| In recent years,maglev train develops rapidly and has a broad prospect.The braking system is the key technology of maglev train,which ensures the speed,safety and comfort of maglev train.Abnormal loss of brake lining appears during the actual operation of maglev train.Specifically,the short use time of the brake lining,frequent replacement and the friction contact surface of the brake lining has groove damage traces,and the surface is rough.In order to solve the problem of abnormal wear of maglev train,it is necessary to carry out the optimization research of maglev train brake lining.In this paper,according to the normal service conditions of maglev train brake lining,the friction and wear properties of the existing gate materials at different speeds are tested including low speed uniform velocity test(simulating conventional braking)and high speed braking test(simulating emergency braking).By means of metallography,surface morphology and elemental composition,the surface analysis of brake lining was carry out,the mechanism of abnormal wear of the brake lining was deduced and analyzed,and the optimization scheme of brake lining material was proposed.According to the test results of brake performance,the formula technology without abnormal wear was screened out and the 1:1 real size brake lining test was carried out.Secondly,the brake lining/rail mechanical braking form of maglev train is a typical friction pair under the magnetic field environment,so the influence of magnetic field strength on the friction and wear properties of the brake lining material /Q235 steel was also studied in this paper.Finally,in order to establish the relationship between a magnetic field--abrasive oxidation and adsorption--the dry friction and wear performance,explored the mechanism of magnetic abrasive dust adsorption in dry friction and surface oxidation mechanism.A kind of abrasive collecting device was designed.The most typical 45 #carbon steel in the study of magnetic field dry friction was set as friction pair,the influence of the abrasive collecting device to magnetic field of friction was analyzed,the quantitative analysis of wear debris was also carried out.According to the above tests and analysis,the following conclusions are drawn:1.The abnormal wear of the maglev train occurred in the uniform friction test condition below 6km/h,and the surface adhesion of brake lining and Q235 disc was serious.In the speed range of 6km/h to 12km/h,the existing brake lining produced temporary abnormal wear in the early and middle stages of friction,but the continuous test of the brake lining runs well and gradually stable,and no serious wear occurs.A stable friction state was maintain in the friction process above 12km/h(20km/h for uniform speed test and 100km/h to 140km/h for initial braking speed).2.Abnormal wear of brake plate for maglev vehicle mainly occurs in the process of low speed braking,and its mechanism of abnormal wear was analyzed as follows:At the beginning of the friction process,the carbon film is gradually consumed.When the carbon film is exhausted,the grinding phase(chromium)particles in the brake lining material are larger,which agglomerate and stick to the surface of Q235 brake disc in the friction process,forming a small bulge.Under the condition of low speed braking,the friction heat is small and the surface temperature is low.At this time,the hardness of chromium is high and it adheres to the surface of Q235,which produces cutting effect on the brake lining and causes abnormal wear of the brake plate.3.In this study,the low speed friction and wear test and high speed brake friction test were carried out on 12 brake lining formulations.The final results show that when the wear enhancing phase(chromium)is replaced by alumina,the brake lining sample has no abnormal wear,and the brake performance test results are the best.The final bench test results show that the low speed test results of the optimized brake plate meet the expectations,which can maintain low wear and stable friction coefficient without damaging the disk surface.However,after the speed is increased,the abnormal wear problem of the magnetic levitation brake plate was basically solved.4.In the magnetic field,the friction and wear properties of the existing brake lining materials at different velocities in low-speed and uniform tests are tested and compared with the data in the non-magnetic field environment.The friction coefficient of the brake lining material in the magnetic field decreases and the wear rate decreases.As the increase of speed,the friction coefficient of brake material decreases.5.After using the wear debris collection device and weighing 45 steel pins,45 steel plates and wear debris,In the magnetic field,the total mass of the pin,disc and chip after friction is increased compared with that before friction.The incre ased mass is the oxygen content of the chip and surface oxidation fixation.With the increase of magnetic field intensity,the mass and average particle size of the chip produced in the friction process of 45 steel decrease sharply,and the oxidation degree of the debris increases.In the magnetic field environment,the friction system has mass gain due to oxidation,and the wear debris is captured by the magnetic field to form "three-body wear",which repeatedly participates in the friction process and makes the particle size refined.The refined wear debris is repeatedly rolled to form oxide film on the surface,which increases the wear resistance of the material. |
