Factors that should be considered in the selection of O-rings

1. Working medium and working conditions When selecting the material of the O-ring, the compatibility with the working medium must be considered first. 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 occasions, the temperature rise due to frictional heat must be considered. Different seal materials have different physical and chemical properties, see ' Seal Material Characteristics Table'. 2. Sealing form According to the load type, it can be divided into static seal and dynamic seal; according to the sealing purpose, it can be divided into hole seal, shaft seal and rotary shaft seal; according to its installation form, it can be divided into radial installation and axial installation. During radial installation, for shaft seals, the deviation between the inner diameter of the O-ring seal and the diameter d2 to be sealed should be as small as possible; for hole seals, the inner diameter should be equal to or slightly smaller than the diameter d1 of the groove. When installing axially, the pressure direction should be considered. Under internal pressure, the outer diameter of the O-ring should be about 1-2% larger than the outer diameter d3 of the groove; under external pressure, the inner diameter of the O-ring should be about 1-3% smaller than the inner diameter d4 of the groove. Other factors that affect the sealing performance 1. The hardness of the O-ring seal The hardness of the O-ring material is the most important indicator for evaluating the sealing performance. The hardness of the O-ring determines the compression amount of the O-ring and the maximum allowable extrusion gap of the groove. Since the nitrile seal of Shore A70 can meet most of the conditions of use, if there is no special description for the sealing material, the nitrile rubber seals of Shore A70 is generally provided. 2. Extrusion gap The maximum allowable extrusion gap gmax is related to system pressure, O-ring section diameter and material hardness. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap gmax. If the gap g exceeds the allowable range, the O-ring will be squeezed out or even damaged. 3. The O-ring is used as a rotary shaft seal. The O-ring can also be used as a rotary shaft seal for low-speed rotary motion 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 standards; when the peripheral speed is greater than 0.5m/s, the phenomenon that the elongated rubber seals ring will shrink after being heated must be considered, so the seal is selected. The above phenomenon can be avoided by making the inner diameter of the ring about 2% larger than the diameter of the shaft sealed by it. After the sealing ring is installed in the groove, the sealing ring is compressed radially, and the O-ring sealing ring forms a small amount of corrugation in the groove, thereby improving the lubrication conditions. Company website: https://www.orksealing.com/
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