Research On Key Problems In Structural Design Of Vertical Screw Vacuum Pump

In recent years,screw vacuum pumps have been paid more and more attention by industry R&D personnel,manufacturers and users.As the screw vacuum pumps is widely used in many fields,the horizontal screw vacuum pump cannot fully meet the need due to its structure,such as lots of impurities working environment or high vacuum cleaning requirements.Although horizontal screw vacuum pumps are not well suited for the above specific environments,compared with other dry vacuum pumps(such as claw pumps,multi-stage Roots systems,and scroll pumps),the screw vacuum pump has a wide pumping range,a compact structure,no friction in the pumping chamber components,and a long service life.Therefore,it is extremely urgent to develop a novel vertical screw vacuum pump to meet the needs.The vertical screw vacuum pump has the advantages of a wide working range,difficulty in liquid deposition,strong ability to remove impurities,easy on-line cleaning and maintenance,etc.It is suitable for vacuum distillation,vacuum separation,material purification,material drying,etc.,which is favored by the pharmaceutical,chemical,petroleum and other industries.Therefore,this paper studies the key issues of the structure design encountered in the development of vertical screw vacuum pump.Firstly,in order to design a screw rotor suitable for vertical screw vacuum pump,four kinds of double-head rotor profiles have been developed.These rotors have self-balancing characteristics,which do not need to be treated like the conventional single-head screw rotor,which increases the stability and ensures the long-term stable operation of the vertical screw vacuum pump.Secondly,the self-engagement characteristics of the four rotors and the sealed characteristics are tested.Finally,the pumping speed of the four double-headed screw rotors are calculated,and the advantages and disadvantages of four double-headed lines are given.The most suitable screw rotor is selected for the vertical screw vacuum pump.Secondly,in order to test the stability of the rotor during operation,the vibration of the single-head and double-head screw rotors have been simulated using Ansys software,which proves that the rotor vibration of the double-head screw is small,and it is more suitable for the vertical screw vacuum pump.Finally,the double-head linear screw rotor adopted in this paper has a smaller volume utilization coefficient than the traditional single-head screw rotor.Therefore,in order to ensure higher vacuum degree,five-stage variable pitch screw rotor can be used to improve the compression ratio.However,at pump start-up stage,the gas in the pump cavity is compressed and the pressure will be higher than the outlet pressure,which will result in high gas temperature and serious compression power.It will also result in the rotor volume expansion leading to the rub between the rotors and the wall which causes the coating peeling,therefore,puts forward the intermediate exhaust valve can be used to solve the large compression ratio screw vacuum pump in the initial operation stage of compression problem.This chapter is put forward to open a vent valve in the middle of the variable pitch screw vacuum pump.Taking five sections of varying pitch of the rotor as an example,after the analysis of rotor structure and pumping process,the thermodynamics related formulas were used to calculate the parameter of gas inside the cavity of the changed with position curve,so as to study the transformation law of thermodynamic parameters.This method can be used to verify whether the intermediate vent valve can effectively solve the over-compression problem and provide a reference for the design of the position of this valve.The results have great technical,social and economic significance for improving the design level of domestic screw vacuum pump,enriching the domestic screw vacuum pump product,increasing the application scope of screw vacuum pump,promoting the application of energy-saving and environment-friendly dry screw vacuum pump products and promoting the energy-saving and emission reduction of manufacturing industry.