Which synthetic rubbers are commonly used to manufacture auxiliary sealing rings? What are their respective features?

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Rubber is a polymer material with excellent elasticity. It possesses good elasticity and certain strength, as well as excellent airtightness, water resistance, wear resistance, temperature and pressure resistance, and corrosion resistance; it is therefore a widely used material for auxiliary sealing rings. Rubber is divided into natural rubber and synthetic rubber. Natural rubber outperforms synthetic rubber in terms of elasticity, strength, processability, and overall performance, but it is inferior to synthetic rubber in terms of temperature resistance, corrosion resistance, and resistance to dissolution. By using different rubber compound formulations, mixing, and vulcanization processes, synthetic rubbers with distinct properties can be obtained. 1) Nitrile rubber (NBR) is a copolymer of butadiene and acrylonitrile. Nitrile rubber with a typical acrylonitrile content of 40% exhibits good oil resistance and aging resistance, as well as properties such as heat resistance, wear resistance, and corrosion resistance; it is widely used in equipment that comes into contact with gasoline and other oils. It is also resistant to alkali and non-oxidizing dilute acids, but not resistant to oxidizing acids (such as nitric acid and chromic acid), aromatics, esters, ketones, ethers, halogenated hydrocarbons, etc. Nitrile rubber cannot be used in refinery condensate oil due to the presence of substances such as aromatics. It is also not suitable to be used at low temperatures. 2) Silicone rubber (MVO): Silicone rubber is a linear polymer elastomer formed by the polymerization of dimethylsiloxane along with other silicone monomers, in the presence of acidic (or basic) catalysts. Silicone rubber has a wide operating temperature range of (-100~350°C) and high thermal stability, allowing it to be used for extended periods at temperatures between 200~300°C. It is mainly used for sealing substances such as animal and vegetable oils, mineral oils, oxygen, weak acids, and weak bases in high and low temperatures. Its disadvantages are low strength, poor wear resistance, and high cost. 3) Fluororubber (FPM): Fluororubber is a synthetic polymer elastomer containing fluorine atoms, and it features resistance to high temperatures, oils, and the corrosion caused by various chemicals. Currently, there are three types of fluororubber: FPM2301, also known as fluororubber 23-11, which boasts excellent resistance to strong acids; FPM2602, or fluororubber 26-41, which has better heat and solvent resistance than FPM2301, but inferior processability; and FPM2461, or fluororubber 246, which offers even better heat and solvent resistance than FPM2602. The fluororubber primarily used in the manufacture of auxiliary sealing rings at present is FPM2602. It can be used for extended periods at 250°C, and for short periods at 300°C. Its corrosion resistance is among the best among elastomers, but its performance at low temperatures is poor, and its high cost limits its range of applications.