Optimization of automotive brake lining material and processing

Application of asbestos in automobile brake lining gives a satisfactory friction characteristics from point of view of vehicle dynamics. However; asbestos is considered a probable cause of some carcinogenic effects. Accordingly; the objective of this work is to improve the brake lining characteristics both from point of view of health hazards by minimizing the asbestos content and from point of view of automobile brake stability requirements by using the most suitable constituents and processing conditions. To achieve this goal an experimental work has been conducted through which 95 different samples of brake lining were tested and analyzed. These samples were prepared with different percentages of asbestos content at different processing conditions. The samples were then examined using the Friction Assessment and Screening Test machine (FAST) which gives the change of friction coefficient, temperature, and wear rate during a test period of 90 minutes for each sample. Analysis of the experimental results shows that it is possible to decrease the asbestos content in the brake lining by 30% (from 50% to 35%) while obtaining improved lining friction and wear characteristics under suitable processing conditions: hot molding (pressure of 160 bar, temperature of 150 degrees C, and molding time of 1.0 min./mm. thickness) and post curing (temperature of 150 degrees C and time of 2 hrs.). Replacing of the 5% copper by 5% aluminum chips of grain size less than 150 microns showed satisfactory results. Application of these results to produce an actual disk brake lining and testing it using a dynamometer that simulates the different regimes of automobile braking shows a satisfactory stable performance.