O-Ring
O-ring is a type of rubber sealing ring with a circular cross-section. Due to its O-shaped cross-section, it is called an O-ring rubber sealing ring, also known as an O-ring. It began to appear in the mid-19th century as a sealing element for steam engine cylinders.
Due to its affordable price, simple manufacturing, reliable functionality, and easy installation requirements, O-ring is the most common mechanical design for sealing. O-rings can withstand pressures of tens of megapascals (kilopounds). O-rings can be used in static applications as well as dynamic applications where there is relative motion between components, such as the shaft of a rotary pump and the piston of a hydraulic cylinder.
O-rings
Appearance: A circular ring with an O-shaped cross-section and a smooth overall
Application: sealing
Material: Circular rubber sealing rings, nitrile rubber, fluororubber, etc
Specification standards
O-ring specifications and standards
The specifications and models of O-rings mainly include UHSO ring specifications, UHPO ring specifications, UNO ring specifications, DHO ring specifications, piston rod O-ring specifications, high-temperature resistant O-rings, high-pressure resistant O-rings, corrosion-resistant O-rings, and wear-resistant O-rings.
The standards for O-rings mainly include the national standards GB 1235-76 and GB3452.1-92; Japanese standard P TYPE, G TYPE, S TYPE, SS/V TYPE, F TYPE; American standard AS568, British standard series; European Standard Series
The technical requirements for O-rings include appearance requirements, size requirements, and material physical performance requirements.
Appearance requirements comply with GB/T3452.2-2007
Material requirements comply with HG/T2579-2008
The size requirements comply with GB/T3452.1-2005
Application Introduction
YX O-ring for holes
Product use: Used for sealing pistons in reciprocating hydraulic cylinders. Scope of application: TPU: general hydraulic cylinders, general equipment hydraulic cylinders. CPU: Hydraulic cylinders for construction machinery and oil cylinders for high temperature and high pressure. Material: Polyurethane TPU, CPU, rubber.
Product hardness: HS85 ± 2 ° A Working temperature: TPU: -40~+80 ℃, CPU: -40~+120 ℃ Working pressure: ≤ 32Mpa Working medium: hydraulic oil, emulsion.
YX hole with O-ring stopper
Product Usage: This standard is applicable for use with YX type sealing rings when the working pressure of the oil cylinder is greater than 16MPa, or for protecting the sealing ring when the oil cylinder is subjected to eccentric force Working temperature: -40 to+100 degrees. Working medium: hydraulic oil, emulsion, aquatic product Hardness: HS 92 ± 5A Material: polytetrafluoroethylene.
YX O-ring for shaft
Product use: Used for sealing the piston rod in reciprocating hydraulic cylinders. Scope of application: TPU: general hydraulic cylinders, general equipment hydraulic cylinders. CPU: Hydraulic cylinders for construction machinery and oil cylinders for high temperature and high pressure. Material: Polyurethane TPU, CPU, Rubber Product Hardness: HS85 ± 2 ° A Working Temperature: TPU: -40~+80 ℃ CPU: -40~+120 ℃ Working Pressure: ≤ 32Mpa Working Medium: Hydraulic oil, emulsion.
O-ring has excellent sealing performance and high working life. The working life of dynamic pressure sealing is 5-10 times higher than that of conventional rubber sealing products, and can reach up to tens of times. Under certain conditions, it can have the same life as the sealing substrate.
The friction resistance of O-ring is small, and the dynamic and static friction forces are equal, which is 1/2-1/4 of the friction force of "0" - shaped rubber ring. It can eliminate the "crawling" phenomenon of movement at low speed and low pressure.
O-ring is highly wear-resistant and has an automatic elastic compensation function after the sealing surface wears out.
O-ring has good self-lubricating performance and can be used for oil-free sealing.
The O-ring structure is simple and easy to install.
O-ring working pressure: 0-300MPa; Working speed: ≤ 15m/s; Working temperature: -55-250 degrees.
O-rings are suitable for media such as hydraulic oil, gas, water, mud, crude oil, emulsion, water ethylene glycol, and acid. class
Scope of application
O-ring seal, although its structure is simple and inconspicuous, its function is not insignificant
O-ring seals are suitable for installation on various mechanical equipment, providing sealing function in static or moving states under specified temperature, pressure, and different liquid and gas media.
Various types of sealing components 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-ring seals are mainly used for static seals and reciprocating seals. When used for rotary motion sealing, it is limited to low-speed rotary sealing devices.
O-ring seals are generally installed in grooves with rectangular cross-sections on the outer or inner circle to provide sealing function.
O-ring seals still provide good sealing and shock absorption in environments that are resistant to oil, acid, alkali, abrasion, chemical erosion, and other factors. Therefore,
O-ring seals are the most widely used sealing components in hydraulic and pneumatic transmission systems.
Advantage
Compared with other types of seals, O-ring seals have the following advantages
-Suitable for various sealing forms: static sealing, dynamic sealing
-Suitable for various materials, with standardized sizes and grooves, and strong interchangeability
-Suitable for multiple modes of motion: rotary motion, axial reciprocating motion, or combined motion (such as rotary reciprocating combined motion)
-Suitable for various sealing media: oil, water, gas, chemical media, or other mixed media. By selecting appropriate rubber materials and designing appropriate formulas, effective sealing can be achieved for oil, water, air, gas, and various chemical media. The temperature range is wide (-60 ℃~+220 ℃), and the pressure can reach 1500Kg/cm2 when used in conjunction with a reinforcing ring.
--Simple design, compact structure, easy to assemble and disassemble
The cross-sectional structure of the O-ring is extremely simple and has a self sealing effect, ensuring reliable sealing performance.
Due to the extremely simple and standardized structure of the O-ring itself and its installation location, installation and replacement are very easy.
-Multiple types 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
-Low cost
-The dynamic friction resistance is relatively small
Representation method
GB/T3452.1-2005for example: O-ring 7.5 × 1.8-G-N, in GB/T3452.1-2005,
7.5 represents the inner diameter of the large ring of 7.5 millimeters, / 1.8 represents the cross-sectional diameter of the rubber ring of 1.8 millimeters / GB/T3452.1 represents the standard number / 2005 represents the year of publication of the standard. for example:
O-ring 7.5 × 1.8-G-N,
7.5- inner diameter d1
1.8- section diameter d2
G - series
N - grade
Material using HG/T2579-2008 method
JB/T7757.2-2006.
For example: O-ring 7.5 × 1.8-G-N,
7.5- inner diameter d1 / 1.8- section diameter d2
G - series N - grade
Material: P - nitrile rubber, E - EPDM rubber, etc.
International standard
A=American standard S568,
B=British standard BS1516,
C=Chinese C92 standard,
V.S.P.G=Japanese standard,
R=French standard
Groove Size
(unit: mm)
If significant expansion is required, the groove width can be increased by 20%.
Material classification
Natural Rubber (NR) is made of rubber latex collected from rubber trees and is a polymer of isoprene. Has good wear resistance, high elasticity, tensile strength, and elongation. It is prone to aging in the air, becomes sticky when exposed to heat, expands and dissolves easily in mineral oil or gasoline, and is resistant to alkali but not strong acid. ·It is a raw material for making adhesive tape, rubber hose, and rubber shoes, and is suitable for making shock absorber parts and products used in automotive brake oil, ethanol, and other liquids with hydroxide ions.
S B R styrene butadiene copolymer is a copolymer of butadiene and styrene. Compared with natural rubber, it has uniform quality, less foreign matter, but weaker mechanical strength, and can be mixed with natural rubber for use.
Advantages:
Low cost non oil resistant material
Good water resistance, good elasticity when hardness is below 70
Poor compression when high hardness
Can use most neutral chemicals and dry, nourishing organic ketones.
Disadvantages: Not recommended to use strong acids, ozone, oils, esters, fats, and most hydrocarbons. widely used in the tire industry, footwear industry, The textile and conveyor belt industries, etc.
Butyl rubber (IIR) is polymerized from isobutene and a small amount of isoprene, retaining a small amount of unsaturated groups for sulfur addition. Due to the less movement of methyl steric hindrance molecules compared to other polymers, it has less gas permeability, greater resistance to heat, sunlight, and ozone, and good electrical insulation properties; It has high resistance to polar solvents such as alcohols, ketones, esters, etc., and is generally used at a temperature range of -54~110 ℃.
Advantages: ·
Impermeability to most general gases
Good resistance to sunlight and ozone
Exposure to animal or vegetable oils or oxidizable chemicals
Disadvantages: not recommended for simultaneous use with petroleum solvents, kerosene, and aromatic hydrocarbons. ·Used for making rubber parts that are resistant to chemicals and vacuum equipment.
Hydrogenate Nitrile (HNBR)
It is a type of nitrile rubber that removes some double chains after hydrogenation. After hydrogenation, its temperature and weather resistance are much improved compared to ordinary nitrile rubber, and its oil resistance is similar to that of ordinary nitrile rubber. The general temperature range for use is -25~150 ℃.
Advantages:
It has better wear resistance than nitrile rubber
It has excellent corrosion resistance, tensile resistance, tear resistance, and compression resistance
It has good resistance to ozone, sunlight, and other atmospheric conditions
It is generally suitable for laundry or dishwashing cleaning agents.
Disadvantages: It is not recommended to be used in alcohol, ester, or aromatic solutions. Air conditioning and refrigeration industry, widely used as sealing components in environmentally friendly refrigerant R134a systems. ·Automotive engine system seals.
Ethylene propylene rubber (EPDM) is made by copolymerizing ethylene and propylene to form a main chain that does not have 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 temperature range for use is -50~150 ℃. Excellent resistance to polar solvents such as alcohols, ketones, ethylene glycol, and phosphate hydraulic oils.
Advantages:
Good weather resistance and ozone resistance
Excellent water and chemical resistance
Can use alcohols and ketones
High temperature vapor resistance, good gas impermeability
Disadvantages: not recommended for food use or exposure to aromatic hydrogen. Sealing components for high-temperature steam environments.
Sanitary equipment seals or components.
Rubber components in the braking system.
Seals in radiators (car water tanks).
Nitrile rubber (NBR) is made by copolymerization of acrylonitrile and butadiene, with an acrylonitrile content ranging from 18% to 50%. The higher the acrylonitrile content, the better the resistance to petroleum and hydrocarbon fuel oils, but the low-temperature performance deteriorates. It is generally used at a temperature range of -25~100 ℃. Nitrile rubber is one of the most commonly used rubbers for oil seals and O-rings.
Advantages:
It has good resistance to oil, water, solvents, and high-pressure oil.
Has good compression, wear resistance, and elongation.
Disadvantages: not suitable for use in polar solvents such as ketones, ozone, nitro hydrocarbons, MEK, and chloroform.
Used for making 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, especially sealing parts. It can be said to be the most versatile and cost-effective rubber seal.
CR chloroprene rubber (Neoprene, Polychloroprene) is polymerized from chloroprene monomer. The vulcanized rubber has good elasticity and wear resistance, is not afraid of direct sunlight, has particularly good resistance to atmospheric aging, is not afraid of intense distortion, is not afraid of refrigerants such as dichlorodifluoromethane and ammonia, and is resistant to dilute acid and silicone ester lubricating oils, but not to phosphate ester hydraulic oils. It is prone to crystallization and hardening at low temperatures, has poor storage stability, and has a large expansion in mineral oils with low aniline points. The general temperature range for use is -50~150 ℃.
Advantages:
Good elasticity and good compression deformation.
The formula does not contain sulfur, making it very easy to make.
It has anti animal and vegetable oil properties and will not be affected by neutral chemicals, fats, oils, various oils, and solvents.
It also has flame retardant properties.
Disadvantages: it is not recommended to use strong acids, nitro hydrocarbons, esters, chloroform, and ketones in chemicals. ·Seals resistant to R12 refrigerant. ·Rubber parts or seals on household appliances.
Suitable for making various parts that come into direct contact with the atmosphere, sunlight, and ozone. suitable for various fire-resistant and chemically corrosion-resistant rubber products.
Chlorosulfonated polyethylene (Hypalon, Polyethylene)
It is a synthetic rubber patented by DuPont. Excellent heat resistance, weather resistance, and ozone resistance; It also has good acid resistance and is commonly used in oxidation resistant drugs (nitric acid, sulfuric acid). The general temperature range for use is -45~120 ℃.
Advantages:
Good resistance to ozone, oxidation, and flames
Similar physical properties to chloroprene rubber and excellent acid resistance
Excellent abrasion resistance
Same low friction surface as nitrile rubber
Resistance to oil agents and solvents is between nitrile rubber and chloroprene rubber
It is recommended to use water to prevent leakage
Disadvantages: not recommended to be exposed to concentrated oxidizing acids, nitro hydrocarbons, esters, ketones, and aromatic hydrocarbons.
Silicone rubber SI
It is composed of silicon (- si-o-si) bonded together. It has excellent heat resistance, cold resistance, ozone resistance, and atmospheric aging resistance. Has excellent electrical insulation performance. The tensile strength is inferior to general rubber and does not have oil resistance.
Advantages: after being formulated, the tensile strength can reach 1500PSI and the tear resistance can reach 88LBS.
It has good elasticity and good compressibility.
It has good resistance to neutral solvents, excellent heat resistance,
Excellent cold resistance,
Excellent resistance to ozone and oxide corrosion,
Excellent electrical insulation performance,
Good insulation and heat dissipation.
Disadvantages: not recommended to be used in most concentrated solvents, oils, concentrated acids, and diluted sodium hydroxide. ·Seals or rubber parts used in the household appliance industry, such as rubber parts in electric kettles, electric irons, and microwave ovens.
Seals or rubber parts in the electronics industry, such as phone buttons, shock absorbers in DVDs, seals in cable connectors, etc. ·
Seals on various products that come into contact with the human body, such as water bottles, water dispensers, etc.
Silicone Fluororubber FLS
Fluorinated Silicone Rubber is a type of silicone rubber that has undergone fluorination treatment, and its general properties combine the advantages of both fluororubber and silicone rubber; It has excellent oil resistance, solvent resistance, fuel oil resistance, and high and low temperature resistance, and is generally used at temperatures of -50~200 ℃.
Advantage:
Suitable for special purposes, such as resisting corrosion from oxygen-containing chemicals, aromatic hydrogen containing solvents, and chlorine containing solvents.
Disadvantages: It is not recommended to expose it to brake fluid, ketones, and solvents on space components.
Fluororubber FKM/FPM
Fluoro Carbon Rubber refers to rubber molecules containing fluorine, which can be classified into various types based on the fluorine content (i.e. monomer structure). The widely used hexafluororubber was first marketed by DuPont under the trade name "Viton". High temperature resistance is superior to silicone rubber, with excellent chemical resistance, resistance to most oils and solvents (except ketones and esters), weather resistance, and ozone resistance; The cold resistance is relatively poor, and the general temperature range for use is -20~250 ℃. The special formula can withstand low temperatures up to -40 ℃.
Advantage:
Can withstand heat up to 250 ℃
It has the ability to resist most oils and solvents, especially all acids, aliphatic
hydrocarbons, aromatic hydrocarbons, and animal and vegetable oils
Disadvantages: not recommended for use in ketones, low molecular weight esters, and mixtures containing nitrate. ·Automobiles, locomotives, diesel engines, and fuel systems.
Seals for chemical plants.
Perfluororubber FFKM/FFPM (Perfluoroelastomer)
Advantage:
Best heat resistance characteristics
Excellent chemical resistance properties
Low Outgassing Characteristics
Excellent anti plasma properties
Disadvantages:
Poor low-temperature resistance
High raw material prices
The production difficulty is relatively high. Perfluorocarbon series products are widely used in the semiconductor industry and information related industries, including PVC, CVD, etching processes in thin film processes, and various high vacuum sealing processes.
Acrylic rubber ACM
Polyacrylate rubber is an elastic material mainly composed of Alkyl Ester Acrylate, which has excellent resistance to petrochemical oil, high temperature, and weather. However, it has weaker mechanical strength, compression deformation rate, and water resistance, slightly worse than general oil resistant rubber. The general temperature range for use is -25~170 ℃.
Advantage:
Suitable for automotive transmission oil
Has good antioxidant and weather resistance properties
Capable of resisting bending deformation
Excellent resistance to oil products
Suitable for automotive transmission systems and power steering wheels
Disadvantages:
Not suitable for use in hot water
Not suitable for use in brake fluid
Not capable of withstanding low temperatures
Not applicable to phosphate esters, automotive transmission systems, and power system seals.
Polyurethane rubber PU
Polyurethane rubber has excellent mechanical properties, with high hardness, elasticity, and wear resistance that are difficult to compare with other types of rubber; The aging resistance, ozone resistance, and oil resistance are also quite good. The general temperature range for use is -45~90 ℃.
Advantage: Wear resistant and high pressure resistant
Disadvantages: not resistant to high temperatures, industrial high-pressure and wear-resistant seals, such as hydraulic cylinder seals.
High voltage and high charge system
Materials selection
The material used as O-rings include nitrile rubber, carboxylic nitrile, fluororubber, ethylene propylene rubber, hydrogenated nitrile rubber, silicone rubber, chloroprene rubber, fluorosilicone rubber, polyurethane, chlorohydrin rubber, styrene butadiene rubber, butyl rubber, natural rubber, ethylene/vinyl acetate rubber, polyacrylate rubber, perfluororubber, and so on. Due to different formulations, the performance indicators of the same type of rubber also vary greatly. So simply filling in nitrile rubber or butyronitrile 40 in the material column is inaccurate. The Ministry of Chemical Industry has specific standards for materials used for O-rings, such as: HG/T 2579-1994、HG/T 2021-1991、HG/T 2333-1992、HG/T 3089-2001、HB 5290-1991 Wait. HG/T 2579-1994 specifically removed the specific categories of materials and only provided some performance indicators of the materials.
Hardness selection
The choice of O-ring hardness is quite important. If the hardness of the sealing ring of a water pump turbine in a certain power station is 70 (Shore), it often peels off or even cuts horizontally. Then, an 85-90 (Shore) sealing ring is used, and the effect is ideal.
Low hardness, easy to install, but prone to peeling, installation damage, extrusion, and even pressure explosion. The hardness is too high, making installation inconvenient.
Usually, the hardness of O-rings is 40-90 IRHD, but in use, 70 IRHD is generally more suitable, except for silicone rubber, which generally uses 60 IRHD.
Repair of O-ring
The uncured O-ring rubber material is a viscous fluid under high temperature and pressure. However, during the molding vulcanization stage, the rubber material quickly fills the mold cavity, and the excess part (in order to prevent rubber shortage, the rubber material filled in the mold cavity must be kept in a certain excess) overflows during vulcanization, forming overflow (also known as waste edge or flash edge). Once the overflow edge is formed, it must be removed in order to make the appearance neat and beautiful. This process is commonly known as trimming. The requirements for trimming are precise size and neat appearance. In actual production. The trimming of products is often time-consuming and labor-intensive. For products with strict requirements, even a slight mistake during trimming may result in waste, and it must be treated with caution. Generally speaking, the smaller the size specification and the more complex the configuration of the product, the higher the difficulty of trimming and the more waste there are.
The trimming of O-rings can be divided into three categories: manual, mechanical, and frozen:
1. Hand trimming. The operator holds a cutting tool and gradually repairs the overflow edge along the outer edge of the product. This is the most primitive method. Low efficiency and difficult to guarantee quality, especially for O-rings with small size and high precision requirements, it is difficult to achieve thorough and clean results, and it is easy to damage the connection between the product body and the overflow edge. Often leaving tooth marks and gaps, resulting in residual problems such as oil and gas leakage that affect sealing. Additionally. The dependence of manual edge trimming on operational proficiency is also prominent.
2. Mechanical trimming. In order to improve efficiency and quality, mechanical trimming has emerged. The common type is a specialized electric edge trimming machine with a rotating blade. The blade used needs to be highly compatible with the size of the product. If there are overflow edges on both the inner and outer edges of the product. It can be designed as a double-edged, multi blade design. To achieve a one-time completion. The machining accuracy of mechanical trimming is higher than that of manual trimming, and the efficiency is also doubled. Especially for products with the first mock examination and multiple cavities, matching cutters can be designed according to the arrangement and distribution of products. After the product is molded. Can be fully fitted and cut in one go. With the help of heating, dozens can be repaired at once. The key is to control the cutting temperature well to prevent adhesion after being too high.
3. Frozen trimming. Remove the edges of the vulcanized finished product together with the waste edges under freezing conditions. This technology was jointly invented and improved by Japan's Showa Carbonate and China's Zhaoling Precision. Over the past few decades, with the selection and replacement of refrigeration media and the improvement of mechanical actions, frozen edge trimming has also undergone several generations of improvements, becoming increasingly mature and perfect. The work efficiency and processing quality have been significantly im
INSTALLATION REQUIREMENTS
1、 Requirements for installing O-rings
Before installing the O-ring (O-ring rubber seal), check the following:
1. Whether the introduction angle is processed according to the drawing and whether the sharp edges are chamfered or rounded;
2. Whether the inner diameter has removed burrs and whether there is contamination on the surface;
3. Have the seals and parts been coated with grease or lubricant (to ensure the compatibility of the elastomer medium, it is recommended to use the sealed liquid for lubrication);
4. Do not use lubricating grease containing solid additives, such as molybdenum disulfide and zinc sulfide.
2. Manual installation of O-ring
1. Use tools without sharp edges;
2. Ensure that the O-ring (O-ring rubber seal) is not twisted and should not be excessively stretched;
3. Try to use auxiliary tools to install O-rings (O-ring rubber seals) and ensure correct positioning;
4. O-rings (O-ring rubber seals) bonded with sealing strips must not be stretched at the connection.
3. Install screws, splines, etc
When the O-ring (O-ring rubber seal) is stretched and needs to pass through screws, splines, keyways, etc., an installation spindle must be used. The spindle can be made of soft and smooth metal or plastic, without burrs or sharp edges.
When installing the compression screw, the screw should be tightened proportionally and not tightened in order of direction.
Design usage
Improper design and use of O-rings can accelerate their damage and loss of sealing performance. Experiments have shown that if the design of each part of the sealing device is reasonable, simply increasing the pressure will not cause damage to the O-ring. Under high pressure and high temperature working conditions, the main cause of O-ring failure is the permanent deformation of the O-ring material and the gap bite caused by the O-ring being squeezed into the sealing gap, resulting in distortion of the O-ring during movement.
Permanent deformation
Due to the fact that the synthetic rubber material used for O-ring seals is a viscoelastic material, the initially set compression amount and rebound blocking ability will gradually lose permanent deformation after prolonged use, ultimately leading to leakage. The main reasons for the loss of sealing performance of O-rings are permanent deformation and loss of elasticity. The following are the main causes of permanent deformation
(1) The relationship between compression rate, elongation and permanent deformation
(2) The relationship between temperature and O-ring relaxation process
(3) Working pressure and permanent deformation of the media
The compression permanent deformation rate of O-ring material is related to temperature. When the deformation rate is 40% or greater, leakage will occur, so the heat resistance limits of several rubber materials are: nitrile rubber at 70 ℃, EPDM rubber at 100 ℃, and fluororubber at 140 ℃. Therefore, various countries have made regulations on the permanent deformation of O-rings. The size changes of O-rings made of Chinese standard rubber materials at different temperatures are shown in the table. O-rings of the same material have a lower compression permanent deformation rate at the same temperature for O-rings with larger cross-sectional diameters. The situation in oil is different. Due to the fact that the O-ring is not in contact with oxygen at this time, it usually occurs in a dynamic sealing state. If the O-ring is properly assembled and used under appropriate conditions, it is generally not easy to roll or twist during reciprocating motion, because the contact area between the O-ring and the groove is larger than the frictional contact area on the sliding surface, and the resistance ability of the O-ring itself can prevent twisting. The distribution of friction also tends to keep the O-ring stationary in its groove, because static friction is greater than sliding friction, and the roughness of the groove surface is generally not as good as that of the sliding surface.
Twisted damage
There are many reasons that can cause distortion damage, among which the most important is due to uneven clearance between the piston, piston rod, and cylinder barrel, excessive eccentricity, and uneven diameter of the O-ring section. Due to the uneven friction force experienced by the O-ring over a week, some parts of the O-ring experience excessive friction, resulting in distortion. Usually, O-rings with smaller cross-sectional sizes are prone to uneven friction. The reason for causing distortion is that the cross-sectional diameter of the O-ring used for movement is larger than that of the O-ring used for fixation. ）In addition, due to the coaxiality deviation, unequal sealing heights, and uneven cross-sectional diameter of the O-ring in the sealing groove, some parts of the O-ring may be compressed too much, while others may be compressed too little or not compressed. When there is eccentricity in the groove, that is, when the coaxial deviation is greater than the compression amount of the O-ring, the seal will completely fail. Another harm of large coaxiality deviation in the sealing groove is that it causes uneven compression of the O-ring along the circumference. In addition, due to uneven cross-sectional diameter, material hardness, lubricating oil film thickness, and surface roughness of the sealing shaft, some parts of the O-ring slide along the workpiece surface while the other part rolls, resulting in distortion of the O-ring. Movement makes the ring easily damaged due to twisting, which is an important reason for the damage and leakage of the sealing device. Therefore, improving the machining precision of the sealing groove and reducing eccentricity are important factors to ensure the reliable sealing and service life of the O-ring. The installation of the sealing ring should not be in a twisted state. If it is twisted during installation, twisting damage will occur quickly. In work, the phenomenon of distortion can cut the O-ring, causing a large amount of oil leakage, and the cut O-ring can mix with other parts of the hydraulic system, causing major accidents.
In order to prevent distortion and damage to the O-ring, the following points should be noted during design
(1) The concentricity of the O-ring installation groove should be considered from two aspects: easy processing and no distortion.
(2) The cross-sectional size of the O-ring should be uniform, and lubricating oil or grease should be fully applied to the sealing area during each installation. Sometimes a felt ring type oiling device soaked in lubricating oil can also be used.
(3) Increase the cross-sectional diameter of the O-ring, and the cross-sectional diameter of the O-ring for dynamic sealing should generally be larger than that for static sealing; In addition, O-rings should be avoided from being used as seals for large diameter pistons.
(4) When twisting damage occurs under low pressure, a sealing ring can be used to protect the retaining ring.
(5) Reduce the surface roughness of the cylinder barrel and piston rod.
(6) Use low friction coefficient materials to make O-ring seals.
(7) O-ring can be replaced with a sealing ring that is less prone to distortion.
Abrasive wear
When the sealed gap has relative motion, dust and sand particles in the working environment adhere to the surface of the piston rod and are carried into the cylinder along with the oil film as the piston rod moves back and forth, becoming abrasive particles that invade the surface of the O-ring seal, accelerating its wear and causing it to lose its sealing performance. To avoid this situation, a dust ring must be used at the extended shaft end of the reciprocating sealing device.
The influence of sliding surface on O-ring
The roughness of the sliding surface is a direct factor affecting the friction and wear of the O-ring surface. Generally speaking, a smooth surface has less friction and wear, so the roughness value of the sliding surface is often very low (Ra0.2-0.050 μ m). However, experiments have shown that a surface roughness that is too low (Ra below 0.050 μ m) can have adverse effects on friction and wear. This is because the tiny surface roughness can maintain the necessary lubricating oil film. Therefore, it is necessary to choose appropriate surface requirements. The material of the sliding surface also has an impact on the lifespan of the O-ring. The greater the hardness, wear resistance, and ability to maintain smoothness of the sliding surface material, the longer the lifespan of the O-ring. This is also an important reason for the chrome plating on the surface of the hydraulic cylinder piston rod. Similarly, it can be explained that sliding surfaces made of copper or aluminum alloys with the same roughness have more severe friction and wear on sealing rings than steel sliding surfaces. Sealing rings with low hardness and high compression are not as durable as those with high hardness and low compression.
Friction and the Application of O-rings
Calculation formula for friction force of O-ring of dynamic sealing ring
Friction and wear are important influencing factors for O-ring damage in dynamic sealing devices. The degree of wear mainly depends on the magnitude of frictional force. When the liquid pressure is small, the magnitude of the friction force of the O-ring depends on its pre compression amount. When the working fluid is subjected to pressure, the frictional force increases with the increase of working pressure. When the working pressure is less than 20MPa, there is an approximate linear relationship. When the pressure is greater than 20MPa, as the pressure increases, the increase in contact area between the O-ring and the metal surface gradually slows down, and the increase in friction force also correspondingly slows down. Under normal circumstances, the service life of O-rings will decrease approximately in a square relationship with the increase of liquid pressure. The increase in friction causes a significant amount of frictional heat to be generated between the rotating or reciprocating shaft and the O-ring seal. Due to the fact that most O-rings are made of rubber, their thermal conductivity is extremely poor. Therefore, frictional heat can cause rubber aging, leading to ineffective O-ring and damaging its sealing performance. Friction can also cause damage to the surface of the O-ring, reducing the amount of compression. Severe friction can quickly cause surface damage to the O-ring and loss of sealing. When sealing for pneumatic reciprocating motion, frictional heat can also cause adhesion, leading to further increase in frictional force. During low-speed motion, frictional resistance is still a factor that causes crawling in sports seals, affecting the performance of components and systems. So for sports seals, friction is one of the important properties. The friction coefficient is an evaluation index of friction characteristics, and synthetic rubber has a relatively high friction coefficient. Due to the fact that the seal is usually in a mixed lubrication state with working oil or lubricant during motion, the friction coefficient is generally below 0.1. The magnitude of friction largely depends on the surface hardness and roughness of the sealed component. The Joule heating effect of rubber materials refers to the phenomenon of rubber in a stretched state contracting when exposed to heat. When installing the O-ring, in order to prevent it from moving in the sealing groove and from twisting when used as a reciprocating seal, it is generally placed in a certain degree of tension. But if this installation method is used for rotational motion, it will produce adverse results. The O-ring seal, which was originally tightly clamped on the rotating shaft, contracts due to the frictional heat generated by the rotational motion, thereby increasing the clamping force. In this way, frictional heat → contraction → increased clamping force → frictional heat →... This repeated cycle greatly promotes the aging and wear of the rubber.
If you need help navigating this process to find the seal that suits your project, please consult DMB seal team. We have over 15 years building relationships with global seal manufacturers, providing you with thousands of types of seals, gaskets, O-rings, and other special products suitable for any application.
