Advantages, disadvantages, and application ranges of O-rings made from different materials

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I. Overview of O-rings 1. Definition of O-rings O-rings are rubber sealing rings with a circular cross-section; they are called O-rings because of their O-shaped cross-section, and they are also known as O-seals. It first appeared in the mid-19th century, when it was used as a sealing element for steam engine cylinders. 2. Application range of O-rings: O-ring seals are suitable for use in various mechanical devices, where they provide sealing functionality in stationary or moving conditions, under specified temperatures and pressures, as well as in the presence of different liquid and gas media. Various types of sealing elements are widely used in machine tools, ships, automobiles, aerospace equipment, metallurgical machinery, chemical processing machinery, construction machinery, building machinery, mining machinery, petroleum machinery, plastic machinery, agricultural machinery, as well as various types of instruments and meters. O-ring seals are mainly used for static sealing and reciprocating motion sealing. When used for sealing rotary motion, it is limited to low-speed rotary sealing devices. O-rings are generally installed in grooves with a rectangular cross-section on the outer or inner circumference to provide sealing. O-rings continue to provide excellent sealing and shock absorption in environments resistant to oil, acids, alkalis, abrasion, and chemical corrosion. Therefore, O-ring seals are the most widely used type of seal in hydraulic and pneumatic transmission systems. 3. Advantages of O-rings Compared to other types of seals, O-ring seals have the following advantages: (1) Suitable for various sealing applications: static sealing and dynamic sealing. (2) Suitable for various applications; the dimensions and grooves are standardized, ensuring high interchangeability. (3) Suitable for various types of motion: rotational motion, axial reciprocating motion, or combined motion (such as combined rotational and reciprocating motion). (4) Suitable for a variety of different sealing media: oil, water, gas, chemical media, or other mixed media. (5) By selecting appropriate rubber materials and employing proper formulation design, effective sealing against oil, water, air, gas, and various chemical media can be achieved. It has a wide temperature operating range (-60°C to +220°C), and the pressure can reach 1500 Kg/cm2 when used in a fixed configuration (when used together with a reinforcement ring). (6) The design is simple, the structure is compact, and it’s easy to assemble and disassemble. 4. The cross-sectional structure of the O-ring is extremely simple; it also has a self-sealing effect, ensuring reliable sealing performance. Due to the extremely simple design of the O-ring itself and its mounting structure, as well as its standardization, it is very easy to install and replace. (1) There are a variety of material types available, which can be selected based on the different fluids: Nitrile rubber (NBR), Fluororubber (FKM), Silicone rubber (VMQ), Ethylene propylene rubber (EPDM), Chloroprene rubber (CR), Butyl rubber (BU), Polytetrafluoroethylene (PTFE), Natural rubber (NR), etc. (2) Low cost. (3) Relatively low dynamic friction resistance. Image 2: Representation method of O-rings. 1. Representation method according to GB/T342.1: Inner diameter d1 × wire diameter d2. When complying with the national standard GB3452.1, for example, in the case of an O-ring with dimensions of 20*2.4, II-2, GB1235-XX: 20 indicates that the inner diameter of the ring is 20 millimeters, 2.4 represents the cross-sectional diameter of the rubber ring, II-2 specifies the type of rubber used, GB1235 is the standard number, and XX denotes the year in which the standard was issued. 2. The notation method of GB/T3452.1-2005. For example: O-ring 7.5×1.8-G-N. Here, 7.5 refers to the inner diameter, 1.8 refers to the cross-sectional diameter; G indicates the series, and N indicates the grade. 3. The material is selected in accordance with the methods specified in HG/T2579-2008. 4. JB/T7757.2-2006: Method of designation for O-rings used in mechanical seals. For example: O-ring 7.5×1.8-G-N, where 7.5 represents the inner diameter, 1.8 represents the cross-sectional diameter, G denotes the series, and N indicates the grade. Materials: P for nitrile rubber, E for ethylene propylene diene monomer rubber, etc. III. Classification, advantages, and disadvantages of O-ring materials: 1. Natural rubber NR (Natural Rubber) is made from latex collected from rubber trees; it is a polymer of isoprene. It possesses excellent wear resistance, high elasticity, tensile strength, and elongation. It ages easily in air, becomes sticky when heated, and swells and dissolves readily in mineral oil or gasoline. It is resistant to alkalis but not to strong acids. It is a raw material for making tapes, hoses, and rubber shoes, and is suitable for producing shock-absorbing parts as well as products used in liquids containing hydroxide ions, such as automotive brake fluid and ethanol. 2. Styrene-butadiene rubber SBR (Styrene Butadiene Copolymer): a copolymer of butadiene and styrene. Compared to natural rubber, it has more uniform quality and fewer impurities, but its mechanical strength is lower; it can be used in combination with natural rubber. (1) Advantages: • Low-cost non-oil-resistant materials. 　• Good water resistance; it has good elasticity at hardness levels below 70. 　• At high hardness, it exhibits poor compressive distortion. 　• Most neutral chemicals, as well as dry and oily organic substances, can be used. (2) Disadvantages: • It is not recommended for use in strong acids, ozone, oils, esters, fats, and most hydrocarbons. • It is widely used in the tire industry, shoe industry, textile industry, and conveyor belt industry, among others. 3. Butyl Rubber IIR is synthesized by polymerizing isobutylene along with a small amount of isoprenes; it contains a small number of unsaturated groups that are used for vulcanization. Due to the steric hindrance posed by the methyl groups, its molecular movement is limited compared to other polymers, resulting in lower gas permeability. It exhibits good resistance to heat, sunlight, and ozone, as well as excellent electrical insulation properties. It also has strong resistance to polar solvents such as alcohols, ketones, and esters. Its typical operating temperature range is from -54 to 110°C. (1) Advantages: • Impermeable to most common gases. 　• It has good resistance to sunlight and ozone. 　• It can be exposed to animal or vegetable oils, or to oxidizable chemicals. (2) Disadvantages:
• It is not recommended to use it simultaneously with petroleum solvents, mineral spirits, and aromatic hydrocarbons. • Used for making rubber parts for chemical-resistant and vacuum equipment. 4. Hydrogenated nitrile rubber HNBR (Hydrogenated Nitrile): Hydrogenated nitrile rubber is obtained by hydrogenating nitrile rubber, which removes some of its double bonds in the process. After hydrogenation, its heat resistance and weather resistance are significantly improved compared to ordinary nitrile rubber; its oil resistance remains similar to that of regular nitrile rubber. The typical operating temperature range is -25~150°C. (1) Advantages: • It possesses better wear resistance compared to butyl acrylate rubber. 　• It has excellent resistance to corrosion, tension, tearing, and compressive deformation. 　• It exhibits good resistance to ozone, sunlight, and other atmospheric conditions. 　• Generally, it is used in detergents for washing clothes or dishes. (2) Disadvantages: • It is not recommended for use in solutions of alcohols, esters, or aromatic compounds. • The air conditioning and refrigeration industry makes extensive use of seals in environmentally friendly refrigerant R134a systems. 　• Seals for automotive engine systems. 5. EPDM (Ethylene propylene Rubber) is formed by the copolymerization of ethylene and propylene; its main chain does not contain double bonds, which gives it excellent heat resistance, aging resistance, ozone resistance, and stability. However, it cannot be vulcanized using sulfur. To solve this problem, a small amount of a third component with double bonds is introduced into the EP backbone, allowing it to be vulcanized with sulfur to form EPDM; its typical operating temperature range is -50 to 150°C. It exhibits excellent resistance to polar solvents such as alcohols, glycols, ethylene glycol, and phospholipid-based hydraulic fluids. (1) Advantages: • It has good weather resistance and ozone resistance. 　• It has excellent water resistance and chemical resistance. 　• Alcohols and similar substances can be used. 　• Resistant to high-temperature steam, and has good impermeability to gases. (2) Disadvantages: • Not recommended for use in food applications or exposure to aromatic hydrogens. • Seals for high-temperature steam environments. 　• Seals or parts for bathroom fixtures. 　• Rubber components in the braking system. 　• Seal in the radiator (car radiator). Image 6: NBR (Nitrile Rubber) is produced by the copolymerization of acrylonitrile and butadiene, with the acrylonitrile content ranging from 18% to 50%. The higher the acrylonitrile content, the better the resistance to hydrocarbon fuels derived from petrochemicals; however, the performance at low temperatures deteriorates. Its typical operating temperature range is -25 to 100 °C. Nitrile rubber is one of the most commonly used rubbers for oil seals and O-rings today. (1) Advantages: • It possesses good resistance to oil, water, solvents, and high-pressure oils. 　• It has good compressive set resistance, wear resistance, and elongation strength. (2) Disadvantages: • Not suitable for use in polar solvents, such as ozone, nitrohydrocarbons, MEK, and chloroform. • Used for manufacturing fuel tanks, lubricant tanks, and rubber parts used in fluid media such as petroleum-based hydraulic oils, gasoline, water, silicone greases, silicone oils, diester-based lubricants, and glycol-based hydraulic oils, especially sealing parts. It can be said to be the rubber seal with the widest range of applications and the lowest cost at present. 7. Neoprene CR (Neoprene, Polychloroprene) is formed by the polymerization of chloroprene monomers. Rubber that has been vulcanized possesses good elasticity and wear resistance; it is not affected by direct sunlight, has excellent resistance to atmospheric aging, can withstand intense twisting, is resistant to refrigerants such as dichlorodifluoromethane and ammonia, as well as dilute acids and silicone-based lubricants. However, it is not resistant to phosphate-based hydraulic oils. It crystallizes and hardens easily at low temperatures, has poor storage stability, and experiences significant swelling in mineral oils with a low aniline point. The typical operating temperature range is -50~150°C. (1) Advantages: • Good elasticity and excellent compressive deformation. 　• The formula does not contain sulfur, so it is very easy to produce. 　• It has properties resistant to animal and vegetable oils. 　• Its physical properties are not affected by neutral chemicals, fats, oils, various types of oils, or solvents. 　• It has flame-retardant properties. (2) Disadvantages: • The use of strong acids, nitrohydrocarbons, esters, chloroform, and similar chemicals is not recommended. • Seals resistant to R12 refrigerant. • Rubber parts or seals on home appliances. • Suitable for manufacturing various parts that are in direct contact with the atmosphere, sunlight, and ozone. • Suitable for various flame-resistant and chemically resistant rubber products. 8. Chlorosulfonated polyethylene adhesive CSM (Hypalon, Polyethylene). Chlorosulfonated polyethylene is a synthetic rubber covered by a patent held by DuPont. It exhibits good heat resistance, weather resistance, and ozone resistance; it also has good acid resistance, and is often used in environments exposed to oxidizing chemicals such as nitric acid and sulfuric acid. The typical operating temperature range is from -45 to 120°C. (1) Advantages: • Good resistance to ozone, oxidation, and flames. 　• Its physical properties are similar to those of neoprene, and it offers better acid resistance. 　• Excellent wear resistance. 　• It has a low-friction surface similar to that of nitrile rubber. 　• Its resistance to oils and solvents is between nitrile rubber and neoprene. 　• It is recommended to use water to prevent leaks. (2) Disadvantages: • Exposure to concentrated oxidizing acids, nitrohydrocarbons, esters, and similar compounds as well as aromatic hydrocarbons is not recommended. 9. Silicone Rubber SI: The main chain of silicone rubber is composed of silicon atoms linked together by -Si-O-Si bonds. It exhibits excellent heat resistance, cold resistance, ozone resistance, and resistance to atmospheric aging. It has excellent electrical insulation properties. Its tensile strength is lower than that of ordinary rubber, and it lacks oil resistance. (1) Advantages: • After modification, its tensile strength can reach 1500 PSI and its tear resistance can reach 88 LBS. • It has good elasticity as well as good compressive set resistance. • It exhibits good resistance to neutral solvents. • It has excellent heat resistance. • It also has excellent cold resistance. • It offers great resistance to erosion by ozone and oxidants. • It possesses excellent electrical insulation properties. • It provides good thermal insulation and heat dissipation capabilities. (2) Disadvantages: • It is not recommended for use in most concentrated solvents, oils, concentrated acids, and diluted sodium hydroxide. • Seals or rubber parts used in the home appliance industry, such as those found in electric kettles, ironing boards, and microwave ovens. • Seals or rubber components in the electronics industry, such as phone buttons, shock-absorbing pads inside DVDs, and seals in cable connectors. • Seals on various items that come into contact with the human body, such as water bottles and water dispensers. 10. Fluorinated Silicone Rubber FLS: Fluorinated silicone rubber is obtained by fluorinating silicone rubber, and its general properties combine the advantages of both fluororubber and silicone rubber. It exhibits good resistance to oils, solvents, fuel oils, as well as extreme temperatures; its typical operating temperature range is from -50 to 200°C. (1) Advantages: • Suitable for special applications, such as those requiring resistance to the corrosion of oxygen-containing chemicals, solvents with aromatic hydrogens, and chlorinated solvents. (2) Disadvantages: • Exposure to brake fluid, similar solutions, and hydrazine is not recommended. • On space components. 11. Fluororubber FPM (Fluoro Carbon Rubber) is a rubber that contains fluorine in its molecules, and there are various types depending on the fluorine content (i.e., the monomer structure). The widely used fluororubber based on hexafluoride was first introduced by DuPont under the trade name “Viton”. It has better high-temperature resistance than silicone rubber, and exhibits excellent chemical resistance, resistance to most oils and solvents (except alcohols and esters), weather resistance, and ozone resistance; its cold resistance is relatively poor, with a typical operating temperature range of -20 to 250°C. Special formulations can withstand low temperatures down to -40°C. (1) Advantages: • Can withstand temperatures up to 250 ℃. • Resistant to most oils and solvents, especially all acids, aliphatic hydrocarbons, aromatic hydrocarbons, and animal and vegetable oils. (2) Disadvantages: • Not recommended for use with similar low-molecular-weight esters and nitro-containing mixtures. • Cars, locomotives, diesel engines, and fuel systems. 　• Seals for chemical plants. Image 12: Perfluoroelastomer FFPM (1) Advantages: • Best heat resistance • Excellent chemical resistance • Low outgassing properties • Outstanding resistance to plasma (2) Disadvantages: • Poor low-temperature resistance • High cost of raw materials • Difficult to produce • Perfluoro-based products are widely used in the semiconductor industry and information-related industries; their applications include PVC in film manufacturing processes, CVD and etching processes, as well as various high-vacuum sealing processes. 13. Acrylate rubber ACM (Polyacrylate Rubber) is an elastomer synthesized from alkyl ester acrylates as its main components; it exhibits good resistance to petroleum-based oils, high temperatures, and weathering conditions. However, it has weaker mechanical strength, lower compressive deformation resistance, and reduced water resistance, making it slightly inferior to ordinary oil-resistant rubbers. The typical operating temperature range is -25~170°C. (1) Advantages: • Suitable for use in automotive transmission fluids • Possesses good antioxidant and weather resistance • Has resistance to bending and deformation • Offers excellent resistance to degradation of the oil • Appropriate for use in automotive transmission systems and power steering systems. (2) Disadvantages: • Not suitable for use in hot water • Not suitable for use in brake fluids • Lacks low-temperature resistance • Not suitable for use in phosphate esters • Not suitable for use as seals in automotive transmission and power systems. 14. Urethane Rubber PU: Urethane rubber possesses excellent mechanical properties, with high hardness, high elasticity, and good wear resistance – qualities that are difficult for other types of rubber to match. It also exhibits good resistance to aging, ozone, and oils. The typical operating temperature range is -45~90°C. (1) Advantages: • Wear-resistant and pressure-resistant. (2) Disadvantages: • Not heat-resistant. • Industrial pressure-resistant and wear-resistant seals, such as hydraulic cylinder seals. • High-pressure, high-charge system. IV. Chemical Descriptions, Abbreviations, and Aliases of Material Names
Material Name | Chemical Description | English Abbreviation | English Alias
Nitrile rubber | Acrylonitrile-butadiene rubber | NBR | Buna-N
Hydrogenated nitrile rubber | Hydrogenated acrylonitrile-butadiene rubber | HNBR | HNBR
Ethylene-propylene-diene rubber | Ethylene-acrylic acid-butadiene rubber | EPDM | EP, EPT, EPR
Chloroprene rubber | Chloroprene rubber | CR | Neoprene
Silicone rubber | Silicone resin rubber | WMQ | PVMQ
Fluorosilicone rubber | Fluorosilicone rubber | FVMQ | FVMQ
Acrylate rubber | Acrylate rubber | ACM | ACM
Ethylene-acrylic acid rubber | Ethylene-acrylic acid rubber | AEM | Vamac
Styrene-butadiene rubber | Styrene-butadiene rubber | SBR | SBR
Polyurethane rubber | Polyester/polyether urethane | AU/Eu | AU/EU
Natural rubber | Natural rubber | NR | NR
Styrene-butadiene rubber | Styrene-butadiene rubber | SBR | SBR

V. Temperature Range for Use of O-Rings
Basic Properties: NBR, HNBR, EPDM, FKM, CR, ACM, AEM, SBR, AU/EU, VMQ, FVMQ, NR
High temperature (standard, °F): 212, 300, 300, 390, 250, 350, 300, 212, 212, 390, 400, 220
High temperature (special, °F): 250, –, –, –, –, –, –, –, 480, –, –
Low temperature (standard, °F): –22, –22, –60, 5, –40, 0, –40, –40, –40, –65, –75, –60
Low temperature (special, °F): –60, –40, –, –30, –, –, –, –, –, –

VI. Comparison of Material Properties
1. Selection of Materials for O-Rings
Materials used for O-rings include nitrile rubber, carboxynitrile rubber, fluororubber, ethylene-propylene rubber, hydrogenated nitrile rubber, silicone rubber, chloroprene rubber, fluorosilicone rubber, polyurethane rubber, chloroprene rubber, styrene-butadiene rubber, butyl rubber, natural rubber, ethylene/epoxyacetic acid rubber, polyacrylate rubber, perfluororubber, and more. For the same type of rubber, its performance parameters can vary significantly depending on the formulation. Therefore, it is inaccurate to simply enter nitrile rubber or nitrile-40 in the material field. The Ministry of Chemical Industry has specific standards for the materials used in O-rings, such as HG/T 2579, HG/T 2021, HG/T 2333, HG/T 3089, HB 5290, etc. HG/T 2579 specifically omits the specific categories of materials, providing only some performance indicators for them. 2. The selection of the hardness for the O-ring is quite important. In a certain power plant, the seals used for the pump turbines had a hardness of 70 (Shore), which caused them to peel off or even break apart horizontally; switching to seals with a hardness of 85–90 (Shore) yielded excellent results. 3. It has low hardness and is easy to install, but it is prone to peeling, installation damage, extrusion, and even pressure explosion. It has too high hardness and is inconvenient to install. 4. Typically, the hardness of O-rings ranges from 40 to 90 IRHD, but 70 IRHD is generally more appropriate for use; this is an exception for silicone rubber, where 60 IRHD is usually used.