Prepation And Characterization Of Cu/graphite Friction Materials

Cu/graphite friction materials has been widely used in brake and clutch device due to its better braking effect and compresive performance. Different preparation technology, composition and the ratio of components, the performance of Cu/graphite friction material is different. In order to explore the influence of process parameters on the material, this article is based on wet mixing process,using vacuum heating-press sintering, prepared Cu/graphite friction materials,characterized of the microstructure of materials, and studied influence of the mixing process, graphite content, chromium content on the mechanical and friction and wear behavior, and according to the results to analysis the friction and wear mechanism, and then explored Cu/graphite friction material performance by adding foam copper.First of all, in the process of wet mixing, as wet mixed media,the addition of kerosene has greater effects on the structure and properties of materials. According to the SEM characterization of materials found that, with the increase of content of kerosene, the mixed powder particle size increases gradually, particle shape gradually turned long strip into a ball. The material performance tests show that the more content of kerosene, the lower the mechanical properties of sintered specimen,the larger friction coefficient, but have less effect on the rate of wear rate, the wear rate have slightly rising trend in general. By comprehensive comparison, we found that when the content of kerosene is between 5 %~8 %, components were well-mixed, the materials have good comprehensive performance. In addition, the mixing time also can produce some influences on the properties of materials, as the extension of mixing time, particle size increases at first then decreases, and the surface coarse degree was decreased.the density, hardness, strength of sintered specimens also showed a trend of increases at first then decreases in performance which is same as the influence of mixing time for the particle size. For the friction and wear performance, mixing time and the friction coefficient along with the change of velocity is larger when the mixing time is longer; For wear rate, with the increase of mixing time, the wear rate increased slightly. The performance of the sintered samples analysis shows that the mixing time in 4~8 h is more reasonable.Then, the content of different materials is also the important factors influencing the material performance, which mainly includes artificial graphite,chromium and copper foam material. In order to explore their effects on the material, respectively test the corresponding mechanical, friction and wear properties of the materials and do SEM analysis. When the graphite content increased from 10 % to 19 %, compression and shear strength of the sample havefallen by half, yielding strength and elongation decreases; With the increase of graphite content, the coefficient of friction decreased, and the more graphite content, the lower decrease amplitude and the smaller change with speed. Wear rate have slightly complex relationship along with the change of graphite, elevated with the increase of the content reduced first. Chromium have little effects on the mechanical properties of the material, when the content is increased from 1 % to7 %,the mechanical properties of the sintered samples slightly increased but increased little. For the friction and wear performance, with the increase of chromium content, the friction coefficient increased, and wear rate decreased. In addition, compared with materials without copper foam found the mechanical properties of the sintered samples with copper foam decreased and the friction coefficient, wear rate increased.The friction mechanism of materials related to the change of the friction velocity, when friction velocity is low,the wear is mainly abrasive wear and adhesive wear; When the friction is at high speed, the wear is mainly oxidation wear.