Study On Thermal-magnetic Coupling Lubrication Characteristics And Mechanism Of Magnetorheological Grease

Magnetorheological grease(MRG)is a kind of smart material whose rheological properties respond quickly and change reversibly under the action of magnetic field.It is usually prepared by magnetic particles uniformly dispersed in grease matrix.MRG is similar to grease in the absence of magnetic field,which can effectively overcome the traditional magnetorheological fluid(MRF)settlement and leakage problems.When a certain magnetic field is applied,the magnetic particles in the MRG form a chain structure with a certain yield strength along the direction of the magnetic field.The structural strength of the MRG is enhanced.Because of the controllable rheological properties of MRG.It has great application prospects in the field of lubrication behavior control of friction pairs.However,friction is inevitably accompanied by temperature rise effect,and the MRG based carrier fluid has significant heat flux effect,which makes its application in the field of controlled lubrication facing challenges.At present,the research on MR lipids mainly focuses on the optimization stage of the preparation process of MR lipids.Which lacks the characterization of frictional properties and rheological properties under thermal-magnetic coupling conditions.Therefore,it is difficult to provide theoretical basis for reliable service of MR lipids as lubricating medium under wide temperature range conditions.In this study,a new type of nano-sized MRG was prepared using nano-sized manganese ferrite material as magnetic particles,and then a method of adding magnetic source to the MR device was proposed according to the contact form.Then,the thermal-magnetic coupling lubrication characteristics of the MRG were studied for the ball-plate contact form.Finally,the thermal-magnetic coupling rheological test was conducted for the MRG combined with the tribological test results.Specific research contents and conclusions are as follows:(1)Nano-sized manganese ferrite particles with superparamagnetism were selected as magnetic particles of MRG by vibrating sample magnetometer.Their particle size and shape were characterized by transmission scanning electron microscopy.Nano MRG with different mass fractions of magnetic particles was prepared by mixing the nano magnetic particles with grease,heating and stirring.(2)Taking ball bearings as point contact model samples,roller bearings as linear contact model samples.And plain bearings as noncontact model samples.The idea of placing permanent magnet rings on the structure of MR lubricated bearings was proposed,through which discrete magnetic fields were generated to form magnetic loops in the bearing structure.The structural model of MR lubricated bearings was designed.The magnetic field strength is analyzed numerically according to the contact position in the contact model.The distribution of oil film pressure,temperature and magnetic field under different eccentricities of the noncontact model was further explored.(3)The design and construction of the friction test bench were completed according to the requirements of the thermal-magnetic coupling working conditions.The feasibility analysis was carried out on the thermalmagnetic coupling requirements of the friction test bench by combining the software with the test.Then,the contact friction test of the thermalmagnetic coupling reciprocating ball plate was carried out with the MRG as lubricant.The lubrication performance of MRG under thermal and magnetic coupling was investigated.(4)Magnetic field scanning and rate scanning of MRG under the action of thermal-magnetic.Study to coupling were carried out the changes of the rheological parameters of MRG at different temperatures and magnetic field intensities.Then,Herschel-Bulkey rheological model was used to obtain the shear yield stress value of MRG by means of data fitting.Finally,the variation law of shear yield stress with the increase of magnetic field intensity was explored.This article establishes a new lubrication method that utilizes magnetic field regulation to weaken the influence of temperature.Provide technical support for the development of lubricants in aerospace,highspeed railway,and other fields.The research results provide a new idea for lubrication design under wide temperature range conditions.