Research On Key Technology For Dry Screw Vaccum Pump With Internal Compression

Dry screw vacuum pump is a kind of vacuum equipment.In recent years,the development of vacuum pump has been increasingly confined by application occasions of vacuums,and the traditional vacuum systems,which cannot meet the clean,oil-free and corrosion-resistant requirements,is gradually being replaced by oil-free vacuum cleaner.Dry screw vacuum pumps belong to this type of vacuum pumps,among which the inner compression screw vacuum pumps can significantly reduce the driving energy.With China's active promotion of energy saving and environmental protecting requirements,it becomes a trend to develop dry screw vacuum pump that can achieve energy conservation.Screw vacuum pump is a non-contact type dry pump,whose core element is a Pair of screw rotors with meshing clearance.The performance of Paired screw directly affects the performance and competitiveness of the whole screw vacuum pump.Therefore,theoretical and experimental researches on the structure of Paired screw provide a theoretical basis and designing basis for the research and development of dry screw vacuum pump,which is of great practical value and theoretical significance.The ideal working conditions for screw vacuum pumps require less stages,high pumping speed and low operating power consumption.It is difficult to realize the traditional screw vacuum pumps that transport air with equal volume in practice.In order to solve these problems,this Paper,based on the sealed type profile,proposes a three-segment internal compression screw rotor.It generates a new idea,by ensuring a larger amount of intake air inlet to upgrade pumping caPacity,gradient compression with smooth transition to enhance the effectiveness of compression,and transporting air with equal volume of the rear to guarantee limit pressure.Simulation and experimental study of screw vacuum pumps within compressed screw vacuum pumps under the guidance of the idea are carried out.In this Paper,the research content and results are as follows:Chapter I presents the background,purpose and significance of the research;it also gives an overview of the development history and research status,current problems as well as the trends of dry screw vacuum pump at home and abroad;besides,it presents the main objects and contents of this thesis.Chapter II analyzes the existing four common kinds of screw end face profiles and reveals its sealing characteristics as well as the advantages and disadvantages.It establishes end face profile design theory for conjugate screw rotor,which can be used for any type of twin-screw rotor profile designed to exPand the existing profile inadequate analysis and improvement.According to design criteria of screw rotor's end face profile,a strict sealed-type screw rotor's profile is established,which builds the foundation to establish a Pair of screw engagement model and internal compression screw rotor.Chapter III reveals operating characteristics of existing types of internal compression screw vacuum pumps and proposes a design method for three-segment compression screw rotor with smooth transition.A reduced-stage screw rotor,with three-segment internal compression volume and gradual-changing increment,is designed.Self-balancing screw rotor with internal compression is constructed,and self-balancing screw rotor optimization design model is established.This chapter also lays the foundation for the comParison and analysis of different screw vacuum channels,and for the research on reduced-stage screw vacuum pumps.In chapter IV,based on the basic assumptions and the mass conservation law,aperture flow coefficient method with isentropic flow is proposed to calculate the mass flow,and the working process model of screw vacuum pumps is established;based on common channels,connection topology of working cavity chamber is constructed and minimum gap area calculation method of four channels is put forward.Also in this chapter,a discrete,multi-stage model of screw vacuum pump with seal-shaped whirlpool is constructed,and the calculation model with multi-stage screw vacuum pump working characteristics is also proposed.In chapter V,according to the test standards,the operating characteristics test platform of the screw vacuum pump is established;at the same time,the operating characteristics of the screw vacuum pumps with several different types of profile is simulated and tested,which verified the simulation value is in good agreement with the project value.In Chapter VI,taking the factors affecting the operating characteristics of previous chapters into consideration,the Paper designs and development screw vacuum pumps with three segments gradient screw rotors and variable pitch screw rotors.Pumping speed and power consumption with different inlet pressure of the screw vacuum pumps are simulated and tested,and the curves of operating characteristics have been drawn.The efficiency of the two types of pumps is more than 85%,and saves more than 40% energy under the working pressure of 10000 Pa below,compared with costant pitch screw vacuum pump,which's pumping speed is equal to the two pumps,among which the three sections and gradient screw vacuum pumps obtains more than 33% energy conservation under full pressure range.In Chapter VII,the research contents of this thesis are summarized and the further study is proposed.