COMB3

Dimensions

Installation drawing

Materials

Metal cage - Spring

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

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.

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.

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.

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.

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.

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

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

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.

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 6194-1.

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:

Shaft design

Shaft 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 as a result of low thermal conductivity, which can lead to a disruption in the transport of heat, an increase in temperature in friction areas with the combi seal, as well as a potential softening

Shaft hardness

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

Surface roughness

The recommendations below must be considered for the quality of the shaft 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

Shaft tolerance

The shaft must have a tolerance of h11, in line with standard ISO 286-2

Chamfer

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

Shaft run out

The shaft run out is a deviation between the current shaft axis and the theoretical rotation axis. It is important to reduce the shaft run out as much as possible by positioning the 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.

Eccentricity

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

Shaft machining

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

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

Machining guidelines for surface adjustments

Housing design

Surface roughness

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

Standard conditions for combi seals with an apparent metal cage:

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

Tolerance of the bore diameter of the housing

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

Chamfer

We urge you to fit a chamfer on the housing. We recommend opting for:
20° (+/-5°) x 1.5 mm