permanent deformation

Since the O-ring material is a synthetic rubber is a viscoelastic material, so the amount of the initial setting compression and rebound clogging after prolonged use, it will gradually be lost permanently deformed and eventually leak. Disappearance of permanent deformation and elastic O-ring sealing performance lost the main reason, the following is the main reason causing permanent deformation.
1) compression ratio and the amount of stretch between the permanent deformation
O-ring used for making various formulations of rubber in a compressed state, the compression stress relaxation phenomenon is backing bearings at this time, the growth of the compressive stress decreases with time. Use of the longer, the greater the compression ratio and the amount of stretch, the stress relaxation caused by the rubber decrease the greater the stress, lack of flexibility so that the O-ring, loss of sealing capacity. Therefore, the allowable conditions of use, to lower the compression ratio is desirable. Increase the cross sectional dimensions of the O-ring is to reduce the compression ratio the easiest method, but this will bring an increase in structure size.
Should be noted that, in calculating the compression ratio it is often overlooked when the O-ring in the assembly caused by stretching a cross-sectional height is reduced. O-ring cross-sectional area change is inversely proportional to the change of its circumference. Meanwhile, the role of the tension, O-ring cross-sectional shape will change, on the performance of its height reduced. In addition, under the action of surface tension, O-ring outer surface becomes more flat, ie, section height slightly reduced. This is also the O-ring compression stress relaxation of a performance.
O-ring section deformation degree, also depends on the O-ring material hardness. The same amount of the stretching, the hardness of the O-ring, the cross-sectional height greater decreased, from this point of view, should be selected according to the conditions of use as a low hardness material. The liquid under pressure and the tension of the rubber material of the O-ring will gradually plastically deformed, the cross-sectional height is reduced accordingly, resulting in the final loss of sealing capability.