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The use of each O-ring is different. When selecting an O-ring, we must consider its working environment and conditions, sealing requirements, physical properties, etc. For example, we have to choose clothes that are suitable for ourselves. Which O-rings are suitable for machinery, which are suitable for the automotive industry, which are suitable for electronic products, we must consider the various physical properties of O-rings In order to achieve the real needs of customers. So, when we choose O-rings, what specific factors should we consider:
1) Working medium and working conditions
When selecting the O-ring material, the compatibility with the working medium must be considered first. Secondly, comprehensive consideration should be given to the working conditions such as pressure, temperature, continuous working time, and operating cycle of the seal. If used in rotating applications, the temperature rise due to frictional heat must be considered. Different seal materials have different physical and chemical properties.
2) Sealed form
According to the type of load, it can be divided into static seal and dynamic seal. According to the purpose of sealing, 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. For radial installation, the deviation between the inner diameter of the O-ring and the diameter of the seal should be as small as possible for the shaft seal; for the seal for the hole, the inner diameter should be equal to or slightly smaller than the diameter of the groove. When installing axially, consider the direction of pressure. Under internal pressure, the outer diameter of the O-ring should be approximately 1% ~ 2% larger than the outer diameter of the groove; when under external pressure, the inner diameter of the O-ring should be approximately 1% ~ 3% smaller than the inner diameter of the groove.
3) Other factors affecting sealing performance
①0-ring hardness The hardness of the O-ring material is the most important index 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.
② Extrusion gap The maximum allowable extrusion gap is related to the system pressure, the diameter of the O-ring section and the hardness of the material. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap value. If the clearance exceeds the allowable range, the 0-ring will be extruded or even damaged.
③ Compression permanent deformation Another index for evaluating the sealing performance of O-rings is compression permanent cross-section of the selected material. Under pressure, the O-ring, which is an elastic element, undergoes elastic deformation, and permanent plastic deformation also occurs with increasing pressure. Generally, in order to prevent permanent plastic deformation, the maximum compression amount allowed for a 0-ring is about 30% in a static seal and about 20% in a dynamic seal.
④ Pre-compression amount The O-ring is installed in the groove. To ensure its sealing performance, an initial compression amount should be reserved. For different applications, the amount of pre-compression relative to the cross-sectional diameter W is also different. Generally, it is about 15% ~ 30% in static seal, and about 9% ~ 25% in dynamic seal.
⑤Stretching and compression When installing the O-ring in the groove, it must be stretched or compressed. If the values of tension and compression are too large, the cross section of the O-ring will be excessively increased or decreased, because 1% stretching will reduce the diameter of the section by about 0.5%. For hole seals, the 0-ring is best in a stretched state with a maximum allowable stretch of 6%; for shaft seals, the O-ring is best compressed along its perimeter, with a maximum allowable compression of 3 %.
We don't know how to choose the right O-ring, we can consider these factors such as working medium, working conditions, seal form, etc., so that we can avoid taking many detours. We Haisheng Rubber will customize O-rings according to the specific requirements of customers. We have professional engineers at Haisheng Rubber to provide professional answers to customers.
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