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

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Advantages, disadvantages, and application areas of O-rings made from different materials I. Overview of O-rings 1. Definition of O-rings O-rings are rubber sealing elements with a circular cross-section; they are called O-rings because of their O-shaped cross-section, and they are also known as O-type 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 serve to 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 rectangular-cross-section grooves on the outer or inner circumference to serve as seals. O-ring seals maintain excellent sealing and shock-absorbing properties in environments exposed to oils, acids, alkalis, abrasion, and chemical erosion. Therefore, the O-ring is the most widely used type of seal in hydraulic and pneumatic transmission systems. 3. Advantages of O-rings: Compared with other types of seals, O-ring seals have the following advantages: (1) Suitable for various sealing applications: static sealing and dynamic sealing. (2) Materials suitable for various applications, with standardized dimensions and grooves, offering high interchangeability. (3) Suitable for various types of motion: rotational motion, axial reciprocating motion, or combined motion (such as rotational-reciprocating combined 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 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) Simple design, compact structure, and easy to install and remove. 4. The cross-sectional structure of the O-ring is extremely simple, and it has a self-sealing effect, ensuring reliable sealing performance. Due to the extremely simple design of both the O-ring itself and the mounting area, as well as the standardization involved, it is very easy to install and replace it. (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. II. Notation methods for O-rings 1. The notation method according to GB/T342.1: inner diameter d1 × wire diameter d2. To comply with the national standard GB3452.1, for example, in the case of an O-ring with dimensions of 20*2.4, II-2, here 20 indicates that the inner diameter of the ring is 20 millimeters, 2.4 represents the cross-sectional diameter of the rubber ring, which is 2.4 millimeters. 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, where 7.5 represents the inner diameter, 1.8 represents the cross-sectional diameter, G denotes the series, N indicates the grade 3, and the material is determined in accordance with the standards 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, N indicates the grade; the material type is indicated by P for nitrile rubber, E for EPDM rubber, etc. III. Comparison of O-ring material types along with their advantages and disadvantages: 1. Natural Rubber NR – Made from latex extracted from rubber trees; it is a polymer of isoprene. It has excellent wear resistance, high elasticity, tensile strength, and elongation. It ages easily in air, becomes sticky when heated, expands and dissolves easily in mineral oil or gasoline; it is resistant to alkalis but not to strong acids. It is a raw material for manufacturing tape, hoses, and rubber shoes, and is suitable for producing shock-absorbing components 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 material. • Good water resistance; it has good elasticity at hardness levels below 70. • It exhibits poor compression set at high hardness. • 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 strong resistance to heat, sunlight, and ozone, as well as good electrical insulation properties. It is also resistant 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: • Not recommended for use together with petroleum solvents, mineral spirits, and aromatic hydrocarbons. • Rubber parts used to manufacture chemical-resistant and vacuum equipment. 4. HNBR (Hydrogenated Nitrile): Hydrogenated nitrile rubber is obtained by hydrogenating nitrile rubber to remove some of the double bonds; as a result, its temperature resistance and weather resistance are significantly improved compared to ordinary nitrile rubber, while its oil resistance remains similar to that of ordinary nitrile rubber. The typical operating temperature range is -25~150°C. (1) Advantages: • Better wear resistance compared to nitrile rubber. • It boasts excellent resistance to corrosion, tension, tearing, and compression set. • It exhibits good resistance to ozone, sunlight, and other atmospheric conditions. • Generally, it is used in detergents for washing clothes or dishes. (2) Disadvantages: • 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 food use or for exposure to aromatic hydrocarbons. • Seals for high-temperature steam environments. • Seals or parts for bathroom fixtures. • Rubber parts in the braking system. • Seal in the radiator (car radiator). 6. NBR (Nitrile Rubber) is synthesized 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 petrochemical hydrocarbon fuels, but 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 has good resistance to oil, water, solvents, and high-pressure oils. • It has good compression set, wear resistance, and tensile 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 fluids, gasoline, water, silicone greases, silicone oils, diester-based lubricants, and glycol-based hydraulic fluids, 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, 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 to 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 appliance items. • 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 with 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, analogs, and phenylhydrides is not recommended. 9. Silicone Rubber SI: The main chain of silicone rubber is composed of silicon atoms connected by -Si-O-Si bonds. It possesses 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 compressional set resistance. • It exhibits good resistance to neutral solvents. • It has excellent heat resistance and also 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 excellent resistance to oils, solvents, fuel oils, as well as high and low temperatures; its typical operating temperature range is -50~200°C. (1) Advantages: • Suitable for special applications where resistance to corrosion by oxygen-containing chemicals, solvents containing aromatic hydrogens, and chlorinated solvents is required. (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 containing 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. 12. Perfluoroelastomer FFPM (1) Advantages: • Excellent heat resistance • Outstanding chemical resistance • Low outgassing properties • Good resistance to plasma (2) Disadvantages: • Poor low-temperature performance • High cost of raw materials • Difficult to produce. Perfluoroelastomer 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 component; 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 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 appropriate for use as seals in automotive transmission and power systems. 14. Polyurethane Rubber PU: Polyurethane rubber has excellent mechanical properties – it boasts high hardness, high elasticity, and good wear resistance, qualities that are difficult to match among other types of rubber. It also exhibits good resistance to aging, ozone, and oils. The typical operating temperature range is -45~90°C. (1) Advantages: • Wear-resistant, resistant to high pressure. (2) Disadvantages: • Not resistant to high temperatures. • Industrial seals that are resistant to high pressure and wear, such as hydraulic cylinder seals. • High-pressure, high-charge system. IV. Chemical Descriptions, Abbreviations, and Alternative Names of Materials
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-propylene diene rubber | EPDM | EPM, EPR
Chloroprene rubber | Chloroprene rubber | CR | Neoprene
Silicone rubber | Silica resin rubber | WMQ | PVMQ
Fluorosilicone rubber | Fluorosilicon rubber | FVMQ | FVMQ
Acrylate rubber | Acrylate rubber | ACM | MAC
Vinyl acetate ethylene acrylate rubber | Vinyl acetate-ethylene acrylate rubber | AEM | Vamac
Styrene-butadiene rubber | Styrene-butadiene rubber | SBR | SBR
Polyurethane | 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 Using 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, chloroprene rubber, styrene-butadiene rubber, butyl rubber, natural rubber, vinyl/ethylacetic 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 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.