Two-channel extruder with mixer

In an extruder provided with a hopper at one end and a restricted nozzle at the opposite end and two press screws arranged coaxially in one another within an outer jacket, each of said screws being provided with a male thread for feeding in the direction of said nozzle, said male threads extending into an outer annular space between said jacket and the outer press screw and extending into an inner annular space between said two press screws, means operatively connected to the outer press screw to rotate the outer press screw and means maintaining the inner of said two press screws stationary, said outer press screw being provided with window-like openings communicating with said inner press screw in the area of said hopper and separate feed means in said hopper to separately feed to the area between said outer jacket and said outer press screw and to the area between said outer press screw and said inner press screw through said window-like openings, the improvement consisting in that said threads on each of said screws are oppositely oriented and a mixing element is positioned between said nozzle and said press screws, said mixing element being an annular ring mounted on said outer press screw and having blade-type mixing tools extending into said outer annular space and blade-type mixing tools extending into said inner annular space with openings communicating between said mixing tools extending from said inner annular space to said outer annular space.