Type O sealing ring design, improper use will accelerate the damage to the O type sealing ring, loss of sealing performance. The experiment shows that the design of each part of the sealing device is reasonable, the pressure is increased, and the failure of the O type sealing ring can not be caused. Under high pressure and high temperature working conditions, the main reason is the failure of O type sealing ring gap and permanent deformation of O type O type sealing ring seal is squeezed into the sealing gap caused by the bite of a O type sealing ring distortion phenomenon in motion.
1, O type sealing ring material of the permanent deformation
As the synthetic rubber material O type sealing ring is viscoelastic material, so the initial set pressing amount and rebound blocking ability after a long time working, will produce permanent deformation and gradually lost, eventually leak. The disappearance of permanent deformation and elastic force is the main reason for the loss of the sealing performance of the O type sealing ring. The following is the main reason for the permanent deformation of the O - shaped sealing ring.
1) of various kinds of permanent deformation and tensile compression ratio relationship between quantity and type O sealing ring material produced by O type rubber sealing ring, will produce compression stress relaxation phenomenon in a compressed state at this time, the compressive stress decreases with the increase of time. The longer the use of time, compression ratio and the larger the amount of tension, the stress relaxation of the rubber stress caused by the larger, so that the O type of sealing ring flexible enough to lose the sealing ability. Therefore, it is desirable to try to reduce the compression ratio under the conditions that are allowed. Increasing the section size of the O seal is the easiest way to reduce the compression rate, but this can lead to an increase in the size of the structure.
It should be noted that when the compression rate is calculated, the O type seal ring is often neglected in the assembly of the cross section height caused by the tension. The change of section area of O type sealing ring is inversely proportional to the change of its perimeter. At the same time, due to the role of tension, the section shape of the O seal ring will also change, it is shown that the height of the shape of the sealing ring is reduced. In addition, under the action of surface tension, the outer surface of the O type sealing ring becomes more flat, that is, the section height is slightly reduced. This is also a kind of O type sealing ring compression stress relaxation.
Type O sealing ring section of the degree of deformation, but also depends on the hardness of the O type sealing ring material. In the same amount of tension, the hardness of large O type sealing ring, the section height also decreases more, from this point of view, should be in accordance with the use of the conditions of low hardness material. Under the action of the liquid pressure and the tension, the O type sealing ring of the rubber material also will gradually occur plastic deformation, the section height of the O sealing ring will be correspondingly reduced, resulting in the final loss of sealing ability.
2) the relationship between temperature and the relaxation process of O type sealing ring
The use of temperature is another important factor that affects the permanent deformation of the O type seal ring. High temperature will accelerate the aging of rubber materials. The higher the working temperature, the greater the compression of the O seal ring. When the permanent deformation is greater than 40%, the O type sealing ring has lost the sealing ability and leakage. The initial stress value formed in the rubber material of the O type sealing ring due to the compression deformation is gradually reduced with the effect of the relaxation process and the temperature drop of the O type sealing ring. Temperature in the work of the sub zero O type of sealing ring, O type sealing ring initial compression may be due to a sharp reduction in the temperature and reduce or completely disappear. In the case of -50 ~ -60, the rubber material with low temperature resistance will completely lose the initial stress, and the initial stress at this time will not be more than 25% when the temperature is low. This is because the initial compression of the O type sealing ring depends on the linear expansion coefficient. Therefore, when selecting the initial compression, it is necessary to ensure that the relaxation process and the temperature drop caused by the stress drop is still sufficient sealing ability.