SIMMERRING® COMBI SEAL | Freudenberg FST

Materials

Metal cage - Spring

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

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Application Material Standard Characteristics Metal cage Non-alloy standard steel AISI
(DIN ) Cold rolled steel Metal cage Nickel chrome steel AISI 304
(DIN 1. - V2A) Standard stainless steel Metal cage and spring Chrome-nickel-molybdenum steel AISI 316
(DIN 1. - V4A) Stainless steel highly resistant to corrosion Spring Steel for springs AISI -
DIN Cold drawn carbon steel wire Spring Nickel chrome steel AISI 302
(DIN 1.) 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

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

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

PU (Polyurethane)

Polyurethane is a material that has the elastic properties of rubber. The proportion in its composition (diisocyanate, polyol, chain extender) is determined by its properties. This material is characterised by a strong mechanical resistance, good wear resistance, high elastic modulus, good flexibility and a very good ozone and oxidation resistance.

Chemical resistance Pure aliphatic hydrocarbons (propane, butane)
Mineral oils and greases
Silicone oils and greases
Water up to +50°C Compatibility issue Ketones, esters, ethers, alcohols and glycols
Hot water, steam, alkalis, amines and acids Temperature range -30°C/+90°C
-30°C / +110°C with our special PU (+150°C over a short time)

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

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

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

Technical data

Technical data NBR 75 Shore A FKM 75 Shore A ACM 75 Shore A HNBR 75 Shore A Temperature -30°C/+80°C -20°C/+100°C -25°C/+90°C -30°C/+90°C Speed 4 m/s 6 m/s 5 m/s 5 m/s Pressure 0.02 - 0.05 MPa 0.02 - 0.05 MPa 0.02 - 0.05 MPa 0.02 - 0.05 MPa Accepted axial offset Medium Medium Medium Medium Level of pollution Moderate Moderate Moderate Moderate

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

The graph below compares the different combi seal profiles according to their permissible speed and their capacity to resist different levels of pollution.

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Temperature elevation

The lips of the combi seal are subjected to a higher temperature due to the rotation of the shaft, pressure and increased friction on the shaft. 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.

By definition, the temperature at the edge of the seal is raised when the rotation speed (and thus the linear speed) as well as the shaft diameter increases.

Fluids

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.

Seal design

Tolerance for the outside diameter of the seal (ØD)

The table below indicates the pre-tightening for combi seals on the diameter of the housing in line with standard ISO -1.

Housing ØD1 Tolerances on the outside diameter ØD of the seal Roundness tolerance Apparent metal cage Rubber coating Coating with grooves Apparent metal cage Rubber coating ØD1 ≤ 50.0 + 0.10 / + 0.20 + 0.15 / + 0.30 + 0.20 / + 0.40 0.18 0.25 50.0 < ØD1 ≤ 80.0 + 0.13 / + 0.23 + 0.20 / + 0.35 +0.25 / + 0.45 0.25 0.35 80.0 < ØD1 ≤ 120.0 + 0.15 / + 0.25 + 0.20 / + 0.35 + 0.25 / + 0.45 0.30 0.50 120.0 < ØD1 ≤ 180.0 + 0.18 / + 0.28 + 0.25 / + 0.45 + 0.30 / + 0.55 0.40 0.65 180.0 < ØD1 ≤ 300.0 + 0.20 / + 0.30 + 025 / + 0.45 + 0.30 / + 0.55 025% of the outside diameter 0.80 300.0 < ØD1 ≤ 500.0 + 0.23 / + 0.35 + 0.30 / + 0.55 + 0.35 / + 0.65 025% of the outside diameter 1.00 500.0 < ØD1 ≤ 630.0 + 0.23 / + 0.35 + 0.35 / + 0.65 + 0.40 / + 0.75 - - 630.0 < ØD1 ≤ 800.0 + 0.28 / + 0.43 + 0.40 / + 0.75 + 0.45 / + 0.85 - -

Tolerance for the inside diameter of the seal (Ød)

Free and without constraint, the inside diameter of the sealing lip is always smaller than the diameter of the shaft. The pre-tightening or interference denotes the difference between these two values. Depending on the shaft diameter, the diameter of the sealing lip is generally considered to be less, 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 shaft 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 shaft rotation, which reinforces the pumping effect of the rubber's micro-striations. Below are the types of return pumping leads that can be made:

The graph below sets out the pumping level of the rubber's micro-striations:

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