PT Fundamentals

Product Training ManualPower Transmission Fundamentals for V-Belt Drive Systems

• Basic calculations to assist in installation and problem-solving • Belt Drive Advantages • Product Types • Balancing Standards • Installation & Maintenance

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INDEX

Chapter 1 - Power Transmission Fundamentals1.1 Calculation of the Circumference of a Circle ...................................................................................................... 31.2 Force ....................................................................................................................................................................... 5 1.2.1Definition .............................................................................................................................................................5 1.2.2Motion ................................................................................................................................................................ 6 1.2.3TorqueCalculation ............................................................................................................................................. 71.3 Work .......................................................................................................................................................................121.4 Speed and Velocity .............................................................................................................................................. 141.5 Power .....................................................................................................................................................................161.6 Efficiency ...............................................................................................................................................................191.7 Ratio .......................................................................................................................................................................201.8 Service Factors ....................................................................................................................................................23

Chapter 2 - Drives: Belts, Bushings & Sheaves 2.1 What are the Advantages of a Belt Drive System? ........................................................................................... 252.2 Belts ..................................................................................................................................................26 V-BeltClassifications .............................................................................................................................................27 2.2.1.1 Lightduty&Fractionalhorsepower(F.H.P)V-Belts .....................................................................................27 2.2.1.2 ClassicalV-Belts ...........................................................................................................................................28 2.2.1.3 DeepWedge/GrooveorNarrowV-Belts .....................................................................................................29 2.2.1.4 Cogged/Raw-EdgeV-Belts .........................................................................................................................30 2.2.1.5 BandedBelts ................................................................................................................................................30 2.2.1.6 V-Ribbed/PolyV-Belts .................................................................................................................................31 2.2.1.7 Double/HexagonalV-Belts ..........................................................................................................................31 2.2.1.8 VariableSpeedBelts.....................................................................................................................................32 2.2.2 OtherBeltTypes ...........................................................................................................................................32 2.2.2.1 StandardFlatbelts ........................................................................................................................................32 2.2.2.2 Standard/TrapezoidalSynchronousBelts ...................................................................................................33 2.2.2.3 H.T.B./CurvilinearSynchronousBelts .........................................................................................................34 2.2.3 BeltLength ..................................................................................................................................................35 2.2.3.1 Parallelaxis,uncrossedbeltdrive ................................................................................................................36 2.2.3.2 Arcofcontact ................................................................................................................................................372.3 Drive Components Materials ................................................................................................................................38 2.3.1 Gray/CastIron ..............................................................................................................................................38 2.3.2 DuctileIron ..................................................................................................................................................38 2.3.3 SinteredMetal ...............................................................................................................................................39 2.3.4 TableofMechanicalProperties .....................................................................................................................392.4 Bushings ..................................................................................................................................................40 2.4.1 QD(QuickDetachable)InterchangeableBushings ......................................................................................40 2.4.2 Taper-Lock/BoreBushings ..........................................................................................................................43 2.4.3 SplitTaperBushings .....................................................................................................................................43

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2.5 Sheaves ..................................................................................................................................................44 2.5.1 SheaveBody ................................................................................................................................................45 2.5.2 SheaveClassifications&Terminology ..........................................................................................................46 2.5.2.1 LightDutyFixed&BushTypes .....................................................................................................................46

2.5.2.2 Adjustable/F.H.P&Integral ..........................................................................................................................47 2.5.2.3 Classical&NarrowBeltDrives .....................................................................................................................50 2.5.2.4 ApplicationTablebyClasses ........................................................................................................................51 2.5.3 BalancingStandards(MPTA)........................................................................................................................52 2.5.3.1 GeneralInformation ......................................................................................................................................52 2.5.3.2 StaticorSingle-PlaneBalancing ..................................................................................................................52 2.5.3.3 DynamicorTwo-PlaneBalancing .................................................................................................................55

Chapter 3 – Drive Selection Program

PleaseseeourOn-lineProgramforthissectionatwww.maskapulleys.com

Chapter 4 - Installation & Maintenance

4.1 Bushing Mounting .................................................................................................................................................57 4.1.1 TypesofMounting ........................................................................................................................................57 4.1.2 Tightening ..................................................................................................................................................584.2 V-Belts & Sheaves .................................................................................................................................................59 4.2.1 MountingStructure .......................................................................................................................................59 4.2.2 CenterDistanceAdjustment .........................................................................................................................59 4.2.3 V-BeltInstallation ..........................................................................................................................................60 4.2.4 Tensioning ..................................................................................................................................................63 4.2.4.1 MeasuringTechniques ..................................................................................................................................64 4.2.4.2 Run-inPeriod ................................................................................................................................................67 4.2.5 IdlerPulleys ..................................................................................................................................................68 4.2.6 Maintenance .................................................................................................................................................69 4.2.7 BeltStorage ..................................................................................................................................................694.3 Typical Problems ..................................................................................................................................................70 4.3.1 DriveMisalignment .......................................................................................................................................70 4.3.2 SheaveCrackedinHub ................................................................................................................................70 4.3.3 Vibrations ..................................................................................................................................................71 4.3.4 OverTension .................................................................................................................................................71 4.3.5 HighRatiowithShortCentertoCenterDistance .........................................................................................724.4 Couplings ..................................................................................................................................................73 4.4.1 FlexibleCouplingTypes ................................................................................................................................73 4.4.2 ShaftMisalignment .......................................................................................................................................75 4.4.3 ElastomericElementCouplings ...................................................................................................................76

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Chapter 1POWER TRANSMISSION FUNDAMENTALS

Inthisfirstchapterwewillendeavortofamiliarizeyouwithconceptsrelatedtodifferenttransmissionapplications.Variousnotionsofmechanicsandgeometryrequiredtomakeagoodselectionofdrivecomponentswillbepresented.Thesefundamentalcalculationbasicsareoftenfoundinengineeringreferencemanualsbuttheyhavebeenincludedtoshowhowtheycanbeappliedtoproblem-solvingwithbelttransmissionapplications.Youarethereforeencouragedtoexaminethischapteranddotheaccompanyingexercisesasgroundworkforcalculatingcriticalfactorsencounteredwheninstallingdrivecomponents.

1.1 Calculation of the Circumference of a Circle

Oneof themostcommonbasicgeometricfiguresusedwhendesigning a power transmissioncomponent isthecircle. Thecircle is thegeometrical shapeonwhich theentirepower transmissionprocess isbased.Thecircumferenceisdefinedasthemeasurementofthecircle’scontour;asimplemethodofobtainingthisdimensionisbymeasuringtheexactlengthofstringneededtogoaroundthecircle.

Circumference (C)

Circle Center

Radius (R)

Diameter (D)

Fig. 1.1: Illustration of a Circle’s Main Geometric Parameters

Tocalculateacircle’scircumference,wemustknowthattheratiobetweenthecircumferenceandthediameterisaconstant.ThisconstantisnamedPi(π,Greekletter).Itsvalueis 3.1416.

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Formulastocalculatethecircumference( C )ofacircleare:

C = � • D or C = 3.1416 X D

also, C = �(2R) ⇒ C = 2�R knowingthat D representsthediameterand Rtheradiusofacircle(Fig.1.1)

Example 1.1 Calculateacircle’scircumferenceifthediameteris4".

Answer: C = �D = 3.1416 X 4 = 12.566 inches

Ifa4"diskwasrolledonaflatsurface,adistanceof12.566"wouldbecoveredwitheach completeturn.

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1.2 Force

1.2.1Definition

Forceisdefinedastheactionthatonebodyhasonanotherbody.Whenanappliedforceonanobjectisgreaterthananyexistingforce,thiscanresultinadisplacementofastaticbody,accelerateanddecelerateabodyinmovementorresultinadistortionofsomekind.Thisisreferredtoasactionandreaction.

Forcecanbeaccuratelydeterminedwhenthemagnitude,directionandthepointofcontactareindicated.Inthefollowingdiagrams,theforce’sdirectionandpointofcontactarerepresentedbyavector(arrow)(seeFig.1.2).ThemeasurementunitofforceintheEnglishSystemispoundandtheunitsymbolis “lb”.Inthisexample,theweightofoneunitofmassisequaltooneunitofforce.

NOTE:ThisprincipledoesnotapplywhenusingtheMetricSystem.

When torque is not taken into consideration, all parallel forces can be subtracted if they are from opposingdirections, or combined if they are in the samedirection, to obtain a single force: resultant force. Whencalculatingtheresultantforce,itisimportanttokeepinmindthestatusofeachappliedforce(+or-)asthiswilldirectlyinfluencetheresultsobtained.However,referencetothepositiveornegativestatusisneededonlywhencalculatingmathematicalequations(Example1.2);itismorepracticaltodrawasimplediagramoftheappliedforces.(Ref.Fig.1.3)

Magnitude

Application point Direction

20 lb

Fig. 1.2: Diagram of a force

20lbs 20lbs 40lbs 20lbs

20lbsResultant=0

Fig. 1.3: Addition of collinear forces (Example 1.2)

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Example 1.2 Infigure1.3,forceisappliedtoeachsideofablock.(Inthisdiagram,thearrowrepresentsthepointofapplicationandtheforce’sdirection)Calculatetheresultantforceforeachdiagram,assumingthatthereisnofrictionbetweentheobjectandtheground.

Answer:

The leftdiagramhasa resultant forceofzero (20 lb.–20 lb.=0 )and thus remainsmotionless.Thelawofstaticdictatesthatthetotalsumofforcesmustequalzero.

Therightdiagramhasaresultantforceof20lb.(40lb.–20lb.=20lb.),thuspushingtheblocktotheright.Inthisexample,theblockmovesinthedirectionoftheresultantforceandonlyanopposingforce,likefriction,couldstopthemovement.

1.2.2 Motion

Twomajortypesofmotionexist;theyarelinearandangularmotions.Themovementofatrainonarailwaytrackis anexample of linearmotion. On theother hand, a turningpulley is a goodexample of angularmotion.Mechanicalpowertransmissiongenerallyimpliesthereforeangularmotionandtheusageofrotatingelements,suchas:shafts,couplings,gearreducers,chaindrives,sheavesandbelts.

Motionalwaysrequiresanexternalforceorenergy.However,motioncanbemeasuredwithoutreferencetotheinitialforce.Forexample,youcancalculatethespeedofanobjectevenifyoudon’tknowtheforceusedtopowerit.Theinteractionbetweenmotionandforceareveryimportantconceptstounderstandinanytransmissiondrivesystem,aswewillseelateron.

Linear Motion Angular Motion

Fig. 1.4: Linear and angular motion

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1.2.3 Torque Calculation

Intheprecedingsubheading,wesawthatforcecancauseanobject tomovelinearly(example1.2)but itcanalsomakeitturn.Torquecorrespondstoatwistingforceandresultsfromtheactionofanappliedforceonabodyatacertaindistancefromthecenteraxis.Thedistancebetweenthepointwhereforceisappliedandtherotarycenterisusuallycalledtheleverarm.Sothetendencyforanysystemsubmittedtotorqueistoturnonit’srotationaxis(example:tighteninganutwithawrench,pushingthepedalsonabicycle,abeltturningapulley,etc.).

Torqueiscalculatedbymultiplyingthemagnitudeoftheforcebytheleverarm.

Tocalculatetorque ( T ),usethisformula:

T = F x ror

T = F x R

knowingthatF=forceandr=theleverarm(youcanreplacerbytheradiusRforacircularbody,suchasapulley,whenforce isappliedontheoutercircumference). For thisreason, torque isexpressed inpounds-inches (lb.-in).Hence,torqueresultsfromthedirectionandmagnitudeoftheappliedforceandtheleverarm.

Important: The component force of torque must be at a 90o angle with the lever arm via the point of contact and the rotary center (Fig. 1.5).

Fig. 1.5: Diagram of torque force

centeraxis

TR

F

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r=10in

15lbs

150lb.-in

Example 1.3 A5"diameterpulleyisinstalledonashaft.Thepulleybearsaweightof10pounds (Fig.1.7).Whatistheinducedtorque?

Answer: Theleverarmmeasures2.5inches(diameterdividedbytwo).Thedistancebetweenthepointof contactandtherotarycentercorrespondstotheradiusofapulley.Theweightistheonlyforce producingtorque.

T = F x R

T = 10 [pounds] x 2.5 [inches] = 25 lb./ in.

D

Torque

10pounds

Fig. 1.7: Torque from a suspended weight on a pulley (Example 1.3)

Fig. 1.6: Virtual lever arm

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Example 1.4 Usingthesameexample,supposewewanttocalculatetheleverarm;theforceandtorqueareknown.Iftheinducedtorqueis50lb.-inandthesameweight(10lb.)issuspendedonthepulley,howlongshouldtheleverarmbe?

Answer: UsethesameformulatocalculatetheR(leverarm)thistime:

R= T

= 50 [lb • in] F 10 [lb]

R = 5"

Thisillustratesthesignificanceoftheleverarm.Thesameweightsuspendedfromapulleytwicethesize(thusdoublingtheleverarmlength),requirestwiceasmuchtorqueasinexample1.3.

Atthispoint, itwillbeusefultoexaminethenotionofresultanttorque,aswedidwithresultantforce.Multipletorquecanbeaddedorsubtracteddependingontheirdirection,butmustbeonthesamecenteraxis.Theconventionsignusedforthedirectionofatorqueis(+)foraclockwisedirectionand(-)foracounterclockwisedirection(Fig.1.8).Thefollowingexamplewillhelpyoutounderstandhowresultanttorqueworks.

Clockwise ( + ) Counter - Clockwise ( - )

Fig. 1.8: Torque convention sign

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Example 1.5 Calculatethetorquefromtherotatingpointofthebeamintheillustrationbelow(Fig.1.9).Afterapplyingtheweights,towhichsidewillthebeamtiltaccordingtotheresultingtorque?

Answer:Torquefromleftweightappliedoncenteraxis(counterclockwise-): T = F x R = 100[pounds] x 30[inches] = 3000 lb•in

Torquefromrightweight(clockwise+): T = F x R = 30[pounds] x 50[inches] = 1500 lb• in

TheresultantTorqueiscounterclockwise: T = 1500[lb• in] – 3000[lb• in] = – 1500 lb• in Thebeamwilltilttotheleft.

Fig. 1.9: Example 1.5

100lb. 30lb.

50"30"

Example 1.6 With reference to Fig. 1.9, at what distance from the rotary point would a 50-lb.weighthavetobeplacedtobalancethebeamhorizontally?

Answer:First,example1.5indicatedthatthesystemhasacounterclockwiseresultanttorque.Inthiscase,theonlywaytostabilisethebeamwouldbetoplaceaweighttotherightsideoftherotarypoint.Thetotalsumofalltorquemustequalzerotoattainequilibrium,aswasseenwiththestaticlawofforce(example1.2).

Resultant Torque = 1,500[lb.• in] – 3,000[lb.• in] + 50[lb.] x d = 0

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50[lb] x d = 3000[lb • in] – 1500[lb • in]

d = 3000[lb• in] - 1500[lb.• in] d = 30"

50 [lb]

*** Even if a body doesn’t move, it could have an induced torque.***

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1.3 Work

Inthecontextofthismanual,worksignifiestheactioncarriedoutwhenaforcecausesanobjecttomove.Workequals thedegreeof forceapplied toabody,multipliedby thedistancecovered inmovement. Nowork isrecordedintheabsenceofmovement.Notethatenergyisalsoconsideredaformofworkbutshouldnotbeconfusedwiththenotionofpower(ref.Section1.5.)

Inlinearmotion,workresultsfromthedegreeofforceappliedtoanobjectandthedistancecovered.Ontheotherhand,angularmotionresultsfromthetorqueappliedtoanobjectandtheangularmovement.

Workisusuallyexpressedinft.-lb.orin.-lb.Torquehasthesameunitsofmeasure,butinvolvesthedistancefromtherotarycenter to thepointofcontactwhereaswork iscalculatedbymeasuring thetotaldistancecoveredbetweentheinitialandfinalposition.

Theformulasare:

Linear system: Work resulting from a force U = F x d or

Rotational system: Work resulting from a torque U = T x θ

knowingthatU=work,F=force,T=torqueandd =thedistancecoveredbyonebodysubjectedtoagivenforce.Tocalculatetheworkresultingfromatorque,displacementismeasuredbytheangle

(θ )inradians(1radian=57.3degreesor1800/π).

Example 1.7 Afilingcabinetispushedonawoodenfloor(Fig.1.10).Theforceappliedtomovethefilingcabinet is10 lb. Thedistancecoveredis120inches. What is theworkvalue?

Answer:

U = F x dU = 10 lb. x 120 inU = 1,200 in- lb.

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10lb.

120"


Example 1.8 Youhavetotightenanutonastructure.Youuseatorquewrenchwithtwoarms,6incheslongoneachside.Ifyouappliedaconstantforceof6lb.totheextremityofeacharmandturnedthenut900(¼ofaturn),calculatehowmuchworkisinvolved.

Answer:

1.Calculatingtorqueononearm T1 = F x d T1 = 6 lb. x 6 in = 36 lb.-in

2.Calculatingtheresultanttorque T = T1 + T2 = 36 [ lb.- in ] + 36 [ lb.-in ] = 72 lb.-in

3.Converttheangletoradians π rad = 180o

π/2 rad = 90o

3.Calculatingtheworkinvolved U= T x θ U= 72 [ lb.-in] x (π/2) U= 72 [ lb.-in] x (1.57) = 113 lb.-in

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1.4 Speed and Velocity

Oncethenotionofmovementhasbeenunderstood,itisimportanttodetermineandquantifythespeedanobjectmoves.Todoso,wehavetocalculatethevelocity(speed)ordistancethatanobjectmovesinagivenunitoftime.Inlinearmotion,thedisplacementequalsthedistancecoveredandinangularmotionthedisplacementisanangle.

Theformulastocalculatevelocityare:

linear velocity (v):

v = d t

whered=distance,t =timeandvisexpressedinin/secorft/sec.

and angular velocity (ω):

ω = θ t

whereωisexpressedinrad/sec.Anothermorepracticalformulatocalculatethespeedforangularmotionistocountthenumberofrevolutionsper

minute(rpm).However,tangentialspeed(vT)isanotherimportantmeasurementtounderstandwhendesigningabelt-drivesystemorchoosingaV-belt.Itisusuallyexpressedinfeetperminuteandcorrespondstothebeltvelocity.Whenabeltispulley-driven,thespeedatthepointofcontactisdifferentfromtherotaryspeedofthepulley.Forexample,ifusingabicycleonatreadmillmachineyoucouldcomparethemovingconveyortoabeltandthebicyclewheeltoapulley.Thebicyclistdoesnotneedtoknowtherotaryspeedofthebicyclewheelstocalculatethesurfacespeedorthebeltspeedbecauseasaspeedometercanindicatethistohim.However,whendesigningabeltdrivesystemyouusuallyhavetodeterminetherimspeed.Todoso,thesamemethodofconversionmustbeappliedasthatusedbyacarorbicyclespeedometer.

Hereareseveralpracticalformulastoknowinordertocalculatetangentialvelocityorbeltspeed.

TherelationbetweenVTandωis:

ω [rad / min] = 2� x RPM&

vT= ω x R vT = 2� x R x RPM = � x D x RPM

Withreferencetoabelt drive system,theformulatofindbeltspeedis:

Belt Drive velocity[ft/min]=Pulley Diameter[in]x π x RPM x 1/12 [ft/in]or

FPM=Pulley Diameter[in]x 0.2618 x RPM

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Please note that the fraction 1/12 hasbeenaddedtotheformulatoconvertthepulleydiameterintofeet.Youalsoneedtorememberthattheoutsidediametershouldnotbeusedforcalculatingbeltspeedwhenworkingwithvariablepulleys,astheradialpositionwillvary

Belt speed

Fig. 1.11: Belt Speed

Example1.9 Calculatethebeltspeeddrivenbya5inchpulleywitharotaryspeedof2,000rpm.

V-beltdrive[ft/min]=5[in]x3.1416x2000[rpm]x1/12[ft/in]V-beltdrive[ft/min]=2,618ft/min

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1.5 Power

Inmechanicalengineering,powerisameasureofperformanceorcapacityandisdefinedastheamountofworkperformedinagiventime.Themostworkaccomplishedintheleastamountoftime,equalsgreaterpower.TheformulastocalculatePower(P)are:

P = U

t

or

P = T x ω P = F x v

KnowingthatU=work,t =time,v=linearvelocity,T=torqueand F=Force.Theunitsofmeasurementforpowerareusuallyin-lb./sec,ft.-lb./sec,butcouldvarydependingontheunitsusedintheformula.

Example 1.10 Calculatethepowerrequiredtolifta500lb.weight20ft.in60seconds.(Fig.1.12)

Answer:

P = U = F x d t t

P = 500[lb] x 20 [ft] X 12 [in]= 2000 in•lb 60 [sec] [ft] sec

500lb.

20ft


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IMPORTANT

InthePTindustry,thetermhorsepowerisoftenusedasapowerunit,commonlycalledforce.Evenifthis

expressioniscurrentlyused, itshouldnotbeconfusedwiththedefinitionofforcethathasalreadybeen

given. Inordertoavoidconfusion,itisbettertousethecorrecttermofpower.

TheformulastocalculatePowerinhpare:

HP = U [ft·lb] = P[ft·lb/sec] 550·t[sec] 550

or

HP = U [ft·lb] = P[ft·lb/min] 33000·t[min] 33000

Example1.11 Usethepreviousexample(Fig.1.12)tocalculatepowerexpressedinhp.Answer:

HP = P [ft-lb.] 550 t [sec]

HP = 500[lb.] x 20[ft] 550 x 60 sec

HP = 0.303 hp

Inthecaseofangularmotion,thereisobviouslyaformulatocalculatepoweraswell.Thepreviouslydiscussedformulasoftorqueandangularvelocityareinvolved.

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Hereistheformulatocalculatepowerusingspeedrevolution(RPM) ornumberofrotationsa minuteandtorque (T):

P = 2π x T x RPM

Therefore, the power in hp (HP) can be calculated using the following formulas:

HP = T[lb·ft]·RPM

5252

or

HP = T[lb·in]·RPM

63025

Example 1.12: AV-beltdrivensystemispoweredbya2hpelectricmotor.Themotorhastwooperationalspeeds:1,140rpmand570rpm.Calculatethetorqueatbothspeeds. Hint:Rewritetheequationtofindthetorque.

Answer:Speed 1- 1,140 rpm

HP = T[lb·ft]·RPM 5252

T[lb·ft] = 5252·HP= 5252x2 = 9.21 lb ·ft RPM 1140

Speed 2- 570 rpm

T[lb·ft] = 5252·HP= 5252x2 = 18.4 lb ·ft RPM 570

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1.6Efficiency

Inmosttransmissionsystems,frictionforcesandheatdissipationaccountforaconsiderablelossofpower.InthecaseofaV-beltdrivensystem,aconsiderablelossisexperiencedfrombeltslip.Mechanicalefficiencyismeasuredintermsofinputandoutputpower,where100%equalsmaximumperformanceorzeropowerloss.Theformulaformechanicalefficiencyis:

Example 1.13 Calculatetheefficiencyofatransmissionthathasaninputpowerof10hpand9hpattheoutput.

Answer:Efficiency(%)=HPOutputx100 HPInput

Efficiency(%)=9hpx100 10hp

Efficiency(%)=90%

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1.7 Ratio

Aratioisaproportionalfactorbetweentwosimilarobjectsofdifferentsizes.Inabeltdrivesystem,aratioisusedtodeterminethespeedrelationbetweentwopulleys.Thespeedratiowouldbestableifslippagedidnotoccur;howeverasbeltslipisinevitable,theratiovaries.Iftheratiois>1werefertoaspeedupsystem;iftheratiois<1itisaspeedreductionsystem.Inbothcases,theratioisobtainedusingthedimensionsoftheinputdrive(driver)pulleyandtheoutput(driven)pulley.

Rs =

ω1 = RPM1 = D2

ω2 RPM2 D1

whereRSisthespeedratio,D1diameterofdriverpulley,D2diameterofdrivenpulley.

***FOR V-BELT DRIVES, REPLACE DIAMETER(D) BY THE PITCH DIAMETER(PD)***

Example 1.14: Calculatetheratiobetweena2inchdriverpulleyanda5inchdrivenpulley.Answer:

Rs

=

D2 =5 2.5 : 1 D1 2

Example 1.15: Calculatethespeedratiobetweenadriverpulleyturningataspeedof500rpmandadrivenpulleyat2,000rpm.Ifthedrivingpulleyis4inchesindiameter,whatisthedimensionofthedrivenpulley?

Rs

= 500 1: 4

2000

Whenthedriverpulleyhascompletedonerevolution,thedrivenhasturned4times.

Rs

= 500 =

D2 D2= 500 x 4" = 1" 2000 4" 2000

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Ratioscannotbeaddedorsubtracted;onlymultipliedordivided.Forexample,todeterminethespeedratioofadrivenpulleyinacompounddrivewithfourpulleys(seeFig.1.13),ratiosaremultipliedtomaketheconnectionbetweentheinputpulleyD1andoutputpulleyD4.

However,thediameterofthefourpulleyscanbecalculatedonlyinacompounddrivewherethespeedsofthedrivingpulleyandthedrivenpulleyareknown.Inthiscase,seethefollowingsteps(ref.Example1.16):

1. The first step is to form a fraction with the driving pulley speed as thenumeratorandthedrivenpulleyspeedasthedenominator.

2. Afterthat,reducethisfractiontoitslowestterms.3. Dividethenumeratorandthedenominatorintotwopairsoffactors(apair

beingonefactorinthenumeratorandoneinthedenominator).4. Ifnecessary,multiplyeachpairbyatrialnumberthatwillgivepulleysof

suitablediameters(seeexample1.16).Thistrialnumberhasaninfluenceonthecost,soitshouldbereducedasmuchaspossiblewhileretainingthepowerrequired.

Example 1.16: Inthecompounddriveabove,ifthespeedofpulleyD1is575rpm,andthespeedofpulleyD4is1,200rpm,whatisthediameterofthefourpulleys?

(Step 1) Rs =

575 1200

(Step 2)reducethefractiontoitslowestterms

23 48

(Step 3) Divideintotwofractions

23 = 1x2348 2x24

(Step 4)multiplybytrialnumber8and1 (1x8) x (23x1) = 8x23

(2x8) x (24x1) 16x24

Thevalues8and23inthenumeratorrepresentthediametersofthedrivenpulleys,D2andD4,andthevalues16and24representthediametersofthedriverpulleys,D1andD3..Thepulleydiametersmustrespectthedesign.D3>D4>D1>D2;verify24>23>16>8.

Note:Whenthedimensionsobtainedarenotstandardmanufacturersizes,thepulleyscanbereducedbydividingthediameterofeachonebythesamenumbersoastoobtainastandarddimension.Thissignifiescostsavingsandareductioninthedesignspacerequired.JustbesurethattheystillmeettherequiredHPrating.

D3

D2

D4

D1


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Example 1.17: IfthediameterofthepulleysD1=40,D2=15,, D3=36, and D4=48andthespeedofpulleyD1is695,findthespeedofthedrivenpulleyD4.

D2 X D4 = RPM1 N4 = D1 x D3 X RPM1 =

40 x 36 X 695 = 1390 rpmD1 D3 RPM4 D2 x D4 15 x 48

Hence,theoverallratiobetweentheinputdriveD1andoutputdriveD4isequalto:

RPM1

= 695 = D2 X

D4 = 1 : 2RPM4 1390 D1 D3

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1.8 Service Factors

When designing components formanufacturing industries, engineersmust take into account factory inducedfactorssuchasoperatingtimes,thetypeofdrivingunitandtheload.Thisservicefactorisusedtoadjustthehorsepowerrequirementstoreflectactualhorsepowerneedsinordertoensurenormalservicelife.Aservicefactorcanbecomparedtoasafetyfactororsafetyprecaution.

Manufacturingcompaniesdecided tousea formulabasedonproductioncondition factors to foreseepossible

abuse throughexcessivewearand tear andadapt their transmission systemsaccordingly.Various tablesbasedonproductionconditionsarereferredtowhendesigningpowertransmissionsystems.Environmentalfactors(heat,abrasivedust)arenottakenintoconsiderationbutcertainlyaffectthelifeofadrivesystem.You’llseehowtheseservicefactortablesareusedwhendesigningabeltdrivesysteminchapter3.

Theformulaforcalculatingaservicefactoris:

Ks = P'

P

KnowingthatKSrepresentstheservicefactor,P’thedesignpowerandPtherequirementpower

Example1.18 Ifabeltdrivesystemhasaservicefactorof1.4,andtherated(required)poweris40hp,howmuchpowerisneeded?

Answer:

Ks = P'

P

P' = P · Ks = 40[hp] · 1.4 = 56hp

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Chapter 2DRIVES: BELTS, BUSHINGS & SHEAVES / PULLEYS

Hex

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Shea

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2.1 What are the Advantages of a Belt Drive System ?

InChapter1itwasillustratedthatforceandpowercanbetransmittedindifferentmanners.Themostcommonlyusedsystemstotransmitpowerfromadrivershafttoadrivenshaftarebelt-drivesystems(Fig.2.2a),gear-drivesystems(Fig.2.2b)andchain-drivesystems(Fig.2.2c).

(a) (b) (c)

Fig. 2.2: Illustration of different drive systems

Thereareanumberofadvantagestousingabeltdrivesystemascomparedtoothersystems.Itisalsoreferredtoasa“frictiondrive”aspoweristransmittedasaresultofthebelt’sadherencetothepulley.Amongthedifferentbeltdrivesystems,the“V”beltdriveisaveryeconomicalspeedreducingoptionthatiscommonlyusedinindustrial,automotive,commercial,agriculturalandhomeapplianceapplications.Thelistbelowpresentstheadvantagesofabeltsystemwhenitiswell-designedandusedinaproperenvironment.

Advantages of “V” belt drives are:

* Easyandeconomicalinstallation.

* Nolubricationrequired.

* Clean&lowmaintenance.

* Elasticityofbeltshelpsshockloaddampening.

* Quiet,smoothoperation.

* Longlifeexpectancywhenwelldesigned.

* Goodmechanicalefficiency. In addition, should a rotational component become blockedwhile in operation, considerable damage can be

causedtotheentirepowertransmissionsystem.Thisriskcanbegreatlylessenedwithabeltdrivesystem,

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asabeltwillslipifthesystemblocks,thusreducingtheriskofbreakage;thisadvantageisnotavailablewithachainorgearsystem.However,thisadvantageisoffsetbythefactthatstandardfrictiondrivescanbothslipandcreepandsodonotofferexactvelocityratios,norprecisiontimingbetweeninputandoutputshafts.Itisthusveryimportanttochoosetherightdrivedesignbasedontheapplication.

2.2 Belts

BeltdrivesareoneoftheearliestpowertransmissionsystemsandwerepopularduringtheIndustrialRevolution.Atthetimeflatbeltswereusefulforconveyingpoweroverlargedistancesandweremadefromleather.However,due to thedemands formorepowerfulmachinery,and thegrowthof largemarketssuchas theautomobileindustry,newtypesofbeltsweredesigned.Inordertomeethigherstandardsofperformance,V-belts,withatrapezoidalor“V”shape,andmadefromrubber,neoprene,urethaneorsimilarsyntheticmaterials,replacedflatbelts.

• Thebelt’sinsidesurfacemustbemadefromamaterialthatensuresadherencetothepulleygroovethroughfrictionforceandreducesthebelttensionrequiredtotransmittorque.

• Thetoppartofthebelt,calledthetensionorinsulationsection,containsfibercordsforincreasedstrengthasit carries the loadof the traction force,whereas thebottom,or compressionsection,hasbeendesigned towithstandcompression.

(1) PROTECTIVE COVERGenerallya toughandelasticcovermade fromaspecial rubber-impregnated fabricthatisslip-resistantanddurable.Thisheatresistantlayerservestoprotectthebelt’sinnercomponents.(2) INSULATION SECTIONThissectionhelpsholdsthetensionmembersinplaceandactsasabinderforgreateradhesionbetweenthecordsandtheothersections.Inthismanner,heatbuild-upisreducedresultinginextendedbeltlife.(3) TENSION MEMBERSPre-stretched cords (polyester, aramide, steel, fiberglass,..) provide high tensilestrengthandminimizestretch.(4) COMPRESSION SECTIONMadefromatoughrubbercompoundthatexertsawedgingforceagainstthepulleygroovetoincreaseadherencewithoutdeformation.

Thetorqueobtaineddependsonthebelt’sresistancetotheappliedtensionandthedegreeofadherencetotheinnerwallsofthepulleygroove.Forthisreason,abeltdrivesystemshould never be lubricatedasitdependsonfrictiontotransmitpower,incontrasttochainorgearsystemsthatfunctionthroughpurecontactpressure.Theinsidefaceofthebeltshouldnevertouchthebottomofthegroove(Ref.SeeFig.2.4)

Fig. 2.3 V-Belt

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2.2.1V-BeltClassifications

All belt sizes are classified by cross-section and length dimensions. Thebeltidentificationnumberincludesaletter,indicatingthecross-section,followedbyup to3digits. Thecross-section indicates the topwidth,depthand“V”angledimensionsofVbelts.Industrialbeltsaremeasuredin terms of outside and inside (pitch) lengths (section 2.2.2.2). ThedifferenttypesofV-Beltsmentionedbelowareininches.Todeterminebelt nomenclature in metric, youmust refer to a belt manufacturer’scatalog.

Fig. 2.4: Sheave Cross-Section 2.2.1.1 Light duty & Fractional horsepower (F.H.P) V-Belts

ThistypeofV-beltwasdesignedforlight-dutyapplicationsoflessthan1hp,whichiswhytheyarereferredtoasF.H.P.or fractionalhorsepower. TheV-shape results in improvedperformance for conventional speedoperations inamore compact format, as compared to flat pulleys. Thesebeltsareusedonlywith small1-groovepulleysforsingle-beltpowertransmission.

Fig. 2.5: Light duty V-Belt Cross-sections

ForthistypeofV-belt,thecross-sectionisidentifiedbytheletter “L”precededbyupto5figures(1to5),whichwhendividedby8indicatesthetopwidth.Thisis trueforallbeltsexceptthe“5L”,ofwhichthewidthisnot5/8butrather21/32.Itisinterestingtonotethatthereisacorrespondingheightforeverytopwidth.Thenumberthatfollowstheletter“L”indicatestheoutsidelengthmultipliedby10.

Fig. 2.6: Light duty 3D Cross-sections

Example 2.1 Whatarethedimensionsofa4L990V-belt?Answer: 4/8=½-inchtopwidth,5/16-inchheightand99inchesoutsidelength

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2.2.1.2 Classical V-Belts

ClassicalV-beltsareusedasmuchinheavy-dutyaslightduty(A&B)applicationsbecauseofthelargeselectionofcross-sectionsavailable.Theyareavailableindifferentbelttypesandmaterials.AllclassicalV-beltswithidenticalcross-sectionswilloperate insheaveswithgrooves for thatparticularcross-section. Baldor•Maskaoffersacompleteselectionofclassicalsheaves.

1/2" 21/32"

13/32"5/16"

7/8"

17/32"

1 1/4"

3/4"

1 1/2"

1"

40o 40o 40o 40o 40o

A B C D E

Fig. 2.7: Classical V-Belt Cross-sections

ClassicalV-beltsareidentifiedby5letters:A, B, C, D, & E.Unlikemostbelts,thecross-sectionisidentifiedbyasingleletter,followedbytheapproximateinsidelength.

4Land5LV-beltsarerespectivelyinterchangeablewithtypeA&Bbelts,althoughtheBbeltisslightlyhigherthanthe5L.TypeAandBbeltsareavailableinalargervarietyofsizesthanthe4Land5L.Pleasenotehoweverthatdifferentbelttypesshouldnotbecombinedonthesamepulleywithseveralgrooves.

AllclassicalV-beltscanbeusedaloneorcoupledwithotheridenticalcross-sectionbeltstotransmituptohundredsofhpunits.

Example 2.2 WhatarethedimensionsofaB228V-belt?Answer: 21/32-inchtopwidth,13/32-inchthickand228inchesinsidelength.

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2.2.1.3 Deep Wedge / Groove or Narrow V-Belts

NarrowV-beltsare recommended fordrivesystems that requirecompactdesign,higherspeedand increasedhorsepower.Theyhaveamorepronounced“V”shapeandareusedinapplicationssimilartothoseofmultipleclassicalV-belts.Theyhaveagreaterhorsepowercapacitythanconventionalbeltsduetoincreasedsurfacecontactwiththepulleywall.

Fig. 2.8: Narrow V-Belt Cross-sections

3/8"

5/16"

5/8"

17/32"

1"

7/8"

3V 5V 8V

Threestandardcross-sectionscover theentire rangeofdrive requirements, as compared to five for classicalV-belts.Thisresultsinreducedinventoryforthistypeofbeltandpulley.3VbeltsareusedwithA&Bsheaves,5VdealswithB&Csheavesand8VcoversD&Ecross-sections.

Since greater horsepower capacity can be obtained, the drivesystem can be designed with shorter centers and smallersheaves. Overall drive dimensions can be reduced by asmuchas40%.Smaller,lightweightdrivesystemsreflectcostsavingsthroughreducedsizecomponentsorcantransmituptotwicethehorsepowerofclassicalsectionbeltswithinthesamespace.

Aswith light duty belts, the initial number, when divided by 8,indicates the topwidth. The last numbermultipliedby tenindicatestheoutsidecircumference.

Example 2.3 Whatisthebeltidentificationnumberofa140incheslengthnarrow V-beltwitha3/8inchwidth?

Answer: 3V1400

Fig 2.9: Narrow V-Belt (3D Cross-section) Fig. 2.9: Narrow V-Belt (3D Cross-section)

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2.2.1.4 Cogged / Raw-Edge V-Belts

CoggedV-beltsareofferedasafeatureonbothclassicalandnarrowconfigurations.Theletter“X”isaddedtothecross-sectionidentificationletter(ex.AX,BX,CX&3VX,5VX).

The notches that are cut in the underside render the beltmore flexible, resulting in increased surface contact.For this reason, cogged belts are especially useful for highperformance,highspeedapplicationsoperatingwithsmallersheaves. When subjected to difficult operating conditions,theuseofcoggedbeltsallowsforincreasedsurfacecontact,resultinginimprovedheatdistribution.

• Usedinheavytrucksandbusesbecauseoflongerservicelifeandreducedbendingstress.

• Increasedtorquecapacityeveninhigh-speedoperations.

• Lessslippage.

2.2.1.5 Banded Belts

BandedV-beltsareidentifiedbytheletter“R”placedbeforethecross-sectionidentificationletter.Thestandardcross-sectionidentificationfor classical bandedV-belts is: RB-RC-RD. The standard cross-section identification for narrow V-belts is: R3V-R5V-R8V. TheadvantagesofclassicalordeepwedgeV-beltsaremultipliedbythestrengthofseveralbeltsinone.

Advantages & Features:

• Recommendedforapplicationswithvertically-mountedshaftsorextendedcenter-to-centerdistances.

• Assureslateralrigidityandguidesthebeltsintothepulleywallsinastraightline.

• Designedforheavy-dutydriveswhereshockloadingisaproblemandwheremultiplematchedsinglebeltstendtorolloverorjumpoff.

Fig. 2.10: Narrow V-Belt (3D Cross-section)

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2.2.1.6 V-Ribbed / Poly-V Belts

V-ribbedbeltsareacombinationdesignofflatandV-shapedbelts.Youcanthusbenefitfromthebestofbothworlds–increasedV-beltpowertransmissioncoupledwiththeflexibilityofflatbeltsthatfunctionwellathigherspeeds.Themultipleribsprovidemuchmorestabilitythanaflatbelt.

ThebelttensionmustbealittlehigherthanwithclassicalV-belts,butperformsupto30%morepower.Thistypeofbeltisrecommendedwhendriveratiosareashighas40:1andrequiresmallpulleys.Somecross-sectionV-ribbedbeltsarecapableoftransmittingupto1,000hp.


• ThemultipleV-ribbeddesignprovidesmoreeffectivesurfacecontactareathanconventionalV-belts.

• Theuseofsmaller,lessexpensivesheaveswithshortercenterdistances.

• Flexibilityallowsmulti-pulleydrives.

• Highspeedcapabilityinserpentinedriveswithlimitedspace

2.2.1.7 Double / Hexagonal V-Belts

DoubleV-beltsareusedonequipmentwherethedrivenshaftsrotateinadirectionoppositetothatofthedrivingshaft.Usuallythedriveranddrivenshaftsrotateinthesamedirection;anexampleofsuchanexceptionisthatofserpentinereversebenddrives,wherethis typeofV-beltisused.

ThedoubleV-beltdrivesfromboththetopandbottomsurface.Thecross-sectionsareidenticaltoclassicalV-beltsbutwith twodriving surfaces. StandarddoubleV-beltsare identifiedbyduplicate letters in thebelt codefollowedby theinsidelength.

Fig. 2.15: Doubled V-BeltDoublesidedV-beltsare generallyfoundinagriculturalandtextileapplications.

Fig 2.12: Poly-V Belt

Fig. 2.13: Serpentine Drive

Fig. 2.14: Doubled V-Belt cross sections

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2.2.1.8 Variable-Speed Belts

Variable or adjustable V-belts are uniquely designed to transmit powerin applicationswhere there is a varying speed-ratio. This is the casewhenworkingwithadjustablepulleysthathavebeendesignedwithtwomoveableflangesthatcanbeadjustedinwidth.

Variable-speedbeltshavecross-wiserigidityandlengthstabilityforoptimumperformancebecauseoftheincreased

widthatthetopofthebeltinproportiontothethickness.Variablespeed beltsalsorequirelengthwiseflexibilitytobendaroundsmallsheaveswithoutexcessstrainthatcouldshortenbeltlife.


• IndustrialapplicationsofvariablespeedV-beltsarepumps,fans,blowers,conveyors,&mixers.Consumerapplicationsincludemotorcycles,snowmobilesandgolfcarts.

• Thebeltadjustseasilywithinthepulleygroove,thusallowingforawiderangeofspeedratios.

2.2.2 Other Belt Types

2.2.2.1 Standard Flat belts

FlatbeltshavebeenreplacedbyV-beltsinmostindustrialapplicationsbecauseofimprovedresistanceandreducedsize.However,theflatbeltisstilloneofthebestsolutions forhighspeedapplicationsasgreatas15,000ft./min.Duetotheirheightandweight,V-beltsaresubjecttoincreasedcentrifugalforcewhereaslighterflatbelts,whosecenterofgravityisclosertothepulley’ssurface,maintainbettersurfacecontactathigh speeds.

Pulleysusedwithflatbeltsmusthavealargersurfaceareatotransmitthesameamountofpower.Infact,inordertoattaintheequivalentcoefficientoffriction,flatbeltsmustbeconsiderablylargerastheyaremuchthinner.(SeeFig.below)

Thesmallbendingcross-sectionoftheflatbeltcauseslittlebendingloss.Thisfact, togetherwitheven runningand theabsenceof pulleywedgeeffects,leads tohigherflatbeltefficiency.Themaximumefficiencyattainedbyflatbeltsis98%compareto96%forV-belts.

Advantages & Features:•Flatbeltsarecapableoftransmittingpoweroverlongdistances.

•Theyarestillusedbecauseoftheirflexibilityinserpentinedrivesandinapplicationswherebeltsmustbetwistedtoachievereverseshaftrotation.

•Increasedflexibilityresults inlessbendingloss.

Fig 2.16: Variable speed V-Belt Fig 2.16: Variable speed V-Belt

Fig 2.17: Standard flat Belt sections

Flat Belts

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2.2.2.2 Standard / Trapezoidal Synchronous Belts

Usedprimarilywherethemotionof inputandoutputshaftsmustbepreciselymatched,synchronousbeltsarealsoknownastimingbeltsorpositive-belts.Transmissionisproducedthroughevenlyspacedteethontheinsidesurfaceofthebeltthatengagematinggroovesinapulley. There isnobeltslipandthespeedratio isconstantandprecise.Thoughvisually similar,thistypeofbeltisnottobeconfusedwithcoggedbelts.AswithV-belts, therearedual-sided timingbeltswith teethonbothsides forreversed-motionandserpentinedrives.

Thesebeltsarefoundinawidevarietyofprecisiondriveapplicationsincludingrobots,machinetoolsandplotters.High-volumeapplicationsincludedrivingandtimingoverheadcamshaftsinautomotiveengines.Speedsvaryfromafewinchesperminutetomorethan16,000FPMandloadcarryingcapacitycanvaryfromfractionaltohundredsofhorsepower.

240 / L / 075 Belt Pitch Length Tooth Pitch Belt width (24.0 inches) (3/8 inch) (0.75 inches)

• Smoothengagementofbeltwithpulleyallowshighspeedoperations.

• Idealwhereback-lash,noiseandmaintenanceofchaindriveswouldbeundesirable.

• Timingbeltsweighonlyafractionascomparedtoalternativemethodsforthesamehorsepowerrequirements.

• Thecleanoperationisidealforcontaminationsensitiveenvironments,suchasindustrialfoodprocessing.

Fig 2.18: Synchronous belt Fig 2.18: Synchronous belt

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Belt PitchesOnsynchronousbelts,pitchisthedistancebetweenthecenteroftwoadjacent

teethasmeasuredalong thepitch line. Thepulleypitch linemust bethe same as the belt pitch line in order to be synchronized. For thisreason, thepulley’spitch is thedistancebetweengroovecenters,andthepulleypitchcircleismeasuredmidwaybetweentheareasoftensionandcompressionofthebelt.

Thebeltpitchline(simplycalledpitchfornarrowv-belts)islocatedwithinthetensionmemberandcoincideswiththepitchcircleofthepulleymatingwithit.ThedistancebetweenthepitchlineandtheoutsideofthepulleyiscalledthePitchLineDifferential.Anychangeinbeltconstructionthataltersthepitchlinedifferentialrequiresacorrespondingchangeinthepulleydiameters.Timingbeltsmustberunwithpulleyswithanidenticalpitch.

Belts-inordertohandleawiderangeofloads,speedsandapplicationsathighestpossibleefficiencies-aremadein

fivestockpitches.Consequently,whendesigningbeltdrives,aswithgearorchaindrives,circularpitch(usuallyreferredtoaspitch)isafundamentalconsideration.

2.2.2.3 H.T.B. / Curvilinear Synchronous Belts

H.T.B.isanabbreviationforHighTorqueBeltsandfollowsthesamedrivedesignrulesasthetimingpulley.Theseroundedformbeltsallowforalltheadvantagesthatcomefromsynchronousrubberbeltsonapplicationsthatpreviouslycalledforrollerchainsandgeardrives.

Thestandard-trapezoidal tooth timingbeltpresentedaboveperformspoorly inhightorqueapplicationsandhighpowerdrivesatlowerspeeds.Toovercomethisdrawback,theHighTorqueBelt(HTB)wasdevelopedusingamoreefficienttoothprofile.

HTBtimingbeltsareclassifiedbytoothprofile,beltpitchlength,toothpitchandbeltwidthinmillimeters.

720 / 8M / 30 Belt Pitch Length Tooth Pitch Belt width (mm) (mm) (mm)

Among the advantages are :

*Highertorquetransmissionatlowerspeeds*Highpowertransmissionoverawidespeedchange*Improvedmeshingtoreducetoothjump*Higherresistancetotoothshear*Lesstoothwearduetofriction

Fig. 2.20: High torque belt

PitchDiameter

BeltPitchLine

SprocketPitchDiameter

OutsideDiameter

Fig 2.19: Synchronous Drive

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2.2.3 Belt LengthThebeltlengthequalsthesumofthelengthofbothstraightsectionsandbothlengthsincontact

withthesheaves.

C

D2

D1

02

01

Fig 2.21: Diagram to calculate belt length

The variables of this system are:

D1:Datumdiameterofthedrivingpulley/sheave(in)D2:Datumdiameterofthedrivenpulley/sheave(in)C: Distancebetweensheaves’rotaryaxis(centerdistance,in)θ1etθ2:Arcofcontactbetweenthebeltand,respectively,thedrivingandthedrivensheaves(degreeor

radius(ifindicated))

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2.2.3.1 Parallel axis, uncrossed belt drive

Thisisthemostcommonbeltsystemset-upintheindustry.Theinstallationmethodisillustratedbelow.(Fig.2.21)

Thearcofcontactforthesmallersheaveis:

θ1 = 2 cos-1 D2 - D1

2C

or

θ1 ≈ 180 - 60·(D2 -D1 ) C

Thearcofcontactforthelargersheaveis:

θ2 = 360 - 2 cos-1 D2 - D1

2C

or

θ2 ≈ 180 + 60·(D2 -D1 ) C

Therefore,theformulatocalculatethetotallengthis(anglesareinradians):

L=√4C 2 - (D2 -D1 )

2 + 1 (D2 θ2 -D1 θ1 )

2

Toacceleratethecalculation,thefollowingformulacanalsobeused:

L≈2C + π (D2+D1 ) + (D2 -D1 )2

2 4·C

or

L≈2C + 1.57(D2+D1 )+ (D2 -D1 )2

4·C

Theaboveformulaappliestounequalpulleys(differentdiameters);theformulatocalculatethebeltlengthforequalpulleys(samediameters)is:

L≈2C + D·π or L≈2C + D·3.1416

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2.2.3.2 Arc of contactThearcofcontact(θ1etθ2Fig.2.21)determinestoagreatextentabelt-drivesystem’scapacitytotransmitpower.

Forefficientoperation,theminimumbeltwrap,orarcofcontact,ofthesmallestpulleyshouldbe120o.Themaximumarcofcontactthatcanbeobtainedis180o.Thisisachievedwhenthetwopulleysareofequaldiameter.

Theformulasusedinsections2.2.3.1.illustratethatthearcofcontactincreaseswiththecentertocenterdistance.Theminimumarcofcontactnecessaryinapowertransmissionsystemthushasadirectinfluenceonthedesignofthecentertocenterdistanceofthepulleys.

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2.3 Drive Components Materials

BeforeconsideringtheremainingprincipalcomponentsofaV-beltdrivesystem,suchasbushingsandsheaves,wewilldiscusstheimportanceofselectingthepropermaterialwhendesigningthepart.

Oneofthemostcommonferrousmetalsusediscastiron.Thisisacost-efficientmaterialthatadaptswelltothemoldingprocess,andisrecommendedevenforcomplexparts.ThefollowingisadescriptionofthemechanicalandphysicalpropertiesofthetwomaintypesofcastironthatBaldor•Maskaworkswith.

2.3.1 Gray/Cast Iron

Thepropertythatdifferentiatesgraycastironfromplaincarbonsteelisthepresenceofpuregraphiteintheformofflakes.Duringthemoldingprocess,althoughmostofthecarbonmixeswithiron,theremainingelementsformgraphite.Thepresenceofgraphitecontributestograycast iron’s high vibration absorption andwear resistance.On the other hand, the graphiteflakescreateweaknessplaneswhichresultinslightlyreducedtensilestrength.Grayironalsohasgreatercorrosion resistanceundermostconditionscompared toplainsteel. For thosereason,coupledwithawiderangeofcastingproperties,machineframesandengineblocksaremanufacturedfromthismaterial.

ThemajorityofBaldor•Maskapulleysusedinstandardapplicationsaremanufacturedfromgraycastiron;howevertheyarenotrecommendedforoperationsthatareatriskofexperiencingexcessiveshockloadsorhighspeed.Forthisreason,certainitemsaremadefromductileironforimprovedstrength.

2.3.2 Ductile Iron

Ductile iron has greater resilience and ductility, as it’s name denotes, than gray cast iron.Graphite is present in a nodular (small, round lumps) rather than flaky form. Corrosionresistanceiscomparabletothatofgray.

This stronger material is recommended for operations that could experience occasionaljolting.Comparedtogray,ductileironcannotbemachinedaseasily.Italsohaslessvibrationabsorbency. However, themechanical properties are similar to steel and it is used in theproductionofgears,crankshafts,wheelhubs,etc.

Inaddition,otheradvantagesofductileironascomparedtogray,isthatitallowsforareductioninsizeandweightofthepart,andhasaddedresistancetoimpactfailure.Baldor•MaskaisoneoftheonlycompaniesthatoffersabroadrangeofQDBushingsinductileiron.

Fig 2.22: Cast iron

Fig 2.23: Ductile iron

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2.3.3 Sintered Metal

Sinteredmetalprocessinghasbecomeverypopularinthelast20years.Easilyadaptedtomassproduction,thisprocesshasbeenusedintheautomobileindustryandcanproducecomplexpartswithhightolerancesandverylittlewasteduringmolding.Inaddition,theferrousalloysavailablehaveexcellentmechanicalpropertiesatacompetitiveprice,duetoeconomicalprocessingmethods.

Whereascastedmetalsmustbebrought to themeltingpoint, this rawmaterial isapre-determinedmixtureofdifferentalloysinafine,granularform(powder)ofwhichsmallamountsundergohighpressurecompactingfrompressesequippedwithasetofmatrixesandpunchesthatdeterminetheshape.Atthisstage,thepartusuallyhastherequiredshape,butnotthemechanicalresistancerequired.

Inordertoacquirethenecessaryresiliencefoundincastedmetal,theparticlesneedtobebindedtogether.Thisisdonebyheating thepartsoveraspecificperiodof timecalledsintering,at temperatures justunder themeltingpoint.Thecontrolledtemperaturegeneratesmetallurgicalbinderswithinthepartwithoutalteringtheshapeduetoexcessiveheat.Uponcomingoutofthefurnace,thepartisafinishedproduct,unlessspecialmachiningortreatmentsareneeded.

Auniqueadvantageofthissinteringprocessisthepossibilityofadjustingthebasicpowder“recipe”to includespecial additives that can either increase corrosive resistance, improved machinability or increased partdensity.Althoughsinteredmetalhasdifferentmechanicalpropertiesthanthatofcastedmetal,theresultsarenonethelessverycompetitive.Baldor•Maskawasoneofthefirstcompaniestomarketandtakeadvantageofsinteredmetalprocessingforcertainproductlines.

2.3.4 Table of Mechanical Properties

MATERIAL GRADETENSILE

STRENGTHMIN. ( PSI )

YIELD STRENGTHMIN. ( PSI )

ELONGATION ( PERCENT )

MODULUSOF ELASTICITY

( X 106 PSI)Grey cast iron 30 30,000 30,000 <1.0 13-16.4Ductile iron 65-45-12 65,000 45,000 12 24Sintered Metal FC-0205-40 40,000 40,000 <1.1 17.5

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2.4 Bushings

Allpowertransmissioncomponentsmusteitherbeattachedorconnectedtoashaft.Abushingistheintermediaryelementusedtomountorattachasheave/pulleytoashaft.Inbelttransmissiondrivesystems,thebushingisinstalledinthehubofthepulleyandissecuredwithscrews,thusexertingapressureonthehub.Thispressureiscreatedbyatapergeometryprinciplethatcanalsobeobservedwhenamaleconicalobjectisinsertedintothematingsurfaceofthecorrespondingfemalepart.Thebushinghasathinslitdownthesidethatenablesittobecompressedevenlyaroundtheshaftduringinstallation,whichresultsfromtheaxialforceappliedwhenfittingthebushingintothesheavehub.Mosttaperedbushingscompensatefornormalvariationsinshaftandcomponentdimensionaltolerances.

Bushingsareavailable inanumberofdifferentboresizes forvariousshaftdimensionsandsafelypermitpowertransmissionasthego-betweentheshaftandthesheave.Theygreatlyreducethenumberofstandardsheavesrequiredorhavingtomachinethepartforeverydifferentshaftsize.(Fig.2.1)

2.4.1 QD (Quick Detachable) Interchangeable Bushings

QDbushingshavea straight borewitha taperedbarrel on theouter surface thatmatchesthepulleyhub.QDbushingshaveafullsplitthroughtheflangeandbarreltopermitatightclampingactionontheshaft.Theyareeasytoinstall,eliminatefrettingcorrosionbetweentheboreandtheshaftandareanexcellentchoiceforV-beltdrivesystems.

Capscrewsareusedtotightenandsecurethebushingontotheshaft.Toassemble,thebushingandsheaveareslippedovertheshaft.Whenthetaperedsurfacesfirstmeet,thefitbetweenthebushingboreandtheshaftisrelativelyloose.Whenthecapscrewsaretightened,thesplitclosespartiallyandthebushinggripstheshafttightly.

Baldor•MaskaoffersaninterchangeableQDBUSHING(QDisaregisteredtrademarkandmanufacturedunderlicense).

• PrecisionmachiningofthetaperedboreinthehuboftheQDsheaveandthetaperedmatingsurfaceofthebushinginsureasnugandprecisionfitbetweenthesheaveandthebushing.

• Thesplitisfull(notpartial).Asthecapscrewsaretightened,atremendouspressureisgenerated,withagripequivalenttothatofapressfit,ontheshaft.

• Bushingsshouldnotbere-boredastheconcentricity(perfectcenter)willbelost.However,thismaybepossibleforapplicationswithaverylowRPM,.

• ItisveryIMPORTANTnottouseanytypeoflubricantonanysurfaceofthebushingormatinghub.

2.24: QD Bushing

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Baldor•Maska,andallotherM.P.T.A.members,manufacture“QD”bushingsconformtostandardiseddimensionsinordertoassuretotalinterchangeability.

Illustration of QD Bushing SD - 1 ¾ Bushing“SD” StockBore1¾ Keyseat3/8x1/8**

SK - 40

Bushing“SK” StockBore40(metricsystem) Keyseat12x8

Insomecases,astheboreincreasesindiameter,ashallowkeyseatisprovidedduetoinsufficientmetalthickness.Thisdoesnotaffect thebushing’sability to transmit the load.Therectangularkey,onflatkeyas it isalsoreferredto,fitsintothestandardkeywayintheshaft.

SK 1-3/4 Bushing“SK” StockBore1-3/4 Keyseat3/8X3/16

**Shallow Keyseat.

Bushing “L”

(“H” - Cross Reference)

Bushing “JA to J” Inclusive

Bushing “M to W” Inclusive

Bushing “S” Taper 3/4" per FT on Diameter - B -

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Standard Keyseat Shallow Keyseat

Fig. 2.26: Keyseat

Types of Keyseat

Note:Themetricsystemdoesnot refer tokeyseatorkeywaydimensions,asdoes the Imperialsystem; instead,dimensionsaregivenforthekeyitself,whichisrectangularinshape.ThismeetsISOstandards.

Formoreexplanationsaboutbushingmountingandproperwrenchtorque,pleaseconsulttheInstallation&MaintenanceChapter.

Important

English System: Square key -

rectangular keyway

Metric System: Rectangular key -

square keyway

Baldor•Maskaoffers threedifferent typesof bushings. Thedifference is basedon the shaft diameter and thenumberofholesintheflange.BushingsLtoJhavethesamenumberofholesandtappedholes.Asthenumberofholesincreases,theadmissibletorqueonthesheaveincreases.OnlybushingsMtoShavetappedholestosecuremounting.

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2.4.2 Taper-Lock / Bore Bushings

Withmorethanamillionpresentlyinoperation,andinitiallylimitedtoEurope,manycompaniesworld-widenowconsider“TaperLock”bushingsasstandardmounting components in the PT industry. This type of bushing does nothaveaflange,resultinginacompact,neatdesignthatispreferredincertainapplications.

They are not interchangeable with QD type bushings as the taper has adifferentangleandtappedholesinthehubarenotinthesameposition(asplitholeontheinsideoftheTaperlockhubvs.completeholesinthesideoftheQDhub).Theyareinstalledontotheshaftwithsetscrewsinsteadofstandardbolts,aswithQDBushings.

Taper Lock Installation

1. LineupthesmoothholesoftheTaperLockbushingwiththethreethreadedholesinthesheavehub.2. Threadthecapscrewsintothesheavehub.Note:Thethreadedholesinthebushingareusedtoremovethe

bushing.

Asthecapscrewsaretightened,thebushinguniformlysupportsthehubalongtheentirecircumference.

* Frequentlymatchedwithsprockets,gearsandtimingbelts;notnecessaryinV-Beltdrives(“over-design”)

* Suitablewhenexcessivetorqueisapplied(H.T.D.).Shearforces,thatactonthescrewswhensubmittedtoaexcessivetorque,dosooveralargersurfacearea(diameterXlength)insteadofactingonthescrewssectionarea,asisthecasewithQDbushings.

2.4.3 Split Taper Bushings

AscomparedtoQDstyle,Splittaperbushingsweredesignedwithtwodifferentfeatures.First,thereisakeywayonbothsidesofthebarrel;theadditionalkeythatfitsintothehubbearsthepressureofshearingforceswhentorqueisappliedtothepulley,ratherthanactingonthesetscrewsaswithQDstylebushings.Secondly,theSplittaperbushing,asit’snamerefers,issplitonlythroughthebarrelortaper,andnotthroughtheflange.

Splittaperbushingsareavailablewithasimpleordoublesplitbarrel.Shafttolerancesonapplicationshavetobe tighter with this type of bushing, as comparedtoQDbushings,whichhavegreaterflexibilityandmoreuniformclampingforce.

Fig. 2.27: Taper-Lock

Fig. 2.28: Split Taper-Lock

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2.5 Sheaves

AsheaveisdefinedasaV-groovedwheelusedtotransmitpowerormotioninconjunctionwithaV-belt.Sometermsassociatedwithsheavesareexplainedandillustratedbelow.

Groove Shapedportionofasheave;width,depthandanglearedeterminedbythebeltsection used.Groovesaremachinedtomeetstandardtolerances.

Face Width Distancemeasuredacrossgrooves-definedas«F»dimensionintheBaldor•Maskacatalog.

Outside DiameterDimensionmeasuredaroundtheoutersheavediameter- definedasO.D.intheBaldor•Maskacatalog.

Pitch Diameter Dimensionmeasuredaroundthesheavewherethebeltpitch linemeetsthesheavegroovewall-definedasP.D.inthe Baldor•Maskacatalog.(seeFig.2.29)

Datum System

AnewstandardforclassicalV-beltsandsheaveshasbeenrecentlyestablishedwhereinthetitle“DatumSystem”replacedthedesignation“PitchSystem”,and“PitchDiameter”became“DatumDiameter”.Withreferencetoclassicalsheaves,thenew“PitchDiameter”valueequalsthesheave’soutsidediameterseeingasthetopofthebeltarrivesatthesameheight.Theonlyexceptionisthatofan“A”beltfittedwitha“B”sheave,asthetopofthebeltisbelowtheO.D.The“DatumSystem”isacompromisethattheMPTAchoseasthemostaccurateapproximatevalueofthe“PitchLine”thatservesasthestandardforallbeltmanufacturers,soastocompensatefortheslightdifferencesbetweenthedifferentcompanies.

F

O.D.P.D.

Fig. 2.29: Sheave nomenclature

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2.5.1 Sheave Body

Thestructureofthesheavebodydifferswithsize.Largersheavesdonotneedtobesolidorfullinordertomeetthemechanical requirements. Forexample,a30-inchsolid sheavewouldbeveryheavyandexpensive.Baldor•Maskaengineersdeterminetheamountofmaterialnecessaryintheconstructionofeachpartforhigh-qualityperformanceandsecuritythatmeetsindustrystandards.

Sheavescomeinseveralforms,beingeithersolid,webbedorarmdesign,dependingontheoutsidediameter.The typeof design is indicated in theBaldor•Maskacatalog in the column “T” (type). TheBaldor•Maskanomenclatureorlistingforthethreeclassificationsisasfollows:

TYPE B - Block Diameter ~ 0" to 6"

TYPE W - WebDiameter ~ 6" to 14"

TYPE A – ArmDiameter ~ Over 14"

Fig. 2.30: Sheave body

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2.5.2SheaveClassifications&Terminology:

Sheavesmustbedesignedtoworkefficientlywithbeltssoastodeliver thenecessarypower. Oneof themostimportantfactorsisthedesignofthegroove,asthisisthebeltcontactzone.Standardidentificationclassificationforpulleysincludethebeltcross-section,numberofgrooves,anddiameter.AllBaldor•Maskasheavescanbegroupedintothreefamily-types.

2.5.2.1 Light Duty Fixed & Bush Types

Typicalapplicationsforthistypeofsheavesarepumps,mixers,compressors,conveyors,fansandblowersdrivenbymotorsupto10HP.Baldor•Maskadoesnotmanufactureordistributepulleysfor2Lbeltsastheydonotneedtobemadefromcastiron.

PartClassificationNumber:

MA80X1/2 1groovefixedbore MBL77 1groovebushtype(3L)&A(4L)V-belts A(4L)&B(5L)V-beltsO.D.=8.0in Lbushing½Boresize O.D.=7.7in.

2MA80X1/2 2groovesfixedbore 2MBL77 2groovesbushtypeA(4L)V-belts A(4L)&B(5L)V-beltsO.D.=8.0in Lbushing½Boresize O.D.=7.7in.

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2.5.2.2 Adjustable/ F.H.P & Integral

Adjustable sheaves offer the flexibility of adapting to varying driving shaftspeedsthroughexpansionofthepulleywalls.Inthisway,thebeltpitchusedvariesdependingontheadjustedwidthofthesheave,resultinginthepossibilityofdifferentspeedratios.

Adjustablespeedsheaveshaveoneortwogrooveswithflangesthatcanbeadjustedinwidth,sothebeltmovesinaradialmovementwithinthegroove(seeillustrationbelow).Theprincipleoftheadjustablepitchsheaveisthatone of the discs forming theV-shaped groove (inwhich the belt rides)ismovable.When thedisc ismovedcloser, thebelt rideshigher in thegrooveandthepitchdiameterofthesheaveislarger.Whenthediscismovedapart,thebeltrideslowerandthepitchdiameterbecomessmaller,therebyproducingaspeedandratiochange.

Fig. 2.32: Ratio variation – Close and Open

Important

Baldor•Maskaadjustablespeedsheavesareusedonlyforstaticpitchdrivedesign.

• AdjustableLightDuty(H.V.A.C.)MVL

Thisadjustablesheaveismadetoaccommodate“3L”,“4L”,or“5L”belts.

MVLadjustablelightdutysheavesaredesignedtobeusedwithF.H.P.(fractionalHP)motors.

Fig. 2.31: Adjustable sheave

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•AdjustablePitchV-BeltSheaves(8000series)

Baldor•MaskavariablepitchV-beltsheavesareprecisionmachinedcast toprovidemaximumstrength,andalsoensuresmoothandquietoperation.Groovesareaccuratelymachinedandsmoothlyfinishedtoprovideproperbeltseating.Theyareusedwith“4L”or“A”and“5L”or“B”V-belts.

Thedatumdiameterof thesheave isadjustedby loosening thesetscrews in the

hubsandturningthethreadedflangeto thedesiredsetting, thenre-tighteningthesetscrews.

Bothsingleanddoublegrooveadjustablesheavespermitvariationsofasmuchas30%inspeed.

Bothsingleanddoublegroovesofthe8000seriesaresuitablefordrivesupto25hp.

•AdjustablePitchV-BeltSheaves(MVS)

TheMVSsheaveoffersseveralsignificantadvantages.Thissheaveisavailablein6sizesandisdesignedfor“A”-”B”or“5V”belts.Capacitiesrangeupto40hpat1,750rpm.

Thespeedisinfinitelyvariable,andasonlyonescrewcontrolsbothmovableflanges,accurategroovespacingisassuredatalltimes.Nolubricationisneeded.

Adjustable Pitch V-Belt Sheaves

Fig. 2.33: 2 groove 8000 series

O.D.

H

E F E

L

INBO

ARD

OU

TBO

ARD

Fig. 2.34: MVS series

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Step pulleys (MAS)

- Combinationof3stepsupto5(equalnumberofpossiblespeedratios)

- DesignedforA,4L&3LV-Belts.- From2to6inchdiameters.- Commonlyusedforvaryingspeedswithdrillpresses&wood

lathes.

Fig. 2.35: Step pulleys

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2.5.2.3 Classical & Narrow Belt Drives

Classical(conventional)V-Beltsareavailableindifferenttypesanddesigns.AllclassicalV-beltswiththesamecross-sectionwilloperateinsheaveswithgroovesforthatparticularcross-section.Baldor•Maskaoffersacompleteselectionofclassicalsheaves.ThisfamilyincludessheavesforclassicalV-beltsandnarrowV-belts.Inaddition,A/BCombination(codeB)sheavescanbeusedwitheither“A”(4L)or“B”(5L)V-belts.

Part Designation number:

2B64-SDS 2grooves 1-3V8.00-SDS 1grooveA(4L)&B(5L)V-belt 3V-beltP.D.=6.4in O.D.=8.0inBushingsizeSDS (P.D.=7.95in)

BushingsizeSDS

1C110-SF 1groove 3-5V4.40-SDS 3grooves“C”V-belt 5V-beltP.D.=11in O.D.=4.4inBushingsizeSF (P.D.=4.30in)

BushingsizeSDS

4D150-F 4grooves 4-8V44.5-M 4grooves“D”V-belt 8V-beltP.D.=15in O.D. =44.5inBushingsizeF (P.D.=44.3in)

BushingsizeM

ImportantDuetothemechanicalpropertiesofgreyandductilecastiron,partsmadefromgrayironcanoperateuptomaximum

rimspeedsof6,500feetperminute.SpeedsinexcessofthisrateMUSTusepartsmadefromductileiron,whichhasamaximumsafeoperatingspeedof9,500feetperminute.

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2.5.2.4 Application Table by Classes

TableshowingallsheavefamiliesmanufacturedbyBaldor•Maskawithalimitedlistofindustrialapplications.

FAMILY SHEAVES APPLICATIONS

Light Duty Fixed & Bush Types

MFAL

Fans,Blowers,H.V.A.C.,WoodProcessingEquipment,Pumps,Conveyors,PrintingMachines,MachineTools,MixersandCom-pressors

Upto3hp

MA-MB-MAL-MBL

Fans,Blowers,H.V.A.C.,WoodProcessingEquipment,Pumps,Conveyors,PrintingMachines,MachineTools,MixersandCom-pressors

Upto10hp

Adjustable/ F.H.P & Integral

MVL

Fans,Pumps,Conveyors,Ma-chineTools,MixersandCompres-sors

Upto2hp

8000

Fans,Pumps,Conveyors,Ma-chineTools,MixersandCompres-sors

Upto25hp

MVS

WoodProcessingEquipment.,AirMovingEquipment,ConveyorsSystems,BottlingPlant

Upto40hp

Classical & NarrowV-Belt Drives A/B-C-D-3V-5V-8V

PulpandPaperMillsEquipment,SawMillEquipment,MiningEquip-ment,Crushers,Pumps,Compres-sorsScreens,Extruders

Upto500HP

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2.5.3 Balancing Standards (MPTA)

2.5.3.1 General Information

When a unit turns in a circular path, a hypothetical inertia force known ascentrifugal forceexertsapulling influenceon theelementaway from thecenterduringtherotationalmovement.Thiscanbeillustratedbytyinganobjecttooneendofaropeandtheotherendtoarotatingaxisofthecenterofthepart.Asthespeedincreases,theobject is liftedintotheairuntil itattainsahorizontalposition.

Inpowertransmissionsystems,ifthemassofarotatingbodyisunevenlydistributedaroundtherotationaxis,thecentrifugal forceswillbeunbalanced. Thiscausesvibration,noiseand reducedcomponentsservice life. Asecondaryoperationcalledbalancingiscarriedouttominimizetheseeffectsbyalteringthecenterofgravitytocorrespondwiththeaxisofrotationofthecenterofthepartsoastobeevenlydistributed.

Every rotating component is eventually unbalanced to somedegree; partsmanufacturedwith absolute balancewouldbeacostlyprocessfortheconsumer.Forthisreason,itmustbedeterminedtowhatdegreeasheavemustbebalancedfortheindustrialapplicationinquestion.WewillnowconsiderthetwotypesofbalancinginuseintheindustryandapprovedbyMPTA:single-planeanddouble-planeoperations.

2.5.3.2 Static or Single-Plane Balancing

Single-planebalancing isabasicsecondaryoperationandcommonlyusedmethod that is recommended forallproducts. Aone-planeabsolutebalancedsystemcanbe illustratedbyauniformdiskwith thecentermassperfectlyalignedwiththeshaftaxis.

Fig. 2.37: Balanced Force on shaft

Balanced Forceon Shaft Axis of rotation

(Shaft)

Center of gravityconcentric with the axis of rotation

M

Fig 2.36: Centrifugal force

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However,shouldthediskhaveaholeatacertaindistancefromthecenter,thesystemwouldbeunbalanced.Toillustrate,ifarodwithanironballwasattachedtoonesideofashaft,theballcouldbecomparedtoexcessweightononesideofthedisk.

Fig. 2.38: Unbalanced Force on shaft

Unbalanced Forceon Shaft

Unbalanced Equivalent Mass

Axis of rotation(Shaft)

Hole in Disk Shifts Center of Gravity to the Opposite Side

Astherotationalspeedincreases,thecentrifugalforcecausestheshafttofeelthepullofthenon-balanceddisk.Inordertooffsetthesituation,acounterweightmustbeaddeddirectlyoppositetotheextramass.Inthiscase,anidenticalamountofmassmustbeeliminatedbyboringanotherholeoppositethefirstone.

Fig. 2.39: Balanced Force on shaft


Unbalanced Equivalent Mass

Balanced Mass



Drilled Hole for Balanced

Themethodfordeterminingwheretheholeshouldbeboredinordertobalancethepartorsheaveconsistsofplacingitonanhorizontalshaftsuspendedfromtwocarefullylevelledverticalsupports,asillustratedinFigure40.Ifthesheaveisnotbalanced,theshaftwillturnuntiltheheaviersideisonthebottom.Ahole(orholes)is(are)boreduntilthesheaveisinstaticbalance,orremainsmobileregardlessofwhatpositionitisplacedin.

A A

Fig. 2.40: Balancing – Vertical position

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A second method thatisalsousedtobalanceasheaveconsistsofmountingthesheavehorizontallyonaverticalarborplacedontableB,whichissupportedbyaknife-edgebearing.ApendulumCissuspendedfromtableB.Totestthestaticbalanceofthesheave,itiscounter-balanceduntiltheindicatorisstableinthecenterofthestationaryscaleD.Thereareseveralotherdevicesfortestingstaticbalancethataresimilarindesigntothesestandardprinciples.

Thenomographbelowshowsthemaximumspeedlimit(inRPM)forstandard statically balanced sheaves of a given diameter andfacewidth.

To use the nomograph, lay a straightedge ruler between thediameterandfacewidthreadingsandtakethemaximumRPMrecommended for standard balance where the ruler edgecrossestheslantedline.IftheRPMoftheapplicationexceedsthe maximum recommended, two-plane balancing should becarriedout.

64

60

55

50

45

40

35

30

28

26

24

22

20

18

16

14

12

109

8

7

6

5

4 1.5

2

2.5

3

3.5

4

4.5

5

6

7

8910

12

1416182024283236

MAX RPM RECOMMENDEDFOR STANDARD BALANCE

FACE

WID

TH IN

INCH

ES

50004600

44004200

3800

3400

30002800

26002400

2200

2000

1800

1600

1400

12001100

1000

900

800700

600

500

640

725

860

960

1460

1750

2900

3500

1160

Fig. 2.42: Nomograph-Max RPM for one-plane balancing

B

C

D

Fig 2.41: Balancing – Horizontal position

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Todeterminewhetherdynamicbalancingisrecommended,thefollowingformulacanalsobeused:

RPM = 15500 √D • F

DistheDiameterininchesFisFaceWidthininches

TheresultantRPMisthemaximumrecommendedoperatingRPMforsheaveswithasingleplanebalance.

Example 2.4 Ifa20in.x10in.diameterfacewidthsheaverunsfasterthan1,100rpm, dynamicbalancingisrecommended.Theresultobtainedwiththe formulais1,096rpm.

2.5.3.3 Dynamic or Two-Plane Balancing

Asheavemayhaveundergonesingle-planebalancingandyetnotbesufficientlybalancedforcertainoperations,suchaswhenthesheaverotatesathighspeedsandhasarelativelylargefacewidth.Undertheseconditionsadifferenttypeofbalancingisnecessary.

Two-planebalancingisanoperationwherebalancecorrectionsaremadeandmeasuredattwoplanesonthecomponentaxis(Fig.2.43).(Thisisnotasfullydynamicbalancing,butratherpartiallydynamicbalancing.)Theareasaffectedmustbewellseparatedtoeffectivelyproduceatwo-planebalance(seeMPTAnorm).Hence,two-planebalancingactsonnon-balancedunitsofmasseswhichdonotliewithinanarrowplane;insteadtheyarespreadalongthelengthofthecomponent.


Unbalanced Equivalent

Mass --1st Plane


Mass --1nd Plane



Fig. 2.43: Unbalanced Force on shaft – Two planes

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Factors suchas themassof the imbalance, thedistance from the rotational center, the speed (RPM), and thedistancebetweentheimbalancealongtheaxiallength,allaffectthedegreeofimbalanceandmustbeexaminedinordertojustifytwo-planebalancing.Ingeneral,thelongeracomponentinrelationtoitsdiameter,thegreaterthepossibleneedfortwo-planebalancingatacertainspeed.

Onceagainwewillrepresentanequivalentsituationusingarodandironballoneachendoftheshaft.Whentheyarerotated,notonlydoestheweightcauseapullonthefirstrod,butbecausetherearetworodspullingateachendoftheshaft,therotatingshaftalsovibrates.Inthiscase,theapplicationasshowninFig.2.43wouldappeartobeinbalanceifsubmittedtoonlysingle-planebalancingoperations.However,two-planebalancingwouldbeneededwiththisexamplewhereinthesheavesarebalancedwithreferencetoplanes(Fig.2.44)

Inconclusion,thetypeofbalancingrequired,whetheritbesingle-planeor2ndplane,isusuallydeterminedbytheaxiallengthoftheparts.Two-planebalancingisrecommendedonlyincertaincaseswheretheproductfacewidthisrelativelylargeandtheoperationalspeedrelativelyfast,orwherebalanceisconsideredverycritical.Two-planebalancingisconsideredasanoptionandmustbespecificallyrequested.

Whennon-balancedportionsareatoppositeendsor indifferentplanes,balancingmustbecarriedoutsoas tocounteractthecentrifugalforceofthesheavesathighspeeds.DynamicBalancingthenconsistsofpositioningthecounter-balancingweightsaccordingtotheirweight,theirpositionontheaxisofrotationandtheirangularpositions.

Fig. 2.44: Balanced Force on shaft – 2nd planes

Drilled Holesfor Balanced


Mass --1st Plane

Balanced Mass

Balanced Mass


Mass --1nd Plane



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Chapter 4 INSTALLATION & MAINTENANCE

4.1 Bushing Mounting

4.1.1 Types of Mounting

Therearetwowaystomountabushingwithasheaveontoashaftthatleavesthecapscrewsaccessiblefromtheoutside;eitherwayisacceptable.

Bushing flange toward machine or motor

1.Aligntappedholesinbushingflangewithdrilledholesinsheavehub.

2.Insertcapscrewsthroughdrilledholesinsheavehubandthreadlooselyintotappedholesinbushingflange.

3.Positionassemblyonshaftandtightencapscrewsprogressivelyanduniformly.

To remove

1.Removecapscrewsandthreadintotappedholesinsheavehub.Tightenprogressivelyuntilbushingisfreefromsheavetaper.

2.Removeassemblyfromshaft.

Bushing flange away from machine or motor

1.Aligndrilledholesinbushingflangewithtappedholesinsheavehub.

2.Insertcapscrewsthroughdrilledholesinbushingflangeandthreadlooselyintotappedholesinsheavehub.

3.Positionassemblyonshaftandtightencapscrewsprogressivelyanduniformly.

To remove

1.Removecapscrewsandthreadintotappedholesinbushingflange.Tightenprogressivelyuntilbushingisfreefromsheavetaper.

2.Removeassemblyfromshaft.

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IMPORTANTWhen mounting, do not use any lubricant.

Tighten screws with the appropriate wrench torque.

4.1.2 Tightening

Tightenscrewsevenlyandprogressively.Neverallowthesheavetobedrawnintocontactwiththebushingflange.Iftoomuchpressureisappliedwhentighteningthescrews,excessstrainwillbecreatedinthehubcausingittocrack.

Forthecorrectwrenchtorque,pleaserefertothefollowingtable.

PROPER WRENCH TORQUETO TIGHTEN SCREWS

BUSHINGNo.

SCREWSIZE

TORQUEWRENCH

OPEN END OR SOCKET WRENCH

TORQUECAPACITY

Inches Ft.-Lbs. LENGTHInches Pull / Lbs. In.-Lbs.

L 1/4 6 4 18 1,200JA no.10 5 4 15 1,000SH 1/4 9 4 27 3,000

SDS-SD 1/4 9 4 27 5,000SK 5/16 15 6 30 7,000SF 3/8 30 6 60 11,000E 1/2 60 12 60 20,000F 9/16 75 12 75 30,000J 5/8 135 15 135 45,000M 3/4 225 15 180 85,000N 7/8 300 15 240 150,000P 1 450 18 300 250,000W 11/8 600 24 300 375,000S 11/4 750 30 300 625,000

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4.2 V-Belts & Sheaves

With proper installation and maintenance, V-belts will have a longer, more cost-effective service life. MainguidelinesonhowtocorrectlyinstallaV-beltdrivewillnowbediscussed.

4.2.1 Mounting Structure

Drivetensioningcanimposeexcessiveloadonthestructurethatsupportsthemotor,reducer,andotherdrivenequipment.Forexample,a100-hpdrivethatrunsa1,760-rpmmotor,theforceinducedbybelttensioncaneasilyexceed2,500lb.It’simportantthereforetodesignthemountingstructureinanappropriatemannertosupportthisloadwithoutdeflectionunderstaticanddynamicloadconditions.Otherwise,allofthecaretakenduringinstallationwouldbefutile.

4.2.2 Center Distance Adjustment

V-beltdriveunitsshouldallowforanadjustmentofthedistancebetweenthedrivingandthedrivensheaves.ThecenterdistancemusthaveaminusallowancetopermiteasyinstallationoftheV-beltsinordertoavoidanystrainordamageandaplusallowancetoallowforanadjustmenttothedesiredtension.Inmostcases,theminusallowanceis1.5%ofthecenterdistanceandtheplusallowanceis3%.

Motor base ormotor slide rails are themost common adjustablemechanisms for tensioning a drive. Thesedevicesareavailableinavarietyofmodels,includingspring-loadedversionsthatautomaticallycompensateforbeltelongation.Forinstallationsthatdonotallowforanadjustablecenterdistance,theuseofanidlerpulleyisrecommended.

Example 4.1 Ifthecentertocenterdistanceofadrivebeltsystemis40in.,calculatetheallowancerequiredforinstallationandremovalofthebeltdrive.

Answer: Theminusallowance=40[in]x1.5%=40x0.05=2in. Theplusallowance=40[in]x3.0%=40x0.03=1.2in.Themaximumvalueofthecentertocenterdistanceshouldthereforebeatleast42in.andtheminimumdistanceshouldbeequaltoorlessthan38.8in.

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4.2.3 V-Belt Installation

Step 1 : Replacing V-belts

- Reduce thecenter-to-centerdistancebetween thedriverand thedrivensheavesbymoving themotor-plateinwards.Thisreducestensionandallowsforslackinthebeltbetweenthesheaves.

- Removetheusedbeltsfromthesheavesandexaminethegroovesurfacesforanydamage.

Step 2: Sheave Inspection

- Checkforwearonthesidewalls,cracking,reinforcingnyloncordsandoilysurfaces.

- The wear of the V-groove in the sheave can be measured with a “go-no-go” belt gauge available from Baldor•MaskaPartNo.006346.

It’sveryimportanttoknowiftheV-groovewallshavebeensubjectedtoexcessivestraincausedbyimproperbelttensionormisalignmentbetweenthedrivingandthedrivensheaves.IftheV-groovesurfacehasdeterioratedorbeendamaged,thedefectivepartsmustbereplacedwithnewones.Wornsheavescanreducebeltlifebyasmuchas50%.

Step 3: Cleaning Sheaves

- Useastiffbrushtoremoveallforeignmatterfromthesheavethatcouldabradebelts.DonotusebrushesthatcouldscratchthesurfaceofthegroovewallsasthesescratchescangrazetheV-belt’souterskinwhenrotating,thussystematicallydestroyingit.

- Pulleygroovesshouldbefreefromrust,oil,grease,dustandburrs.

Step 4: Sheave Alignment

Simple alignment for angular and parallel offset

ThequestionofalignmentisnotascriticalinV-beltsdrivesaswithothersystems,forexampletheyareinherentlymoreforgivingofmisalignmentthansynchronousbeltdrives.Nonetheless,beforeinstallingV-belts,verifythatthesheavesareproperlyalignedandparallelasaprerequisitetopropertensioning.Pooralignmentrendersaccuratetensioningimpossibleandcausesaloadimbalanceacrossthebeltspan.

Thefirststepconsistsofverifyingwhetherthedriveshaftsareparallel,andthesheavesareintheproperpositionontheaxis.Thisprocedurecanbycheckedwithsufficientaccuracythroughuseofamachinist’sstraightedgeruler,orbyplacingatightlydrawnpieceofstring,acrossthefacesofthesheavestoseeifallfourpointsofcontactaremade.

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Fig. 4.1: Alignment – Use of a straightedge or a string

However, if there isadifference in thesidewall thicknessof thesheaves, thismethodwill notbesufficientlyaccurate.Forthisreason,thismethodwillbeeffectiveonlywhenthesheavesareamatchedpair.Whenthisisnotthecase,thesheavesmustbealignedparallelbytheirgrooves.Thisisthepreferredalignmentmethodwithanydrive.

Inordertodeterminewhatdegreeofmisalignmentisacceptable,andatwhatpointitbecomesexcessive,alignmentmustbequantifiedandcomparedtothebeltmanufacturer’srecommendationsforvariousdrives.Anexampleofthisfollows:

Maximum allowable offset

Type V-belt Synchronous belt Angular offset (deg.) 0.5 0.25

Fig. 4.2: Angular offset

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Type V-belt Synchronous belt Parallel offset (in. / ft. of center distance.) 0.1 0.05

Fig. 4.3: Parallel offset

Example 4.2 Witha5ft.centerdistance,whatistheallowableparalleloffsetforaV-beltdrive?Answer:V-beltparalleloffset=5x0.1=0.5in.max

Other types of misalignment

Theprecedingprocedureillustratedaquickmethodforcheckingsheavealignmentasseenfromoneangleonly.ThismethodisusefulonlywhentheengineshaftsareparallelhorizontallyinastraightlineasseeninFig.4.1.Infact,sheavesthathavebeeninstalledonashaftcanbemisalignedifthedrivenshaftdoesnothavethesameangleasthedrivershaft(forexample,dipstowardstheground)asopposedtothehorizontalsurface(Fig.4.4).Inthiscase,thetwoshaftswouldhavetobeplacedparalleltoeachotheratthisplane.Toverify,youwouldhavetolookfromanotherangleandrepeatthestepsforcheckingmisalignmentwithalevelgauge.Thistypeofmisalignmentshouldnotbeconfusedwitha1/4thor1/8thturndrivedesign.

Fig. 4.4: Other type of misalignment

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Step 5: V-Belt Installation

- Verifythatthereplacementbeltsareofthecorrespondingsize.TheV-beltcross-sectionmustbecompatiblewiththeVsectioninthegroove.

Asdiscussedinchapter2,V-beltsaremadeofdifferentmaterialsandofvarieddesigndependingontheapplication.Inaddition,similarcross-sectionbeltsfromdifferentmanufacturersdonotnecessarilyhavethesamefeaturesandcandifferinstretchcapacityandfrictioncoefficients.Forthisreason,beltsfromthesamemanufacturershouldbeusedwithmultiplegroovesheaves.

NeverusenewandusedV-beltsonthesamedesign,eveniftheusedbeltsseemtobeingoodshape.Beltsshouldalwaysbeinstalledinmatchedsets.Ifonebeltneedstobechanged,thewholesetshouldbereplaced.IftheV-beltsarenotoftheexactsamelength,itwillresultinrapidwearofthenewbeltsandunequaldistributionoftheload,thusreducingbeltlifesignificantly.

- Adjustthecenter-to-centerdistanceinordertoslidethebeltsoverthesheaves.Themotormustshiftenoughtoallowthebeltstoberemovedorinstalledwithoutforcingthem.

- Neverleverbeltsoverthesheavegroovesasthismayinjurethereinforcementscords.

- Installthenewbeltsoverthesheavessothattheslacksideofallbeltsisonthesameside,eitherthetoporthebottomofthedrive.

- Increasethedrivecenterdistancetopre-tensionthebelts(seenextsectionforcorrecttensioning).

4.2.4 Tensioning

One of the most important factors that determines the efficiency of a V-belt drive is proper belt-tensioning.Insufficientbelttensionwillcausebeltslippage,resultinginreducedpullingcapacity.Toincreasetension,asseenearlier,wehavemerelytoincreasethecenterdistance.However,beforeattemptingtotensionanydrive,it isimperativethatthesheavesbeproperlyinstalledandalignedasstatedinaprecedingsection(section4.2.2).

Theeffectsoflowtensiononasynchronousbeltareequallydisastrous.Lowtensionallowsthebeltteethtorideuponthesprocketteeth,thusplacingseverestressontheteeth.Underheavyloads,thedrivecanjumpteeth(ratchet),whichleadstorapidbeltfailure.

IftoomuchtensionisappliedtotheV-belts,theservicelifeofbeltsandbearingswillbeconsiderablyreduced.Drivetensionthatistoohighcanhaveother,far-reachingconsequences.Unduestressisplacednotonlyonthebelt,butthebearingsandshaftingaswell.Earlybeltfailureisthenorm,asexcessivetensionover-stressesbeltcords.Bearingoverloadalsoleadstoearlyfailure,andcanresultinmotorandreducerdamage.

• Incorrecttensioncandestroybeltsandequipment.• Alignmentaffectsbelttension.• Tensioncanbemeasuredwithasimplespringscaleoracousticalinstrument.

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4.2.4.1 Measuring Techniques

V-beltsandsynchronousbeltshavebeengreatlyimprovedcomparedtoonlyafewyearsago.Theydeliveralotmorepowerinasmallerpackage.Inordertobenefitfromthisimprovement,itisessentialthattheybecorrectlyalignedandtensioned.Allittakesisafewsimpletoolsandtechniquestoeasilyandaccuratelytensionadrive,inordertoyieldthehighperformancedesignedintothem.

DeflectionForceMethod

Themostcommonmethodfortensioningadjustmentiswithatensionmeteroranothertypeofspringscaletool.Thistoolmeasuresthedeflectionforcewhenpressedtotheopenspanofthebeltdrive.CarryingoutthefollowingprocedureswillobtainadequatetensioningformostV-beltdriverequirements:

Step1: Followingthebeltinstallationprocedurealreadydiscussed,arrangethebeltssothatboththetopandbottomspanshaveaboutthesamesag.Applytensiontothebeltsbyincreasingthecenterdistanceuntilthebeltsaresnug(Fig.4.5).

Step 2: Operatethedriveafewminutestoseatthebeltsinthesheavegrooves.Observetheoperationofthedriveunderthehighestloadcondition(usuallystarting).Aslightbowingoftheslacksideofthedriveindicatespropertension.Iftheslacksideremainstautduringthepeakload,thedriveistootight.Excessivebowingorslippageindicatesinsufficienttension.Ifthisisthecase,stopthedriveandtightenthebeltsuntilalltheslackistakenup.Furtherincreasethetensionuntilonlyaslightbowontheslacksideisapparentwhilethedriveisoperatingunderload.

Step 3: Stopthedriveandusethemetertomeasuretheforcenecessarytodepressoneofthecenterbelts1/64-inchforeveryinchofbeltspan.Forexampleadeflectionfora50inchbeltspanis50/64or25/32-inch.Ifthedeflectionexceeds50/64in.foreveryinchofspanlength,thedriveneedstobetensionedhigher.Ifthedeflectionisless,drivetensionisexcessiveandshouldbereduced.

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Fig. 4.5: Belt Tension – Deflection force method

t =√C2 - D1 - D2 2

The amount of force required to deflect the belt shouldmatch upwith the deflection force data noted in thechartbelow.NotethatthedeflectionforcevarieswithV-beltsfromtheinitialrun-invalues,whicharehigher(reflectinghigherrun-intensioning)thanthenormalvaluesobtainedaftertherun-inperiod.

StandardV-beltTensioningDeflectionForceTableForBaldor•MaskaBlueFlexBelts

BeltCross-Section SmallerPulleyDiameterRange(in.)

DeflectionForce

Run-in(lbs) Normal(lbs)

A3.0-3.63.8-4.85.0-7.0

3-3/84-1/45-1/8

2-1/42-7/83-3/8

AX3.0-3.63.8-4.85.0-7.0

4-1/856

2-3/43-1/4

4

B3.4-4.24.4-5.25.4-9.4

46

7-1/8

2-5/84

5-1/4

BX3.4-4.24.4-5.25.4-9.4

5-1/47-1/8

9

3-1/24-3/4

6

C 7.0-9.09.5-16.0

11-1/415-3/4

7-1/210-1/2

CX 7.0-9.09.5-16.0

13-1/217-1/2

911-3/4

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D 12.0-16.018.0-22.0

24–½33

16-1/222

E 21.6-27.0 48 32

3V 3.40-4.204.20-10.6

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1620

8-1210-15

5VX 4.40-10.911.8-16.0

1822

10-1412-18

8V 12.5-17.018.0-22.4

3640

18-2720-30

Step 4: Restarttheunitandallowthebeltstoseatthemselvesinthesheavegrooves.

Step 5: Stop the unit after a few hours andmeasure all belt tensions (Refer toStep 3). Note:During the initial run-inperiod,itcanbeexpectedthatthebelttensionwillneedtobere-adjustedbeforeobtainingthecorrectdeflection.Repeattheprocedureuntilalloftheslackistakenoutofthebelts.

Step 6: Restarttheunit.Steps4and5areoftenoverlookedduringbeltinstallation,butre-checkingthetensionisaveryimportantstepintheefficientoperationandmaintenanceofV-belts.Assuch,itisworthtakingalittleextratimetodoso,asyouwillseeinthenextstep.

Step 7: Seesection4.2.4.2onRun-inperiod

Elongation method

Belttensioncanbemeasuredbymarkinglines10inchesapartacrossthebelts’topsurfacesat90degreestothelengthonaninstalledbelt.Applytensionuntil thegapincreasesbythedesiredpercentage.For2percenttension,thelinesonthetensionedbeltwouldbe10.2inchesapart.Mechanicalfailuremayresultwhenbelttensioningisexcessive;2to2.5percentelongationshouldberegardedasthelimit.Thisprocedureisnormallyusedtotensiondrivesusingbandedbeltsthatrequireadeflectionforcebeyondtherangeofconventionalequipment.Theelongationmethodisnotsuitablefortensioningsynchronousbeltsthatareconstructedwithfiberglassoraramidecordsthathavealmostnoelasticity.Thismethodisaccurateonlywhenusinglongbelts;thedeflectionmethoddiscussedaboveisthestandard,recommendedproceduretofollow.

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4.2.4.2 Run-in Period

Thefirst48-hoursfollowinginstallationisthemostcriticaltimeforV-belttensionverification.Theinitialstretchistakenoutofthebeltduringthisrun-inperiod,anditsettlesdeeperintothegrooveofthesheaveafterthesoftrubbersurfaceofthebelt’souterenvelopeisabradedawaycausingthebelttorunslack.Toavoidconsiderableslippage,frictionalburning,andotherirreparabledamagetheslackonthenewbeltsmustbetakenup.

Itisveryimportanttoverifythetensiononanewdrivefrequentlyoverthefirstfewdaysbyobservingtheslackside.Adjustthebeltaccordingtothenormaltensiondatagiveninthechartuntilallsignsofstretchinghavebeeneliminated.Thisprocessmustberepeateduntilallofthestretchhasbeeneliminated.Afteroperatingforseveraldays,thebeltswillseatthemselvesinthesheavegroovesanditmaybenecessarytoreadjustthetensionsothatthedriveshowsaslightbowontheslackside.Beingvigilantatthisstagewilleliminateearlydamageandpromotelongerbeltlife.Itwillalsoimprovethemechanicalefficiencyofthemotor,andthedrivenmechanicalequipment,byreducingwearonrotatingmechanicalcomponents.

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4.2.5 Idler Pulleys

The preferred location for an idler pulley is always onthe slack side of the drive (Fig. 4.6). An inside idlerimposeslessstressonthebelt,andshouldbelocatednearthelargersheavetominimizethereductioninthearcofcontactwiththesmallersheaveorsprocket.Ifanoutsideidleristheonlyoption,locateitnearthesmallersheave as this enhances the arc of contact with thesmallersheave.Itisimportantthattheidlerdiameterisnotinferiortothesmallestsheaveinthedrive.

• Aninsideidlerdecreasesthearcofcontactonadjacentwheels.

• Anoutsideidlerincreasesthearcofcontactonadjacentwheels.

IdlersareoccasionallyusedinthedesignofconventionalV-beltandtimingbeltdrivesforvariousreasons:

1. Toprovidetake-upforfixedcenterdrives.2. Toclearobstructions.3. Tosubduebeltwhiponlongcenterdistance.4. Tomaintaintension.5. Toimproveapoordesign,suchasaverysmallsheavedrivingaverylargesheave.

Ifatallpossible,theuseof idlersshouldbeavoided.Theyeitherreducethehorsepowerratingorshortenbeltlife.However,asstatedearlier,idlersshouldbelocated,ifatallpossible,ontheslacksideofthedrive.Thisisespeciallytruewhenspringloadedorweightedidlersarebeingused,asthiskeepsthespringforceortheweighttoaminimum.

slack

tight

IDLER

DRIVER

OUTSIDE IDLER

slack

tight

IDLER

DRIVER

INSIDE IDLER

Fig. 4.6: Idler – Recommended position

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4.2.6 Maintenance

Make V-belt drive inspections periodically.

• Checkbelttensionregularly.

• Neverapplybeltdressing,asthiswilldamagethebeltandcauseearlyfailure.Theyoftenhaveasolventeffectuponrubbercompounds,whichmaytemporarilyincreasefriction,butdoessoattheexpenseofrapidV-beltdeterioration.

• V-beltsshouldbekeptcleanandfreeofoil,greaseanddust.

• Foroutdoormachinery,avoidexposingbeltstodirectsunlight.

• Factorsaffectingultimatebeltlifeincludetemperature(anincreaseintemperatureof10°Cor18°Fcancutlongevity by 50%), the power pulse characteristics of the engine, abrasives and chemical contamination,abnormallytightorloosetensioning,wornpulleys,andmisalignment.

• HightemperaturesareharmfultolongV-beltperformance.Forthisreason,avoidtightfittingmountingandsafetyguardsthatmayobstructtheventilationopenings.

Theessentialfactorstowatchforwhenusingbeltsare:keepingthemclean,anysignificantchangesintemperature,thehumiditylevel,andthepresenceofchemicalproductsorfumes.Thedegreetowhichtheseelementsarepresentdirectlyaffectsbeltlifeandperformance.Manyapplicationsrequirebeltswitharesistantsubstanceorfabriccasingasaprotectionagainstacidsandsolvents.

4.2.7 Belt Storage

StorageconditionshaveadirectinfluenceonV-beltlife.Inadequatestoragemaycausedamagetobeltsandthusreducebeltlife.

• Storingbeltsonsheavessavesspaceandisthebestwayofstoring.Shorterbeltsmaybestackedinsinglefileoneontopoftheother,whilelongbeltsshouldbefolded3or5times.

• V-beltsshouldbestoredwithoutstressi.e.withouttension,pressureoranyotherformofdeformation.

• Dampstorageroomsareunsuitable.Thisleadstomildewformationwhichdeterioratesthebelt’sjacket.

V-beltsshouldbestoredinacoolanddryplacewithtemperaturesvaryingfrom10ºto20ºC.Arelativehumidityofbetween20%-60%offersthebeststorageconditionsashumiditymaycauseafungustoformonbelts.Theyshouldalsobekeptawayfromdirectsunlightorarcweldersandhighvoltageapparatus.

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4.3 Typical Problems

4.3.1 Drive Misalignment

Beltdrivemisalignmentisoneofthemostcommoncausesofprematurebeltfailure.Itreducesbeltdriveperformanceandcausesunevenweartoonesideofthebelt.Abeltcanbedamagedinaslittleasonehour,toacoupleofdays,ifthesheavesorpulleyshavebeenimproperlyalignedduringinstallation.

Alldrivecomponentsshouldbecheckedtoverifythattheyareallwell-tightenedandinplace.Ifthemisalignmentcomesfromdesign,theunitshouldberevisedinordertoeliminatetheproblem.Misalignmentmayforceabelttorolloverinthesheave,oritcanthrowtheentireloadontoonesideofthebelt,thusstretchingorbreakingthecords.

Angularmisalignment(Fig.4.1)results inacceleratedbelt/sheavewearandpotentialstabilityproblems insinglegrooveV-beltdrives.Ifthesameproblemoccurswithamultiplegroovepulley,unequalloadsharingresultstoeachbeltandleadstoprematurefailure.

4.3.2 Sheave Cracked in Hub

Whenmountingabushingbytighteningthescrews,excessivetorquecancrackthesheaveasaresultoftoomuchpressureagainstthehub.Neverallowthesheavetobedrawnintocontactwiththeflangeofthebushing,andneverlubricatethebushingorthesheave(lubricationcanincreasethelateralforcesuptoseventimeswiththesametorquevaluesoncapscrews).

Fig. 4.7: Excessive torque - High pressure against the hub

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4.3.3 Vibrations

Fig. 4.8: High level of vibration

Vibrationsarethemostseriousproblemthatcandevelopwithadrivedesign.Therearetworeasonsastowhythisissuchadifficultproblem:Firstofall,thecauseoftheproblemisverytrickytodiscover,asallofthemechanism’componentscouldbethesourceofthevibrations.Secondly,vibrationsinvolvetheentiredrivedesign;theproblemisthusnotlimitedtothesheaveorbelt,whichareeasilyreplaced.

StepOne involvesfinding themain sourceof vibrations– is theentiredesignoutof balance? Is thedesigninaccurateasfarasthechoiceofcomponentsisconcerned?Hasthereoccurredamechanicalbreakingofapart,etc.?Thesecondstepistoapplytherequiredcorrections.However,ifthedesignerhastodealwithahighlevelofvibration,thentheuseofspecializedcomponentsshouldbeconsidered(rollingjoint,coupling,etc.).

4.3.4 Over Tension

Overbelttensionresultsinacceleratedwearoftheshaftbearings.Thesolutionistoreducethecenterdistancetolowerthetension,asdiscussedinSection4.2.4.

Fig. 4.9: High tension – Overloaded bearings

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4.3.5 High Ratio with Short Center to Center Distance

Inordertoincreasethearcofcontactonadrivedesignedwithahighratio,itwillbenecessarytoinstallanidlerpulley.Thistensioningdevice,asmentioned,shouldbeinstalledontheslackside.

Wrong Design

Fig. 4.10: Increase the arc of contact

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4.4 Couplings

Couplingsareaverypracticaldevicedesignedtotransmitmechanicalpowerfromoneshafttoanothershaftbyconnectingthemtogether,buttheyarealsodesignedtoaccomplishseveralothertasks.Therearemorethanfiftytypesofmechanicalshaftcouplingsusedindifferentindustrialapplications,andtheycanbedividedintothreemaincategories:(1)flexible,(2)rigidand(3)universaljoints.

Rigidcouplingsareused toconnectshafts thatarepreciselyaligned,whereasflexiblecouplingsandU-jointsaccommodatevaryingdegreesofmisalignmentbetweenshafts.U-jointsareusedwithapplicationswherepowermustbetransmittedfromaninputshaftthatissituatedatacertainangletotheoutputshaft.

Inmanyapplicationscouplingsmaybeabletoaccommodatemisalignmentanddampenvibrationsorshockload.For this reason,most industrialapplicationsuseflexiblecouplings, rather than the rigid types,becauseofthesemultiplepracticalfunctions.

4.4.1 Flexible Coupling Types

Initially,flexiblecouplingsweredividedintotwotypes:non-lubricatedandlubricated.Thenon-lubricatedmodelisfabricatedforthemostpartfromelastomericorplasticandthemetallicpartsrequirelubrication.

1. Non-lubricated -Disc -Elastomeric

2. Lubricated -Grid(spring) -Gear

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Themostcommonlyusedcouplingsarethosethatallowforthegreatestflexibility(minorshaftmisalignmentandaxialcapacity)whileproducingthelowestexternalloadsonequipment.Thetypeofcouplingselecteddependsoneachone’s capacitiesandcharacteristicswith regards toeachapplication’sneeds. Themost importantcharacteristicstakenintoconsiderationareoftenthepowerandspeedcapabilities.

Severalparametersmustbeconsideredinorderto make the best coupling(s) choice:

1. Typeofprimemoverandloadcharacteristics2. Shaftdiametersandkeysizesorsplineconfiguration3. Horsepowerratingoftheequipmenttobecoupled4. Maximumoperatingspeed5. Maximumoperatingmisalignment6. Clearancelimitations7. Ambientconditions

Metallic types arebestsuitedtoapplicationsthatrequireorpermit:

• Torsionalstiffness• Operationinrelativelyhighambienttemperaturesand/orpresenceofcertainoilsorchemicals;• Electricmotordriveonly(metallictypesarenotgenerallyrecommendedforgas/dieselenginedrives);• Relativelyconstant,low-inertialoads(generallynotrecommendedfordrivingreciprocalpumps,compressors,

andotherpulsatingmachinery)

Elastomeric typesarebestsuitedtoapplicationsthatrequireorpermit:

• Torsionalsoftness(absorbsshockandvibration,improvedtoleranceofenginedriveandpulsatingorrelativelyhigh-inertialoads)

• Greaterradialsoftness(allowsmoreangularmisalignmentbetweenshafts,putslessreactionaryorsideloadonbearingsandbushings)

• Lighterweight/lowercost,intermsoftorquecapacityrelativetomaximumborecapacity• Smootherandquieter

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4.4.2 Shaft Misalignment

Therearefourtypesofshaftmisalignment:parallel,endfloat,angularandtorsionaldeflection.

• ParallelOffsetMisalignment

Shaftcenterlinesareparallelanddonotmeet.

• EndFloat Shaftfloatsorexperienceslongitudinalmovement.

• AngularMisalignment

Shaftcenterlinesmeetatanangle.

• TorsionalDeflection

Twistingloadaroundshaft;oneshaftmovesslightlyaheadoftheotherone.

• Dampingvibration

Also,sometypesofflexiblecouplingsdampenvibrationsandreducenoise.

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4.4.3 Elastomeric Element Couplings

Elastomericcouplings transmit torquebetween twoshaftsbymeansofanelastomericmaterial. (natural rubber,urethane, etc.). These flexible elements may be primarily stressed in tension, compression, shear or anycombinationofstresses.TheMaskaflexcouplingusesshearstressandgenerallyproduceslowershaftloadswhensubjectedtoparalleloffsetmisalignmentbecauseitistortionallysofter.

Elastomeric Coupling Alternatives

Compression-typecouplingsgenerallyoffertwoadvantagesoversheartypes.First,becauseelastomericcouplingshaveahigherloadcapacityincompressionthanshear,compressiontypescantransmithighertorqueandtolerategreateroverload.Second,theyofferagreaterdegreeoftorsionalstiffness,withsomedesignsapproachingthepositive-displacementstiffnessofmetalliccouplings.

Shear-typecouplingsinturnoffertwogeneraladvantagesovercompressiontypes.First,theyaccommodatemoreparallelandangularoffset,whileinducinglessreactionarybearingload.Thismakesthemespeciallyappropriatewhereshaftsmayberelativelythinandsusceptibletobending.Second,theyofferagreaterdegreeoftorsionalsoftness,whichinsomecasesprovidesgreaterprotectionagainstthedestructiveeffectsoftorsionalvibration.TheMaskflexcouplingshownhereisashear-typecoupling.

The MASKAFLEX coupling is anelastomeric coupling composed of twoflanges.Thiscouplinghasaflexiblerubbertire with tension-member cords, such asnylon,thatcarrytheload.Thesecordsarevulcanizedintothetireshape.Thismodelisalsocalledatirecoupling,namedafterit’sresemblancetoacartire.

The two flange hubs are equipped withclampingplates,whichgripthetireshapedelementbyitsinnerrims.Thetirecouplingistorsionallysoftandcandampvibrations.Highradialsoftnessaccommodatesangularmisalignmentupto4degreesandparalleloffsetupto1/8”. Thisuniqueelastomericcouplinghasthecapabilitytoallowupto¼”ofaxialshaftmovement.Thesepropertiescoverawidevarietyofapplications,suchasthose using internal combustion engines.Design variations are available, includingan inverted tire coupling in which the tireelement arcs inward toward the axis thathasbeendesignedforhigherRPMservice.

MASKAFLEXcouplingtiresaremanufacturedfrom;•Standard(NaturalRubber):Thisunitisdesignedfortemperaturesbetween42C°and+82C°.

Fig 4.12: Maskaflex coupling

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Baldor Electric CompanyP.O. Box 2400

Fort Smith, AR 72902-2400 U.S.A.Ph (479) 646-4711 • Fax (479) 648-5792

International Fax (479) 648-5895www.baldor.com • www.maskapulleys.com

© Baldor Electric CompanyBEC-16

Printed in U.S.A.05/08 FARR 200

Contact your nearest Baldor Sales Office at these World Wide locations, or visit www.baldor.com

United StateS ArizonA Phoenix Power reps, inc. 4211 South 43rd Place Phoenix, Az 85040 Tel.: 602-470-0407 Fax: 602-470-0464 ArkAnSAS Clarksville Wade Black & Associates, inc. 1001 College Avenue Clarksville, Ar 72830 Tel.: 479-754-9108 Fax: 479-754-9205

CAliForniA Hayward Golden Gate Baldor 21056 Forbes Street Hayward, CA 94545-1116 Tel.: 510-785-9900 Fax: 510-785-9910

Commerce Power reps, inc. 6480 Flotilla St. Commerce, CA 90040 Tel.: 323-724-6771 Fax: 323-721-5859

ColorAdo denver rocky Mountain Baldor, inc. 3855 Forest Street denver, Co 80207 Tel.: 303-623-0127 Fax: 303-595-3772

ConneCTiCuT Wallingford eMS, inc. 65 S. Turnpike road Wallingford, CT 06492 Tel.: 203-269-1354 Fax: 203-269-5485

FloridA Tampa J.k. kessler & Assoc. inc. 3906 east 11th Avenue Tampa, Fl 33605 Tel.: 813-248-5078 Fax: 813-247-2984

GeorGiA Alpharetta Sarka Sales Agency, inc. 62 Technology drive Alpharetta, GA 30005 Tel.: 770-772-7000 Fax: 770-772-7200

illinoiS Bolingbrook Windy City Baldor, inc. 340 remington Blvd. Bolingbrook, il 60440 Tel.: 630-296-1400 Fax: 630-226-9420

indiAnA indianapolis The Scott Group, inc. 5525 W. Minnesota St. indianapolis, in 46241 Tel.: 317-246-5100 Fax: 317-246-5110

ioWA des Moines Baldor industrial Solutions 1800 dixon St., Suite C des Moines, iA 50316 Tel.: 515-263-6929 Fax: 515-263-6515

MArylAnd elkridge Baldor of Baltimore, llC 6660 Santa Barbara road, Suite 22-24 elkridge, Md 21075 Tel.: 410-579-2135 Fax: 410-579-2677

MASSACHuSeTTS Worcester redman & Associates 6 Pullman Street Worcester, MA 01606 Tel.: 508-854-0708 Fax: 508-854-0291

MiCHiGAn Sterling Heights industrial rotating Products 5993 Progress drive Sterling Heights, Mi 48312 Tel.: 586-978-9800 Fax: 586-978-9969

MinneSoTA rogers Perkins Power-Motion Products 21080 134th Ave. north rogers, Mn 55374 Tel.: 763-428-3633 Fax: 763-428-4551

MiSSouri kansas City rPM Solutions 1501 Bedford Ave. kansas City, Mo 64116 Tel.: 816-587-0272 Fax: 816-587-3735

St. louis Alderson industrial Sales, inc. 10254 Page industrial drive St. louis, Mo 63132-1314 Tel.: 314-426-0606 Fax: 314-426-0607

neW JerSey Pennsauken Childs & Assoc., inc. 1035 Thomas Busch Hwy Pennsauken, nJ 08110 Tel.: 856-661-1442 Fax: 856-663-6363

neW york Auburn Baldor ny - Penn inc. one ellis drive Auburn, ny 13021 Tel.: 315-255-3403 Fax: 315-253-9923

norTH CArolinA Greensboro Motion resources, inc. 1220 rotherwood road Greensboro, nC 27406 Tel.: 336-272-6104 Fax: 336-273-6628

oHio West Chester Baldor Cincinnati, inc. 2929 Crescentville road West Chester, oH 45069 Tel.: 513-771-2600 Fax: 513-772-2219

Macedonia engineered Sales, inc. 8929 Freeway drive Macedonia, oH 44056 Tel.: 330-468-4777 Fax: 330-468-4778

oklAHoMA Tulsa Baldor oklahoma 7170 S. Braden, Suite 140 Tulsa, ok 74136 Tel.: 918-366-9320 Fax: 918-366-9338

oreGon Tualatin d.l. Hermanson & Assoc. 20393 SW Avery Court Tualatin, or 97062 Tel.: 503-691-9010 Fax: 503-691-9012

PennSylvAniA new kensington Baldor Pittsburgh 159 Prominence drive new kensington, PA 15068 Tel.: 724-889-0092 Fax: 724-889-0094

TenneSSee Memphis Baldor Power Solutions, llC 3126 norbrook dr. Memphis, Tn 38116 Tel.: 901-346-4722 Fax: 901-346-4725

TexAS dallas kilpatrick Sales 2920 114th St – Suite 100 Grand Prairie, Tx 75050 Tel.: 214-634-7271 Fax: 214-634-8874

Houston Baldor electric of Southern Texas 10355 W. little york road, Suite 300 Houston, Tx 77041 Tel.: 281-977-6500 Fax: 281-977-6510 uTAH Salt lake City rocky Mountain Baldor, inc. 2230 South Main St. Salt lake City, uT 84115 Tel.: 801-832-0127 Fax: 801-832-8911

WiSConSin new Berlin Baldor Power Solutions, llC 1960 South Calhoun road new Berlin, Wi 53151 Tel.: 262-784-5940 Fax: 262-784-1215

CanadaAlBerTA edmonton Baldor Motors & drives (Alberta), ltd. 4053 92 Street edmonton, Alberta T6e 6r8 Tel.: 780-434-4900 Fax: 780-438-2600

BriTiSH ColuMBiA Port Coquitlam Canadian electro drive (1982), ltd. 1538 kebet Way Port Coquitlam, BC v3C 5M5 Tel.: 604-421-2822 Fax: 604-421-3113

MAniToBA Winnipeg industrial Agencies 54 Princess Street Winnipeg, MB r3B 1k2 Tel.: 204-942-5205 Fax: 204-956-4251

onTArio Toronto Baldor electric ontario, inc. 2750 Coventry road oakville, on l6H 6r1 Tel.: 905-829-3301 Fax: 905-829-3302

QueBeC Montreal Baldor Quebec Atlantique inc. 5155, rue J.A. Bombardier Saint-Hubert, QC J3z 1G4 Tel.: 514-933-2711 Fax: 514-933-8639

MEXICO Baldor Sales officeoficina Corporativa de ventas y Centro de distribución Blvd. al Aeropuerto km. 2 Col. San José el Alto león , Gto. CP 37545 Tel. (47) 7761 2030 Fax (47) 7761 2010

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