Release time：2023.01.12
Source: This website
In the petrochemical industry, sealing is very important. Many leakage accidents are caused by the failure of seals, and seal failure is closely related to the aging of rubber seals. Here is a look at the reasons for the aging of seals with Xiaobian.
First of all, look at the performance of the aging seals.
① The seals become soft and sticky: the hot oxygenation of natural rubber and the aging of chlorol rubber.
② Seals become hard and brittle: thermal oxygen aging of butadiene rubber, nitrile rubber, styrene butadiene rubber aging.
③ Cracks in seals: ozone aging of unsaturated rubber, photooxygen aging of most rubber, but the shape of the crack is not the same.
(4) Moldy seals: aging of rubber organisms and microorganisms.
Due to the above reasons, the physical and chemical properties of the seals are changed directly. Changes in physical and chemical properties of seals: specific gravity, thermal conductivity, glass transition temperature, melting point, refraction, solubility, expansion, fluidity, molecular weight, molecular weight distribution, cold resistance, breathable, permeable, transparent and other properties.
Changes in the physical and mechanical properties of seals: tensile strength, elongation, shear strength, fatigue strength, elasticity, wear resistance are reduced.
The change of electrical properties of seals: the change of insulation resistance, dielectric constant, dielectric loss, breakdown voltage and other electrical properties, and the decrease of electrical insulation.
What are the reasons for the aging of seals?
The role of oxygen: oxygen in rubber with rubber molecules free base chain reaction, molecular chain fracture or excessive crosslinking, resulting in the change of silicone rubber products performance. Oxidation is one of the important causes of rubber aging.
Thermal action: Increasing the temperature can cause thermal cracking or thermal crosslinking of silicone rubber products. But the basic function of heat is activation. Increasing the oxygen diffusion rate and activating oxidation reaction, so as to accelerate the rubber oxidation reaction speed, which is a universal aging phenomenon - hot oxygen aging.
The role of water: the role of water has two aspects: silicone rubber products in wet air rain or soak in water, easy to destroy, this is because the water-soluble substances in rubber and water tsuen and other components are dissolved by water extraction. Especially under the alternating action of water immersion and atmospheric exposure, the destruction of rubber seals will be accelerated. But there are also some cases in which water does not destroy rubber, or even delay aging.
The role of ozone: ozone chemical reactive oxygen is much higher, more destructive, it is also the molecular chain fracture, but the role of ozone on rubber with rubber deformation or not and different. When used for deformation of rubber (unsaturated rubber), there will be cracks in the direction of stress, that is, the so-called "stress cracking", as used for non-deformation of rubber, only the surface of the oxide film without cracking.
Cause of light: The shorter the wave, the more energy it has. It is the high energy ultraviolet rays that damage the rubber. Uv can not only directly cause the break and crosslinking of rubber molecular chains, but also generate free groups due to the absorption of light energy, which can trigger and accelerate the oxidation chain reaction process. The light also plays a heating role on the seal, but with (the heat effect is different), the light will make the rubber seals with high rubber rubber rate appear mesh cracks, that is, the so-called "light external cracks".
Mechanical stress: due to the viscosity of polymer, the sealing ring in the deformation cycle, the relaxation process is too late to complete, and then into the next deformation cycle, the rubber sealing ring internal deformation is increasing. When the stress is large, the molecular chain breaks and generates free radicals, leading to the oxidation chain reaction of rubber seal molecules. When the rubber sealing ring is repeatedly deformed, the mechanical stress will weaken the valence force in the molecular chain of the rubber sealing part, so the activation energy of its oxidation reaction is reduced. The oxidative cracking reaction of rubber sealing ring molecules was accelerated. The reduction of oxidation activation energy is the end of the process of transforming mechanical energy into chemical energy in the fatigue process. When the rubber seals are repeatedly deformed, the hysteresis phenomenon occurs, causing internal friction, which makes the rubber material generate heat inside, and accelerates the oxidation chain reaction of the rubber seals.
Other effects: There are other electrochemical corrosion, radiation and biological effects, etc.
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