O-ring is a kind of sealing product with simple appearance and structure, various specifications and huge demand. The sealing quality and life of O-ring depends on the dimensional accuracy and rubber. Generally, the rubber is required to have certain mechanical strength, tear resistance, good heat resistance, oil resistance, chemical resistance and small compression permanent deformation under the conditions of use, which are its main indicators. According to the use requirements, there are generally requirements for heat resistance and oil resistance, and the rubber used is mostly nitrile rubber. For oil-resistant sealing products requiring higher temperatures (such as 150~C-190℃), acrylic rubber can be used. Fluorine rubber is used for oil-resistant rubber products requiring higher temperatures, and silicone rubber is used for heat resistance. When the working pressure is high, the way to increase the hardness of the O-ring rubber is to increase the filling amount of carbon black, but if the filling amount is too high, mixing is difficult, and the basic physical properties of the vulcanized rubber are damaged, and the rubber is also prone to scorching. When using the same type of rubber, such as nitrile rubber, in order to improve heat resistance and oil resistance and reduce compression set, a peroxide (such as DCP) vulcanization system or an effective sulfur vulcanization system (low sulfur and high promoter) can be used. These two vulcanization systems can generate more carbon-carbon cross-linked structures and single sulfur cross-linked structures, effectively improving the heat resistance and oil resistance of the vulcanized rubber and reducing compression set.
In the filling and reinforcement system of the heat-resistant and oil-resistant rubber formula of the O-ring, thermal cracking carbon black, spray carbon black or semi-reinforced carbon black with low activity are mostly used. These carbon blacks are characterized by coarse particles, good elasticity of the rubber, low heat generation, low compression set, and can be filled in large quantities to reduce the cost of the rubber. If the O-ring is used under dynamic sealing conditions, it is necessary to increase the tear resistance, and some high-activity high-wear-resistant carbon black can be used in combination. Fluororubber rubber is a self-reinforcing rubber. If activated carbon black is added, the mechanical properties of the rubber will be reduced. Therefore, a small amount of thermal cracking carbon black or spray carbon black with low activity and coarse particles is generally filled.