The flow visualization method of studying internal mixing has been shown to be a powerful tool for determination of the critical factors inluencing flow and mixing efficiency. Correlation of visualization with results obtained for ″practical″ rubber mixing confirms the validity of the method for the prediction of flow in conventional mixing operations. Fill factor is identified as one of the key variables influencing mixing uniformity. From the dependence of mix uniformity on fill factor derived from a B Banbury having two-wing rotors, fill factors of 0. 7-0. 8 are shown to give the best results. This range of fill factors provides an adequate and continual filling of the region in front of the rotor tip and ensures that the high stresses required for the fracture of particle material aggregates are generated. It also permits the formation of voids behind the rotor tips. Such voids appear to be essential for the disordering of streamline flow patterns and for promoting effective axial transfer of material.
