The product to be converted is prepared in the form of a dough with binder/moisture, and is feed in the Extruder. The die roller design of extruder operates with two rolles. One is the Knurling (pressing) roller and other is the die roller. The perforation size of the roller decides the size of the needle / granules & hence the size of Pellets to be formed. The size of the extrusions that come out are finite length with the help of a adjustable cutter attached.
The twin screw design of extruder operates with a set of conveying screens which transfer the material to the pressing cams which further press the material to a particular size of mesh. The size of the noodles is decided from the size of the Die mesh fixed.
The spheres obtained from the twin screw design has lesser bulk density compared to pellets produced by the roller design extruder. In other words the compressional forces that act in a die roller design extruder are for more than the other resulting in compact and DENSE pellets. It again depends upon applications & product chooses the correct machine for the optimum utility.