At present, the development of various vacuum pumps is more and more affected by vacuum applications. The general vacuum system can not meet the requirements of clean and oil-free corrosion resistance. Therefore, in recent years, the market demand of dry vacuum pumps is very large, and the vacuum products have been updated. A large number of oil-free vacuum systems have been replaced by oil-free and clean vacuum systems. Almost every large vacuum company abroad produces various types of dry vacuum pumps. Screw vacuum pump is a non-contact dry pump. It is an ideal pump in the early 1990s. It occupies the market with its advantages of wide pumping speed range, simple and compact structure, no friction of air extraction chamber components, long service life, low energy consumption and no oil pollution. However, most of its manufacturing technology is mastered by foreign countries. China is still in its infancy, and the market has great demand for dry pumps At present, the development of various vacuum pumps is more and more affected by vacuum applications. The general vacuum system can not meet the requirements of clean and oil-free corrosion resistance. Therefore, in recent years, the market demand of dry vacuum pumps is very large, and the vacuum products have been updated. A large number of oil-free vacuum systems have been replaced by oil-free and clean vacuum systems. Almost every large vacuum company abroad produces various types of dry vacuum pumps. Screw vacuum pump is a non-contact dry pump. It is an ideal pump in the early 1990s. It occupies the market with its advantages of wide pumping speed range, simple and compact structure, no friction of air extraction chamber components, long service life, low energy consumption and no oil pollution. However, most of its manufacturing technology is mastered by foreign countries. China is still in its infancy, and the market has great demand for dry pumps Present situation of dry vacuum pump Due to its superior performance, dry screw vacuum pump has become the preferred vacuum equipment in microelectronics, semiconductor, pharmaceutical, precision processing and other industries in Europe, America and Japan. On the basis of screw compressor, Japan has long developed the multi head rotor profile of vacuum pump and put it into the market. Several German vacuum equipment companies have also gradually developed equal pitch and variable pitch rotor profiles, and have done a lot of research on rotor and body cooling. Key technical problems of screw pump: Structure of dry screw pump: The structure of screw vacuum pump is mainly composed of screw rotor, shell, cooling circulation and sealing materials. The transmission shaft is connected with the driving rotor and drives the driven rotor to rotate through the synchronous gear. A cooling water channel is opened on the shell to cool the temperature of the rotor and exhaust port. The synchronous gear and bearing are lubricated with oil. The interior of the bearing and housing is sealed by seals to achieve the effect of oil-free. The structure of dry screw vacuum pump is similar to that of oil-free screw compressor in sealing and lubrication. Generally, mechanical seals are used at the exhaust end of vacuum pumps, and double lip seals are commonly used at the inlet side. In terms of transmission mode, at present, the common is direct connected motor, which is connected with rotor by coupling, and very few are driven by belt or chain. Due to no internal compression process, the exhaust temperature of equal pitch screw pump is very high (about 110 ℃). If the cooling effect is not good, it will cause deformation of rotor and casing and affect the sobbing effect. Therefore, cooling the casing is an essential link, and water cooling is a common method. Cooling water is supplied to the outer side of the bearing in the casing body to cool the casing and then the rotor. Laibao company applies water cooling inside the rotor to increase the service life of the rotor and achieve good cooling effect. However, this kind of structural design (two-stage type) requires certain technical and processing level support. Sometimes the cooling effect cannot be achieved by water cooling, so the cooling gas (mostly nitrogen) is usually passed near the rotor at the exhaust end. Now the mainstream screw vacuum pump abroad adopts this method. This method has several advantages: it can cool the casing of the rotor and reduce the exhaust temperature; Second, when the gas contains particles, it can prevent particle deposition or chemical reaction from causing explosion. Overview of dry vacuum pumps produced by domestic and foreign companies (1) KDP and SDV series screw vacuum pumps of Taher company. Taher acquired Kenny vacuum. Kenny is a professional manufacturer of vacuum equipment in the United States with a long history. It is also in a world position in the manufacturing of screw vacuum pump. KDP series is a vacuum pump with equal pitch rotor, and SDV is a variable pitch screw pump. Both are water-cooling systems, and air cooling systems can be selected. SDV is an improvement based on KDP. The variable pitch screw pump can realize the internal compression of gas, reduce the exhaust temperature, and save 30% energy compared with the same pitch. Niflon coating is adopted on the rotor, i.e. the layer is Ni and the second layer is PFA. Even if the PFA is worn, the Ni layer can achieve corrosion protection, and kalrez perfluorinated rubber sealing ring is adopted. SDV series is the screw vacuum pump mainly promoted by Kenny company. (2) The srewtine series screw oil-free compression vacuum pump officially launched by LeiBao company in Germany at the end of 2002 is a dry pump specially designed for industrial applications (non semiconductor applications). It is a new design and is specially used to solve the difficult vacuum problems in industrial applications. Such as dust, tar, etc. The pump also adopts variable pitch rotor with internal compression process. There is no internal valve in the pump cavity, so it has strong resistance to dust and tar. The screw of the pump adopts internal hollow cooling, which can reduce the rotor temperature and thermal deformation, so the service life of the screw is prolonged. (3) Cobran series screw pump of Germany puxu company is a vacuum pump for manufacturing process, which is especially suitable for various process flows in chemical and pharmaceutical industries. Puxu is one of the suppliers of vacuum pumps, blowers and compressors in the world. The quality of vacuum pumps is high. Compared with other manufacturers, puxu has a high market share in Europe and the price is expensive. (4) VSA / VSB series of Richler, Germany. VSA is an equal pitch rotor with good market evaluation and stable performance. VSB Series event pitch rotor design (non-linear tooth shape design), like other companies, changes the power consumption and exhaust temperature of the pump through internal compression. Without two-stage compression and intermediate cooling, a single stage can achieve very high vacuum. The sealing element is improved. The static sealing element is preferably PTFE or the sealing element added with PTFE. The dynamic sealing element uses double sealing lips on the suction side of the vacuum pump, and a simple sealing ring with gas overflow prevention is used on the exhaust side of the vacuum pump to prevent solid substances from entering the pump. (5) Japanese manufacturers. Screw vacuum pumps are widely used in Japan, and are widely used in semiconductor and LCD industries. Yoshimura soldiers of Dahuang Co., Ltd. applied for patents on single head first-class screw rotors for a long time and made in-depth research on rotors. Hitachi also made research on screw pump in the early stage. 3. Research prospect: The domestic research of dry screw vacuum pump is still in the initial stage, and many technical problems have not been solved. For example, the rotor coating anti-corrosion technology, reducing the temperature of the exhaust port and increasing the utilization rate of the rotor area are still very difficult. When extracting some active gas, due to the high exhaust temperature, it also needs to be considered in the design. When used in the occasion where the volume needs to be controlled, how to reduce noise should also become the research direction, However, its superior performance determines that it will dominate the vacuum equipment industry, just like the dominant position of screw compressor in the industry.