Oriented Preparation Technologies And Tribological Performance Of Hard Magnetic Brake Friction Material For Automobiles

As the most important component material of the automobile brake,brake friction material's tribological properties can affect the vehicle braking reliability and even the safety of drivers as well as passengers.Many factors affecting the friction and wear properties,but the most fundamental factor is the inherent performance of friction materials.Recently,our research group has carried out a lot of basic research in the field of new functional friction materials.A variety of high-performance automotive magnetic friction material formulations have been developed for improving the effectiveness and reliability of friction braking.However,the research on preparation technologies of magnetic friction materials is insufficient.Using the traditional preparation technology is inefficient to make full sue of beneficial functions of magnetic components.Consequently,the research on the preparation and tribological properties of magnetic friction materials has great theoretical values and practical significances for further improving the performance of brake friction materials and developing the friction braking technology controlled by the magnetic field.The magnetic orientation technology was introduced into the traditional preparation process of organic friction materials in this paper.The orientation preparation process of hard magnetic brake friction material was designed and optimized.The effects of magnetic orientation on the tribological and magnetic properties were studied.Firstly,the formular of hard magnetic brake friction material for automobiles was determined based on the patents proposed by our research group.The preparation process based on magnetic orientation was designed:mixing,magnetic orientating,hot pressing,heat treating,cutting and magnetizing.The performance testing methods were researched,and the orientation mold as well as multipoint magnetic measuring device based on hall sensors were designed and established.Secondly,the surface modifications of anisotropic NdFeB magnetic powder and nano Fe₃O₄were carried out by KH-550 silane coupling agent,and the preparation process parameters were set by uniform design method.The standard tribological tests were carried out after preparations of brake pad samples.Fuzzy comprehensive evaluation?FCE?and analytic hierarchy process?AHP?were applied to optimize different process parameters,and the sample optimal process parameter was determined.The mathematical relationship model between tribology properties and preparation process was fitted by SPSS software,and the theoretical optimal parameter were solved by MATLAB software.After comparing tests of tribological properties,the actual optimal process parameters were determined as:35minutes of mixing time,350V of orientation excitation voltage,180?of hot pressing temperature,20MPa of molding pressure,6 minutes of pressing time.Thirdly,the influence law and mechanism of orientation magnetic strength and direction on tribological and magnetic properties of hard magnetic brake friction materials were studied by the orientation preparation tests under different magnetic field parameters,and standard tribological tests as well as microanalysis tests.It was found that with the increasing of orientation magnetic strength in a certain range,both remanence induction intensity and friction stability were increased,while the wear rate were decreased.The excessive orientation magnetic strength increased the magnetic agglomeration and worsened tribological properties,while the magnetic orientation with variable direction could break the magnetic agglomeration effectively and improve the tribological properties.Lastly,braking tribological properties of the hard magnetic brake friction material for automobiles were studied by single and repeated simulation braking tests under different initial braking speeds and pressures.The results showed that the hard magnetic brake friction material prepared in this paper has good adaptabilities in different speeds and pressures;it can maintain suitable and stable friction coefficients and low wear rates during the braking process;it can adapt to the extreme braking conditions such as repeated braking at high initial braking speed.