Performance processing and application of the hott

Properties, processing and application of heat vulcanized fluorosilicone rubber

important characteristics of fluorosilicone rubber

oil resistance, solvent resistance and chemical resistance

compared with methyl vinyl silicone rubber, fluorosilicone rubber has excellent oil resistance, solvent resistance and chemical resistance; Even compared with fluororubber, it has good oil resistance and solvent resistance. It shows excellent durability after impregnation in the same medium, temperature and time. It can be said that fluorosilicone rubber is the only elastomer resistant to non-polar media at -68 ℃ ~ 232 ℃

fluorosilicone rubber also has good resistance to methanol containing gasoline. Even in the gasoline/methanol (85vol%/15vol%) mixed system, the hardness, tensile strength and volume of its vulcanizate change little. After 500h long-term immersion test, all physical properties are almost unchanged

heat resistance

the high temperature decomposition of fluorosilicone rubber is the same as that of silicone rubber, that is, side chain oxidation, main chain fracture, side chain thermal decomposition and various composite reactions. Because the decomposition products will also cause the fracture of the main chain, the heat resistance is usually worse than that of silicone rubber, and the oxidation aging has begun at the temperature of 200 ℃. However, by adding a small amount of heat stabilizers such as iron, titanium and rare earth oxides, it can be significantly improved, and it has sufficient heat resistance even at a high temperature of 250 ℃

the effect of temperature on fluorosilicone rubber is greater than that of silicone rubber, but smaller than that of fluorosilicone rubber. Fluorosilicone rubber at 150 ℃ has also been studied abroad × 2000h、175℃ × 5000h、200℃ × The service life under 4000H is second only to methyl vinyl silicone rubber

cold resistance

fluorosilicone rubber, like ordinary silicone rubber, has good low temperature performance. Because fluorosilicone rubber is a linear polymer with soft Si-O as the main chain, its low-temperature properties are better than those of fluorosilicone rubber with C-C as the main chain. Among them, fluorosilicone rubber (ls-2370u) has better low-temperature characteristics, and its brittleness temperature is as low as -89 ℃, while the general fluorosilicone rubber is about -30 ℃

electrical properties, radiation resistance

the electrical properties of fluorosilicone rubber are similar to those of ordinary silicone rubber, but they are particularly valuable because they change little under harsh conditions such as high temperature, low temperature, humidity, oil, solvents, chemicals, ozone and so on

the radiation resistance of fluorosilicone rubber is not outstanding, but the radiation aging resistance is better than methyl vinyl silicone rubber

physical and mechanical properties

fluorosilicone rubber is the same as ordinary silicone rubber, and the mechanical strength (especially tear strength) of vulcanizate is relatively low. Therefore, improving and improving the strength of fluorosilicone rubber is also an important research topic

Dow Corning silicone company developed high-strength and tear resistant fluorosilicone rubber (us-2332u) very early. The research on high-performance fluorosilicone rubber in China mainly focused on the 1980s. Although some progress has been made in basic research and application research, there is still a big gap compared with foreign countries

other characteristics

fluorosilicone rubber has excellent weather aging resistance and maintains good performance even after 5 years of exposure. Ozone is one of the most generated gases during the aging of elastomers, but the fluorosilicone rubber has no cracks or cracks after dynamic or static tests

in addition, fluorosilicone rubber has good mildew resistance, physiological inertia and anticoagulation

processing technology of fluorosilicone rubber

mixing

although fluorosilicone rubber is a solid, it has high plasticity and does not need to be plasticized. It can be directly mixed by open mixer or internal mixer. The dosing sequence or mixing process is as follows:

raw rubber (fluorosilicone rubber + a small amount of silicone rubber) → white carbon black + structural control agent + processing aids → glue pouring, thin pass (5 times) → heat treatment → refining + cross-linking agent → thin pass (8 ~ 10 times) → flake out and parking (more than 12h) → ready for use

when using the open mill for mixing, it is best to equip the dust-proof or air extraction device above the open mill roller to reduce the flying of white carbon black. During the mixing process, no other impurities or colloidal particles shall be mixed, the temperature shall be controlled below 40 ℃, and sufficient cooling water shall be opened. The mixing time of each batch of rubber is about 20 ~ 40min. The glue loading depends on the specification of the open mixer, generally Φ 160mm × 320mm open mill is 1 ~ 2kg, Φ 250mm × 620mm is 5 ~ 8kg

as for mixing with internal mixer, it can not only improve production efficiency and reduce labor intensity, but also reduce the flying of silica and improve the operating environment. The dosing sequence of internal mixer mixing is basically similar to that of open mixer, but the requirement of dosing interval is not strict. The mixing time of each batch of rubber is about 8 ~ 18min, and the filling coefficient of internal mixer should be controlled in the range of 0.7 ~ 0.75. The rubber discharge temperature is related to the type of filler, which should generally be controlled in the range of 50 ℃ ~ 70 ℃

heat treatment

when the fumed silica without surface modification is used as the reinforcing agent, the structure control agent must be added to the compound. Therefore, the heat treatment of rubber compound has become a necessary process

the main purpose of heat treatment is to further combine the structure control agent with silica; Eliminate low molecular volatiles. Generally speaking, the condition of heat treatment is 160 ℃ ~ 200 ℃ × 1～1.5 h。

filtration

for extruded products, calendered products, gelatinized products and diaphragm products, mechanical impurities and undistributed compounding agent particles are one of the main factors leading to product quality problems. Therefore, the rubber used in the above products must be filtered. When filtering, the rubber filter can be used, or the ordinary extruder can be used to replace it. The temperature of the barrel and screw should be controlled to the minimum, and the filter specification should be 120 ~ 200 mesh

remanufacture

after parking, the gel content increases and the plasticity decreases, so it must be remanufactured during use. The rubber back refining should be enough, and the back refining is insufficient, the rubber softness is poor, and the surface is uneven; However, if the refining is excessive, the rubber surface will become sticky, which is not conducive to operation, especially for fluorosilicone rubber

vulcanization

fluorosilicone focuses on the development of special fibers, filter materials, high-temperature functional membranes, high-performance resin based composites, high-temperature insulation materials, high-temperature functional coatings, high-temperature special adhesives based on thermoplastic polyimide (PI) engineering plastic resin, heteronaphthalene biphenyl polyethersulfone ketone copolymer resin (PPESK), processing and molding of high-end fluoroplastics. Unlike other ordinary rubbers, vulcanization is divided into sections The second stage is completed twice. A short vulcanization time (1.5 ~ 15min) can only make the products reach the degree of finalization; After two-stage vulcanization (3 ~ 6h), the complete vulcanization can be achieved, and the physical properties of the vulcanizate can stabilize

mold vulcanization is most suitable for the processing of O-rings, cups, diaphragms, oil seals, gaskets, jackets and other products; Atmospheric hot air vulcanization and pressurized steam vulcanization are mainly used for the processing of extruded products, calendered products and glued products such as rubber hoses, tapes, tapes, rubber ropes, wire and cable coatings. The equipment used for vulcanization can be selected according to the product type, and the vulcanization conditions can be determined according to the product specification, thickness and vulcanization system. The first stage vulcanization conditions of molded products and extruded products are shown in Table 1 and table 2 respectively. Table 1 one stage vulcanization conditions of molded products

Table 2 one stage vulcanization conditions of extruded products

Application of fluorosilicone rubber

fluorosilicone rubber is an elastomer material with the characteristics of both silicone rubber and fluororubber. Compared with methyl vinyl silicone rubber, the biggest advantage is oil resistance and solvent resistance; Compared with fluororubber, although there is little difference in the resistance to alkane solvents, its resistance to aromatic solvents is better than fluororubber, and its good solvents are only ketones with large polarity and small molecules. Fluorosilicone rubber has better heat resistance, cold resistance and compression set, and its physical properties are less dependent on temperature. It shows excellent properties from low temperature to high temperature. Secondly, products with low hardness can be made even without plasticizer. Therefore, fluorosilicone rubber is widely used as a new high-performance elastomer material

fluorosilicone rubber is mainly used in aerospace, vehicles and ships, electronic communications, precision instruments, petrochemical industry, medical and health care and other fields, but at present, the largest market demand is still rocket, satellite, automobile, aircraft manufacturing industry

aviation film: the film used for the valve in the pressure regulating pipeline of the oil tank and the film used for the vent valve of the oil tank (the fluorosilicone rubber coating and polyester cloth used in the kerosene steam of -55 ℃ ~ 200 ℃ and RP kerosene of 150 ℃ are difficult to implement; the degradation mechanism of the material is not very clear film)

static and dynamic seals: gaskets, cups, valves

automotive products: fuel level indicator sensor hose, atomizer oil pump diaphragm, fuel pump diaphragm, corrugated sheath, engine crankshaft rear seal ring, cylinder gasket, fuel pump seal, fuel tank cover gasket, fuel tank refueling gasket, oil filter seal

others: seals resistant to fluorine and chlorine oil, fluorine and bromine oil, trichloro biphenyl, H2S solution and liquid nitrogen

in the production and sales for so many years, we have achieved the national experimental machine leader, the original Yashi Industrial College (end)