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Fractional lobed elements overcome the limitations of standard screw elements and provide
greater flexibility in the design of individual elements, especially enhancing elongational
mixing and allowing greater shear uniformity – key aspects in converting a screw device into
a mixing vessel. In the figure below, two instances are shown. In one the fractional lobed
design is used as a Kneading Block and in the other as a continuous mixing element.
Fractional Lobed Kneading Blocks
Fractional Lobed Mixing Element
Increase in intake capacity with Shovel elements
There is generally enough space in an extruder to process materials with bulk density of
about 1 g/cc. Most applications are therefore solely limited by the torque that the equipment
is designed to overcome. However, materials that are in the form of fine powders, trap a lot
of air and have low bulk density. Further, the action of the screw in conveying the material
creates an action similar to a snow snowplough that pushes the material to the side rather
than forward. This action is more pronounced at higher speeds, fluidizing the material and
further reducing the forward conveying action. Materials that have high specific gravity but
low bulk density trap a lot of air. Talcum powder is one such material.
Game Changing
Technological Innovations in
MELT COMPOUNDING
THE EXTRUDER TIMES / ISSUE 10 / AUGUST 2010
Figure 4
Special Mixing Elements that enhance
performance in mixing zone.
Figure 5
Shovel Elements that enhance performance
in intake