O Ring Seals on the deformation of the relevant knowledge, the following King King to give you a brief introduction.
As the O Ring Seals with the synthetic rubber material is a viscoelastic material, so the initial set of the amount of compression and rebound blocking capacity after a long period of use, will produce permanent deformation and gradually lost, and ultimately leakage. Permanent deformation and elasticity of the O Ring Seals is the main reason for loss of sealing performance.
1, the temperature of the O Ring Seals permanent deformation
The use of temperature is another important factor affecting the permanent deformation of the O Ring Seals. High temperature will accelerate the aging of rubber materials. The higher the operating temperature, the greater the compression set of the O Ring Seals. When the permanent deformation of more than 40%, O Ring Seals on the loss of sealing capacity and leakage. The initial stress value formed in the rubber material of the O Ring Seals due to compression deformation will gradually decrease as the relaxation process of the O Ring Seals and the temperature drop. The O Ring Seals, which operates at zero temperature, may initially reduce or completely disappear due to a drastic decrease in temperature. In the case of -50 ~ -60 ° C, the low temperature rubber material will completely lose the initial stress; even low temperature rubber material, the initial stress at this time will not be greater than 20 ℃ when the initial stress of 25%. This is because the initial compression of the O Ring Seals depends on the coefficient of linear expansion. Therefore, when selecting the initial compression amount, it is necessary to ensure that there is sufficient sealing capacity after the stress drop due to the relaxation process and the temperature drop.
The temperature of the work of the O Ring Seals, should pay special attention to the rubber material recovery index and deformation index.
In summary, in the design should try to ensure that the O Ring Seals with a suitable operating temperature, or use high and low temperature O Ring Seals material to extend the service life.
2, the compression rate and the amount of stretch affect the permanent deformation
The compressive stress relaxation phenomenon occurs in the compressed state, and the compressive stress decreases with the increase of the time. The longer the use of time, the greater the compression rate and the amount of elongation, the elastic stress relaxation caused by the greater the stress drop, so that the O Ring Seals elasticity, loss of sealing capacity. Therefore, it is advisable to try to reduce the compression rate under permissible use conditions. Increasing the cross-sectional dimension of the O Ring Seals is the easiest way to reduce the compression rate, but this increases the size of the structure.
It should be noted that people in the calculation of compression rate, often overlooked O Ring Seals in the assembly when the tensile caused by the reduction of the cross-section height. The change in the cross-sectional area of the O Ring Seals is inversely proportional to its perimeter variation. At the same time, due to the role of tension, O Ring Seals cross-sectional shape will change, it shows the height of the reduction. In addition, under the surface tension, the outer surface of the O Ring Seals becomes more flat, that is, the cross-sectional height is slightly reduced. This is also a performance of the O Ring Seals compression stress relaxation.