OEMCorporation

GUIDELINESFORDESIGNANDSPECIFICATION

OFFANSHAFTS

OEMCorp.1660ThomasPainePkw.DaytonOH45459-937-435-3433

OEMCorporationGuidelinesFor

DesignandSpecificationsofFanShafts

OEMCorporationspecializesinthemanufactureofhighqualityshaftsforgeneralpurposeaxialandcentrifugalfans.OEMproducesstraight,centerlessgroundshaftsupto215/16indiameter,straight,centerlessgroundtubularshaftsupto2indiameter,andmachinedstepshaftsupto4indiameter.ThefollowingdesignguidelineshavebeendevelopedbasedonOEMsyearsofexperienceinthemanufactureoffanshafts,andareintendedtoprovideOEMscustomerswithinformationonthedesign,materialselectionandspecificationoffanshaftsthatwillresultinmosteconomicalshaftdesignTherearenumberoffactorsthatneedtobeevaluatedinthedesignofshaftsforgeneralpurposedans,whicharecoveredinthesecondsectionoftheseguidelines,thatleadtotheselectionofthefanshaftdiameterandmaterialselectionforaparticularapplication.OEMrecommendsthefollowingspecificationsanddraftingpracticesforgeneralpurposefanshafts.Followingtheserecommendationswillresultinthemosteconomicalfanshaftdesignandwillminimizequestionsofinterpretationofdrawings.Thedesignspecificationscoveredare:

1.MaterialSpecifications2.ShaftDiameterTolerance3.TIRRunoutTolerance,andMeasurement4.SurfaceFinish5.FlatandKeyseatSpecification,andTolerance6.DimensioningRecommendations

1.MaterialSpecificationsInmostfanshaftapplication1045Steelhasadequatemechanicalpropertiestomeettherequirementsforsafeshaftdesign,andselectionof1045Steelwillresultinthemosteconomicalshaftdesign.Theselectionofhigherstrengthmaterialswillresultinhighercostsandshouldbeavoidedunlesstheadditionalyieldstrengthisdictatedbytheshaftapplication.BecausetheavailabilityofbarstockinalldiametersandgradesissometimeslimitedOEMrecommendsspecifyingarangeofmaterialsthatwillallowOEMtoprovidethemosteconomicalmaterialavailable.

Therecommendedmaterialspecificationis:ShaftMaterialshallbe1018to1060Steel.

OEMCorp.1660ThomasPainePkw.DaytonOH45459-937-435-3433

2.ShaftDiameterToleranceOEMrecommendsshaftdiametertolerancesasshownbelow,andontheattachedOEMdimensionalchart.

NominalSize andTolerance5/8 .6248/.62383/4 .7498/.74881 .9998/.998813/16 1.1873/1.186317/16 1.4373/1.4363111/16 1.6873/1.6863115/16 1.9373/1.936323/16 2.1870/2.185527/16 2.4370/2.4355211/16 2.6870/2.6855215/16 2.9370/2.9355

3.RunoutTIROEMrecommendsaspecificationtoleranceonTIRof0.002/footofshaftlength.OEMchecksandstraightensshaftstothisspecification.TheTIRismeasuredattheindicatedwheellocationoratthecenteroftheshaftwiththeshaftsupportedinVblocksattheindicatedbearinglocations.ItisrecommendedthattheapproximatewheelandbearinglocationsbeindicatedonthedrawingsasshowninFigure1.4.SurfaceFinishOEMscenterlessgrindingprocessprovidesanexcellentsurfacefinishsuitableforpillowblockbearingapplication.OEMcanalsoprovideshaftswithimprovedsurfacefinishforsleevebearingapplicationatadditionalcost.Recommendationsforsurfacefinishesatlowermicroinchvaluesshouldbeobtainedfromthebearingmanufacturer.ContactOEMforquotationswhenspecifyingspecialsurfacefinishrequirements.OEMrecommendsthefollowingsurfacefinishspecification:

ShaftSize SurfaceFinishUnder1 25Microinch1to13/16 32Microinch17/16to111/16 42Microinch115/16andover 46Microinch

OEMCorp.1660ThomasPainePkw.DaytonOH454599374353433

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5.FlatandKeyseatSpecificationandToleranceKeyseats

Thelengthofakeyseatshouldbespecifieddefiningtheusablekeyseatlengthnotincludingthecutterradiusattheend(s)ofthekeyseat.Therecommendedlengthandpositiontoleranceforkeyseatsis+/-0.060.Thedepthofthekeyseatshouldbespecifiedasthedimensionfromthebottomofthekeyseattotheoppositesideoftheshaft,whichcanbeaccuratelymeasured.TherecommendedtoleranceonthiskeyseatdimensionandkeyseatwidthareshownontheattachedOEMdimensionalchart.ThekeyseatdimensionsarebasedontheuseofBarStockkeys.

FlatsThelengthofflatsshouldbespecifiedastheoveralllengthoftheflatincludingtheradiusattheend(s)oftheflat.Therecommendedtoleranceonthelengthandpositionofaflatis+/-0.060.Thedepthoftheflatshouldbespecifiedasthedimensionfromthebottomoftheflattotheoppositesideoftheshaft,whichcanbeaccuratelymeasured.TherecommendedtoleranceonthisdimensionisshownontheattachedOEMdimensionalchart.6.DrawingDimensioningOEMrecommendsthattheshaftdrawingshowtheshaftdimensionsandspecificationsasshowninfigure1.UsingtheseguidelineswillminimizequestionsofdrawinginterpretationbetweenOEMandthecustomer.

OEMCorp.1660ThomasPainePkw.DaytonOH45459-937-435-3433

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ShaftDesignConsiderationsForGeneralPurposeFans

Thereareanumberdesigncharacteristicsthatneedtobeevaluatedtodeterminetheshaftsizeandmaterialselectionforafanapplication.Thisdiscussionislimitedtothedesignofstraightsolidshaftsupto215/16indiameterwithonefanwheelmountedbetweenbearings,ormountedcantileveroutboardofthebearings.Thesamegeneralprinciplesapplytootherfanapplications,howevertheprocessismorecomplexwhendealingwithmultiplefanwheelsonasingleshaft,applicationsrequiringstepshafts,orforoperationathighspeedsoratelevatedtemperatures.Therearefourdesigncharacteristicsthatneedtobeevaluatedfordeterminationofthefanshaftdiameterandmaterialrequirement.

A.CriticalSpeedB.TorsionalStiffnessC.CombinedTorsionandBendingStressD.BearingSelectionforAdequateBearingLife

Inadditiontotheabovedesigncharacteristicsthereisoneareathatisoftenoverlookedinthephysicaldesignofthefan,andthatisthelocationofthedrivenpulleytothedrivesidebearing.Forfansthepredominatefactorindeterminingthefanshaftsizeistheloadonthedrivesidebearing.Theloadonthedrivesidebearingcanbeminimizedbymountingthepulleyasclosetothebearingasispractical.Inadditiontoreducingtheloadonthebearingthebendingmomentontheshaftisalsoreduced.Itisgoodgeneralpracticetodesignthefanassemblytokeepthedrivenpulleyascloseaspracticaltothedrivesidebearing.1.ShaftCriticalSpeedTheshaft,fanwheel,andpulleyassemblywillhavenaturalfrequencydependentontheweightandlocationofthecomponents.Operationatthisnaturalfrequency,calledthecriticalspeed,willallowtheassemblytovibrateexcessivelydotoevenasmallunbalanceintherotatingassembly,andcanleadtofanfailure.Theshaftdesignshouldbesuchthatthemaximumoperatingspeedisnomorethan80%ofthecriticalspeed.Typicalgeneralpurposefansuseselfaligningcartridgeorpillowblockbearingandtheshaftcanbeconsideredassupportedattheendsratherthanfixed.Forthisconditionthecriticalspeedoftheshaftcanbecalculatedfromthefollowingformulaforfanswherethefanwheelismountedbetweenbearings.(Thisequationassumesthedeflectionoftheshaftdototheweightofthepulleyisnegligible.)

OEMCorp.1660ThomasPainePkw.DaytonOH45459-937-435-3433

3

3

1018Steel-Allowableshearstress=8600psi1045Steel-Allowableshearstress=12000psi

Theshaftsizerequiredforsafestresslevelsisgenerallymuchlessthanthatrequiredforadequatebearinglifeorsafeoperatingspeed,sotheuseofsteelswithallowableshearstresshigherthan1018steelisanunnecessarycost.4.BearingLifeThebearingsizeandtyperequiredtoprovideadequateL10bearinglifeisdependentontheloadonthebearingfrombeltpullandthefanwheelweight,theoperatingspeedandtheloadratingofthebearing.TheloadonthedrivesidebearingfromthebeltpullisthepredominatefactorindeterminingthebearingsizeandtyperequiredtoprovideadequateL10bearinglife.Thebearingmanufacturershandbooksdefinethemethodsofcalculatingbeltpull,bearingload,andtheL10life.GeneralpurposefansareusuallydesignedtohaveanL10lifeintherangeof20,000to80,000hours,andinmostapplicationsthedesiredbearinglifewillbethedeterminingfactorfortheshaftsizeselection.SummaryAlloftheabovefactorsshouldbeevaluatedintheprocessofdesigningtheshaftforfanapplications,eventhoughthebearingsizerequiredorthecriticalspeedarethemostpredominatefactorsleadingtotheshaftdiameterselection.Itisalsorecommendedthatmoredetailedmethods,suchasFEAanalysis,ofevaluatingthesecharacteristicsbeusedoncriticalapplications.References:

MachineryHandbook,23rdEdition,IndustrialPressFanEngineering,BuffaloForgeCo.,Buffalo,NYRodynVibrationCorp.1932ArlingtonBlvd.,Suite223,

Charlotsville,Va.22903Tel.804-296-3175

OEMCorp.1660ThomasPainePkw.DaytonOH45459-937-435-3433