When selecting the O-ring material, the first consideration is the compatibility with the working medium. It is also necessary to comprehensively consider the working conditions such as pressure, temperature, continuous working time, and operating cycle at the seal. If used in rotating applications, the temperature rise due to frictional heat must be taken into consideration. Different seal materials have different physical and chemical properties.
2, sealed form
According to the type of load can be divided into the static seal and dynamic seal; according to the sealing application can be divided into hole seal, shaft seal, and rotary shaft seal; according to its installation can be divided into radial installation and axial installation. In the radial installation, for the shaft seal, the deviation between the inner diameter of the O-ring and the diameter d2 to be sealed should be as small as possible. For the hole seal, the inner diameter should be equal to or slightly less than the diameter d1 of the groove.
When installing axially, consider the direction of pressure. When the internal pressure, the O-ring outer diameter should be about 1-2% larger than the outer diameter d3 of the groove; when the external pressure, the inner diameter of the O-ring should be about 1-3% smaller than the inner diameter d4 of the ditch.
Other factors that affect sealing performance
1, O-ring hardness
O-ring seal material hardness is the most important indicator to assess the sealing performance. The hardness of the O-ring seal determines the compression of the O-ring and the maximum allowable extrusion clearance for the groove. Since the Shore A70 nitrile seal can meet most of the conditions of use, if the sealing material is not specifically stated, a nitrile rubber of Shore A70 is generally provided.
2, extrusion gap
The maximum allowable extrusion gap gmax is related to the system pressure, O-ring seal cross-sectional diameter, and material hardness. In general, the higher the working pressure, the smaller the value of the maximum allowable extrusion gap gmax. If the gap g exceeds the allowable range, it will cause the O-ring to squeeze out or even damage.
3, O-ring seal used as a rotating shaft seal
O-rings can also be used as rotary shaft seals with low rotational speeds and short operating cycles. When the peripheral speed is lower than 0.5m/s, the O-ring can be selected according to the normal design standard; when the peripheral speed is greater than 0.5m/s, the elongated rubber ring must be considered to shrink after being heated, so the seal is selected. The circle has an inner diameter approximately 2% greater than the diameter of the shaft it seals. This phenomenon can be avoided. After the sealing ring is installed in the groove, the sealing ring is radially compressed, and the O-shaped sealing ring forms a slight ripple in the groove, thereby improving the lubrication conditions.