The screw should be single flighted,constant pitch,with the pitch
equal to the diameter and the
length equal to 24 diameters.It should be bored for cooling.Screw
Flights should be flamehardened.
The screw should be AISI4140 chrome plated.Since flexible PVC
compounds can cover a wide range of
hardnesses,the screw design and dimensions are less critial than
for rigid pvc.
Mixing pins and other types of mixing sections are often
incorporated in a screw design to enhance dispersion,espeically
when adding concentrates to a naturalbased compound.Screws with
pins typically have 12-14 flights in the metering section.
Barrier screws are still another type of design that can be used
for extruding flexible PVC.
Hard Chrome Plating treatment:
Thickness of Hard Chrome Plating Layer: 0.03-0.08mm
Hardness of Hard Chrome Plating Layer: ≥950HV