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HELIX ANGLE
The helix angle is the angle of a screw flight
relative to a plan perpendicular to the screw axis. 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):
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Helix Angle |
= |
arctangent of |
Lead |
|
π 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 is more common in two stage screws
and special mixing screws than in metering screws.
For further
information on Westland Corporation's patented Eagle™ Mixing Screw, go to The
"Eagle™" or
The "Barrier Eagle™ pages.
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