Multi-screw, extrusion-compounding machine with modular mixing elements

Abstract

Multi-screw, extrusion-compounding machines having co-rotating screw assemblies incorporating sets of modular mixing elements of non-symmetrical geometries with relatively large wing tip clearances. These sets of non-symmetrical modular mixing elements are removably mountable at any suitable axial locations along their respective rotationally-driven screw shafts for optimizing performance in relationship to particular plastic material and particular additives being compounded. The non-symmetrical geometries provide dynamic wedging pressurization for repeatedly propelling relatively large circumferential flows of the plastic material through large shear clearances. Due to the relatively large shear clearances, the plastic material is mixed at less elevated and more uniform temperatures than usually occurs with use of prior symmetrical kneading blocks or kneading discs. At less elevated temperatures most plastic materials exhibit increased viscosities. Thus, the resultant increased viscosities enable the plastic material to be processed at higher shear stresses for enhancing dispersive mixing, in spite of the relatively large clearances which are being utilized. Thus, operators of extrusion-compounding machines are provided with desirable flexibility in adapting them for enhanced performance in matching machine processing functions with the processing characteristics and parameters of plastic materials and additives being compounded.