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   SBR is an unsaturated hydrocarbon polymer. Physical and chemical reactions will occur under the action of light, heat, oxygen and ozone, but its oxidation is slower than that of natural rubber, and the aging reaction is slower even at higher temperatures. The aging effect of light on rubber is not obvious, but the ozone resistance is worse than that of natural rubber. The brittleness temperature is about minus 450C, and the low temperature performance is slightly worse.Compared with general general rubber, it has the following advantages and disadvantages: 1. Advantages (1) The rubber compound is not easy to be scorched and oversulfurized, and the vulcanization flatness is good. (2) Wear resistance, heat resistance, oil resistance and aging resistance are all better than natural rubber. Good high temperature wear resistance, suitable for passenger tires. (3) During processing, the molecular weight will not decrease after a certain level, so it is not easy to over-smelt, and the plasticity is uniform. The hardness of the vulcanizate varies little.(4) Increasing the molecular weight can achieve high filling. Oil-extended styrene-butadiene rubber has good processing properties. (5) It is easy to use with other unsaturated general-purpose rubbers, especially with natural rubber and cis-butadiene rubber. The shortcomings of styrene-butadiene rubber can be overcome by formula adjustment.2. Disadvantages (1) The strength of pure glue is low, and it can be used only after adding high activity reinforcing agent. The difficulty of adding compounding agents is greater than that of natural rubber, and the dispersibility of compounding agents in rubber is poor. (2) There are many trans-structures, irregular structures, and benzene rings on the side groups, so the hysteresis loss is larger than that of natural rubber, the heat generation is higher, the elasticity is lower, and the cold resistance is also slightly worse. But after oil filling can reduce heat generation.(3) The unvulcanized rubber has large shrinkage, low strength and inferior adhesion properties than natural rubber. (4) The vulcanization speed is slower than that of natural rubber. (5) The flexural cracking resistance of vulcanized rubber is better than that of natural rubber, but the crack propagation speed is faster. Poor hot tear properties.

What is the guide belt:       The guide belt is a belt-shaped member that guides the moving parts. Its main function is to guide. In order to realize the function of guidance, it must support the guided member, and guide and correct its motion trajectory. In order to realize the guiding function well, it also requires isolation, shock absorption and noise reduction of the guiding parts.        Guide belts are mainly used in oil cylinders and cylinders. Due to their excellent performance, they are also widely used in other motion mechanisms.1. Main requirements:(1) .Support and positioning The piston and piston rod are radially supported and positioned in the cylinder barrel.(2). Isolation Isolate the two pairs of motion pairs of piston and cylinder, piston rod and guide sleeve to prevent direct scratches, abrasions and strains between the motion pairs. Especially when the motion pairs are all steel parts, they must be isolated, otherwise they will be easily strained.(3). Anti-friction The guide belt also has an important role to reduce the friction and friction work between the moving parts, reduce the ineffective work and heat.(4). Vibration absorption and noise reduction Reduce system vibration and noise2. Materials:       It is mainly filled with tetrafluoroethylene and phenolic cloth, and there are also a very small amount of polyoxymethylene, nylon and soft metal.3. Use:       Supplied in rolls or open loops. The open ring can be directly installed and used, but it must be cut when the roll is used, and the cutting length must be calculated in advance: there can only be one opening, the opening form is an oblique 45° opening, and the opening distance is about 3-15mm, or the diameter of the guide ring 3-5% of .       Under normal circumstances, the openings are oblique openings. Straight openings or zigzag openings are rare and have specific uses and purposes. There are two purposes for the opening. The first is to facilitate installation. If it is not opened, it is an integral ring, which is difficult to install or impossible to install, so it must be opened. Secondly, the opening and a certain opening distance are reserved to facilitate the automatic coordination of volume changes. Otherwise, the movement may be stuck or the moving parts may be pulled due to the excessive expansion of the guide belt under certain conditions. Coiled ones are relatively cheap, and the same coil can be used to make guide rings of different sizes.(1). The phenolic cloth is generally open ring, and a small amount is roll(2). Tetrafluoroethylene is generally rolled, and a small amount is open ring4. Production method:       Extrusion method (low cost, large batch) and cutting and shaping method (high cost, small batch, flexible production, many fancy styles)5. Bearing capacity:       It varies according to the hardness of the material. The general phenolic cloth is hard and has a large bearing capacity, while the one filled with tetrafluoroethylene is softer and has a lower bearing capacity.6.the use of temperature:       Generally, the use temperature range of phenolic cloth is -40 ~ 120 ℃. Filled with tetrafluoroethylene can be used at -200 ~ 200 ℃, but the bearing capacity decreases with the increase of temperature.7.life:       Phenolic cloth guide belts are prone to physical aging at higher temperatures (greater than 80°C) and certain working media. The material gradually becomes hard and brittle, and finally cracks and scratches the working surface. There is no similar problem with tetrafluoroethylene guide tape.8. friction coefficient:       The dry friction coefficient of tetrafluoroethylene guide belt and steel is 2-10%, and the wet friction coefficient is 0.1-4%. The dry friction coefficient of phenolic cloth and steel is 20-40%, and the wet friction coefficient is 10-20%.9.medium resistance:       Tetrafluoroethylene is resistant to all working media, and phenolic cloth is not resistant to working media with water or brake fluid.10. Pollution bearing capacity:        The tetrafluoroethylene guide belt has excellent dirt holding capacity, which can block the dirt in the working medium for the main seal and prevent damage to the main seal. Generally, when a phenolic cloth guide belt is installed, a tetrafluoroethylene guide belt should be installed, and its purpose is to block pollution.11. Running speed:       The tetrafluoroethylene guide belt can be used for very high-speed or very low-speed oil cylinders. The phenolic cloth guide belt is not ideal for very high and very low speeds due to its large friction coefficient.12. Application:      The phenolic cloth guide belt has a strong bearing capacity. For oil cylinders with large eccentric load, the guide belt must be installed, such as various heavy-duty oil cylinders, high-pressure oil cylinders, and large oil cylinders.      The tetrafluoroethylene guide belt has a small friction coefficient and a strong dirt holding capacity, and is practically used in all types of oil cylinders, especially high-speed oil cylinders, high-efficiency, low-friction oil cylinders, and various construction machinery oil cylinders.13. use note:       Rolled guide belts are generally cut as needed before installation. Two issues need to be paid attention to when cutting: angle and length. The angle should be guaranteed to be about 45°, and the length should ensure that the opening size is up to standard.       In a word, if the load capacity is the main consideration, it is recommended to use the phenolic interlayer guide belt, and in all other cases, the filled tetrafluoroethylene guide belt is preferred.

1. Leakage of gasketsThere are four types of leakage phenomenon in general gaskets: interface leakage, penetration leakage, diffusion leakage, and damage leakage. （1）. Interface leaks The interface will leak at the sealing interface due to insufficient gasket compression, improper flange joint surface finish, and flange deformation. For interface leakage, it can be prevented by using soft gasket to clamp in the flange face.（2）. Penetration leakage Since most of the soft materials are made of fibers, they are easily soaked by the medium, especially the pressure. Due to capillary phenomenon, the medium will permeate to the low pressure side, forming permeation.（3）.Diffusion leakage Driven by the concentration difference, the medium leaks through the material transfer generated by the sealing gap or the capillary of the sealing material. Diffusion is the result of molecular motion and is not unidirectional. When the sealing pressure difference is extremely small or in a vacuum state, or when sealing permeable substances such as nitrogen and hydrogen, as well as highly toxic and radioactive substances, special attention should be paid to the leakage and diffusion.（4）.Destroy the leak The working conditions of the sealing part are relatively bad, the thermal deformation is large, it is often subjected to vibration, impact, improper installation, excessive tightening force, repeated use, compression deformation, internal stress concentration, damage beyond the fatigue strength, material aging, deterioration, etc. will cause damage to leaks. This kind of leakage has the greatest impact and great harm, so it is necessary to strengthen prevention. 2. Gasket sealing mechanism The function of the gasket is caused by the blocking effect on the internal medium formed by the contact pressure of the sealing material on the joint surface and the elastic restoring force to the external tightening force. 3. Classification and structure of gaskets Gaskets are divided into three categories: non-metallic gaskets, non-metallic and metal combined gaskets and metal gaskets. The common materials are rubber, leather, asbestos board, cork, PTFE, tinplate, steel, aluminum, copper and stainless steel.    4. the selection of gaskets The selection principle of the gasket: according to the working pressure, working temperature, the corrosiveness of the sealing medium and the form of the sealing surface.（1）. Temperature influence In normal temperature and low pressure, use non-metallic soft honey gasket; in medium pressure and high temperature, choose metal and non-metal combination gasket or metal gasket; when temperature and pressure fluctuate greatly, choose good elasticity or self-tightening type Gaskets; in low temperature, corrosive media or vacuum conditions, gaskets with special properties should be considered. （2）.Influence of flange form Different flange forms require different gaskets. Smooth-faced flanges are generally only used for low pressure, with soft thin gaskets; under high pressure, if the strength of the flange is sufficient, smooth-faced flanges can also be used, but thick soft gaskets should be used, or inner belt reinforcement should be used. Wound gasket for ring or reinforcement ring. In this case, metal gaskets are also not suitable, because the required pressing force is too large, resulting in large deformation of the bolts, making the flange difficult to seal. If a metal gasket is to be used, the smooth surface should be reduced to reduce the contact area with the gasket. In this way, under the condition of the same bolt tension, the compressive stress of the reduced narrow smooth surface will increase.

       Construction machinery, also known as construction machinery, is mainly used for mechanical and electrical equipment for the construction, renovation and maintenance of various buildings. Widely distributed in industrial and civil construction, urban construction, national defense construction projects, transportation construction, mining and other raw material industrial construction and production, agriculture, forestry and water conservancy construction, sanitation and environmental protection industries. It contains a wide range of types, such as excavators, loaders, cranes, pump trucks, pile drivers, hydraulic breakers, pavers, graders, rock drills, etc.       Although construction machinery looks extremely complex, the common characteristics that can be summarized are:1. Usually work outdoors.2. The work site often changes, and some can move by themselves.3. The working environment is usually dusty or stained.      Nowadays, construction machinery generally adopts hydraulic transmission, because hydraulic transmission has the following obvious advantages compared with mechanical transmission:1. The power-to-volume ratio is large and the location arrangement is easy.2. It can realize stepless speed change.3. It is easy to realize overload protection.4. Less shock, vibration and noise.      However, hydraulic transmission also has disadvantages compared with mechanical transmission:1. It is easy to leak and not friendly to the environment.2. High manufacturing precision is required.3. Low efficiency.4. The transmission ratio is not fixed.     Due to the special working environment of construction machinery, its hydraulic system has the following characteristics:1. The working hours are irregular, and sometimes work continuously for a long time.2. The working environment is outdoors, the working temperature difference is large, and the working environment is dusty.3. The machine itself walks. Due to the limitation of volume and weight, the hydraulic oil tank is generally relatively small.4. Due to the volume and weight, the working pressure of the hydraulic system is high, usually above 20MPa, and the highest is about 40Mpa.Construction machinery sealing system requirements:High and low temperature resistanceBecause of continuous work for a long time, if it is outdoors in summer, the hydraulic oil temperature of the machine may exceed 100°C, which requires the seal to be resistant to high temperature. If it is outdoors in winter, the temperature may be around -40°C when it is just turned on, and the seals are required to be resistant to low temperatures. Therefore, the sealing system is required to withstand a wide temperature range.Stain resistantThe machine itself walks. Due to the limitation of volume and weight, the hydraulic oil tank is generally relatively small.Due to the volume and weight limitations of the system, it is impossible to install an ideal filtration and cooling system. High temperature, high pressure, and high speed cause the hydraulic oil to deteriorate easily, and the mechanical parts are also prone to erosion and stains.There are many stains and impurities in hydraulic oil, but it cannot be thoroughly filtered, which is the aspect of endogenous stains.All kinds of dust in the working environment may be very large, and it will inevitably enter the hydraulic system in multiple ways, causing oil pollution, which is an external stain.Therefore, the sealing system is required to be resistant to stains.Good sealing performanceBecause the system works outdoors, there is no leakage oil recovery system, and the working medium will directly pollute the environment after leakage, so external leakage requirements are strict. At the same time, for the requirements of hydraulic oil heating control, pressure maintaining or maintaining position, the internal leakage requirements are also very strict.High pressureThe working pressure of the hydraulic system is high, usually above 20MPa, and the highest is about 40Mpa, which is higher than the general industrial hydraulic system pressure, so the sealing pressure resistance requirements are high.DurableBecause the system pressure is high, the temperature is high, and the wear is particularly serious, the seal is required to have good wear resistance.Low coefficient of frictionFor construction machinery such as excavators and pump trucks, the hydraulic system pressure is high, the cylinder action speed is fast, and the wear of the seal is particularly serious. Therefore, the friction coefficient of the seal must be low, so that the seal has good wear resistance and suitable life. .Key points of engineering mechanical seal design:1. Select a reasonable sealing scheme, focusing on the above requirements.First of all, the dustproof performance must be good. More than 80% of the failures of the hydraulic system are directly or indirectly derived from the stains in the system.2. Choose the best sealsFor seals of the same structure, the product quality of each company varies greatly. On the whole, the quality of large foreign seal companies is relatively stable, but the probability of encountering fakes is too high. Sometimes the so-called direct supply is not reliable. In terms of domestic seals, most of them are not very good, but at present, some manufacturers' products have been chasing or even surpassing imported products, with stable and reliable quality, such as tetrafluoroethylene and rubber seals produced by Damson Sealing.3. Select the appropriate sealing materialThere are many types of sealing materials, including many metals, plastics and rubbers. The same material has different performances from different companies. On the other hand, the same seal has different performances in different working conditions or different sealing schemes, so it must be carefully considered when choosing.Note: Be sure to consider seals under the premise of a reasonable sealing scheme, then consider the sealing material, and then consider the seal manufacturer. If you don't have enough sealing experience, it is best to consider the sealing company first, and let the sealing company consider the sealing scheme and other issues, such as  DMS Seals Technology Co.,LimitedKey points for the use of engineering mechanical seals:1. There must be a dust-free site during installation to prevent dust from being brought into the system during installation2. All installation parts must be clean, iron filings, rust, paint, welding slag, etc.3. Prevent dust from entering from the fuel tank port and other places (such as refueling).4. Replace the filter element on time. When working, the hydraulic system will have internal stains, which must be removed by replacing the filter element.5. The hydraulic oil will gradually deteriorate and oxidize during operation, and the hydraulic oil must be replaced on time.6. When replacing oil pipes or other parts at the work site, special attention should be paid to dust and pollution.