Fluororubber is a kind of polymer elastomer with fluorine atoms attached to carbon atoms of main chain or side chain which was developed in 1950s. Fluororubber has excellent heat resistance, weather resistance, ozone resistance, oil resistance and chemical resistance, low gas permeability, and belongs to self extinguishing rubber. The disadvantage of fluororubber is poor elasticity and cold resistance, poor processing property and expensive price. Over 40 years, its performance has been improved continuously, which has been widely used in various sealing parts, rubber tubes, rubber cloth and oil tank which require medium resistance and high temperature resistance, and become irreplaceable special rubber.
Main properties of 1 fluororubber
1.1 mechanical properties of type 26 fluororubber are generally 10-20Mpa after coordination, 150% ~ 300% elongation, and 20-40kn/m tear strength, but its elasticity is poor. The friction coefficient of fluororubber (0.8) is smaller than that of NBR (0.9-1.5).
1.2 at present, the high temperature resistance of fluororubber is excellent. Fluororubber can work for a long time at 200-250 ℃ and short time at 300 ℃, and f246 has better heat resistance than F26. The tensile strength and hardness of fluororubber decreased with the increase of temperature. The tensile strength and hardness change characteristics are that, under 150 ℃, the temperature increases and decreases rapidly; between 150-260 ℃, the decrease trend is slow with the increase of temperature.
The properties of fluororubber at different temperatures are different
Performance 24 ℃ 50 ℃ 204 ℃
Tensile strength, MPA 126.96.36.199
Elongation at break,% 330 12080
Shore a hardness, 756563
1.3 corrosion resistance of fluororubber has * * corrosion resistance. It has excellent stability to organic liquid, different fuel oil and lubricating oil, and has good corrosion resistance to most inorganic acids, hydrocarbons, benzene and toluene, and it is not resistant to low molecular esters, ethers, ketones and some amines.
1.4 the performance of hot water and superheated steam resistance rubber's stability on hot water not only depends on the material of the body, but also on the mixing technology of the rubber. For fluororubber, the vulcanized fluororubber with peroxide is better than that of the rubber with amine and phenol curing system. It should be said that the resistance of fluororubber to hot water and superheated steam is generally, which is not as good as EPDM. After soaking in hot water at 180 ℃ x 24h, the volume change is not more than 10%, and the physical properties have not changed much.
1.5 compression long deformation property fluororubber is used for sealing at high temperature, and compression deformation is the key. Viton type fluororubber has been widely used, which is inseparable from its improvement of compression deformation. DuPont company of the United States has been committed to improving the resistance of fluororubber to compression deformation in 1960s-1970s, and has achieved remarkable results.
1.6 the low temperature resistance of fluororubber is poor, and its elastic limit temperature is -15-20 ℃. With the decrease of temperature, the tensile strength of the product increases, and it appears strong and tough at low temperature. When the standard sample with 2mm thickness is measured, the brittleness temperature is about-30 ℃, when the thickness is 1.87mm, it is -45 ℃; when the thickness is 0.63mm, it is -53 ℃; when the thickness is 0.25mm, it is -69 ℃. The general temperature of fluororubber can be slightly lower than the brittle temperature. As specified in mil-25879d, the temperature of use is -40-205 ℃. The temperature limit of foreign perfluoroethylene rubber in aerospace engine is -35 ℃.
1.7 the performance of vitona after 10 years of natural storage is still satisfactory. In the air with ozone concentration of 0.01%, no obvious cracking occurred after 45 days. Its weather and ozone resistance are also satisfactory.
1.8 electrical properties of fluororubber are not very good, and only suitable for low frequency and low voltage. Temperature has a great influence on its electrical properties, such as when it rises from 24 ℃ to 184 ℃, its insulation resistance decreases by 5 orders of magnitude.
1.9 the gas solubility of the gas permeable fluororubber is relatively large, its diffusion speed is relatively small, and the total gas permeability is very small. In the fluororubber, the filling of the filler fills the gap inside the rubber, which makes the air permeability of the vulcanizate smaller, which is very beneficial for vacuum sealing. If fit fit, fluororubber can solve 10^-7 PA vacuum seal.
1.10 the flame retardant fluororubber can be burned when it is burned, and HF gas will be decomposed during combustion, which is corrosive and toxic. To leave the fire is to extinguish itself.
The modification of 2 fluororubber is aimed at the shortcomings of elasticity, poor cold resistance and high price of fluororubber. Researchers have done a lot of research to improve the performance of the rubber. There are two main directions for rubber modification: one is to introduce ether bond into the main chain of fluororubber through the development of fluoroether rubber and fluorosilicone rubber, which increases the flexibility of macromolecules, greatly improves its low temperature performance and retains the original characteristics of fluororubber, but it greatly limits its popularization and application due to its high cost of development and production; the second is rubber combined use, which will make fluorine rubber more flexible The purpose of the combination of rubber and some general rubber and special rubber is to obtain materials with excellent performance and low cost. Due to the structural characteristics of fluororubber, it is difficult to choose the co vulcanization system, and the unique characteristics of the fluororubber will be reduced partially after being used. The research on the combination of domestic and foreign is not widely carried out. Up to now, the modification of fluororubber mainly stays in fpm/acm, fpm/epdm and other directions. But fluororubber has the high performance which can not be replaced by other rubber. How to improve the shortcomings of fluororubber by using the research, and not to reduce or even improve its unique characteristics, is still a field worthy of attention.