Practical methodology for validating constitutive models for the simulation of rubber compounds in extrusion processes

Rubber profile manufacturers have strong incentives to optimize the design of their extrusion dies and reduce the longer development times. Computational fluid dynamics (CFD) modeling is today the most effective alternative to traditional methods for adjusting die geometry and extrusion parameters. However, in practical terms, CFD modeling is often hindered by particular features of the extrusion process such as the lack of a single constitutive equation for all types of rubber flow. This article proposes a practical methodology based on simulation results and experimental data from an easy-to-build 4-channel die to help in the selection of the most adequate constitutive model of a rubber blend. The methodology was validated in a particular ethylene-propylene-diene monomer (EPDM). Characterization experiments were first carried out to obtain three constitutive models: Herschel-Bulkley, Bird-Carreau, and power law. Then, the EPDM was extruded in the manufactured die, and the total rubber that passes through the 4-channel die together with the inlet pressure was measured. CFD simulations of the 4-channel die were lastly analyzed. In our case study, the Bird-Carreu model, experimentally obtained by dynamic mechanical analysis, turned out to be the best candidate model for the EPDM studied. Subsequently, we demonstrated that a valid constitutive equation can be effectively selected by applying the methodology proposed with relatively low cost.