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Distributive mixing spreads components through the melt; dispersive mixing breaks agglomerates or reduces the size of a dispersed phase. A twin-screw configuration often needs both, but the balance should follow the defect and formulation rather than a preference for higher shear. First identify the problem, then compare mixing quality within the line's thermal and mechanical limits.

Choose a conical twin screw extruder or a parallel twin screw extruder by the PVC formulation, required production window and machine configuration, not the geometry label alone. Compare equivalent process duties, then check accepted output, product quality, energy use and mechanical compatibility. For an existing line, decide whether you need replacement parts or a different machine architecture before requesting a quotation.

Extruder screw pitch is the axial spacing between adjacent flights; lead is the axial advance of the same helix through one complete turn. They are equal on a regular single-start section, but not on every screw. Choose a lead change by its effect on feeding, melting and pressure delivery, rather than assuming that wider spacing guarantees more good output.

Extruder screw channel depth describes the space between the screw root and a defined outer reference. A deeper channel provides more space, but it does not automatically deliver more good output against die resistance. Choose the profile by its feeding, melting and pumping duties, with the actual dimensions, material and matching barrel defined.

Single screw extruder L/D ratio is the specified working length divided by the nominal screw diameter. Choose it by the space needed for feeding, melting, mixing, venting and pressure development, not by assuming a longer screw delivers more output. Confirm the measurement datums and machine compatibility before comparing quotations.

​Extrusion screw compression ratio describes the reduction in channel volume from feeding to metering; for conventional screws with the same lead in both zones, it is commonly expressed as feed channel depth divided by metering channel depth. Choose it with the actual depths, transition length, feedstock and barrel design, not from the polymer name alone. A higher ratio is not automatically a better screw.