Abstract
Composite friction materials used in the braking system of vehicles are composed of different ingredients (typically up to 20 materials). The overall physical properties of these products are determined by the type and percentage of the individual ingredients in the final composition and consequently, may differ from one product to another. This paper studies the cure characteristics of railroad composite brake blocks during compression molding. Numerical simulations using the control volume/finite element method (CV/FEM) are utilized to predict temperature fields and cure conversion during the process. As railroad brake blocks are normally thick-sectioned parts, a three-dimensional modeling routine is developed. The model combines heat conduction and mass balance equations employing an appropriate cure kinetics equation. The required material data for the numerical simulation is obtained experimentally for a brake block available commercially. The effect of processing parameters and material properties on cure is studied by performing numerical simulations for different molding conditions and materials with different thermophysical properties. The effect of the heat of reaction on the thermal events of cure is also investigated using the numerical simulation in absence and in presence of that parameter, and assuming different values. For a rubber-based friction material, temperature distribution and molding time are not influenced by the heat of reaction released during cure. Moreover, the results indicate that the thermophysical properties of the brake blocks are much more effective than molding conditions in reducing the cycle time. Since the thermophysical properties are governed by the ingredients of the friction material, these properties can be improved in the formulation designing stage by including the appropriate ingredients. The results obtained by numerical simulation can be helpful to the designer of the compound, in order to achieve a brake block with both good braking performance and suitable processing properties.
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