O-rings are among the most widely used and versatile sealing elements in mechanical engineering. Thanks to their simple design, reliability and the availability of a wide range of materials, they are suitable for both static and dynamic applications across various industrial sectors.
A correctly selected O-ring provides long-term reliable sealing performance and prevents leakage of liquids or gases, even under demanding operating conditions. The selection of the appropriate design depends mainly on the operating medium, temperature, pressure, installation conditions and required service life.
Main advantages of O-rings
- simple and proven design,
- minimal space requirements,
- bi-directional sealing capability,
- quick and easy installation,
- wide range of applications for static and dynamic sealing,
- availability of numerous materials suitable for different operating conditions.
O-ring surface treatments
To improve the performance and service life of O-rings, various surface treatments can be applied. These treatments reduce friction, facilitate installation and enhance sealing performance under specific operating conditions.
Dimensions
The O-ring’s size is defined by the d1 inside diameter and by the ring’s d2 thickness.
O- ring’s ø d1 x d2
When determining the size of O-rings cross-section, it is advisable to choose the largest cross-section that is structurally possible for the given case.
The installation space dimensions must meet the following conditions:
- Permissible elongation of the d1 inside diameter is 6 % (exceptionally 8 %) and its permissible depression is 3 % (exceptionally 4 %);
- Upon packing of fixed parts, the d2 diameter must be reduced at least by 10 %, for packing axially moving parts at least by 6 %. Maximum permissible compression is 25 %.
Radial installation (static and dynamic)
On sealing by inside diameter it is recommended to select such O-ring size so as the difference of the d1 inside diameter and of the d4 tight diameter be as low as possible. On sealing by outside diameter it is suitable to select such O-ring size so as the d1 inside diameter be equal to or smaller than the d3 groove diameter.
Axial installation (static)
In the case of the O-ring’s installation, considered should be first of all the direction of the pressure incidence. On application with inside pressure it is suitable that the O-ring’s dimensions be by 1 to 2 % higher than the d5 groove diameter. For packing of inside pressure the O-ring is designed by 1 to 3 % smaller than the inside diameter of the d6 groove.
Specification of materials
| Material | Temperature range | Usage | Hardness |
|---|---|---|---|
| NBR Acrylnitrile-Butadiene-Rubber | – 30 °C + 110 °C | standart material for hydraulic and pneumatic compression fluid on mineral-oil base animal and vegetable oils heavily inflame fluids, aliphatic hydrocarbons (propane,butane,gas) silicon oils water up to +80°C, air, bio-oils, from synthetic ester and vegetable oils | 60 – 90 |
| EPDM Ethylene-Propylene-Dien-Rubber | – 60 °C + 150 °C | hot water, vapour, brake fluid, washing means alcohols, ketones, KFZ-cold water heavily inflame fluids on the phosphorus-acid base organic and anorganic acids and bases | 70 |
| Silicone | – 70 °C + 230 ° | hot air, oxygen, ozone, UV-rays aliphatic engine and transmission oils, animal and vegetable oils brake fluids | 70 |
| FPM Fluorine-Rubber | – 20 °C + 260 °C | mineral oils aliphatic, aromatic and chlorine hydrocarbons gas, super-gas, diesel-propellants heavily inflame fluids on phosphate-ester base, silicon oils acids, lyes | 80 |
| AU Polyurethane | – 25 °C + 80 °C | mineral hydraulic oils mineral engine and transmission oils gas, diesel aliphatic hydrocarbons and air | 90 |
| FFKM Perfluoroelastomer | – 15 °C + 300 °C | aggressive media, strong acids and bases, organic solvents, hydrocarbons, oils, fuels, hot water and steam | 60 – 90 |
FFKM O-rings – modern solutions for the most demanding operations
FFKM is a perfluoroelastomer that, thanks to its significantly higher fluorine content than classic FPM, achieves excellent chemical and temperature resistance.
The introduction of FFKM O-rings marked a generational advancement in sealing technology, providing solutions for applications where conventional elastomers could not perform. FFKM O-rings withstand extremely aggressive chemical environments and continuous high temperatures ranging from 270 °C to 330 °C.
Thanks to these properties, FFKM O-rings are used in the most demanding industries, including chemical processing, semiconductor manufacturing, pharmaceuticals, energy, petrochemicals, food processing, and aerospace. Their long service life reduces maintenance frequency and replacement intervals, lowering operational costs.
These O-rings are ideal whenever reliable sealing is required for aggressive media, steam, hydrocarbons, or a wide temperature range.
O-ring hardness
It is determined in particular in accordance with the height of operation pressure and dimension of packed groove.
For high pressure and big seam harder materials are selected so as to prevent it from being impressed into the seam.
Classification of O-rings in accordance with their application
Static sealing
Static sealing is of such a kind where mutually packed parts do not move.
- sealing under screw-head
- for pipe joints
- sealing of lids
Dynamic sealing
In the case of a moving sealing, mutually packed parts move axially, helically, oscillate, or rotate.
- hydraulic and pneumatic devices requiring small installation space
- for low strokes and relatively small diameters
Freudenberg Catalogue EN – Standard Types
For more information about the availability of your desired O-ring size and material, please do not hesitate to contact us.