O-rings are a toroidal gasket; it is an elastomer ring with a circular cross-section designed to fit into a groove and compressible during assembly between two or more parts, creating a seal at the interface.
The O-ring can be used in static or dynamic applications (where there is a relative movement between the parts and the O-ring). An example of dynamic application can be the rotating shafts of the pump and the pistons of a hydraulic cylinder.
O-rings are one of the most common types of seals used in the design of machines because they are inexpensive, easy to manufacture, reliable and have simple installation requirements. They can withstand dozens of megapascals of pressure.
A successful seal design using O-rings requires a rigid mechanical installation, which leads to a predictable deformation of the sealing ring. The rest is reduced to calculating the mechanical stress on the contact surfaces of the sealing ring. As long as the pressure of the liquid does not exceed the contact pressure of the sealing ring, there can be no leakage. The pressure of the contained liquid is transferred through a substantially incompressible O-ring, while the contact tension increases with increasing pressure. For this reason, the O-ring can easily hold high pressure until it is mechanically damaged. The most common o-ring failure is extrusion through mating parts.
O-ring materials can be exposed to high or low temperatures, chemical attack, vibration, abrasion a, d movement. Elastomers are selected in accordance with the field of application.
There are sealing materials that can withstand temperatures as low as -200 ° C or up to 250 ° C. At low temperatures, almost all technical materials become stiff and lose the ability to seal; at high temperatures, the material often burns or decomposes. A chemical attack can destroy the material, lead to the formation of cracks or cause the rubber to swell. For example, NBR seals can crack under ozone exposure even at very low concentrations, unless they are protected. Swelling when in contact with a liquid with a low viscosity causes an increase in size, and also reduces the tensile strength of the rubber. Other irregularities in seal operation may be caused by the wrong ring size for a particular notch, which may cause rubber extrusion.
Elastomers are sensitive to ionizing radiation. In typical applications, O-rings are well protected against weakly penetrating radiation, such as ultraviolet and soft X-rays, but more penetrating radiation, such as neutrons, can cause a rapid deterioration in the properties of the O-ring. In such environments, soft metal seals are used.
There are several common o-ring failures:
- Installation damage
- Spiral defects
- Explosive decompression
O-rings are designed to seal hydraulic, fuel, lubrication and pneumatic devices designed for operation at temperatures from -60 to 200 C, depending on the rubber group and at a pressure of:
- up to 50MPa in fixed joints and up to 32 MPa in mobile connections in mineral oils, liquid fuels, emulsions, lubricants, fresh and sea water;
- up to 40 MPa – in fixed connections and up to 10 MPa – in mobile connections in compressed air.
The sealing rings are made of the following accuracy groups:
1 – for mobile connections (manufactured in agreement with the manufacturer)
2- for mobile and fixed connections
Search for the sealing ring is carried out by its designation.
(010 -…) The first three digits represent the diameter of the surface (stem) on which the ring is put – 10mm.
(…- 014 -…) The second three digits mean the diameter of the surface (cylinder) into which the ring is inserted – 14mm.
(…- 25) The last two digits represent the diameter of the cross-section of the ring-2,5 mm, multiplied by 10.
So the actual size of the O-ring may slightly differ from the designation: the inner in the direction of decrease, the outer, on the contrary, the increase.
Designation: 010-014-25 Size: 9.7×14.7×2.5mm.