Investigation Of New Completely Meshing And Variable Pitch Rotor For Twin-screw Vacuum Pumps

The twin-screw vacuum pump is a kind of positive displacement pump.The screw rotor determines the performance of twin-screw vacuum pump,such as the ultimate vacuum and pumping speed.The involute on the existing screw rotor cross-section cannot smoothly connect the addendum arc and the dedendum arc,and discontinuity of space contact leads to large interstage leakage.In order to solve the problems above,two kinds of new meshing models is established in this paper.According to these two new meshing models,a new type of completely meshing screw rotor is proposed.The design method,main structure parameters and meshing performance are studied,and the influence of the main structure parameters on the working performance of the twin-screw vacuum pump are analyzed.The working process of the completely meshing screw rotor is numerically simulated,the sealing performance and high temperature thermal deformation of the completely meshing screw rotor are compared with the existing screw rotor.The existing variable pitch rotors have problems of small internal volume ratio,serious leakage between stages,and poor dynamic balance performance.To solve these problems,this paper studies the design method of variable-pitch screw rotor and builds a selfbalancing conical screw rotor with variable pitch.The two new meshing models solve the problem of difficult smooth connection between two concentric arcs on the cross-section of screw rotor.Compared with the commonly used cycloid-involute screw rotors,the cross-section of the proposed screw rotor has a completely smooth connection between the composition curves,which leads to better meshing performance.The proposed screw rotor has advantages of smooth,continuous and short space contact line,no leakage channel,and better interstage sealing performance.Under the same working conditions,the maximum circumferential thermal deformation of the new completely meshing screw rotor is small,which can reduce the interstage leakage caused by excessive assembly clearance.According to the constructed variable pitch screw rotor design method,a selfbalancing conical screw rotor with variable pitch was proposed.The cross-section profile changes continuously in the process of spiral expansion.The law of tooth wide growth conforms to the law of gas pressurization,which can reduce the size of the vacuum pump,increase the suction volume,and increase the internal volume ratio.The study of this paper enriches the types of screw rotors,and has important theoretical and engineering significance for design and optimization of twin screw vacuum pumps.