Abstract: A rotor element for use in extrusion and compounding machinery that incorporates means for mixing a low viscosity or immiscible additive with high viscosity base stocks such as polymer melts. The rotor incorporates a combination of one or more helical flights with an array of mixing pins arranged in the cylindrical screw root.

Abstract: A screw-type extrusion apparatus adapted for the extrusion of a viscous primary extrusion stock and particularly adapted for the mixing into said primary extrusion stock of an additive of lower viscosity, which comprises (a) an elongated barrel, (b) means for introducing the primary stock into an upstream end of said barrel, (c) means for discharging extrusion stock from a downstream end of said barrel, (d) a rotatable screw worm axially disposed within said barrel for advancing the primary stock from the upstream end of said barrel to the downstream end of said barrel, said screw having a screw root and affixed to said root at least two axially separated stages of helically threaded screw flights, and (e) an injector for introducing the additive into the barrel at an axial position intermediate to the two said stages of screw flights, said injector extending inward through said barrel wall and having an inlet external to said wall and an outlet positioned substantially at the surface of said screw root.