Driving Shaft Fatigue Analysis And Optimal Design Of ? Type Profile Twin-Screw Pumps

The twin-screw pump has the advantages of stable flow,stable pressure,strong self-absorption ability,high efficiency and stability,and is widely used in petrochemical,shipping,sewage treatment and some other fields.However,due to the complex conveying medium and working atmosphere,the screw pump is prone to be broken by fatigue failure,so the research of driving shaft fatigue analysis have great significance.In this paper,taking the design of the ? type profile twin-screw pump for an oil production and storage system as the applied background,the working characteristics of rotor system of twin-screw pump under rated condition is analyzed and the load model of driving rotor is established.Based on the S-N curve of material used for the shaft obtained from fatigue test,the fatigue property of the driving shaft is analyzed.Furthermore,the optimization design of the shaft structure is carried out in order to improve the reliability of the spindle.The screw rotor profile equation and the three-dimensional model of rotor system are established,and the dynamic balance of screw rotor is optimized.The pressure distribution in the liquid-path of twin-screw pump under the standard running condition is calculated by FLUENT software,which provides data support for load prediction of twin screw pump driving shaft.Considering the gravity,gear transmission,medium pressure,gap flow and other factors,the load model of twin-screw pump spindle is established including axial force and radial force,which lay the foundation for the fatigue analysis and optimization design of twin-screw pump shaft.An axial tensile fatigue test of 05Cr17Ni4Cu4Nb stainless steel is conducted in this paper,and the complete S-N curve of this material is acquired.Then considering the stress concentration,mean stress correction and other factors,the fatigue life of the main shaft made of this kind of material used in the oil production and storage system is analyzed with the ANSYS Workbench software.The result shows that the fatigue life of the shaft meets the requirement.But based on the fatigue reliability design theory,the fatigue reliability of the shaft is only 0.8643.In order to solve the problem of low fatigue reliability of the driving shaft,based on the response surface method and finite element analysis,the structure optimization model of spindle is established.In this model,the spindle diameter,chamfering degree and the shaft extension of power end are selected as optimal variables,the limit value of variables and normal maximum deformation of the spindle are considered as the constraint conditions,and the minimization of the equivalent alternating stress on the spindle dangerous section is taken as the optimization objective.The optimization results show that the quantity of the equivalent alternating stress on the spindle dangerous section reduces by 26.2%,and the quantity of the normal maximum deformation decreases by 25.2%compared with the original design.In addition,the infinite life reliability and fatigue safety factors both meet the design requirements.