MEASUREMENT OF VELOCITY PROFILES IN REVERSE-SCREW ELEMENTS OF A TWIN-SCREW EXTRUDER

A laser Doppler anemometer was used to measure velocity components for the flow of a Newtonian fluid in a reversing section of a pilot-scale corotating twin-screw extender. Measurements were made at a Feed axia l position in the intermeshing (nip) region and the translational regi on (away from the nip). Tangential and axial velocity profiles reached a maximum in the middle of the screw channel, indicating pressure flo w Leakage flow through the gaps between screw flights and backflow tow ard the hopper were observed only in the nip region. No reversal of fl ow was detected in the translational region. Measured velocity profile s showed substantially higher shear rates in the reversing section of the screw as compared to those in the font,ard-conveying section.