In daily work, the use of sealing rubber O-rings is not paid attention to, so that the O-rings lose their sealing performance.
1. Compression ratio and stretching amount. Various formulations of rubber used to make O-rings will produce compressive stress relaxation in the compressed state. At this time, the compressive stress will decrease with the increase of time. The longer the use time, the greater the compression ratio and the greater the amount of stretching, the greater the stress drop caused by the relaxation of the rubber stress, so that the O-ring has insufficient elasticity and loses its sealing ability.
Note: It is advisable to try to reduce the compression ratio under permissible usage conditions. Increasing the cross-sectional size of the O-ring is the easiest way to reduce the compression ratio, but this will increase the size of the structure.
It should be noted that when calculating the compressibility, the reduction in section height caused by the tension of the O-ring during assembly is often ignored. The change in the cross-sectional area of the O-ring is inversely proportional to the change in its circumference. At the same time, due to the action of tension, the cross-sectional shape of the O-ring will also change, which means that its height is reduced. In addition, under the action of surface tension, the outer surface of the O-ring becomes flatter, that is, the cross-sectional height is slightly reduced. This is also a manifestation of O-ring compressive stress relaxation.
The degree of deformation of the O-ring section also depends on the hardness of the material of the O-ring metal seal. In the case of the same amount of stretching, the O-ring with high hardness will also reduce the cross-sectional height. From this point of view, the material with low hardness should be selected as far as possible according to the conditions of use. Under the action of liquid pressure and tension, the O-ring of the rubber material will gradually undergo plastic deformation, and its cross-sectional height will decrease accordingly, so that the sealing ability is finally lost.