NBR

Definition: What Is NBR?

NBR stands for nitrile butadiene rubber (in German: Nitril-Butadien-Kautschuk). It is a synthetic elastomer material. Elastomers are rubber-like materials that deform under load and largely return to their original shape afterward. Precisely this recovery capability is decisive for many sealing applications, because it maintains contact pressure at the sealing point.

NBR is a copolymer made of acrylonitrile (ACN) and butadiene. A copolymer consists of two different building blocks linked in a shared chain structure. In sealing technology, NBR is used very frequently, because in many applications it is resistant to mineral oils, lubricating oils, greases, and numerous fuel-like hydrocarbons. As a result, NBR fits particularly well with classic hydraulic and lubricant environments.

Structure and Key Material Properties

NBR combines two building blocks with clear effects: butadiene provides elastic properties, while acrylonitrile (ACN) increases the interaction with non-polar, oily media and therefore often improves oil and fuel resistance. Which properties an NBR sealing material actually shows in operation, however, depends not only on the polymer but strongly on the recipe.

In practice, the term compound is therefore almost always used. A compound is the specific rubber mixture consisting of base elastomer plus additional ingredients such as fillers, plasticizers, and a cross-linking system. Cross-linking (chemical “bridges” between polymer chains) determines, among other things, how well the material keeps its shape under temperature, pressure, and motion. For seals, this coupling of recovery capability, mechanical strength, and media resistance is central, because static and dynamic sealing points generate different load profiles.

Influence of ACN Content

The ACN content is one of the most important adjustment variables in NBR. It influences the trade-off between media resistance and low-temperature behavior.

For seal selection, this means: if a sealing system works mainly in oily media, an NBR with a suitable ACN setting is often chosen. When the seal has to remain flexible at low temperatures, the trade-off becomes stronger and the selection becomes compound- and application-driven.

Compound Instead of Just Material Name

The short name “NBR” only describes the material family. Whether a seal works reliably with a specific medium and temperature profile is decided by the approval of the specific compound. This applies in particular when several influences occur simultaneously — for example temperature cycles, pressure peaks, and continuous media exposure. Therefore, temperature range and media list should be derived from the data sheet of the mixture, not from a general NBR assignment.

Application in Sealing Technology: Media, Temperature, Components

NBR is widespread in hydraulics and pneumatics, because it frequently offers a good compromise of resistance, mechanical load capacity, and cost. In many systems, the question “what does the seal come into contact with?” arises very early. When mineral-oil-based hydraulic oils, lubricating oils, or greases dominate, NBR is often an obvious candidate.

The temperature range is in practice frequently described with approx. $-30\hspace{0.17em}°C$ to $+100\hspace{0.17em}°C$ as a guideline value. This indication is deliberately rough, because medium, pressure, type of motion, and cross-linking can noticeably shift the actual application range. For a reliable design, what counts is therefore the combination of temperature and medium and time — that is, also aging and extraction of mixture components.

Typical NBR Sealing Components

• O-rings (static and dynamic, depending on installation situation),
• Radial shaft seals (rotary seals),
• Wipers / scrapers (protection against dirt ingress, often in the cylinder area),
• Diaphragms (separating and regulating media, e.g., in valves).

Typical Media Resistance

NBR frequently shows good resistance against:

• Mineral oils and mineral-oil-based hydraulic oils,
• Lubricating oils and greases,
• many fuel-like hydrocarbons.

By contrast, with special hydraulic fluids or less common media, the specific recipe decides. Here, a case-by-case check is sensible, because swelling, hardness change, or loss of strength can depend strongly on the compound.

Temperature Range (Practical Guideline)

As an orientation, $-30\hspace{0.17em}°C$ to $+100\hspace{0.17em}°C$ is often cited for NBR. This range is not a guarantee but a starting point for assessment. As soon as high continuous heat, strong temperature cycles, or aggressive media are added, the selection should be supported by data sheet values and possibly testing. In sealing technology, this matters because even moderate deviations in temperature and medium can noticeably influence service life.

Limits and Distinction from HNBR

NBR has clear advantages in many oily systems but shows weaknesses with ozone, UV radiation, and weathering. This becomes relevant as soon as seals are used permanently outdoors or when ozone-polluted environments are present. For certain special hydraulic fluids or polar solvents, NBR is also not automatically suitable. In such cases, compatibility must be checked, because the chemical interaction can turn out significantly different from mineral oil.

HNBR is the close relative — hydrogenated nitrile butadiene rubber. Through hydrogenation, the polymer structure becomes more stable, which typically improves the heat and aging behavior. In addition, HNBR is perceived as more mechanically robust in many applications, although here too the specific mixture remains decisive.

When HNBR Instead of NBR?

• higher application temperatures,
• stronger thermal aging over long times,
• increased mechanical loading at the sealing point.

The decision is usually made when not just a single property becomes tight, but when the overall load profile (temperature, medium, motion, service life) demands more reserves.

In closing: for reliable material selection, data sheets of the specific compound and possibly application-specific tests are sensible — especially with special media or critical temperature profiles.