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3 key reasons for the permanent deformation of the O-ring seal

by:ORK      2022-11-20
Because the styrene-butadiene rubber raw material used for the O-ring is a viscoelastic raw material, the clamping amount and resilience set in the early stage will block the working ability after long-term application, which will cause permanent deformation and gradually lose, and finally cause leakage. Permanent deformation and elastic regression are the key reasons for the loss of sealing properties of O ring manufactures. Zhongshan Mingchun Silicone Factory has been engaged in the production, manufacture, development and design of O-ring seals for more than 10 years. Now I will share with you the key reasons for the permanent deformation of O-ring seals. There are the following three levels: 1. Temperature hazards o Permanent deformation of the seal ring Application temperature is another key factor that endangers the permanent deformation of the o-ring seal. High temperatures can accelerate the embrittlement of elastomeric materials. The higher the operating temperature, the greater the shrinking permanent deformation of the O-ring. When the permanent deformation exceeds 40%, the O-ring will lose its sealing ability and leak. The original in-situ stress value generated in the elastomer material of the o-ring due to shrinkage deformation will gradually decrease or even subside with the relaxation process of the o-ring and the effect of temperature reduction. For O-rings operating at subzero temperatures, the original shrinkage will be reduced or completely subsided due to the substantial reduction in temperature. Under the condition of -50~-60°C, the temperature-resistant elastomer material will completely lack the original in-situ stress; even if the temperature-resistant elastomer material, the original in-situ stress at this time is not easy to exceed the original in-situ stress at 20°C. 25%. This is due to the original shrinkage of the O-ring due to the expansion coefficient. Therefore, when choosing the original shrinkage, it is important to ensure that there is still sufficient sealing capacity after the ground stress is reduced due to the entire relaxation process and the temperature reduction. In general, Mingchun silicone manufacturers feel that: in the design concept, we should ensure that the O-ring has a suitable operating temperature as much as possible, or use high- and ultra-low temperature resistant O-ring materials to increase the service life. 2. The compression ratio and the amount of tension are harmful to permanent deformation. Various secret recipes of vulcanized rubber seals commonly used in making O-ring seals will cause reduced stress relaxation in the case of shrinkage. At this time, the shrinkage of the ground stress will increase with time increase and decrease. The longer the application time, the greater the compression ratio and the greater the amount of tension, the greater the reduction of the ground stress caused by the stress relaxation of the vulcanized rubber, so that the o-ring has insufficient ductility and loses its sealing ability. Therefore, it is available to find ways to reduce the compression ratio under the allowable application criteria. Increasing the cross-sectional size of the o-ring is an effective way to reduce the compression rate, but this will result in an increase in the construction size. It should be noted that when dividing by the compression ratio, the reduction in the cross-sectional aspect ratio caused by the tension of the O-ring in the assembly line is ignored. The change in the total cross-sectional area of ​​the O-ring is inversely proportional to the change in diameter between the two. At the same time, because of the effect of tensile force, the cross-sectional shape of the O-ring seal will also change greatly, which is mainly manifested in the reduction of its aspect ratio. In addition, under the effect of interfacial tension, the outer layer of the O-ring is becoming more and more flat, that is, the cross-sectional aspect ratio is slightly reduced. This is the main manifestation of O-ring reduction stress relaxation. The level of cross-sectional deformation of the o-ring seal also depends on the strength of the material of the o-ring seal. Under the condition of the same amount of tension, the high-strength O-ring seal also reduces the cross-sectional aspect ratio more. From this point of view, the low-strength material should be used as much as possible according to the application standard. Under the effect of liquid working pressure and supporting force, the o-ring of elastomer material will also slowly deform plastically, and its cross-sectional aspect ratio will be relatively reduced, and eventually lose its sealing ability. 3. The working pressure of the material at work causes the permanent deformation of the O-ring seal The working pressure of the material at work is the key factor that causes the permanent deformation of the O-ring seal. The pressure of contemporary hydraulic machinery is increasing day by day. The long-term high pressure effect will cause permanent deformation of the O-ring. Therefore, a moderate pressure test elastomer material should be used according to the pressure in the design concept. The higher the pressure, the higher the strength and high pressure resistance properties of commonly used raw materials should be. In order to improve the impact resistance of the o-ring material and improve the ductility of the raw material (especially to improve the ductility of the raw material at ultra-low temperature and reduce the permanent deformation of the raw material, it is usually necessary to improve the secret recipe of the raw material and add flame retardants. However, , O ring manufactures with flame retardants, infiltrating substances in the work for a long time, the flame retardants will be slowly digested and absorbed by the substances in work, causing the volume of the O-rings to shrink, and even causing the O-rings Causes negative shrinkage (that is, there is a gap between the o-ring and the surface of the hydraulic seal). Therefore, when divided by the shrinkage of the o-ring and the development of the stamping die,This amount of shrinkage should be taken into account. The suppressed O-ring should be soaked in the working substance for 5~10 days and nights to maintain the necessary specifications. The shrinking permanent deformation rate of the O-ring material is temperature dependent. When the deformation rate is 40% or more, leakage will occur, so the temperature resistance boundaries of several types of plastic pellets are: nitrile rubber 70 °C, EPDM rubber 100 °C, fluorine rubber seals 140 °C. Therefore, all countries in the world have made requirements for the permanent deformation of the O-ring. The specification change of the O-ring of Chinese standard elastomer material at different temperatures is shown in the table.
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