. Onemethod for stopping a hub is illustrated in Figure 7. The retainingnut is backed off sufficiently to allow the hub to move slightlymore than the distance it was advanced at installation. Two stepsshould be taken to safely dissipate the kinetic energy:

Figure 7Mechaical Stop for Hydraulic Hu Removal. Note hedistortio f a lead rig asors the kietic eergy of hus.

First, a lead washer (inimum 1/8 in thick) should be installedbetween the hub and the nut.

Second, the gap should be made only 0.010 in to 0.020 in widerthan the oiginal advance. A larger gap will allow the hub to attaina too-high velocity. The lead washer will absorb the energythrough deformation. The authors know of one case where, without a lead washer an with a wide gap, the threaded portion of theshaft was snapped off!

Even with al these precautions, personnel should never stand inline wih the sha when hubs are being removed.Ater a stop is provided, hydraulic pressure should be pplied

slowly. A too-quick increase in pressure will not give time for theoil to wet the interace completely, and localized scoring couldoccur. It is ven possible that it will take the hub a few minutes topop out.

If the machine is very cold, chances re the oil (which becomesmore viscous at low temperatures) will not completely penetratebetween the hub and the shat, nd the hub cannot be removed. Onesolution to this problem is to apply some heat to the hub. However,heating the hub above 250F cn be detrimental. First, because oilswill lose much of their lubricating properties, nd second, because-rings can be scorched and will no longer seal. Therefore, heat isbest used in moderation, and as last resort.

In order to eliminate ll risk relted to hydraulic hub removal,a procedure which requires the use of the installation tool (Figure4) during disssembly was developed many years ago by Calistrat.his procedure cosists of the following steps:

Remove the sh ut.D Mout the collapsed istallatio tool. et the sha threads

with thin oil and rotate the tool until it butts against the shashoulder. 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 records). If the gap is less than required,the wrong installation tool was probably selected for removal.

D Coect the hydraulic lies. Connect the installation tool tothe low-pressure oil pump (,000 psi minimum). Connect the highpressure oil pump (40,000 psi minimum) to the hole providedeither in the center of the sha or on the outside diameter of thehub, depending on the design. Both pumps must be equipped withpressure gauges. Loosen the vent plug of the installation tool andpump all air out retighten the plug.

D Pump oil ito the istallatio tool. The piston will advanceuntil it contacts the hub. Continue pumping until the pressure isbetween 100 to 200 psi. Check for leaks.

D Expad the hu ump oil between the hub and the shaft byusing the high-pressure pump. While pumping, watch both pressure gauges. hen the high-pressure gauge reaches about 20,000psi, the pressure at the low-pressure gauge should start increasing


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160 PROCEEDINGS OF THE TWENTY-SECOND TURBOMACHINERY SYMPOSIM

rapidly. This pressure increase is caused by the force that the hubexerts on the installation tool and is an indication that the hub isfree to move. Note: depeding on the interference used and onother conditions the dilation pressure could reach 35000 psibefore the hub will start moving.

Wait a while In case the low pressure at the installation tooldoes not increase even if the high pressure reaches 30000 psi waitabout one-half hour while maintaining the pressure. It takes timefor the oil to penetrate in the very narrow space between the hub

and the sha. Usually there should be no need to exceed 30000 psiunless a very high interference was used at installation.

Allow the hu to move After the pressure at the installationtool icreases slowly open the valve at the low-pressure pump(note: this valve could become hot as the energy stored in the hubis dissipated there; wear protective gloves). The oil from theinstallation tool will ow back into the pump and allow the hu tomove. The pressure at the high-pressure gauge will drop. Do notallow it to fall below 5000 psi. I f it does close the low-pressurevalve and pump more oil at the high-pressure pump. Continue theprocess until the valve at the low-pressure pump is completelyopen and the pessur at the installation tool becomes zero.

Remove the hu Release the high pressure and back of theinstallation tool until only two or three threads are still engaged.

Pump the high-pressure pump and the hub will slide of the shaft.When the hub contacts the installation tool release all the pressureand remove the tool. The hub should now come off the shat byhand. Do not remove the installation tool unless the pressure iszero!

Ispect the 0rigs Reusing even slightly damaged ringsinvites trouble. The safest procedure is to always use new seals anddiscard the old ones.

FAILUE AEAs with any new device or method failures are bound to happen

in the beginning either due to poor traiing or to negligence.Although the risk of sudden release of stored energy can bedangerous the authors now of no injuries related to hydraulic hubremoval.

Case 1

n a ca lat a a compro w s od with newkeyless shas. New couplings were purchased and installed. A fewdays after startup one of the couplings spun on the shaft whichbecame severely damaged. A new sha was made and a new hubwas purchased. It was noticed during the installation that the forcenecessary for hub advance was much larger than expected. The hubwas immediately removed and a sheet of rubber was found on theshaft. What happened? The person who purchased the -ringseals unaware of the need for backup rings ordered -rings thatwere as wide as the grooves. Evidently the seals were too large andexceeded the cross sectional area of the grooves. They becameextruded between the bore and the shaft. Instalation of correctseals solved the problem.

Cae 2

A keyless hub could not be removed because not enoughpressure could be created to dilate it. The hub had to be cut forremoval. Observation of the bore revealed that:

Sand was trapped between the bore and the sha. Sandgranules prevented a god onact but provided sucient frictionfor torque transmittal.

The backup rings were installed at the face (rather than back)of the -rigs. Combined with the gap at the interface created bythe sand the -rings were blown off the grooves and pressurecold no longer be built.

Case 3

Seven out of eight coupling hubs in two compressor trainsslipped on their shas during operation. The hubs became weldedonto the shafts and the trais operated successfully until the firstscheduled maintenance shutdown. The coupling hubs had to be cutoff for removal. Observation of the bores revealed that the coupling manufacturer applied a dry coating on all couplig hubsurfces including the bores as protection against rust or corrosion. This coating acted as a dry lubricant at the bore practicallyeliminating any friction. The problem would not have occurred ifeither the bores were not coated or if the hubs had been lapped(they were not). To eliminate such occurrences the manufacturerdiscontinued the dry coating method and the user made lappingmandatory at installation. As a point of interest the coted coupling hubs were installed by the compressor manufacturer not bythe user.

ONLUIONHydraulc removal of couplings can be used either with keyed

or keyless hubs.The method has (apparent) disadvantages:

Couplings cost more (but the additional costs are quicyreovered by shortening the removal time).

Mechanics require better traiing.

Specialized tools are required.

The method has many advantages:

It is faster than brute force and consistently successful.

It eliminates the need of open ames.

It eliminates the possibility of shaft and bore damage. In keyless hubs it eliminates the stress concentrations created

by keyays

EFEENE

I. Calistrat M. M. "Hydraulically Fitted Hubs Theory andPractice Proceedigs of the Nith uromachierySymposiumThe Turbomachinery Laboratory The Texas A&MUniversity System College Station Texas pp. 1-10 (1980)

2 Munyon R. E. and Zilberman J, "Hydraulic Removal ofKeyed Hubs Internatioal Power Transmissio and GearingConference pp. 807-813 (1989)

3 Calistrat M. M.Flexible Coupling Installation National

Conference on Power Transmission pp. 21-35 (1981)

Coupling Hubs

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