Development And Performance Study Of New Magnetic Grease

Since the 21st century,China’s shield technology has been developed from scratch,and shield machine is widely used in large tunnel excavation as an infrastructure tool,which is a high-tech equipment integrating optical,mechanical,electrical,hydraulic,sensing and information technology.The main drive lubrication place,articulation place and shield tail sealing performance are key problems to ensure the normal operation of the shield machine,of which the main bearing seal is the most important.This thesis is a research project on magnetic grease based on the sub-project"Research on new materials and methods for main drive seal of tunneling machine"of the National Key Research and Development Program.Based on the design of split flap type induction tooth magnetic liquid seal for main drive bearing of shield machine proposed by the group in the early stage,the thesis is based on the research of new materials and methods of magnetic grease.For the above mentioned problems of EP₂greases used in the main bearings of shield machines during the tunneling process,which have high consumption and cannot be reused because of mixed impurities,a new type of grease is developed to solve the problem of waste of original materials in order to make the shield project have better economy.The main work of the thesis includes:（1）Nanoscale magnetic particles Fe₃O₄@Si O₂ with a core-shell structure are prepared by chemical co-precipitation method,and the prepared magnetic nanoparticles are characterized in a diversified manner,which included infrared spectroscopy,X-ray diffraction,transmission electron microscopy and vibrating sample magnetometer analysis.The results show that the magnetic particles prepared in this paper form a core-shell structure with a specific saturation magnetization intensity of 47.18 emu/g and are superparamagnetic.（2）The Fe₃O₄@Si O₂ nanoscale magnetic particles are mixed with EP2 grease in2:10,4:10,6:10,1#,2#and 3#magnetic grease samples are prepared and their performance are characterized,including the analysis of stability,magnetic performance,rheological performance,extreme pressure performance and exclusion performance of magnetic grease,the magnetic grease has viscoelastic property similar to magnetorheological plastic body,linear viscoelastic zone is between 0～0.1%;the extreme pressure performance of the grease used in this paper is PB=63kgf,which meets the requirement of PB≥60kgf for shield machine grease,and the extreme pressure performance of 1#sample meets the requirement.（3）Using the magnetic field simulation module and erosion model of COMSOL Multiphysics finite element simulation software,simulation of magnetic field and erosion of the wear experimental device developed by our group are carried out,also the conducted wear experiments on the prepared magnetic grease with different mass fractions are carried out,the results show that with the increase of speed,the erosion range gradually becomes smaller and forms concentrated pitting,the overall wear is small,but the micrometer level wear can be measured by micrometer,and the wear of magnetic grease on the contact surface under normal working condition will not lead to seal failure.