Technical Details of Twin‑Start ElementStructural Geometry• Two helical screw flights on cross-section with standard Erdmenger fully intermeshing profile. Twin screws intermesh and wipe each other to realize self-cleaning. • Available versions: large-pitch deep channel (SK), standard-pitch medium channel depth (SE), gradual transition (SKN). • Under the same outer diameter: screw channel depth and free volume sit between single-start and three-start elements. Its shear rate is lower than three-start elements and higher than standard fully intermeshed single-start elements. • Assembly phase: Twin-start elements are mounted with a 90° phase offset between twin screws. • Model marking examples: SK‑44/44, SE‑30/30. Available in forward and reverse threads. Material Configuration• 38CrMoAlA nitrided steel: For general pellet compounding. • WR5: For glass fiber and mineral high-wear working conditions. • WR13: Wear and corrosion resistance for battery powder and corrosive melts. • Nickel-base alloy: For highly corrosive reactive extrusion. Manufacturing Process• Integral forging and quenching & tempering heat treatment. • CNC grinding of Erdmenger thread profile. • Strict control of meshing clearance. • Large fillet at thread root to reduce material adhesion. • Guarantee high torque bearing capacity of spline and interchangeability of elements. Process Parameter Characteristics• Shear level: Low shear • Conveying capacity: Forward conveying. SK with large pitch focuses on solid feeding; SE with small pitch focuses on melt pressure build-up • Shear heat: Low • Mixing type: Barely any dispersive mixing, only weak distributive mixing, mainly for conveying • Self-cleaning: Excellent, no stagnant dead zones, suitable for frequent color changeover • Free volume ranking: Single‑start > Twin‑start > Three‑start • Heat transfer: Moderate, between single-start and three-start elements | Functions of Twin‑Start Element•Universal material conveying for all process sections SK (large-pitch deep-channel twin-start): Used in feeding section to improve solid material grabbing, suitable for pellets and ordinary powder. SE (standard twin-start): Used in melting section, vacuum devolatilization section and metering section for melt conveying and melt pressure build-up. Large-lead twin-start elements are mostly applied in venting sections with partial material filling to facilitate volatile release. Small-lead twin-start elements are used for pressure boosting and increased filling degree. • Excellent self-cleaning suitable for multi-grade color change Threads of twin screws wipe mutually without material dead zones. It shortens purging time for color change and reduces charred specks for heat-sensitive materials. •Balance of volume, torque and shear Compared with single-start elements: slightly higher shear but greatly improved self-cleaning, safe for melt zone application. Compared with three-start elements: larger channel volume and milder shear, less prone to glass fiber breakage, suitable for glass fiber reinforced and shear-sensitive materials. •Basic carrier for screw configuration Freely combined with transition elements, kneading blocks and various mixing elements. Combinations of different pitches realize the full process: solid conveying – compression – melting – devolatilization – metering. |
