In the industrial field, the choice of sealing rings is crucial. Fluorine rubber (FKM) and nitrile butadiene rubber (NBR), as common sealing materials, have different chemical compositions and physical properties, and are suitable for different working conditions. In order to help engineers and technicians better understand the advantages and disadvantages of the two, this paper will conduct a comprehensive comparison of fluorine rubber and nitrile rubber seals from the aspects of chemical composition, physical properties, mechanical properties, application fields and so on.
1. Chemical composition and molecular structure
Fluororubber (FKM) :
Fluororubbers are a class of fluorinated synthetic rubbers, which are usually copolymerized by vinylidene fluoride (VDF), hexafluoropropylene (HFP) and other fluoroolefin monomers. Fluorine rubber contains a high proportion of fluorine atoms, fluorine content is usually between 66% and 70%. Fluorine rubber's C-F bond (bond energy of about 485 kJ/mol) is very stable, which gives it excellent chemical resistance and thermal stability. The higher the fluorine content, the stronger the chemical resistance and high temperature resistance of the material, but the flexibility and low temperature performance will be correspondingly reduced.
Nitrile butadiene rubber (NBR)
Nitrile rubber is composed of butadiene (BD) and acrylonitrile (ACN). The content of acrylonitrile is usually between 18% and 50%, the higher the content, the better its oil resistance, but the low temperature flexibility is poor. The presence of polar cyanide group (-CN) in the molecular chain of NBR makes it have strong oil resistance, especially excellent resistance to mineral oil and petroleum-based oil.
2. Physical performance comparison
Temperature resistance:
Fluorine rubber (FKM) : Its temperature range is wide, usually between -20°C and 200°C, and some special models of fluorine rubber can even work at high temperatures above 250°C, suitable for sealing applications in high temperature environments.
Nitrile butadiene rubber (NBR) : The temperature range is -40°C to 120°C, the heat resistance is not as good as fluorine rubber, suitable for medium temperature environment. NBR with high acrylonitrile content has better heat resistance, but it is not recommended for use under extreme high temperature conditions.
Chemical resistance:
Fluororubber (FKM) : Fluororubber has excellent resistance to a variety of chemicals, especially in acid, alkali, oil, fuel and other media. FKM has good tolerance to most polar solvents (such as ketones and esters), but is sensitive to high concentrations of alcohol solvents and some amines.
Nitrile butadiene rubber (NBR) : NBR performs well in mineral oils, petroleum-based oils, and lipid media, but is less tolerant to certain polar organic solvents (such as ketones, aromatic compounds). Strong acids and alkalis can also erode NBR.
Weather resistance:
Fluororubber (FKM) : It has strong resistance to ozone, ultraviolet light, oxygen and other aging factors in the natural environment, and is very suitable for long-term exposure to outdoor use.
Nitrile butadiene rubber (NBR) : Poor weather resistance and ozone resistance, prone to aging under ultraviolet light and ozone, so it is usually only used indoors or in protected applications.
3. Mechanical properties comparison
Wear resistance:
Fluororubber (FKM) : Due to its hard structure, the wear resistance of fluororubber is relatively poor, and it is not suitable for frequent friction or heavy-duty friction application scenarios.
Nitrile butadiene rubber (NBR) : Nitrile butadiene rubber is excellent in wear and mechanical fatigue resistance, and is widely used in seals that require friction resistance, such as oil seals and O-rings.
Elasticity and flexibility:
Fluororubber (FKM) : it can still maintain good elasticity under high temperature conditions, but it will gradually harden and even lose flexibility in low temperature environments. Such materials may become brittle at extremely low temperatures (below -20°C).
Nitrile butadiene rubber (NBR) : Nitrile butadiene rubber has excellent elasticity in low temperature environments, especially at low temperatures, which is more flexible and suitable for occasions where low temperature flexibility is required.
Resistance to compression permanent deformation:
Fluororubber (FKM) : It has good resistance to compression and permanent deformation under high temperature and high pressure conditions, and can still maintain the sealing effect after long-term use.
Nitrile butadiene rubber (NBR) : at room temperature, NBR has a good compression resistance to permanent deformation, but when used in a high temperature environment for a long time, it is prone to compression deformation.
4. Comparison of application fields
Fluororubber (FKM) :
Due to its excellent chemical and high temperature resistance, fluororubbers are widely used in demanding working conditions such as:
Engine seals in the aerospace field
Seals in petrochemical equipment
High-temperature components in the automotive industry, such as engine seals
Corrosion resistant equipment for the pharmaceutical and food industries
Nitrile butadiene rubber (NBR)
Due to its excellent oil resistance and low cost, nitrile butadiene rubber is mainly used in the following fields:
Oil seals, O-rings, hoses in the automotive industry
Seals and gaskets in mechanical equipment
Sealing system of lubricating oil and fuel oil pipelines
Seals in hydraulic systems
5. Economic cost analysis
Fluorine rubber (FKM) because of its complex production process and expensive raw materials, its cost is high, and it is usually used in high-performance, high-demand applications. Nitrile butadiene rubber (NBR) is widely used in large-scale industrial production because of its low production cost. For applications where particularly high temperature and chemical resistance are not required, NBR is a more economical choice.
6. Summary and suggestions
Fluororubber (FKM) and nitrile butadiene rubber (NBR) have their own advantages and limitations. The following factors should be considered in the specific selection:
Fluororubbers (FKM) : suitable for high temperature, high pressure, highly corrosive chemical media environment, especially aerospace, petrochemical, automotive engines and other areas with high sealing requirements.
Nitrile butadiene rubber (NBR) : it is suitable for medium temperature and medium chemical corrosion environment, especially in situations with high oil resistance requirements, such as the automotive industry and general mechanical equipment.
The choice of the two should be balanced according to the working environment, performance requirements and budget. If the working environment temperature is higher or the chemical medium is more complex, fluorine rubber will be a better choice; In less demanding and cost-sensitive applications, NBR will provide a good price/performance ratio.