Design And Experimental Study Of Symmetrical Embedded Magnetic Fluid Rotary Seal

Small size of rotating shaft seal leakage problem widely exists in manufacturing industry,such as carbon dioxide laser,coating machine rotating shaft,their sealing way is mainly rubber seal,packing sealing and other contact sealing methods,but these kind of sealing methods in the dynamic sealing conditions are very easy to lead to seal failure due to friction and wear,resulting in a large amount of leakage,and ultimately affect the reliability of the product.These problems can be avoided with magnetic fluid seals.Therefore,designing a reasonable magnetic fluid sealing structure and preparing a magnetic fluid with strong applicability and applying it to the sealing of small-sized rotating shafts can avoid problems such as reduced reliability and sealing failure of sealing components caused by friction and wear,and can also effectively extend equipment life and improve product processing quality.In this paper,a new symmetrical embedded magnetic fluid seal structure was designed based on the prepared diester-based magnetic fluid by chemical co-precipitation method.The magnetic field simulation of the designed symmetrically embedded magnetic fluid seal structure was carried out using the finite element method,and the influence of the seal gap and the number of pole teeth on the pressure resistance of the symmetrically embedded magnetic fluid seal was revealed.The theoretical pressure resistance values of the symmetrically embedded magnetic fluid seal and the common magnetic fluid seal with the same parameters are calculated according to the magnetic fluid seal pressure resistance theory,and the effects of the volume of the magnetic fluid,the sealing clearance and the number of pole teeth on the pressure resistance of the symmetrically embedded magnetic fluid seal are investigated by experimental methods and compared with the theoretical pressure resistance values.The main work of this study was as follows:（1）Based on the theory of chemical coprecipitation,Fe₃O₄magnetic nanoparticles and Fe₃O₄diester based magnetic fluids were prepared with Fe Cl₃·6H₂O and Fe Cl₂·4H₂O as raw materials.The results show that the Fe₃O₄magnetic particles are cubic spinel structure,the magnetization can reach 77.93 emu/g,the particle size distribution is uniform,and the main distribution range is 10 nm～20 nm;The saturation magnetization and viscosity of the Fe₃O₄diester based magnetic fluid after double coating increase with the increase of the mass fraction of magnetic particles.When the mass fraction of magnetic nanoparticles is 25%,the viscosity is 25.8 m Pa·s,and the saturation magnetization is 25.3 emu/g.When the content of magnetic nanoparticles is 40%,the viscosity of magnetic fluid is 33.6 m Pa·s,and the saturation magnetization reaches 31.5 emu/g（2）Based on the prepared diester-based magnetic fluid,a symmetrical embedded magnetic fluid seal structure was proposed and designed.The magnetic field finite element method was used to simulate the symmetrical embedded magnetic fluid seal structure and to determine the optimum pole tooth height of 1 mm and the optimum pole tooth width of 0.3 mm for the seal.（3）A combination of numerical simulation and experimental research was used to study the effects of magnetic fluid volume,number of pole teeth,sealing clearance,and rotational speed on the pressure resistance of symmetric embedded magnetic fluid seals.The results were compared with the theoretical pressure resistance values of ordinary magnetic fluid seals under the same parameters.（4）The experimental results show that the experimental pressure resistance of the symmetrically embedded magnetic fluid seal is in good agreement with the theoretical pressure resistance.When the number of teeth increases,the pressure resistance of the symmetrical embedded magnetic fluid seal increases;when the seal gap increases,the pressure resistance of the symmetrical embedded magnetic fluid seal decreases.when the radial seal gap and the axial seal gap are both 0.1 mm,the pressure resistance is the strongest,and then drops sharply;When the number of radial pole teeth is 2,the number of axial pole teeth is 6,the radial seal gap and axial seal gap are 0.1mm,the seal pressure resistance increases with the increase of the magnetic fluid injection volume,when the magnetic fluid injection volume reaches 0.2 m L,the pressure resistance value no longer increases,then the magnetic fluid injection volume reaches the saturation value;If the rotation speed of the rotating shaft is less than 600 rpm,the pressure resistance capacity of the symmetric embedded magnetic fluid rotating seal is not affected by it,and can be regarded as a static seal;The experimental and theoretical pressure resistance values of the symmetrical embedded magnetic seals are much higher than the theoretical pressure resistance values of the ordinary magnetic seals with the same parameters,which fully reflects the superiority of the symmetrical embedded magnetic seal structure.