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This Zone is also called the pumping zone in an extruder. The compounded polymer melt is transported towards the die by drag flow caused by
the rotating action of the screws. Screws with higher degrees of fill with shorter leads are optimum for this zone for creating the pumping effect.
The required pressure is based on the die design -
0
0
3
P=(2L
t
)/R
Where
t
=
mg
And
g
=4Q/(
p
R )
2
[
t
= Shear Stress (MPa-N/mm ), L=Length of the zone (mm)
p
=3.14159(Constant), R=Die Radius (mm)
3
0
Q=Volumetric Flow Rate (mm /s),
g
=Shear rate ( /s) ]
This zone pumps the homogeneous compounded melt at constant temperature and pressure. The performance of the optimally designed
screws is conserved only if the excessive cooling in this zone is avoided.
Metering forms the final processing zone in an Extruder. The function of this zone is to build the required pressure for filtration of foreign
particles (if called for) and at the die for a continuous streamlined output. The nature of equipments placed after the metering zone such as
Screen Changers, Breaker Plates, Die heads and Die Plates would be dealt in detail in a future article.
see below.
Zone # 6 The METERING ZONE
-10-
C O N C L U S I O N
A good compound is the result of the right chemistry coupled with the right extrusion technology. This is all about putting the right kind of work - always a result of
optimally configured screw design. Optimal configuration has the right elements in the right place for the right application and process parameters. Functional
understanding of the potential characteristics of each element is the starting point for undertaking this task. Every Characterization table forms the quick reference
guide for formation of configuration for different applications. Future articles will focus on the effects of combining different elements, the role of process
parameters and the effect of clearances / geometry in processing.
Acknowledgment: Mr. C.J.Chetan M.Tech., for his contributions.
This article is contributed by Dr. Babu Padmanabhan, Chief Executive
Officer and Founder of STEER Engineering Pvt Ltd. He is a Ph.D in
Mechanical Engineering from Virginia Polytechnic Institute and State
University Blacksburg VA.
See: www.drbabupadmanabhan.com
For more information please visit www.extruderprocessingzone.com
THE EXTRUDER TIMES / ISSUE 05 / JANUARY-MARCH 2008
1
Choice of material of construction (MOC)
generally has no effect on the function of the
zones. However, wear (or increased clearances)
can have serious effect. It is to avoid wear that
the right material has to be chosen keeping in
mind the ‘specific wear mechanism’.
2
SFE and RSE screws follow the Erdmenger
design and are fully wiping profiles. SKE, DSK
and SFV are modified screw profiles that have
incomplete wiping profiles.
3
Mixing at the time of melting has some
difficulty. Certain materials that have the
tendency to agglomerate will do so before it is
mixed into the polymer. Therefore, pre-mix
preparations become vital.
Reference