Impacts of Rotor Design, Screw Design, and Processing Parameters in a Farrel Continuous Mixer

Continuous mixers, which consist of a section with non-intermeshing counter-rotating rotors and a single-screw extruder, were developed for thermoset rubber and are often used for compounding of heavily filled thermoplastics. Due to the high mixing efficiency and tight control of shear levels, they may be suited for other compounding other material systems. Little work, however, has been reported on compounding with these mixers, and preliminary work with polypropylene showed interesting limitations of the mixing parameters. Therefore, this study investigated the effects of nine rotor designs, two single-screw designs, rotor speed, feed rate, and orifice setting on the residence time and melt temperature in a Farrel Compact Processor. In general, single-stage rotors produced lower mixer residence times and melt temperatures compared to longer two-stage and high dispersion rotors. Higher rotor speeds and feed rates and smaller orifice openings generally reduced mixer residence times. Higher rotor speeds increased mixer melt temperatures, whereas higher feed rates and smaller orifice openings produced lower mixer melt temperatures. The single-screw design impacted the residence time but not the melt temperature. Overall, the results of this work provided strategies for optimizing the processing parameters and rotor design selection when melt compounding with continuous mixers.