Helix Angle

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The helix angle is the angle of a screw flight relative to a plan perpendicular to the screw plane. Although the helix angle is not commonly altered from the standard square pitch, such a change can have a significant impact on processing.

The standard helix angle for most injection and extrusion screws is 17.6568º and is calculated as follows (a square pitch screw):

Helix Angle = arctangent of Lead/∏ x Diameter

A change to a smaller helix angle, hence more flight turns per diameter:

  • reduces the axial melting length;
  • conveys stiffer materials with greater ease (and less torque);
  • reduces the rate at which material is conveyed.

Changes in the helix angle are more common in two stage screws and special mixing screws than in metering screws.

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