Optimal vulcanization of 2D-3D EPM/EPDM thick elements through peroxidic mixtures

In the present paper, a numerical procedure for the optimal vulcanization of 2D and 3D thick rubber elements by means of peroxides mixtures is presented. When dealing with the curing process of thick EPM/EPDM items, the main problem in industrial practice is constituted by the different temperatures which undergo internal (cooler) and external regions. Indeed, while internal layers remain essentially unvulcanized, external coating is always over-vulcanized, resulting in an overall average tensile strength insufficient to permit the utilization of the items in several applications where it is required a certain level of performance. A possibility to improve rubber output mechanical properties is the utilization of mixtures of at least two peroxides, one highly active at high temperatures (i.e. for external layers), the other at lower (internal regions). In this framework, a genetic algorithm with zooming and elitist strategy is adopted for the determination of optimal input parameters to use for the production of complex 3D/2D thick items. Vulcanization external temperature T (c) , rubber exposition time t and different peroxides mixtures are assumed as input production parameters, whereas output mechanical property to optimize is represented by the average tensile strength of the item. The GA approach proposed exploits a zooming-elitist strategy, consisting in the subdivision of the population at each iteration into two sub-groups, depending on individuals grade of fitness. Two meaningful examples of engineering interest, consisting of a 3D thick rubber docks bumper and an extruded (2D) relatively thick wheatear strip are illustrated, using different mixtures (50-50%, 25-75% and 75-25% molar ratios) of two peroxides. Optimal production T (c) and t parameters are obtained for all the cases analyzed. Numerical simulations show how different mixtures of peroxides may (a) reduce optimal curing time at almost constant optimized tensile strength or (b) increase optimal tensile strength with an acceptable increase of the curing time.