Optimal design and development of two-segment variable-pitch screw rotors for twin-screw vacuum pumps

The built-in volume ratio of the twin-screw vacuum pump plays a crucial role in determining its applications. The screw rotor with larger built-in volume ratio has lower power consumption and lower discharge temperature, which is beneficial to obtain a higher ultimate vacuum. In order to improve the built-in volume ratio of screw rotors, and then develop a twin-screw vacuum pump with high ultimate vacuum, this paper presented a two-segment variable-pitch screw rotor generated by sweeping a constant cross-sectional profile along helixes. Effects of geometric parameters including the radius ratio and central angle on the rotor structure, area utilization and pumping speed of the proposed variable-pitch screw rotor were analyzed. Consequently, a pair of intermeshing two-segment variable-pitch screw rotors were optimized and manufactured, and a prototype of a twin-screw vacuum pump was developed. The performance of the proposed variable-pitch screw rotor was verified by the performance experiment of the developed prototype. Results show that the proposed two-segment variable-pitch screw rotors exhibits many distinct advantages of high ultimate vacuum, easy to process, and low noise and vibration; and its ultimate vacuum can quickly reach 0.1Pa. The developed screw rotors are of great significance for improving the performance and application of the twin-screw vacuum pump.