Lubrication Analysis Of Contact Pair And Vibration Characteristics Study For Three-Screw Pump

Three-screw pump is indispensable core equipment for high-tech ships,marine engineering,high-end petrochemical equipment and advanced machine tools.Vibration can reflect the hydraulic performance and reliability of three-screw pump,which is a key index to evaluate the advancement of the pump.The technical drawings,production equipment and process of high-end three screw pump in our country are introduced from abroad.However,the low vibration and high reliability three-screw pump products and technologies are tightly controlled by foreign countries,and there is no low vibration design mechanism and relevant standards in domestic.This paper intends to explore the vibration mechanism and sensitive factors of three-screw pump,and provide basic theory for the design of low vibration and high reliability pump.According to the research idea of excitation source,transmission path and vibration response,the lubrication performance of three-screw pump contact pair and pump vibration characteristics were studied.The main contents include:The screw surface equation and contact line equation were derived based on the spatial analytic geometry theory.The time-varying fluid load model of screw working process was constructed.The effects of working length,outlet pressure and center angle of tooth profile on fluid load characteristics were studied by vector algebra method.The results showed that The fluid load and the outlet pressure was linear positive correlation;The fluid load of the central screw was distributed in radial symmetry and canceled out each other.The radial load of driven screw was asymmetric,and the number of mutation changes in one cycle was related to the working length and lead.The fluid load in the three screw axis connection direction was sensitive to the center angle of tooth profile.Fluid load of screw pump could be reduced by selecting appropriate screw design parameters.The hydrodynamic pressure lubrication model of screw bushing was established,and the distribution rule and characteristics of oil film pressure were analyzed.The results showed that the influence of pressure boundary on oil film was mainly in relative negative pressure area.Fit clearance has significant influence on oil film pressure and lubrication property of screw bushing contact pair,which was an important factor affecting lubrication performance of pump.The amplitude and position of the highest oil film pressure were affected by the inclination and deflection of screw.The oil film pressure distribution was more uniform when the screw rotor was inclined at a proper small angle.The elastohydrodynamic lubrication model of the contact pair between the central and satellite screws was established.A two-dimensional hydrodynamic pressure lubrication governing equation with two direction variable velocity and velocity gradient terms in length direction of contact line was derived.An iterative method of load calculation which could consider the effect of the real geometry of the screw contact area on the pressure distribution was proposed.The results showed that the minimum oil film thickness of radial straight chamfering and circular arc chamfering scheme was much larger than that of theoretical profile.However,the maximum pressure was obviously lower than that of theoretical profile.The reason that the radial straight chamfered screw rotor has a longer wear life than the unmodified theoretical screw was explained from the perspective of microscopic characteristics.Based on the hydrodynamic pressure model of screw-bushing contact pair,the effects of the surface texture of bushing,the optimization schemes of elliptical section bushing and circular oil wedge bushing on the contact pair performance were studied.The results showed that the bearing capacity of the oil film could be increased and the contact torque could be reduced by choosing suitable texture parameters.The circumferential bearing capacity of the oil film could be increased and the directivity of each performance could be decreased by choosing elliptical section bushing or circular oil wedge bushing.The screw rotor was more adaptable to the changing load and the rotor stability was enhanced.The experimental device of three-screw pump was developed to verify the hydrodynamic pressure lubrication model of screw bushing contact pair.And the oil film pressure of screw-bushing contact pair and pump vibration characteristics were studied experimentally.The results showed that the vibration characteristics and performance of the pump were significantly affected by rotor dynamics and screw rotor size matching.