NBR O-rings: the standard material for oils and greases
NBR is the economical standard elastomer for seals in oil, fuel and hydraulic applications. We cover its properties, media resistance, temperature limits and what matters for design and installation.
- NBR (nitrile-butadiene rubber) is the most affordable and most widely used standard O-Ring material.
- Strengths: good resistance to mineral oil, fuel and greases, high abrasion resistance, good low-temperature flexibility.
- Temperature range: −30 °C to +100 °C, briefly up to +120 °C, special compounds down to −50 °C.
- Weaknesses: ozone, weathering, polar solvents, hot water and steam.
- For higher temperatures or broader chemical resistance: HNBR or FKM as an alternative.
What are NBR O-rings?
NBR, or nitrile-butadiene rubber, is one of the most widely used elastomers for sealing elements alongside FKM and HNBR. The material stands out for its favourable mechanical properties and broad resistance profile. The only real limit on the wide range of applications for these O-rings is their restricted high-temperature suitability. But there is a solution for that too.
HNBR, or hydrogenated nitrile-butadiene rubber, extends the high-temperature range of NBR and is therefore suitable for even more demanding applications. However, many standard applications can be covered economically with NBR O-rings. They are also known colloquially under trade names such as Perbunan or Europrene.
Compared with other O-Ring materials, NBR is the most economical option. When higher temperatures or broader chemical resistance are required, FKM O-rings or HNBR O-rings are the high-performance alternatives to consider.
The 5 key advantages of NBR O-rings
NBR O-rings are a good fit whenever the application calls for pronounced flexibility at low temperatures. Alternatives with similarly good low-temperature suitability include silicone, CR, EPDM or FKM, which should be selected for the specific application based on their media resistance.
Even in static applications, the machine parts being sealed can move. Fluctuating pressure conditions likewise cause O-rings to shift within the installation groove, resulting in mechanical wear. Thanks to their abrasion resistance, however, NBR O-rings are barely susceptible to this kind of material weakening. They retain their mass and thus maintain the sealing effect for longer. This makes NBR O-rings a suitable option even for dynamic applications.
NBR also has a low compression set. This means the O-ring returns to its original cross-section after prolonged deformation and can reliably close the sealing gap. NBR is also the standard material for pneumatic and hydraulic applications, where the O-rings benefit from their resistance to products based on mineral oil.
The 3 most common application areas for NBR O-rings
In the automotive industry, temperature suitability is just as decisive as resistance to SAE engine oils. For the highest temperature loads, alternative materials such as HNBR offer greater reserves.
Applications in the chemical and process industries are highly diversified. Material selection and sizing are carried out with the best possible assessment of the installation situation and requirement profile. The goal is to minimise the risk of downtime in highly interconnected production chains caused by failing O-rings. NBR has its place here alongside many other materials.
How resistant are NBR O-rings to different media?
Mineral oils and products based on them are found in almost all technical systems, for example as hydraulic oils, fuels or lubricants. NBR O-rings show good resistance on contact with these media. Thanks to the high abrasion resistance of NBR, this potential can also be exploited in practice.
| NBR is resistant to | NBR is not resistant to |
|---|---|
| Water | Ozone and weathering |
| Aliphatic hydrocarbons such as mineral oil, hydraulic oil or heating oil | Polar solvents such as acetone |
| Dilute acids and bases | Aromatic and chlorinated hydrocarbons |
| Water-based hydraulic fluids | Glycol-based brake fluid |
| Vegetable and animal fats | Hot water and steam |
When using NBR O-rings, the material's susceptibility to attack by ozone must be taken into account. Even improper storage in ambient air can cause deep cracks in the O-ring, leading to premature seal failure. This is particularly problematic for pre-assembled NBR seals. Airtight storage in a relaxed state provides a remedy. For O-rings subject to particularly high stress, choosing a compound with special ozone protection additives is recommended.
NBR also shows weaknesses when used in hot water and steam. As an alternative, HNBR offers a significant increase in resistance to ozone attack and for hot water applications. The material is produced by hydrogenating NBR and also has a higher upper service temperature. Our media resistance overview shows which material suits which medium.
How high is the temperature resistance of NBR?
NBR is a synthetic rubber known above all for its good oil and fuel resistance. Its temperature resistance varies depending on composition and influences the range of applications.
Which material can withstand how much, from EPDM through FKM to FFKM (ECOLAST), broken down by hot water and steam.
To the hot water and steam table →Influence of acrylonitrile content on temperature flexibility. The acrylonitrile content in NBR has a significant influence on temperature resistance. An NBR material with an 18 percent acrylonitrile content shows good low-temperature flexibility down to about −38 °C, while a material with a 50 percent acrylonitrile content only offers low-temperature flexibility down to about −3 °C. A higher acrylonitrile content improves oil and fuel resistance but reduces flexibility at lower temperatures. A higher polymer content therefore doesn't automatically make a compound better — it always depends on the specific application.
| Acrylonitrile content | Low-temperature flexibility |
|---|---|
| 18 percent | down to about −38 °C |
| 50 percent | down to about −3 °C |
General temperature limits of NBR. In general, NBR is suitable for a temperature range of −30 °C to +100 °C. For short periods, NBR can withstand temperatures of up to +120 °C. However, there are special NBR compounds that can be used down to −50 °C. These properties make NBR a versatile material for a variety of industrial applications.
Some sources state that NBR is resistant up to +120 °C and down to −50 °C. These extended limits increase versatility, particularly in applications with high mechanical strength and abrasion resistance requirements, such as in the automotive industry and in the manufacture of seals and hoses. In summary, NBR is an extremely useful material for applications that require resistance to oil and fuel as well as a degree of flexibility across different temperatures.
What are the mechanical properties of NBR O-rings?
The good abrasion behaviour and compression resistance benefit NBR O-rings in static sealing applications. Even when the machine elements move relative to each other due to changing pressure conditions or external influences, the sealing rings can bridge the altered sealing gap. This also applies after high pressure has acted on the O-ring for an extended period. If the O-ring shifts within the groove, hardly any particles are released from its surface.
This combination of properties makes NBR O-rings suitable for light dynamic applications too, unlike most alternative materials. We are happy to discuss which Shore hardness suits your pressure conditions on a case-by-case basis.
What do I need to consider when designing the groove?
The following key points apply for reliable sealing with NBR O-rings:
- Design the groove in accordance with ISO 3601.
- Ensure a minimum cross-section compression of 6% for static applications.
- Choose a lower compression for dynamic sealing.
- For pressure acting from outside, allow for up to 6% stretch over the groove's inner diameter.
- For pressure acting from inside, plan for 1 to 3% compression at the groove's outer diameter.
At high temperatures, the service life of NBR O-rings is strongly linked to cord thickness. The reason: with larger cross-sections, volume increases considerably more than surface area. This reduces the capacity for mass transfer relative to the O-ring's mass. As a result, larger cord thicknesses slow down the ageing mechanism caused by contact with oxygen. This consideration should be factored into sizing.
What should be considered during installation?
- Provide lead-in chamfers of between 15 and 20 degrees.
- Deburr bores, even those that are only passed over during installation.
- Round off sharp edges with a minimum radius of 0.1 to 0.3 mm.
- Do not stretch the O-ring's inner diameter by more than 50% during installation.
- Use suitable installation aids such as assembly cones or silicone grease.
- Avoid twisting the O-ring.
Frequently asked questions
What kind of material is NBR?
What is NBR 90?
Up to what temperature is NBR resistant?
What is NBR not suitable for?
What alternatives are there to NBR O-rings?
