Sealing Arrangement Design Guide

Sealing arrangement design guide

The complete SKF bearing and CR sealing system.... 3

Bearing damage – a sign of sealing problems ............ 4

The seal ........................................................................... 6Function ........................................................................ 6Types ............................................................................ 6Radial shaft seals ......................................................... 8Materials ....................................................................... 9The environment ........................................................... 11The shaft ....................................................................... 14The housing bore.......................................................... 15

Seal selection ................................................................. 16Grease retention ........................................................... 18Oil retention .................................................................. 18Exclusion ...................................................................... 19Exclusion/retention ....................................................... 19Separating two liquids................................................... 20Containing high pressure.............................................. 20Restricted space ........................................................... 21Installation restrictions .................................................. 21

Seal installation .............................................................. 22

Repairing worn shafts.................................................... 24

Seal maintenance ........................................................... 26

Seal check list................................................................. 27

A brief history of CR Industries .................................... 29

The SKF Group – a worldwide corporation.................. 30

2

Contents Sealing arrangement design guide

Since taking over CR (Chicago Raw-hide) in 1990, SKF is not only the worldleader in rolling bearings but also inshaft sealing technology. Combiningthe very wide experience of SKF withrolling bearing applications throughoutthe world and the know-how of CR inrespect of seals has strengthened SKF competence in these fields. It alsoforms a solid foundation for further inno-vations in bearing and seal technology.

Whatever the bearing arrangement, itcomprises not only the bearing but alsothe components immediately associ-ated with the bearing. Besides shaftsand housings these include the seals,the performance of which is of vital im-portance to the cleanliness of the lub-ricant. Contaminants have a profoundeffect on bearing life and the SKF NewLife Theory allows this to be quantified.

For the designer this means thatbearings and seals should be viewedas an integrated system and should betreated as such. When designing thesealing arrangement and selecting theseals, therefore, the requisite life of thebearing(s) and the lubricant must betaken into consideration.

For the maintenance engineer, itmeans that seal wear and bearing failure are not inevitable and can be avoided by using a different seal or a seal of different material, or bychanging maintenance routines etc.

For SKF, it means that increasingattention is being paid to seals for bearings as well as to seals in general.It also explains why CR, the largestAmerican producer of radial shaft seals,now forms part of the SKF Group.

CR has always devoted considerableresources to research and develop-ment of new designs, materials andmanufacturing of seals. These effortsare now concentrated at a researchcentre in Elgin, Illinois, USA, which isprobably the largest research facility ofits kind in the world. The ongoingdevelopment of sealing technologybrings benefits to the original equipmentmanufacturer as well as to the end user.Design and material improvementsenhance the contaminant exclusionand lubricant retention properties of theseals – so essential to long seal life,long bearing life, and last but not least,long machine life.

SKF bearings and CR seals comple-ment each other and are always thecorrect choice for bearing and sealingarrangements of all kinds.

3

The complete SKF bearing and CR sealing system

More information about bearing damage will be found in publication PI 401”Bearing failures and their causes”.

The calculated life of a bearing is de-fined as the period of time for which thebearing will operate until signs of fatigueset in, and since most bearings fail forother reasons, it may be argued thatmost bearing failures are premature.

The development of the SKF NewLife Theory has made it possible totake into account not only the effects ofmaterial and lubricating conditions onbearing life in addition to bearing load,but also the effect of contaminationand the bearing damage it produces.Solid contaminants, depending on par-ticle size, hardness and brittleness willproduce indentations and/or wear onthe bearing surfaces. Water will affectthe efficiency of the lubricant and alsoits rust inhibiting properties. Contam-ination in the lubricant can dramatic-ally reduce bearing life so that goodsealing is of vital importance.

When a seal fails, contamination caninfiltrate the bearing area and enter thelubricant and then the bearing. Also,lubricant may be lost from the bearing,leading ultimately to dry running andbearing failure. Information regardingthe influence of lubrication and contam-ination on bearing life can be found inthe SKF General Catalogue.

Bearings can, of course, fail for reasons other than seal or lubricantbreakdown. These reasons includeoverloading, either as a result of apply-ing too heavy a load or as a result ofmisalignment or faulty mounting. Otherreasons are overheating, excessivevibration or the passage of electric current through the bearing.

Bearing damage – a sign of sealing problems

4


Corrosion Greyish-black streaks across the racewaysat intervals corresponding to the spacing ofthe rolling elements (in this case cylindricalrollers) indicate that water has penetratedthe bearing during standstill. General rustindicates the presence of water or othercorrosive substances.

Wear caused by inadequate lubrication Worn or mirror-like surfaces, possibly withcoloured (brownish) bands, indicate poorlubrication.

Indentations caused by contaminant particles Indentations on the raceways of rings androlling elements indicate the presence ofcontaminants in the bearing. Even soft par-ticles such as cellulose or textile fibres cancause indentations if they are large enough.

Surface distressSmall shallow craters with crystalline ap-pearance can result from momentary briefmetal-to-metal contact. The cause may beeither the use of an unsuitable lubricant, orthe loss of lubricant through the seal.

Smeared roller ends and guide flangesScored and discoloured roller ends orflange surfaces are caused by inadequatelubrication of the roller end/flange contact.In some cases this may be because lub-ricant has been lost.

Wear caused by abrasive particles Pitting (small indentations) and/or wear ofthe surfaces of the raceways on rings androlling elements and a darkening of thelubricant indicate the presence of contam-ination.

5

Bearing damage that may be seal related

Function The purpose of a seal is to prevent thepassage of media of all types betweenthe mating surfaces of components;the surfaces may be either stationaryor in motion. The seal should be suffi-ciently capable of deformation to beable to compensate for any surfaceirregularities but also be strong enoughto withstand operating pressures. Thematerial(s) from which the seal ismade should also be able to withstandthe operating temperatures, and haveappropriate chemical resistance.

Types There are several different types ofseal; for example, DIN 3750 distin-guishes between the following basictypes:

1. seals in contact with stationary surfaces,

2. seals in contact with sliding surfaces,

3. non-contacting seals, 4. bellows and membranes.

Seals in contact with stationary sur-faces are known as static seals andtheir sealing effect depends on the radialor axial deformation of their cross sec-tion when installed. Gaskets (➔ fig )and O-rings (➔ fig ) are typical ex-amples of static seals.

Seals in contact with sliding surfacesare used to seal the passage betweenmachine components which moverelative to each other either linearly orin the circumferential direction. Theseseals, known as dynamic seals, haveto retain lubricant, exclude contam-inants, separate different media andwithstand differential pressures.

There are various types of dynamicseal, including packings and piston

21

The seal

6


Static seal: gasket

Static seal: O-ring

Dynamic seal: radial shaft seal

1

2

3

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rings, which are used for linear oroscillating movement. However, radialshaft seals (➔ fig ) constitute themajor type and are used in widely differing applications in all branches of industry. Other popular dynamic seal types include mechanical seals(➔ fig ), V-ring seals (➔ fig ) andfelt seals.

The non-contacting or non-rubbingseals function by virtue of the sealingeffect of a narrow, relatively long gapwhich may be arranged axially, radi-ally or as a combination of radial andaxial gaps. Non-rubbing seals, whichrange from simple gap-type seals tomulti-stage labyrinths (➔ fig ) arepractically without friction and do notwear. They are, therefore, particularlysuitable for high-speed and high-temperature operation.

Bellows and membranes are used toseal components which have limitedmovement relative to each other.

Because of the importance ofradial shaft seals for the efficientsealing of bearing arrangements,this guide deals almost exclusivelywith radial shaft seals and their ap-plication as well as with the variousdesigns and executions.

6

54

3

7

Dynamic seal:mechanical seal

Dynamic seal: V-ring seal

Dynamic seal:labyrinth seal

6

5

4

Radial shaft sealsRadial shaft seals consist of

– a cylindrical outside diameter of pres-sed steel (shell) or elastomer whichprovides a static seal in the housingbore, gives a sufficiently tight fit forthe seal in the bore, and enables theseal to be properly installed;

– a sealing lip of elastomer, which sealsagainst the shaft; the sealing lip hasan edge formed by pressing, cuttingor grinding, which is normally heldagainst the surface of the shaft(counterface), with a defined radialforce, by a garter spring.

The principal components of a typicalradial shaft seal are shown in the ad-jacent illustration (➔ fig ). The sealshown has a simple L-shaped steelshell to which the sealing element ofelastomer is bonded. An additionalsecondary or dust lip may also be pro-vided. This protects the primary sealinglip from solid contaminants.

Seals with inner shells have en-hanced radial stiffness. The inner shellis advantageous where installationconditions are difficult.

CR produces radial shaft seals of all the standard types covered by ISO 6914/I (DIN 3760 and DIN 3671)(➔ fig ). The CR radial shaft sealrange also includes special designs, in particular for heavy engineering ap-plications (➔ fig ).

The sealing lips of CR radial shaftseals are produced in various materialsand in two executions which differ inthe form of the sealing lip edge. The“conventional” edge is straight and traces a relatively narrow path on thecounterface. CR Waveseals on theother hand have a hydrodynamicallyformed edge which traces a sinusoidalpath on the counterface. The Wavesealrepresents the most important develop-ment in radial shaft seals over the past25 years. The axial relative movementof the form-pressed Waveseal lip onthe counterface provides hydrodynamicproperties, pumping lubricant back intothe bearing arrangement and deflectingcontaminants.

The garter springs of standard CRradial shaft seals, which press the seal-ing lip against the counterface with the

9

8

7

8

The seal

a b c

Type 1 Type 2 Type 3

Type 4 Type 5 Type 6

Radial shaft sealsto ISO 6194

All-rubber radialshaft seal a) with open

spring groove b) with Spring-

Lock c) with Spring-

Kover

Shell

Bearing side

Primary sealing lip

Hinge

Garterspring

Sealingelement

Environment

�

�

Typical radialshaft seal

7

8

9

0

50

100

150

200

250

300

-100

-50

4

0

12

5

7

910

8

12

10

6

2

67

Acrylonitrile butadiene (NBR) Commonly referred to as nitrile rubber,this material has good resistance tomost mineral oils and greases and canbe used at temperatures of between −50 and +100 °C and for short periodsup to +120 °C. These seals can alsotolerate dry running of the lip for briefperiods.

Variants of this material are availablefor use with fuels, industrial fluids andcertain synthetic lubricants.

Duralip (X-NBR)Duralip is a carboxylated nitrile rubberwhich combines the good properties of nitrile rubber with a very high wearresistance. The material is used forlarge seals and Duralip seals should

9

Materials The performance and reliability of aradial shaft seal are largely dependenton the material from which the sealinglip is made. Where seals regularly failafter a short period of operation, it may be advisable to replace them with seals of another material, e.g. one which is more wear-resistant suchas CR LongLife fluoro rubber. Althoughmore expensive to buy, the reducedmaintenance and downtime may makethem an economic proposition.

Normally materials based on acrylo-nitrile butadiene are used for radialshaft seals. For CR seals, the materialsdescribed in the following are used.

Relative wear resistance

Silicon

e

Polyac

rylat

e

Nitrile

rubb

er

Leat

her

Durali

p

Durat

emp

Long

Life

PTFE

Long

Life

fluor

o ru

bber

Temperature, °C

LongLife PTFE

LongLife fluoro rubber

Silicone Leather Nitrile rubber

Polyacrylate

Duralip

Duratemp

necessary radial force, are located ingrooves. These grooves enclose some180° of the spring (➔ fig ). Thelarge seals of the HDS and HS designsare an exception. They have a Spring-Lock, one “wall” of the groove beingextended so that some 270° of thespring is enclosed (➔ fig ). Thusthe spring is protected during difficultand dirty installation conditions and isprevented from leaving the groove. Incases where even greater protection is required for the garter spring, sealswhich have the Spring-Lock can alsobe supplied fitted with Spring-Kover (➔ fig ), a flexible cover of elasto-mer material, so that the spring is com-pletely enclosed.

9c

9b

9a

LongLife PTFEPolytetrafluoroethylene (PTFE) has achemical resistance which far exceedsthat of all the materials described aboveand the material is mainly used forspecial seals. Dry running is permittedand the operating temperature range is −70 to +260 °C although care shouldbe taken when using them above +200 °C so that they do not overheat.The risks are the same as those out-lined under fluoro rubber.

Other materials used in seals The shells and any metallic reinforce-ments are made of deep drawn car-bon steel as standard. Free surfacesare treated for protection against cor-rosion. To special order they may bemade of stainless steel although notfor all cross sections and widths.

The garter springs are made of harddrawn carbon steel wire except thoseof the large HDS and HS seals whichare made of stainless steel as standard.

Bore-Tite is a special CR non-hardening material used as a coatingon some sizes of seal with steel out-side diameter This green coating isresistant to most oils, greases, aqueous acids, alkalis, salts, alcoholsand glycols. It is not compatible witharomatics, ketones or esters.

be used where abrasive material suchas scale, sand and grit is likely to collect at the shaft seal area.

Duratemp (H-NBR)This is a special hydrogenated nitrilerubber which offers improved tensilestrength and resistance to wear, heat,hardening in hot oil, ozone and weath-ering. In some cases, aerated oils may be a problem. The operating temperature range is −30 to +150 °C.

Polyacrylate elastomer (ACM) This material is more heat resistantthan nitrile rubber or Duralip. It can be used at temperatures between −40and +150 °C and, in the presence ofsome fluids, it can even withstand temperaures up to +175 °C. Seals ofthis material are resistant to oxidationand ozone and are well suited for usewith many EP (extreme pressure) lubricants. They should not be usedwith water or aqueous solutions (acids,alkalis etc.) nor should the lips be allowed to run dry.

Silicone rubber (MVQ)Silicone rubber seals can operate attemperatures ranging from −70 to +160 °C. The material absorbs lub-ricant, minimising friction and wear.However, compatibility with oxidisedoils and some EP additives is poor. Thelip should be protected against abras-ive contaminants and should not beallowed to run dry.

LongLife fluoro rubber (FPM) Fluoro rubber is highly resistant to heatand chemicals. Fluoro rubber seals canbe used even under arduous environ-mental conditions at temperatures be-tween −40 and +200 °C. The seals arealso resistant to a wide range of chem-icals including most of the fuels, hy-draulic fluids and special lubricantswhich destroy nitrile rubbers, polyacry-late elastomers and silicone rubbers.The lip can withstand short periods ofdry running.

Their drawback is that, if over-heated, they will emit dangerous fumes,and even after they have cooled downagain, they are dangerous to handle.

10

The seal

11

speeds under pressure are given inthe table below (➔ Table )

Seals used in hydraulic pumps andmotors are exposed to a relatively con-stant pressure differential. In this typeof application, special seals which aresuitable for differential pressures shouldbe used. These have shorter lips butthey are more robust. The CR radialshaft seal for such conditions is theCRWA5 design. This heavy-duty sealincorporates a Waveseal lip and canaccommodate pressures of 0,63 MPaat low circumferential speeds and 0,34 MPa at higher speeds.

LubricationFor radial shaft seals to perform satis-factorily over a long period of time, it isessential that adequate lubrication isprovided for the sealing lip. This pre-vents direct contact between the edgeof the sealing lip and the counterfaceand reduces friction and therefore wear.Dry running of the sealing lip for anyappreciable period of time must beavoided. For this reason, the counter-face should be oiled or greased whenthe seal is installed to guarantee initiallubrication of the sealing lip. However,dry running can also occur, for example,when a machine is restarted after a longperiod of standing still, as it takes sometime for lubricant to reach the sealinglip/counterface contact. In such cases,direct contact between the shaft andlip increases, causing heavy wear or”stick-slip”. Leakage will result and thesealing lip will possibly be destroyed.

Where seals are not used to retainlubricant, grease or oil must be suppliedseparately to the sealing lip. In excep-tional cases, and where there are two

1sealing lips or an additional secondary(dust) lip, an initial fill of grease in thefree space between the two lips maybe sufficient.

The use of CR LongLife materials(fluoroelastomers and PTFE) or othersimilar wear-resistant lip materials isrecommended to compensate in partfor inadequate lubrication.

Temperature Both low and high temperatures affectseal performance. Typical rubbermaterials become hard and brittle atlow temperatures. When the lip be-comes stiff, it cannot prevent leakage nor contaminant penetration. The static sealing between the housingbore and the radial shaft seal may alsobe impaired, e.g. if the seal shell andhousing bore are made of differentmaterials which contract at differentrates in the cold.

For low temperatures, therefore, aseal lip material having special lowtemperature properties should be con-sidered, particularly if the seal is to be subjected to temperatures below −50 °C. To minimise the thermalcontraction problems outlined above, itmay be sensible to use a seal with anoutside diameter of elastomer.

The use of seals with a rubber out-side diameter is also recommendedwhere temperatures are high and thehousing is of a material which expandsmore rapidly than steel.

Friction, shaft speed, high fluid vis-cosity and heat transfer along the shaftall contribute to increased temperat-ures in the thin film of lubricant onwhich the sealing lip rides and cancause the lubricant film to break down.Lack of lubrication is one of the com-mon causes of early seal failure.

If it is not possible to reduce thetemperature in the lip/counterface contact zone, a new seal with differentlip material should be used. CR pre-mium seal lip materials, such as Long-Life fluoro rubber, have relatively highthermal and wear resistance and usu-ally last longer than nitrile rubber seals.

The environmentEven the best sealing mechanism between housing bore and seal out-side diameter as well as between seal-ing lip and shaft counterface cannotguarantee optimum seal performance.Besides these geometric considera-tions, the entire surroundings must be taken into account. Therefore, themost important environmental andoperating conditions will be briefly discussed.

Contamination Contaminants such as water, dust ormud do more than just prevent optimumseal performance. If they enter the bear-ing area they can pollute the lubricant,cause corrosion, wear and prematurebearing failure. To prevent bearingdamage, heavy-duty seals with thesealing lip facing the contaminants areused. If the amount of contamination isminimal and the function of the primaryseal is to provide fluid retention, then a V-ring or a seal with a secondary lipcan be used for exclusion.

Pressure Standard radial shaft seals performbest and last longest if the pressure onboth sides of the seal is the same. Theslightest amount of pressure increaseon the inside of the seal will cause thesealing lip to be pressed against thecounterface, thus widening the path ittraces. Friction will increase in the con-tact and heat will be generated. Therise in temperature will cause the sealto wear rapidly. An extreme excesspressure in the housing can even forcethe seal out of the bore. Permissible

Table

Differential Shaft speedspressure Rotational Circumferential

max permissible max

MPa r/min m/s

0,02 3 000 5,60,035 2 000 3,20,05 1 000 2,8

Permissiblespeeds underpressure

1

500

80 90 100 110 120 130 140

1000

1500

2000

2500

10

80 90 100 110 130

20

30

40

50

60

70

80

90

100

120

12

The seal

TemperatureSeal life as a functionof temperature

LubricantSeal life as a functionof lubricant

Relative seal life, %

Temperature under sealing lip, °C

Temperature, °C

LongLife fluoro rubber

Nitrile rubber

Test conditions

Seal: CRW1, nitrile rubberShaft diameter: 76,2 mmRunout: 0,13 mmDeviation from coaxiality: 0,13 mmNo. of seals tested: 150

SAE 30 fluidAutomotive oilto API GL-5

Mean seal life, h

Speed The maximum circumferential speed at the sealing lip at which the seal willstill perform efficiently is determined byseveral factors simultaneously. Theseinclude sealing lip material and design,shaft finish at the counterface, pres-sure, temperature, shaft eccentricity,lubrication and cooling of the sealinglip/counterface contact, and the pres-ence of any chemicals. General guide-line values for permissible speeds will be found in the table opposite (➔ Table ). The values given arevalid when a mineral oil provides goodlubrication, cooling is adequate, andthere is no pressure differential acrossthe seal.

2

Retained fluidThe chemical resistance of the seal tothe fluid which it is to seal is an import-ant selection criterion. If the seal lipmaterial is not compatible with the fluidto be retained, the seal will be unableto prevent leakage. Temperature is alsoimportant. As temperature increases,any chemical reaction will be acceler-ated and any aggressiveness will beheightened.

When the seal is to retain oil it shouldbe remembered that as temperatureincreases, the viscosity of the lubric-ating oil decreases. Some lubricantadditives may have detrimental effectson the seal materials.

Further information on the chemicalresistance of the seal materials used

by CR will be found in the SKF cata-logue 4006 “CR seals” which will besent on request.

Coaxiality and runout The eccentricity of the shaft is one ofthe many factors influencing the perfor-mance and life of a seal. It is expres-sed as deviations from coaxiality andrunout and should be kept as small aspossible, particularly in cases wherethere is a pressure differential acrossthe seal.

Coaxiality

Deviation from coaxiality is also refer-red to as shaft-to-bore misalignment(STBM) i.e. when the centrelines or

13

axes of the shaft and housing bore do not coincide and causes an unevenforce distribution around the sealinglip. One section of the lip will be moreheavily stressed, leading to an enlarge-ment of the contact of the lip with thecounterface and thus to prematurewear. The opposite section of the lipwill be unloaded and its sealing effi-ciency reduced.

Runout

Runout (dynamic runout, DRO) is thedynamic eccentricity of the shaft, or theamount by which the shaft does notrotate about the true centre. Particu-larly at high speeds, there is a dangerthat the sealing lip, because of its iner-tia, will be unable to follow the shaft. Ifthe distance between the sealing lipand the counterface on the shaft isgreater than that required to maintainhydrodynamic lubrication, leakage willoccur. It is therefore recommendedthat the seal be positioned as close tothe bearing as possible and that bear-ing clearance should be as small aspossible. Lip flexibility is important –the closer the lip is to the seal face, the smaller the runout which can betolerated. Thus, by selecting a suitableseal design and lip material, largerrunouts can be permitted.

Table

CR seals Circum-(Design) ferential

speedmax

– m/s

Radial shaft sealsCRS, HMS 14CRW, CRWA 18HDS 25HS 7,5 ... 12

Mechanical sealsHDDF 2

V-ring sealsWithout extra location/support 7With axial location 7 ... 12With support ring 10 ... 20

Axial clamp sealsCT 25

Permissible circumferentialspeeds

2

ing on the direction of rotation. Plungegrinding is a suitable method of avoid-ing directionality.

Tolerances The shaft diameter d1 in the counterfacearea should be machined to toleranceh11. Deviations from circularity shouldbe within IT8 (➔ Table ).

Shaft endsIn order to be able to install the sealwithout damaging the sealing lip, shaftends (as well as any shoulders) shouldhave a lead-in or radius (➔ Table ).The transitions should be burr-free andblended.

3

3

The shaftTo obtain reliable sealing and a suffi-ciently long service life, the counterfaceon the shaft for radial shaft seals shouldmeet the following requirements.

Shaft materialThe seals perform best on medium tohigh carbon steel which may be eitherthrough hardened or case hardened toa surface hardness of the counterfaceof 55 HRC or 600 HV, the case depthshould be at least 3 mm. Lower hard-ness can be permitted, for example,when circumferential speeds are low,lubrication is good, or contaminationabsent. Ceramic coated and chromiumor nickel-plated surfaces are alsoacceptable, provided they are finishedto the recommended surface rough-ness. Brass, bronze and alloys of alu-minium, zinc or magnesium are notrecommended.

Surface finishThe contact area between the sealinglip and counterface is of vital import-ance to sealing efficiency. The surfaceroughness to ISO 4288 of the counter-face should be kept within the followingguideline values:

Ra 0,2 ... 0,8 µm Rz 1 ... 4 µm Rmax 6,3 µm

The surface should not be smootherthan the lower limits for Ra and Rz asotherwise lubricant supply to the con-tact may be impaired. The rise in tem-perature which would result from this,particularly at high circumferentialspeeds, would lead to hardening andcracking of the seal lip and to prema-ture seal failure. If the surface is toorough, the seal lip will wear and seallife will again be foreshortened. If thevalue of Rmax is exceeded, the sealmay leak.

The surface should be machined sothat there is no directionality, as other-wise there is a risk of leakage, depend-

14

Table

Shaft Shaft diameter Circularity Chamfer dimensionsdiameter deviationsNominal (Tolerance h11) (Tolerance IT8) C rover incl. high low max min min

mm µm µm mm mm

10 0 −90 22 0,75 110 18 0 −110 27 1 118 30 0 −130 33 1,25 1,5

30 50 0 −160 39 1,7 250 80 0 −190 46 2 280 120 0 −220 54 3,5 4

120 180 0 −250 63 3,5 4180 250 0 −290 72 3,5 4250 315 0 −320 81 5,5 6

315 400 0 −360 89 5,5 6400 500 0 −400 97 5,5 6500 630 0 −440 110 6,5 7

630 800 0 −500 125 6,5 7800 1 000 0 −560 140 7 81 000 1 250 0 −660 165 7 8

1 250 1 600 0 −780 195 7 8

This corner must beburr-free and blended

The seal

Shaft tolerances:counterface/chamfer dimensions

15/30°C

r

3

Table

Housing bore/seal Bore diameter Seal outside diameter tolerancesoutside diameter deviation Steel RubberNominal (Tolerance H8)over incl. high low high low high low

mm µm µm µm

18 +27 0 +200 +80 +300 +15018 30 +33 0 +200 +80 +300 +15030 50 +39 0 +200 +80 +300 +150

50 80 +46 0 +230 +90 +350 +20080 120 +54 0 +250 +100 +350 +200120 180 +63 0 +280 +120 +450 +250

180 250 +72 0 +350 +150 +450 +250250 300 +81 0 +350 +150 +450 +250300 315 +81 0 +450 +200 +550 +300

315 400 +89 0 +450 +200 +550 +300400 500 +97 0 +450 +200 +550 +300500 630 +110 0 +500 +220 – –

630 800 +125 0 +500 +240 – –800 1 000 +145 0 +550 +250 – –1 000 1 250 +165 0 +600 +270 – –

1 250 1 600 +195 0 +650 +300 – –

The housing bore The requisite interference fit, the correctstatic sealing and proper seal installa-tion will be assured if the housing boremeets the demands outlined below.The following recommendations applyto housings of steel or cast iron.

Tolerances The bore in the housing (diameter d2)should be machined to tolerance H8(➔ Table ). The tolerances for theoutside diameter of the seal of steel orelastomer are included to enable theprobable interference between housingbore and seal outside diameter to becalculated.

Surface finishIt is recommended that the surfaceroughness to ISO 4288 of the housingbore should be kept within the followinglimts. For seals with rubber or Bore-Titecoated steel outside diameters:

Ra 1,6 ... 6,3 µm Rz 10 ... 25 µm Rmax 25 µm

and for seals with steel outside dia-meter without coating:

Ra 0,8 ... 3,2 µm Rz 6,3 ... 10 µm Rmax 10 µm

Lead-in In order for the seal not to be damagedwhen it is being installed, the leadingor entering edge of the bore should bemade according to the illustrationabove.

4

Bore-Tite coatingCR applies a coating of Bore-Tite tothe outside diameter of selected sealswith steel shells as standard. Bore-Titeis a water-based polyacrylate sealantwhich is green in colour. It is non-har-dening and fills slight irregularities inthe housing bore. In most cases theelastic Bore-Tite coating provides anadequate static seal between the sealoutside diameter and the housingbore.

Bore-Tite is resistant to most oils,greases, aqueous acids, alkalis, salts,alcohols and glycols. It is not compat-ible with aromatics, ketones or esters.

15

Chamfer width2,3 mm for 15°1,5 mm for 30°

This corner must be burr-free and blended

Housing bore andseal outside dia-meter tolerances

15/30°

4

This matrix can only provide a rough guide and the final seal selection shouldonly be made after a more detailed examination of sealing properties withrespect to the actual operating conditions and environment. If several seal desig-ns and materials are shown together then the ratings apply to the specifieddesign/material.

Signs and symbols+ + + Very well suited (very good) D Duralip (special nitrile rubber)+ + Well suited (good) P Polyacrylate elastomer+ Suitable (normal) R Nitrile rubber− Less suitable (satisfactory) V Fluoro rubber− − Unsuitable (poor) � Special design/execution

to order( ) Option

Seal types

16


Seal selection

CR seals are intended to seal the interface between a rotating and anon-rotating machine component or between components in relativemotion. Their purpose is to

– retain lubricant, – exclude contaminants, – separate fluids or gases, and – withstand differential pressures.

They should also perform efficientlywith a minimum of friction and wear incritical applications and where operat-ing conditions are unfavourable.

To meet the requirements, CR sealsare produced in many designs and different materials. Each different execution, because of its design andmaterial, exhibits special propertieswhich make it particularly suitable fora given application.

Many factors influence the choice ofseal. As well as the operating condi-tions, these include

– type of lubrication, – circumferential speed of the sealing

lip, and – coaxiality deviations and runout,

the choice is also affected by the en-vironmental conditions and how theyaffect the seal from chemical, mecha-nical and thermal points of view.

The available space, efficiency re-quirements and last but not least eco-nomic considerations must all be takeninto account when selecting a seal. Depending on the application, one ormore of the influencing factors willdominate. Therefore, it is not possibleto establish general rules for sealselection. The following recommenda-tions are intended to highlight the pro-perties of the various seal designs andto facilitate selection.

The matrix provides an overview ofthe seals, their design characteristics

CR Seals: design and properties

CRS1 CRSH1

CRSA1 CRSHA1 HMSA27

CRW1 CRWH1

CRWA1 CRWHA1

HDS1, 2 HDS3

HDSA1,2

HMS1

HMSA1, 2, 3

HMS4

HMSA7

HS5

HS6, 7, 8

Radialshaftseals

Ste

el

Ela

stom

er

Des

ign

Mat

eria

l

a =

rub

bing

b =

non

-rub

bing

Design

Shell (outside Sealing lip Secondarydiameter) (primary) lip

Mechanical seals HDDF R Steel

V-ring seals VR R (V) R (V)

Axial clamp seals CT R R

normal R, V

HMSA27normal R,V

a: CRS(H)ABore-Tite b: HMSA27

Bore-TiteWave-

R, V (P)seal

Bore-TiteWave-

R, V (P) bseal

normal R, D, V

normal R, D, V a

normal R

normal R a

R, V (P) normal R, V (P)

R, V (P) normal R, V (P) a

R, D, Vnormal R, D, V

one-piece

R, D (V)normal R, D (V)

split

and their suitability for different applica-tion conditions.

A more detailed presentation of theseals and their properties as well as the available range will be found in thecatalogue ”CR seals”. The matrix canonly provide a rather rough classi-fication of the seal designs as differen-tiation is limited by the number of sym-bols used.

17

Tig

ht fi

t

Rou

gh s

urfa

ce

The

rmal

exp

ansi

on

Spl

it ho

usin

g bo

re

Eas

e of

inst

alla

tion

Hou

sing

bor

e/ou

tsid

e di

amet

er

Sea

ling

lip/

coun

terf

ace

Slid

ing

spee

ds≤

14 m

/s

Slid

ing

spee

ds>

14

m/s

Tem

pera

ture

s≤

100

°C

Tem

pera

ture

s>

100

°C

Run

out

Coa

xial

ity d

evia

tion

Gre

ase

Oil

Mod

erat

e pa

rtic

ulat

eco

ntam

inat

ion

Hea

vy p

artic

ulat

eco

ntam

inat

ion

Med

ia

Suitability

Seating conditions Pressure Operating conditions Mediadifferential

+ + +− − − − + + − + − + V + + + + + + − V

CRSH

+ + + − − − − + + − + − + V + + + + + + + + V

CRSH

+ + ++ − − − + + +

+ + ++ + + + V + + + + + + + + − �CRWHA CRW5

+ + ++ − − − + + +

+ + ++ + + + V + + + + + + + + + + V

CRWHA CRWA5

+ + + − − − − + + + + + + + + V + + + + + + + + D V

+ + + − − − − + + + + + + + + V + + + + + + + + + + D V

+ + − − − − + + − + − + − − + + + + + − − − −

+ + − − − − + + − + − + − − + + + + + + + − −

+ + + + + + + + + − + − + V + + + + + + + − −

+ + + + + + + + + − + − + V + + + + + + + + V

− − + + + + + + + + + − − − − + V + + + + + + + D V

− − + + + + + + + + − − − − − + V + + + + + + + + D V

+ + + + + + + + + + + + + − − − − + − − − − − − − + + + + + + + + + − −

+ + + + + + + + + + − − − + V + + + + + + + + + + + + V

+ + + + + + + + + + + + − − + + + + + + − − − − + + + − −

Oil retentionGrease retention

18

Seal selection

Greases are generally easy to retain in a bearing arrange-ment because of their relatively high consistency. This, therefore, places comparatively small demands on the seal and most types of seal can be used.

Radial shaft seals without garter spring, e.g. the CR HMdesign, are very suitable where circumferential speeds arelow. They should be installed with their lip facing the grease,i.e. for bearing arrangements, the lip should point inwards.

However, spring-loaded radial shaft seals are equally suitable for grease retention. If frequent relubrication isrequired, it is recommended that at least one of the seals is mounted with its lip facing outwards. This enables excessgrease to escape past the sealing lip, thus preventing abuild-up of grease and the consequent generation of heat.In cases where it cannot be guaranteed that grease will besupplied to the sealing lip, it is recommended that a sealwith secondary lip is used and the space between the twolips filled with grease. Because of the unfavourable coolingconditions associated with grease lubrication, the permissiblespeeds are only approximately half those for the same seal,when it is used for oil retention.

In addition to radial shaft seals, without or with garterspring, V-ring seals and felt seals are also appropriate forgrease lubrication.

Lubricating oils, particularly those with low viscosity, aremore difficult to retain in a bearing arrangement than greases. Therefore, radial shaft seals with garter spring are used almost exclusively, e.g. CR seals of the CRW1 or HMS4 designs.

Where operating conditions are rough, contaminationheavy and circumferential speeds relatively low, mechani-cal seals of the HDDF design are particularly suitable.

In normal cases, CRW1 seals with a hydrodynamicallyformed Waveseal lip are adequate. This lip has a sinusoi-dally formed sealing edge which has an axial pumpingaction inwards as well as outwards, irrespective of thedirection of shaft (or housing) rotation. When the sealingposition should also be protected against dust or other finesolid contaminants, the use of a radial shaft seal withsecondary (dust) lip, e.g. of the CRWA1 design, is recom-mended.

V-ring seals can also be used to retain oil. They shouldbe arranged on the oil side and be axially supported on theshaft.

HM14 CRW1 V-ring Felt seal CRWA1 HMS4 HMSA7 HDDF

Exclusion

V-ring seals are excellent for keeping contaminants out.They rotate with the shaft, act as flingers, and seal against a counterface at right angles to the shaft.

When radial shaft seals are used primarily to excludecontaminants, the sealing lip should face outwards. Wherecircumferential speeds are low and operating conditionsnormal, virtually all types of radial shaft seal can be used.

Where operating conditions are unfavourable or arduous,the use of Waveseal designs with hydrodynamic sealingaids is recommended, e.g. of the CRW or heavy-duty HDSdesigns. To reinforce the sealing effect, two seals can bemounted in tandem or a double lip seal with the lips ar-ranged in tandem can be used.

Alternatively, a V-ring seal or CT axial clamp seal can bemounted outside the radial shaft seal. This prevents coarsecontaminants from penetrating to the sealing lip of the radialshaft seal. The sealing lip of the V-ring or axial clamp sealcan run against the face of the housing or against the backface of the radial shaft seal.

Contaminant exclusion and lubricant retention are oftenequally important. In many cases the use of a radial shaftseal of the CRWA design which has a secondary (dust) lipwill provide adequate protection.

Another way of solving the problem is to use two sealswith their lips pointing in opposite directions, e.g. two CRWor two HDS seals.

Highly efficient, double direction seals can be obtainedusing two opposing V-rings with an intermediate machinedthrust washer as the counterface for both seals.

For extremely difficult environmental conditions it is pre-ferable to use CR mechanical seals of the HDDF design,provided the sliding speed of the sealing surfaces is withinthe permissible range.

Exclusion/retention

19

V-ring CRW1 HDS2 CT3 2 × HDS3 2 × V-ring

��

In cases where it is necessary to separate two liquids fromeach other, two different solutions are available, the choicebeing governed essentially by the space available and bythe required sealing efficiency.

The first solution is to use two radial shaft seals with theirlips pointing in opposite directions (back-to-back).

The second is to use radial shaft seals of the HDSD or D designs which also have their two lips pointing in differentdirections.

Radial shaft seals used for the separation of two liquidsmust always have spring-loaded lips. Where there is a riskthat one or both sealing lips can run dry, it is recommendedthat the space between the two lips is filled with a rollingbearing grease which will then provide an adequate lubric-ant film.

Special radial shaft seals are usually required if there is aconsiderable differential pressure across the seal. Standardseals can normally only withstand differential pressures of0,07 MPa maximum, and only at relatively low circumferen-tial speeds.

CR radial shaft seals of the CRWA5 and CRW5 designsare able to withstand pressure differentials of up to 0,63 MPaat circumferential speeds of up to 5 m/s.

When a seal is under pressure, the sealing lip will bepressed harder against the counterface so that friction andtemperature will increase in the contact. If speeds are high,this will lead to accelerated wear which will considerablyshorten the life of both seal and counterface. It is thereforenecessary to balance pressure and circumferential speedagainst each other in such applications.

Occasional pressure differentials may make the use of asecond seal necessary. A radial shaft seal can be used withits lip directed towards the higher pressure, or a V-ring, withits lip pointing towards the low pressure side is also suitable.

Where differential pressures exist, it is necessary to pro-vide some form of axial retention for the seal at the low pres-sure side to prevent it from being pressed out of the housingbore. Where standard seals are used, it is also advisable toprovide support for the sealing lip so that the force on it pro-duced by the excess pressure will be reduced.

Containing high pressureSeparating two liquids

20

Seal selection

2 × CRW1 HDSD2 CRW5 CRWA5 HDW1 HDS3

Restricted space

Often the available space is insufficient for a standard radialshaft seal. A special seal design with narrow shell or lowcross section is required, or a V-ring seal can be fitted out-side the seal cavity.

Where radial and axial space are limited and large-dia-meter shafts are involved, radial shaft seals of the HS designcan be used.

For cases where a V-ring can be used, an economic seal-ing arrangement will be achieved; the V-ring seals are verysimple to install. The V-ring seals axially, exerting a lightpressure on the counterface, which may be a stationary, oreven rotating, machine component.

Installation restrictions

Where it is difficult, or even impossible, to install a seal eitherduring assembly or maintenance, by passing it over the endof a shaft, V-ring seals, or split radial shaft seals of the HS6,HS7 and HS8 designs may be the solution.

These are all-rubber seals without any reinforcement andare easy to install. Once on the shaft they are held togetherby the garter spring which is joined by a control wire or threaded connector, or by a hook and eye. They should beaxially secured in the housing bore by a cover plate, whichmay be either split or in one piece.

Split HS seals, depending on their design, are suitable for circumferential speeds of up to 7,5 to 10 m/s. They areavailable for shaft diameters from 170 to 4 500 mm (approx-imately).

The V-ring seals are elastic and can be stretched. Theymay therefore be mounted by stretching over other compon-ents. If, however, the exchange of a V-ring seal entails thetime-consuming dismounting of various components it isstrongly advisable – where the particular bearing arrange-ment permits – to mount one or two spare seals on the shaftduring the initial assembly. In this way the worn V-ring caneasily be removed by cutting and the replacement ringquickly and simply located in the desired position.

21

HMS1 HS5 HS8 V-ring CRWH1 HDS3 V-rings

��

Guidelines for proper installation

❏ Check that the dimensions of the selected seal match those of shaftand bore.

❏ Check the new seal for any damage (dents, scores or cuts). Never usedamaged seals. Carefully clean the seal if it has become dirty.

❏ Chamfer and blend the housing bore corner to prevent damage to theoutside surface of the seal.

❏ Check to see that the counterface on the shaft is undamaged (no bruises, scratches, cracks, rust or raised areas).

❏ All shaft edges over which the seal has to be passed must be cham-fered or rounded.

❏ Lightly grease or oil the seal before installation.

❏ After installation, check to see that other machine components or shaftshoulders do not rub against the seal.

Seal installation

No matter how well constructed a sealis, or how well suited it is for an applica-tion, incorrect installation will prevent itfrom performing properly. In fact, im-proper installation resulting from lackof knowledge or care (including clean-liness) is the most common cause ofpremature seal failure.

Since radial shaft seals should havean interference fit in the housing bore,the use of a mechanical or hydraulicpress with suitable accessories is re-commended when mounting. It is veryimportant that the pressure is appliedevenly around the whole circumferen-ce of the seal and preferably as closeas possible to the outside diameter. Ifa suitable press is not available a soft-faced mallet and bearing cup or mount-ing dolly can be used. Blows to theseal itself should be avoided, so as not to damage the sealing lip. It is alsopossible to use a wooden block andhammer to drive the seal home.

22


23

After installationOnce radial shaft seals have beeninstalled, care should be taken to seethat they do not become contaminated,e.g. with paint, if the equipment is tobe painted. This also applies to thecounterface area on the shaft. Theseals can be protected during paintingby cardboard discs, for example. Anyhousing vents should also be maskedso that they do not become clogged.After painting has been completed, allthe masking material must be removedbefore operating the equipment.

If painted or lacquered equipment isto be baked or unpainted equipment isto be heated for any reason, careshould be taken not to apply directheat to the seals and to ensure thatthey are not heated to a higher temper-ature than the maximum permissiblefor the material.

If seals have to be cleaned, e.g. forinspection, warm soapy water (notabove 30 °C) can be used, and theseals should be allowed to dry at roomtemperature. Solvents such as trichloro-ethylene, carbon tetrachloride or hydro-carbons should be avoided. Sharp-edged objects, wire brushes, emerycloth, sand paper etc. should not beused.

If no suitable tools are available, a woodenblock and hammer can be used. To avoidskewing of the seal the blows should beapplied centrally.

As the seal outside diameter is slightly larger than the housing bore, the use of apress and mounting tool is recommended,so that the force can be applied evenlyaround the seal and that the seal will beproperly seated in the bore.

Before installing the seal, check that housing bore and shaft are clean and apply lubricant to seal.

to select a suitable size of sleeve. Provided the mean value is within thediameter range of the sleeve, it willhave a sufficient interference fit on theshaft and will not wander. No adhesiveis required.

LDSLV repair sleevesFor larger shafts (from approximately200 to approximately 1 250 mm dia-meter) LDSLV repair sleeves are avail-able. These are made of high-strength,hot-rolled steel, are surface treated, andhave a hardness of 96 HRB. The wallthickness is 2,4 mm. The outside con-tact surface for the seal is fine machin-ed and chromium plated to enhance itswear and corrosion resistance.

There are two alternative ways ofemploying LDSLV repair sleeves. Eitheran appropriate sleeve is mounted onthe shaft over the damaged counter-face, and a seal which has a 4,8 mm larger bore than the original used asthe replacement, or the shaft can bemachined down by 4,8 mm. In this latter case the original size of seal canbe used as the replacement.

When replacing seals, the counterfacearea on the shaft should always bechecked for wear and other damage.Excessive water, heavy contamination,high temperatures, inadequate seal liplubrication and high speeds can allcause the seal lip to wear a groove inthe counterface. Once this has happen-ed, simply installing a new seal will notprevent leakage, and the shaft mustbe repaired. This may involve costlyreworking of the shaft which normallymeans dismantling the equipment and attendant downtime. CR Speedi-Sleeves have been designed to pro-vide a fresh counterface surface inminutes. They are simply pushed overthe damaged counterface making theshaft as good as new at a minimumcost.

Speedi-SleevesThese shaft repair sleeves are extreme-ly thin-walled and enable the originalseal size to be used. It is not neces-sary to keep extra seal sizes in stock orto make special records. The standardSpeedi-Sleeve range is for shaft sizesof 12 to 200 mm diameter. All sizeshave a wall thickness of 0,254 mm.The sleeves are made of high qualitystainless steel and have a hardness of95 HRB. The surface finish lies betweenRa = 0,25 and 0,5 µm and is withoutmachine lead (directionality). In manycases they provide a better counterfacefor the sealing lip than the original shaftseating. Normally, the Speedi-Sleevecan be mounted directly on the cleanedshaft, but if the surface is scored orotherwise damaged, it may be benefi-cial to apply an epoxy filler just beforethe Speedi-Sleeve is installed.

To determine which size of Speedi-Sleeve to use, the shaft should be care-fully cleaned and the diameter meas-ured in three planes at 120° at an undamaged position. The arithmeticalmean of these measurements is used

24


Repairing worn shafts

Use the average of three shaft diametermeasurements taken in planes at 120°when selecting sleeve size

Place flanged end of Speedi-Sleeve on toshaft first

Gently apply the installation tool (suppliedwith sleeve) over the sleeve until it abutsthe flange.

Gently tap the centre of the installation toolusing a soft-faced hammer or mallet untilthe sleeve reaches its correct position.

When the sleeve has been correctly posi-tioned, the flange can be removed if de-sired.

25

26


Seal maintenance

When to inspect and replace Unlike bearing life, seal life cannot becalculated. The purpose of seals is to contain lubricants and exclude con-taminants, and their role is sacrificialwhen they are used to protect bear-ings, i.e. they are used to help the bear-ing achieve its required life. As sealfailure is almost entirely governed byenvironmental conditions, the only “lifeformula” which can be applied to sealsis experience.

As the environment plays such adominant part in determining seal life,and as the amount of contaminationthe seal encounters influences its use-fulness, it may be expected that a sealoperating in a dirty, dusty environment,or one subjected to routine wash-downswill not last nearly as long as a sealused in a clean, dry environment.

Machine operating cycles, shaftspeeds and operating temperatures all influence maintenance and replace-ment intervals. One thing is certain,however, and that is that seals are thecomponents of a bearing arrangementwhich keep lubricant in the arrange-ment and keep it clean so that longbearing life can be realised.

Seal replacement should not auto-matically entail simply replacing theseal with a new one of exactly the samedesign. If it is found that the oil has become dirty, for example, it may beworthwhile upgrading the whole sealingarrangement. A tougher, more chemi-cally resistant material may be calledfor, or additional sealing elements maybe required to ward off contaminants.

Generally speaking, a seal shouldbe replaced just as soon as the firstsigns of wear or leakage are discovered.

There are other causes of prematureseal failure besides contamination.

Improper installationA common cause of early failure arisesduring installation. The seal may be

allowed to get dirty, the lip is not pro-perly lubricated at the start, correcttools are not used, or the seal is notproperly seated in its housing. Theseproblems can be rectified through pro-per training in mounting procedures.

Change of lubricant Frequently, new lubricants with addit-ive packages are introduced with aview to extending service intervals formachinery and equipment. However,many of these additives can producenegative reactions in the sealing ma-terials. If rapid seal failures suddenlystart to occur where none has beenexperienced before, the cause may bea changeover to an “improved” lubric-ant.

Wrong replacement seal A simple error in taking the wrong partnumber or designation can result insudden “mysterious” seal failure, e.g. anitrile rubber seal might be installedinstead of a much more resistant fluororubber seal, although the design isotherwise identical.

Wrong seal choiceThe choice of a seal which is unsuit-able for the particular application isalso a cause of premature seal failure.A systematic investigation of such sealfailures by an expert will soon exposethe cause. If adequate experience isnot available in-house it is advisable toeither conduct trials or to contact SKFfor assistance with the selection.

27

❏ The seal should be properly stored in a cool, dust-free, moderatelyventilated room, preferably at temperatures of between +15 and +25 °Cand a relative humidity below 65 %.

❏ The original packaging should be intact and the seal should be keptlying down in the original packaging until immediately before use.Seals should never be hung from pegs or nails.

❏ The correct installation tools should be available.

❏ The work area should be clean and protected against dirt from theenvironment.

❏ The chosen seal should be checked to see that its maximum permiss-ible circumferential speed will not be exceeded.

❏ The chosen seal should be checked to see that it can withstand themedia involved.

❏ The chosen seal should be checked to see that it is suitable for theoperating temperature.

❏ The lubricant to be used (including additives) must be compatible withthe seal material.

❏ The counterface region of the shaft should have a hardness appropri-ate to the application, but at least 35 HRC.

❏ The counterface should be machined to tolerance h11 and have a formtolerance to IT8.

❏ The surface should have a roughness Ra of 0,25 to 0,5 µm and be without machine lead.

❏ The shaft end and any edges over which the seal must pass, should bechamfered or rounded.

❏ The housing bore should be machined to tolerance H8.

❏ The housing bore should have a lead-in of up to 30° to facilitate mount-ing.

❏ The deviation from coaxiality should be within the permissible limits(e.g. max. 0,25 mm for a shaft diameter of 75 mm).

❏ The runout should be within the permissible limits (e.g. max. 0,25 mmfor a shaft diameter of 75 mm).

❏ Whenever possible, the equipment should be vented to minimise thepressure differential across the seal.

By checking the points listed and follow-ing the advice, the service life of theseal, and of any bearing it protects, willbe maximised. For additional informa-tion on the selection and use of seals,please contact SKF.

Seal check list

29

A brief history of CR Industries

CR Industries was founded inAmerica in 1878 as ChicagoRawhide. The company cured or

tanned hides, which were natural by-products of the busy Chicago stock-yards, and turned them into rawhide

leather belting. These were the beltsthat literally drove the industrial development of the AmericanMidwest.

In the early 1900s CR worked closely with Henry Fordand other automotive pioneers to produce leather productsfor early automobiles. In 1928, the company patented thefirst self-contained shaft seal, initially designed for use inautomobile wheel hubs.

In the mid-1930s, CR pioneered the development ofcustom formulating, compounding and moulding of elasto-mers (synthetic rubber) to develop higher performance sea-ling materials. This produced other innovations in manufac-turing processes, new sealing techniques and expandedindustrial applications.

Today, CR is the world’s leading supplier of fluid sealingdevices for the truck, automotive, agricultural machinery andmachine tool industries. CR also produces seals foraerospace applications, earth moving equipment, house-hold appliances and a wide variety of pumps, hydraulicsystems, motors and sub-assemblies.

The CR range comprises more than 200 types of seal,over 3 000 stock sizes and over 10 000 variants for the shaftdiameter range of 3 to 4 500 mm. CR has an ongoing pro-gramme of work to improve the performance and reliabilityof their products. New sealing units, for example, for theautomotive industry, and the development of new materialsand processes will further expand the range of applications.

CR has received quality manufacturing awards from morethan 200 companies. The company has been part of theSKF Group since 1990.

development has also played a vitalrole, resulting in many examples ofepoch-making innovations.

The business of the Group consistsof bearings, seals, special steel and acomprehensive range of other high-tech industrial components. The experi-ence gained in these various fieldsprovides SKF with the essential know-ledge and expertise required in orderto provide the customers with the mostadvanced engineering products andefficient service.

SKF is an international industrial Groupoperating in some 130 countries and isworld leader in bearings.

The company was founded in 1907following the invention of the self-align-ing ball bearing by Sven Wingquist and,after only a few years, SKF began toexpand all over the world.

Today, SKF has some 42 000 em-ployees and more than 80 manufactur-ing facilities spread throughout theworld. An international sales network includes a large number of sales com-panies and over 7 000 distributors andretailers. Worldwide availability of SKFproducts is supported by a compre-hensive technical advisory service.

The key to success has been a con-sistent emphasis on maintaining thehighest quality of its products and services. Continuous invest-ment in research and

30

The SKF Group – a worldwide corporation

31

The SKF house colours are blue and red,but the thinking is green. The latest exampleis the new factory in Malaysia, where thebearing component cleaning process con-forms to the strictest ecological standards.Instead of trichloroethylene, a water-basedcleaning fluid is used in a closed system.The cleaning fluid is recycled in the factory'sown treatment plant.

The SKF Engineering & Research Centre is situated just outside Utrecht in TheNetherlands. In an area of 17 000 squaremetres (185 000 sq.ft) some 150 scientists,engineers and support staff are engaged inthe further improvement of bearing perform-ance. They are developing technologiesaimed at achieving better materials, betterdesigns, better lubricants and better seals – together leading to an even better unders-tanding of the operation of a bearing in itsapplication. This is also where the SKF NewLife Theory was evolved, enabling thedesign of bearings which are even morecompact and offer even longer operationallife.

SKF has developed the Channel concept infactories all over the world. This drasticallyreduces the lead time from raw material toend product as well as work in progressand finished goods in stock. The conceptenables faster and smoother informationflow, eliminates bottlenecks and bypassesunnecessary steps in production. TheChannel team members have the know-ledge and commitment needed to share theresponsibility for fulfilling objectives in areassuch as quality, delivery time, productionflow etc.

SKF manufactures ball bearings, roller bearings and plain bearings. The smallestare just a few millimetres (a fraction of aninch) in diameter, the largest several metres.In order to protect the bearings effectivelyagainst the ingress of contamination andthe escape of lubricant, SKF also manu-factures oil and bearing seals. SKF's subsidiaries CR Industries and RFT S.p.A.are among the world's largest producers of seals.

© Copyright SKF 1995Publication 4293/I EReg. 751 · 8 000 · 1995-03

Documents

Sealing Arrangement Design Guide