Research Of Hydrodynamic Lubrication Mechanism And Optimization Of Pump Water-lubricated Bearings

Nowadays,energy saving,environmental protection and innovation have become the focus of national strategy.Using water instead of mineral oil as lubricant has become a trend.Water-lubricated bearing used in pumps has become a hot topic especially in equipment and device used in water environment operation due to its green,low cost,compact structure,easy to maintenance and sustainability.At present,although there are many domestic and foreign experts studying water lubricated bearing materials and lubrication characteristics,the hydrodynamic lubrication mechanism,loading characteristics and structure design and optimization of water-lubricated bearings are still immature.Water has the shortcoming of low viscosity,easy cavitation,etc,the pump water-lubricated bearings easily operate under boundary lubrication and mixed friction based on the practical experience or the oil-lubricated bearing design theory and can not meet the life and reliability requirements.Thus,it is very important to study the theory of lubrication mechanism,structural design and optimization of hydrodynamic water-lubricated bearings.Considering the physical characteristics of water and based on the lubrication theory,this paper studies the influence of pump water-lubricated bearing structure parameters and operating conditions on the hydrodynamic lubrication mechanism and loading characteristics by both numerical calculation and experiments,and forms the law for the structure design and optimization of pump water-lubricated bearings under common conditions.Finally,according to the practical working condition of the guide bearing in horizontal axial flow pump 500ZWB-4,the hydrodynamic water-lubricated guide bearing is designed.A PTFE based composite suitable for the water lubricated bearing is developed and the design rationality of the water-lubricated bearing are verified using the special water-lubricated bearing test rig under the bearing immersed directly in the water and the bearing supplied by water.This study includes the following four aspects:(1)Based on the theory of computational fluid dynamics,the numerical simulation method for hydrodynamic water lubrication is investigated,and the numerical calculation method is verified by experiments.This method considers the physical characteristics of water as lubricants including the cavitation effect and the flowing state,and it can analyze the hydrodynamic lubrication characteristics of water lubricated bearings effectively by proper mesh generation.(2)The influence of clearance,length-to-diameter ratio,diameter and structure of water grooves on the lubricating characteristics of hydrodynamic water-lubricated bearings including eccentricity ratio,the minimum film thickness,pressure distribution and hydrodynamic friction coefficients are studied.Through conducting a large number of numerical analysis and analyzing the numerical results,the design reference to diameter selection of the pump hydrodynamic water-lubricated bearing under normal operating conditions is given.The influence of bearing structure on bearing hydrodynamic lubrication characteristics and the design reference to bearing diameter selection can accelerate the design and optimization of pump water-lubricated bearings.(3)The influence of working conditions of water-lubricated bearings on the bearing lubrication characteristics including eccentricity ratio,the minimum film thickness,pressure distribution and hydrodynamic friction coefficient are studied.The intrinsic relationship among bearing eccentricity ratio,bearing structure parameters,operating conditions,water physical parameters and hydrodynamic lubrication characteristics are revealed.The relation curves of water-lubricated bearing eccentricity ratio with hydrodynamic load-carrying characteristics(Sommerfeld number)for bearings with L/D = 0.5,0.75,1.0,1.25 and 1.5 are given.The influence of bearing operating conditions on hydrodynamic lubrication characteristics and the relation curves of bearing eccentricity ratio with hydrodynamic load-carrying characteristics can aid the design and optimization of pump water-lubricated bearings quickly and effectively.(4)Using the design rules and reference curves of hydrodynamic water-lubricated bearing obtained in thepaper and optimizing structure of water grooves with the numerical method,the hydrodynamic water-lubricated bearing used in horizontal axial flow pump(500ZWB-4)are designed.A PTFE based composite modified by PEEK and carbon fiber is developed and its mechanical properties and friction and wear behavior are studied.The bearing lubrication characteristics are studied by two test methods using the built hydrodynamic water-lubricated test rig.The friction coefficient and pressure distribution of the bearing are measured using the test method with the bearing immersed directly in the water;the eccentricity ratio and the water film distribution of the bearing are measured using the test method with and the bearing supplied by water.Finally,the design rationality of the water-lubricated bearing is verified.