Download - Description of standard shaft seals types (in accordance with ...Tisan Oy rotary shaft seals Description of standard shaft seals types (in accordance with DIN 3760) A Rubber covered

Tisan Oy rotary shaft seals

Description of standard shaft seals types (in accordance with DIN 3760)

A RubbercoveredO.D.,metalinsert,sealinglipwithgarterspring

AS RubbercoveredO.D.,metalinsert,sealinglipwithgarterspringand additionaldustlip.

B Outermetalcase,sealinglipwithgarterspring

BS Outermetalcase,sealinglipwithgarterspringandadditionaldustlip

C Outermetalcasewithreinforcingmetalinnerring,sealinglipwith garterspring

CS Outermetalcasewithreinforcingmetalinnerring,sealinglipwith garterspringandadditionaldustlip


Technical DataDescriptionofrotaryshaftseal

Working PrincipleTheareabetweenthesealingedgeandtheshaftisthemostimportant.Thesealingeffectisachievedbypre-loadingthesealinglip,makingitsinternaldiameterslightlysmallerthantheshaftdiameter.Thegarterspringensuresconstantmechanicalpressureandmaintainstheradialforcetotheshaft,flatteningthesealingedgetoadefinedwidth.Sealingisprovidedbythesurfacetensionofthehydrodynamicoilfilmbetweenthesealflattenedareaandtheshaft.Oilthicknessmustbebetween1and3µmtoavoidleakage.Themeniscusactsasaninterfacebetweentheoutsideairandthefluid.Anybreakinthemeniscuswillresultinleakage.Thiscanoccuriftheshaftcontainsscratchesalongthesealpath.


Metal caseThemetalinsertorcaseisusedtogivestrengthandrigiditytotheseal.NormallyitismadeofcoldrolledsteelinaccordancewithDIN1624.

Garter springThegarterspringmaintainstheradialforceexertedbythesealingliparoundtheshaftsurface.NormallyproducedingarmonicspringsteelwireSAE1074(DIN17223)orstainlesssteelwireChromeNickelAISI302(DIN1.4300).

Elastomeric sealing materials1 Nitrile rubber NBRThiselastomerisacopolymerofbutadieneandacrylonitrileandisusedforthemajortyofconventionalfluidsealingapplications.

Physicaldata

- Workingtemperaturerange:-30°C-+120°Cinoil(atthesealinglip)- Tensilestrength:upto20MPa- Standardcolour:black

Advantages:- Goodresistancetomineraloilandgrease- Goodresistancetowaterandradiatorfluid- Hightearstrength

Limitations:- Poorresistancetohigh-alloyedhypoidoil- Poorresistancetoozone,weatheringandsunlight- Notresistanttoautomotivebrakefluid(glycolbased)- Poorresistancetopolarfluids(ketones,ethers,esters)- Poorresistancetochlorinatedhydrocarbons(carbontetrachloride,trichloroethylene)- Poorresistancetoaromaticsolvents

2 Fluorinated rubber FPM (VITON from DuPont, FLUOREL from 3M)

Physicaldata

-Workingtemperaturerange-20°C-+200°C(atthesealinglip)-Tensilestrength:upto15MPa-Standardcolour:brown

Advantages:-Excellentresistancetomineraloilandaboveallhigh-alloyedhypoidoils-Excellentacidresistance-Goodresistancetoaromaticandchlorinatedhydrocarbons-Excellentresistancetoageing,ozoneandweathering


Limitations:-Limitedcoldflexibility-Poorresistancetopolarfluids(ketones,ethers,esters)

Rotating speed

Thistablebelowgivesanindicationoftherotaryorlinearvelocityoftheshaftinrelationtovariouselastomerswhicharepermissibleundernormalconditionsofuse.

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Chemical resistance

Installation and operationShaftTheshafthardnessandsurfacefinishareofprimaryimportanceforefficientsealingandforachievingausefullife.Basicallythehardnessshouldincreasewithincreasingperipheralspeed.AccordingtoDIN3760minimumhardnessrequiredis45HRC.Ataperipheralspeedof4m/sthehardnessshouldbe55HRCandat10m/s60HRC.Recommendedminimumhardnessdepth.0,3mmifshaftsarenotfullyhardened.

SurfacefinishasspecifiedbyDIN3760mustbeRa0.2to0.8µm,butwerecommend0.2to0.5.Roughersur-facesgeneratehigherfriction,hencehighertemperatures.Machiningdefectsandscratchesontheshaftmustbeavoided.

Evenverysmalldefectscouldbesufficienttoincreasethefilmthickness,eventuallyrupturingthemeniscusandcausingleakage.Itisalsoimportanttoavoidspiralgrindingormarks,becausetheycancause a pump-ing effect andleakage.

Finishingoperationsemployingforwardfeedprocessesshouldonlybeusedinexceptionalcases.Theuseofagrindingwheelwithgritsize“60”to“100”isrecommended.Dressingofthegrinding wheel shouldbedonewithaclusterdiamondatadressingspeedofc.0,25m/min.

- Individualadvancesofthegrindingwheel:0,03–0,04mm- grindingwheelrevolutions: c.1500rpm- shaftrevolutions(counter-rotating) 80–100rpm

RecommendedmachiningtoleranceisISOh11accordingtoDIN3760.

Themountingendortheshaftshouldhaveachamferinclinedby15°-30°withroundedandpolishededge.

Thebestworkingconditionistohaveashaftrotatingperfectlycentredandconcentrictotheaxisoftherotaryshaftseal.Obviouslythisisnotpossibleandinevitablysomeshaftrunoutisalwayspresent



Thereforethesealinglipmustcompensateforit.Thehighertherotationspeedis,thesmallercanbethepermissibleshaftrunoutwhichcanbecompensatedbythesealinglip,becausetheinertiaofthesealinglippreventsitfromfollowingtheshaftmovements.Itisthereforeadvisabletoinstallthesealimmediatelyadjacenttothebearingandminimizebearingplay.

Eccentricitybetweenshaftandhousingborecentersmustbeavoidedasmuchaspossiblesoastoreduceunilateralload(wear)ofthesealinglip.



Housing bore

Agoodpressfitoftheshaftsealontothehousingboreisvital.Theresultisstableinstallation.

MachiningtolerancesofthehousingborediameterforrotaryshaftsealsareH8accordingtoISOstandardUNI-6388-68

Therecommendatedroughnessofthehousing-coveredseal: Ra=1.6to4µm.R=4to12.5µm-externalouterring: Ra=1.2to8µm.R=3to8µm

Toeaseinstallationtheentranceofthegrooveshouldhaveachamferinclinedby10°-20°andadepthac-cordingtothethickness.

Note:Ifthehousingismadeofamaterialwithahighcoefficientofexpansion,mustthisbetakenintoconsid-erationwhendefiningtheinterference(tightness)withtheseal.

Axialpositioningandalignment

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1Thesealismountedagainstastopontherearside.Thispresentsnoparticularproblem,providedthatpres-sureisappliedat“A”toinsertitandnotat“B”.

2Herethereisnoaxialstop.Themountingtoolpositionsthesealbothaxiallyandperpendicularly.

3Thesealismountedagainstastoponthefrontside.Thisshouldbeavoidedastheelastomerat“B”couldbecompressedandthesealwilltendtomoveoutofposition.

4Thehousinghasashoulderasin3,butthesealispositionedbythemountingtool.Thiscaseispreferabletocase3.

Recommendationsfortheassemblytool

GOOD

TO BE AVOIDED

Timeshouldbeallowedduringassemblyinordertoallowtheelastomertimetosettle.Thesealmustbeheldinpositionforafewsecondsoncemounted,toavoidtoolargeareturnmovement.

Itisveryimportantthatthesealnotremaindiagonallyinthehouse.Theangletolerancemaynotexceedthevaluesinthetablebelow.Seal AngleØ tolerance(a)<25 0,1mm25-80 02mm80> 0,3mmBigger angle lead to a pumping effect.



PressureTheeffectivepressuretowhichasealissubmittedisthedifferencebetweenthepressuresofthefluidsoneachofitstwosides(oneofwhichisoftentheatmosphere).Itisclearthatthesealinglipshouldbefoundonthesidewhichhasthehigherpressure.Intheory,thelipsealforrotaryshaftsisnotapressureseal.However,mostsealswillresistpressuresoftheorderof0.5barswithoutspecialprecautions,ifthevelocitiesdonotexceed3m/s.Athigherpressures,thereisariskthatthelipmaybeturnedbackonitselforpressedontotheshaftwithaforcewhichgivesrisetoanunacceptabletightnessandfrictionaltorque.Atlowvelocitiesmostsealswillbearpressuresofupto3or4barswiththeadditionofasupportingbush.

LubricationHouseWhilethefirstmeansofavoidingdamagetotheoutsideofthesealistopayattentiontothehousingcharacter-istics,thesecondmeans,whichisjusasimportant,islubrication:- beitofthehousing,- ortheoutsideoftheseals,- orbothatthesametime.

Thisnotonlyavoidsdamagetotheseal,butalsoensuresabetteraxialpositioning.Asealwhoseoutsidediameterisnotlubricatedwillcertainlybedamagedontheoutsidewhenitismountedinadryhousing(elastomercovercutorripped,sealinglacquerremoved).

ShaftLubricationisveryimportantforagoodfunctionandlifeoftheseal.Thesealinglipdoesnotactuallyrunontheshaftdirectly,butonanoilfilm,calledmeniscus.Thethicknessofthemeniscusisusuallybetween1-3µm,butisaffectedbymanyfactorssuchasoilviscosity,shaftsurfacefinishandsealradialload.

Alsowhentheunitisstartedup,theoilwillalwaystakesometimebeforeitreachesthelipoftheseal(fromafewsecondstoafewtenthsofsecondsdependingtotheapplication).Ifitisthefirststart,andiftheliphasnotbeenlubricatedatassembly,itwillfunction“dry”dynamically,whichwillleadtogreatwearandtheriskoftotaldeterioration.Thefirstfewhoursofoperationiscalledthe“bedding-in”time.Thisisnecessarynotonlyforthemeniscustoform,butalsoforthesealingedgetoflatten.Duringthistimelimitedleakageispossible.

Adequatelubricationstronglyreducesfrictionbetweensealinglipandshaftandalsoactsasacoolanttothegeneratedheat.Thelowerthetemperaturecanbekept,thelongerwillbethelifeexpectancyoftheseal.Shouldthefluidhavepoorlubricatingcapability(waterandaqueoussolutions),dustlip-type(AS,BSorCS)rotarylipsealsmustbeused.Insuchacasemakesuretofillthespacebetweenthetwolipswithgrease.Thefrictionheatalsodependsontheperipheralspeedoftheshaft.

WAOandWBO

arespeciallydesignedrotaryshaftsealstobeusedforneedlebearingapplications.Thesealsarereinforcedwithsteelinsertandhaveasinglelipwithoutspring.

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