Transfer mixer assembly for use with an extruder screw of a polymer extruder or the like

An extruder mixer assembly for use with a screw-type polymer extruder including a barrel defining an elongated cylindrical bore having inlet and outlet ends and a driven screw rotatable in the barrel about a longitudinal center axis of the bore, the screw having a feed end and a discharge end and comprising at least one helical thread having plural turns creating a helical channel in the space between successive turns of the thread and having a minimum clearance to the surface of the bore to feed plastic or fluid material along the screw to said discharge end;

• said mixer assembly having means for mixing and pumping toward said outlet end said material fed thereto from the discharge end of said screw comprising a stator assembly fixed within said barrel adjacent said outlet end having outer cylindrical surface portions fitted within and conforming substantially to the surface of said cylindrical bore and supported against rotation in the bore and having a stator bore provided with a radially inwardly facing groove-interrupted contoured material working first surface, a rotor member driven from the discharge end of said screw having a groove-interrupted outwardly facing material working contoured second surface confronting said first surface rotatable within said stator bore, said first and second surfaces being of generally cylindrical configuration each having continuous helical grooves cut therein along a helical path which changes in depth with length from a small minimum depth to a larger maximum depth but never disappearing and having a plurality of axially spaced circumferential grooves encircling the associated surface along respective planes perpendicular to said center axis subdividing said first and second surfaces into axially spaced serially arranged mixer sections with portions of said helical grooves extending between the circumferential grooves defining each section, the helical grooves being disposed at a helix angle of less than 45.degree. to provide groove pumping of the material toward said outlet end and producing transfer of the material from the rotor member grooves to the stator assembly grooves and back to the rotor member grooves several times during progression of the material along the length of the mixer assembly.