6

Radial Shaft Sealtechnical overview

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general radial seal information

How Radial Shaft Oil Seals Work

Theareabetweenthesealingedgeandtheshaftisthemostimportant.Thesealingeffectisachievedbypreloadingthesealinglip,makingitsinternaldiameterslightlysmallerthantheshaftdiameter.Thegarterspringensuresconstantmechanicalpressureandmaintainstheradialforcetotheshaft,flatteningthesealingedgetodefinedwidth.Sealingisprovidedbythesurfacetensionofthehydrodynamicoilfilmbetweenthesealflattenedareaandtheshaftcreatingameniscus.Oilthicknessmustbebetween1and3umtoavoidleakage.Themeniscusactsasaninterfacebetweentheoutsideairandthefluid.Anybreakinthemeniscuswillresultinleakage.Thiscanoccuriftheshaftcontainsscratchesalongthesealpath.

Metal Case

Themetalinsertorcaseisusedtogivestrengthandrigiditytotheseal.Normalyitismadeofcoldrolledsteal.Toavoidrustorchemicalattack,stainlesssteelcanbeused.

Garter Spring

Thegarterspirngmaintainstheradialforceexertedbythesealingliparoundtheshaftsurface.Normallyproducedinharmonicspringsteelwireorstainlesssteelwire.Forspecialapplications,stainlesssteelspringscanbeprovided.

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Shaft Tolerances

shaft tolerance

Theshaftsurfacefinishisofprimaryimportanceforefficientsealingandforacheivingausefulseallife.Theshafthardnessshouldincreasewithincreasingperipheralspeed.Ataperipheralspeedof4m/sthehardnessshouldbe55HRCandat10m/s60HRC.Recommendedminimumhardnessdepthis0.3mmifshaftsarenotfullyhardened.

Lubricationisalsoveryimportant.Roughsurfacesgeneratehigherfriction,hencehighertempaeratures.Machiningdefectsandscratchesontheshaftmustbeavoided.

Evenverysmalldefectscouldbesufficienttoincreasethefilmthickness,eventuallyrupturingthemeniscusandcausingleakeage.Itisalsoimportanttoavoidspiralgrindingorgroovemarks,theycancauseapumpingeffectandleakage.

over to lower upper0 3 0 -0.063 6 0 -0.0756 10 0 -0.09

10 18 0 -0.1118 30 0 -0.1330 50 0 -0.1650 80 0 -0.1980 120 0 -0.22

Shaft Tolerance

(Metric)Shaft Diameter Tolerance (mm)

up to 4.000 +/-0.003

over 4.000 to 6.000

+/-0.004

over 6.000 to 10.000

+/-0.005

over 10.000 +/-0.006

Shaft Tolerance

(Inch)Nominal Shaft

DiameterTolerance

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shaft eccentricity

Eccentricitybetweenshaftandhousingborecentersmustbeavoidedasmuchaspossiblesoastoreduceunilateralload(wear)ofthesealinglip.

shaft eccentricity

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bore Tolerances

Bore tolerance

Maintainingproperborecharacteristicsisimportantiftheintegrityofthesealingsystemistoremainintact.Toprovideproperfitofanoilseal,thedimensionsrelativetoBoreToleranceshouldbefollowed.

3.001 to 6.000 +/- 0.00156.001 to 6.000 +/- 0.00210.001 to 6.000 +/- 0.002 / -0.00420.001 to 6.000 +/- 0.002 / -0.00640.001 to 6.000 +/- 0.002 / -0.010

Bore Tolerance

(inch)Bore Diameter Bore Tolerance

over 6 to 10 +0.022 / -0.000over 10 to 18 +0.027 / -0.000over 18 to 30 +0.033 / -0.000over 30 to 50 +0.039 / -0.000over 50 to 80 +0.046 / -0.000over 80 to 120 +0.054 / -0.000over 120 to 180 +0.063 / -0.000over 180 to 250 +0.072 / -0.000over 250 to 315 +0.081 / -0.000over 315 to 400 +0.089 / -0.000

Bore Tolerance

(Metric)Bore Diameter Bore Tolerance

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shaft run out

shaft run out

Thebestworkingconditionistohaveashaftrotatingasperfectlycenteredandconcentrictotheaxisoftherotaryshaftsealaspossible.Obviously,thisisnotpossibleandinevitablysomeshaftrunoutisalwayspresent.

Therefore,thesealinglipmustcompensateforit.Thehighertherotationspeedis,thelessthepermissableshaftrunoutcanbe,whichiscompensatedbythesealinglipbecausetheinertiaofthesealinglippreventsitfromfollowingtheshaftmovements.Itis,therefore,advisabletoinstallthesealimmediatelyadjacenttothebearingandminimizebearingplay.

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permissable shaft speed grid

Thetemperatureonthesealinglipisthemediumtemperatureincreasedbythetemperaturecausedbyfrictionalheat.

Thehighertheeffectiveoperatingtemperatureis,thefastertheageingoftheelastomerwillbe,thusaffectingtheperformanceofthesealinglipandtheshaft.

Frictionalheatdependsonsealdesignandmaterial,peripheralspeed,sealinglippreloadingspringforce,shaftdesignandsurfacefinish,lubrication,andmedium.

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Permissable pressure

Permissible pressure

Inmostapplications,thereislittleornodifferentialpressure.Wheretherotaryshaftsealisexposedtopressure,however,thesealinglipispressedagainsttheshaft,thusincreasingfrictionandtemperature.Insomecases,thepressurecanevencauseoverturningofthesealinglip.

Whenover0,2barathigherperipheralspeedsorover0,5baratlowperipheralspeeds,backupringsorspeciallydesignedrotaryshaftsealswithstrongersealinglipsandsupportingmetalinsertsmustbeused.

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General elastomer information

Themostimportantcomponentofoilsealsistheelastomermaterial.Youmustconsidertheenvironmentalconditionsandthefunctionofthesealasfollows:goodchemicalresistance,goodresistancetoheatandlowtemperatures,goodresistancetowater,lowcompressionset,goodelasticity,andrawmaterialcost.

Inordertosatisfyvarioussealingconditions,TRUSEALhasmanycompoundsavailableforyourapplication:

BASE POLYMER NITRILE POLYACRYLATE SILICONE FLUORILASTOMERTemperatureRange

-40F-250F-30C-120C

-20F-300F-30C-150C

-80F-400F-60C-200C

-30F-400F-35C-200C

OilResistance Excellent Excellent Good ExcellentAcidResistance Good Fair Fair ExcellentAlkaliResistance Good Notrecommended Notrecommended FairWaterResistance Good Fair Fair GoodHeatResistance Good Excellent Excellent ExcellentColdResistance Good Fair Fair FairWearResistance Excellent Excellent Excellent ExcellentOzoneResistance Good Excellent Excellent Excellent

Material Advantages DisadvantagesNitrile CommonlyreferredtoasBuna-Nor

NBRandiscoploymerofButadienceandAcryonirile.Goodresistance,coldflow,tearresistance.

Poorresistancetoozoneandweatheraging.Poorcoldtemperaturelimit,dryrunningadility,waterresistance.Lowermechnicalstrength.Fairresistancetowater,dryrunning.Lowtemperatureresistanceisfair.

Polyacrylate PlymerisiedacrylicacidestersorPAandACM.Goodresistancetomineraloils,hypoidgearoilsE.P.additives,greases,agingandflexcracking.

Lowresistancetohydrocarbonfluidslikegasolineorparaffinfluidsorsteamaboutto50psi.

Fluoroelastmer Goodtemperatureresistance.CommonlychosenashightemperaturereplacementforNitrileorPolyacrylate.

Silicone Broadtemperaturerange.Goodozoneresistance.Resistanttocompressionset.

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Type of Fluid to be Sealed Lip MaterialNitrile Polyacrylate Silicone Fluorilastomer

EngineOil Excellent Excellent Good ExcellentGearOil Good Good Notrecommended ExcellentTurbineOilNo.2 Good Good Good ExcellentMachineOilNo.2 Good Good Fair ExcellentAutomaticTransmissionFluid Excellent Excellent Fair ExcellentPetroleumBaseLubricatingOil Excellent Excellent Fair ExcellentGasoline Fair Notrecommended Notrecommended ExcellentLightOil/Kerosene Fair Notrecommended Notrecommended GoodCuttingOil Excellent Good Fair ExcellentGrease Excellent Excellent Excellent ExcellentE.P.Lubricants Good Excellent Notrecommended ExcellentWater-Glycol Excellent Notrecommended Good GoodAlcohol Excellent Notrecommended Good Fair20%HydrochloricAcidSolution Fair Fair Fair Excellent30%SulfuricAcidSolution Fair Fair Notrecommended Excellent

fluid compatibility

metal case and spring

caseSAE NO. AISI NO. APPLICATION COST SUGGESTION1008-1010 1008-1010 General Low Byusingfullyrubber

covereddesignwithcarbonsteelcasecanreducecost.

30304 34 SpecialcorrosionResistancecondition

High

springSAE NO. AISI NO. APPLICATION COST1070-1080 1070-1080 General Low30304 304 Specialcorrosion

Resistancecondition

High

C5210R C5210 SpecialcorrosionAgingresistance

Higher

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Interchange table & Material Tolerances

shaft seal interchange table

TRUseal

TypesSC TC TCN VC DC SB TB SA TA

Simrit-Freudenberg BA BASL BABSL BAOF BADUO B1 B1SL B2 B2SL

Goetze 827N 827S 827SK 827NO 827D 822N 822S 824N 824SKako DG DGS DGSP DE DGD DF DFS DFK DFSK

Simmerwerke A ASL AOF ADUO B BSL C CSLStefa CB CC CF CD CK BB BC DB DCGaco A FA SA DUPLEX ABI

Pioneer Weston R21 R23 R26 R22 R4 R6 R1Paulstra IE IEL IO IELR EE EEL EEP

Chicago Rawhide HMS4 HMSA7 CRW1 CRWA1 CRWH1 CRWHA1National 35 32 48 47 45 41

NOK SC TC TCN VC DC SB TB SA TADictomatik WA WAS WASY WAO WAD WB WBS WC WCS

FP G GP GAP GSM G2 L1 L1P L2 L2P

material tolerances

MaterialMinimum

TemperatureMaximum

TemperatureMinimum

TemperatureMaximum

Temperature

NBR -67 212 -55 100FPM -13 482 -25 250ACM 14 302 -10 150SIL -67 437 -55 225EPDM -67 302 -55 150PTFE -58 482 -50 250CR -40 212 -40 100

fahrenheit celsius

Material Temperature Range

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standard shaft seal types

Description of Standard Shaft Seal Typessc Rubber covered O.D., metal insert, sealing lip with garter spring

tc Rubber covered O.D., metal insert, sealing lip with garter spring and additional dust lip

tcn Reinforced sealing lip for overpressure, with or without additional dust lip

dc Twin sealing lips with two garter springs

vc Sealing lip without garter spring

vg Rotary shaft seal for needle bearing applications, without garter spring

sb Outer metal case, sealing lip with garter spring

tb Outer metal case, sealing lip with garter spring and additional dust lip

sa Outer metal case with reinforcing metal inner ring, sealing lip with garter spring

ta Outer metal case with reinforcing metal inner ring, sealing lip with garter spring and additional dust lip

vb Outer metal case, sealing lip without garter spring

va Outer metal case with reinforcing metal inner ring, without garter spring

ec End covers