Preparation And Study Of Mullite Fiber Reinforced Paper-based Friction Material

Since entering the new century, the sustainable development of economy and technology has improved the people’s living standard, which makes people have higher requests to automobile performance including higher security and more good comfort, so the wet paper-based friction materials in automotive clutch must have higher friction performance. How to improve heat resistance and the friction stability of the materials, and prolong the service life of the materials has become the main research questions of paper-based friction material. Therefore, the purpose of the paper is preparing paper based friction material with a high friction coefficient, low wear rate and long service life, and it mainly research the tribological performances of mullite fiber and modified mullite fiber reinforced paper-based friction material.Firstly, the paper-based friction materials were prepared by adding the different mullite fiber content(30%, 40%, 50% and 60%) into the materials. The results showed that the interfacial pore number of paper-based friction material gradually increased, and friction torque curve became stable, and the friction coefficient and wear resistance were greatly improved with the increase of mullite fiber content. But as the mullite fiber content was 60%, the friction coefficient decreased, and wear resistance and braking stability became worse due to the large number of fibers fracture and debonding. When mullite fiber content of the friction material was 50%, the material had the best friction and wear performance.In order to further study the influence of mullite fiber on paper-based friction materials, the different length of mullite fibre(100um, 500 um and 900um) were added respectively into the materials to research the influence of fiber length on friction properties of the materials. The results showed that when the mullite fiber length is 100 um, the surface of the material is compact, and the pores of friction surface was less, and the friction coefficient and wear resistance were lower than the 500um; when the mullite fiber length is 900 um, mullite fibers easily bridged each other, and the surface of the material had a large number of pore structures. The bridging fibers were easily broken and debonded by the shear force during the braking process, which resulted in high wear rate of the material. When the mullite fiber length is 500 um, the pore number of the material surface was suitable, and thermal resistance of the material was the best than others, and the material surface structure can keep more stable, and friction coefficient and wear resistance was best.Finally, in order to solve the debonded problem of mullite fiber, the mullite fiber modified in different preparation temperature and time were added into the materials to study the effect of the modified mullite fiber on friction and wear properties of the friction materials. The results showed that the methyl acrylic acid coverage amount of mullite fiber surface gradually increased, and the material interface bonding performance improved, which brought about the increase of friction coefficient and wear resistance, as the modified temperature of mullite fiber gradually increased. When the modified temperature exceeded 75℃, the covering amount of the methyl acrylic acid decreased, and the material interface bonding performance weakened to lead to the decreasing of the friction coefficient and wear resistance. When the modified temperature was 60℃, the material had the highest friction coefficient and the lowest wear rate than others. Meanwhile, it is also found that the methyl acrylic acid coating amount of the mullite fiber surface gradually increased, and the surface of the material gradually became dense, which brought about the increase of interfacial bonding strength, the friction coefficient and wear resistance of the material, as the modified time prolonged. But when the modified time is over 60 min, the density and pore number of the material surface reduced to cause the increase of wear rate and the decrease of the friction coefficient. Therefore, when the modified temperature and time of mullite fiber was respectively 60℃ and 60 min, the paper-based friction material had the best friction and wear performance.