Frikční kompozity používané v brzdových systémech osobních automobilů a jejich modifikace při třecím procesu

Abstract

Friction composites (FC) in brake linings are very important part of brake systems in cars. They affect their frictional characteristics as they are modified during the braking process. The aim of the dissertation thesis is to determine reactions between pyrite, molybdenite and stibnite, which are used as solid lubricants and copper and other components of the friction composites. Three sets of FC samples, differing in the content of mentioned sulphides, were prepared and tested in the laboratory. The samples were examined for friction tests in the laboratory equipment for brake linings testing, while the brake discs were exposed to temperatures from 200°C to 500°C or 600°C. The samples were heated at the same temperatures using the muffle furnace as well. The original samples, the friction layer after the mechanical tests and the surface of the samples after heating in the furnace were analysed using XRD, XRFS and SEM / EDX methods. Samples of abrasion dust released during the friction process were collected and further processed. The mixture of the copper powder and the above mentioned sulphides were heated in the furnace at the temperatures from 200°C to 600°C. These powder samples were analyzed using XRD and XRFS methods. It was proved, that the modification of the FC at the friction layer begins to occur at the temperature of 200°C (loss of some components) and at 300°C it leads to the formation of new phases. Oxides of Cu, Fe, Mo and Sb as well as some ternary sulphides (chalcopyrite CuFeS2, bornite Cu5FeS4, skinnerite Cu3SbS3) are created. While heating in the furnace, new phases are formed at temperatures approximately 100°C higher, while the formation of the new phases, e. g. chalcopyrite, occurs only during the friction process. The actual temperature of the friction layer is significantly higher than the measured temperature of the brake discs. Additional effects apply to the braking process as well. Pressure and friction magnify the reaction area and increase the mutual contact between the individual components of the composite.