Screw air compressor has a series of unique advantages such as simple structure, reliable work and convenient operation, so it has been widely valued by the industry since its birth. After years of development, the screw air compressor is widely used in the flow rate of 1 " 60 M3/MIN and the pressure range of less than 20 Barg. In Europe, the United States, Japan and other western economically developed regions, the share is close to 100% (almost completely replace the piston air compressor), and more than 99% of them are double screw air compressor.
According to the number of screws, it is divided into double screw air compressor and single screw air compressor.
1.Double screw air compressor’s principle introduction
Double screw air compressor was born in the 1930s. It consists of a pair of rotors arranged in parallel and mutually engaged. When working, one rotor rotates clockwise and the other rotates counterclockwise, then the air is compressed to the desired pressure during mutual engagement.
Double screw compressor has extremely high mechanical reliability and excellent power balance, very convenient operation and maintenance. Since the date of publication has attracted great attention from the industry. After a large number of theoretical research work and production practice of many scientific research institutions and manufacturing enterprises, double screw compressor has become mature and perfect in the 1970s, and has achieved great market success, witch is the leading product in the current market.
At present, the screw air compressor produced by well-known compressor manufacturers are double screw air compressor, and of the screw air compressor sold in the market, more than 99% are double screw air compressor.
2.Single screw air compressor’s introduction
Single screw air compressor originated in the 1960s, and as we can see from the name, the compressor is characterized by only one screw rotor. But in fact, the single screw air compressor has three rotating axes, namely, consisting of a screw rotor and two planetary gears perpendicular to the screw rotor. As a member of the screw air compressor family, single screw air compressor has similar advantages to double screw air compressor, but it has not been promoted on a large-scale due to the following problems that are difficult to solve in industry.
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Too many moving parts: the single screw air compressor has three rotating axes, and the rigidity of the screw and the planetary gear difference is large, the easy deformation is not uniform in motion, so it is difficult to ensure the mutual engagement accuracy, witch means the volume efficiency is low.At the planetary gears in single screw compressors sold in the present market are all made of nonmetallic materials, which have poor wear resistance. In the process of high-speed operation, the internal leakage increases due to greater wear, so the flow rate decreases greatly after working for a period of time. Generally, after 3000 to 4000 hours of operation, the average flow rate decreases by 5-10%. Therefore, the economy of single screw air compressor in industrial application is extremely poor. In addition, the meshing accuracy caused by uneven deformation is difficult to ensure, and the mechanical stability of the whole equipment will be reduced, so the failure rate is high and the maintenance rate is high, which further limits its application range.
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The materials of the planetary gear need to be further improved. As one of the core components of single screw compressor, its main function is to seal. If the planetary gear made of steel is selected, a large gap must be left between the planetary gear and the screw due to the large expansion coefficient and large expansion amount of steel, which not only causes more leakage and low efficiency, but also easily causes major failures. Although the above problems can be solved by using composite materials, due to the low strength and poor wear resistance of the current composite materials, they will not only be damaged soon under the action of shear force and mechanical friction during operation, resulting in increased internal leakage and decreased efficiency. How to find a material with high strength, small expansion and wear resistance as soon as possible has become another big problem that manufacturers need to solve. However, as far as the current progress of materials science is concerned, it is difficult to get a fundamental solution in the short term.
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The screw profile needs further optimization. Because of the existence of the above two problems and there is no good solution in the foreseeable future, the promotion of single-screw air compressor is limited. Therefore, scientific research institutions and large air compressor manufacturers have not invested much in the research of single screw profile, and have not made great progress. How to find the best screw profile is another important work before large-scale promotion. However, due to the poor market prospects and the small investment of major manufacturers, it is difficult to fundamentally improve in the short term.
Generally speaking, the double screw air compressor is not only technologically advanced, but also fully mature and widely used in practical application. Although the single screw air compressor is unique in principle, it is still in the experimental process because of some decisive factors, and its products still need to be further improved, so it can not be widely popularized and applied in the market as a mature product.
