the simmering.pdf

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The Simmerring®

Reliability right from the beginning

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

Basics for preventing damage

The Simmerring®



1. Reliable sealing

2. Shaft surfaces Requirements and working forms

The Simmerring®

Erich Prem • Rolf Vogt



© 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 any

reproduction or dissemination to third parties may only occur through us.

Protective charge: 10.00 Euro

4

5© Freudenberg Simrit GmbH & Co. KG

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 the

intrusion 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 Vogt Manager Product Development Industry

Erich PremProduct Development Industry

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 be

avoided. In the fi rst 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 Simmer

developed 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.

© Freudenberg Simrit GmbH & Co. KG

1. Reliable sealing

How a Simmerring functions 10

Leakage defi nition 11

Analysis of leakage causes 13

Damage scenarios 18

Handling and installation 25

Troubleshooting 31

Summary 37


Shaft surface requirements 40

Surface treatment process 41

Leading test 53

Summary 55

Supplementary literature 56

Contents

7

1. Reliable Sealing

© 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

specifi cations 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 „defi ned“ leakage that is

necessary for a Simmerring to achieve

suffi cient lubrication and thus a long

operating life.

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

Gas orfl uid 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 the tribological system

Dust lip

Grease fi llingShaft surface shear

Lubricant

How a Simmerring functions

Reliable sealing


Leakage defi nition: the standard, leakage terms, cause, classifi cationUsing standard test conditions, the lack of tightness is determined by the amount of the sealed fl uid - over and above any moistness which may occur in normal operating conditions – which gets past the sealing edge and can be collected and measured, when the seal is run for a defi nite time on a test-rig. This collected and measured amount of media from the test-rig experiment is defi ned 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 face

of 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 during

further 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 release

procedures 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 sealing

edge caused by excessive thermal load

during operation

Leakage defi nition


■ Hardening of the elastomer caused by

excessive thermal/mechanical load

and/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

system

■ Vibrations 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 the

design 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.

Classifi cation 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,

fi lm 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 defi nes 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: Leakage classes

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 defi nition


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 fi t and on 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 improper

installation

■ 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 that

seal 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 diffi cult to determine the causes of

leakage from seals that have already been in

operation 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 all

the relevant information on each failure, but

above all to receive the actual seal and shaft

themselves for damage analysis.

You can fi nd 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 important

causes of leakage and the corresponding

corrective measures in more detail:

Static leakage at the press-fi t■ The housing bore is too rough which is

especially critical in Simmerring B1 seal

designs. Nominal:

Rmax

< 6.3-16 µm for B1 design

(metallic outer case)

Rmax

< 10 -25 µm for BA design

(rubber coated outer case)

■ Sharp-edged chamfer area and/or too

steep a chamfer angle on the housing bore

■ Simmerring B1: develops longitudinal

furrows

■ Simmerring BA: elastomer can be sheared

off

Static leakage at the sealing lip■ Shaft 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 undefi ned 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:

■ Ra 0.2 - 0.8 µm

■ Rz 1 - 5 µm

■ Rmax

< 6.3 µm

These roughness values ensure minimal

sealing edge wear of the radial seal shaft

independently from the machining method

and normally independent of the operating

conditions. 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 surface

structures can nowadays be precisely

detected and thus the relevant grinding

process parameters can be selectively

modifi ed [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 hardened

accumulations 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, incorrect

lubricant 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 especially

with 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 examples

should 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 to

40 °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

fi rst 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 be

drawn 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

15°–25°

15°–25°

Leakage causes


responsible for the leakages. Assuming

the correct material selection and the

corresponding profi le 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

■ RoughnessR

max

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, surface damage, tribo-oxidation

■ Precise concentricity

■ Cost-efficient manufacturing

■ Utilisation through the medium

■ 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 the radial 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 side contact surface

Sealing edge

Sealing edge:Pre pressedTrimmedbi directional helixUni directional helix

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

There must not be any loose or fi rmly attached particles on the sealing edge

Damage scenarios


Damage caused by thermal overloadThe sealing edge of new Simmerrings has a

contact width of approx. 0.3 mm. The gap

height amounts to approx. 1 µm. 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 elastomer

is 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 formation on the sealing edge

Fig. 8: Tears in the sealing edge

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

Fig. 7: Deposits in the leading area

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

Damage scenarios


Damage due to chemical-physical interplayNot all lubricants are compatible with the seal

materials. 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 edge

temperature in conjunction with the shearing of

the lubricant under the sealing edge can

signifi cantly accelerate damaging interplay.

Fig. 15: Blister formation through chemical interplay

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

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

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

Fig. 17: Abrasion/bronze and decomposition products from the lubricant 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 contaminationTrue, 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 can

quickly 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 during greasing of the radial shaft seals

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

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

Damage scenarios


Damage due to excessive wearRadial shaft seals wear extensively if there is

partial 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 or

similar) 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 by excessive pressure being applied

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

Fig. 28: Groove formation as a result of increased pressureat the aggregate

Fig. 25: Groove formation with signifi cant 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 fi tting tools

Fig. 33: Damage to the shaft surface due to improper handling

Mechanical damageRadial shaft seals react very sensitively to

mechanical damage which occur almost

exclusively during handling and installation.

Sharp edges on shaft or housing chamfers,

assembly via grooves and gear teeth and

inadequate fi tting tools are fi rst on the list.

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

Damage scenarios


Case studyDisappointing early failures are frequently

associated 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 apparent leakages

Fig. 35:Optimally greasedSimmerring

Fig. 36:Optimal sealing edge of a Simmerring after 1000 operating hours. The sealing edge is free from deposits, cleanly shouldered and hasrunning width < 0.5 mm

Damage scenarios

and dust lip. This can, depending on the

operating conditions, lose its consistency in a

very short amount of time and it oils out and

thus causes an apparent leakage.


Handling and installation:Practical handling and tipsThe effects of improper installation of a radial shaft seal are frequently underestimated by the user. The operating lifespan is also already determined during the installation. Many unfortunate customer complaints could be avoided if preventative measures like installation training or internal auditing were performed more frequently [Supplementary literature 6].

Requirements for a proper installationThere are numerous possible imperfections.

At fi rst glance, many appear trivial but the

ramifi cations could be severe. Even the tiniest

amount of sealing edge damage can lead to

a premature failure of the radial shaft seal.

Therefore, it is important, for example, that:

■ Attention is paid to damaged packaging

■ Simmerrings are left in their original

packaging as long as possible prior to

installation

■ The Simmerrings are protected from dust

and dirt

■ The Simmerrings do not come into contact

with sharp objects like metal shavings (even

fi ngernails!) or sharp edges of the fi tting

tools or shaft and housing chamfers

■ That greased Simmerrings are stored

closed or covered

■ The amount of grease between sealing

edge and dust lip amounts to a maximum

of 40 % of the volume (otherwise

"apparent leakages" may occur)

■ The Simmerrings are greased in a defi ned

manner (amount, placement, cleanliness)

■ The sealing edge preferably only comes in

contact with the lubricant that will later be

used for sealing (starting aid with

insuffi cient lubrication)

Check in the housing and shaft design that

the insertion chamfer (angle and length) are

absolutely free of burrs according to the

guidelines [cf. Fig. 5, page 17].

Storing SimmerringsSimmerrings should be stored under the

following conditions:

■ Temperatures > –10 °C to 25 °C maximum

■ Humidity < 65 %

■ No direct light

■ No direct sunlight

■ Adequate packaging

■ Warehouses must not use ozone-emitting

equipment

The storage time for Simmerrings manu-

factured from NBR, ACM, HNBR should

not exceed 5 years. The storage time for

Simmerrings manufactured from FKM, VMQ

should not exceed 7 years. The storage time

may be extended after a corresponding test

by a maximum of 3 years for the former and

5 years for the latter [for further information

see DIN 7716].

Handling and installation


Hammer fi ttingFor hammer fi tting (used frequently for large

Simmerrings) a mounting plate is used. There

is the risk that the seal can be deformed when

an excessive punctual stress occurs during the

Fig. 37:Fitting with hydraulic or pneumatic press die. Attention: Diameter of the metallic stop must be 5 mm to 10 mm larger than the outer diameter of the Simmerring

Fig. 38:Fitting back face forwardAttention: Outer diameter of the fi tting mandrel approx. 0.5 mm smaller than the inside diameter of the Simmerring. Ask us if needed

Fig. 39:Not this way please!Seal inserted at an angle

Fig. 40:Not this way please!Too small diameterof the press die

Fig. 41:Permissible hammer fi ttingAttention: Fitting plate must be used!

Fig. 42:Not this way please!Incorrect hammer fi tting


fi tting. When using adhesive to glue the

seal into the housing, it is essential that

no adhesive gets onto the shaft or onto

the sealing lip.


Fitting toolThe fi tting tools used must exactly match the

respective 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 fi xed in the bore

Fitting notesIf the fi tting is performed using a pneumatic or

hydraulic press, the fi tting speed of 100 to

500 mm/min for Simmerrings with a

rubberised static part and 1000 mm/min for

Simmerrings 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 is

recommended that the seal not be fi tted 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 fi tting, the sealing lip must not

come into contact with sharp-edged

chamfers, edges, grooves or similar since

early failures are otherwise certain to

happen. Fitting collars must also exhibit no

excessively rough surfaces or scratches.

Fig. 44:The permitted tangential deviation in the housing

depends on the seal type and the shaft diameter



■ When fi tting an aggregate part with a

pre assembled Simmerring, a centering

bolt 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 running

location. 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 fi tting (above) and fi tting for repair of the aggregate (below)

Fitting of Simmerring cassette sealsCassette seals are mainly used when very

heavy dirt accumulation is present. The fi tting

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 µm and Ra < 1.5 µm (turned surface

is suffi cient) through the slip ring of the

cassette.



Fig. 46: Proper fi tting of the cassette

Fitting tips■ Simmerrings 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 chamfer

should be checked fi rst (geometry,

dimensions, burr free).

■ The fi tting force can be greatly reduced

by 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 small

groove 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 of

two.

■ 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 a

blast 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 grease

mandrel 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 errorsIt has proven benefi cial to perform an

internal 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 Simmerring must sit deeply enough in the housing bore

A holding groove prevents the seal from springing back

Not this way please!The cylindrical static part of the Simmerring must not be in contact with the housing bevel



The compilation of possible sources of error during the fi tting and handling of Simmerrings by the user should help our customers recognise pitfalls and choose corresponding remedial measures. Please consult our technical support.

Troubleshooting: Sources of errorand recommended remedial actions

Sources of error Possible errorsConsequences for

the sealing function

Cause of the problem

Remedial action

Receipt of goods

Damage to the packaging

Contamination of Simmerrings

From reduced lifespanto immediate leakage

Incorrect transport packaging

Test the parts for conta-mination, visual and signifi cant changes, improve handling, optimise packaging

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

Non-compliance with the storage conditions according to DIN 7716

Installation of faulty Simmerrings

Reduced lifespan

Non-compliance with the storage requirements

Storage conditions according to DIN 7716 must absolutely be complied with


Installation and use of contaminated Simmerrings

From no infl uence to immediate leakage as well as reduced lifespan

Dust, dirt

Clean Simmerring before installation using suitable cleaning agent (DIN 7716), Open original packaging fi rst at the installation location

Damage of the Simmerring

Installation of damaged Simmerrings

Immediate leakage or reduced lifespan

Premature ageing due to improper storage

Open the original packaging fi rst at the installation location

Transport (from intermediate storage to installation location)

Damage to the packaging


From reduced lifespanto immediate leakage

Improper handling Blocking of and special clearance procedure for parts in damaged cartons, test for contamination

Intermediate storage at the installation location (consumable amounts)


Installation of a contaminated Simmerring

From no infl uence to immediate leakage as well as reduced lifespan through added wear caused by dust, dirt

Clean Simmerring before installation using suitable cleaning agent (DIN 7716)

Troubleshooting


Sources of error Possible errorsConsequences

for the Sealing function


Remedial action

Open storage of pre-greased Simmerrings

Contamination of the grease

From no infl uence to immediate leakage as well as shortened lifespan through added wear

Caused by dust, dirt from the surroundings

Always cover the packaged unit and protect from dust and dirt, only remove the required consumable amount

Unsuitable Storage containers

Contamination, damage if the Simmerring spring snaps out

From no infl uence to Immediate leakage as well as shortened lifespan through added wear

Accumulation of dirt and moisture in the storage container, sharp-edged corners

Bottom opening, easy to clean containers with no sharp edges

Preparation of the Simmerring for installation

Improper opening or removal from the packaging

Cuts or similar damages on the outerdiameter, snapping out of the spring, installation of the Simmerring without spring

From immediate leakage to reduced lifespan

Sharp-edged or unsuitable tools or opening methods

Suitable packaging and tools, special caution and instruction of the assembly fi tter

Greasing of the Simmerring with contaminated oil or grease

Contamination of the Simmerring

From immediate leakage to reduced lifespan through increased wear

Dust, dirt Protect the grease container from contamination and keep closed when not in use

Unsuitable oil for lubricating the shaft

Chemical infl uence on the seal material, squeaking (stick-slip)

Reduced lifespanthrough increased wear

Unfavourable lubrication, no contact oil with the Simmerring material

Discuss oil types with customer consultant, never use graphite grease

Too much grease between sealing edge and dust lip

Grease discharge during installation or operation

Apparent-leakage Incorrect amount of grease

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

Too much grease on the oil side

Grease discharge draws oil leakage with it

Leakage leads to failure

Incorrect fi ttinginstructions

No grease on the oil side

No or too little grease

Insuffi cient lubrication of the dust lip, increased dirt entry, rubber abrasion

Reduced lifespanthrough increased temperatures in the dust lip area or through premature wear

Incorrect instructions or wrong dosage amount

Position the grease amount on the dust lip

Application of grease to incorrect area

Insuffi cient lubrication on the dust lip

Reduced lifespanthrough increased temperatures in the dust lip area or through premature wear, apparent leakage

Incorrect instructions or wrong dosage amount. Incorrect greasing unit or incorrect greasing mandrel

Use pregreased Simmerrings, modify the construction of the grease applicator

Applicationof the grease

Contamination, chemical infl uences, damages

From immediate leakage to reduced longevity

Dirt, dust, application tool, cleaning tool, for damages or sharp edges on the greasing mandrel

Check for cleanliness, suitable tools. Information and training of the fi tting technicians

Greasing of a Simmerring without grease chamber

Apparent-leakage None Insuffi cient/incorrect information

Select a different seal type

Troubleshooting


Sources of error Possible errorsConsequences for the sealing

function


Remedial action

Installation: Fitting/mounting fi xture, mounting location, fi tting technician

Incorrect design of the fi tting mandrel

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

From no leakage to immediate leakage, reduced lifespan through uneven wear

Customisation:Simmerring – shaft – housing – fi tting mand-rel. Mounting fi xture incorrect

Co-ordinate adjustment with Freudenberg, observe the suggestions of the DIN 3761, Simrit catalogue recommen-dation

Contaminated fi tting 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 fi tting mandrelregularly

Damaged fi tting mandrel

Damage to the Simmerring


Fitting mandrel not OK Regular checking

Incorrect fi tting mandrel

Damage to the Simmerring


Mix-up/no assignment: Simmer-ring-fi tting mandrel

Correct fi ttinginstructions

Too high a fi ttingspeed

Spring back and/or skewed position of the Simmerring, Damage to the outer diameter, snapping out of the spring

Uneven wear, reduced lifespan, static leakage

Fitting speed/hammer fi tting

Comply with recommended max. speed

Too high a press-in force for a fi tting to stop

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


Press-in force too high/fi tting to stop

Reduce the press-in force/force limit/end stop on the fi tting mandrel/do not press-in to stop: Path limitation

Press-in path too short/too long

Sealing lip and dust lip running on incorrect location

From no infl uence to Immediate failure/early failures

Fitting mandrel or mounting fi xture not OK

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

Hammer fi tting Damage to the Simmerring and of the installation chamber/snapping out of the spring, skewed position

From immediate failure to reduced lifespan

Improper fi tting In a series production, a hammer fi tting should not be used/in the case of re-pairs with hammer fi tting, select a stable seal design

Fitting location unclean (remove cigarette ashes), sharp edges/metal chips

Seal or mounting fi xture contaminated or damaged

From immediate failure to reduced lifespan

Dirt, sharp edges Keep fi tting location clean and free from dama-ge. Qualifi cation/clearly and simply displayed ins-tructions: Visualisation/sen-sitisation for sealing compo-nents

Troubleshooting



function


Remedial action

Simmerring running location (shaft) on fi tting location

Scratched shaft Damage to the sealing lip during insertion of the shaft

From immediate failures to reduced lifespan

Transportation damage/missing shaft protection/improper storage and handling of the shaft

Check the shaft before installation/DIN 3761 observe/use suitable protective covers and transport container/do not store or transport shaft as bulk cargo

Contaminated shaft Damage and contamination of the sealing lip during insertion of the shaft


Insuffi cient shaft protection/unsuitable transport container/unclean handling

Clean shaft before installation/use suitable protective covering and transport container

Corroded shaft Damage and contamination of the sealing lip during insertion of the shaft


Insuffi cient corrosion protection/humidity too high/ storage too long/insuffi cient-transport container or missing covering

Check shaft before the installation for corrosion/never use a corroded shaftApply suitable corrosion protection/recondition corroded shafts

Corrosionprotection

Chemical reaction with the Simmerring material or the sealed oil

Reduced lifespan Unsuitable material combination or corrosion protection material

Co-ordinate adjustment with Freudenberg/test the corrosion protection material for suitability with the Simmerring material in the laboratory

Installation of the shaft, poor sliding on of the Simmerringsealing lip or the dust lip diaphragm onto the shaft

Spring snaps out/upending of the diaphragm or dust lip

Reduced lifespan Insuffi cient lubrication/chamfer of the shaft not OK/SL covering too large/incorrect Simmerring design

Suffi cient lubricationfrom Simmerring and shaft/observe Freudenbergrecommendation to the shaft chamfer. Match Simmerring construction with the fi tting as well as the installation room

Blind fi tting: Long shafts/heavy shafts/tipping of the shaft

Spring snaps out/upending of the sealing lip or dust lip/skewed position or damage to the Simmerring

From reduced lifespan to immediatefailure

Insuffi cient guiding of the shaft

Match Simmerring construction with the fi tting as well as the installation space/select suitable sealing concept

Housing bore

Two-part housing

Combination with incorrect Simmerring static part design

Static leakage Unsuitable Static part design

One part housing/select outer rubber coating or partial rubber coating/sealing lacquer or adhesive are unsuitable here

Troubleshooting



function


Remedial action

Cast housing pores/blow holes/casting sand

From static leakage/increased wear to reduced lifespan through casting sand

Casting quality not suffi cient/insuffi cient cleaning

Pores and blow holes maximum 1/3 of the static part width/improve cleaning

Die-cast housing (Al, Mg)

Press fi t not suffi cient/skewedposition/spring back or wandering out of the Simmerring (with outer rubber coating)

Insecure fi tting/reduced lifespan

Housing bore too fi ne/unsuitable static part design

Rz > 10 µm and < 25 µm/

select outer rubber coating


Electrochemical corrosion (for metallic press fi t)

Static leakage/damage from metal part or housing

Voltage potential (quiescence potential)

Suitable factory pairing/select outer rubber coating


Damage to the bore frommetallic press fi t

Static leakage/reduced lifespan/bore scratched (not OK) in the case of repair

Unsuitable static part design

Select outer rubber coating

Plastic housing Damage to the bore from metal press fi t/ infl uence of thermal expansion or too smooth surface

Static leakage/reduces lifespan

Unsuitable material pairing or static part design

Select outer rubber coating

Insert chamfer in the housing in combination with an outer rubbercoating on the Simmerring

Shearing off of rubber with outer rubber coating/ skewed position/springback of the Simmerring

Static leakage Burr formation on the transition from the chamfer to the bore/chamfer too large or too small/Simmerring is out of round

Ensure freedom from burrs/observe recommendation of the DIN 3761 with regards to the chamfer

Housing bore Shearing off of rubber/Simmerring

Static leakage Chamfer too large Select chamfer = 15° – 20°

Handling of aggregates with seal already installed in the production line

Seal laying open or unprotected

Contamination/ hardening of the elastomeric material

From reduced lifespan to immediateleakage

Dirt and dust in the surrounding area UV light/ozone

Select suitable covering of the seal for protection against damage and for avoiding negative infl uences like ozone or UV light/select suitable sealing system, which protects itself/careful fi tting/detailed instructions

Troubleshooting



function


Remedial action

Seal laying open or unprotected

Damage From reduced lifespan to Immediate leakage

Mechanical effect of components, objects or working processes on the seal/insuffi cient transportation protection for loose parts

Select suitable covering for the seal for protection against damage and for avoiding negative infl uences like ozone or UV light/select suitable sealing system, which protects itself/careful fi tting/detailed instructions

Corrosion of the shaft or housing

Corrosion at the sealing lip running location

Reduced lifespan High humidity/insuffi cient corrosion protection

Corrosion protection/covering of the seal/limit humidity

Transport Spring snaps out Reduced lifespan Unsuitable transportation container/Simmerring centred on mandrel

Suitable transportation container/perform a check of the spring seating before the installation

Fitting Damage to the sealing lip

From reduced lifespan to immediate 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 diffi cult

issue. Damage scenarios show the most important causes that

lead to failure of the seal and provide the fi rst 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 failures

can be traced back to improper installation. Practical

information for the proper storage, for the corresponding

fi tting 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

Shaft surfaces


Shaft surface requirements

To 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 a

corresponding 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 shafts

it is recommended in accordance with

DIN 3760 or 3761:

Ra 0.2 - 0.8 µm

Rz 1 - 5 µm

Rmax

6.3 µm

■ 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 maintain

the 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 processes

There is an abundance of possible surface

treatment processes for shafts:

■ Grinding

■ Turning

■ Tangential turning

■ Roller Burnishing

■ Peening

■ Superfi nishing/honing

■ Polishing

■ Quickpoint grinding

■ Outer grinding

However, not all of these processes are

suitable in combination with Simmerrings.

The most important are evaluated according

to 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 failures

of 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 of

rotation 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 plunge

grinding 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.



Residual lead can cause leakage.Although prescribed surface roughness values

have 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 uid

transport through the threads, corresponding

to the direction of rotation, can exceed the

natural pumping capacity of the seal.

Sparking out time is crucialThe 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 parameters can 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 time amounted to 3 minutes!)



Infl uence 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/working material

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

Check during the process

Rotational speed working material Rotational speed grinding disc

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

Tool and working material must rotate in counter directions

Dressing traverse speed Infl uences the slope of the conveying thread

< 0.1 mm/rotation Dressing should only occur in one direction

Dressing tool Can cause a leading structure

Multi grain diamondSingle grain diamond

Dressing infeed Infl uences roughness values

approx. 0.02 mm

Sparking out time Infl uences cross section of the conveying thread

Complete sparking out, at least 30 seconds

Most common causes forlead affl icted surfaces

Infeed depth Can cause leakage >> as Rmax

from the previous machining process

Grinding disc/granulation

Infl uences the roughness parameters R

a; R

z; R

max

Example: 60 –100; Aluminium oxide 60KL8V25 (white) Dimensions 400 x 50 x 127

Concentricity of the tools and working material axis

Creates leading structure on the surface

Concentricity as small as possible



many companies for economic reasons. With

only a few exceptions, the sealing area of the

shaft 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 and

more 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 defi ned 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, in

theory, 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 sealed

area, thus opposed to the effect of the leading

of the shaft. Of signifi cant importance here is

that the seal be capable over a longer period

of time of pumping these fl uid volumes back

since the sur face 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 signifi cantly



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 shafts

often proves to be more diffi cult 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 fi eld, even values of > 0.1 mm/revolution were tested positively, but larger values should not be specifi ed 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 roughness parameters:

Ra 0.1– 0.8 µm

Rz 1– 4 µm

Rmax

< 8 µm

Achievable qualities: Roundness < 2 µmTrue running < 2 µmTolerances from IT 5– IT 6Roughness R

z von 2– 4 µm

Roughness Ra von 0.2– 0.8 µm


materials must be utilised depending on

the shaft material. Furthermore, the above

mentioned manufacturing parameters

cannot always be copied.


influenced by the sealing lip design

(profile, lead type), the radial force and

above 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 critical direction 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 radius

■ cutting 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 les

■ Pumping 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 is

qualitatively 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 prerequisite

for a shaft seal to work reliably.

The surface quality of turned shafts is

signifi cantly 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 effi cient alternative to the

manufacturing processes up to now for

running surfaces of radial shaft seals. The

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

process is based on the kinematics of the

turning space with a linear feed rate and

features:

■ 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 Ra 0.2 - 0.6 µm and

Rz 1 - 3 µm.

Fundamental tests at Simrit have confi rmed

that tangentially turned, hardened shaft

surfaces 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 fi nishing process

is 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 the

surface, 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 diffi cult for a lubricant fi lm

to 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 roller

bur nished fi nishes are suitable as counter

surfaces for Simmerrings.

Adherence to the manufacturing parameters is importantA prerequisite is that the surface

roughness values should be as follows:

Ra 0.1 - 0.8 µm

Rz 0.8 - 5 µm

Rmax

< 7 µm

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 reproduci ble 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 operating

conditions 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 fi nalises the roller

burnishing process and the production

parameters, he/she should consult with the

seal manufacturer [you can fi nd an enquiry

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

PeeningPeening of shafts is also used for

strengthening 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 fi nished 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 lubricant

under the sealing contact.

Frictional torque and hence the power loss of

radial shaft seals on peened surfaces is

therefore 10–30 % 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

signifi cantly 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 the

shaft in the area of the sealing lip is also

markedly less.

Peened structures are also suitable as counter surfacesProcess parameters have to be defi ned 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 undefi ned

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 µm).

Here too, the designer should hold

consultations with the seal manufacturer

when he stipulates "peening" and the

process parameters.

Honing, Superfi nishingA criss cross surface texture is created

through honing or superfi nishing. This has the

advantage that the lubricant binds well to it

and that a suffi cient lubrication is ensured

even under adverse conditions. This positive

structure for the lubricating fi lm adherence is

achieved by the tool performing translatory

movement while the shaft rotates. A criss

cross structure results which appears neutral

at fi rst glance.



Honed or superfi nished 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 were

faultily 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 this

type 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 processesOuter 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 suitable

as a counter direction point for

Simmerrings.



Quickpoint grindingEmpirical data for quickpoint grinding is

inconclusive. 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 direction point 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 abrasive

wear-resistance due to the reforming

process.


Fig. 61: Plunge-cut turning of shafts. While successful applications were realised for soft machining, machining with hardened material is more diffi cult due 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 turning threads

=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 measurementsBesides the adherence to the specifi ed

roughness variables like Ra, R

z and 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 fulfi lled is diffi cult 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 quantitatively

record 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 uence

of 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 fi nal selection, he/she should defi ne the

process parameters together with the seal manufacturer and,

considering the actual operating conditions, determine the

ideal radial shaft seal. For protection or fi nal verifi cation,

aggregate tests should be performed.

Use our fax form at www.simrit.de, so that we can develop

the optimum solution together with you.

Summary


Supplementary literature

[1] Simrit Catalogue(orderable at www.simrit.com)

[2] J. Schneider/L. Schreiber:Tangential turning – an innovative manufacturing

process for the machining of shaft surfaces for

radial shaft seals.

13th International Sealing Conference Stuttgart

2004

[3] T. Kunstfeld/W. Haas:Reliable sealing with radial shaft seals: Alternative

manufacturing processes for the creation of shaft

running surfaces.


2004

[4] S. Buhl/T. Kunstfeld/W. Haas:Sealing with radial shaft seals.

Drive technology 42 (2003) No. 6

[5] J. Schneider/L. Schreiber:With Tangential Turning for Lead-Free Surfaces.

Factory and Operation 6/2002

[6] R. Vogt/E. Bock: Shaft surface structures and their effect on the

tightness and wear behaviour of radial shaft seals.

VDI Seminar Reliable Sealing.

Baden-Baden 2000

[7] H. Raab/W. Haas: Tribological Partners. Radial shaft seals and counter

surfaces.

Drive Technology 38 (1999)

You can fi nd further information about the topic "Simmerrings and shaft surfaces" in the following literature:

[8] Shaft Requirements for Rotary Lip Seals.RMA 1999

[9] W. Guth/R. Vogt:New fi ndings with the surface machining of shafts

for radial shaft seals.

II. Hamburg Technical Sealing Colloquium 1998

[10] R. Vogt/D. Johnston:The Sealing Performance of Elastomer Rotary

Lip Seals on Turned Shafts. SAE-Congress 1998

[11] DIN 3760/DIN 3761

You can fi nd information on new surface measurement procedures at:

[12] N. Rau/V. Kruppke/M. Seibold:Measurable observations of the functional

behaviour of turned sealing surfaces.


2004

[13] N. Rau/V. Kruppke/M. Seibold:Leading structures on ground sealing surfaces and

their effect on the sealing function.

11th International Sealing Conference Dresden

1999

[14] Factory and Operation 1999

[15] Breitmeier:Lead measuring length LMT.

www.breitmeier.com

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