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Silicon carbide is a new type of ceramic, and it is the best friction pair material found so far, with various excellent properties such as physical properties, thermal properties and chemical properties, and even radiation proof properties are no exception. In terms of adhesive performance, silicon carbide forms a protective film of silicon oxide, which is wettable by most liquids. The thermal conductivity of silicon carbide is 10 times that of aluminum oxide. These properties, combined with its exceptional hardness, give it a very long service life both on its own and on the abrasive material of mechanical seals Its corrosion resistance is very good. In strong oxidizing medium, it only reacts at a high temperature of 500~600°C, and it is resistant to almost all acids and alkalis.
The manufacturing methods can be divided into hot pressing sintering SiC, atmospheric pressing sintering SiC, reaction sintering SiC, chemical vapor reaction SiC (also known as siliconized graphite) and chemical vapor deposition SiC. The first three are monolithic silicon carbide, and the latter two are SiC coatings formed on the graphite surface. The different performances created by the three different manufacturing methods are as follows：Atmospheric pressing sintering SIC and hot pressing sintering SiC both have a density of over 97% while reaction sintering SiC has a certain amount of free silicon and pores; chemical vapor deposition SIC and chemical vapor reaction SiC both have a surface layer of SiC and a substrate of graphite. Their common feature is that the end faces of the friction pair of the mechanical seals are dense and extremely hard SiC. Their performances are shown in the following two figures.
The same problem that should be paid attention to when using SiC: choose different SiC according to the different conditions of use. For large-volume products, atmospheric pressure sintering or reaction sintering SiC is suitable; for products with complex shapes, atmospheric pressure sintering SiC that is easy to form should be used, and the price is lower; if the medium is a strong oxidant, atmospheric pressure sintering and hot-pressing sintering SiC should be used. Use hot-pressed sintered SiC under high PV value; if the medium contains solid particles, you should choose SiC itself paired or SiC paired with cemented carbide. SiC is a brittle material with poor strength and impact toughness. When designing the sealing ring of the mechanical seal, it should be considered that the shape of the SiC ring should be simple, and it is not suitable to slot and drill holes on the ring to avoid and reduce stress concentration; the speed of grinding should be higher, and the amount of cutting tool should not be too large to avoid chipping; It is strictly forbidden to knock during assembly; Shockproof measures should be taken for packaging; In addition, careful installation and use are required.
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