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
Tisan Oy rotary shaft seals
Technical DataDescriptionofrotaryshaftseal
Working PrincipleTheareabetweenthesealingedgeandtheshaftisthemostimportant.Thesealingeffectisachievedbypre-loadingthesealinglip,makingitsinternaldiameterslightlysmallerthantheshaftdiameter.Thegarterspringensuresconstantmechanicalpressureandmaintainstheradialforcetotheshaft,flatteningthesealingedgetoadefinedwidth.Sealingisprovidedbythesurfacetensionofthehydrodynamicoilfilmbetweenthesealflattenedareaandtheshaft.Oilthicknessmustbebetween1and3µmtoavoidleakage.Themeniscusactsasaninterfacebetweentheoutsideairandthefluid.Anybreakinthemeniscuswillresultinleakage.Thiscanoccuriftheshaftcontainsscratchesalongthesealpath.
Tisan Oy rotary shaft seals
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
Tisan Oy rotary shaft seals
Limitations:-Limitedcoldflexibility-Poorresistancetopolarfluids(ketones,ethers,esters)
Rotating speed
Thistablebelowgivesanindicationoftherotaryorlinearvelocityoftheshaftinrelationtovariouselastomerswhicharepermissibleundernormalconditionsofuse.
102030405060708090100200
Tisan Oy rotary shaft seals
Tisan Oy rotary shaft seals
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
Tisan Oy rotary shaft seals
Tisan Oy rotary shaft seals
Thereforethesealinglipmustcompensateforit.Thehighertherotationspeedis,thesmallercanbethepermissibleshaftrunoutwhichcanbecompensatedbythesealinglip,becausetheinertiaofthesealinglippreventsitfromfollowingtheshaftmovements.Itisthereforeadvisabletoinstallthesealimmediatelyadjacenttothebearingandminimizebearingplay.
Eccentricitybetweenshaftandhousingborecentersmustbeavoidedasmuchaspossiblesoastoreduceunilateralload(wear)ofthesealinglip.
Tisan Oy rotary shaft seals
Tisan Oy rotary shaft seals
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
1234
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.
Tisan Oy rotary shaft seals
Tisan Oy rotary shaft seals
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.
Tisan OySalmitie 4
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Tisan Oy rotary shaft seals