HNBR is the abbreviation for hydrogenated acrylonitrile butadiene rubber. It is produced by the selective hydrogenation of NBR.

HNBR has the following properties compared to NBR:

• Heat resistance up to 150 °C for peroxide cross-linked HNBR rubber.
• Good mechanical properties and abrasion resistance.
• Good resistance to weathering and ozone.
• HNBR is available in the hardness ranges Shore A 45-98 and can thus be adapted to the tasks.
  
  

Physical properties of HNBR

Hydrogenated acrylonitrile butadiene rubber as a vulcanizate made from NBR has excellent resistance to oils, greases and hydrocarbons. The aging behavior is favorable for industrial applications and low abrasion is observed under mechanical stress. The acrylonitrile content in the range of 18 % - 50 % allows the following properties to be specifically influenced: Swelling resistance, gas permeability, low-temperature flexibility and compression set. At 18 % acrylonitrile content, the material is flexible down to -38 °C low temperature.

This synthetic rubber forms the basis for materials in a wide variety of applications due to its technological properties. Radial shaft seals, hydraulic and pneumatic seals, toothed belts and O-rings are manufactured on the basis of this material HNBR. The material is also used in many kinds of seals, hoses, rubber gloves and rubber threads.oil and fuel resistance is moderately acceptable. In contrast, HNBR products with 50% acrylonitrile content are more suitable for the range above -3 °C, but with optimum properties in terms of fuel and oil resistance. Elasticity and gas permeability thus decrease with increasing acrylonitrile content. The compression set also deteriorates.

This synthetic rubber forms the basis for materials in a wide variety of applications due to its technological properties. Radial shaft seals, hydraulic and pneumatic seals, toothed belts and O-rings are manufactured on the basis of this material HNBR. The material is also used in many kinds of seals, hoses, rubber gloves and rubber threads.

HNBR - Resistance or chemical stability

• Against butane, propane, mineral oils and gasoline, HNBR exhibits good swelling resistance.
• This also applies to vegetable and animal oils as well as greases.
• Lubricating oils and hydraulic oils of groups H, H-L, H-LP and greases based on mineral oils.
• Flame retardant pressure fluids of the groups HFA, HFB and HFC.
• Light heating oil and diesel fuel are substances to which HNBR is resistant to swelling.
• In super fuels, medium swell resistance is noted.
• In aromatic hydrocarbons such as benzene or trichloroethylene, HNBR is highly resistant to swelling.
• This applies to esters, glycol ether-based brake fluids and polar solvents.

HNBR - density

Density is a so-called material constant that is always the same, even with different dimensions of the test specimen. Density testing is simple, fast and can provide information about the elastomer compound used in a large number of cases. For determining the density of hydrogenated acrylonitrile butadiene rubber and of elastomers in general, the following method has become established: the "Archimedes principle". The test specimen is first weighed in air and then in spirit or ethanol. It is easier with water, but measurement errors occur more quickly. This is due to the high surface tension. Special density scales then automatically calculate the respective material density on the basis of the buoyancy.

The procedure sounds simple, but requires a certain amount of experience. In the case of foamed elastomers, the density is determined differently. In this case, special wire baskets are used to determine the density. Here, the calculation of the volume and the determination of the weight of a test specimen are helpful. Based on these two values, the density can finally be calculated.

The density is not only dependent on the base elastomer. Fillers and additives during production also change the density. For this reason, the individual elastomer families are classified into specific density ranges. Unfortunately, these overlap. Fluoroelastomers such as FKM/FFKM, for example, are easily recognized by their high density of 1.8-2.6 g/cm³. NBR and HNBR, on the other hand, have a density in the range of 1.10-1.45 g/cm³. This means that density determination can be used to rule out confusion, for example when using O-rings..

Mechanical Properties of HNBR

Hydrogenated acrylonitrile butadiene rubber is clearly more effective than NBR in its mechanical properties as well as chemical resistances for many kinds of applications. Although it is more expensive than NBR, its properties make it ideal for timing belts in vehicles. Here, in addition to its better thermal properties, its mechanical strength is particularly appreciated. This strength is mainly in demand for rod and piston seals. O-rings, diaphragms, bellows and radial shaft seals are also preferred applications.

In wind turbines, for example, shaft seals in sealing lip design made of HNBR have proven their worth. Special sealing rings with reinforcement can also be used in bearings with large diameters. The very high stability of these sealing rings is generally highly appreciated. For this purpose, they are specially manufactured from ozone-resistant HNBR. So anyone who thinks seals are undemanding mass-produced goods is mistaken: they are an essential component for ensuring the efficiency, reliability and performance of bearing arrangements and systems. The same applies, of course, to timing belts in vehicle engines.

Thermal properties of HNBR

Hydrogenated acrylonitrile butadiene rubber has exceptionally good thermal properties. Thus, the value material can be used in a wide range and is characterized by excellent low-temperature resistance as well as very good hot-air resistance. The mechanical properties differ only slightly in the respective low or high temperature ranges.

Temperature resistance of HNBR

Hydrogenated acrylonitrile butadiene rubber is used in the temperature range from -30 °C up to +150 °C. Temperatures of up to 170 °C are even possible for short periods, as demonstrated by the special shaft seals used in wind turbines. In addition to the applications mentioned, HNBW is also frequently used in air conditioning systems. It is very compatible with the refrigerant R134A and therefore the first choice for air conditioning systems.

Hydrogenated acrylonitrile butadiene rubber is the hydrogenated version of NBR, also called nitrile rubber. NBR is a copolymer of ACN and 1,3-butadiene. Remaining double bonds of 1,3-butadiene monomer units are still contained in the NBR backbone. These double bonds are to some extent susceptible to chemical attack and thermal decomposition as well as oxidation. Therefore, NBR can be hydrogenated in a catalytic hydrogenation process to hydrogenated acrylonitrile butadiene rubber.

The manufacturing process itself begins with an emulsion of polymerized NBR. This polymer is then dissolved in a suitable solvent. After dissolution, hydrogen gas is added. A noble metal catalyst causes the selective hydrogenation of the double bonds from the NBR to begin at a certain temperature and pressure. The degree of hydrogenation varies in the range from 80% to 95%. In this range, the different properties of HNBR are thus specifically achieved.

Hydrogenated acrylonitrile butadiene rubber is used in many areas of industry. These include mechanical engineering, plant engineering, medical technology, aircraft construction and many other areas. Products manufactured from HNBR include timing belts, O-rings, lip seals, bellows and diaphragms. The product range is extensive and various HNBR grades enable specific applications with properties specially set during manufacture.

HNBR in mechanical engineering

In mechanical engineering, O-rings and shaft seals are mainly made of HNBR. Due to their properties, they ensure excellent durability and thus operational reliability of the equipment thus equipped.

HNBR O-rings

O-rings made of HNBR are used in areas where elastomers such as NBR reach their limits. The more complex manufacturing process means that O-rings made of HNBR are more expensive than rings made of other elastomers. However, these higher costs are offset by the longer service life, better thermal resistance and optimum properties compared with chemical products.

HNBR in the automotive industry

In the automotive industry, hydrogenated acrylonitrile butadiene rubber, used as timing belts, has become indispensable. Here, this material represents the optimum to guarantee mechanical stability, elasticity, temperature resistance and chemical resistance for this application. Shaft sealing rings are also made of HNBR..

HNBR timing belt

In automotive engineering as well as in mechanical engineering, the timing belt is an element that is exposed to high thermal loads and, in some cases, oils and greases as well as fuels. Hydrogenated acrylonitrile butadiene rubber is an optimum material for all these loads, as it is far superior to other elastomers in this respect.

HNBR Simmerrings

Every engine and turbine works with Simmerrings. These are used specifically on shafts of all types to prevent the escape of grease or oil. Good temperature resistance is required in the process. These conditions combined with chemical resistance make hydrogenated acrylonitrile butadiene rubber an ideal material for Simmerrings.

HNBR bellows

Bellows require a high degree of elasticity. This, combined with the high temperature resistance, makes hydrogenated acrylonitrile butadiene rubber an excellent material for bellows.

• HNBR vs. NBR: HNBR has a significantly higher temperature resistance than NBR and is resistant to mineral oils, animal and vegetable fats as well as HFA and HFC fluids. HNBR is excellent for use with steam, hot water and the refrigerant R134A. HNBR can also be used with mineral oils and hot water at temperatures of up to 150 °C, since NBR can only withstand temperatures of up to 100 °C. The higher weathering and UV resistance of HNBR compared to NBR should also be emphasized.
  
  

• HNBR vs. VITON: FPM VITON is fluororubber as a registered trademark of Du Pont. FPM and FKM are considerably more expensive than HNBR. Therefore, O-rings made of HNBR are often preferred when high chemical and thermal resistance is expected. However, the temperature range for VITON goes up to over 200 °C compared to a maximum of 150 °C for HNBR.
  
  

• HNBR vs. EPDM: EPDM is not recommended if resistance to oil and gasoline is required resistance to oil and gasoline is required. HNBR is well suited for this purpose. Likewise, the density and hardness of EPDM are lower than those of HNBR.
  
  

• HNBR vs. LATEX: The comparison of HNBR and LATEX also shows that the harder HNBR is more suitable for use in areas with high temperature loads and required chemical resistance. This results in advantages for toothed belts and O-rings as well as for use as bellows or sealing rings for large-diameter shafts.