Study On Lubrication Mechanism Of Micro-nano Magnetic Liquid At Solid-liquid Interface

The wear caused by friction process on the surface of mechanical parts can directly affect its working performance or even result in the failure of the mechanical equipment.Micro-nano magnetic fluid,a type of new lubricant,can effectively ameliorate problem of friction and wear on the surface of mechanical parts,and improve its lubrication performance to keep the equipment operating stability,because it possesses both fluidity of liquid and magnetism.As the main loading part of rolling mill,the running stability of hydrodynamics bearing directly influence working performance of rolling machinery.At the high speed and heavy load working conditions,the rising temperature of oil film can lead to declining of lubricant viscosity.At this time,lubrication method changes from hydrodynamic lubrication to boundary lubrication or even dry fiction,which would cause failure of Babbitt bush such as plastic flow,scratch,creep,wear and desquamate.These situations have a strong impact on running stability of hydrodynamics bearing and can decrease the service life of the bearing.Micro-nano magnetic fluid can effectively solve these difficulties because of its great lubrication characteristics and controllability.And with the external magnetic field,the viscosity is greater,the load capacity is larger and the wear is slighter,so it can generate continuous oil film in the load area.It’s very important to stable running of hydrodynamics bearing with high speed that the lubrication mechanism of micro-nano magnetic fluid is explored deeply.Magnetic fluid can effectively improve wear of bearing bush,and it can effectively extend the service life,decrease bearing’s failure rate and improve the productivity of relative equipment.In this paper,the hydrodynamics bearing lubricating with micro-nano magnetic fluid is studied as follows:Firstly,aiming at the external magnetic field,three external magnetic flied models,permanent magnet,Helmholtz coils and solenoid,are designed.A solenoid is manufactured as the external magnetic flied in this paper,and the distribution of magnetic intensity is studied by method of combining theory calculation and experimental measure.The mathematic model of magnetic intensity generating by a solenoid is deduced according to Biot-Savart Law.The mathematic model is validated by measurement experiment.The results showed that solenoid is reasonable to apply as external magnetic field,and its theory works.The largest magnetic intensity is in the lubrication area of hydrodynamics bearing,which is benefit for the bearing.Secondly,correlative lubrication experiments of hydrodynamics bearing are done.Based on chemical coprecipitation method,three ferrofluid are prepared with different concentration.The magnetic particles are Fe₃O₄,disperser is oleic acid and base oil is S-320.According to the above successful fluid,experimental measurement of viscosity is done to analyze the influence of oil-film pressure,temperature and magnetic intensity on viscosity.The results show that magnetic intensity can counteract the negative effect of temperature on viscosity in some extent.And with the external magnetic field,the influence of oil pressure on viscosity is greater.But viscosity is hardly affected until magnetic fluid reaches magnetic saturation.This part provides datas for the next dynamics simulation.Finally,the lubrication mechanism of micro-nano magnetic liquids at solid-liquid interface are studied by comparing two lubrication processes,traditional oil sliding against Babbitt and FF sliding against Babbitt,using molecular dynamics simulation.According to actual condition of hydrodynamics bearing,the correlative working parameters of the two different lubrication systems are set.And Forcite tool is used to calculate the sliding simulation of two lubrication system.The results showed that the friction coefficient of Babbitt decreases about 50%under FF lubrication.Besides,FF has superior physical and chemical properties and its structure is more stable due to stronger valence and van der Waals interactions.In addition,FF has greater heat dissipation ability.