Views: 2454 Author: Site Editor Publish Time: 2020-07-29 Origin: Site
With the development of science and technology, more and more old technologies are replaced by new ones. Taking the seal industry as an example, the traditional seals include mechanical seal, spring seal, pump seal, gland packing, elastomer bellows seal, non contacting mechanical seal, etc. Now, a new kind of seal appears, that is ceramic seal.
Ceramic seal is a kind of sealing device made of engineering ceramic materials to prevent the leakage of fluid medium. It has the advantages of small specific gravity, high melting point, high hardness, good chemical stability and corrosion resistance.
Ordinary ceramic materials cannot be used to make ceramic seals. Ceramic seal is mainly made of engineering ceramics, such as alumina, silicon carbide, etc. these materials can be made into alumina seal ring, silicon carbide seal ring, etc. In the traditional sealing elements, the common metal seal and non-metal seal have the characteristics of poor corrosion resistance and temperature resistance, which makes the life of the sealing elements low. The sealing elements made of engineering ceramics have been widely used because of their high temperature resistance, high hardness and good chemical stability. The development and research of engineering ceramics, the improvement of processing technology and its good comprehensive mechanical properties provide a broad prospect for the application of engineering ceramics.
The surface characteristics of ceramic materials can be fully utilized when engineering ceramic materials are used as seal pair. As with the surface of metal materials, although the surface roughness of ceramic materials after grinding is low, there are still micro irregularities on the surface, that is, there are many micro convex, typical micro convex can form a certain angle with the surface. In addition, some micro cracks and other defects may be produced on the surface and sub surface of ceramic materials in the process of processing.
In addition to the micro convexity on the surface, ceramic materials are also covered by a thin film. There may be an adsorption layer at the outermost layer, which is determined by the type of ceramic materials. For non alumina ceramics, it can be covered by an oxide layer. For alumina ceramics, it is oxide structure. This kind of coating is mostly composed of surface physical adsorption membrane formed by condensed water vapor or hydrocarbon in the atmosphere. However, the micro structure of ceramic materials is composed of many tiny particles and holes. These micro irregularities provide conditions for the coverage of the physical adsorption film. Therefore, the formation of the adsorption layer can hinder the wear of ceramic materials, thus ensuring good sealing.
Poor sealing performance will cause leakage. Leakage is a mass transfer phenomenon on isolated objects. In the ceramic seal, there is micro unevenness on the contact surface, so the sealing performance of ceramic seal is different before and during running-in, which is closely related to the working time of seal pair. Before running-in, the contact clearance of ceramic seal is large, and the sealing performance is poor at this time. With the passage of time, the gap between the two contact surfaces gradually reduces to almost zero, which makes the sealing performance significantly improved.