Mixing Efficiency in an Intermeshing Internal Rubber Mixer Under Variable Rotor Speed and Rotor Wear Conditions

This study investigates the effect of rotor speed and wear on mixing efficiency in an intermeshing internal rubber mixer operating under partial fill conditions. A three-dimensional CFD model was created utilizing dynamic remeshing to resolve intricate rotor-rubber interactions and capture the developing air-rubber interface using a volume-of-fluid (VOF) method. The rubber compound was modeled using the Carreau-Yasuda viscosity model. The Manas-Zloczower mixing index (MI) was used to assess mixing performance. Increasing rotor speed from 35 to 50 rpm expands elongation-dominated zones by up to 800% indicating improved dispersive mixing. Further increase in speed produced little additional benefit. It was also revealed that 35 rpm is helpful when bulk mixing is prioritized, providing a 5.4% increase in moderate-MI states. Rotor wear of up to 10% of the rotor blade height inhibits elongational flow development by up to 60% while increasing bulk mixing by up to 35%, suggesting that mildly worn rotors may remain useful for bulk-mixing-dominated applications, although this requires experimental confirmation. Analysis of rubber volume fraction evolution and velocity fields showed that localized high-velocity jets intensified with rotor speed but weakened with wear. The findings provide practical considerations for maintaining compound homogeneity and improving mixer performance in industrial rubber compounding.