An O ring is a torus shaped ring with a circular cross-section that is used as a mechanical seal or gasket. It can be made using various materials like elastomers, thermoplastics such as PTFE and metal. The primary function of an O-ring is sealing in static and dynamic applications.
Rubber O rings or Elastomeric O rings are used as an O ring Seal to prevent the loss of fluid or gas. A typical seal assembly consists of a gland that contains and supports the O ring.
Material Selection Criteria for Rubber O-rings
The choice of your base elastomer or material is made based on two primary factors:
- Operating Temperature
During compression, a seal changes from its original state and overtime, with exposure to excessive temperatures, beyond a material’s limit, there will be a loss in the elastic memory of the seal. This will result in leakage and system failure.
2. Media that needs to be sealed
All elastomers undergo physical or chemical changes when they come in contact with aggressive media. The limit of permissible volume change – shrinkage or swelling – that an elastomer can tolerate, will determine the material of choice for an O-ring seal.
What are the materials used in making Rubber O-rings?
In the following points we will go through the various materials or basic elastomers that are used for Rubber O-ring Seals. Depending on requirements of heat resistance, chemical resistance and other physical influences, the base elastomer and the hardness of the finished product (O-ring Seal) are determined.
- Acrylonitrile-Butadiene (NBR)
Nitrile rubber is the general term for acrylonitrile-butadiene copolymer. The physical properties of the copolymer vary greatly based on the content of acrylonitrile in it. NBR is a versatile compound as it has good mechanical properties and high wear resistance. It is resistant to heat up to 100 deg. C. However, it is not recommended for outdoor applications, as it is not resistant to ozone, weather and atmospheric aging.
- Styrene Butadiene Rubber (SBR)
Styrene Butadiene Rubber (SBR) O-rings are used in highly abrasive conditions. SBR is known to have good physical properties such as impact strength, good resilience, tensile strength, and excellent abrasion resistance with favorable ageing characteristics. The weaknesses of SBR are that it requires reinforcement and has sub-par low temperature resistance.
- Ethylene Propylene Diene Monomer (EPDM)
EPDM copolymer is made of Ethylene and Propylene. They are particularly used in outdoor applications and in brake systems that use fluids having glycol base. They have good low temperature resistance and are also resistant to ozone, steam, weather and atmospheric ageing. They are used very often in Automobile Industries. They are not compatible with mineral oil products such as oils, greases and fuels.
- Chloroprene Rubber (CR)
Chloroprene rubber was the first synthetic rubber that was developed commercially. It exhibits good ozone, ageing and chemical resistance. It has good mechanical properties over a wide temperature range from -40 deg C to 121 deg C. It also shows good resistance to high aniline point oils.
- Silicone Rubber
Silicone is a polymer of silicon, carbon, hydrogen and oxygen. It is generally stable and non-reactive, and can maintain its properties across a wide temperature range. This material is used when the retention of the initial shape of the product is required.
- Fluoroelastomer (FKM)
Fluoroelastomers have excellent resistance to mineral oils, greases, certain aliphatic and aromatic hydrocarbons, ozone, weather and aging. They are also resistant to certain solvents, chemicals and high temperatures. Due to their resistance to petroleum based greases and oils, they are widely used in Oil & Gas, Chemical, Automotive and Aerospace applications. FKM Compounds come under the category of High Performance Elastomers.
- Fluorosilicone (FVMQ / FSL)
Fluorosilicone rubber is a type of silicone rubber with the fluorine group attached to the main polymer chain. As a result, FVMQ seals are more stable with resistance to a wide range of oils, acids, fuels and non-polar solvents. FVMQ also has good compression set resistance and maintains excellent tensile strength.
- Hydrogenated Nitrile (HNBR)
This is created by the Hydrogenation of NBR. HNBR has superior mechanical characteristics such as high strength, higher heat resistance and wear behavior in dynamic applications. It also helps to reduce extrusion.
- Perfluoroelastomer (FFKM)
FFKM is a champion polymer in sealing applications. It has the widest operating temperature range than any other compound due to the presence of more fluorine than even FKM elastomers. It is also resistant to a wide variety of chemicals and solvents such as hot amines, sour gases and hydrocarbons.
- Tetrafluoroethylene Propylene (FEPM)
Tetrafluoroethylene Propylene (FEPM) is a high performance elastomer composed of tetrafluoroethylene and propylene. It is compatible with a wide variety of chemicals such as bases, amines, water, engine oils, ozone and alcohols. But it is important to note that it is not compatible with chlorinated and aromatic hydrocarbons and even acetone.
What are the applications or uses of Rubber O-rings?
- Aerospace:
Sealing Systems: Used in aircraft engines, fuel systems, and hydraulic systems to ensure reliable sealing under extreme temperatures and pressures.
- Automotive:
Engine Components: Provide reliable seals in fuel injectors, coolant systems, and turbochargers.
Transmission Systems: Used in automatic and manual transmissions to prevent fluid leaks and ensure smooth operation.
- Oil and Gas:
Used in valves, pumps, and flanges to prevent leaks and maintain system integrity under high temperatures and aggressive chemicals.
- Chemical Processing:
Pumps and Valves: Provide chemical resistance and prevent leaks in pumps and valves handling aggressive chemicals.
- Pharmaceutical and Food Industries:
Sterile Environments: Used in equipment that requires strict hygiene standards, such as mixers, pumps, and filling machines.
- Semiconductor Manufacturing:
Vacuum Systems: Essential for maintaining vacuum integrity in semiconductor manufacturing processes.
Chemical Resistance: Provide reliable sealing in the presence of aggressive chemicals used in semiconductor fabrication.
What are the properties of Rubber O-rings?
Rubber O-rings are versatile sealing components with a range of properties that make them suitable for various applications. Here are some of the key properties of rubber O-rings:
1. Elasticity and Resilience:
- Elasticity: Rubber O-rings can return to their original shape after deformation, allowing them to create an effective seal by filling gaps.
- Resilience: They can withstand repeated cycles of compression and decompression without significant loss of performance.
2. Compression Set Resistance:
Rubber O Rings have a lower compression set enabling good sealing performance. This means that the level of deformation is less under a compressive load.
3. Chemical Resistance:
Different rubber materials offer varying levels of resistance to oils, solvents, chemicals, gases.
- Nitrile (Buna-N): Good resistance to oils, fuels, and other petroleum-based fluids.
- Viton (FKM): Excellent resistance to high temperatures, chemicals, and oils.
- EPDM: Good resistance to water, steam, and weathering, but poor resistance to oils and fuels.
4. Temperature Range:
Rubber O rings can operate in a wide variety of temperatures, depending on the material:
- Silicone O Rings & FVMQ O Rings can operate at temperatures as low as -70° C
- FFKM O Rings can operate at temperatures as high as +315° C
5. Hardness:
Hardness is measured on the Shore-A scale, typically ranging from 35 to 95. The appropriate hardness depends on the application, with softer O-rings providing better sealing on uneven surfaces and harder O-rings offering better resistance to extrusion.
6. Tear and Abrasion Resistance:
Rubber O rings have varying degrees of resistance to tearing and abrasion. Materials like Polyurethane have excellent resistance to abrasion, while others like Silicone are more prone to tearing.
7. Permeability:
Permeability refers to a material’s ability to resist gas or liquid to pass through it. The extent of Permeability of Rubber O rings can vary depending on the type of the elastomeric material.
Fluorocarbon (FKM) offers very good permeability to gases, and is also highly resistant to a wide variety of harsh chemicals. As a result, it’s the ideal choice in Chemical Processing Industries.
8. Electrical Insulation:
Rubber O-rings are generally good electrical insulators, which can be beneficial in certain applications.
9. Ageing and Weather Resistance:
This refers to the ability of O Rings to resist ageing due to exposure to Ozone, UV Light, and environmental conditions:
- EPDM: Excellent resistance to Ozone, UV Light and Weathering.
- Silicone: It also offers excellent resistance to Ozone and Weathering.
10. FDA Compliance:
Special rubber compounds and Some specific elastomeric grades in Silicone, EPDM can be formulated to be compliant with US FDA regulations for use in food, beverage and pharmaceutical applications.
11. Cost Effectiveness:
Elastomeric O-rings are generally cost-effective, offering a high performance-to-cost ratio. They are easy to manufacture and replace, making them a practical choice for many sealing applications.
