High performance fluororubber O-ring

As a kind of synthetic polymer elastomer containing fluorine atoms on the main chain or side chain carbon atoms, fluororubber has incomparable high temperature resistance, chemical medium resistance and aging resistance properties, and has become an indispensable and irreplaceable basic material in modern industry, especially in the high-tech field.

Beijing Institute of Aeronautical Materials has been conducting research on the compounding technology of fluoroelastomer since the 1970s, and has successively developed a series of fluororubber compounds with different properties and functions, which have been successfully used in aviation, aerospace, shipping, petroleum, automotive industries and other fields. In this paper, according to the performance characteristics of this series of fluororubber, it is classified and introduced.

1. It is well known that the low compression permanent set fluororubber series, as a rubber seal, is one of the main properties to ensure its sealing capacity. As an elastomer with excellent heat resistance and medium resistance, fluororubber is mainly used as movable and fixed seals, which requires it to have a low compression permanent deformation value. Since the advent of fluororubber raw rubber in the 1950s, the research on its compounding technology has focused on reducing the compression set performance of rubber compound for a long time, including the improvement of raw rubber synthesis process and the addition of different curing systems. Through in-depth study on filler system, low compression set fluororubber with different hardness grades has been successfully developed in China.

The low compression permanent set fluororubber can be used to manufacture movable or fixed seals working in air, petroleum base lubricating oil, fuel oil, hydraulic oil and diester synthetic lubricating oil. The long-term working temperature is – 20 ℃~250 ℃, which can be lower than – 20 ℃ or higher than 250 ℃ for some parts, and 300 ℃ in the short term. Due to different hardness grades, their application ranges are also different. FX-4 compound has low hardness and high elongation, and is suitable for making high-temperature conductor sleeve sealing gasket and O-ring contacting with oil; FX-5 rubber is mainly used to manufacture rubber seals for aeroengines; FX-6 rubber material has high hardness and good extrusion resistance, and can be used for rubber seals with high temperature and pressure, such as ultra deep well oil exploration.

2. The existence of fluorine atoms on the main bond or side chain of fluororubber macromolecule to improve the low humidity performance has a strong shielding effect on the carbon carbon main bond of polymer due to its extremely high electronegativity, which makes it have excellent high temperature resistance and medium resistance stability. However, the existence of fluorine atoms also reduces the flexibility and increases the rigidity of the entire macromolecule chain, resulting in poor low-temperature performance. In order to improve the low temperature performance of fluororubber, fluoroether rubber has been developed abroad in the early 1970s. Ether bond containing monomers (perfluoroalkyl vinyl ethers) are introduced into the macromolecular structure, which improves the flexibility of polymer macromolecular chains. The low temperature performance is significantly improved. For example, the glass transition temperature of VitonGLT fluoroether raw rubber is about 14 ℃ lower than that of fluororubber F246. The only disadvantage is its high price.

The FX-13 developed by Beijing Institute of Aeronautical Materials through rubber blending technology and a small amount of fluoroether rubber has improved the low-temperature performance of fluororubber, and its brittleness temperature can reach – 45 ℃. It has been successfully used to manufacture the servo mechanism seals of Long March series launch vehicles, ensuring the success of many commercial launches of Long March series rockets. The use of blending technology not only effectively improves the low-temperature performance of fluororubber, but also greatly reduces its price compared with fluoroether rubber.

3. When fluororubber products with low friction coefficient are used as movable seals, such as lip seals, due to the high rotating speed of the rotating shaft, when the lubrication state is poor, the heat generated in the sealing area is large, resulting in adhesive cracks of the rubber, increased adhesion, and serious wear of the rotating shaft. The FX-10 fluororubber was developed by adding antifriction filler to the raw rubber, which effectively reduced the friction coefficient of the rubber compound and improved the thermal conductivity of the rubber compound. The compound has been successfully used in aeroengine rubber cups.

4. The fluororubber fluororubber with improved process performance has excellent high temperature resistance and medium resistance, but there are problems such as poor die adhesion, hot tearing and mold filling fluidity in the processing process. Through the research on the matching system, the developed FX-70H brown fluororubber has improved the vulcanization process of fluororubber. The vulcanization time is short, the temperature is low, and the rubber can be molded and vulcanized in only 8 minutes at 16 ℃, with good molding fluidity, Vulcanized rubber has high elongation at break, excellent hot tearing property and high qualification rate of molded products, which greatly improves labor productivity and reduces production costs.

The successful development of fluororubber with different properties mentioned above has made great contributions to national defense and civil industry, and some of its technologies are in the leading position in China. In addition, in order to solve the bonding problem between fluororubber and metal skeleton, matching room temperature curing and high temperature curing adhesives have been developed in China, and have been widely used.