1.Length-to-Diameter Ratio (L/D)
It determines the duration of heating, compression, and mixing that materials undergo.
Large L/D: Enables more complete plasticization, more uniform mixing, and more thorough degassing. The final products feature higher density and strength, with fewer bubbles and volatile substances.
Small L/D: May lead to uneven plasticization, resulting in the formation of crystal spots or insufficient mechanical strength.
2.Compression Ratio
It compacts and shears materials to promote plasticization.
Optimal ratio: Ensures excellent plasticization and dense melt.
Excessively high ratio: Causes excessive shear heat, leading to material degradation (e.g., PP becomes brittle, PVC turns yellow).
Excessively low ratio: Results in insufficient plasticization, leaving raw material residues in the sheet and poor mechanical strength.
3.Mixing Elements (Barrier Section / Pins, etc.)
They provide intense shear and flow division to break up agglomerates.
Enhanced distributive mixing: Eliminates color differences and crystal spots.
Improved distributive mixing: Reduces anisotropy, resulting in more uniform transverse/longitudinal properties of the sheet.
4.Venting Section Design
It extracts moisture and low-molecular volatile substances in the decompression zone.
Excellent venting effect: Significantly reduces internal bubbles and surface silver streaks in the sheet, improving transparency and mechanical strength.
Critical importance: Essential for hygroscopic materials (such as PC and wood-plastic composites).
5.Screw Material and Surface Finish
They affect wear resistance, corrosion resistance, and material adhesion.
Poor material quality: Wear leads to contamination (black spots), while corrosion causes color differences.
Rough surface finish: Material adhesion and stagnation occur, resulting in degradation and yellowing.
There is no "best" screw, only the "most suitable" one. An ideal screw configuration requires achieving an optimal balance between sufficient plasticization and prevention of overheating degradation, as well as between intense shear mixing and preservation of material properties.