Theoretical And Experimental Research On Magnetorheological Fluids Seal

Magnetorheological fluid is a mixed solution composed of micron-sized magnetic particle,surfactant and base carrier.The magnetorheological fluid has the fluidity under the action of no magnetic field or weak magnetic field,and is magnetized into a solid-like structure under the action of a strong magnetic field,and has obvious viscoplastic properties.At present,in the large sealing gap,the magnetic fluid seal has a problem of poor sealing,and as the sealing gap increases,the pressure resistance of the magnetic fluid decreases greatly.Based on this,the research of magnetorheological fluid seal is proposed.In addition to the advantages of magnetic fluid sealing,magnetorheological fluid sealing is suitable for large gap sealing,high pressure resistance sealing,has the advantage of long service life and simple processing and manufacturing.The magnetorheological fluid seal relies on a permanent magnet as a magnetic source to generate a large magnetic field gradient in the tiny seal gap formed by the magnetic shaft and the pole piece.Under the action of the magnetic field force,the magnetorheological fluid is adsorbed in the sealing gap to serve as a sealing function.Under the action of weak magnetic field,the magnetorheological fluid forms a liquid sealing ring in the sealing gap formed by the pole teeth and the shaft,which acts as a sealing.Under the action of strong magnetic field,the magnetic particles in the magnetorheological fluid are magnetized into a solid-like structure,and the yield stress of the magnetorheological fluid is significantly increased.In the sealing process,the actual withstand voltage capability of the magnetorheological fluid needs to take into account the influence of the yield stress of the magnetorheological fluid,in addition to the influence of the magnetization pressure.The magnetized magnetic particles form a chain or mesh complex skeleton structure along the direction of the magnetic field,and there will be tiny pores between the structures,and some of the channels forming the pores will communicate with each other.When the sealing medium reaches these pore structures,a slight leak will occur through these tiny channels,causing a drop in pressure in the sealed chamber.At present,the study of magnetorheological fluid sealing does not involve pressure drop and micro-leakage during magnetorheological fluid sealing.The magnetorheological fluid in the sealed gap under the action of a strong magnetic field has the property of a porous medium.Based on this and the theory of porous media,the stress controllability,electromagnetic theory,sealing principle and ferrofluid mechanics of magnetorheological fluid under the action of magnetic field,the theory of magnetorheological fluid seal is found.In practical applications,the factors affecting the performance of magnetorheological fluid sealing are mainly the performance of magnetorheological fluid,the size of the sealing gap,the width of the pole teeth,etc.The magnetorheological fluid sealing structure is determined by considering the above factors.Magnetorheological fluids currently available on the market are generally used in damping,vibration damping and other equipment,and are not completely suitable for magnetorheological fluid sealing.Therefore,the magnetorheological fluid was first developed and characterized in the research process.Secondly,the finite element analysis method is used to analyze the magnetic field of the magnetorheological fluid seal.The magnetic field distribution of the magnetorheological fluid seal structure with or without magnetorheological fluid,different sealing gap and different tooth width is obtained.The theoretical withstand voltage value during the magnetorheological fluid sealing process is obtained.Thirdly,the Fluent module in ANSYS is used to numerically analyze the sealing performance of magnetorheological fluids with different porosity under the action of strong magnetic field,and the result present the pressure and leakage velocity in the magnetorheological fluid seal chamber and the intermediate air region.Then,the experimental study on the magnetorheological fluid seal was carried out,and the static and dynamic sealing performance of the magnetorheological fluid seal under different initial pressures,different sealing gaps and different tooth widths were obtained.It has been found through research that the tooth width has little effect on the magnetorheological fluid seal.During the static pressure sealing process,as the sealing gap and the initial pressure in the sealing chamber increase,the pressure drop rate in the sealing chamber gradually increases.When the pressure in the sealed chamber is smaller than the theoretical withstand voltage caused by the magnetic field force,the pressure in the magnetorheological fluid seal chamber slowly decreases linearly with time;the leak in the sealed chamber increases with the increase of pressure.The rate gradually increases,and the pressure in the middle air region first increases to the maximum and then decreases;when the pressure is greater than the theoretical withstand voltage,the pressure in the sealed chamber and the intermediate air region decreases parabolically with time.Finally,by comparing the theoretical and experimental results,the magnetorheological fluid seal can be simplified into a porous medium model,which can explain the sealing performance of the magnetorheological fluid reasonably,and provide a certain practical application for the subsequent magnetorheological fluid seal.