Twin screw extruder with thread-free mixing zones
Twin screw extruder with thread-free mixing zones
Apparatus for mixing material in a twin screw extruder by longitudinally advancing material by the interengaging threads of two screws in the housing of a single screw extruder such that a plurality of separate streams of material are advanced by the threads of the screws, combining the separate streams of material in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement around one of the screws, and thereafter dividing the combined stream back into separate streams downstream of the thread-free zone.
In order to carry out different processing operations, it is known to form the screws of a twin screw extruder with different screw sections which consist, in particular, of a succession of screw and kneading elements. Such processing operations are, for example, mixing, melting and homogenizing plastic materials upon the addition of additive and filler elements, by developing shearing forces while maintaining a given temperature profile dependent on the material being processed.
By providing screw elements of different pitch, the efficiency of the conveyance and the pressure built-up in the extruder are particularly influenced and a desired development of shearing forces to obtain an optimum mixing action is made possible.
In DE-PS 815,641, it is known to improve the mixing action in the sheet production extruder by arranging baffle plates on alternate sides on the screw shafts, so that the material being processed is forced to pass in continuous exchange from one screw shaft to the other.
Adherence of residues of product to the baffle element limits the flow of material and is also disadvantageous.
In the twin screw extruder the interengaging threads of the two screws in the housing of the twin screw extruder longitudinally advance the material in a plurality of separate streams and these separate streams of material are combined in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement for confinement around one of the screws whereafter the combined stream is divided back into separate streams downstream of the thread-free zone.
Apparatus for mixing material in a twin screw extruder by longitudinally advancing material by the interengaging threads of two screws in the housing of a single screw extruder such that a plurality of separate streams of material are advanced by the threads of the screws, combining the separate streams of material in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement around one of the screws, and thereafter dividing the combined stream back into separate streams downstream of the thread-free zone.
In order to carry out different processing operations, it is known to form the screws of a twin screw extruder with different screw sections which consist, in particular, of a succession of screw and kneading elements. Such processing operations are, for example, mixing, melting and homogenizing plastic materials upon the addition of additive and filler elements, by developing shearing forces while maintaining a given temperature profile dependent on the material being processed.
By providing screw elements of different pitch, the efficiency of the conveyance and the pressure built-up in the extruder are particularly influenced and a desired development of shearing forces to obtain an optimum mixing action is made possible.
In DE-PS 815,641, it is known to improve the mixing action in the sheet production extruder by arranging baffle plates on alternate sides on the screw shafts, so that the material being processed is forced to pass in continuous exchange from one screw shaft to the other.
Adherence of residues of product to the baffle element limits the flow of material and is also disadvantageous.
In the twin screw extruder the interengaging threads of the two screws in the housing of the twin screw extruder longitudinally advance the material in a plurality of separate streams and these separate streams of material are combined in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement for confinement around one of the screws whereafter the combined stream is divided back into separate streams downstream of the thread-free zone.