The development history of single screw machine

The development history of single screw machine

1. The history and current situation of single screw compressor

　　 In 1960, France's B. Zimmern proposed the idea of ​​a single screw compressor and obtained a patent. In 1962, the first prototype was trial-produced, and it was officially produced and put on the market by Peugeot in the early 1970s. In the late 1970s, countries such as the Netherlands, the United Kingdom, and Japan successively developed and produced single-screw compressors for refrigeration and air-conditioning, with two types: open type and semi-closed type. At the end of the 1980s, technology was advanced to develop and manufacture single-screw compressors for compressing various gases (including air, flammable, explosive and toxic gases) used in petroleum, chemical, mining and other industries. At present, manufacturers in Britain, France, the United States, Japan, the Netherlands and other countries can produce single screw compressors of different specifications.

　　 At present, the main foreign manufacturers of single screw compressors are: 　　

　　 1. Japan

　　 Mitsui Seiki Corporation (MITSUR SEIKI)

　　 Komatsu Manufacturing Co., Ltd. (KOMATSU)

　　DAIKIN INDUSTRIES

　　MITSUBISHI ELECTRIC

　　 Iwata Coating Machine Industry Co., Ltd. (IWATA AIR COMPRESSOR MGT)

　　 2. United States

　　DRESSER-RAND (DRESSER-RAND)

　　 GRIMMER SCHMIDT (GRIMMER SCHMIDT)

　　 CHICAGO PNEUMATIC

　　 US Navy (US NAVY)

　　3. France

　　 Peugeot Motor Company (PEUGOT)

　　 CREPLLE (CREPLLE)

　　4. United Kingdom

　　 APV company (APV HALL PRODUCTS)

　　 5. Netherlands

　　Gratha

　　 2. The structural characteristics of single screw compressor and comparison with twin screw compressor-

　　Single-screw compressor is composed of a cylindrical screw and two symmetrically arranged flat planetary gears which form a meshing pair, which is installed in the casing. The screw groove, the inner wall of the casing (cylinder) and the star gear constitute a closed volume. The power is transmitted to the screw shaft, and the screw drives the star wheel to rotate. The gas (working medium) enters the screw groove from the suction chamber, and is discharged through the exhaust port and the exhaust chamber after being compressed. The role of the star wheel is equivalent to the piston of a reciprocating piston compressor. When the star wheel teeth move relative to each other in the screw groove, the enclosed volume gradually decreases and the gas is compressed.

　　The screw of the single screw compressor has 6 screw grooves, the star wheel has 11 teeth, which is equivalent to 6 cylinders, and the two star wheels mesh with the screw grooves at the same time. Therefore, each rotation of the screw is equivalent to 12 cylinders working.

　　 It is well known that screw compressors (including twin screw and single screw) account for a large proportion z* in rotary compressors. From the perspective of the international market, during the 20 years from 1963 to 1983, the annual growth rate of screw compressor sales worldwide was 30%. At present, twin screw compressors account for 80% of medium capacity compressors in Japan, Europe and the United States. As single-screw compressors and twin-screw compressors in the same working range, in comparison, twin-screws account for more than 80% of the entire screw compressor market due to its good processing technology and high reliability. Single screw compressors account for less than 20%. The following is a brief comparison of the two compressors.

　　1. Structure

The screw and star wheel of a single screw compressor belong to a pair of spherical worm pairs, and the screw shaft and star wheel shaft must be spaced perpendicularly; the female and male rotors of the double screw compressor are equivalent to a pair of gear pairs, and the female and male rotor shafts are kept in parallel. . From the structural point of view, it is difficult to ensure the matching accuracy between the screw and the star wheel of the single-screw compressor, so the operating reliability of the whole machine is lower than that of the double screw.

　　2. Drive method

　　 Both compressors can be directly connected to the motor or driven by a pulley. When the speed of the twin-screw compressor is high, the speed increasing gear is required.

　　3. Speed

Because the screw shaft and the star wheel shaft must maintain a vertical space, the position accuracy is very high, so the compressor speed cannot be too high, generally less than 3500 rpm; while the speed of the twin screw compressor can be very high, the current speed of a cold Carrier screw compressor Has reached 9000rpm. As the speed of the compressor increases, the leakage of the refrigerant is bound to be reduced, and the volumetric efficiency of the compressor and the cold capacity of the refrigeration system are increased. On the other hand, when the cooling capacity remains unchanged, the volume of the compressor is reduced, especially when a high-efficiency heat exchanger is added, the volume of the entire chiller can also be reduced.

　　4. Efficiency (the smaller the specific power, the better)

　　The single screw compressor has high efficiency at 1500～3500rpm, and the specific power is 6.0～6.4 kwm3/min. The twin screw compressor has high efficiency at 3000～9000rpm, and the specific power is 6.0～6.3 kwm3/min.

　　 5. Cooling capacity adjustment method

　　The air volume adjustment methods of the two compressors are basically the same, and both can be adjusted continuously by sliding valve or stepwise adjustment by plunger. When the slide valve is used for adjustment, the twin-screw compressor needs one slide valve, while the single-screw compressor needs two slide valves at the same time, so the structure becomes complicated and the reliability is also reduced.

　　6. ​​Assembly and maintenance

　　 Since the screw shaft and the star wheel shaft of the single-screw compressor must be kept vertical in space, its axial and radial position accuracy is very high, so the assembly and maintenance convenience of the twin-screw compressor is reduced.

　　 Three, the problems of single screw compressor

At present, the market share of domestic and foreign twin-screw compressors is far greater than that of single-screw compressors. This is because the technical conditions for producing twin-screw compressors are quite mature, and single-screw compressors have processing technology and performance due to structural characteristics. And reliability declines. Summarizing domestic and foreign research, development and related technical data, it is found that the key problems existing in current single screw compressors mainly include the following aspects.

　　1 Design and manufacturing process of meshing pair profile

　　 Screw and star gear meshing pairs are the heart of single screw compressors. Its profile design and processing technology are directly related to the performance and reliability of the whole machine. Compared with the twin screw compressor rotor profile, the screw and star wheel profile is more complicated, and the processing technology is poor, and the production efficiency is low. In this way, the matching accuracy between the screw and the star wheel is difficult to guarantee, and the life and reliability of the compressor are reduced.

　　 2. Leak

Single-screw compressors use gap seals. Due to the complex geometric shapes of the screw and star gear meshing pairs, they form more matching gaps, so there are many gas leakage channels. According to the literature, single-screw compressors have 9 leakage channels. It may cause the increase of external leakage of the refrigerant in operation, the decrease of volumetric efficiency, and the appearance of insufficient refrigeration capacity of the refrigeration system.

. 　　3. Star wheel wear

　　 The rapid wear of the star wheel is the most important form of failure of a single screw compressor. During compressor operation, due to the transmission error caused by the machining accuracy of the meshing pair, the assembly accuracy and the thermoelastic deformation of the rotor, the star wheel flutters in the screw groove, and the star wheel teeth frequently collide with the screw groove, destroying the meshing The lubricating oil film between the pair may cause excessive wear of the star gear teeth, or even breakage of the gear teeth, which will cause refrigerant leakage and reduce the efficiency and reliability of the refrigeration system.

　　 IV. Conclusion

In summary, at the current level of single-screw compressor technology, it still has shortcomings such as difficult to ensure meshing accuracy, poor assembly, difficult to control leakage gap, and rapid wear of star gear teeth. Compared with well-developed twin-screw compressors, they still lack strong market competitiveness.