What is a sealing ring

What is a sealing ring

What is a sealing ring?

The sealing ring is a ring cover composed of one or several parts, which is fixed on one ring or washer of the bearing and contacts with another ring or washer or forms a narrow labyrinth gap to prevent the leakage of lubricating oil and the invasion of foreign objects. The sealing ring is a kind of rubber ring with circular cross section. Because its cross section is O-shaped, it is called O-shaped sealing ring. It is one of the most widely used hydraulic and pneumatic transmission systems. It is usually called O ring in Taiwan enterprises and Japanese enterprises.

O-ring is generally made of nitrile rubber, natural rubber, chloroprene rubber, ethylene propylene rubber, fluorine rubber, silicon rubber and blend rubber. Besides O-type, there are triangle type, rectangle type, D-type, T-type, square type, heart type, X-type, five edge type, olive type, etc.

Material and application of sealing ring

The selection of sealing ring material is of great significance to its sealing performance and service life. The performance of the material directly affects the performance of the sealing ring.

• 1. NBR nitrile rubber sealing ring: suitable for petroleum hydraulic oil, glycol hydraulic oil, diester lubricating oil, gasoline, water, silicone grease, silicone oil and other media. Is the most widely used, the lowest cost of rubber seals. Not suitable for polar solvents such as ketones, ozone, nitrohydrocarbons, MEK and chloroform. The general temperature range is – 40 ~ 120 ℃.
• 2. HNBR hydrogenated nitrile rubber sealing ring: excellent corrosion resistance, tear resistance and compression resistance, ozone resistance, sunlight resistance and weather resistance. It has better abrasion resistance than NBR. It is suitable for washing machine, automobile engine system and refrigeration system using new environment-friendly refrigerant R134a. It is not recommended to use in alcohol, ester or aromatic solution. The general temperature range is – 40 ~ 150 ℃.
• 3. SIL silicone rubber sealing ring: excellent heat resistance, cold resistance, ozone resistance and atmospheric aging resistance. It has good insulation. But the tensile strength is worse than that of ordinary rubber and it has no oil resistance. Suitable for household appliances such as electric water heater, electric iron, microwave oven, etc. It is also suitable for all kinds of products that have contact with human body, such as kettle, water dispenser, etc. It is not recommended to use in most concentrated solvents, oil products, concentrated acids and sodium hydroxide. The general temperature range is – 55 ~ 250 ℃.
• 4. Viton fluorine rubber sealing ring: high temperature resistance is better than silicone rubber, has excellent weather resistance, ozone resistance and chemical resistance, cold resistance is poor. It is resistant to most oils and solvents, especially acids, aliphatic hydrocarbons, aromatic hydrocarbons and animal and vegetable oils. It is suitable for sealing requirements of diesel engine, fuel system and chemical plant. It is not recommended for ketones, low molecular weight esters and mixtures containing nitrate. The general temperature range is – 20 ~ 250 ℃.
• 5. FLS fluorosilicone rubber sealing ring: it has the advantages of both fluorosilicone rubber and silicone rubber, and has good oil resistance, solvent resistance, fuel oil resistance and high and low temperature resistance. It can resist the erosion of oxygen-containing compounds, aromatic solvents and chlorine containing solvents. Generally used for aviation, aerospace and military purposes. Exposure to ketones and brake oil is not recommended. The general temperature range is – 50 ~ 200 ℃.
• 6. EPDM EPDM rubber sealing ring: good weather resistance, ozone resistance, water resistance and chemical resistance. Can be used for alcohols and ketones, also can be used for high temperature steam environment sealing. It is suitable for bathroom equipment, car radiator and car brake system. It is not recommended for food use or exposure to mineral oil. The general temperature range is – 55 ~ 150 ℃.
• 7. CR chloroprene rubber sealing ring: it has excellent sunlight resistance and weather resistance. It is not afraid of dichlorodifluoromethane, ammonia and other refrigerants, resistant to dilute acid and silicone grease lubricating oil, but has large expansion in mineral oil with low aniline point. It is easy to crystallize and harden at low temperature. Suitable for all kinds of atmosphere, sunlight, ozone environment and all kinds of fire-resistant, chemical corrosion-resistant sealing environment. It is not recommended to use in strong acids, nitrohydrocarbons, esters, chloroform and ketones. The general temperature range is – 55 ~ 120 ℃.
• 8. IIR butyl rubber sealing ring: excellent air tightness, heat resistance, sunlight resistance, ozone resistance and insulation performance; It has good resistance to polar solvents such as alcohols, ketones and esters, and can be exposed to animal and vegetable oils or oxidizable compounds. Suitable for chemical resistant or vacuum equipment. It is not recommended to use with petroleum solvent, kerosene or aromatics. The general temperature range is – 50 ~ 110 ℃.
• 9. ACM acrylic rubber sealing ring: excellent resistance to oil, high temperature resistance and weather resistance, but mechanical strength, compression deformation rate and water resistance are slightly poor. Generally used in automotive transmission system and power steering system. Not suitable for hot water, brake oil, phosphate. The general temperature range is – 25 ~ 170 ℃.
• 10. NR natural rubber sealing ring: good wear resistance, elasticity, breaking strength and elongation. However, it is easy to age in air and become sticky when heated. It is easy to expand and dissolve in mineral oil or gasoline. It is resistant to alkali but not strong acid. It is suitable for use in brake oil, ethanol and other liquid with hydroxyl ion. The general temperature range is – 20 ~ 100 ℃.
• 11. PU polyurethane rubber sealing ring: the mechanical properties of polyurethane rubber are very good, and the wear resistance and high pressure resistance are far better than other rubbers. Aging resistance, ozone resistance and oil resistance are also quite good, but it is easy to hydrolyze at high temperature. Generally used for high pressure, wear-resistant sealing link, such as hydraulic cylinder. The general temperature range is – 45 ~ 90 ℃.
• 12. Metal rubber sealing ring: made of stainless steel wire, without any rubber components, with strong use characteristics. For example: in high vacuum, high and low temperature, strong radiation, and a variety of corrosive environment to maintain normal work. The skin of sealing ring is made of different materials such as stainless steel, copper, polytetrafluoroethylene and so on according to different uses. The coated metal rubber component is used as the lining core, which has the advantages of high sealing strength, good effect and reusability. The sealing ring core is made of different wire diameter and density, which is suitable for different pressure situations. The general application range is – 80 ~ 800 ℃. This kind of sealing ring is expensive because of its high cost. But good performance, a wide range of use environment, have been unanimously recognized by people.

Performance of sealing ring

In addition to the general requirements of sealing ring materials, the following conditions should also be noted for the sealing ring:

• (1) It is full of elasticity and resilience;
• (2) Appropriate mechanical strength, including expansion strength, elongation and tear strength.
• (3) It has stable performance, is not easy to swell in medium, and has small thermal shrinkage effect (Joule effect).
• (4) It is easy to process and keep precise size.
• (5) No corrosion of contact surface, no pollution of medium, etc.

The most suitable and commonly used material to meet the above requirements is rubber, so the sealing ring is mostly made of rubber material. There are many kinds of rubber, and new rubber varieties appear constantly. When designing and selecting, we should understand the characteristics of various kinds of rubber, and make reasonable selection.

Classification of sealing rings

V-ring
The utility model is an axial acting elastic rubber sealing ring, which is used as a shaft non pressure seal. The sealing lip has good mobility and adaptability, which can compensate for large tolerance and angle deviation, prevent internal grease or oil leakage, and prevent external splashing or dust invasion.
O-ring
Mainly used for static seal and reciprocating seal. When used for rotary motion seal, it is limited to low speed rotary sealing device.
Rectangular seal ring
Generally, it is installed in the groove with rectangular section on the outer circle or inner circle to play a sealing role.
Y-ring
Widely used in reciprocating sealing device.
In addition, there is spring tension (spring energy storage) seal ring, which is a spring added into PTFE sealing material, including O-type spring, V-type spring and U-type spring.
YX type sealing ring for hole
Application: used for sealing piston in reciprocating hydraulic cylinder. Scope of application: TPU: general hydraulic cylinder, general equipment hydraulic cylinder. CPU: hydraulic cylinder for construction machinery and cylinder for high temperature and high pressure. Material: Polyurethane TPU, CPU, rubber.
Product hardness: HS85 ± two ° A working temperature: TPU: – 40 ～ + 80 ℃, CPU: – 40 ～ + 120 ℃, working pressure: ≤ 32Mpa, working medium: hydraulic oil, emulsion.
YX type hole retaining ring
Application: this standard is applicable to the use of YX type sealing ring when the working pressure of oil cylinder is greater than 16MPa, or to the protection of sealing ring when the oil cylinder is eccentrically stressed. Working temperature: – 40 ～ + 100 ℃.
Working medium: hydraulic oil, emulsion, aquatic product hardness: HS 92 ± 5A material: polytetrafluoroethylene
YX type sealing ring for shaft
Application: used for sealing piston rod in reciprocating hydraulic cylinder. Scope of application: TPU: general hydraulic cylinder, general equipment hydraulic cylinder. CPU: hydraulic cylinder for construction machinery and cylinder for high temperature and high pressure.

• Material: Polyurethane TPU, CPU, rubber product hardness: HS85 ± two ° A working temperature: TPU: – 40 ～ + 80 ℃ CPU: – 40 ～ + 120 ℃ working pressure: ≤ 32Mpa
• Working medium: hydraulic oil, emulsion.

YX type retaining ring for shaft
Application: this standard is applicable to the use of YX type sealing ring when the working pressure of the oil cylinder is greater than 16MPa, or to protect the sealing ring when the oil cylinder is eccentrically stressed. Working temperature: – 40 ～ + 100 ℃
Working medium: hydraulic oil, emulsion, aquatic product hardness: HS 92 ± 5A material: polytetrafluoroethylene according to: enterprise standard
O-ring rubber seal

• Application: the O-type rubber sealing ring in this standard is suitable for hydraulic and pneumatic system and various mechanical equipment and components. It can be used for sealing under the specified pressure, temperature and different liquid and gas medium in static or moving state.
• Working temperature: – 40 ～ + 230 ℃.
• Working pressure: < 10 ～ 220kg, f /cm.
• Working medium: air, water, oil, product hardness: 40 ~ 85 ± 2A material: nitrile rubber, silicon rubber, fluorine rubber, ethylene propylene rubber.

Retaining ring for O-ring

• Application: this standard is applicable to use with O-ring when the cylinder pressure is greater than 10MPa. Working temperature: – 100 ～ 200 ℃.
• Working medium: hydraulic oil, emulsion, water material: polytetrafluoroethylene, according to JB / zq4224-86, suitable for gb1235-76.

J-type frameless dust ring

Combined seal ring

• Application: it is used in reciprocating oil cylinder, cylinder, piston rod or valve stem exposed place to prevent dust. Scope of application: TPU: construction machinery, general machinery, cylinder, all kinds of valves, etc.
• CPU: construction machinery oil cylinder, oil cylinder with bad working condition.
• Material: polyurethane, nitrile rubber.
• Working temperature: – 40 ~ 120 ℃.
• Product hardness: HS 80 ± 5A according to JB/T6657-1993.

The working life of dynamic pressure seal is 5-10 times higher than that of conventional rubber seal products, up to tens of times. Under some conditions, the working life of dynamic pressure seal can be the same as that of seal matrix.
The friction resistance of the sealing ring is small, and the dynamic and static friction are equal, which is 1/2-1/4 of the friction of the “0” rubber ring. It can eliminate the “creeping” phenomenon of low speed and low pressure.
The sealing ring has high wear resistance, and the sealing surface has automatic elastic compensation function after being worn.
The sealing ring has good self-lubricating performance. It can be used as oil-free lubrication seal.
The sealing ring has the advantages of simple structure and convenient installation.
Working pressure of sealing ring: 0-300mpa; Working speed: ≤ 15m / S; Working temperature: – 55-250 ℃.
Applicable media of sealing ring: hydraulic oil, gas, water, mud, crude oil, emulsion, water glycol, acid, alkali, chemicals, etc.

Types and forms of oil cylinder sealing ring

Construction machinery is inseparable from the oil cylinder, and the oil cylinder is inseparable from the seal. The common seal is the seal ring, also known as the oil seal, which can isolate the oil and prevent the oil from overflowing or passing through. Here, Yang sorted out some common types and forms of cylinder sealing rings for you.

The common seal rings used in hydraulic cylinder are as follows: dust ring, piston rod seal ring, buffer seal ring, guide support ring, end cover seal ring and piston seal ring.

Dust ring
The dust ring is installed on the outside of the end cover of the hydraulic cylinder to prevent external pollutants from entering the cylinder. According to the installation method, it can be divided into snap in type and press in type. Pay close attention to mechanical engineer to acquire more mechanical knowledge.

Basic form of snap in dust ring
Snap in type dust ring is the most common. As the name suggests, the dust ring is stuck in the groove of the inner wall of the end cover, which is used in less harsh environmental conditions. The material of snap in dustproof ring is usually polyurethane, and there are many variations in its structure. For example, the h-and k-sections are double lip structure, but they are always the same.

Some variants of snap in dust ring
The press in dust ring is used under severe and heavy load conditions. It is not stuck in the groove. Instead, it is wrapped with a layer of metal to increase the strength and pressed into the end cover of the hydraulic cylinder. There are many types of press in dust rings, including single lip and double lip.

Press-in dust ring and some variants
Piston rod sealing ring
Piston rod seal ring, also known as u-cup, is the main piston rod seal, which is installed inside the end cover of hydraulic cylinder to prevent hydraulic oil leakage. The piston rod seal ring is made of polyurethane or nitrile rubber. In some cases, it needs to be used together with the support ring (also known as the retaining ring). The support ring is used to prevent the seal ring from extrusion deformation under pressure. There are also many variants of piston rod seals. Pay close attention to mechanical engineer to acquire more mechanical knowledge.

Common types of piston rod seal ring

Some variants of piston rod seal ring
Buffer seal ring
As an auxiliary piston rod seal ring, the buffer seal ring is used to protect the piston rod when the system pressure suddenly increases. There are three common types of buffer seals. Type A is a single sealing ring made of polyurethane. Type B and type C are two-piece type, which are used to prevent seal extrusion and allow the seal to bear higher pressure.

Several common forms of buffer seal ring
Guide support ring
The guide support ring is installed on the end cover and piston of the hydraulic cylinder, which is used to support the piston rod and piston, guide the piston to do linear motion, and prevent metal to metal contact. The materials are plastic, bronze coated with polytetrafluoroethylene, etc.

It is respectively used for the guide support ring on the end cover of the hydraulic cylinder and the piston.
End cover sealing ring
The end cover seal ring is used to seal the cylinder end cover and the cylinder wall. It is a static seal to prevent the leakage of hydraulic oil from the gap between the end cover and the cylinder wall. It is usually composed of NBR O-ring and support ring (retaining ring).

Piston sealing ring
The piston seal ring is used to isolate the two chambers of the hydraulic cylinder and is the main seal in the hydraulic cylinder. Usually two-piece, the outer ring is made of PTFE or nylon, and the inner ring is made of NBR. There are also a variety of variants, including the use of bronze coated with polytetrafluoroethylene, and so on. Polyurethane u-cup is also used in single acting oil cylinder.

Several common forms of piston sealing ring

Advantages of sealing ring

• 1. The sealing ring should have good sealing performance in the working pressure and a certain temperature range, and it can automatically improve the sealing performance with the increase of pressure.
• 2. The friction between the sealing ring device and the moving parts should be small and the friction coefficient should be stable.
• 3. The sealing ring has strong corrosion resistance, is not easy to be aged, has long working life, good wear resistance, and can automatically compensate after wear to a certain extent.
• 4. Simple structure, convenient use and maintenance, so that the seal ring has a longer life.

Installation and use of sealing ring

Precautions for installation and use of sealing ring:

• (1) Do not install the wrong direction and damage the lip. If you have 50 on your lips μ If the distance is more than 10 m, it may cause obvious oil leakage.
• (2) Prevent forced installation. Instead of hammering in, use a special tool to press the sealing ring into the seat hole, and then use a simple cylinder to protect the lip through the spline. Before installation, apply some lubricating oil on the lip to facilitate installation and prevent burns during initial operation. Pay attention to cleaning.
• (3) To prevent overdue use. The service life of the rubber seal of dynamic seal is generally 3000 ~ 5000h, and the new seal ring should be replaced in time.
• (4) Replace the sealing ring with the same size. In strict accordance with the requirements of the manual, select the same size of the seal ring, otherwise it can not guarantee the compactness and other requirements.
• (5) Avoid using old seals. When using a new sealing ring, it is also necessary to carefully check its surface quality to ensure that there are no defects such as small holes, protrusions, cracks and grooves, and that it has enough elasticity before using.
• (6) During installation, all parts of the open hydraulic system should be cleaned strictly first. It is better to use special tools to prevent fingers from being scratched by sharp metal edges.
• (7) When replacing the sealing ring, the groove of the sealing ring should be strictly checked, the dirt should be removed, and the groove bottom should be polished.
• (8) In order to prevent oil leakage caused by damage, it is necessary to operate according to the regulations. Meanwhile, it is not allowed to overload for a long time or put the machine in a relatively bad environment.

Precautions for sealing ring

• 1. Clean the installation position;
• 2. Remove the burr in the process of seal installation;
• 3. Apply lubricant on the seal;
• 4. Protect the sealing surface from damage;
• 5. Check and confirm that the size of the seal is correct;
• 6. For the seals that need to be deformed, use the corresponding tools to install them.

Application scope of sealing ring

Hardware and plastics, water supply and drainage, HVAC, fire protection, pharmaceutical, shipping and other piping systems, automobiles, locomotives, various machinery, household appliances, electronics, toys, sports equipment, pneumatic components and sanitary ware.

Failure mode of sealing ring

The material of sealing ring can withstand high or low temperature, chemical corrosion, vibration, wear and movement. The elastomer can be selected according to the situation.
The sealing ring material can withstand the temperature as low as – 200 ℃ or as high as 250 + C. In the low-end market, almost all engineering materials become rigid and cannot be sealed; In the high-end market, the material usually burns or decomposes. Chemical erosion of degradable materials leads to brittle cracking or expansion. For example, NBR seals can crack when exposed to gases with very low ozone concentrations unless protected. By contacting the rubber with a low viscous fluid swelling results in an increase in size and also a decrease in tensile strength. Other faults can be caused by using the ring in a specific groove with the wrong size, which may cause the rubber to squeeze.
Elastomers are sensitive to ionizing radiation. In typical applications, the seal ring is well protected from less penetrating radiation such as ultraviolet and soft X-rays, but more penetrating radiation such as neutrons can cause rapid deterioration. In such an environment, the use of soft metal seals.

Source: China Gaskets Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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