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OTB

OTB

Description

The OTB profile is an inverted shaft seal composed of a single internal metal cage with a rubber coating on the outside and a primary sealing lip with integrated spring and an additional anti-pollution sealing lip.

Advantages

Good radial rigidity, particularly for large diameters
Good stability when assembled, preventing the bounce-back effect
Sealing for low and high viscosity fluids
Modern primary sealing lip with low radial forces
Protection against undesirable air contaminants

Technical data

Applications

All types of rotative applications
Rotating hubs
Fixed shafts

Materials

Rubber

ACM 70 - 75 Shore A
EPDM 70 - 75 Shore A
FKM 70 - 75 Shore A
HNBR 70 - 75 Shore A
NBR 70 - 75 Shore A

Metal cage

Steel - AISI 1010
Stainless steel - AISI 304
Stainless steel - AISI 316

Spring

Steel - AISI 1070 - 1090
Stainless steel - AISI 316

Dimensions
Materials
Conditions
for use
Seal design
Shaft design
Housing design

Dimensions

Installation drawingLogement pour bague d'étanchéité inversée - Housing groove for inverted shaft seal

Materials

Metal cage - Spring

The table below shows the materials that we can offer for metal cages and springs.

Application Material Standard Characteristics
Metal cage Non-alloy standard steel AISI 1010
(DIN 1624)
Cold rolled steel
Metal cage Nickel chrome steel AISI 304
(DIN 1.4301 - V2A)
Standard stainless steel
Metal cage and spring Chrome-nickel-molybdenum steel AISI 316
(DIN 1.4401 - V4A)
Stainless steel highly resistant to corrosion
Spring Steel for springs AISI 1070 - 1090
DIN 17223
Cold drawn carbon steel wire
Spring Nickel chrome steel AISI 302
(DIN 1.4300)
Stainless steel for springs with a high carbon content

Rubbers

ACM (Polyacrylate)

Polymers containing ethyl acrylate (or butyl acrylate) have a small amount of monomer, which is necessary for cross-linking; ACM is a material with better heat resistance than NBR. It is often used for automatic gearboxes.

Chemical resistance Mineral oils (motor oils, gear box oils, ATF oils)
Atmospheric and ozone agents
Compatibility issue Glycol-based brake fluids (Dot 3 & 4)
Aromatic and chlorinated hydrocarbons
Water and steam
Acids, alkalis and amines
Temperature range -25°C to + 150°C (short-term peak at +160°C)
-35°C / +150°C with particular ACMs
AEM (ethylene acrylate rubber)

As a methyl acrylate and ethylene copolymer, AEM is considered to be more resistant to heat than ACM. Its characteristics make it an intermediary between ACM and FKM.

Chemical resistance Cooling fluids
Aggressive mineral oils
Atmospheric agents
Water
Compatibility issue Aromatic solvents
Strong acids
Brake fluids
Gearbox oils
ATF oils
Temperature range - 40°C to + 150°C
CR (Polychloroprene)

This CR-based rubber is used in the refrigeration industry and for ventilation systems. This chloroprene was the first synthetic rubber to be developed and marketed.

Chemical resistance Paraffinic mineral oils
Silicone oils and greases
Water and water-based solvents for use at low temperatures
Refrigerant fluids
Ammoniac
Carbon dioxide
Atmospheric and ozone agents
Limited chemical resistance Naphthenic mineral oils
Aliphatic hydrocarbons (propane, butane, petroleum)
Glycol-based brake fluids
Compatibility issue Aromatic hydrocarbons (benzene)
Chlorinated hydrocarbons (trichlorethylene)
Polar solvents (ketone, acetone, acetic acid, ethylene-ester)
Temperature range -40°C / +100°C (short-term peak at +120°C)
EPDM (Ethylene Propylene Diene Monomer rubber)

As an Ethylene Propylene Diene Monomer copolymer, EPDM is commonly used for hot water taps, cooling systems, brake systems, dishwashers and washing machines.

Chemical resistance Hot water and steam up to +150°C
Glycol-based brake fluids (Dot 3 & 4) and silicone-based brake fluids (Dot 5)
Organic and inorganic acids
Cleaning agents, sodium and potassium alkalis
Hydraulic fluids (HFD-R)
Silicone oils and greases
Polar solvents (alcohols, ketones and esters)
Atmospheric and ozone agents
Compatibility issue Mineral oils and greases
Hydrocarbons
Low impermeability to gas
Temperature range -45°C / +150°C (short-term peak at +175°C)
FFKM (perfluorinated rubber)

FFKM has the best characteristics for resistance to high temperatures, with an excellent chemical inertia. This FKM-based rubber is very often used for high-temperature hydraulic and pneumatic systems, industrial valves, injection/fuel systems, motor seals and high-vacuum systems.

Chemical resistance Aliphatic and aromatic hydrocarbons
Polar solvents (ketones, esters and ethers)
Organic and inorganic acids
Water and steam
High-vacuum system
Compatibility issue Coolants (R11, R12, R13, R113, R114, etc.)
PFPE
Temperature range -15°C/+320°C
FKM (fluorinated rubber)

Depending on their structure and fluorine content, the chemical resistance and resistance to the cold in fluororubbers can vary. This FKM-based rubber is very often used for high-temperature hydraulics and pneumatics, for industrial valves, injection/fuel systems, motor seals and high-vacuum systems.

Chemical resistance Mineral oils and greases, ASTM n°1, IRM 902 and IRM 903 oils.
Fire-resistant liquids (HFD)
Silicone oils and greases
Mineral and vegetable oils and greases
Aliphatic hydrocarbons (propane, butane, petroleum)
Aromatic hydrocarbons (benzene, toluene)
Chlorinated hydrocarbons (trichlorethylene)
Fuel (including high alcohol content)
Atmospheric and ozone agents
Compatibility issue Glycol-based brake fluids
Ammonia gas
Organic acids with a low molecular weight (formic and acetic acids)
Temperature range -20°C / +200°C (short-term peak at +230°C)
-40°C / +200°C with particular FKMs
FVMQ (fluorosilicone rubber)

The FVMQ has mechanical and physical properties that are very similar to those of the VMQ. However, the FVMQ offers better resistance to fuels and mineral oils. However, resistance to hot air is not as good as that of the VMQ.

Chemical resistance Aromatic mineral oils (IRM 903 oil)
Fuels
Aromatic hydrocarbons with low molecular weights
(benzene, toluene)
Temperature range -70°C/+175°C
HNBR (Hydrogenated Nitrile Butadiene Rubber)

This HNBR-based rubber is obtained through selective hydrogenation of the NBR's butadiene groups. It is commonly used for power-assisted steering and for air conditioning.

Chemical resistance Aliphatic hydrocarbons
Mineral and vegetable oils and greases
Fire-resistant fluids (HFA, HFB and HFC)
Diluted acids, saline solutions and bases for operation at an average temperature
Water and steam up to +150°C
Atmospheric and ozone agents
Compatibility issue Chlorinated hydrocarbons
Polar solvents (ketones, esters and ethers)
Strong acids
Temperature range -30°C / +150°C (short-term peak at +160°C)
-40°C / +150°C with particular HNBRs
NBR (Nitrile Butadiene Rubber)

Nitrile rubber (NBR) is the general term for acrylonitrile-butadiene copolymer. The ACN content can vary between 18% and 50%. While the acrylonitrile content is important, the resistance to oil and fuel is more so. Conversely, the elasticity and compression set are not as good. The NBR has good mechanical properties and good wear resistance. However, its resistance to atmospheric agents and the ozone is relatively low.

Chemical resistance Aliphatic hydrocarbons (propane, butane, petroleum, diesel fuel)
Mineral oils and greases
Fire-resistant fluids (HFA, HFB and HFC)
Diluted acids, low-temperature alkaline and saline solutions
Water (up to +100°C max)
Compatibility issue Fuels with high aromatic content
Aromatic hydrocarbons (benzene)
Chlorinated hydrocarbons (trichlorethylene)
Polar solvents (ketone, acetone, acetic acid, ethylene-ester)
Strong acids
Glycol-based brake fluids
Atmospheric and ozone agents
Temperature range -30°C / +100°C (short-term peak at +120°C)
-40°C / +100°C with particular NBRs
VMQ (silicone rubber: methyl vinyl polysiloxane)

This FVMQ-based rubber is very often used in fuel systems.

Chemical resistance Animal and vegetable oils and greases
Water for operation at an average temperature
Diluted saline solutions
Atmospheric and ozone agents
Compatibility issue Superheated steam up to +120°C
Chlorinated hydrocarbons with a low molecular weight (trichlorethylene)
Aromatic hydrocarbons (benzene, toluene)
Temperature range -60°C / +200°C (short-term peak at +230°C)

The table below gives an overview of the physical, chemical and mechanical characteristics for each of the materials.

Characteristics/Materials ACM AEM CR EPDM FFKM FKM FVMQ HNBR NBR VMQ
Abrasion resistant 2 3 2 2 4 2 4 2 2 4
Resistance to acids 4 3 2 2 1 1 3 1 3 3
Chemical resistance 4 2 2 1 1 1 1 2 2 2
Resistance to cold 4 2 2 2 3 4 2 2 2 2
Dynamic properties 3 3 3 2 3 2 4 1 2 4
Electrical properties 3 3 3 2 1 4 1 3 3 1
Flame resistant 4 4 2 4 1 1 2 4 4 3
Heat resistant 1 1 2 2 1 1 1 1 2 1
Sealing water 1 1 2 2 2 2 4 2 2 4
Oil resistant 1 3 2 4 1 1 2 1 1 2
Ozone resistant 1 1 2 1 1 1 1 2 4 1
Tearing resistant 2 3 3 1 4 3 4 2 2 4
Traction resistant 3 2 2 1 2 1 3 1 2 4
Water/vapour resistant 4 4 3 1 2 3 3 1 2 3
Resistance to atmospheric agents 1 1 1 1 1 1 1 2 3 1

1. Excellent properties 2. Good properties 3. Average properties 4. Poor properties

Chemical compatibility

A "Chemical compatibility guide" catalogue can be downloaded from the Documentation section. You can also use our online "Chemical compatibility" tool free of charge.

These two tools give you the option of measuring the behaviour of our materials that come into contact with the majority of existing fluids. The data displayed is the result of rigorous testing of the ambient temperature and in consultation with previous publications. Test results are not fully representative due to the specific features of your application. The tests performed actually do not consider additives and impurities that may exist under the actual conditions of use, nor the potential elevation of temperatures. Other parameters can also alter the behaviour of our materials, such as the hardness, persistence, abrasion, etc. We therefore recommend performing your own tests to verify the compatibility of our materials according to your specific application. Our technical team can provide you with any additional information.

Conditions for use

Speed

The table below indicates the relationships between the linear speed, the rotation speed and the recommended material.

Maximum speed for inverted shaft seals

Linear speed calculation: s (m/s) = [Ø rotating hub (mm) x speed (rpm) x π] / 60,000

Pressure

The inverted shaft seals are generally used in unpressurised environments, or for pressures between 0.02 and 0.05 MPa (maximum).

Temperature

The table below indicates the temperature limits, depending on the materials and fluids used.

Media Maximum temperature, depending on the materials
ACM AEM EPDM FKM HNBR NBR VMQ
Mineral oils Oils for motors +130°C +130°C - +170°C +130°C +100°C +150°C
Oils for gearboxes +120°C +130°C - +150°C +110°C +80°C +130°C
Oils for hypoid gears +120°C +130°C - +150°C +110°C +80°C -
ATF oils +120°C +130°C - +170°C +130°C +100°C -
Hydraulic oils +120°C +130°C +150°C +130°C +90°C -
Greases - +130°C - - +100°C +90°C -
Fire-resistant
fluids
HFA group - Emulsion with more than 80% water - - - - +70°C +70°C +60°C
HFB group - Opposite solution (water in oil) - - - - +70°C +70°C +60°C
HFC group - Polymer aqueous solution - - +60°C - +70°C +70°C -
HFD group - Water-free synthetic fluids - - - +150°C - - -
Other fluids EL + L heating oil - - - - +100°C +90°C -
Air +150°C +150°C +150°C +200°C +130°C +90°C +200°C
Water - - +150°C +100°C +100°C +90°C -
Water for washing - - +130°C +100°C +100°C +100°C -
Temperature range Min. -25°C -40°C -45°C -20°C -30°C -30°C -60°C
Max. +150°C +150°C +150°C +200°C +150°C +100°C +200°C

The lip of the seal is subjected to a higher temperature due to the hub rotation, and the significant pressure and friction on the mechanical parts. Good lubrication is therefore necessary to allow for a better release of heat and thus limits the temperature rise in the parts subjected to friction.

Fluids

The data below refers mainly to standard shaft seals, but it can also apply to inverted shaft seals.

Mineral oils

In general, this type of oil has few additives and is therefore perfectly suitable for all of the rubbers used for the rotary shaft seals. The following oils are suitable for revolving applications:

  • motor oils
  • gearbox oils
  • hypoid oils
  • ATF oils for automatic gearboxes
  • transmission oils
synthetic oils

This type of oil is used to improve different characteristics such as the resistance to ageing, resistance to high temperatures, viscosity, etc. and has a good compatibility with the majority of rubbers used for the seals for the rotary shaft. Tests may need to be performed beforehand to measure the degree of compatibility of this type of oil with the materials used. Among the synthetic oils are:

  • brake fluids
  • fluids for automatic gearboxes
  • fluids for suspensions
  • fluids for steering systems
  • fluids for hydraulic transmissions
Hypoid oils

This type of oil contains special components such as EP additives. These enable lubrication and thus limit any seizing at the bearings, for example. When affected by heat, these additives have the tendency to lead to deposits on the sealing lip. That is why we recommend using seals for the rotating shaft with a sealing lip comprising return pumping leads in order to limit the increase in temperature and above all, to reduce these potential carbon deposits.

Greases

Greases are generally applied to bearings etc. and require specific adaptation to provide favourable operating conditions for the rotary shaft seal. To prevent the lip of the seal from sustaining more significant pressures than planned, we recommend positioning the lip seal on one side of the bearing in such a way so that the lip is not prematurely destroyed. We also recommend reducing the rotation speed by 50% when lubricated, to ensure that less heat escapes during friction.

Aggressive fluids

It is critical to choose the correct material to better resist different aggressive fluids (acids, solvents, chemical products, etc.). For applications in a rotating environment, we recommend using materials such as FKM rather than NBR. For operations that are dry or use very little lubrication, and where the rubbers do not resist certain aggressive fluids, we advise you to use our PTFE seals for the rotary shaft.

Seal design

Tolerance for the inside diameter of the seal (Ød)

The table below sets out the pre-tightening for shaft seals on the diameter of the fixed shaft.

Shaft diameter
Ød1 (mm)
Tolerances on the inside diameter Ød of the ring Roundness tolerance
Apparent metal cage Rubber coating Coating with grooves Apparent metal cage Rubber coating
Ød1 ≤ 50.0 -0.20 / -0.10 -0.30 / -0.15 -0.40 / -0.20 0.18 0.25
50.0 < Ød1 ≤ 80.0 -0.23 / -0.13 -0.35 / -0.20 -0.45 / -0.25 0.25 0.35
80.0 < Ød1 ≤ 120.0 -0.25 / -0.15 -0.35 / -0.20 -0.45 / -0.25 0.30 0.50
120.0 < Ød1 ≤ 180.0 -0.28 / -0.18 -0.45 / -0.25 -0.55 / -0.30 0.40 0.65
180.0 < Ød1 ≤ 300.0 -0.30 / -0.20 -0.45 / -0.25 -0.55 / -0.30 0.25% of ØD 0.80
300.0 < Ød1 ≤ 500.0 -0.35 / -0.23 -0.55 / -0.30 -0.65 / -0.35 0.25% of ØD 1.00
500.0 < Ød1 ≤ 630.0 -0.35 / -0.23 -0.65 / -0.35 -0.75 / -0.40 - -
630.0 < Ød1 ≤ 800.0 -0.43 / -0.28 -0.75 / -0.40 -0.85 / -0.45 - -

Tolerance for the outside diameter of the seal (ØD)

Free and without constraint, the outside diameter of the sealing lip is always bigger than the diameter of the rotating hub. The pre-tightening or interference denotes the difference between these two values. Depending on the hub diameter, the diameter of the sealing lip is generally considered to be greater, between 0.8 and 3.5 mm.

Pumping leads

The sealing lip operates with low lubrication and significant heating at the point of contact with the rotating hub during higher stresses with elevated temperatures and speeds, and with the seal close to the bearing exercising a considerable pumping effect.

To maintain the lubrication, we recommend integrating diagonal pumping leads on the primary sealing lip, on the air side oriented in the direction of the support's rotation, which reinforces the pumping effect of the rubber's micro-striations. Below are the types of return pumping leads that can be made:

Pumping leads for shaft seals

Shaft design

Fixed shaft installation for the inverted shaft seal

Surface roughness

The recommendations below must be considered for the quality of the shaft surface area.

Standard conditions for inverted shaft seals with an apparent metal cage:

  • Ra = 0.8 to 3.2 µm
  • Rz = 6.3 to 16.0 µm
  • Rmax ≤ 16.0 µm

Shaft diameter tolerance

The shaft diameter must have a tolerance of H8, in line with standard ISO 286-2

Shaft diameter
Ød1 (mm)
Tolerance
H8 (mm)
3.0 < Ød1 ≤ 6.0 - 0.018 / 0
6.0 < Ød1 ≤ 10.0 -0.022 / 0
10.0 < Ød1 ≤ 18.0 -0.027 / 0
18.0 < Ød1 ≤ 30.0 -0.033 / 0
30.0 < Ød1 ≤ 50.0 -0.039 / 0
50.0 < Ød1 ≤ 80.0 -0.046 / 0
80.0 < Ød1 ≤ 120.0 -0.054 / 0
120.0 < Ød1 ≤ 180.0 -0.063 / 0
180.0 < Ød1 ≤ 250.0 -0.072 / 0
250.0 < Ød1 ≤ 315.0 - 0.081 / 0
315.0 < Ød1 ≤ 400.0 -0.089 / 0
400.0 < Ød1 ≤ 500.0 -0.097 / 0

Fixed shaft widths

The table below provides information on the width of the groove and the recommended radius.

Height
H1 (mm)
Width Radius
R2 max (mm)
L2 min
H1 x 0.85
L1 min
H1 + 0.30
7.00 5.95 7.30 0.50
8.00 6.80 8.30
10.00 8.50 10.30
12.00 10.30 12.30 0.70
15.00 12.75 15.30
20.00 17.00 20.30

Housing design

Rotating support installation for the inverted shaft seal

Rotating hub material

Suitable materials are:

  • ordinary C35 and C45 steels used in mechanical construction
  • 1.4300 and 1.4112 stainless steels for sealing water
  • sprayed carbide coatings
  • graphite
  • malleable cast iron
  • materials with a CVD and PVD coating

Not appropriate:

  • hard chrome coatings due to irregular wear
  • plastic materials resulting from low thermal conductivity, which can lead to a disturbance in the transport of heat, an increase in temperature in friction areas with the shaft seal, as well as a potential softening

Rotating hub hardness

The hardness of the rotating hub will depend on the linear speed (in m/s) and the level of pollution.

Rotation speed Hardness in HRC
s ≤ 4 m/s 45 HRC
4.0 < s ≤ 10.0 m/s 55 HRC
s > 10.0 m/s 60 HRC

Surface roughness

The recommendations below must be considered for the quality of the housing surface area.

Standard conditions:

  • Ra = 0.2 to 0.8 µm and 0.1 for demanding applications
  • Rz = 1.0 to 4.0 µm
  • Rmax ≤ 6.3 µm

For pressurev > 0.1 MPa:

  • Ra = 0.2 to 0.4 µm and 0.1 for demanding applications
  • Rz = 1.0 to 3.0 µm
  • Rmax ≤ 6.3 µm

Rotating hub tolerance

The hub must have a tolerance of H11, in line with standard ISO 286-2

Rotating hub diameter
ØD1 (mm)
Tolerance
H11 (mm)
3.0 < ØD1 ≤ 6.0 0 / +0.075
6.0 < ØD1 ≤ 10.0 0 / +0.090
10.0 < ØD1 ≤ 18.0 0 / +0.110
18.0 < ØD1 ≤ 30.0 0 / +0.130
30.0 < ØD1 ≤ 50.0 0 / +0.160
50.0 < ØD1 ≤ 80.0 0 / +0.190
80.0 < ØD1 ≤ 120.0 0 / +0.220
120.0 < ØD1 ≤ 180.0 0 / +0.250
180.0 < ØD1 ≤ 250.0 0 / +0.290
250.0 < ØD1 ≤ 315.0 0 / +0.320
315.0 < ØD1 ≤ 400.0 0 / +0.360
400.0 < ØD1 ≤ 500.0 0 / +0.400
500.0 < ØD1 ≤ 630.0 0 / +0.440

Chamfer and radius

You are strongly advised to install a chamfer on the hub so as not to alter the primary sealing sealing lip of the shaft seal during assembly. Please refer to the table below.

Rotating hub diameter
ØD1 (mm)
Chamfer diameter
ØD3 (mm)
Radius
R (mm)
ØD1 ≤ 10.0 ØD1 + 1.50 2.00
10.0 < ØD1 ≤ 20.0 ØD1 + 2.00 2.00
20.0 < ØD1 ≤ 30.0 ØD1 + 2.50 3.00
30.0 < ØD1 ≤ 40.0 ØD1 + 3.00 3.00
40.0 < ØD1 ≤ 50.0 ØD1 + 3.50 4.00
50.0 < ØD1 ≤ 70.0 ØD1 + 4.00 4.00
70.0 < ØD1 ≤ 95.0 ØD1 + 4.50 5.00
95.0 < ØD1 ≤ 130.0 ØD1 + 5.50 6.00
130.0 < ØD1 ≤ 240.0 ØD1 + 7.00 8.00
240.0 < ØD1 ≤ 500.0 ØD1 + 11.00 12.00

Hub run out

The hub run out represents a deviation between the current axis of the rotating hub and the theoretical rotation axis. It is important to reduce the rotating hub run out as much as possible by positioning the inverted shaft seal as close as possible to the bearing. The table below sets out the maximum permissible values depending on the rotation speed and the sealing lip material.

Hub run-out for inverted shaft seals with spring

Eccentricity

The shaft and hub must be assembled centred on one another in order to remove any unilateral radial load at the sealing lip of the ring.

Eccentricity for inverted shaft seals with spring

Rotating hub machining

Correct machining of the rotating hub is essential to the proper operation of the sealing system.

  • Plunge grinding: preferred machining method to ensure the absence of striations on the hub (0 +/- 0.05°)
  • Turning: suitable for shafts used with a unidirectional sense of rotation

Machining guidelines for surface adjustments

Parameters Requirements
Speed of the part to be machined 30 to 300 rpm
Wheel speed 1500 to 1700 rpm
Surfacing feed < 0.02 mm/turn
Dressing tool multi-grain dressing diamond, single drain dressing diamond
Grinding rate feed approximately 0.02 mm
Spark duration full spark, 30 secs min.
Passing depth > Rmax of the old machining operation
Eccentricity of the tool and part to be machined the best possible

Only on request