EXPERIMENTS WITH AN INSTRUMENTED TWIN-SCREW EXTRUDER USING A SINGLE-STEP GRANULATION EXTRUSION PROCESS

Preliminary studies with an instrumented, co-rotating twin-screw extruder were performed. The variation of water content of the extruded mass is dependent on the accuracy of both dry powder and granulation liquid feed rate. Using a given powder feed rate it is easy to vary the water content by changing the liquid feed rate. Operating the twin-screw extruder in this way the extruder barrel is not completely filled with wet mass. The steady state mass is dependent on both screw speed and mass flow rate. This leads to different behaviour of extrusion process variables compared to extruders with completely filled barrels. With a central composite design the influence of screw speed and water content on passage time, steady state mass and the process variables corrected power consumption, pressure and end temperature of extrudate were studied. Water content is the most important variable for the extrusion process variables. For further studies it is strictly recommended either to control the water content or to use it as a variable.