Study On Exhaust Mechanism And Rotor Structure Optimization Of Screw Vacuum Pump With Variable Pitch

The variable pitch screw vacuum pump is taken as the research object in this paper and the exhaust mechanism model of variable pitch screw vacuum pump was established.The pumping process of variable pitch screw vacuum pump is analyzed,and the variation law of various performance parameters of variable pitch screw vacuum pump is studied.The variable pitch rotor structure is optimized and the compression power consumption is effectively reduced.The main research contents and achievements are as follows:(1)The common variable pitch rotor structures are analyzed and summarized.Based on smooth connection condition,the polynomial equation of variable pitch spiral involute rotor show constructed by polynomial fitting,and the mathematical model of variable pitch rotor structure is established.It provides a theoretical basis for the structural design of variable pitch rotor.(2)The leakage passage in different stages of the pump cavity is reasonably simplified according to the characteristics of the involute rotor screw vacuum pump.The flow calculation models of different leakage channels in different flow regimes are analyzed and determined.Under the condition of neglecting the variation of the temperature in the pump cavity,the change of the gas flow state in the whole passage is considered.According to the law of conservation of mass and ideal gas equation of state,the gas transport model of variable pitch screw vacuum pump is established,which provides a theoretical basis for predicting the performance of the screw vacuum pump in the design stage.(3)The variation rules of various performance parameters of variable pitch screw vacuum pump are analyzed and studied and the results show that the gap between the top of the rotor and the inner wall of the pump cavity is reduced at the exhaust end,while the decrease of the gap between the rotors is beneficial to improve the pumping performance of the pump.The difference between the performance of equal pitch screw vacuum pump and variable pitch screw vacuum pump is analyzed and compared and the results show that the equal pitch screw vacuum pump has the advantage of the ultimate pressure,and the variable pitch screw vacuum pump has a great advantage in power consumption.(4)The performance of four different rotor structure variable pitch screw vacuum pumps is analyzed and compared.The variable pitch rotor structure is optimized to reduce the power consumption and improve the performance of variable pitch screw vacuum pump.