Advantages and Disadvantages of O-rings

Overview of O-rings
 
1. Definition

O-rings are rubber sealing rings with a circular cross-section. Because their cross-section is O-shaped, they are called O-form sealing rings, also known as O-rings. It began to appear in the middle of the 19th century when it was used as the sealing element of the steam engine cylinder.
 
2. Application range
 
O-rings are suitable for installation on various mechanical equipment, and they can seal under the specified temperature, pressure and different liquid and gas media in the static or moving state. 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.
 
O-ring sealing is mainly used for static seal and reciprocating seal. When used for rotary motion sealing, it is limited to a low-speed rotary sealing device. The O-ring is generally installed in the groove with a rectangular cross-section on the outer circle or inner circle to seal.
 
O-rings still play a good sealing and damping role in oil, acid, alkali, abrasion, chemical erosion and other environments. Therefore, O-rings are the most widely used seals in the hydraulic and pneumatic transmission system.
 
3. Advantages of O-rings

Compared with other types of sealing rings, O-rings have the following advantages:
(1) Suitable for various sealing forms, including static sealing and dynamic sealing
(2) Suitable for various materials, with standardized dimensions and grooves and strong interchangeability
(3) Suitable for a variety of motion modes: rotary motion, axial reciprocating motion or combined motion (such as rotary reciprocating combined motion)
(4) Suitable for many different sealing media: oil, water, gas, chemical media or other mixed media
(5) By selecting suitable rubber materials and proper formula design, it can effectively seal oil, water, air, gas and various chemical media. The temperature range is wide (-60℃ - +220℃), and the pressure can reach 1500Kg/cm2 (used together with reinforcing ring) in fixed use.
(6) Simple design, compact structure and convenient assembly and disassembly
 
4. The cross-sectional structure of the O-ring is extremely simple, with a self-sealing function and reliable sealing performance. Because the O-ring itself and the structure of the installation part are extremely simple and standardized, the installation and replacement can be very easy.
 
(1) There are many kinds of materials.
It can be selected according to different fluids: nitrile rubber (NBR), fluoro rubber (FKM), silicone rubber (VMQ), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), butyl rubber (BU), polytetrafluoroethylene (PTFE), natural rubber (NR) and so on.
(2) Low cost
(3) The dynamic friction resistance is relatively small.
 
Advantages and disadvantages of O-ring materials:
 
1. Natural rubber NR 

Natural Rubber is made of rubber tree latex, which is a polymer of isoprene. It has good wear resistance, high elasticity, breaking strength and elongation. It is easy to age in air, sticky when heated, easy to expand and dissolve in mineral oil or gasoline, alkali-resistant but with poor acid-resistant. It is the raw material for making adhesive tapes, rubber hoses and rubber shoes, and is suitable for making shock-absorbing parts and products used in liquid with hydroxyl groups such as automobile brake oil and ethanol.
 
2. Styrene-butadiene rubber SBR 

Styrene-Butadiene Copolymer is the copolymer of butadiene and styrene, compared with natural rubber, with uniform quality and less foreign matter, but weak mechanical strength, so it can be blended with natural rubber. It is widely used in the tire industry, footwear industry, cloth industry and conveyor belt industry, etc.
 
(1) Advantages:
Low-cost non-oil resistant material
Good water resistance, hardness below 70 and good elasticity
When the hardness is high, it has poor compression skew.
Most neutral chemicals and dry and nourishing organic ketones can be used.

(2) Disadvantages:
It is not recommended to use in strong acids, ozone, oils, oil esters and fats and most hydrocarbons.
 
3. Butyl rubber IIR 

Butyl Rubber is polymerized by isobutylene and a small number of isoprenes, with a small number of unsaturated groups that are kept for sulfur addition. Because the steric hindrance molecules of the methyl group move less than other polymers, the gas permeability is less, and the resistance to heat, sunlight and ozone is great. The electrical insulation is good with the resistance to polar solvents such as alcohols, ketones, esters, etc. Generally, the temperature range is from -54℃ to 110℃. It is used to make rubber parts for chemical-resistant and vacuum equipment.
 
(1) Advantages:
Impermeable to most general gases
Good resistance to sunlight and ozone
Capable of being exposed to animals or vegetable oils or oxidizable chemicals

(2) Disadvantages:
It is not recommended to use petroleum solvent, rubber kerosene and aromatic hydrogen.
 
4. Hydrogenated nitrile rubber HNBR

Hydrogenated nitrile rubber is a nitrile rubber in which part of double chains is removed after hydrogenation. After hydrogenation, its temperature resistance and weather resistance are much improved compared with ordinary nitrile rubber, and its oil resistance is similar to that of ordinary nitrile rubber. The general temperature range is from -25℃ to 150℃. It is used in the refrigeration industry, which is widely used as seals in the R134a system. It is used in the seal of the automobile engine system.
 
(1) Advantages:
Compared with butyl rubber, it has better wear resistance;
Excellent corrosion resistance, tensile resistance, tear-resistance and compression distortion;
Good resistance to ozone, sunlight and other atmospheric conditions;
Generally, it is suitable for cleaning agents for washing clothes or dishes

(2) Disadvantages:
It is not recommended to use in alcohol, ester or aromatic solutions.
 
5. Ethylene propylene rubber EPDM
 
Ethylene propylene Rubber is copolymerized by ethylene and propylene, and its main chain is not double-stranded, so it has excellent heat resistance, aging resistance, ozone resistance and stability, but it cannot be sulfur-added. In order to solve this problem, a small amount of the third component with double chains is introduced into the EP main chain, and EPDM can be obtained by sulfur addition. The general temperature range is from -50℃ to 150℃, with excellent resistance to polar solvents such as alcohol, ketone, ethylene glycol and phosphate hydraulic oil. It is used for seals in high-temperature water vapor environments, sanitary ware seals or parts, rubber parts in braking (braking) systems, seals in radiators (car water tanks).
 
(1) Advantages:
Good weather resistance and ozone resistance;
Excellent water resistance and chemical resistance;
Alcohols and ketones can be used;
Resistant to high-temperature steam and good impermeability to gas
 
(2) Disadvantages:
Not recommended for food use or exposure to aromatic hydrogen

6. Nitrile rubber NBR

Nitrile Rubber is made by copolymerization of acrylonitrile and butadiene. The acrylonitrile content ranges from 18% to 50%. The higher the acrylonitrile content is, the better the resistance to hydrocarbon fuel oil of petrochemical oil can be, but the low-temperature performance will become poor. Generally, the temperature range is from -25℃ to 100℃. Butadiene rubber is one of the most commonly used rubbers for oil seals and O-rings. It is used to make fuel tanks, lubricating oil tanks and rubber parts, especially sealing parts, in fluid media such as petroleum hydraulic oil, gasoline, water, silicone grease, silicone oil, diester lubricating oil and glycol hydraulic oil.
 
(1) Advantages:
Good oil, water, solvent and high-pressure oil resistance;
Good compression deflection, abrasion resistance and elongation
 
(2) Disadvantages:
It is not suitable for use in polar solvents, such as ketones, ozone, nitro hydrocarbons, MEK and chloroform.
 
7. Chloroprene rubber CR

Chloroprene rubber is composed of polymerization of chlorobutanol monomer. The vulcanized rubber has good elastic wear resistance, which is not afraid of direct sunlight, with particularly good atmospheric aging resistance. It is also not afraid of intense distortion, refrigerants such as dichlorodifluoromethane and ammonia. It is resistant to dilute acid and silicon ester lubricating oil but is not resistant to phosphate ester hydraulic oil. It is easy to crystallize and harden at low temperature, with poor storage stability and has a large expansion in mineral oil with a low aniline point. The general temperature range is from -50℃ to 150℃.
 
(1) Advantages:
Good elasticity and good compression deformation;
The formula contains no sulfur, so it is very easy to make.
It has the characteristics of resisting animals and vegetable oils.
It will not affect physical properties due to neutral chemicals, fats, oils and solvents.
With flame-proof characteristics
It is recommended to use in R12 refrigerant resistant seal.
It is recommended for rubber parts or seals on household appliances.
It is recommended for making all kinds of parts that are in direct contact with the atmosphere, sunlight and ozone.
It is recommended for all kinds of rubber products that are resistant to fire and chemical corrosion.

(2) Disadvantages:
It is not recommended to use in strong acids, nitro hydrocarbons, esters, chloroform and ketones.

8. Chlorosulfonated polyethylene adhesive CSM
 
(Hypalon, Polyethylene) Chlorosulfonated polyethylene is a synthetic rubber patented by DuPont. It has good heat resistance, weather resistance, ozone resistance, and good acid resistance. It is often used in oxidation-resistant drugs (nitric acid, sulfuric acid), and the general temperature range is from -45℃ to 120℃.
 
(1) Advantages:
It has good resistance to ozone, oxidation and flame.
It is similar to those of neoprene in physical properties and has better acid resistance.
Excellent abrasion resistance
It Has the same low friction surface as nitrile rubber.
The resistance to oil and solvent 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 oxidized acids, nitro hydrocarbons, esters, ketones and aromatic hydrogen.
 
9. SIlicone rubber Si
 
The main chain of silica gel for silicone rubber is composed of silicon (-si-o-si). It has excellent heat resistance, cold resistance, ozone resistance and atmospheric aging resistance. It has good electrical insulation performance. Its tensile strength is worse than ordinary rubber and it has no oil resistance. It is used in seals or rubber parts for the household appliances industry, such as rubber parts in electric kettles, electric irons and microwave ovens. It is used for seals or rubber parts in the electronic industry, such as mobile phone keys, shock pads in DVD, seals in cable connectors, etc. It is used for seals on various articles in contact with the human body, such as kettles, drinking fountains, etc.
 
(1) Advantages:
The tensile strength can reach 1500PSI and its tear resistance can reach 88LBS after the formula is prepared.
Good elasticity and good compression skew
It has good resistance to neutral solvents.
Excellent heat resistance
Excellent cold resistance
Excellent resistance to ozone and oxide erosion
Excellent electrical insulation performance
Good heat insulation and heat dissipation
 
(2) Disadvantages:
It is not recommended to use in most concentrated solvents, oil products, concentrated acids and diluted sodium hydroxide.
 
10. Silicone fluorine rubber FLS

Fluorinated silicone rubber is a kind of silicone rubber, which is fluorinated, and its general properties have the advantages of fluoro rubber and silicone rubber. Its oil resistance, solvent resistance, fuel oil resistance and high and low-temperature resistance are excellent, and the general service temperature is from -50℃ to 200℃.
 
(1) Advantages:
It is suitable for special applications, such as the corrosion resistance of oxygen-containing chemicals, aromatic hydrogen-containing solvents and chlorine-containing solvents.
It is suitable for use on the space machine.
 
(2) Disadvantages:
It is not recommended to expose to the solution of brake oil, ketone and grease.
 
11. Fluorocarbon FPM
 
Fluoro Carbon Rubber is rubber with fluorine in its molecule, which can be classified into various types according to fluorine content (i.e. monomer structure). At present, hexafluoride fluoro rubber, which is widely used, was first listed by DuPont under the trademark "Viton". Its high-temperature resistance is better than silicone rubber, with excellent chemical resistance. It also has resistance to most oils and solvents (except ketones and esters), weather resistance and ozone resistance, while having poor cold resistance. The general temperature range is from -20℃ to 250℃. Its special formula can withstand low temperature to -40℃. It is used for automobiles, locomotives, diesel engines and fuel systems. It is used for seals for chemical plants.
 
(1) Advantages:
Resistant to heat up to 250℃;
Resistant to most oils and solvents, especially all acids, aliphatic hydrocarbons, aromatic hydrocarbons and animal and vegetable oils.
 
(2) Disadvantages:
It is not recommended for ketones, low molecular weight esters and mixtures containing nitrate.
 
12. Perfluororubber FFPM (Perfluoroelastomer)

Perfluorinated series 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.

(1) Advantages:
Optimum heat resistance
Excellent chemical resistance
Low Outgassing
Excellent Plasma resistance
 
(2) Disadvantages:
Poor resistance to low temperature
The higher price of raw materials
Difficult Production

13. Acrylate rubber ACM
 
Acrylate rubber is an elastomer composed of Alkyl Ester Acrylate as the main component, which is excellent in petrochemical oil resistance, high-temperature resistance and weather resistance, but weak in mechanical strength, compression deformation rate and water resistance, slightly worse than ordinary oil-resistant rubber. The general temperature range is from -25℃ to 170℃. It is used for automobile transmission systems and power system seals.
 
(1) Advantages:
Suitable for automobile transmission oil
Good antioxidant and weather resistance
With the function of resisting bending deformation
Excellent resistance to oil products
Suitable for automobile transmission system and power steering wheel
 
(2) Disadvantages:
Not suitable for hot water
Not suitable for brake oil
Without the function of resisting low temperature
Not suitable for phosphate ester
 
14. Polyurethane urethane rubber PU

Polyurethane rubber has quite good mechanical properties. Its high hardness, high elasticity and abrasion resistance are difficult to compare with other rubbers. It also has good aging resistance, ozone resistance and oil resistance. The general temperature range is from -45℃ to 90℃. It is for industrial high-pressure and wear-resistant seals, such as hydraulic cylinder seals and high voltage power systems.
 
(1) Advantages:
Wear resistance and high-pressure resistance
 
(2) Disadvantages:
Non-resistance to high temperature

Material Name

O-ring Service Thermometer
Comparison of material properties
 
1. Selection of O-ring materials
Materials used as O-rings include nitrile rubber, carboxylic nitrile, fluoro rubber, ethylene-propylene rubber, hydrogenated nitrile rubber, silicon rubber, chloroprene rubber, fluorosilicone rubber, polyurethane, chlorohydrin rubber, styrene-butadiene rubber, butyl rubber, natural rubber, ethylene/ethylene propionic acid rubber, polyacrylate rubber, perfluoro rubber.
 
The same kind of rubber has great changes in performance index due to different formulations. Therefore, it is inaccurate to simply fill in NBR or NBR -40 in the material column.
 
2. The choice of O-ring hardness is more important. For example, the sealing ring of a water pump-turbine with the hardness of 70 (Shore) in a power station is often peeled off or even cut off transversely. After the sealing ring with a hardness of 85 or up to 90 (Shore) is used, the effect becomes better, which is ideal.
 
3. Materials with low hardness and easy installation are prone to peel, leading to damage, extrusion and even pressure explosion. Materials with too high hardness have inconvenient installation.
 
4. Generally, the hardness of the O-ring is from 40 to 90 IRHD, but 70IRHD is generally suitable in use. While for silicone rubber, 60 IRHD is generally used.