HNBR O-rings | Materials explained simply | Sealing Academy (2024)

Advantages | Areas of application | Media resistance | Temperature resistance | Mechanical properties| Design

HNBR (hydrogenated acrylonitrile butadiene rubber) is one of the elastomers with the widest range of applications in industry.

Not only sealing rings, but also timing belts and hydraulic hoses are made from this material.

This already shows the potential of HNBR for use as an O-ring: The combination of good mechanical strength and a high maximum operating temperature characterizes HNBR sealing elements.

It is also resistant to mineral oil-based media. HNBR is produced by partially or fully hydrogenating the O-ring material NBR (acrylonitrile butadiene rubber).

This step enables key improvements in the properties of HNBR compared to NBR, above all resistance to weathering and ozone as well as higher temperature resistance.

Many heavily loaded NBR O-rings are increasingly being replaced by variants made of the higher-performance but also more cost-intensive HNBR. Practitioners also know HNBR under the trade names Therban® or Zetpol®.

1. high resistance to oil and grease based on mineral oil
2. low gas permeability to gas and vapor
3. good mechanical properties
4. wide temperature range
5. suitable for dynamic applications

The fact that HNBR is also used as a material for timing belts in the automotive industry makes it clear: O-rings made from this material are suitable for use indynamic seals.

When O-rings seal components that are in motion against each other, they are subject to particular stress. Friction occurs under these conditions, which can cause material loss on the O-ring.

Added to this is the increased temperature input into the material, which can lead to a change in the internal structures. Due to their properties, HNBR O-rings can withstand both loads and can be used for dynamic applications with sufficient durability.

The wide temperature range, coupled with resistance to mineral oil-based products, makes HNBR O-rings suitable for seals in automotive drives.

In combustion engine components, the O-rings come into contact with hot media such as cooling water, fuels, air or oil, which can also occur as a mixture.

In addition to these mass applications, HNBR O-rings also qualify for special industries such as gas exploration. This is due to the material’s particularly low permeability to gas and vapor.

In addition to the increased temperature range, HNBR is also superior to the base material NBR due to its improved resistance to oxidative attack. This is an important addition to the already broad durability profile for practical use.

HNBR is resistant to:
– Aliphatic hydrocarbons
– Animal and vegetable fats and oils
– Water and water vapor within the upper continuous temperature of 150 degrees
– Flame retardant pressure fluids: HFA, HFB, HFC fluids
– Light heating oil and diesel fuel
– Acids, bases and salt solutions diluted at low temperature
– Ozone and weather

HNBR swells strongly in aromatic hydrocarbons such as benzene or trichloroethylene.

This swelling causes a significant reduction in the mechanical properties of HNBR O-rings. However, these return after the material has dried again. The resistance of HNBR O-rings to oil depends largely on the acrylonitrile (ACN) content of the material compound.

A higher proportion of the mixture increases the insensitivity, but at the same time causes a deterioration in the low-temperature behavior. The right HNBR material should therefore be selected depending on the specific application.

This allows the maximum performance of HNBR O-rings to be utilized.

HNBR O-rings have a temperature resistance of -30°C to +150°C.

The temperature range of common grades of HNBR O-rings extends from -30 to +150 degrees.

Depending on its composition, HNBR is also suitable for low temperatures down to -40 degrees. This means that HNBR covers similarly low temperatures as the alternative sealing materials NBR,FKMorFFKM.

In terms of maximum continuous temperature, HNBR is comparable toACMorEPDM. The market offers FKM orVMQbut also materials with a significantly higher upper temperature limit.

Thermally aged HNBR O-rings show significantly lessswellingin contact with the media. The loss of mechanical properties is also less pronounced.

This is due to a higher cross-linking density compared to the starting material. In general, the temperature and media resistance of O-ring materials must always be evaluated in context.

For example, the temperature ranges of HNBR O-rings in contact with certain media can deviate significantly from the general specifications. The choice of material must therefore always be based on the specific application.

1. Excellent abrasion resistance Abrasion
2. High tensile strength
3. Resistant to explosive decompression

HNBR O-rings stand out from the multitude of O-ring materials primarily due to their excellent abrasion resistance.

Together with the temperature suitability, this makes HNBR O-rings insensitive to friction in dynamic seals.

The high tensile strength of the material also contributes to its suitability for this application. Other materials with goodabrasion resistanceare EPDM, NBR, CR and FKM.

Due to its high mechanical strength, HNBR is also particularly resistant toexplosive decompression. This phenomenon occurs when there is a rapid drop in pressure in a gas-bearing sealing system. In response, the gas in the O-ring expands considerably.

If the natural gas permeability of the O-ring material is not sufficient for this, the gas makes its own way through the structure of the material. This results in permanent damage to the O-ring, which manifests itself in cracks and blistering.

The low gas permeability and insensitivity to explosive decompression play an important role, especially for long-term use in the oil and gas industry. The industry has therefore developed its own standard in the form of NORSOK M-710.

As with FFKM and FKM, compliant HNBR O-rings are also available.

Groove design of HNBR O-rings

1. Compression in the groove should be approx. 20% for static use
2. Select lower compression for dynamic sealing
3. 20% of the groove should still be free after grouting
4. Always design grooves according to the standard tables available on the market
5. Permanent elongation after installation should be less than 6%
6. Permanent compression after installation should be less than 6%

Assembly of HNBR O-rings

1. Clean the groove space thoroughly before installation
2. Do not expand elastic O-rings by more than 50% during installation
3. Provide insertion slopes between 15 and 20 degrees
4. Deburr drill holes, even if they are only passed over during assembly
5. Round off sharp edges with a minimum radius of 0.1 to 0.3 mm
6. Use silicone grease to make assembly easier
7. Avoid twisting the O-ring

Seals such as O-rings made of HNBR are basically comparable to the widely used material NBR.

However, O-rings made of HNBR (hydrogenated NBR) are more resistant to high temperatures and aggressive media. In addition, HNBR O-rings can be used even better for dynamic applications compared to NBR O-rings.

You can easily view the data sheet for our HNBR O-rings directly on our website and download it if you wish.

Link to the data sheet

HNBR is particularly resistant to aliphatic hydrocarbons and fats and oils.

This makes HNBR the perfect material for the automotive industry and gas and water systems.

HNBR is very similar to NBR. The “H” in HNBR indicates that the NBR has been hydrogenated. In other words, HNBR is an NBR that has been saturated with additional hydrogen atoms.

This results in the following 3 parts:

1. temperature resistance up to +150°C
2. higher media resistance
3. higher abrasion resistance