1. Overview
Screw air compressors have a series of unique advantages such as simple structure, reliable operation and convenient operation, so they have been widely valued by the industry since their birth. After years of development, screw air compressors have been widely used in the flow range of 1~60M3/MIN and pressure range of less than or equal to 20Barg. The market share in economically developed Western regions such as Europe, the United States, and Japan has been close to 100% (almost completely replacing piston air compressors), and more than 99% of them are twin-screw air compressors.
2. Classification of screw air compressors
1. According to the number of screws, they are divided into twin-screw air compressors and single-screw air compressors.
2. According to whether lubricating oil is involved in the compression process, they are divided into oil-free screw air compressors and oil-injected screw air compressors.
3. Introduction to the principle of twin-screw air compressors
Twin-screw air compressors were born in the 1930s. It consists of a pair of parallel and intermeshing rotors. When working, one rotor rotates clockwise and the other rotates counterclockwise. In the process of mutual meshing, the air is compressed to the required pressure. Twin-screw compressors have extremely high mechanical reliability and excellent dynamic balance, and are also very convenient to operate and maintain. Since their introduction, they have attracted great attention from the industry. After a lot of theoretical research and production practice by many scientific research institutions and manufacturing companies, twin-screw compressors have become mature and perfect in the 1970s, and have achieved great market success. They are the leading products in the current market. At present, the screw air compressors produced by well-known compressor manufacturers at home and abroad are all twin-screw air compressors, and more than 99% of the screw air compressors sold in the market are twin-screw air compressors.
4. Introduction to single-screw air compressors
Single-screw air compressors originated in the 1960s. From the name, the characteristic of this type of compressor is that it has only one screw rotor. But in fact, single-screw air compressors have three rotating shafts, namely, a screw rotor and two planetary gears perpendicular to the screw rotor. As a member of the screw compressor family, the single screw compressor has similar advantages to the twin screw compressor, but it has not been widely promoted due to the following problems that are difficult to solve in industry.
1. There are many moving parts: The single screw compressor has three rotating shafts, and the rigidity of the screw and the planetary gear is quite different. It is easy to deform unevenly during movement, so it is difficult to ensure the mutual meshing accuracy, so the volumetric efficiency is low. In the single screw compressors currently sold on the market, the planetary gears are all made of non-metallic materials with poor wear resistance. During high-speed operation, due to large wear, the internal leakage increases, so the flow rate has a large attenuation after working for a period of time. Generally, after 3000 to 4000 hours of operation, the flow rate decays by an average of 5~10%. Therefore, the economy of single screw compressors in industrial applications is extremely poor. In addition, the meshing accuracy caused by uneven deformation is difficult to ensure, which will also reduce the mechanical stability of the whole equipment, resulting in a high failure rate and high maintenance rate, further limiting its scope of use.
2. The material of the planetary gear needs to be further improved. As one of the core components of a single-screw compressor, the planetary gear is mainly used for sealing. If a steel planetary gear is used, a large gap must be left between the planetary gear and the screw due to the large expansion coefficient and volume of steel. This will not only cause more leakage and low efficiency, but also cause serious failures due to seizure. If composite materials are used, although the above problems can be solved, due to the low strength and poor wear resistance of the current composite materials, they will not only be damaged quickly under the action of shear force and mechanical friction during operation, causing increased internal leakage and reduced efficiency, but also frequent maintenance, increasing the labor intensity and maintenance costs of maintenance personnel. How to find a material with high strength, small expansion and wear resistance as soon as possible has become another major problem that manufacturers need to solve. However, judging from the current progress in materials science, it is difficult to get a fundamental solution in the short term.
3. The screw profile needs to be further optimized. Due to the existence of the above two problems and the fact that there is no good solution in the foreseeable future, the promotion of single-screw air compressors is limited. Therefore, scientific research institutions and large air compressor manufacturers have not invested much in the research of single-screw profiles, and have not made much progress. How to find the best screw profile is another major task before large-scale promotion. However, due to the poor market prospects and the small investment of major manufacturers, it is difficult to make fundamental improvements in the short term.
In general, from the current technological development, twin-screw air compressors are not only technologically advanced, but also fully mature in practical applications and have been widely used. Although single-screw air compressors are unique in principle, they are still in the experimental process due to deficiencies in some decisive factors. Their products still need to be further improved and cannot be promoted and applied on a large scale in the market as mature products.