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Freudenberg Group
www.simrit.com
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Freudenberg Group
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
The
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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®
Reliability right from the beginning
Basics for preventing damage
1. Reliable sealing
2. Shaft surfaces Requirements and working forms
The Simmerring®
Erich Prem • Rolf Vogt
Basics for preventing damage
Reliability right from the beginning
© 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
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
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
11© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG12
■ 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
13© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG14
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
15© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG16
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
17© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG18
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
19© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG20
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
21© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG22
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
23© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG24
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.
25© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG26
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
Handling and installation
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.
27© Freudenberg Simrit GmbH & Co. KG
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
Handling and installation
© Freudenberg Simrit GmbH & Co. KG28
■ 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.
Handling and installation
29© Freudenberg Simrit GmbH & Co. KG
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
Handling and installation
© Freudenberg Simrit GmbH & Co. KG30
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
Handling and installation
31© Freudenberg Simrit GmbH & Co. KG
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
Contamination of Simmerrings
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
Contamination of Simmerrings
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)
Contamination of Simmerrings
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
© Freudenberg Simrit GmbH & Co. KG32
Sources of error Possible errorsConsequences
for the Sealing function
Cause of the problem
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
33© Freudenberg Simrit GmbH & Co. KG
Sources of error Possible errorsConsequences for the sealing
function
Cause of the problem
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
From immediate leakage to reduced lifespan
Fitting mandrel not OK Regular checking
Incorrect fi tting mandrel
Damage to the Simmerring
From immediate leakage to reduced lifespan
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)
From immediate leakage to reduced lifespan
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
© Freudenberg Simrit GmbH & Co. KG34
Sources of error Possible errorsConsequences for the sealing
function
Cause of the problem
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
From immediate failures to reduced lifespan
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
From immediate failures to reduced lifespan
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
35© Freudenberg Simrit GmbH & Co. KG
Sources of error Possible errorsConsequences for the sealing
function
Cause of the problem
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
Die-cast housing (Al, Mg)
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
Die-cast housing (Al, Mg)
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
© Freudenberg Simrit GmbH & Co. KG36
Sources of error Possible errorsConsequences for the sealing
function
Cause of the problem
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
37© Freudenberg Simrit GmbH & Co. KG
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
2. Shaft surfaces Requirements and working forms
Shaft surfaces
© Freudenberg Simrit GmbH & Co. KG40
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.
41© Freudenberg Simrit GmbH & Co. KG
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.
Surface treatment processes
© Freudenberg Simrit GmbH & Co. KG42
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!)
Surface treatment processes
43© Freudenberg Simrit GmbH & Co. KG
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
Surface treatment processes
© Freudenberg Simrit GmbH & Co. KG44
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
Surface treatment processes
45© Freudenberg Simrit GmbH & Co. KG
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
Surface treatment processes
materials must be utilised depending on
the shaft material. Furthermore, the above
mentioned manufacturing parameters
cannot always be copied.
© Freudenberg Simrit GmbH & Co. KG46
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.
Surface treatment processes
Fig. 51:REM image of a milled shaft
47© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG48
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
Surface treatment processes
49© Freudenberg Simrit GmbH & Co. KG
■ 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
Surface treatment processes
Fig. 58: REM image of a blasted shaft
© Freudenberg Simrit GmbH & Co. KG50
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.
Surface treatment processes
51© Freudenberg Simrit GmbH & Co. KG
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.
Surface treatment processes
© Freudenberg Simrit GmbH & Co. KG52
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.
Surface treatment processes
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
53© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG54
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
55© Freudenberg Simrit GmbH & Co. KG
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
© Freudenberg Simrit GmbH & Co. KG56
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.
13th International Sealing Conference Stuttgart
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.
13th International Sealing Conference Stuttgart
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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