radial shaft seals ftl seal technology

8/12/2019 Radial Shaft Seals Ftl Seal Technology

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Freudenberg Group

www.simrit.com

30EN2

525.5

0408Trurnit/BoschDruck,

Landshut

Freudenberg Group

The SimmerringReliability right from the beginning

TheSimm

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Basics

forpreventing

damage

ErichPrem

Rol

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Basics for preventing damage

Y o u r T e c h n o l o g y S p e c i a l i s tY o u r T e c h n o l o g y S p e c i a l i s tY o u r T e c h n o l o g y S p e c i a l i s tY o u r T e c h n o l o g y S p e c i a l i s t


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The Simmerring

Reliability right fromthe beginning



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1. Reliable sealing

2. Shaft surfacesRequirements and working forms

The SimmerringErich Prem Rolf Vogt


Reliability right from the beginning


4/55 Freudenberg Simrit GmbH & Co. KG

Freudenberg Simrit GmbH & Co. KG reserves all rights, especially copyright and the registration

of industrial property rights. Please observe that this document contains company secrets and anyreproduction or dissemination to third parties may only occur through us.

Protective charge: 10.00 Euro

4



Simrit and the Simmerring A 75 year success story

The Simmerring is a universal sealing

component. Its applications range from

agricultural and construction machinery, to two

and four stroke engines in chain saws and

motorcycles, as well as hydrostatic drives in

machine engineering to washing machines

and wind power plants. Simmerrings have the

combined role of sealing a rotating shaft and

a housing from oil loss and preventing theintrusion of moisture and dirt.

To do this, the sealing ring, lubricant and the

shaft surface must be precisely matched to

each other. Because both lubricants as well

as shaft surfaces come in countless designs,

the interplay of the Simmerring with these

components is determined by a multitude of

Dipl.-Ing. Rolf VogtManager Product DevelopmentIndustry

Erich PremProduct DevelopmentIndustry

parameters. The complex interplay of sealing

component, rotating shaft and lubricant not

only present the engineers and technicians at

Simrit with great challenges, they also present

particular challenges to the user. Many

instances of damage and dysfunction arise

simply due to incorrect or at least improper

handling of the Simmerring during installation.

This book will help to clarify the technical

possibilities of the Simmerring component and

its function in the "tribological system". In this

way, production losses caused by improper

handling or its suboptimal application can beavoided. In the first part, possible causes of

failure will be discussed and detailed examples

of damage will be presented. In the second

part, the requirements placed on the shaft

surface will be looked at in depth and how

the current surface treatment processes are

suited to the interplay with the sealing

component will be shown.

Over 75 years ago, Walther Simmerdeveloped the Simmerring at Freudenberg in

Weinheim on Bergstrasse. Over the last 75

years, the sealing component has been

continuously improved and optimised for new

application areas. The resulting wealth of

experience at Simrit is unique and makes this a

book from the experts.



1. Reliable sealing

How a Simmerring functions 10

Leakage definition 11 Analysis of leakage causes 13

Damage scenarios 18

Handling and installation 25

Troubleshooting 31

Summary 37

2. Shaft surfaces Requirements and working forms

Shaft surface requirements 40

Surface treatment process 41

Leading test 53

Summary 55

Supplementary literature 56

Contents

7


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1. Reliable Sealing


9/55 Freudenberg Simrit GmbH & Co. KG10

The sealing effect of a Simmerring is based

on a simple yet ingenious principle: Through

an intelligent interplay of geometry, material

and manufacturing process, a component is

created that works like a microscopic pump.

This "micropump" not only transports fl uids or

gases under the sealing edge, it can also

transport contamination particles as well.

It is also capable of delivering microscopically

small leakages back into the space to be

sealed. This phenomenal characteristic is the

reason why even the most varied types of seal

disturbance variables can be compensated

for to a certain extent (depending on the

specifications of the seal disturbance

variables), such as

Irregularities in the shaft topology

Shaft eccentricities

Housing misalignment

Skewed installation in the housing (wobble).

It is exactly this defined leakage that is

necessary for a Simmerring to achieve

sufficient lubrication and thus a long

operating life.

Fig. 2: Active principle of a Simmerring (schematic)

Gas orfluid entry

Meniscus

Sealing edge

Seal gap

Lubricant entry

Conveyance effect

Access of air

Contact pressure Contact width

Gap height

Sealing zone temperature

Fig. 1:Simmerring in thetribological system

Dust lip

Grease fillingShaft surface shear

Lubricant

How a Simmerring functions

Reliable sealing



Leakage definition: the standard,leakage terms, cause, classificationUsing standard test conditions, the lack of tightness is determined by the amount of the sealed fluid - over andabove any moistness which may occur in normal operating conditions which gets past the sealing edge and canbe collected and measured, when the seal is run for a definite time on a test-rig. This collected and measuredamount of media from the test-rig experiment is defined as the leakage.

A certain amount of leakage is

advantageous for a good long-term

seal but is usually no longer tolerated by

today's users. In practice, it is not always

easy to clearly classify the leakage of a

radial shaft ring. The following defi nitions

should assist:

SealedNo detectable moisture at the seal.

MoistIn the case of normal operating conditions,

a fi lm of moisture present on the sealing

edge area which, however, does not exceed

the back face of the seal.

WetA fi lm of moisture exceeding beyond the

back face with drop formation but not yet

dripping.

Measurable leakageDetectable, small rivulet on the outside of the

seal housing, originating from the back faceof the seal. If radial shaft seals clearly

exhibit leakages (e. g. 1 g/day), these

continue to increase with increasing running

time in approx. 80 % of the cases.

Short-term leakageShort-term fault of the sealing system, e. g.

caused by small dirt particles under the

sealing edge which are removed duringfurther operation (affects approx. 20 % of

leaking radial shaft seals).

Apparent-leakageTemporary leakage that is usually traced

back to over-greasing between sealing lip

and dust lip. For further information, read

DIN 3760 or DIN 3761 respectively as

well as from ISO 6194, in which releaseprocedures in conjunction with leakage

classes are described (supplementary

literature 11).

The cause of measurable leakages can be: Various elongations of seal and housing on

the static side for non-compliance with

tolerances

Material tears, particularly in the sealingedge caused by excessive thermal load

during operation

Leakage definition



Hardening of the elastomer caused by

excessive thermal/mechanical loadand/or incompatibility with the medium

to be sealed

Softening of the elastomer as a result

of swelling from the medium to be

sealed leading to premature wear

of the seal

Corrosion of the shaft underneath the

sealing edge and permanent malfunction

of the sealing system

Failure of the lubricant with dry running

and rapid lip wear as the consequence

Ageing of the pairing elastomer medium

to be sealed

Formation of "oil carbon" in the sealing

edge area which fl oats up resulting

in the malfunctioning of the sealing

systemVibrations in equipment assembly and

shaft, which cannot be followed by the

sealing lip

Permanent ingress of contamination on

the sealing lip from the inside or outside

which results in premature wear to the

sealing lip

Premature wear of the sealing lip through

non-compliance with regulations for thedesign of the running surface on the shaft

(see page 15: The shaft)

Damage to the sealing edge during

transport, handling or installation

These causes are to be analysed and appraised

depending on the running time as early failure,premature failure, failure during the operation

or at the end of the part's sealing lifespan.

Classification of occurring leakagesFor monitoring production parts according

to DIN 3761, the leakage classes according

to table 1 are to be used. Deviating test

conditions are to be agreed upon. In

addition, the so-called zero-leakage with test-

rig tests of 240 h with 12 specimens can be

arranged for release for construction, or for

critical installation locations with special

safety requirements. These zero-leakages can

be subdivided according to the following

criteria:

In the course of normal operating conditions,film of moisture at the sealing edge only

Film of moisture over the sealing edge

area but not passing beyond the back

face; no formation of droplets

Film of moisture passing beyond the back

face and/or formation of droplets, but no

dripping occurs

In tests on assemblies and vehicles, zero-leakage defines that state of the radial shaft

seal during static and dynamic conditions

where the sealed medium does not leak

beyond the outer side of the radial shaft seal.

Table 1:Leakageclasses

Leakage class max. permissible leakage max. permissible leakage per radial shaft seal per 12 radial shaft seals

1 1 g 3 g 2 2 g 6 g

3 3 g 12 g

Leakage definition



Analysis of leakage causes:Static and dynamic leakageTwo kinds of leakage are distinguished with radial shaft seals: Static leakage, which is possible on the press fit andon the sealing lip, and dynamic leakage, which only occurs on the sealing lip.

Upon examining prematurely failing radial

shaft seals (with < 100 operating hours or an

operational performance < 10,000 km) in

detail, failure can be subdivided in the

following way:

30 % attributable to an improper shaft

preparation method [see chapter shaft

treatment/handling]

30 % attributable to an improperinstallation

10 % attributable to a faulty seal [damage

symptoms DIN 3761, part 5]

15 % attributable to apparent-leakage/

premature leakage

15 % attributable to other causes such as

lubricant incompatibility/excessive

temperatures/vibrations/contaminants

Most failures can be avoided through

corresponding installation training or

consulting with regards to the correct shaft

surface preparation method. It is important thatseal and aggregate manufacturers as well as

users are co-operative and that they proceed

systematically with the fault analysis. It can be

Fig. 3: Possible causes of failure for radial shaft seals

Leakage causes



more difficult to determine the causes of

leakage from seals that have already been inoperation over a longer period of time

(months/years or e. g. > 100,000 km). There

are a number of infl uencing parameters and

whose interplay can affect the medium-term

and long-term sealing effect of a radial shaft

seal. The chart [see Fig. 3, page 13] has

proven itself as a sensible analysis instrument

for determining the cause of damage. Using

this diagram, the causes of failure can be

systematically narrowed down. It is important

to know that there is almost never only one

cause of a leak. The interplay of multiple

factors normally leads to leakage. In approx.

80 % of the cases, the cause of failure can be

directly seen on the seal and the shaft. It is

therefore without a doubt of great advantage

for the seal manufacturer to be able to get allthe relevant information on each failure, but

above all to receive the actual seal and shaft

themselves for damage analysis.

You can find the "technical data analysis" form

sheet at www.simrit.de/Schadensanalyse which

summarises the most important information

required for processing a damage claim.

The following describes the most importantcauses of leakage and the corresponding

corrective measures in more detail:

Static leakage at the press-fitThe housing bore is too rough which is

especially critical in Simmerring B1 seal

designs. Nominal:

Rmax

< 6.3-16 m for B1 design

(metallic outer case)R

max< 10 -25 m for BA design

(rubber coated outer case)

Sharp-edged chamfer area and/or too

steep a chamfer angle on the housing boreSimmerring B1: develops longitudinal

furrows

Simmerring BA: elastomer can be sheared

off

Static leakage at the sealing lipShaft is too rough, possibly with

longitudinal furrows caused by the

insertion of a bearing.

Damage to the sealing lip caused by

sharp-edged chamfer or feathered key

groove on the shaft in the sealing lip area

For radial shaft seals with return pumping

action (single or alternating leading), the

sealing lip can be so greatly released

(already at pressures > 0.3 bar ) so that

it only lies on the helix (with non-ventilated housings)

Shaft diameter is too small and/or the

housing misalignment is too great.

Chamfer at the shaft is too small or too

steep so that the sealing lip can tip over

or turn under and the spring can come

off [compare Fig. 3, page 13]

Comment:In dynamic operation of radial shaft seals,

these imponderables can increase the

leakage.

Dynamic leakage at the sealing lipDynamically caused leakages at the

sealing lip occur much more frequently

than static leakages. Hence the causes

are also more complex.The most important infl uencing

parameters are:

Leakage causes



The shaft

Sharp introduced chamfering, scratches,e. g. caused by a bearing that was drawn

onto the shaft [compare Fig. 31, page 23]

Blow holes in the running track area of the

radial shaft seal (pores with a diameter

< 0.05 mm are permissible)

Too smooth or too rough a shaft surface

which can lead to high seal lip wear

An undefined leading of the shaft [compare

Fig. 63, page 53]

can lead to radial shaft seal failure in a very

short amount of time. The shaft surface

topology in particular must be given complete

attention.

The following roughness values must be

adhered to:

Ra0.2 - 0.8 m

Rz1 - 5 m

Rmax

< 6.3 m

These roughness values ensure minimal

sealing edge wear of the radial seal shaft

independently from the machining method

and normally independent of the operatingconditions. Shaft surfaces created through

plunge-cut grinding very often exhibit helical

structures that can lead to leakages within

just a few rotations of the shaft. Measuring

these damaging helical structures is not

easy. In practice, the "thread method" is a

proven method. But not all structures can be

easily measured using this method. Using

new measuring methods, these surfacestructures can nowadays be precisely

detected and thus the relevant grinding

process parameters can be selectively

modified [Supplementary literature 7, 9, 10].

The lubricantsNot all lubricants can be easily sealed. The

complex makeup of the lubricants, the

interaction of the individual additives with

each other and the unavoidable interactions

with the elastomer of the radial shaft seal

can lead to:

Radial shaft seals being chemically

attacked especially at the sealing edge

(Formation of bubbles and fi ller metal

erosion occurrences or even

depolymerisation).

Lubrication additives being deposited at

the shaft in the immediate vicinity of the

sealing lip, developing into hardenedaccumulations with the result being that

even the slightest axial movements of the

shaft cause excessive seal lip wear.

Oil carbon directly on the sealing edge of

the radial shaft seal due to thermal

overloading of the lubricant, caused for

example by high circumferential shaft

speeds, insuffi cient heat dissipation, poor

lubrication of the sealing edge, incorrectlubricant or seal selection. These deposits

can cause tears in the sealing edge,

which signifi cantly alter the seal itself or

simply blister during operation leaving

holes behind.

Radial shaft seals not being lubricated

suffi ciently despite suffi cient supply of

lubricant and thus wearing faster. This

phenomenon can occur especiallywith synthetic lubricants based on

polyalphaolefi n or polyglycol.

Leakage causes



Operating conditions and environmental effectsWhen early failure of radial seal rings occurs,

an incorrect seal selection or critical

operating conditions are often responsible for

the malfunction. A few practical examplesshould make this clear.

TemperatureThe temperatures directly at the sealing edge

of a radial shaft seal are often underesti-

mated. Depending on the circumferential

speeds, oil sump temperature, lubricant,

lubricant supply and seal concept, the sealing

edge temperature can be from 20 C to40 C above the oil sump temperature and in

extreme cases even 60 C (!) above the oil

sump temperature.

PressureWhen aggregates are not ventilated, a

pressure build-up in the housing can occur

due to thermal expansion and the continuous

air conveyance of the radial shaft seal("micropump"). The pressure increases the

seal lip contact pressure. The thermal

loading of the elastomer and the lubricant as

well as the mechanical load increase. The

results are an increased seal lip wear and

reduced running times.

ContaminationMany radial shaft seals fail due to

contamination, even if they have survived the

first hours of operation trouble-free. It is not so

much the contamination present in the inner

part of every aggregate (form sand, wear

debris from rotating parts), but rather the

external contamination stirred up in the

proximity of the seal. The particles can bedrawn into the sealing gap, accumulate there

and may eventually end up underneath the

sealing edge. Not only does the wear of the

seal lip and shaft (shaft running-in) increase, it

can cause the seal lip to loosen enough so

that the lubricant can pass through the seal

gap and reach the surrounding area

unhindered.

The radial shaft seal itselfNaturally, the radial shaft seal can also be

Fig. 4:Housing and

shaft design

Edge roundedand polished

Edge rounded

1525

1525

Leakage causes



responsible for the leakages. Assuming

the correct material selection and thecorresponding profile design are correct, it is

almost exclusively inhomogenities on the

sealing edge that cause a leakage.

An important aid is the testing of the sealing

edge footprint on a glass mandrel. The radial

shaft seal is pulled onto a glass mandrel,

which has the nominal diameter of the shaft

and the sealing edges system is tested. If the

footprint of the sealing edge on the glass

mandrel is homogenous and is closed

completely, the possibility of a self-caused

leak by the radial shaft seal itself is quite low.

Such inhomogeneities can be caused by:

An instable manufacturing process

Materials inhomogeneities

(manufacture-related)Agglomerisation of fi llers

Tool contamination

Improper handling after forming (among

others things)

Further features that should not be present

on radial shaft seals are mentioned in from

the DIN 3761, part 7.

Claims are often made for leaking radial

shaft seals on which there are no noticeable

irregularities and which are practically in

a new state. A positive test run in the

laboratory usually confi rms the assumption

that the seal itself is in a faultless state so

that the cause of the failure generally

focuses on two points:

On the shaft or its surface structure. This

can generate leakages very rapidly.

Approx. 30 % of all early failures are

caused by an improper installation

[See pages 38 ff. for more information.]

No damage,pores, scratches

RoughnessRmax

Rz

Ra

Rp

Shaft surface topography:Grinding, finish rolling,machining in hardened material

Leading freedom

Sufficient corrosion

protection

Fig. 5: Shaft design requirements as counter direction point of the Simmerring

Wear-resistance: Abrasion,adhesions, surfacedamage, tribo-oxidation

Precise concentricity

Cost-efficient manufacturing

Utilisation through themedium

Good heat dissipation

Leakage causes



Damage scenarios: Examples of damageThe damage scenarios show examples of the most important causes of leakage that lead to the failure of theradial shaft seal. With their help, it is possible to narrow down the causes of leakage in each case.

Fig. 6: Design of a Simmerring

Back face

Metal insert

Dust lip

Membrane

Back abutment contact surface

Static part, outside diameter

chamfer

Inner liningFront side

Spring

Spring retaining lip

Front sidecontact surface

Sealing edge

Sealing edge:Pre pressed

Trimmedbi directional helixUni directional helix

The sealing edge must be completely closed.The lead impression must be clean as well

There must not be anyloose or firmly attachedparticles on the sealing

edge

Damage scenarios



Damage caused by thermal overload

The sealing edge of new Simmerrings has acontact width of approx. 0.3 mm. The gap

height amounts to approx. 1 m. Heat

caused by friction is created in this narrow

gap. Approx. 80 % of this is transferred to

the shaft. If this heat is not well dissipated,

the lubricant "cracks" and/or the elastomeris thermally damaged. The results are oil

carbonisation on the sealing edge and/or

thermally-related tear formation in the

elastomer.

Fig. 9: Oil carbonisation beginning in the sealing edge area

Fig. 12: Advanced oil carbonisation and tear formationon the sealing edge

Fig. 8: Tears in the sealing edge

Fig. 11: Oil carbonisation and tear formation beginningon the sealing edge

Fig. 7: Deposits in the leading area

Fig. 10: Extremely strong, strongly adhesive oil carbon depositson the sealing edge

Damage scenarios



Damage due to chemical-physical interplay

Not all lubricants are compatible with the sealmaterials. The base oil has less to do with the

interplay with the elastomers. It is the additives

that have more of an effect. These can attack

the seal material already at 60 80 C. It must

always be observed that the sealing edgetemperature in conjunction with the shearing of

the lubricant under the sealing edge can

significantly accelerate damaging interplay.

Fig. 15: Blister formation through chemical interplay

Fig. 18: Formation of blisters/deposits on the back faceof the radial shaft seal

Fig. 14: Chemical interplay between elastomer and medium as aresult of deposits on the running surface

Fig. 13: Strong chemical filler metal erosion of the sealing edge

Fig. 17: Abrasion/bronze and decomposition products from thelubricant in the sealing edge area

Fig. 16: Strong oil carbon deposits with circumferential groovingin the sealing edge area

Damage scenarios



Fig. 22: Contamination over the entire sealing edge area

Damage due to contamination

True, radial shaft seals are robust sealing compo-nents and can easily compensate for many

disturbance variables. However, they react very

sensitively to contamination in the sealing edge

area. Even during installation, care must be taken

so that no contaminating particles of any kind are

located on the sealing edge since these canquickly lead to leakages, among other problems.

Depending on the application case, corre-

sponding buffer elements such as dust lips, spring

plates or labyrinth seals must be installed.

Fig. 21: Metallic deposits on the running surface

Fig. 20: Contamination between sealing edge and dust lip,e. g. form sand

Fig. 23: Metal shavings and lint on the dust lip caused duringgreasing of the radial shaft seals

Fig. 24: Contamination particles between sealing lip and dust lip causedby improper storage of the seal

Fig. 19: Excessive seal edge wear with circumferential grooveformation in the running surface

Damage scenarios



Damage due to excessive wear

Radial shaft seals wear extensively if there ispartial dry running of the seal, if the housing

inner pressure takes on a value of > 0.3 bar

or if abrasive particles from inside (wear from

gear wheels or worm gears, form sand orsimilar) or from the outside (water, sand, dust

or similar) get under the sealing edge.

Fig. 27: Excessive wear due to poor lubrication

Fig. 29: Excessive wear of the sealing edge caused byexcessive pressure being applied

Fig. 26: Excessive sealing edge wear due to high pressureapplied in conjunction with poor lubrication

Fig. 28: Groove formation as a result of increased pressure

at the aggregate

Fig. 25: Groove formation with significant discolourationof the contact surface air side

Damage scenarios



Fig. 32: Sealing edge damage caused by blind installation

over a spline shaft

Fig. 31: Sealing edge damage due to the use ofimproper fitting tools

Fig. 33: Damage to the shaft surface due to

improper handling

Mechanical damage

Radial shaft seals react very sensitively tomechanical damage which occur almost

exclusively during handling and installation.

Sharp edges on shaft or housing chamfers,assembly via grooves and gear teeth and

inadequate fitting tools are first on the list.

Fig. 30: Sealing edge damage caused bysharp-edged grooves

Damage scenarios



Case study

Disappointing early failures are frequentlyassociated with "apparent-leakage". What

happens quite often is that the user applies too

much grease to the area between sealing lip

Fig. 34:Excessive greasing can

lead to apparentleakages

Fig. 35:Optimally greasedSimmerring

Fig. 36:Optimal sealing edgeof a Simmerring after1000 operatinghours. The sealingedge is free fromdeposits, cleanlyshouldered and has

running width< 0.5 mm

Damage scenarios

and dust lip. This can, depending on theoperating conditions, lose its consistency in a

very short amount of time and it oils out and

thus causes an apparent leakage.


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Fitting tool

The fi tting tools used must exactly match therespective Simmerring as otherwise there is

the risk of irreparable damage.

The Simmerring should preferably be

pressed into the housing using hydraulic

or pneumatic assembly equipment.

Make sure that:

The Simmerring is not inserted at an

angle

The Simmerring does not become

deformed

The Simmerring does not spring back too

far

The Simmering is precisely fixed in the bore

Fitting notesIf the fitting is performed using a pneumatic or

hydraulic press, the fitting speed of 100 to

500 mm/min for Simmerrings with a

rubberised static part and 1000 mm/min forSimmerrings with a metallic static part must

not be exceeded.

Fig. 43:Fitting over a spline shaft (tongue and groove linking)(also for sharp-edged shaft section)

To minimise the spring back and tangential

deviation of rubberised Simmerrings, it isrecommended that the seal not be fitted in

one press but rather that the seal be allowed

to release completely for approx. 1 s at

approx. 1 mm from the end position and then

softly position the seal.

An inclination of more than 0.5 should be

avoided with standard parts.

Examples:

Da 30 mm a = 0,25 mm

Da 60 mm a = 0,52 mm

Da 100 mm a = 0,87 mm

During the fitting, the sealing lip must not

come into contact with sharp-edged

chamfers, edges, grooves or similar since

early failures are otherwise certain tohappen. Fitting collars must also exhibit no

excessively rough surfaces or scratches.

Fig. 44:

The permitted tangentialdeviation in the housing

depends on the seal typeand the shaft diameter

Handling and installation



When fi tting an aggregate part with a

pre assembled Simmerring, a centeringbolt should be used to prevent tilting and

thus damage to the sealing lip.

If additional components of the aggregate

are to be pushed over the running

surface, e. g. bearings with a press fi t

and the same nominal diameter, the

diameter of the running surface is to be

reduced by 0.10 mm for shaft diameters

up to 30 mm, 0.2 mm for shaft diameters

from > 30 mm to 150 mm and 0.30 mm

for shaft diameters >150 mm in order to

prevent damage. The functioning of the

Simmerring is not affected by this

reduction.

Since elastomers have a reversible

behaviour, the sealing lips can be easily

stretched during the short installation time.

Replacing SimmerringsThe following information should be

observed:

New Simmerrings must be installed

for a repair or overhaul of an aggregate.

The sealing lip of the new Simmerring

must not be located on the same runninglocation. Measures for this are the

installation of spacer rings, the exchange

of shaft Sleeves or the selection of a

different press-in depth in the bore

[see Fig. 45].

Fig. 45: Original fitting (above) and fittingfor repair of the aggregate (below)

Fitting of Simmerring cassette sealsCassette seals are mainly used when very

heavy dirt accumulation is present. The fitting

procedure as follows should be adhered to:

1. Press the cassette into the housing

(as for a normal Simmerring).

2. Wet the slip ring lightly with oil or

grease, but better with an alcohol-water

mixture.

3. Push the shaft (diameter tolerance h8 or

smaller) with roughness values Rmax

< 10 m and Ra< 1.5 m (turned surfaceis suffi cient) through the slip ring of the

cassette.




Fig. 46: Proper fitting of the cassette

Fitting tipsSimmerrings with an elastomer press fi t

(BA design) must not be additionally

glued into the housing. However, if the

bore diameter is too great or if there is a

high pressure in the aggregate

(> 0.5 bar), the Simmerring can also be

easily glued (e. g. with Loctite 480).

If a part of the elastomer static part shears

off during the fi tting, the housing chamfershould be checked fi rst (geometry,

dimensions, burr free).

The fi tting force can be greatly reducedby using a lubricant, a wax, or a water-

alcohol mixture which thus prevents

shearing. The water-alcohol mixture has

the advantage that the seal sits very fi rmly

in the bore after the alcohol has

evaporated.

If for whatever reason, the adhesion force

of the Simmerring in the bore is not

suffi cient, it is recommended that a smallgroove be added to the bore housing [see

Fig. 47, page 30].This reliably prevents




the seal from springing back and can

increase the press-out force by a factor oftwo.

Simmerrings occasionally "wander" out of

the housing bore after fi tting. The reason

can almost always be found in the too

small press-in depth of the Simmerring in

the bore.

Note: The cylindrical static part of the

Simmerring must not be in contact with

the housing chamfer [see Fig. 47].

Simmerrings with a pure metallic static

part should be fi xed with an adhesive

(e. g. Loctite 480) or better with a sealing

compound (e. g. Epple 33 or Loctite 574)

in the bore.

Contaminated radial shaft seals should be

lightly rubbed without fail before fi tting

using a lint-free cloth or cleaned with ablast of air.

Even the smallest of dirt particles like lint

can release the sealing edge enough so

that a leakage is certain right after the

installation.

The application of grease between the

sealing lip and dust lip should not be

done with a brush.

A defi ned greasing on site using a greasemandrel matched to the product is best.

The amount of grease should be less than

40 % (except for compression-loaded

Simmerrings).

Through the grease discharge, so-called

apparent leaks frequently exist since 1 g

of washed out or "bleed" grease can

create up to 35 drops of oil (!).

Fig. 47:The correct press-in depth

Preventing potential errors

It has proven benefi cial to perform aninternal installation audit from time to

time. A support manual was created

which contains the most important

parameters that affect the function and

lists the corresponding remedial action

[see the following chapter for this].

Direction: The Simmerringmust sit deeply enough in thehousing bore

A holding grooveprevents the sealfrom springing back

Not this way please!The cylindrical static part of theSimmerring must not be in contact

with the housing bevel




The compilation of possible sources of error during the fitting and handling of Simmerrings by the usershould help our customers recognise pitfalls and choose corresponding remedial measures. Please consultour technical support.

Troubleshooting: Sources of errorand recommended remedial actions

Sources of error Possible errorsConsequences for

the sealingfunction

Cause of theproblem

Remedial action

Receipt of goods

Damage to thepackaging

Contamination ofSimmerrings

From reduced lifespanto immediateleakage

Incorrect transportpackaging

Test the parts for conta-mination, visual andsignificant changes,improve handling,optimise packaging

Storage (larger quantities over longer time period)Intermediate storage (consumable quantities, supply for the installation)

Non-compliance withthe storageconditions accordingto DIN 7716

Installation of faultySimmerrings

Reducedlifespan

Non-compliance withthe storagerequirements

Storage conditionsaccording to DIN 7716must absolutely becomplied with


Installation and use ofcontaminatedSimmerrings

From no influence toimmediate leakageas well as reducedlifespan

Dust, dirt

Clean Simmerringbefore installation usingsuitable cleaning agent(DIN 7716), Openoriginal packaging firstat the installationlocation

Damage of the

Simmerring

Installation of

damaged Simmerrings

Immediate leakage or

reduced lifespan

Premature ageing due

to improper storage

Open the original

packaging first at theinstallation location

Transport (from intermediate storage to installation location)

Damage to thepackaging


From reduced lifespanto immediate leakage

Improper handling Blocking of andspecial clearanceprocedure for parts indamaged cartons, testfor contamination

Intermediate storage at the installation location (consumable amounts)


Installation of acontaminatedSimmerring

From no influence toimmediate leakage aswell as reducedlifespan through addedwear caused by dust,dirt

Clean Simmerringbefore installation usingsuitable cleaning agent(DIN 7716)

Troubleshooting



Sources of error Possible errors

Consequences

for theSealing function

Cause of theproblem Remedial action

Open storageof pre-greasedSimmerrings

Contamination of thegrease

From no influence toimmediate leakageas well as shortenedlifespan throughadded wear

Caused by dust, dirt fromthe surroundings

Always cover the packagedunit and protect from dustand dirt, only remove therequired consumableamount

UnsuitableStorage containers

Contamination,damage if theSimmerring springsnaps out

From no influence toImmediate leakageas well as shortenedlifespan throughadded wear

Accumulation of dirt andmoisture in the storagecontainer, sharp-edgedcorners

Bottom opening, easy toclean containers with nosharp edges

Preparation of the Simmerring for installation

Improperopening orremoval from thepackaging

Cuts or similardamages on the outerdiameter, snappingout of the spring,installation of theSimmerringwithout spring

From immediateleakage to reducedlifespan

Sharp-edgedor unsuitable tools oropening methods

Suitable packagingand tools, special cautionand instruction of theassembly fitter

Greasing of theSimmerring withcontaminated oil orgrease

Contamination of theSimmerring

From immediateleakage to reducedlifespan throughincreased wear

Dust, dirt Protect the grease containerfrom contamination andkeep closed when not inuse

Unsuitable oil forlubricating the shaft Chemical influenceon the seal material,squeaking (stick-slip)

Reduced lifespanthrough increasedwear

Unfavourable lubrication,no contact oil with theSimmerring material

Discuss oil types withcustomer consultant, neveruse graphite grease

Too much greasebetween sealingedge and dust lip

Grease dischargeduring installation oroperation

Apparent-leakage Incorrect amount ofgrease

Max. amount of grease:Approx. 40 % of thegrease space

Too much grease onthe oil side

Grease dischargedrawsoil leakage with it

Leakage leads tofailure

Incorrect fittinginstructions

No grease on the oil side

No or toolittle grease

Insufficient lubricationof the dust lip,increased dirt entry,rubber abrasion

Reduced lifespanthrough increasedtemperatures in thedust lip area orthrough prematurewear

Incorrect instructions orwrong dosage amount

Position the grease amounton the dust lip

Application of greaseto incorrect area

Insufficient lubricationon the dust lip

Reduced lifespanthrough increasedtemperatures in thedust lip area orthrough prematurewear, apparentleakage

Incorrect instructions orwrong dosage amount.Incorrect greasing unit orincorrect greasingmandrel

Use pregreasedSimmerrings, modify theconstruction of the greaseapplicator

Applicationof the grease

Contamination,chemical influences,damages

From immediateleakage to reducedlongevity

Dirt, dust, applicationtool, cleaning tool, fordamages or sharp edgeson the greasing mandrel

Check for cleanliness,suitable tools.Information and training ofthe fitting technicians

Greasing of aSimmerring withoutgrease chamber

Apparent-leakage None Insufficient/incorrectinformation

Select a different seal type

Troubleshooting




Consequences

for the sealingfunction


Installation: Fitting/mounting fixture, mounting location, fitting technician

Incorrect design ofthe fitting mandrel

Damage to the seal,spring snaps out.Simmerring installedat an angle

From no leakage toimmediate leakage,reduced lifespanthrough unevenwear

Customisation:Simmerring shaft housing fitting mand-rel. Mounting fixtureincorrect

Co-ordinate adjustmentwith Freudenberg, observethe suggestions of theDIN 3761,Simrit catalogue recommen-dation

Contaminated

fitting mandrel

Contamination fo

the Simmerring lea-ding to possible da-mage

Premature failures or

reduced lifespan

Dust and dirt at the

working station

Pay attention to cleanliness,

clean the fitting mandrelregularly

Damagedfitting mandrel

Damage to theSimmerring


Fitting mandrel not OK Regular checking

Incorrectfitting mandrel

Damage to theSimmerring


Mix-up/noassignment: Simmer-ring-fitting mandrel

Correct fittinginstructions

Too high a fitting

speed

Spring back and/or

skewed position ofthe Simmerring,Damage to the outerdiameter, snappingout of the spring

Uneven wear,

reduced lifespan,static leakage

Fitting speed/hammer

fitting

Comply with recommended

max. speed

Too high a press-inforce for a fitting tostop

Damage to theSimmerring(bending of the me-tal part)


Press-in force too high/fitting to stop

Reduce the press-in force/force limit/end stop on the fittingmandrel/do not press-in tostop: Path limitation

Press-in path tooshort/too long

Sealing lip anddust lip running on

incorrect location

From no influence toImmediate failure/

early failures

Fitting mandrel ormounting fixture not OK

Check Simmerring for cor-rect seating/set press-in

pathafterwards

Hammer fitting Damage to theSimmerring andof the installationchamber/snappingout of the spring,skewed position

From immediatefailure to reducedlifespan

Improper fitting In a series production, ahammer fitting should notbe used/in the case of re-pairs with hammer fitting,select a stable seal design

Fitting locationunclean(remove cigarette

ashes), sharpedges/metal chips

Seal or mountingfixture contaminatedor damaged

From immediatefailure to reducedlifespan

Dirt, sharp edges Keep fitting locationclean and free from dama-ge. Qualification/clearly

and simply displayed ins-tructions: Visualisation/sen-sitisation for sealing compo-nents

Troubleshooting




Consequences



Simmerring running location (shaft) on fitting location

Scratched shaft Damage to thesealing lip duringinsertion of the shaft

From immediatefailures toreduced lifespan

Transportation damage/missing shaft protection/improper storage andhandling of the shaft

Check the shaft beforeinstallation/DIN 3761observe/use suitableprotective covers andtransport container/donot store or transport shaftas bulk cargo

Contaminated shaft Damage andcontamination of thesealing lip duringinsertion of the shaft


Insufficient shaftprotection/unsuitabletransport container/unclean handling

Clean shaft beforeinstallation/use suitableprotective covering andtransport container

Corroded shaft Damage andcontamination of thesealing lip duringinsertion of the shaft


Insufficient corrosionprotection/humidity toohigh/ storage too long/insufficient-transportcontainer or missingcovering

Check shaft before theinstallation for corrosion/never use a corrodedshaftApply suitable corrosionprotection/reconditioncorroded shafts

Corrosionprotection Chemical reactionwith the Simmerringmaterial or thesealed oil

Reduced lifespan Unsuitable materialcombination or corrosionprotection material

Co-ordinate adjustmentwith Freudenberg/test thecorrosion protectionmaterial for suitabilitywith the Simmerringmaterial in the laboratory

Installation of theshaft, poor slidingon of the Simmerringsealing lip orthe dust lipdiaphragm onto theshaft

Spring snaps out/upending of thediaphragm or dustlip

Reduced lifespan Insufficient lubrication/chamfer of theshaft not OK/SL coveringtoo large/incorrectSimmerring design

Sufficient lubricationfrom Simmerring andshaft/observeFreudenbergrecommendation to theshaft chamfer.Match Simmerringconstruction with thefitting as well as theinstallation room

Blind fitting: Longshafts/heavy shafts/tipping of the shaft

Spring snaps out/upending of thesealing lip or dustlip/skewed positionor damage to theSimmerring

From reducedlifespan toimmediatefailure

Insufficient guidingof the shaft

Match Simmerringconstruction with thefitting as well as theinstallation space/selectsuitable sealing concept

Housing bore

Two-parthousing

Combination withincorrectSimmerring staticpart design

Static leakage UnsuitableStatic part design

One part housing/select outer rubbercoating or partial rubbercoating/sealing lacqueror adhesive areunsuitable here

Troubleshooting




Consequences



Cast housing pores/blow holes/casting sand

From static leakage/increased wear toreduced lifespanthrough casting sand

Casting quality notsufficient/insufficientcleaning

Pores and blow holesmaximum 1/3 of thestatic part width/improvecleaning

Die-cast housing(Al, Mg)

Press fit notsufficient/skewedposition/spring backor wandering out ofthe Simmerring (withouter rubbercoating)

Insecure fitting/reduced lifespan

Housing bore too fine/unsuitable static partdesign

Rz> 10 m and < 25 m/select outer rubber coating


Electrochemicalcorrosion (formetallic press fit)

Static leakage/damage from metalpart or housing

Voltage potential(quiescence potential)

Suitable factory pairing/select outer rubber coating


Damage to the borefrommetallic press fit

Static leakage/reduced lifespan/bore scratched (notOK) in the case ofrepair

Unsuitablestatic part design

Select outer rubber coating

Plastic housing Damage to the borefrom metal press fit/influence of thermalexpansion or toosmooth surface

Static leakage/reduces lifespan

Unsuitable materialpairing orstatic part design

Select outer rubber coating

Insert chamfer in thehousing incombinationwith an outer rubbercoating on theSimmerring

Shearing off ofrubber with outerrubber coating/skewed position/springback of theSimmerring

Static leakage Burr formation on thetransition from thechamfer to the bore/chamfer too large ortoo small/Simmerringis out of round

Ensure freedom from burrs/observe recommendation ofthe DIN 3761 with regardsto the chamfer

Housing bore Shearing off ofrubber/Simmerring

Static leakage Chamfer too large Select chamfer = 15 20

Handling of aggregates with seal already installed in the production line

Seal laying open orunprotected

Contamination/hardening of theelastomeric material

From reducedlifespan toimmediateleakage

Dirt and dustin the surroundingareaUV light/ozone

Select suitable covering ofthe seal for protectionagainst damage and foravoiding negative influenceslike ozone or UV light/select

suitable sealing system,which protects itself/carefulfitting/detailed instructions

Troubleshooting




Consequences



Seal laying open orunprotected

Damage From reducedlifespan toImmediate leakage

Mechanical effect ofcomponents, objectsor working processeson the seal/insufficienttransportationprotection for looseparts

Select suitable covering forthe seal for protection againstdamage and for avoidingnegative influences like ozoneor UV light/select suitablesealing system, which protectsitself/careful fitting/detailedinstructions

Corrosion of theshaft or housing Corrosion at thesealing lip runninglocation

Reduced lifespan High humidity/insufficient corrosionprotection

Corrosion protection/covering of the seal/limit humidity

Transport Spring snaps out Reduced lifespan Unsuitabletransportationcontainer/Simmerringcentred on mandrel

Suitable transportationcontainer/perform a check ofthe spring seatingbefore the installation

Fitting Damage to thesealing lip

From reducedlifespan toimmediate leakage

Keyway gearing Use mounting sleeve

Troubleshooting



Simmerrings are proven, robust and reliable sealing

components. However, they are subject to a natural amount

of wear due to the interplay in the tribological system.

Determining the cause of leakages is therefore a difficult

issue. Damage scenarios show the most important causes that

lead to failure of the seal and provide the first clues. The actual

cause of the damage can, however, only be determined

through a systematic limitation of the possible damaging

mechanisms in conjunction with an immediate analysis of

shaft, lubricant, and radial shaft seal.

Experience shows that roughly 30 percent of early failurescan be traced back to improper installation. Practical

information for the proper storage, for the corresponding

fitting tools for the design of the shaft and the housing as well

as for the correct greasing of the Simmerrings should help

with the removal of these error sources. Moreover, regularly

performed installation audits and training contribute to

helping to isolate weak areas and permanently prevent them.

Summary

Summary


37/55


38/55

2. Shaft surfacesRequirements and working forms


39/55

Shaft surfaces

Freudenberg Simrit GmbH & Co. KG40

Shaft surface requirementsTo be able to ensure trouble-free functioning,

the components in the tribological system

Simmerring lubricant shaft surface must

be optimally matched to each other.

It is not always easy since the processes in

the actual sealing zone are so complex due

to high pressures, temperatures, shearing

forces, infl ow of oxygen and transient

interplay between the seal material and

the lubricant or its additives

[cf. Fig 1, page 10].

The design engineer should thus rely on the

experience that the seal manufacturer can

offer. If the operating conditions are known,

the manufacturer cannot only recommend acorresponding seal, but rather, can also

submit suggestions as to how the shaft

surface should be machined.

The requirements of a shaft or its surface are

only signifi cant at fi rst glance. It should

be burr free

not fall below or exceed the specifi ed

roughness parameters. For ground shaftsit is recommended in accordance with

DIN 3760 or 3761:

Ra0.2 - 0.8 m

Rz1 - 5 m

Rmax

6.3 m

exhibit no damage of any kind, such as

scratches, scoring, pores, corrosion

have suffi cient dimensions, abrasion-

resistance.

For this reason, the shafts should be

hardened for possible inner (casting sand,

residual oil, metal particles, varnish and

outer (water, dust, mud) contamination.

It is also recommended that the shafts be

hardened for pressurised seals and for high

circumferential speeds (> 12 m/s) as well.

Furthermore,

the shaft diameter should be toleranced

to ISO h11

the roundness tolerance IT 8 should

not be exceeded

the lubricant should wet the surface

suffi ciently

the surface should also maintainthe lubricant fi lm under load

(e. g. pressure)

and of increasing importance today,

the machining process should be as

economical as possible.

In order for the shaft to withstand the

technical requirements, the correct

machining method is of great importance.These processes in the order of their

importance are introduced below.



Surface treatment processesThere is an abundance of possible surface

treatment processes for shafts:

Grinding

Turning

Tangential turning

Roller Burnishing

Peening

Superfinishing/honing

Polishing

Quickpoint grinding

Outer grinding

However, not all of these processes are

suitable in combination with Simmerrings.

The most important are evaluated accordingto the latest thinking:

GrindingShaft surfaces for seals are often groundDecades of experience show that plunge-

cut grinding is a safe and proven process

for creating a functional surface for radial

shaft seals. However, there are early failuresof radial shaft seals again and again

which can be traced back to an improperly

prepared shaft.

One of the main requirements of a ground

surface is the absence of lead. This should

ensure no shaft draw direction in the form

of a thread-like structure is present. This

"conveying structure" can have a negative

effect with the corresponding direction ofrotation on the sealing function of the radial

shaft seal. In practice, the requirement

Fig. 48: Grinding of shafts

for "lead-free" shaft surfaces is, however,

virtually impossible. Even when plungegrinding is performed in accordance with

specifi cations, this does not guarantee

a lead free surface.Important process

parameters like constants and, above

all, revolution speed rates are often not

adhered to or checked, the dressing tool

requirements for the grinding disc (feed rate,

cutting depth, cycle) are not adhered to and

the sparking out time is often not suffi cient.External factors such as machine vibrations,

bearing play etc. can have a negative

infl uence on the surface structures. The main

problem is, however, that the effects of

these process parameter changes or process

fl uctuations are not exactly detectable and

measurable.

Surface treatment processes



Residual lead can cause leakage.

Although prescribed surface roughness valueshave been adhered to and the shaft surface is

seen to be in a satisfactory condition, it fre-

quently happens that radial shaft seals leak

within a few operating hours.

The reason for this is the microscopically small

lead on the shaft surface. An individual helix

("thread"), independent of pitch, is not

normally harmful to radial shaft seals, due to

its small cross sectional area. The problem is,

however, that the ground surface normally

has several "threads".

Thus, if the ratio between the grinding disk

and the shaft is, for example, 10:1, it is

possible for a 10-start thread structure to be

set up on the shaft surface whose pitch will

correspond precisely to the dressing feed of

the dressing tool. The result is that the fl uidtransport through the threads, corresponding

to the direction of rotation, can exceed the

natural pumping capacity of the seal.

Sparking out time is crucial

The main factor to be aware of when grind-ing surfaces for radial shaft seals is the

sparking out time. Since a thread structure

can never be avoided, irrespective of pro-

cess parameters, it is necessary for the spar-

king out time to be adequately high to elimi-

nate it altogether. Sparking out times of 30

seconds should be regarded as a minimum.

Figure 49, however, illustrates that the sur-

face of a ground shaft will not be homoge-

nous, even with practically perfect process-

ing and the appropriate sparking out time.

To some degree, abrasive grit will press the

surface peaks to one side or will tear out

whole areas.

The greater the resulting damage which arises

in the axial plane on the shaft, the lower will

be the resistance to fl uid fl ow, resulting in in-creased leakage.

Only exact adherence to the process parameterscan make grinding secureIf the prescribed process parameters are

adhered to, then grinding will be a reliable

production process. Minor imperfections in

the surface texture can and must be com-

pensated for by radial shaft seals.The most important process parameters and

their infl uence on the radial shaft seal are

summarised in Table 2.

TurningIn the last few years, the machining of

hardened shafts has been continually

improved. In the meantime, this technology is

integrated in the manufacturing process at

Fig. 49: REM image of a plunge-cut shaft surface. (The sparking out timeamounted to 3 minutes!)




Influence of the manufacturing parameters for the grinding on the sealing effect

Table 2: Relevant machining guidelines for ground surfaces

Process parameters Consequence Aim Observance

Rotational speed ratioGrinding disc/workingmaterial

Can cause a leading Not in whole numberse.g. 10.5:1

Check during the process

Rotational speed workingmaterial

Rotational speedgrinding disc

Can cause a leading 30 300 rev/min1500 1700 rev/min

Tool and working material mustrotate in counter directions

Dressing traverse speed Influences the slopeof the conveying thread

< 0.1 mm/rotation Dressing should only occur inone direction

Dressing tool Can cause aleading structure

Multi grain diamondSingle grain diamond

Dressing infeed Influences roughnessvalues

approx. 0.02 mm

Sparking out time Influences cross sectionof the conveying thread

Complete sparking out, atleast 30 seconds

Most common causes forlead afflicted surfaces

Infeed depth Can cause leakage >> as Rmax

from theprevious machiningprocess

Grinding disc/granulation

Influences theroughness parametersR

a; R

z; R

max

Example: 60 100;Aluminium oxide60KL8V25 (white)Dimensions 400 x 50 x127

Concentricity of thetools andworking material axis

Creates leading structureon the surface

Concentricity as smallas possible




many companies for economic reasons. With

only a few exceptions, the sealing area of theshaft is still ground. Since one can create a

directional lead on a shaft, this can be utilised

for use in aggregates where one direction of

operation is used primarily:

Engine

Gearbox input

Gearbox output and differential input

(to a degree)

The "helical lead" on the shaft surface can

thus support the radial shaft seal and pump

the sealed lubricant back into the aggregate.

Many attempts under the most varying

conditions have shown that Simmerrings

on turned shafts function perfectly with the

corresponding direction of rotation. More andmore aggregate manufacturers are thus using

a turned shaft as a counter direction point for

the seal.

Hard turning is economicalThe technical success is supported through

the high effi ciency of the process. There is

Fig. 50: Turning of shafts

signifi cant potential for reducing costs in

comparison to other processes.In comparison to grinding for example, the set-

up costs can be reduced by up to 95 %, the

process times by up to 40 % and the machine

purchase costs by up to 50 %.

Another advantage is that the surface texture

with turned shafts is precisely defined and

markedly homogenous [see Fig. 51].

Matching to the direction of rotation is importantFor many application cases, however, the

direction of rotation is not completely clear or

the rotation can occur in both directions.

The seal manufacturer recommends radial shaft

seals with an alternating leading or radial shaft

seals according to DIN 3760 (without leading)

for such applications. Turned shafts with

corresponding direction of rotation can, intheory, convey sizeable lubricant volumes

underneath the seal on account of their leading

("helical threads") and in dependence on the

operating conditions. If one considers the use

of turned shafts for applications with which the

direction of rotation can vary, the seal must be

capable in all operating conditions of being

able to capture the leaked oil quantities and to

be able to pump them back into the sealedarea, thus opposed to the effect of the leading

of the shaft. Of significant importance here is

that the seal be capable over a longer period

of time of pumping these fluid volumes back

since the surface structure of the shaft normally

shows little wear, i.e. remains in tact for long

periods of time.

The pumping effect of the seal is crucialThe critical factor is thus the pumping action

of the radial shaft seal. This is significantly




Table 3: Proven manufacturing parameters for the hard-turning of shafts

Comment:Simmerrings function perfectly

on soft-turned shaft surfaces. Experience

however, shows that the turning of soft shaftsoften proves to be more difficult than the

hard machining. Therefore, different cutting

In practice, the following manufacturing parameters are proven:

Feed rate: 0.03 0.10 mm/revolution(in the testing field, even values of > 0.1 mm/revolution were tested positively,but larger values should not be specified without testing)

Cutting speed: 100 220 m/min(very good results and durability are achieved at 200 m/min)

Cutting edge radius: 0.4 1.2 mm(a radius of 0.8 mm is favourable)

Cutting depth: max. 0.2 mm(very good results are achieved at 0.1 mm)

Cutter material: CBN (Cubic Boron Nitride)Due to the variety of offered cutting materials, we recommend contacting thecutting material manufacturer.

Hardness: 55 65 HCR

Recommended roughnessparameters:

Ra0.1 0.8 m

Rz1 4 mR

max< 8 m

Achievable qualities: Roundness < 2 mTrue running < 2 mTolerances from IT 5 IT 6Roughness R

zvon 2 4 m

Roughness Ravon 0.2 0.8 m


materials must be utilised depending on

the shaft material. Furthermore, the above

mentioned manufacturing parameterscannot always be copied.



influenced by the sealing lip design

(profile, lead type), the radial force andabove all, the material. Furthermore, the

pumping effect is dependent on the

operating conditions themselves, i.e.

primarily from the circumferential speed,

the lubricant temperature and thus the

lubricant viscosity.

Suitability of Simmerrings even for criticaldirection of rotationNumerous tests at Simrit have shown that

Simmerrings on turned shaft surfaces

reliably seal even with "critical" direction

of rotation of the shaft. Not only the turning

parameters such as

cutting speed

feed rate

cutting radiuscutting material

were varied for the test, but also the

operating conditions:

Circumferential speed

Lubricant temperature

Lubricant type

Pressure

Axial movement

Direction of rotation

Shaft diameter

Furthermore, various sealing variants were

considered in the tests:

Profi lesPumping features (uni or bi directional)

Materials (NBR, FKM, ACM, PTFE)

The knowledge and experiences reveal that:

Simmerrings are perfectly capable of

reliably sealing hard or soft turned

surfaces (see also manufacturing

parameters attachment).Depending on the direction of rotation

of the shaft, the surface structure can

additionally support the sealing effect

of the Simmerring.

If the Simmerring is correspondingly

constructed, it can also seal reliably

in both directions.

The friction torque behaviour of

Simmerrings on turned shafts isqualitatively and quantitatively

comparable with that of ground shafts.


Fig. 51:REM image of a milled shaft



Producing high quality surfacesA high quality surface is still a prerequisitefor a shaft seal to work reliably.

The surface quality of turned shafts is

significantly infl uenced by the

machine rigidity

tool cutting geometry/cutting material

stability of machine tool

Before the design engineer thus determines

the "turning" process and the manufacturing

parameters, he/she should consult with the

seal manufacturer [enquiry form at

www.simrit.com].

Tangential turningTangential turning is a new, innovative

and highly efficient alternative to themanufacturing processes up to now for

running surfaces of radial shaft seals. The

Fig. 52: REM image of an improperly machined, turned shaft surfacewith typical "chatter marks" which are caused by vibrations

process is based on the kinematics of the

turning space with a linear feed rate andfeatures:

Shorter main times as with conventional

turning

High tool service life

Possible integration in CNC machines

Avoidance of disadvantages of plunge-cut

turning (chatter marks etc.)

Almost completely burr free

Processing of hard and soft surfaces

The maximum processing width amounts to

28 mm even for hard shafts.

Typical, consistently achievable surface

qualities lie between Ra0.2 - 0.6 m and

Rz1 - 3 m.

Fundamental tests at Simrit have confirmed

that tangentially turned, hardened shaftsurfaces are suitable in principle for

Simmerrings.

Fig. 53: Tangential turning of shafts

Surface treatment process



Fig. 54:REM image of a tangentially turned shaft

Roller burnishingRoller burnishing promotes a strengthening of

the shaft surface. Since this finishing processis often used on shafts, e.g. to increase notch

impact strength for vibrating loads, especially

step-diameter-changes, it is convenient to work

the seal counter surface at the same time.

In addition to straightforward surface

strengthening, this process has the

advantage of neutralising the lead in the

turned basic structure [see Fig. 56].

Due to the high specifi c pressure on thesurface, the "peaks" are pressed down into

the valleys. In the normal case, this will have

the primary effect of, at times drastically

reducing the surface roughness value and

accordingly increasing the load bearing

proportion of the profi le. On a surface which

is too smooth, though, we know that a liquid

will give relatively poor wetting. Thus, under

certain loads, it is difficult for a lubricant filmto form or to be sustained. Depending on the

operating conditions, this can result in thermal

overload at the sealing edge of the shaft seal.

Tests at Freudenberg have indicated that rollerburnished finishes are suitable as counter

surfaces for Simmerrings.

Adherence to the manufacturing parametersis importantA prerequisite is that the surface

roughness values should be as follows:

Ra0.1 - 0.8 m

Rz0.8 - 5 m

Rmax

< 7 m

Prior to roller burnishing it is important that

the shaft surface is turned under defi ned

conditions e. g.:

Pre-machining of shaft at:

feed: 0.05 mm

cut speed: 300 m/min

cut radius: 0.8 m.The subsequent roller burnishing process must

also be performed under precisely controlled

parameters. If it is possible to ensure that the

whole process is reproducible and that the pre-

set parameters can be adhered to, then the

following points can be stated:

Fig. 55:Finish rolling of shafts




Simmerrings work perfectly on roller

burnished surfaces.The function is independent of the direction

of rotation.

The magnitude of the frictional torque or

power loss is not greater than on ground

surfaces.

The wear caused by the seal into the shaft

is reduced because of the strengthened

surface.

Permissable limits with regard to operatingconditions have not yet been completely

determined. Experience indicates that

peripheral speeds of 20 m/s at oil sump

temperatures up to 130 C subject to the

correct selection of seal, will cause no

problems.

Before the manufacturer finalises the roller

burnishing process and the production

parameters, he/she should consult with theseal manufacturer [you can find an enquiry

form for this purpose at www.simrit.com].

Peening

Peening of shafts is also used forstrengthening components (e. g. turbine

blades). In this process the shaft surface is

"blasted" with steel, glass or ceramic beads.

This causes surface strengthening depending

on the blast energy [see Fig. 57].

An addittional effect of this process is that

lubricants adhere excellently to the crater-like

surface structure, and, in particular, wet them

effectively [see Fig. 58].

Fig. 56:REM image of a finished rolled shaft

Fig. 57: Blasting of shafts


Fig. 58: REM image of a blasted shaft



For shaft seals this is an advantage, because

it enables a permanent exchange of lubricantunder the sealing contact.

Frictional torque and hence the power loss of

radial shaft seals on peened surfaces is

therefore 1030 % less than on ground

shafts, depending on operating conditions.

The sealing edge temperature is therefore

correspondingly lower. The results of this is

that the service life of seals, especially at

high load (peripheral speed, oil sump

temperature), is substantially increased.

Damaging oil carbonisation is also

significantly reduced.

This effect also produces a marked reduction

in harmful oil carbonisation. And although

no increase in hardness can be measured

by means of the normal hardness measure-

ment methods, the localised wear on theshaft in the area of the sealing lip is also

markedly less.

Peened structures are also suitableas counter surfacesProcess parameters have to be defined and

adhered to in order to produce the most

favourable surface texture:

peening shot (nature and diameter of

beads): corundum or steel chips are not

suitable materials, because an undefined

structure will be produced as the result

peening pressure

peening duration

peening direction

After the peening process, the surface has

to be cleaned of peening shot dust.If axial movement of the shaft is likely to

occur, it is advisable to polish the peened

surface in order to achieve a slight rounding

of the "crater" peaks. This will reduce wear

on the sealing edge of the radial shaft seal.

In the same way as was found on turned

surfaces, the pump action of the seal must

be large enough to compensate for the

lubrication state, which may actually be too

effective, or to transfer back any micro

leakage into the unit being sealed.

Neutral basic structure necessaryThe peening process is simple and, above

all, cost-effective and can be used to cover-

up minor surface defects (up to approx.

50 m).Here too, the designer should hold

consultations with the seal manufacturer

when he stipulates "peening" and the

process parameters.

Honing, SuperfinishingA criss cross surface texture is created

through honing or superfinishing. This has the

advantage that the lubricant binds well to itand that a sufficient lubrication is ensured

even under adverse conditions. This positive

structure for the lubricating film adherence is

achieved by the tool performing translatory

movement while the shaft rotates. A criss

cross structure results which appears neutral

at first glance.




Honed or superfinished surfaces are only conditionally

suitable as running surfacesThe lubrication ratios are excellent and the

wear of the mating components is small,

however, such structures are not suitable as

counter direction points for radial shaft

seals. While the occurring leakages are in

most cases relatively small, they are not

acceptable in most cases. For pure grease

sealing, the problems are, however,

negligible.

Polishing of surfacesIn the past it was quite common for the

running surfaces of radial shaft seals to be

polished. In the case of repair inparticular,

polishing is still a widely used method for

eliminating small damages or removing dirt.

Often expensive components that werefaultily ground can still be remachined by

polishing [see Fig. 60].

Fig. 59: Honing process

Fig. 60: Polishing of surfaces

While the polishing of surfaces is a cost-

effective process, the disadvantage of thistype of machining is, however, the same as

with grinding: A leading structure on the

surface can be created by the polishing.

If polishing is used as a machining method,

the same roughness parameters as for

grinding are to be adhered to.

Other processes

Outer grindingOuter grinding of shafts creates a

similar structure as with the honing

process. The criss cross structures can

not be reliably sealed.

Plunge-cut turningPlunge-cut turning creates a neutral,

i.e. lead-free, surface texture on the

shaft surface. This is principally suitableas a counter direction point for

Simmerrings.




Quickpoint grinding

Empirical data for quickpoint grinding isinconclusive. At the moment, no well-

founded statements on the general suitability

can be given. Quickpoint ground shafts can

only be used for one direction of rotation

due to their distinctive leading structure

("conveyance" into the sealed space).

Deep-drawn platesDeep drawn places are frequently used for

repair work. Since a remachining of the

shaft is often not possible, the surface is

cleaned and resanded where necessary.

Subsequently, a deep-drawn plate is drawn

on. This then represents the running surface

for the Simmerring.Fig. 62:Deep drawn plate as counter directionpoint of the Simmerring

Deep-drawn plates can be sealedSealing can be just as reliable on such

surfaces (depending on the operating

conditions) as on ground surfaces.

A prerequisite is no damage of any kind:

No pores or blow holes

No scratches or scoring

No material inhomogenities

In order to ensure this, only materials of

the correct quality should be used.

Although the materials used are relatively

soft, they possess suffi cient abrasivewear-resistance due to the reforming

process.


Fig. 61:Plunge-cut turning of shafts. While successful applications were realisedfor soft machining, machining with hardened material is more difficultdue to the tendency to chatter



Fig. 63:Determination of lead on the shaft with the thread method

Movement of the thread =Oil conveyance direction

PencilMark

Movement of the thread =Oil conveyance direction

Shaft with right turningthreads

=Radial shaft seal with left-

leading

Shaft with left turning threads=

Radial shaft seal with right-leading

Leading test

Leading test



Fig. 64: Example of a "calculated" surface structure

Leading measurements

Besides the adherence to the specifiedroughness variables like R

a, R

zand R

max, the

surfaces from plunge-cut ground shafts, as

mentioned already, should be lead-free.

The complete test whether the lead-free

requirement is fulfilled is difficult to conduct.

There are no measuring methods with which

a lead orientation can be reliably measured.

Despite this, representative results can be

determined using the widely used thread

method. A special thread is wetted with oil

and is placed over the shaft to be tested. A

weight (approx. 50 g) ensures an even

enlacement of the shaft. If the shaft rotates,

the thread begins to move axially if a lead

is present.

Although it is not possible to quantitativelyrecord the slope of the lead, this method has

proven itself in practice. It is applied in

slightly varying forms around the world. In

many cases, surface structures that are

damaging to a radial shaft seal can be

proven using this simple method. However,the method has weaknesses. With very small

or very large lead structures, the thread

does not react demonstrably.

All attempts to develop an alternative

method of measurement have failed in the

past. The approach of determining the lead

structure using a mathematical description of

the surface according to the measurement of

the surface texture appears promising [see

Fig. 64].

Still, the measurement and evaluation times

are so high that an implementation in the

production is not always cost-effective. But if

the required hardware and software is

developed in the foreseeable future, this

measuring method could help solve many

problems or help to understand the infl uenceof the various process parameters on the

surface quality.

Leading test



Summary

The surface texture of the shaft infl uences the sealing function

of a Simmerring signifi cantly.

The manufacturer must therefore ensure that the specifi ed

manufacturing process and roughness parameters are

adhered to and that the process is stable.

Besides these requirements, the selection of the correct

machining method determines the ideal system design in

terms of cost-effi ciency and technology. Alternatives to the

proven but expensive plunge-cut grinding exist and were

studied. Reliable sealing is achieved when the Simmerring

is capable of returning the microleakages created by the

shaft surface back into the sealed space.The design engineer has to determine the most functional and

cost-effective combination for the radial shaft seal/machining

method during the planning phase. But before the design

engineer makes a final selection, he/she should define the

process parameters together with the seal manufacturer and,

considering the actual operating conditions, determine the

ideal radial shaft seal. For protection or final verification,

aggregate tests should be performed.

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Summary


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