Design Guide andEngineer’s Referencefor Metal Belts

BeltTechnologieshelpsourclientcompanies

achieveoptimalperformancefrommachinery

forprecisionpositioning,timing,conveying,power

transmission,packaging,andautomated

manufacturingoperations.Formorethan25years,

wehaveprovidedacomprehensiveresource

forapplication-specificdesignandmanufactureof

metalbelts,metaltapes,andpulleys.

Metalbeltspossessmanyuniqueproperties

thatresultinsuperiorprecision,control,longevity,

andcosteffectiveness.Inmanycasesthey

arepreferabletootherbelttypes(suchasrubberand

fiberglass)andotherpowertransmissionormotion

controlcomponents(suchaslinearactuators,lead

screws,andchains).Frequentlytheyaretheonly

designoption.

Toputtheadvantagesofmetalbeltsystems

towork,BeltTechnologiesoffersextensivein-

housecapabilities:

•EngineeringandDesignAssistance

•MetallurgicalConsulting

•HighEnergyBeamFabrication

•CompleteToolingDesignandManufacture

Ourclimatecontrolledfacilitiesareequippedto

producemetalbelts,drivetapes,andcomplementary

pulleysinprototypeandhighvolume

productionquantities.

Thisdocumentisprovidedforinformationandreference.Itisadesignguide,notadesigntextbook.BeltTechnologiescannotacceptresponsibilityforactualdesignsattemptedusingthismanualasabasis.Readersshouldfeelfreetocontactourengineeringstaffforfurtherinformationandadviceonunusuallyperplexingapplications.

Engineerswhospecifymetalbeltshaveoptionsavailabletothemthattheydonothavewhenusingotherproductsormaterials.Someimportantfeaturesandbenefitsarediscussedbelow.

• HIGH STRENGTH-TO-WEIGHT RATIO: Thisisanadvantageinpracticallyeveryapplicationwherehighstrength,lightweight,orbothareimportant.

• DURABILITY: Metalbeltscanwithstandsustainedexposuretoextremesoftemperature,hostileenvironments,andvacuum.Avarietyofalloysmaybeused,eachwithitsownresistancetochemicals,humidity,andcorrosion.Engineersgenerallyselectabeltmaterialbasedonphysicalproperties,availability,andcost.

• NO LUBRICATION:Unlikethelinksofachain,ametalbeltisasingleelementand,therefore,doesnotgenerateanycomponentfrictionthatrequireslubrication.Thisreducessystemmaintenance,improvesreliability,andkeepsthesystemclean.

• NONSTRETCHABLE: Springsteelswithahighmodulusofelasticitymakemetalbeltsvirtuallynonstretchableascomparedtootherbelttypesandchain.Thismakesthemidealinhighperformanceapplicationsforprecisionpositioning.

• SMOOTH OPERATION:Metalbeltsarefreefromthepulsationofchordalactionoftenseeninotherbelttypesandchain.Thisresultsinprecisetranslationofthecontrolsystemmotionprofile.

• ACCURATE AND REPEATABLE: Metaltimingbeltscanbefabricatedwithapitchaccuracyof±0.0005inchesstationtostation.Thishighdegreeofprecisionisextremelyvaluableindesigningindexing,positioning,orprocessingequipment.

• GOOD THERMAL ANDELECTRICAL CONDUCTIVITY: Metalbeltscantransmitenergyintheformofheat,cold,andelectricity.

• NO STATIC BUILD UP:Metalbeltsdischargestaticelectricity,acrucialcapabilityinthemanufactureofelectroniccomponentssuchasintegratedcircuitsandsurfacemountdevices.

• CLEAN:UnlikeHTDorflatneoprenebelts,metalbeltsdonotgenerateparticulateandareidealforfoodandpharmaceuticalprocessing.

• CLEAN ROOM COMPATIBLE: Metalbeltsdonotrequirelubricantsandwillnotgeneratedustthatwouldintroduceforeignsubstancesintocleanroomenvironments.Additionally,theymaybesterilizedinanautoclave.

• PRECISE CONSTRUCTION:Edgesaresmoothanddimensionsaretightlytoleranced.

CHAPTER1WHY CONSIDER METAL BELTS FOR YOUR APPLICATION 2 3

CONTENTS

3WHY CONSIDER METAL BELTS FOR YOUR APPLICATION

4METAL BELTS, DRIVE TAPES, &APPLICATIONS

5 - 6PULLEYS Designs Materials Tolerances TypesofPulleys

7SURFACE TREATMENTS Teflon NeopreneorUrethane Silicone HardCoatAnodize Options

8 - 14DESIGN CONSIDERATIONS SystemDesignGuidelines Loading Accuracy PositioningAccuracy Repeatability BeltTracking Timing Tensioning SystemFrameStiffness ReverseBends CantileveredShafts MagneticPermeability BeltSag ElevatedTemperatures BeltCreep DesignImposedRestrictions BeltLife

15APPENDIX: METALBELTMATERIALS

METAL BELT DESIGN CHECKLISTInside Rear Cover

BeltTechnologieshasproducedthisDesignGuidetogiveengineersareferencepublicationdetailingfundamentalsof

metalbeltdesignandapplication,withtopicsincluding:

•WhyConsiderMetalBeltsfor YourApplication

•MetalBelts,DriveTapes,and Applications

•Pulleys

•SurfaceTreatments

•DesignConsiderations

•BeltLife

•MetalBeltMaterials(Appendix)

Wehopethisinformationhelpsyouunderstandthemanybenefitsofmetalbeltsandgivesyoutheknowledgeyouneedto

specifymetalbeltswithconfidence.

Becausenotwocustomershaveidenticalneeds,BeltTechnologiesdesignseachproducttouniquespecifications.Therefore,itis

importanttokeepinmindthatthisDesignGuidecannotincludeeverypossibleapplication.Theremaybeexcellentapplicationsfor

metalbelts,perhapsyours,thatarenotdescribed.

WeinviteyoutocontactBeltTechnologiestodiscussyourideaswithamemberofourengineeringstaff.Pleaseusethedesign

checklistontheinsidebackcovertohelpusbetterunderstandyourproject.Ourcompany’slong-termsuccessisinlargemeasuredueto

ourabilitytocontinuallyadvancethescienceofmetalbeltsanddevelopnewsolutions.

INTRODUCTION

CHAPTER3 PULLEYS

Allmetalbeltsanddrivetapestravelaroundpulleys.BeltTechnologiescustomdesignsandmanufacturespulleysthatoptimizetheuniquecharacteristicsofmetalbelts.

DESIGNS: Mostpulleysforbeltsystemstakeoneofthreeforms:roundstock,I-beam,orcappedtube.Anyofthesepulleytypesmaybedesignedwithdrivelugtimingpockets,reliefchannels,conventionaltimingteethorBeltTechnologies’patentedballbearingtimingteeth.

Round Stock Becauseoftheirrelativelylowcost,roundstockpulleysareincorporatedintomostsystemdesigns.Normally,roundstockpulleysareusedinsizesupto6”(152mm)outerdiameterwithwidthsupto4”(102mm).

I-Beam Asdiameterandwidthincrease,rotationalinertiaconsiderationsmayrequireapulleywithanI-beamcrosssection.AnI-beamprofileismachinedintoaroundstockpulleyinafashionthatmaintainsthestructuralintegrityofthepulleywhileremovingsubstantialamountsofweight,thereforereducingtheeffectsofrotationalinertia.Machiningholesintothebeamsectionfurtherreducesweight.

Capped TubeThesepulleysemployendcapsattachedtotheendsoftubestockhavingsufficientwallthicknesstoassureadequatestrength.Thecappedassemblyisthenmachinedtomeetrigidspecificationsforroundnessandconcentricity.Again,itiscrucialtoreduceweightwithoutcompromisingstrength.

MATERIALS: Toaddresstheneedsofyourspecificapplications,pulleyscanbemanufacturedfromawiderangeofmaterials.

Aluminum Aluminumwithhardcoatanodizationisafrequentchoice.Thecombinationisstrong,lightweight,tough,andcosteffective.Extremesoftemperaturecanbealimitingfactor,however,andoutgassingmaybeanissueinvacuumenvironments.

Stainless Steel Incorrosiveoperatingenvironments,stainlesssteelisagoodchoice.Stainlesssteelalsooffersexcellentwearandstrengthcharacteristics.

Therearemanydifferentalloysavailable,eachwithspecialadvantages.

Non-Metals Certainplasticscanofferexcellentwearandstrengthcharacteristics.Insomeapplicationsandinhighvolume,plasticcanbelesscostlythanmetalpulleys.

TOLERANCES: Table1showstypicaltolerancesfortheprimarydesigndimensionsoftimingandfrictiondrivepulleys.Thesetolerancesareapplicabletothethreepulleybodydesigns:roundstock,I-beam,andcappedtube.

BELTS WITH AT TACHMENTS: Perforatedmetalbeltscanalsobefittedwithprecisionmachined,cast,ormoldedattachmentstoprovideunsurpassedpositionalaccuracyandrepeatability,toactasaproducttransportdevice,ortocontrolspecificstagesofamanufacturingprocess.Applicationsinclude: •PrecisionPositionIndexingfor AutomatedAssembly •LeadFrameDrives •TimedTransferLines •PackagingSystems

DRIVE TAPES: Metaldrivetapesaremadeofthesamehighqualitystripasmetalbeltsbut,unlikebelts,drivetapesarenotendless.Drivetapesarefittedwithspecializedendattachmentsorperforations.Theycanperformwithzeroornearzerobacklashinapplicationsincluding:

•CarriagePositioning •Plotters •RobotArms •Read/WriteHeadPositioning •OpticalElementDrives

COMBINATION BELTS/TAPES: Often,combinationsofbeltoptionsarerequiredinordertosatisfysystemobjectives.Attachmentsorpocketsmaybeutilizedtolocatecomponentswhileavacuumdrawnthroughthebelt’sperforationisemployedtosecurethecomponentinplaceduringtransport.Specificedgegeometriesmaybedevelopedtoconformtocomponentprofileswhileattachmentslocatethecomponentsandsatisfytimingrequirements.Applicationsinclude:

•TimedPartsNesting •ComponentOrientationand Conveying •AutomatedDimensional/Electrical Inspection •HighSpeedPackaging •Cutting

METAL BELTS, DRIVE TAPES & APPLICATIONSCHAPTER2

PLAIN BELTS: Plainmetalbeltsarecreatedbyweldingtogethertwoendsofametaltapetoformanendlessbelt.Highenergybeamweldingtechniques,pioneeredinthespaceprogram,formahighintegritybuttweldthatisextremelystrongandsmooth.Sometypicalplainmetalbeltapplicationsinclude:

•Conveying •HeatSealing •Casting •Imaging

PERFORATED BELTS: Perforatedbeltsareplainmetalbeltsmanufacturedwithprecisionperforationswhichcanbeproducedmechanicallyorbyusingnon-impactmethods.Theyareusedinapplicationssuchas:

•Timing •CarriagePositioning •VacuumConveying •WebConveying •Indexing

Table 1. Pulley Tolerance Up to 14” Diameter

TIMING PULLEY FRICTION PULLEY

TapeSupportDiameter(O.D.) ±.0015” ±.002 (.025) (.051)

FaceWidth ±.010” ±.010” (.127) (.127)

BoreDiameter +.001”/-0.0000” +.002”/-0.0000” (+.025/-0.00) (+.051/-0.00)

Concentricity .002” .002” (.025) (.025) TimingLocation ±10arcseconds N/A

4 5

Figure 1. Plain Belts

Figure 2. Perforated Belts

Figure 3. Belts with Attachments

Figure 4. Drive Tapes

Figure 5. Combination Belts

Inches(mm) Inches(mm)

COATING CHIEF OPERATING THICKNESS COLORMATERIAL CHARACTERISTICS TEMPERATURE

TEFLON®TFE Anti-Stick upto600ºF .001” Black upto315ºC (.025) Green

TEFLON®FEP CorrosionResistance upto428ºF .001”to.030” Metallic LowTemperature upto220ºC (.025to.75) Gray downto-328ºF downto-200ºC

TEFLON® FoodContact upto600ºF .001”to.006” MetallicSILVERSTONE Approved upto315ºC (.025to0.15) Gray

TEFLON® HardTeflonfor upto446ºF .001”to.0015” Black550 AbrasionResistant upto230ºC (.025to.038)

SILICONE ExcellentRelease upto392ºF .004” VariousRUBBER HighFriction upto200ºC (0.10)

POLYURETHANE HighFriction upto158ºF .008”to.125” VariousMoldable upto70ºC (.203to3.175)

NEOPRENE Compressibility upto158ºF .016”to.250” BlackRUBBER DieCutPockets upto70ºC (.40to6.4)

Surfacetreatmentsgiveengineerstheopportunitytoalterthenaturalsurfacepropertiesofametalbelt,tape,orpulley.Surfacetreatmentsmaybeappliedtooneorbothsurfacesofabeltortape,ortoapulley.Applicationmethodsincludecoating,plating,laminating,andbonding.

Dependingonthemethodselected,thethicknessofasurfacetreatmentmaybeaslittleas.002”.Thesurfacecanbeuniformor,toprovidepocketsonthebeltsurfacefortransportingsmallcomponents,punchedordiecut.Vacuumholescanbecombinedwithpocketsformorepositiveorientationandretentionofdelicatepartsduringtransport. Forprimarymechanicalandphysicalcharacteristicsofpopularsurfacetreatments,seeTable2.

HARD COAT ANODIZE: Hardcoatanodizationisanelectrochemicalprocessusedtoincreasethehardnessandwearcharacteristicsandcorrosionresistancepropertiesofaluminumpulleys.Theprocessformsalayerofaluminumoxidewhichbecomesanintegralpartofthemetal,bothpenetratingandbuildinguponallpulleysurfaces.Thecoatingthicknessisuniformandmirrorstheprecisionofthepulleyitself.

OPTIONS: Therangeofoptionsforsurfacetreatmentsissolargethatitcannotbefullydocumentedinthisguide.Unusualsurfacetreatmentshaveincludedfluorocarboncompounds,coppercladding,goldplating,andpowdereddiamondbonding.Appropriatespecificationswillbeafunctionofapplicationandtechnology.

TheBeltTechnologiesengineeringstaffwillbepleasedtodiscussissuesrelatedtoyourspecificneeds.

Themidcoat,(actuallyabasecoatusedinotherreinforcedsystems),alsocontainsthespecialreinforcingelement,whilethetopcoatisrichinfluoropolymers,andisdedicatedentirelytoreleaseproperties(non-stickcharacteristic).

URETHANE OR NEOPRENE: Bothurethaneandopenorclosedcellneoprenechangethesurfacecoefficientoffrictionofametalbeltandalsocanactasanestfordelicateparts.Thesematerialsaresecurelybondedtoametalbelt.Priortobonding,theycanbediecutwhenaspecificpocketgeometryisimportant.

SILICONE: Whentheenvironmentisnotsuitableforothercoatings,siliconemaybeagoodoption.Siliconehasuniquepropertiesincludingahighfrictionsurface,releaseproperties,theabilitytowithstandelevatedtemperatures,andextremeflexibility.Bondingsiliconetometalbeltscanbedifficult,butworkablesolutionsdoexist.

CHAPTER4SURFACE TREATMENTSPULLEYS CHAPTER3

T YPES OF PULLEYS: Evenwithallthevariationsinform,material,anddesignfeatures,pulleysgenerallyserveoneoftwopurposes:frictiondrivingortiming.

Timing Timingpulleyshaveeitherteethorpockets,locatedradiallyaroundtheoutsidediameterofthepulleybody.Teethengagetimingholesinthemetalbelt;pocketsengagedrivelugsonthebelt’sinnercircumference.Itshouldbenotedthateveninthesepulleys,thedrivingisaccomplishedbyfrictionalforcesgeneratedbetweentheflatbeltandpulleysurfaces.Teethorpocketsareusedonlyfortiming,notforpowertransmission.

Timingelements,particularlytimingteeth,mustbehard.Hardnessisessentialtoensureminimalwearfromsuccessiveengagementsofbeltandpulley.Asanexample,BeltTechnologies’patentedpulleyuseshardenedballbearingsasteeth.

Whendesigningatwopulleytimingsystem,thedrivepulleyshouldbetimedwhiletheidler,ordrivenpulley,shouldbeafrictiondrivepulleywithreliefchannelsforlugsifnecessary.

NOTE:Bothfrictionandtimingpulleyscanbedesignedasnarrowbodiedrolls.Essentially,thenarrowbodiedrollisapulleywhosewidthisnarrowerthanthebeltthatisrunningonit.Theycanmakebelttrackingeasierandreducetotalpulleyweightaswellascost.Thepulleyfaceistypicallynotlessthan1⁄2thewidthofthebelt.

Friction Drive Frictiondrivepulleysaregenerallyflatfacedwithnotimingelement.

Crowningpulleyfacesisnotgenerallyrecommended.Todiscussthereasonswhy,pleasecontactaBeltTechnologiesengineerwhoisfamiliarwithmetalbeltdynamics.Whencrowningisappropriate,twogeometriesmaybeused:fullradiusandtrapezoidal.Afullradiuscrownislessstressfulonthebelt,butismoredifficulttomachineand,therefore,morecostly.Thetrapezoidalcrownismorecosteffectiveandworkswell,butitshouldbeavoidedinapplicationshavinghighbelttensileloadsduetostressrisersatthecrown’stransitionpointsbetweenangledflats.Blendingthesepointscanbehelpfulbutdoesnoteliminatethehighstressrisers.

6 7

Table 2. Surface Treatment Characteristics

Figure 7. Surface Treatments

TEFLON®: Teflonbecameahouseholdwordasanon-stickcoatingforcookware.Teflonisactuallyavailableinavarietyofformulations,eachhavingdistinctoperatingpropertiesregardingreleasecharacteristic,lubricity,resistancetoabrasion,temperaturerange,andcolor.

ECLIPSE®: FDAcompliantEclipsecoatingsarehighreleaseandextremelywearresistantcoatings.It’suniquethree-coat,highcure,internallyreinforced,non-sticksurfaceoffersabrasionresistanceover10timesthatofTeflon.Itishouseholdchemicalresistantandfeatureshighnon-stickproperties,stainresistanceandperformanceathightemperatures.Itisdifferentfromallothernon-stickcoatingsinthatthebasecoatcontainsacarefullychosenandblendedcombinationofresins.

Figure 6. Pocketed and Ball Bearing Pulleys

Inches(mm)

DESIGN CONSIDERATIONS CHAPTER5

3. Determine bendingstress (Sb) on belt.

Asignificantbendingstressisinducedinametalbeltasitisrepeatedlyflexedoverapulley.ThisstressmustbecalculatedandaddedtotheworkingstressS

w(seeStep4)to

determinethetotalstressStonthebelt.

Theformulaforthebendingstressis:

Where:

E=modulusofelasticityinpsi

t=beltthicknessininches

D=smallestpulleydiameterininches

u=Poisson’sRatio

Thiscalculationrequiresanassumptionofbeltthicknessandpulleydiameter.Pulleydiametermaybetheeasiesttodeterminebecauseofspacelimitationorotherdesignrequirements.Ifthisisso,pickthemaximumpossiblepulleydiameter,thencalculatetheappropriatebeltthicknessbasedonTable3.

4. Determine the totalstress (St) on the belt.

Thetotalstressonthebeltisthesumoftheworkingstress(S

w)andthe

bendingstress(Sb

).S

t=S

w+S

b

Where:

b=beltwidth

t=beltthickness

BeltTechnologiesrecommendsthatSt

notexceedonethirdthebeltmaterialyieldstrength.Forfurtherinformation,pleasecontactaBeltTechnologiesengineer.

BeltTechnologiesrecommendsatensionof1000psi(6.9N/mm2)perbeltstrandfortimingbeltsand2000-5000psi(13.8-34.5N/mm2)perbeltstrandforplainbelts.

Sw

=F

1

bxt

(1-u2)DS

b=

Et

NOTE TO THE DESIGNER: Withinformationfromprevioussections,youmayhavebegunthinkingaboutthedesignforyourmetalbelt.Thissectionbuildsontheprevioussectionsbyincorporatingelementswhichwillhelpyouoptimizesystemperformance.Sinceeverydesignisunique,itisnotpossibletodiscusseverydesignconsideration.Youareinvitedtoreviewyourdesignideas,numbers,andmethodswithaBeltTechnologiesengineer.

SYSTEM DESIGN GUIDELINES: Anysystemwithmetalbeltsisgenerallyenhancedbyfollowingtheseguidelines: •Useasfewpulleysaspossible. •Uselargepulleydiameters. •Usepulleysystemswhichavoid reversebending. •Uselargelength-to-widthratios.

LOADING: Propersystemdesignincludesanexaminationofthevariousloadstransmittedtothebeltinuse.Inadditiontosteadystateoperatingconditions,considerationmustbegiventoanyunusualorintermittentconditionssuchaspotentialjam-uploading,highstartuploads,orindexing.Ingeneral,thebeltshouldbedesignedtoensurethathighloading,shoulditoccur,willnotexceedthebelt’sultimatestrength. Todeterminethestressfactoronanygivenbelt,addtogethertheresultsfromthefollowingfourcolumns.

1. Determine theworking load (Fw) onthe belt.

Theworkingloadcanbedeterminedfromthedrivingmotortorquerating,theloadtobemovedoraccelerated,orbyananalysisofthesystemrequirements.Forasimpletwo-pulleysystemasshowninFigure8,theworkingloadonthebelt(Fw)isF

w=F

1–F

2,where:

D1andD

2=pulleydiameters

t1andt

2=torqueactionon

respectivepulleys

F1andF

2=forceonbeltateach

pulleyinNewtons

Fw

isrelatedtothetorquebythe equation:

Andtopowerby:

Where:V=velocityinft/min

Andtoaccelerationby:

Where:

L=loadonbeltinlbs.g=32.2ft/sec2

a=accelerationofloadinft/sec2

Fw

=ma=(L/g)xa

Fw

= 33000xHPV

2. Determine thehighest load (F1) onthe belt.

SinceFw=F1–F2asshowninthetwopulleyexampleinStep1,F1isthegreatestforceonthebelt.Todesignforthestressconditionresultingfromthisforce,weneedtocalculateitsvalue. Forafrictiondrivesystemtooperatewithoutslippage,thetwoforces,F1andF2arerelatedbytheformula:

F1-F

c

F2-F

c

Where: e=2.71828 m=coefficientoffriction betweenbeltandpulley u=angleofwrapinradians ofbeltonpulley F

c=centrifugalforceactingonbelt

Forametalbeltwithastandardfinish(suchas0.4micro-meter)operatingonamachinedmetalpulley,experiencehasshownthevalueofmrangesbetween0.25and0.45.

OneadvantageofathinmetalbeltisthatFcisusuallynegligiblysmallandcanbedisregarded.Thus,inmostcases,theformulacanbesimplifiedto:

SubstitutingforF2andsolvingforF1,thisbecomes:

F1=

Fw

mue-1

mue

F1 mu=e

F2

mue=

8 9

=t

1t

2F

w=

1/2D1

1/2D2

PULLEY DIAMETER BELT LIFETO BELT THICKNESS EXPECTANCYRATIO

625:1 1,000,000 cyclesor greater 400:1 500,000

333:1 165,000

200:1 85,000

Relationshipsarebasedonatwopulleyfrictiondrivesystem.

TYPICAL SIZES ANDSPECIFICATIONS

Metalbeltstypicallyrangeinthicknessfrom0.002”(0.51mm)to0.032+”(0.8mm)resultinginpulleysizesof2”(50mm)to10”(254mm)indiameter.Atypicalmetalbeltwithathicknessof0.005”(0.127mm)witha1,000,000cyclelifewouldrequirepulleyswith3.125”(79.4mm)diameter.Sizerangesvarybyapplicationandloadconsiderations,sopleasetalktoaBeltTechnologiessalesengineerforhelpwithyourdesignideas.

Table 3. Belt Life

Figure 8. Loading Stress

CHAPTER5DESIGN CONSIDERATIONS

Atthispointitisnecessarytoselectvariousparametersandworkbackthroughthecalculationstofindacombinationthatwillsatisfydesignrequirements.Obviously,usingawiderbeltreducesworkingstresswithoutchangingbendingstress.Largerpulleydiametersreducebendingstress,orallowuseofathickerbeltwhichinturnreducesworkingstress.

DESIGN CONSIDERATIONS CHAPTER5 CHAPTER5DESIGN CONSIDERATIONS

BELT TRACKING: Giventhatametalbeltwillnotsignificantlystretchundertension,trackingametalbeltcanbemoredifficultthantrackingotherbelttypes.Ametalbeltwillnotstretchtocompensatefor:

•Lackofsystemsquarenessoralignment •Uncontrolledpulleyshaftdeflection •Differentialloading •Beltcamber

Amongthese,theDesignEngineerisprobablyleastfamiliarwithbeltcamber.Camber,oredgebow,isthedeviationofabeltedgefromastraightline.Everybelthassomecamber.Metalbeltcamberistypicallyaslittleas.050”(1.27mm)in8’(2.44mm).Whenplacedinasquaredtwopulleysystemandtensioned,oneedgeofthebeltwillbetensionedmorethantheotherbecauseithasashorteredgecircumference.Thiswillcausethebelttotrackawayfromthetightedgeoftensiontowardsthelooseedgewhenthebeltisrotated.

Three basic techniques are used to track belts on systems using friction pulleys, timing pulleys, or both: • Pulley axis adjustment • Crowning friction drive pulley • Forced tracking

POSITIONING ACCURACY: Positioningaccuracyisdirectlyrelatedtothebeltpitchtolerance,typically±0.0005”(0.013mm)forametaltimingbelt.Pitchaccumulationcanbemanagedwithcustomizedtooling,shownasPlinFigure9,ornegatively,shownasPsinthesamegraphic.PleaseconsultaBeltTechnologiesengineeronyourrequirement.

REPEATABILIT Y: Repeatabilityistheabilityofasinglepitch,onsuccessiverotationsofthebelt,toreturntoahomepositionwithinaspecifiedtolerance.

Becausemetalbeltsdonotstretch,repeatabilityistypicallyintherangeof0.002”(0.051mm)to0.005”(0.127mm).

Forplainorperforatedbelts,beltswithattachments,ordrivetapes,precisemotioncanbecalculatedwithahighdegreeofaccuracy.ContactaBeltTechnologiessalesengineerforassistanceindeterminingthespecificationsforyoursystem.

Figure 11. Camber

Figure 12. Tracking

Figure 9. Positioning Accuracy

Figure 10. Repeatability

BELT LENGTH ACCURACY: Oneofthemostimportantadvantagesofametalbeltisitsoverallaccuracy.Perforatedbeltsorbeltswithattachmentscanbefabricatedwithpitchaccuraciesof±0.0005”.Plainbeltsanddrivetapescanalsobefabricatedtoahighdegreeofaccuracy.

BELT LENGTH: Tocalculatealengthforametalbelt,usetheformulabelow.Itisimportanttoknowtheidealdesignenvelopeofyoursystembeforecalculatingbeltlength.Largerpulleydiametersusuallyprovideoptimumbeltlife,andpulleydiameterscanbeusedtoestimatebeltthickness.SeeTable3forlifeexpectancy.Onceamaximumpulleydiameterisknown,divideitbythepulleydiametertobeltthicknessrationfromTable3foroptimumbeltlifeinyourapplication.Typicalbeltthicknessrangefrom0.002”[0.05mm]to0.032”[0.813mm],andtypicalpulleydiametersrangefrom2”up.

L=(2xC)+(D+t)p

Where:

L=Beltlength

C=Centerdistancebetweentwopulleys

D=Pulleydiameter

t=Beltthickness

p=3.14159

Thisdefinestheappropriatelengthformetalbeltsystemsincorporatingtwopulleyofidenticaldiameter.Forsystemswithmultiplepulleysorpulleysofdifferentdiameters,pleasecontactaBeltTechnologiessalesengineer.Contactinformationislistedinsidethebackcover.

Theprimaryobjectiveofanyrackingtechniqueistocounteracttheinfluenceofaccumulativenegativetrackingstressesandforces(previouslydefinedassystemsquareness,uncontrolledshaftdeflection,differentialloading,andbeltcamber)withcontrolledstressesandforces,thustuningthebelttorunonthesystem.

ADJUSTABLE PULLEY: BeltTechnologieshaspatentedanIndependentlySteerablePulley(ISP)toaidintrackingofallflatbelts,includingmetalbelts.Inautomatedsystems,theISPcanbefittedwithsensorsandaservomotorpackagetodeliverhands-freeautomatedtrackingofmetalbelts.ContactyourBeltTechnologiessalesengineerforasupplementalengineeringpaperontheIndependentlySteerablePulleyandhowitmightbenefityourapplication.

10 11

BELT STRETCH: Metalbeltsareunique,astheywillnotstretchinnormaloperation,afterachievinganormalpreloadtension.Tocalculatepreloadstretchforaplainbelt,usethefollowingequation.Forperforatedbelts,pleasecontactaBeltTechnologiessalesengineer.

DL=PL/AE

Where:

DL=Stretchininches

P=Tensionloadinpounds

L=Initialbeltlengthininches

A=Beltcross-sectionareaininches E=Young’sModulus (Seematerialstableonpage15)

ZERO BACKLASH: Zeroandnear-zerobacklashpositioningsystemscanbeachievedthroughtheuseofmetalbelts.Runinpairsorwithinventivedesignideas,thesedrivescanbeusedanywheretighttolerancesexistforbackandforthplacementaccuracy.Theillustrationsbelowoffertwotypicalzero-backlashdrivesuggestions.

Zero Backlash Drives

Approximates360º of PulleyRotation

Idler

Master

Slave

340º Pulley Rotation

Output

SYSTEM FRAME STIFFNESS: Astiffsystemframeisnecessarytoallowfineadjustmentsfortimingandbelttracking.Ifthereisuncontrolledflexinthesystemframe,thesystemwillbowwhenthebeltistensioned.Offsettingoneforce(systemflex)withanotherforce(axisadjustment)doesnotprovideacontrolledsystemandcanresultintrackingproblems.Tomakesurethatanyaxisadjustmentsarecontrollable,itisimportanttodesignsufficientstiffnessintothesystem.

REVERSE BENDS: Thebestsystemdesignutilizestwopulleys.Addingreversebendstothesystemaddsbendingstress,compromisingbeltlife.Becauseeachpulleycanhaveasteeringinfluence,trackingproblemscanresult.

CANTILEVERED SHAFTS: Itispreferableforpulleyshaftstohavesolidterminationpointsateachend.Cantileveredshaftscancreateapivot.Whentensionisintroduced,theshaftmaydeflectandcancausetrackingproblems.Ifcantileveredshaftsarenecessary,theirstiffnessmustbeensuredthroughtheframedesignandshaftrigidity.

MAGNETIC PERMEABILIT Y: Magneticpermeabilityiscommonlydefinedasameasureoftheabilityofasubstancetocarrymagnetismascomparedtoair,whichhasapermeabilityof1.

Threehundredseriesstainlesssteelsareconsideredtobenonmagnetic,butthecoldworkingusedtoproducetheirspringtemperandhightensilestrengthresultsinanincreaseinmagneticpermeability.Therefore,a301fullhardhasagreatermagneticpermeabilitythan301halfhard.Generally,316stainlesshasthelowestmagneticpermeabilitybutisdifficulttoobtaininthefullhardcondition.

RefertotheAppendixforratedmagneticpermeabilitypropertiesofcommonmetalbeltalloys.

BELT SAG: Whenthespanbetweenpulleysislong,thebeltcansag.Evenonthetightsideoftensionthereissomesag.Toensurepropertensionandpreventsagging,dragtheworkingsurfaceofthebeltacrossastationarysupportsurfacesuchasultra-highmolecularweightmaterials(UHMW).

TENSIONING: Frictiondrivesystemscanoperatewithtensionsaslooseasabicyclechainandastightasaguitarstring.Belttensionisextremelyimportantintimingsystemsandshouldbekeptaslowaspossible.Ingeneral,lowbelttensionimprovesbeltlifeandreduceswearonothersystemcomponents. Belttensionshouldnotbeincreasedtoreducesagbetweenpulleys(seeBELTSAG,thispage).Overtensionedbeltsmaydevelopacrossbow,muchlikethatonatapemeasure.Inadditiontocrossbow,overtensioningwillcauseunevenmotion,reducerepeatability,andreducebeltlife.

Belttensionshouldbedeterminedbyoperatingthesystemandselectingthelowestpossibleworkabletension.Thiscanbemaintainedthroughtheuseofaircylinders,springs,orjackscrews.

BeltTechnologiesrecommends1000to5000psi(6.9to34.5N/mm2)forfrictionsystemsand1000psi(6.9N/mm2)fortimingsystems.

Timing: Timingpulleysformetalbeltsareeithertoothedorpocketed,eachengagingrespectivebeltperforationsordrivelugs.

Careshouldalwaysbetakeninthedesignoftimingpulleystoensurethatalltimingelementshavesphericalorinvoluteradii.Thisensuressmoothengagementanddisengagementofthebeltandpulley.Toavoidproblemsduetoaccumulatedtolerances,thediameterdifferencebetweendrivinganddrivencomponentstypicallyshouldbeatleast±0.005”(0.127mm)to±0.007”(0.178mm).Zeroornearzerobacklashapplicationsareaspecialcase.

Whenmanufacturingatoothedpulley,eachtimingtoothisinsertedintoaholemachinedinthepulleybody.Greatcaremustbegiventotheradiallocationofeachtoothtoensureoverallpitchaccuracy.

Whiledesigningatimingpulley,itiscriticalthatthepitchdiameterbeattheneutralaxisofthebelt(onehalfthebeltthicknessforathinflatbelt),notatthebase.Sincemetalbeltsaregenerallythin,thereisatemptationtoneglecttheirthicknessincalculatingthepulleytapesupportdiameter.Failuretoincludethebeltthicknessinthesecalculationsresultsinmismatchingoftimingelements.

Thetapesupportdiametercanbedeterminedbytheformula:

Where: N=numberofpitchlengthsor teethonapulley P=perforationpitch t=beltthickness

D= NPp –t

Pulley Axis Adjustment: AdjustingthepulleyaxisinametalbeltsystemasshowninFigure13isthemosteffectivewayoftrackingametalbelt.Beltedgetensionsarechangedinacontrolledmanner,thussteeringthebelt.Thetechniqueisequallyapplicabletobothflatfacedandcrownedpulleys.

Ideally,boththedriveandidlerpulleyswouldhaveadjustableaxes.Inreality,however,onlytheidlerisadjusted.Thedrivepulleyisusuallydifficulttoadjustduetoitsinterfacewithmotorsorotherpowertransmissiondevices.

Crowning Friction Drive Pulleys Whencrownedfrictiondrivepulleysmustbeused,itisinconjunctionwith—notinplaceof—axisadjustment.Thisisbecausecrownedpulleyswillnotself-centerametalbelt.Crownedpulleysworkbestonthinbeltsasthebeltwebmustconformtothecrownedfaceofthepulley.Whileincreasedtensioncanbeusedtoachievebelttopulleyfaceconformity,tensioncannotbesohighastocausepermanentbeltdeformation.Thebestfacegeometryforacrownedpulleyisafullradius,withthecrowningbeingnomorethanthebeltthickness.

Forced Tracking Incaseswheresimpleaxisadjustmentcannotcompletelyeliminateimpropertracking,forcedtrackingmethodssuchascamfollowersorglass-filledTeflon®flangesmaybenecessaryandacceptable.Systemdesignrelationshipsmayneedtochange,suchasusingathickerbeltthanmightbeotherwiserecommended,sinceforcedtrackingtechniquescancontributetoadecreaseinexpectedbeltlife.

AnalternativeforcedtrackingtechniqueforwiderbeltsemploysaVbeltbondedtotheinnercircumferenceofthemetalbelt.Thistwoelementbelt,whichBeltTechnologiescallsMetrak©,distributestrackingstressesontheVbeltratherthanonthemetalbelt,thusmaximizingbeltlifeinaforcedtrackingsystem(Figure14).

Timingteeth,discussedinthenextsection,arefortimingonlyandshouldnotbeusedasatrackingmechanism.

DESIGN CONSIDERATIONS CHAPTER5 CHAPTER5DESIGN CONSIDERATIONS

Figure 14. Forced Tracking

Figure 13. Pulley Axis Adjustment

12 13

Figure 15. Timing Pulleys

DESIGN CONSIDERATIONS CHAPTER5 APPENDIXMETAL BELT MATERIALS

APPENDIX: METALBELT MATERIALS Particularlydemandingapplications,suchasthoseinvolvinghightemperatures,extremelycorrosiveenvironments,orunusualelectricalormagneticrequirementsmayprecludetheuseofcertainalloysformetalbeltsanddrivetapes.ThefollowingMaterialsTablesummarizesimportantselectioncriteria.

Sohowlongcanyouexpectyourmetalbelttolast?Whilenottryingtoavoidwhatisafairquestion,thebestansweris:itdepends.

Itdependsonfactorssuchassystemdesign,materialstrength,environment,stress,tension,surfacetreatments,attachments,etc.Thesamefactorsthathaveanaffectonthedesignofyoursystemandyourmetalbeltsalsoeffectbeltlife.

Withtheprecedinginmind,itisindeedreasonabletosaythatmetalbeltshavethepotentialtosignificantlyoutliveotherbelttypesandchain.Theyalsohavethepotentialtobemoreaccurateandrepeatable,lighterandfaster,andmorecosteffective.

Adiscussionwithamemberofourengineeringstaffcanhelpyouestimatethebeltlifeyoucanexpectinyourspecificapplication.

•Metalbeltsdooperateonpulleyswithdiametersassmallas.25”/6.35mm,butbeltlifeisreduced.

•Beltsoperateinovensupto1,094ºF/590°C,butbecausemuchofthebelt’sstrengthcomesfromcoldworkingorspecificheattreatments,suchhightemperaturesreducebeltstrength.RefertoTable6.

•Doctorbladescaninduceacuppingeffectacrossthebeltwidth.ProperlydesigneddoctorbladessuchasthosemadeofUHMWcanminimizethenegativeeffects.

BELT LIFE: Beltlifemeansdifferentthingstodifferentpeopleanddifferentprocesses.Beltlifeof10,000revolutionsmaybeexcellentforoneapplication;anotherbeltmaymake10,000revolutionseachhour.

Withintheeffectivearc,thebeltandpulleysurfacesareinslidingcontactandthesurfacespeedofthepulleyisgreaterthanthatofthebelt.Thisphenomenoniscausedbydimensionalchangesinthebeltduetothedifferentialforcesactingonitasitpassesaroundthepulley.Asslidingcontactoccurs,frictionalforcesaredevelopedtomatchchangesinbelttensionandpoweristransmitted.

Becausethetensilememberofametalbeltisthemetalbeltwithitsassociatedhighmodulusofelasticity,creepinametalbeltismuchlessthanthatforbeltsmadeofmostothermaterials.

Ifnotcontrolled,however,creepinafrictiondrivemetalbeltresultsinalossofrepeatability.Fortunately,creepinmetalbeltsiseasilycontrolled.

Timingteethorlugsarethemostcommonwaytocombatcreep.Thenumberoftiminglocationsshouldbethesmallestnumberpossiblewhichpreventcreepfromoccurring.Inmanysystemsitispossibletohaveasfewassixtoeighttiminglocationsinthecircumferenceofthepulley.

BELT CREEP: BeltCreepisaphenomenonassociatedwithpowertransmissionbetweenadrivepulleyandthetensilememberofthebelt.Duetocreepinafrictiondrivesystem,thepulleyactuallymovesslightlyfasterthanthebelt.

ConsiderFigure16.The180°ofwrapbetweendrivepulleyandbeltisdividedintotwoarcs:

•Theidlearc(wherenopoweris transmitted)

•Theeffectivearc,alsocalledtheangleof creep(wherepowertransmissionoccurs)

Withintheidlearc,thebeltandpulleysurfacesareinstaticcontactandnopoweristransmitted.Thebeltrunsontothepulleywithtight-sidetensionT1andspeedV1whichmatchesthesurfacespeedV1ofthedrivepulley.Bothspeedandtensionremainconstantascontactcontinuesthroughtheidlearc.

Figure 16. Creep Theory ABistheidlearc.BCistheeffectivearc.

ELEVATED TEMPERATURES: Ifametalbeltwillbeexposedtoelevatedtemperatures,itiscrucialthatthematerialselectedforthebelt,aswellasanyattachmentsorsurfacetreatments,beabletowithstandthetemperature.Considerationalsomustbegiventotheexpansionandcontractionofthematerialsastemperaturefluctuates.Changesduetotemperaturewillimpacttiming,tracking,tension,flatness,andotherfactors.

Table4liststheprincipalalloysusedinspecifictemperaturerangesaswellascorrespondingthermalexpansioncoefficientsandyieldstrengths.Table5illustrateshowphysicalpropertiesof17-7CH-900changeasafunctionoftemperature.

Table 5. Physical Properties vs. Temperature Changes (17-7 CH-900)

14 15

ALLOY TEMPERATURE MEAN COEFFICIENT MEAN YIELD RANGE ºF OF THERMAL STRENGTH OF (ºC) EXPANSION TEMPERATURE 10-6IN/IN/ºF RANGE IN 1000 PSI (cm/cm/ºCx10-6) (N/mm2)

301/302 68ºto400º 9.8 160to135FullHard (20ºto205º) (17.6) (1100to930) 17-7CH-900 400ºto800º 6.6 220to170 (205ºto425º) (11.9) (1500o1170)

Inconel®718 800ºto1,000º 8.4 157to155Solution (425to540) (15.1) (1080to1070)AnnealedandHeatTreated

Table 4. Elevated Temperature Characteristics of Principal Alloys

1002003004005006007008009001000ºF

260

240

220

200

180

240

220

200

180

160

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THERMAL TENSILE THERMAL EXPANSION YIELD MODULUS CONDUCTIVITY COEFFICIENT STRENGTH TENSILE OF (32° TO 212° F) (32° TO 212° F) (0.2% OFFSET ) STRENGTH ELONGATION ELASTICITY POISSON’S DENSITY BTU/FT2/HR/ºF/IN cm/cm/°C x 10-6 1000 PSI 1000 PSI IN 51mm IN 106 PSI RATIO #/IN3 cm/cm/ºC x10-6 (0º to 100º C) MAGNETIC CORROSIONALLOY (N/mm2) (N/mm2) % HARDNESS (in 105 n/mm2) (g/cm3) cal/cm2/sec/ºC/cm (0º to 100º C) in/in/º F PERMEABILITY RESISTANCE

301FULLHARD 160 180 5-15 RC40-45 28 .285 0.29 113 9.4 L-M M (1100) (1240) (1.93) (7.9) (.039) 16.9

301HIGHYIELD 260 280 1 N/A 26 .285 0.29 113 9.4 M-H M (1790) (1930) (1.79) (7.9) (.039) 16.9

302FULLHARD 160 180 1-5 RC40-45 26 .285 0.29 113 9.6 L-M M-H (1100) (1240) (1.93) (7.9) (.039) 17.3

304FULLHARD 160 180 1-5 RC40-45 26 .285 0.29 113 9.6 L-M M-H (1100) (1240) (1.93) (7.9) (.039) 17.3

316FULLHARD 175 190 1-2 RC35-45 28 .285 0.28 97 8.9 L H (1200) (1310) (1.93) (7.9) (.036) 16.0

716FULLHARD 210 260 5-10 RC52 32 .285 0.28 170 5.9 H L-M (1450) (1790) (2.20) (7.9) (.059) 10.6

17-7CONDITIONC185 215 5 RC43 28 .305 0.28 114 8.5 M-H M-H (1275) (1480) (1.93) (7.8) (.037) 15.317-7CH-900 240 250 2 RC49 29 .305 0.28 114 6.1 M-H M-H (1655) (1720) (2.00) (7.8) (.037) 10.9

INCONEL®718 175 210 17 RC41 29 .284 0.29 86 6.6 L HCARBONSTEEL (1200) (1450) (2.00) (7.9) (.030) 11.9

CARBONSTEEL 240 260 7-10 RC50-55 30 .287 0.29 360 5.8 H LSAE1095 (1650) (1790) (2.07) (7.9) (.124) 10.5

TITANIUM 150 165 11 RC35 15 .300 0.17 56 5.5 L H15V-3CR-3AI-3SN (1030) (1140) (1.03) (4.7) (.019) 9.7

INVAR36 50 75 30 RB80 20 .317 0.30 120 2.1 L M-H (340) (520) (1.38) (7.9) 1.2

Table 6. Some of the most popular metal belt alloys and their room temperature engineering properties

A

B

C

T1

T2

V1

V2

DESIGN IMPOSEDRESTRICTIONS: Applicationrestrictionssuchasspacelimitations,orunusualchemical,thermal,electrical,orsystemrequirements,maydemanddesigntrade-offs.Considertheseexamples:

Wehopethisintroductiontometalbelttechnologyprovidedyouwithanunderstandingofimportantdesignconsiderationsandhelpedyouqualifyyourapplication.Ouruniquemetalbelttechnologyhasresultedinawiderangeofsolutionsforalongandgrowinglistofsatisfiedcustomers.Wewillprovidealistofthesecompaniesatyourrequest.

16

Shouldyourequirefurtherassistanceanddesignreview,pleasecontactaBeltTechnologiesengineerbytelephone,faxore-mail.

Pleasefaxthedesignchecklistfromthefacingpagewithyourapplicationinformation.ThankyouforyourinterestinBeltTechnologies.

Completethedesigncheckliston-lineat:www.belttechnologies.com/englishguiderequest.htm

STEEL BELT DESIGN CHECKLISTUse additional sheets for further information, if appropriate

In the U.K., Europe & the Pacific Rim:BeltTechnologiesEurope4thFloor,PennineHouseWashingtonTyneandWearNE371LYUnitedKingdomTel:+44(0)191-415-3010Fax:+44(0)191-415-0333E-Mail:sales@bte.co.ukwww.belttechnologies.co.uk

In the Americas:

BeltTechnologies,Inc.CorporateHeadquarters11BowlesRoadAgawam,MA01001USATel:(413)786-9922Fax:(413)789-2786E-Mail:engineer@belttechnologies.comwww.belttechnologies.com

FROM: ________________________________________________________________ (Name)

________________________________________________________________(Company)

________________________________________________________________(Address)

________________________________________________________________ ________________________________________________________________(Tel/Fax)

1: Use: CONVEY INDEX TIME POSITION POWERTRANSMISSION

2. Size Considerations:

BeltWidth____________________ PulleyDiameter____________________

NumberofPulleys______________ PulleyCenters______________________

3. Loading: BeltSpeed____________________ MaxDriveTorque___________________

Acceleration__________________ StaticLoad________________________

4. Desired Belt Characteristics:

Strength Precision Cleanliness CorrosionResistance ThermalConductance

HighTemperature________________ ºC ºF

5. Quantities: NumberofBeltstobequoted______________NumberofPulleystobequoted___________

6. Please Include a diagram of your system.

In the U.K. , Europe & the Pacific Rim:BeltTechnologiesEurope4thFloor•PennineHouseWashingtonTyneandWearNE371LYUnitedKingdomTel:+44(0)191-415-3010Fax:+44(0)191-415-0333E-Mail:sales@bte.co.ukwww.belttechnologies.co.uk

In the Americas:

BeltTechnologies,Inc.CorporateHeadquarters11BowlesRoadAgawam,MA01001USATel:(413)786-9922Fax:(413)789-2786E-Mail:engineer@belttechnologies.comwww.belttechnologies.com

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