Technical Details of Extensional ElementStructural Geometry• The flow channel periodically contracts and expands along the axial direction with cyclically varied cross-section. Materials are stretched within narrow gaps, and melt folding and restructuring take place in expansion cavities. • Continuous curved profile without angular discs of kneading blocks. • Twin screws intermesh and wipe each other to achieve self-cleaning performance. • It delivers weak forward pumping capacity. • The inner bore adopts involute spline. Normally used in groups. Transition elements are recommended at both ends to eliminate stepped dead zones. Material Configuration• 38CrMoAlA nitrided steel: For general polymer blending and compounding. • WR5: For glass fiber and mineral high-wear working conditions. • WR13: Wear and corrosion resistance for battery materials and corrosive melts. • Nickel-base alloy: For highly corrosive reactive extrusion. Manufacturing Process• Integral forging and quenching & tempering heat treatment. • 5-axis CNC milling of continuous contraction-expansion curved surfaces. • Strict control of meshing clearance. • Fillet treatment for flow channel corners to reduce material adhesion risk. Process Parameter Characteristics• Shear level: Low-medium shear, far lower than KB kneading blocks • Conveying capacity: Weak forward conveying, no severe pressure build-up • Shear heat: Low with slight temperature rise • Mixing type: Excellent distributive mixing + moderate dispersive mixing, dominated by extensional flow • Residence time: Moderately prolonged with narrow residence time distribution • Self-cleaning: Excellent, suitable for frequent color changeover | Functions of Extensional Element•Extensional flow dominated mixing to reduce shear thermal damage. Repeated contraction and expansion of flow channel stretches, peels, folds and restructures materials. Compared with kneading blocks, it reduces molecular chain scission and excessive glass fiber breakage induced by intense shear, protecting heat-sensitive polymers and long glass fiber systems. • Superior phase dispersion for polymer alloy blending. For immiscible blending systems, extensional flow facilitates domain refinement and improves interfacial bonding between two phases, delivering outstanding alloy blending performance. • Moderate dispersion for mild agglomerates. It can break mild agglomerates of color pigments and fillers. Not applicable for hard stubborn agglomerates, which require intense shear from KB kneading blocks. • Good self-cleaning to reduce charred specks. Fully intermeshed mutual wiping without obvious stagnant dead zones, shortening purging time for color change and adapting to multi-grade switching production. •Improve devolatilization and reactive extrusion performance. Stretching continuously renews melt surface and increases specific surface area to facilitate removal of small-molecule volatiles. In reactive extrusion, it enlarges two-phase contact interface and promotes sufficient reaction. |
