The Formation Of Rubber O-rings Aging Of Several Things

- Sep 25, 2017-

The formation of rubber O-rings aging of several things
(A) oxygen: oxygen in the rubber O-rings with the rubber molecules free radical chain reaction, molecular chain cracking or excessive cross-linking, resulting in rubber O-rings function changes. Oxidation is one of the important reasons for the aging of rubber O-ringss.
(B) Ozone: Ozone chemical activity is much higher than oxygen, more damaging, it is also the molecular chain cracking, but the role of ozone on the rubber deformation with the rubber or not the same. When used as a deformed rubber (mainly unsaturated rubber), there is a crack in the direction of the stress acting, that is, the so-called "ozone cracking"; when the rubber is deformed, only the oxide film is formed on the surface without cracking.
(C) Heat: The advancing temperature can cause thermal cracking or thermal crosslinking of the rubber O-rings. But the role of heat is still the role of activation. The forward oxygen lax velocity and the activation of the oxidation reaction are then accelerated by the rate of oxidation of the rubber, which is ubiquitous as an aging representation - thermal oxygen aging.
(D) light: the shorter the light, the greater the energy. On the rubber O-rings damage is the role of high energy UV. In addition to UV can directly lead to the rubber molecular chain cracking and cross-linking, the rubber due to the absorption of light and free radicals, trigger and accelerate the oxidation chain reaction process. By the outside light plays the role of heating. Another feature of the role of light (not the same as thermal effects) is that it is mainly in the rubber surface and health. High rate of plastic samples, both sides will appear reticular cracks, the so-called "light outer crack."
O-ringss are suitable for use in a variety of mechanical equipment, in the specified temperature, pressure, and different liquid and gas medium, in the static or moving state from the sealing effect. In the machine tools, ships, automobiles, aerospace equipment, metallurgical machinery, chemical machinery, construction machinery, construction machinery, mining machinery, petroleum machinery, plastic machinery, agricultural machinery, and various instruments, a large number of applications of various types of seals element. Silicone O-rings Silicone O-rings has excellent heat resistance, low temperature elasticity and particularly excellent resistance to oxidation and ozone, with high air permeability and selectivity to gas permeation. Good electrical insulation (volume resistance greater than 1016 ohms, cm, breakdown voltage above 30kv / mm), resistance to corona and arc resistance. But the addition of conductive carbon black, nickel powder, aluminum powder, silver O-rings is mainly used for static sealing and reciprocating motion seal. For rotary motion seals, only for low speed rotary seals. O-rings is generally installed in the outer or inner circle on the rectangular cross-section of the seal from the role.
As the O-rings 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, the final leakage. Permanent deformation and elasticity of the O-rings is the main reason for the loss of sealing performance, the following is the main cause of permanent deformation of O-rings material.
1) the relationship between the compression rate and the amount of elongation and O-rings material permanent deformation of the O-rings used in the preparation of various formulations of the rubber, in the compressed state will have a compressive stress relaxation phenomenon, at this time, the compressive stress increases with time And reduced. The longer the use time, the greater the compression ratio and the amount of elongation, the greater the stress drop due to the stress relaxation of the rubber, resulting in insufficient elasticity of the O-rings and loss of sealing capacity. Therefore, it is advisable to try to reduce the compression rate under permissible use conditions. Increasing the cross-sectional size of the O-rings 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-rings in the assembly by the tensile caused by the reduction of the cross-section height. The change in the cross-sectional area of the O-rings is inversely proportional to its variation. At the same time, due to the role of tension, O-rings cross-sectional shape will change, it shows the height of the reduction. In addition, under the surface tension, the outer surface of the O-rings becomes more flat, that is, the cross-sectional height is slightly reduced. This is also a performance of O-rings compression stress relaxation.
The degree of deformation of the O-rings section also depends on the hardness of the O-rings material. In the case of the same amount of elongation, the hardness of the O-rings, the cross-section height is also reduced more, from this point of view, should be used in accordance with the conditions of use of low hardness of the material. In the role of liquid pressure and tension, the rubber material O-rings will gradually plastic deformation, O-rings cross-section height will be reduced accordingly, so that the final loss of sealing capacity.

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