What are the materials of O-rings?

komatsu hydraulic cylinder seal kit o ring

What are the materials of O-rings?

The O-ring is a kind of rubber ring with a circular shape, also called an O-ring. O-rings are suitable for installation on various mechanical equipment. O-rings still play a good role in sealing and shock absorption in environments such as oil, acid and alkali resistance, grinding, and chemical erosion. Therefore, O-ring is the most widely used seal in hydraulic and pneumatic transmission systems. In the specified temperature, pressure, and different liquid and gaseous media, it plays a sealing role in the static or moving state.

First of all, let’s talk about what materials are the O-rings made of? Our most common O-ring materials are Nitrile/NBR, Hydrogenated Nitrile/HNBR, Viton/FKM, Silicone/SIL, Neoprene/CR, Perfluoroether/FFKM and Polyacrylate Rubber /ACM, etc. With so many materials, how do we choose the O-ring that suits us? Let Huinuo Xiaobian analyze the advantages and disadvantages of O-rings of different materials. I hope to be helpful.

1. Material characteristics of NBR/nitrile rubber O-ring:

Nitrile rubber is one of the most commonly used rubber materials in oil seals and O-rings. It is widely used, it has good mechanical properties, and it is resistant to mineral-based lubricants and greases. This property is usually determined by the acrylonitrile contained. When the ACN content is low, nitrile rubber has low temperature resistance. , but the oil resistance of nitrile rubber will decrease. On the contrary, with the continuous increase of ACN content, the oil resistance of nitrile rubber will increase, but at the same time, the low temperature resistance will also decrease simultaneously. Then the advantages and disadvantages of nitrile rubber are respectively Which ones?
Advantages of NBR nitrile rubber O-rings:
1. Low cost of use, nitrile rubber is the lowest cost of use among various rubber materials at present.
2. Good resistance to mineral oil and grease.
3. Has good tear resistance and wear resistance.
4. Good low temperature resistance, standard nitrile rubber/NBR can withstand low temperature -30℃, and special NBR can withstand low temperature -40℃.
5. Wear resistance, nitrile rubber has good wear resistance.
Disadvantages of NBR nitrile rubber O-rings:
1. The high temperature resistance is poor. The standard nitrile rubber/NBR material can only withstand high temperature of 100 ℃. When the temperature is higher than 90 ℃, the performance plummets.
2. Nitrile rubber has poor ozone resistance
3. Nitrile rubber has poor weathering resistance and anti-aging properties.
The commonly used colors of NBR/nitrile rubber are black, gray, etc.

Second, HNBR / hydrogenated nitrile rubber O-ring material characteristics:

The research and development of HNBR hydrogenated nitrile butadiene rubber can be traced back to the 1970s. The research on HNBR was carried out by Japan’s Zeon Company. In 1995, Taiwan Seal Manufacturing Company began to use HNBR material to produce sealing rings. HNBR is made of NBR, which is nitrile rubber. A highly saturated special rubber elastic material obtained after oxygenation treatment.
Advantages of HNBR hydrogenated nitrile rubber O-rings:
1. High temperature resistance: Compared with nitrile rubber, the molecular structure of hydrogenated nitrile rubber contains a small amount or no carbon-carbon double bonds, so that HNBR can have good heat resistance (high temperature can reach 160 ℃)
2, ozone resistance, resistance to a variety of chemical media and radiation resistance.
3. It has excellent oil resistance and wear resistance.
Disadvantages of HNBR hydrogenated nitrile rubber O-rings:
1. High cost of use: Because HNBR hydrogenated nitrile rubber not only has the characteristics of NBR low temperature resistance and excellent wear resistance, but also can withstand high temperature of 160 ° C, its use cost is much higher than that of NBR material.
2. When the operating environment is higher than 180℃, HNBR hydrogenated nitrile rubber cannot meet the requirements.
The commonly used colors of HNBR/hydrogenated nitrile rubber are black, gray, blue, etc.

3. Characteristics of FKM/fluororubber O-ring material:

Fluorine rubber English fluororubber, FKM, VITON and FPM are the abbreviations of fluorine rubber. Fluorine rubber first appeared in 1948, and it has a history of more than 70 years in 2020. The tensile strength of fluorine rubber is basically satisfactory. , TFE/PMVE and TFE/P have the highest tensile strength at room temperature, the tensile strength of fluorosilicone rubber/fluorophosphazene rubber is the lowest, and the retention rate of tensile strength of inorganic backbone polymers at high temperature Higher, compression set resistance is an important indicator for fluororubber.
What are the advantages of fluororubber O-rings?
1. High temperature resistance of fluororubber O-rings: This feature is one of the most prominent features of fluororubber. I believe that many people who have been in contact with fluororubber have heard the most words that the high temperature resistant material must be fluororubber material. The fluororubber oil seal can maintain its performance at a high temperature of 200 ° C for a long time, and can reach 240 ° C in a short time.
2. Fluorine rubber O-rings are resistant to a variety of chemical agents: fluorine rubber itself has outstanding resistance to aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, fuel oil, oil and many other organic liquids. In addition, it also has chemical resistance, flame spread resistance, oxidation resistance, ozone resistance and weather resistance. And with the increase of the fluorine content of the fluorine rubber O-ring, the performance of the medium resistance will continue to improve.
So what are the disadvantages of Viton O-rings?
1. The cost of using fluororubber O-rings is high: because the cost of fluororubber raw materials for fluororubber O-rings is much higher than that of nitrile rubber and hydrogenated nitrile rubber, the cost of using fluororubber O-rings is also these ordinary rubbers. N times the material.
2. The fluororubber O-ring has poor low temperature resistance: the standard fluororubber material itself has poor low temperature resistance, and can only withstand low temperature -15 ℃. If you need low temperature resistance -40 ℃, you need to develop special low temperature resistance Fluorine rubber raw material.
The commonly used colors of FKM/fluororubber are brown, black, green, etc.

Fourth, the characteristics of SIL/silicone rubber O-rings:

Silicone rubber is Silicone rubber in English, SIL for short. Silicone rubber O-rings are also very common in production equipment. The tensile strength and elongation at break of silicone rubber have a relatively small relationship with the tensile speed, while silicone rubber SIL tear The strength is strongly dependent on the tensile speed. In the hardness range of 30-80, the residual deformation (permanent deformation) of silicone rubber after stretching or compression is very low.
Advantages of silicone rubber O-rings:
1. High temperature resistance of silicone rubber O-ring: Silicone rubber material has good heat resistance and can be used for a long time in the environment of 180 ℃.
2. The silicone rubber O-ring has the characteristics of oxygen resistance, ozone resistance, ultraviolet resistance and cosmic ray resistance.
Disadvantages of silicone rubber O-rings:
1. Silicone rubber O-rings will be eroded and destroyed in water vapor at 130-140°C, because silicone rubber is generally not recommended for places with superheated water vapor.
2. Silicone rubber O-rings are easily corroded by alkalis, acids, fuels, chlorinated hydrocarbons, ketones, greases, ethers, etc.
3. The mechanical properties of silicone rubber O-rings are relatively poor.
The commonly used colors of SIL/silicone rubber are red, milky white, etc.

5. Characteristics of neoprene/CR material:

Chloroprene Rubber in English, CR for short, chloroprene rubber is also called chloroprene, chloroprene rubber vulcanization hardness range is 30-90 degrees, CAS number is: 126-99-8, the molecular formula of chloroprene rubber is C4H5Cl; CH2CHCClCH2 , molecular weight 88.54.
Advantages of CR/Neoprene O-rings:
1. Neoprene O-ring has good flame retardancy: Neoprene can release a large amount of hydrogen chloride when it is burned, but it is carbonized but does not delay combustion, and it has good self-extinguishing properties. Therefore, the flame resistance of neoprene rubber is the best among general-purpose rubbers.
2. Excellent aging resistance: Due to the electron-attracting and shielding functions of chlorine atoms, neoprene has excellent aging resistance.
Disadvantages of CR Neoprene O-rings:
1. The performance of low temperature resistance is not particularly good, and crystal hardening is easy to occur at low temperature.
2. Poor storage stability. Neoprene rubber is easy to harden and depreciate during storage. Generally, the storage time at 20 °C does not exceed one year, and the storage time at 30 °C does not exceed half a year.
3. Neoprene rubber production process will become more sensitive to temperature.
CR/Neoprene is generally used in black.

6. Characteristics of FFKM/perfluoroether rubber O-rings:

Perfluoroether rubber abbreviated as FFKM, also known as perfluororubber or perfluoroether rubber elastomer, perfluoro O-ring is also called perfluoroether sealing ring, among which the more famous Kalrez rubber series products of DuPont in the United States are also The most representative perfluoroether brand, in terms of molecular structure, FFKM perfluoroether rubber is different from FKM fluororubber in that FFKM perfluoroether rubber has a higher fluorine content.
Advantages of FFKM/perfluoroether rubber O-rings:
1. High temperature resistance of perfluoroether O-rings: Due to the higher fluorine content of perfluoroether rubber, the high-temperature working environment of perfluoroether O-rings can reach 260 °C-290 °C, and the special part number can be up to It still has the sealing ability in the high temperature environment of 316℃.
2. The perfluoroether O-ring has the strongest resistance to chemical media: Since the fluorine content of perfluoroether rubber is between 74% and 76%, the perfluoroether O-ring can withstand a variety of chemical media, such as: strong acid , strong alkali, nitrogen-containing compounds, ketones, hydrocarbons, lipids, alcohols, aldehydes, water vapor, oil, amino compounds and other chemical media corrosion.
Disadvantages of FFKM/perfluoroether rubber O-rings:
Speaking of the disadvantages of perfluoroether O-rings, they are expensive, so they are currently only used in extremely demanding environments.
Perfluoroether O-ring sizes include AS568 series, JISB2401-P series, V series, G series, S series, etc.
Perfluoroether O-rings are currently mainly used in semiconductor factories, petrochemical industries and other industries.

7. Characteristics of ACM/acrylate rubber O-ring material:

Acrylic rubber in English is acrylic rubber, abbreviated as ACM, which is a rubber elastomer obtained by copolymerization of acrylate as the main monomer. Its main chain is a saturated carbon chain, and its side groups are polar ester groups.
Advantages of ACM/Acrylate Rubber O-rings:
It has good resistance to hydrocarbon lubricating oil, hydraulic medium and grease, and the high methacrylate content polymer has better medium resistance.
Disadvantages of ACM/Acrylate Rubber O-rings:
1. ACM is not suitable for brake fluid, grease and ketone, and its resistance to petroleum and gasoline is relatively poor.
2. ACM is not resistant to aggressive fuel and chemical media

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