There are many types of sealing products and different working conditions, such as heat resistance, oil resistance, chemical resistance, and working conditions (static, dynamic, rotating and swinging, etc.), speed, and working pressure. Therefore, the rubber seals used for mechanical seals must first consider the conditions of use or special conditions on the rubber, and then comprehensively consider the reasonable formula and processing technology in the vulcanization promotion system, reinforced filling system, softening system, and protection system. Generally used for mechanical sealing, the rubber must have good elasticity and low compression set to meet the special performance requirements of different product conditions. As a dynamic seal, it is also required that the rubber material has a certain tensile strength, good abrasion resistance and tear resistance.
1.O-ring seal compound
O-ring is a kind of sealing products with simple outline structure, many specifications, and a large number of required products. O-ring seal quality life depends on 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 set under the use conditions, which are its main indicators. According to the requirements of use, generally there are requirements for heat resistance and oil resistance, and nitrile rubber is the most used rubber. Acrylic rubber can be used for oil-resistant sealing products that require higher temperature (such as 150 ~ C-90 ° C). Fluorine rubber for oil-resistant rubber products and silicone rubber for heat resistance are required. When the working pressure is high, the method to increase the hardness of the O-ring rubber is to increase the filling amount of carbon black, but the filling amount is too high, the mixing is difficult, and the basic physical properties of the vulcanizate are damaged, which also makes the rubber
Scorch is liable to occur. In the case of using the same kind of rubber, such as nitrile rubber, in order to improve heat and oil resistance and reduce compression set, a peroxide (such as DCP) vulcanization system or an effective sulfur vulcanization system (low sulfur and high acceleration) can be used. . These two vulcanization systems can produce relatively
The multi-carbon-carbon bond cross-linked structure and the single sulfur bond cross-linked structure effectively improve the heat resistance and oil resistance of the vulcanizate and reduce the permanent compression deformation.
In the filling and reinforcing system of the heat-resistant and oil-resistant compound formula of O-ring seals, thermal cracking carbon black, spray carbon black or semi-reinforcing carbon black with low activity are mostly used. These carbon blacks are characterized by coarse particles , Rubber has good elasticity, low heat generation, low compression set, and can be filled in large quantities to reduce rubber cost. If the O-ring is used under dynamic sealing conditions, the tear resistance needs to be increased, and a part of the highly active high wear-resistant carbon black can be used together. Fluoro rubber compounds are self-reinforcing rubbers. If activated carbon black is added, the mechanical properties of the rubber are reduced, so thermal cracked carbon black or spray carbon black is generally filled with a small amount of coarse particles with low activity.
The oil seal is an important part of the medium seal of the drive shaft, and its quality and life are directly related to the normal operation of the machine. Oil seals are generally used under dynamic conditions and in direct contact with the medium being sealed, such as oils. Therefore, oil seal compounds are required to have good oil resistance, wear resistance and small coefficient of friction. Because the friction between the oil seal and the shaft is very high, especially the lip area is higher, the heat aging resistance of the rubber is better. In addition, it is required that the rubber material has good flow performance to ensure that it is easy to move and fill the entire mold cavity when the mold is vulcanized. The main performance indicators of oil seals are heat resistance and oil resistance. The commonly used rubber compounds are nitrile rubber (long-term use temperature 120 ~ C), acrylic rubber (120 ~ C-170 ° C), fluorine rubber
(170 ° C-220oC). Under normal use of the oil seal, oil leakage failure occurs in the later stage, which is mainly caused by the aging and hardening of the oil seal lip, loss of elasticity and cracking. In order to improve the service life of the oil seal, the heat resistance of the rubber used in the oil seal must be improved. After the rubber type is determined, the vulcanization system is the key. For example, the nitrile rubber compound, the use of DCP peroxide vulcanization system and the addition of a vulcanization assistant (such as magnesium methacrylate) to improve heat resistance can effectively improve heat resistance. For the filling and reinforcing system, because the oil seal requires certain mechanical strength, tear resistance, and good wear resistance, high wear-resistant furnace black, fast-pressing carbon black, and general carbon black and semi-reinforcing carbon are often selected. Black, thermal cracked carbon black, spray carbon black, etc. are used in combination. White carbon black is also commonly used as a filler reinforcement, such as white carbon black alone, in order to improve the mechanical strength can be added silane coupling agent. Another advantage of white carbon rubber is better adhesion to metal framework materials. For fluororubber compounds, it is not suitable to use fine particle activated carbon black. Generally, coarse particle thermal cracked carbon or spray carbon black is used. In order to increase the self-lubricity of the oil seal vulcanizate and reduce the friction coefficient, filler materials such as graphite powder and molybdenum disulfide are often added.
3.Rubber sealing strip
Rubber sealing strip is mainly used in automobiles, airplanes, railways, and various doors and windows of high-rise buildings to prevent outside dust, air, and water from entering the system. Because rubber seals are mostly used in doors and windows of automobiles, trains, airplanes, and high-rise buildings, rubber materials are required to have good weather resistance, aging resistance and good mechanical properties, suitable elongation, permanent compression and cold resistance. performance. The rubber has good processing performance, fluidity and extrusion performance, stable external dimensions, smooth surface, and no impurities or marks on the surface. Rubber sealant rubber is the best EPDM rubber, and it is also the main rubber material often used. It is characterized by good weather resistance. The reinforced filling system of the rubber seal compound formula often uses carbon black varieties with good extrusion performance, small deformation and smooth surface, such as fast extrusion carbon black (N550), or with general purpose, semi-reinforced carbon black, spray carbon Black and so on. For high-end weatherseal products such as cars, the use of carbon black not only meets the requirements of physical and mechanical properties and processability, but also the surface must be smooth and free of particles. Therefore, the content of sieve residue of carbon black must be low and there must be no impurities, that is, carbon black. The purity must be high.
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