Optimization of extrusion production lines for EPDM rubber vulcanized with sulphur: A two-phase model based on Finite Elements and kinetic second order differential equation.

A numerical two-phase approach, based on experimental curometer charts and aimed at predicting the optimal production line parameters (exposition time and cure temperature) for extruded thick rubber items cured with accelerated sulphur is presented. In the first phase, a simple kinetic model based on the actual reticulation reactions occurring during sulphur curing is utilized to fit experimental curometer data. The model is able to predict the degree of crosslinking at successive curing times and at different controlled temperatures and it requires the calibration of only three kinetic constants. The variation of such parameters with temperature is then evaluated by means of three experimental cure curves performed at three different temperatures. Both the case of indefinite increase of the torque and reversion can be handled. In the second phase, considering the same rubber compound of step one, kinetic reaction parameters are implemented in a Finite Element (FE) software, specifically developed to perform thermal analyses on complex 2D geometries. As an example, an extruded cylindrical thick EPDM item is considered and meshed through four-noded isoparametric plane elements. Several FE simulations are repeated by changing exposition time tc and external cure temperature Tn, to evaluate for each (tc,Tn) couple the corresponding mechanical properties of the item at the end of the thermal treatment. An alternating tangent approach (AT) is used to drastically reduce the computational efforts required to converge to the optimal solution associated with the maximization of the average tensile strength.