I. Overview of O-rings
1. Definition of O-rings
O-rings are a type of rubber sealing ring with a circular cross section. Because of its O-shaped cross section, it is called an O-ring, also called an O-ring. It began to appear in the mid-19th century, when it was used as a sealing element for steam engine cylinders.
2. Scope of application of O-rings
O-rings are suitable for installation on various mechanical equipment, and they play a sealing role in a static or moving state at a specified temperature, pressure, and in different liquid and gas media. Various types of sealing elements are widely used in machine tools, ships, automobiles, aerospace equipment, metallurgical machinery, chemical machinery, engineering machinery, construction machinery, mining machinery, petroleum machinery, plastic machinery, agricultural machinery, and various instruments and meters.
O-rings are mainly used for static sealing and reciprocating motion sealing. When used for rotary motion sealing, it is limited to low-speed rotary sealing devices. O-rings are generally installed in grooves with rectangular cross sections on the outer circle or inner circle to play a sealing role.
O-rings can still play a good sealing and shock-absorbing role in environments such as oil resistance, acid and alkali resistance, abrasion resistance, and chemical corrosion resistance.
Therefore, O-rings are the most widely used seals in hydraulic and pneumatic transmission systems.
3. Advantages of O-rings
Compared with other types of seals, O-rings have the following advantages:
(1) Suitable for a variety of sealing forms: static sealing and dynamic sealing.
(2) Suitable for various materials, the size and groove are standardized, and the interchangeability is strong.
(3) Suitable for a variety of motion modes: 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 suitable rubber materials and appropriate formula design, it can achieve effective sealing for oil, water, air, gas and various chemical media. The temperature range of use is wide (-60℃～+220℃), and the pressure can reach 1500Kg/cm2 when used in fixed position (used with reinforcement ring).
(6) Simple design, compact structure, easy installation and disassembly
4. The cross-sectional structure of the O-ring is extremely simple, and it has a self-sealing effect and reliable sealing performance.
Since the O-ring itself and the installation part structure are extremely simple and standardized, installation and replacement are very easy.
(1) A variety of materials
You can choose according to 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 small dynamic friction resistance
II. O-ring representation method
1. GB/T342.1 representation method
Inner diameter d1×wire diameter d2.
Implementation of national standard GB3452.1
For example: O-ring 20*2.4, Ⅱ-2 In GB1235-XX, 20 represents the inner diameter of the large ring is 20 mm, 2.4 represents the cross-sectional diameter of the rubber ring is 2.4 mm, Ⅱ-2 represents the type of rubber used, GB1235 represents the standard number, and XX represents the year the standard was published.
2. The representation method of GB/T3452.1-2005.
For example: O-ring 7.5×1.8-G-N,
7.5--Inner diameter
1.8--Cross-sectional diameter
G--Series
N--Grade
3. The material adopts the method of HG/T2579-2008.
4. The representation method of O-ring for mechanical seals in JB/T7757.2-2006.
For example: O-ring 7.5×1.8-G-N,
7.5--Inner diameter
1.8--Sectional diameter
G--Series
N--Grade
Material: P--Nitrile rubber,
E--EPDM rubber, etc.
III. O-ring material classification comparison and advantages and disadvantages:
1. Natural rubber NR
(Natural Rubber) Made from latex collected from rubber trees, it is a polymer of isoprene. It has good wear resistance, high elasticity, tear strength and elongation. It is easy to age in the air, becomes sticky when heated, and is easy to swell and dissolve in mineral oil or gasoline. It is alkali-resistant but not resistant to strong acid. It is the raw material for making tapes, hoses, and rubber shoes, and is suitable for making shock-absorbing parts and products used in liquids with hydroxide such as automobile brake oil and ethanol.
2. Styrene Butadiene Rubber (SBR)
(Styrene Butadiene Copolymer) Copolymer of butadiene and styrene. Compared with natural rubber, it has uniform quality and less foreign matter, but weaker mechanical strength. It can be mixed with natural rubber.
(1) Advantages:
• Low-cost non-oil-resistant material.
• Good water resistance, good elasticity below hardness 70.
• Poor compression distortion at high hardness.
• Most neutral chemicals and dry and moist organic ketones can be used.
(2) Disadvantages:
• It is not recommended to use in strong acids, ozone, oils, esters and fats and most hydrocarbons.
• Widely used in the tire industry, shoe industry, cloth industry and conveyor belt industry, etc.
3. Butyl Rubber IIR
(Butyl Rubber) is a polymer made of isobutylene and a small amount of isoprenes. It retains a small amount of unsaturated groups for sulfur addition. Because the steric hindrance of the methyl group to the movement of molecules is less than that of other polymers, it has less gas permeability, is highly resistant to heat, sunlight, and ozone, and has good electrical insulation. It is highly resistant to polar solvents such as alcohols, ketones, and esters. The general operating temperature range is -54~110℃.
(1) Advantages:
• Impermeable to most general gases.
• Good resistance to sunlight and ozone.
• Can be exposed to animal or vegetable oils or oxidizable chemicals.
(2) Disadvantages:
• It is not recommended to use it with petroleum solvents, kerosene, and aromatic hydrogen.
• Used to make rubber parts resistant to chemicals and vacuum equipment.
4. Hydrogenated Nitrile HNBR
(Hydrogenate Nitrile) Hydrogenated Nitrile is a type of Nitrile with some double chains removed after hydrogenation. After hydrogenation, its temperature resistance and weather resistance are much higher than those of ordinary Nitrile rubber, and its oil resistance is similar to that of ordinary Nitrile rubber. The general operating temperature range is -25~150℃.
(1) Advantages:
• Better wear resistance than Nitrile rubber.
• Excellent corrosion resistance, tensile strength, tear resistance and compression distortion properties.
• Good resistance to ozone, sunlight and other atmospheric conditions.
• Generally suitable for laundry or dishwashing detergents.
(2) Disadvantages:
• Not recommended for use in alcohol, ester or aromatic solutions.
• In the air conditioning and refrigeration industry, it is widely used as a seal in the environmentally friendly refrigerant R134a system.
• Automobile engine system seals.
5. Ethylene propylene rubber (EPDM)
(Ethylene propylene rubber) is made of ethylene and propylene copolymers. The main chain does not contain double chains. Therefore, it has excellent heat resistance, aging resistance, ozone resistance and stability, but cannot be sulfurized. To solve this problem, a small amount of a third component with double chains is introduced into the EP main chain, which can be sulfurized to form EPDM. The general operating temperature range is -50~150℃. It has excellent resistance to polar solvents such as alcohols, ketones, ethylene glycol and phosphate hydraulic oils.
(1) Advantages:
• Good weather resistance and ozone resistance.
• Excellent water resistance and chemical resistance.
• Can use alcohols and ketones.
• Resistant to high temperature steam and has good impermeability to gases.
(2) Disadvantages:
• Not recommended for food use or exposure to aromatic hydrogen.
• Seals for high-temperature water vapor environments.
• Seals or parts for bathroom equipment.
• Rubber parts in brake systems.
• Seals in radiators (car water tanks).
6. Nitrile Rubber NBR
(Nitrile Rubber) is copolymerized from acrylonitrile and butadiene. The acrylonitrile content ranges from 18% to 50%. The higher the acrylonitrile content, the better the resistance to petrochemical hydrocarbon fuel oil, but the low-temperature performance becomes worse. The general operating temperature range is -25~100 ℃. Nitrile Rubber is currently one of the most commonly used rubbers for oil seals and O-rings.
(1) Advantages:
• It has good oil resistance, water resistance, solvent resistance and high-pressure oil resistance.
• It has good compression, wear resistance and elongation.
(2) Disadvantages:
• It is not suitable for use in polar solvents, such as ketones, ozone, nitro hydrocarbons, MEK and chloroform.
• It is used to make fuel tanks, lubricating oil tanks and rubber parts used in fluid media such as petroleum hydraulic oil, gasoline, water, silicone grease, silicone oil, diester lubricating oil, glycol hydraulic oil, etc., especially sealing parts. It can be said to be the most widely used and lowest cost rubber seal at present.
7. Chloroprene CR
(Neoprene, Polychloroprene) is polymerized from chloroprene monomers. The vulcanized rubber has good elasticity and wear resistance, is not afraid of direct sunlight, has particularly good atmospheric aging resistance, is not afraid of severe distortion, is not afraid of refrigerants such as dichlorodifluoromethane and ammonia, is resistant to dilute acid and silicone ester lubricating oil, but is not resistant to phosphate ester hydraulic oil. It is easy to crystallize and harden at low temperatures, has poor storage stability, and has a large expansion volume in mineral oil with a low aniline point. The general operating temperature range is -50~150℃
(1) Advantages:
• Good elasticity and good compression set.
• The formula does not contain sulfur and is therefore very easy to make.
• It has the characteristics of resistance to animal and vegetable oils.
• It will not be affected by neutral chemicals, esters, greases, various oils, and solvents.
• It has flame retardant properties.
(2) Disadvantages:
• It is not recommended to use in chemicals such as strong acids, nitro hydrocarbons, esters, chloroform and ketones.
• Seals resistant to R12 refrigerant.
• Rubber parts or seals on household appliances.
• Suitable for making various parts that are directly exposed to the atmosphere, sunlight, and ozone.
• Suitable for various flame-resistant and chemical-resistant rubber products.
8. Chlorosulfonated polyethylene glue CSM
(Hypalon, Polyethylene) Chlorosulfonated polyethylene is a synthetic rubber patented by DuPont. It has excellent heat resistance, weather resistance, and ozone resistance; it also has good acid resistance and is often used in places resistant to oxidizing chemicals (nitric acid, sulfuric acid). The general operating temperature range is -45~120℃.
(1) Advantages:
• It has good resistance to ozone, oxidation and flame.
• It has similar physical properties to chloroprene rubber and has better acid resistance.
• It has excellent abrasion resistance.
• It has the same low friction surface as nitrile rubber.
• Its resistance to oils and solvents is between nitrile rubber and chloroprene rubber.
• It is recommended to use water to prevent leakage.
(2) Disadvantages:
• It is not recommended to be exposed to concentrated oxidizing acids, nitro hydrocarbons, esters, ketones and aromatic hydrogen.
9. Silicone Rubber SI
(Silicone Rubber) The main chain of silicone is made of silicon (-si-o-si). It has excellent heat resistance, cold resistance, ozone resistance, and atmospheric aging resistance. It has good electrical insulation properties. The tensile strength is worse than that of ordinary rubber and it is not oil resistant.
(1) Advantages:
• After the formula is adjusted, the tensile strength can reach 1500PSI and the tear resistance can reach 88LBS
• Good elasticity and good compression distortion
• Good resistance to neutral solvents
• Excellent heat resistance
• Excellent cold resistance
• Excellent resistance to ozone and oxide corrosion
• Excellent electrical insulation performance
• Good heat insulation and heat dissipation
(2) Disadvantages:
• Not recommended for use in most concentrated solvents, oils, concentrated acids and diluted sodium hydroxide.
• Seals or rubber parts used in household appliances, such as rubber parts in electric kettles, electric irons, and microwave ovens.
• Seals or rubber parts in the electronics industry, such as mobile phone keys, shock-absorbing pads in DVDs, seals in cable connectors, etc.
• Seals on various items that come into contact with the human body, such as kettles, water dispensers, etc.
10. Fluorinated Silicone Rubber FLS
(Fluorinated Silicone Rubber) Fluorinated silicone rubber is silicone rubber that has been fluorinated. Its general properties have the advantages of both fluorinated rubber and silicone rubber. It is resistant to oil, solvents, fuel oil, and high and low temperatures. The general operating temperature is -50~200℃.
(1) Advantages:
• Suitable for special purposes, such as those that require resistance to corrosion by oxygen-containing chemicals, aromatic hydrogen-containing solvents, and chlorine-containing solvents.
(2) Disadvantages:
• It is not recommended to be exposed to brake fluid, ketones, and hydrazine solutions.
• Space parts.
11. Fluororubber FPM
(Fluoro Carbon Rubber) Rubber containing fluorine in the molecule, there are various types according to the fluorine content (i.e. monomer structure). The hexafluorinated fluorine rubber that is currently widely used was first marketed by DuPont under the trade name "Viton". It has better high temperature resistance than silicone rubber, excellent chemical resistance, resistance to most oils and solvents (except ketones and esters), weather resistance and ozone resistance; its cold resistance is relatively poor, and the general operating temperature range is -20~250℃. Special formulas can withstand low temperatures to -40℃.
(1) Advantages:
• Heat resistant 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 ketones, low molecular weight esters and mixtures containing nitric acid
• Automobiles, locomotives, diesel engines and fuel systems.
• Seals for chemical plants.
12. Perfluoroelastomer FFPM
(Perfluoroelastomer)
(1) Advantages:
• Best heat resistance
• Excellent chemical resistance
• Low outgassing properties
• Excellent anti-plasma properties
(2) Disadvantages:
• Poor low temperature resistance
• Higher raw material prices
• Higher production difficulty
• Perfluorinated products are widely used in the semiconductor industry and information-related industries, including PVC, CVD and etching processes in thin film manufacturing and various high vacuum sealing processes.
13. Acrylic Rubber ACM
(Polyacrylate Rubber) is an elastomer polymerized with Alkyl Ester Acrylate as the main component. It has good resistance to petrochemical oil, high temperature and weather resistance, but is weaker in mechanical strength, compression deformation rate and water resistance, which is slightly worse than general oil-resistant rubber. The general operating temperature range is -25~170℃.
(1) Advantages:
• Applicable to automobile transmission oil
• Good anti-oxidation and weather resistance
• Anti-bending and deformation function
• Excellent resistance to oil products
• Applicable to automobile transmission system and power steering wheel
(2) Disadvantages:
• Not applicable to hot water
• Not applicable to brake oil
• Not resistant to low temperature
• Not applicable to phosphate ester
• Automobile transmission system and power system seals.
14. Polyurethane Rubber PU
(Urethane Rubber) Polyurethane rubber has excellent mechanical properties. Its high hardness, high elasticity and wear resistance are difficult to compare with other rubbers. It also has excellent aging resistance, ozone resistance and oil resistance. The general operating temperature range is -45~90℃.
(1) Advantages:
• Wear-resistant and high-pressure resistant
(2) Disadvantages:
• Not resistant to high temperatures
• Industrial high-pressure and wear-resistant seals, such as hydraulic cylinder seals.
• High-pressure and high-charge systems.
Material performance comparison
1. Selection of O-ring materials
The materials used for O-rings include nitrile rubber, carboxylic acid nitrile, fluororubber, ethylene propylene rubber, hydrogenated nitrile rubber, silicone rubber, chloroprene rubber, fluorosilicone rubber, polyurethane, epichlorohydrin rubber, styrene butadiene rubber, butyl rubber, natural rubber, ethylene/ethylene propylene rubber, polyacrylate rubber, perfluororubber, etc.
The same rubber has different performance indicators due to different formulas. Therefore, it is inaccurate to simply fill in nitrile rubber or nitrile-40 in the material column. The Ministry of Chemical Industry has special standards for materials used for O-rings, such as: HG/T 2579, HG/T 2021, HG/T 2333, HG/T 3089, HB 5290, etc. HG/T 2579 specifically removes the specific categories of materials and only gives some performance indicators of the materials.
2. The choice of O-ring hardness is more important. For example, the hardness of the sealing ring of the water pump turbine of a power station is 70 (Shore), which often peels off or even cuts off horizontally. Later, the sealing ring of 85-90 (Shore) was used, and the effect was ideal.
3. Low hardness and easy installation, but easy to peel off, installation damage, extrusion and even pressure explosion. Too high hardness and inconvenient installation.
4. Usually the hardness of O-ring is 40-90 IRHD, but in use, 70 IRHD is generally more suitable, except for silicone rubber, which generally uses 60 IRHD.