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The adage ‘different strokes for different folks’ holds good when one attempts to deal with
the EPZ (Extruder Processing Zones) of a Co-rotating Twin-Screw Extruder. Within this EPZ
area the ‘key to success’ lies with the exact design of the ‘Element and Barrel’ Configuration.
In the game of Chess, a ‘good formation’ is important to achieve a winning result, since
pieces in isolation cannot perform. This is true in the case of Compounding also. Elements
work best in some combinations, and some elements are more powerful than others.
Indeed, it is true!
Importantly,
1. The design has to deliver the correct amount of work on the product for melting and
mixing.
2. The design should have the capacity to take the product “in” and “out” of the
extruder.
3. Lastly, the design should allow gases or volatiles to escape without the product
leaking out through Vents.
It can be imagined that there are ‘different zones’ (area) inside the extruder performing a
1
series of specific functions . Like a relay race, each zone passes on the ‘baton’ (the material
being processed) to the next zone and until the final stage. Extruder performance
measured by energy consumption, quantity and quality of output, largely depends on the
design of these processing zones. The effective selection of elements is the first step in
design. The right length and combination of elements is the next step. We shall discuss
these various zones and outline the element characteristics, its potential use and certain
design principles.
CONFIGURATION OF
SCREW ELEMENTS IN
A N O V E R V I E W
Zone 1 Intake Zone f
or introducing the material into the extruder.
Zone 2 Melting Zone
for heating the material and therefore melting the material
and achieve partial or total mixing.
Zone 3 Venting Zone
for removing the volatiles & moisture.
Zone 4 Mixing Zone
for ensuring proper mixing.
Zone 5 Vacuum Zone
for completely removing the volatiles & moisture to the
required levels.
Zone 6 Metering Zone
for building up the required pressure at the die.
In the game of Chess, a ‘good
formation’ is important to achieve a
winning result, since pieces in
isolation cannot perform.
This is true in the case of
Compounding also.
-2-
STEER’s Fractional-lobed Kneading
elements (patented) provide a more
uniform shear action vis-à-vis
s tandard knead i ng e l ement s .
For high speed extruders the melt
mixing is greatly enhanced with these
elements having unequal tip width and
multi lobed Geometry.