Packing seal

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　　Packing seals are also called gland packings (Gland Packings) seals, commonly known as packings. Packing seal is the oldest sealing structure. In ancient Chinese water-lifting machinery, cotton stuffing was used to block leaks. The earliest steam engines in the world also used this sealing form. The production and development of oil and natural gas extraction technology in the 19th century led to new developments in packing seal materials. By the 20th century, packing seals were favored by many industrial sectors because of their relatively simple structure, low price, and wide availability. 　　Packing seals are mainly used for dynamic seals in moving parts of process machines and equipment in the machinery industry, such as centrifugal pumps, compressors, vacuum pumps, mixers, reactor shaft seals and reciprocating pumps, reciprocating compressor plungers or piston rods, and screws. Packing sealing principle between the valve stem of the moving valve and the fixed body. After the packing is loaded into the packing cavity, it is axially compressed by the gland. When the shaft and the packing have relative motion, due to the plasticity of the packing, it generates radial force and is in close contact with the shaft. At the same time, the lubricant impregnated in the filler is squeezed out, forming an oil film between the contact surfaces. Since the contact state is not particularly uniform, a "boundary lubrication" state occurs at the contact part, which is called the "bearing effect".” ； The uncontacted concave parts form small oil grooves with thick oil films. The contact parts and non-contact parts form an irregular maze, which prevents liquid leakage. This is called the "maze effect". This is the mechanism of packing sealing. Obviously, good sealing lies in maintaining the "bearing effect" and "maze effect". In other words, maintain good lubrication and proper compression. If the lubrication is poor or the pressure is too tight, the oil film will be interrupted, causing dry friction between the packing and the shaft, which will eventually lead to shaft burning and severe wear. 　　For this reason, the compression degree of the packing needs to be adjusted frequently so that after the lubricant in the packing is lost after running for a period of time, some lubricant can be squeezed out, and at the same time to compensate for the relaxation of the pressing force caused by the volume change of the packing. Obviously, such frequent squeezing of the filler will eventually deplete the impregnating agent, so regular replacement of the filler is necessary. In addition, in order to maintain the liquid film and take away frictional heat, it is also necessary to intentionally allow a small amount of leakage at the packing. 　　Packing seal material properties: 　　①There is a certain degree of plasticity. Under the action of pressing force, a certain radial force can be generated and closely contact the shaft. 　　②Has sufficient chemical stability. It does not pollute the medium, the filler is not swollen by the medium, the impregnating agent in the filler is not dissolved by the medium, and the filler itself does not corrode the sealing surface. 　　③Good self-lubricating properties. Wear-resistant and small friction coefficient. 　　④The shaft has a small amount of eccentricity, and the packing should have sufficient floating elasticity. 　　⑤It is simple to manufacture and easy to fill. 　　Reference article: http://www.jilijie.com/news/shownews.asp?id=228