the best springs you haven’t tried yet

ROTORCLIPCOMPANY,INC.·187DavidsonAvenue·Somerset·NJ08873·USA

Evenifyouroutinelyusespringelementsinyourdesigns,chancesareyouhaven’ttriedwavespringsyet.You’renotalone.Mostengineershaveplentyofexperiencewithtraditionalcoilanddiscsprings,whilesingle-andmulti-turnwavespringsremainsomethingofamystery.Yetwavesprings,particularly

thosemadefromflatwire,shouldbebetterknowngiventheircompellingengineeringadvantages.

Chiefamongtheseadvantagesisanexcellentforce-to-workheightratio.Well-designedwavespringscan

producethesameorevengreaterforcesascoilspringswhoseworkheightsareuptotwiceaslarge.

Goodwavespringsalsoproduceamoreconsistentforceacrossawiderangeofdeflections.Theirdeflectioncurveshaveawider,flatterlinearforceregionthaneithercoilordiscsprings.Wavespringstransmitthosespringforcesonlyintheintendedaxialdirection.Theydon’tsufferfromthetorsionalloadingandtwistingthatcanmakeconventionalcoilspringslesseffective.

Inadditiontotheirfavorableforcecharacteristics,wavespringshaveassemblyadvantages.Manywavespringshavetheabilitytoself-locateinboredholesoronshafts.Andasinglemulti-turnwavespringcanfrequentlyreplaceanentirestackofdiscsprings,eliminatinganassemblystep.

Asdrop-inreplacementsfortraditionalspringelements,wavespringscanimprovetheperformanceofspring-loadedcomponents.Buttomaximizetheengineeringpotentialofwavesprings,youshoulddesignaroundtheiruniquequalities,whichinclude:

THEBESTSPRINGSYOUHAVEN’TTRIEDYETFlatwirewavespringsofferthebestbalanceofsizeandspringforce.Here’swhatyouneedtoknowtodesignwiththesehigh-performancealternativestotraditionalsprings.

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SINGLE-TURN

WAVE SPRING.Applicationsincludebearingpreload,connectorandfluidpowersealsaswellasnoiseandvibrationattenuation.Theytypicallytaketheplaceofstampedwavewashers.

MULTI-TURN

WAVE SPRING.Applicationsincludemechanicalsealsaswellasavarietyofpowertransmissionandfluidpowersystemsusedinautomotive,medicalandindustrialequipment.Thesetypicallyreplacecoiledspringsorstacksofdiscsprings.

Coil springs require as much as twice the working height of a wave spring.

ROTOR CLIP COMPANY, INC.·www.rotorclip.com·Phone:1-732-469-7333·Email:info@rotorclip.com

• Axial Space Savings.Themostimmediatelynoticeablequalityofwavespringsisjusthowmuchaxialspacetheycansave.Instaticapplications,awavespringwilltypicallyneedjust50%oftheworkheightofcoilspringtodeliveranequivalentforce.Indynamicapplications,theworkheightadvantageistypicallyabout30%,lessthanstaticapplicationsbutstillsubstantial.Thereasonforthedifferencecomesdowntothefundamentalsofmulti-turnwavespringdesign.Tominimizethebendingstressesindynamicapplications,thewavespringwilltypicallyrequiremoreturnsthaninastaticapplication.Andmoreturnsresultinadditionalworkheight.

• Consistent Spring Force.Springelementstypicallyexhibitbothlinearandnon-linearforcebehaviors,dependingontheirdeflection.Thislinearbehaviorcanbegraphicallyshownonthespring’sload-deflectioncurve.Ingeneral,thebroaderandflatterlinearregionofthecurve,theeasieritistohitspecificspringforcerequirements.Wavespringshaveaclearadvantageinthisdepartment.Theytypicallyhavealinearforcebetween30and70%deflections.Bothcoilanddiscspringhavemuchnarrowerlinearforceregions(SeeFigure1).Predictablespringforcescanbeabigbenefitinmanyapplications.Mechanicalseals,forexample,successfullyusewavespringstopreloadthesealingsurfaces.Havingapredictablespringforceallowsthesealdesignertostrikethebalancebetweenexcesswearfromtoohighapreloadandleaksfromtoolowapreload.

DESIGN TIP: Alwaysspecify

theloadatworkheight!

• Dimensional Tolerances Improvements.Asidebenefitofawavespring’spredictableforcesinvolvesdimensionaltolerancesforthecavitiesandshaftsthatholdspringelements.Thesetolerancesareoftendrivenbytheneedtoaccommodatethespring’sforce-to-workheightrequirements.Byspecifyingwavespringswhoseforceisrelativelyconsistentacrossarangeofdeflections,it’softenpossibletoloosendimensionaltolerancesonspringcavitiesandshafts.Thisabilityrepresentsamajor,butoftenoverlooked,costfactorinfavorofwavesprings.

• No Torsional Loads.Wheneveryoucompressacoilspringtoitsworkheight,loadsarenotjustintheaxisofcompressionbutalsotorsional.Thesetorsionalloadscancausethepre-loadedcomponenttorotateinuse,potentiallyresultinginexcesswear.Torsionalloadscanalsodecreasethespring’sworkingload.Manyapplications,includingseals,cansufferfromthisrotationalwearproblem.Wavespringsdon’thavethisissue.Theirwaveformscanonlycompressaxially,insomecaseschangingtheirdiameterslightly.

• Increased Travel.Whencomparedtoatraditionaldiscspring,multi-turnwavespringsofferfarmoretravel.Asinglemulti-turnwavespringcaneasilyreplacetheassembliestheusemultiplediscspringstoachievethenecessarytravel.Mostapplicationsrequirerelativelyshorttraveldistances,usuallylessthan1mm.Buttogiveyouanideaofwhat’spossible,we’veengineeredmulti-turnwavespringsthatofferupto50-mmoftravel.Replacingastackeddiscspringassemblywithonewavespringcanresultinbothcostandqualitybenefits.Notonlywillthesinglespringcostlesstoinstallthanthestackeddiscsprings,butitalsoreducesthechancethatthethewrongnumberofdiscspringswillmakeitintoafinishedassembly.

• Dial In Required Stiffness.Wavespringstiffnessisdeterminedbythicknessandtypeofspringmaterialaswellasbythenumberofwavesperturnofspring.Youcaneasilydialinarequiredstiffnessbyoptimizingthenumberofwavesperturnusingwell-knowndesign

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Mechanical seal application

ROTOR CLIP COMPANY, INC.·www.rotorclip.com·Phone:1-732-469-7333·Email:info@rotorclip.com

Comparison Load-Deflection-Curves

Deflection, s[mm]

Load

, F[N

]

Disc Spring

Coil Spring

Multiple Turn Wave Spring

formulas(seeSidebar).Increasingthenumberofwavesperturndoeshaveaninfluenceonfreeheightandcompresseddiameterofthewavespring.Moreturnsalsoincreasesthehysteresissinceeachwaveshassomefrictionassociatedwithit.Alltheseeffectsareeasilyoffset.Youcanaccountforfree-heightanddiametereffectsduringdesign.Andhysteresiscanbeeliminatedbypresettingthewavespring—thatis,compressingtoitsworkheightoverseveralcycles.

• Fast Customization.Unlikestampedproduces,whichrequiretooling,wavespringscanbecustomizedonthefly—bychangingtheparametersofthecoilingequipment.Thisabilityallowsyoutospecifycustomwavespringswithoutworryingaboutcostordelaysassociatedwithcustomtooling.Thiscapabilityisyetanothercostfactorweighinginfavorofwavesprings.

WAVE SPRINGS ARE NOT CREATED EQUAL

Alltheadvantageswe’velaidoutforwavespringsassumethatthespringsaremadefromhigh-qualitymaterials,manufacturedinacontrolledenvironmentandproperlydesignedfortheapplicationathand.AtRotorClip,forexample,weproducethewavespringsinaverticallyintegratedmanufacturingenvironment—inwhichwerollourownflatwireandformitinourownmachines.Verticalintegrationallowstoadjusttobatchtobatchvariationsinourrawmaterials,whichincludeavarietyofsteelsandotheralloys.Italsoallowsustokeeptightstatisticalcontrolonalltherollingandcoilingprocesses.

Whenitcomestowavesprings,theimportanceofthismanufacturingexpertisecan’tbeunderstated.Evensmallvariationsinwirethickness,wavegeometryormetallurgycanallhavedrasticeffectsonawavespring’sperformanceinthefield.Forcecharacteristicsinparticularcansufferifthespringhasn’tbeenmadeproperly.Soitpaystospecifyhigh-qualitysprings.Ifyoudo,you’llbeabletotakeadvantageofallthedesignbenefitswavesspringscanoffer.

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Loaded wave spring

Bearing preload

Load-Deflection Curves Compared

Piloted by Shaft Piloted by Bore

ROTOR CLIP COMPANY, INC.·www.rotorclip.com·Phone:1-732-469-7333·Email:info@rotorclip.com

DIAMETER EXPANSIONThediameterofaflatwirewavespringincreaseswhencompressedintheaxialdirection.Thefollowingformulaisanexampleofitsmaximumachievableoutsidediameterwhencompressedattheblocklevel.

R=WaveRadius*1[mm] Z=NumberofwavesperTurn

SW=RadialWidthofMaterial[mm] θ=Angle,degrees*2[Grad]

X=1/2WaveFrequency*3 Y=MeanFreeHeight*4[mm]

H=FreeHeight[mm] T=ThicknessofMaterial[mm]

*1WaveRadiusR=[(4Y2+X2):8Y]

*2AngleÐ=[ArcSin(X:2R)]

*31/2WaveFrequencyX=[π·Dm:2Z]

*4MeanFreeHeightY=[(H-T):2]

Max.outsidediameterat100%deflection=0.02222·R·Z·θ+SW

FATIGUE STRESS RATIOCalculatingtheratiobetweenWH12andWH2candeterminetherequirednumberofloadcycles.Theresultsarethencomparedtotheguidelinetablevaluestofigureoutfinalnumber.

δ=FatigueStressRatio σ=Calculatedoperatingstressatlowerworkheight[N/mm2]

σ=Materialtensilestrength[N/mmÐ]

σ2=Calculatedoperatingstressatupperworkheight[N/mm2]

FatigueStressRatioδ=(σ

Mat-σ1)

(σMat

-σ2)

FATIGUE GUIDELINES

FatigueStressRatioδ

EstimatedCycleLife

<0.40 <30.000

0.40–0.49 30.000–50.000

0.50–0.55 50.000–75.000

0.56–0.60 75.000–100.000

0.61–0.67 100.000–200.000

0.68–0.70 200.000–1.000.000

>0.70 >1.000.000

NOMENCLATURE

T=ThicknessofMaterial[mm] OD=OutsideDiameter,[mm]

SW=RadialWidthofMaterial,[mm] ID=InsideDiameter,[mm]

F=Load,[N] Dm=MeanDiameter,*[mm]

W.H.=WorkHeight,[mm] B=Deflection[mm]

H=Freeheight,[mm] σ=OperatingStress[N/mm2]

N=NumberofTurns E=ModulusofElasticity,[N/mm2]

Z=NumberofWavesperturn K=WaveFactor**

*MeanDiameterDm=[(OD+ID):2]***WaveFactorK:

NumberofWavesperturn[Z]: 2.0-4.0 4.5-6.5 7.0-9.5 ≥10.0

WaveFactor[K]: 3.88 2.90 2.30 2.13

SINGLE TURN WAVE SPRING WITH GAP OR OVERLAP Theoperatingstressofasingleturnwavespringshouldneverexceedtheminimumtensilestrengthoftheflatwirematerial.Keepdeflectionbetween30and70%.

DeflectionB=F·K·Dm3

·ID

E·SW·T3·Z4 OD

OperatingStressσ =3·π·F·D

m

4·SW·t2·Z2

MULTI-TURN WAVE SPRINGSTheoperatingstressofasingleturnwavespringshouldneverexceedtheminimumtensilestrengthoftheflatwirematerial.Keepdeflectionbetween20and80%.

DeflectionB=F·K·Dm3

·ID

E·SW·T3·Z4 OD

OperatingStressσ =3·π·F·D

m

4·SW·t2·Z2

NESTED MULTI-TURN WAVE SPRINGSTheoperatingstressofasingleturnwavespringshouldneverexceedtheminimumtensilestrengthoftheflatwirematerial.Keepdeflectionbetween30and70%.

DeflectionB=F·K·Dm3

·ID

E·SW·T3·Z4·N OD

OperatingStressσ =3·π·F·D

m

4·SW·t2·Z2·N

FORMULAS FOR SPIRAL WOUND WAVE SPRINGS