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The energy input (enthalpy) required to raise the melt to a temperature of 240ºC containing
60% PolyPropylene(PP) and 40% Talc is 0.128 kWh/kg consisting of an enthalpy of 0.108
kWh/kg for PP and heat input of 0.02 kWh/kg for Talc. As seen from the data, it is possible to
run the extruder with a Specific Mechanical Energy input (SME) of 0.134 kWh/kg even at
1500 RPM. Further the heat-transfer from the barrels is marginal at high speeds. Typically,
an application involving Talc filled PP is run at a specific mechanical energy input of 0.20
kWh/kg. Nearly a third of the energy is saved and the application is run at a considerably
high energy efficiency of 90%.
Compounding involves the ability to optimize performance over several physical properties,
especially strength, elongation (stiffness) and impact. The ability to run the extruder with
control over time (number of turns) and work done (specific energy) allows the compounder
to optimize the physical properties in an advantageous manner.
The co-rotating twin-screw extruder is a versatile device for material preparation. The
earliest generation extruders built in the 1950’s had mean residence time of 300 seconds.
During the past 50 years, the residence time has been reduced to half its original value every
ten years or so with steady increases in shear capacity.
Since the 1990s, state-of-the-art extruders have the capability to reduce the residence time
to less than 10 seconds and mean shear rate to greater than 1000 1/s. However, these
systems have proved to be incapable of creating technological progress in mixing.
The ability to reduce the effect of peak shear and a good understanding of the forces
experienced by the material inside the extruder helps in precise control over the process to
achieve the exact results that are required from the process. The availability of shovel
elements and fractional lobed elements provide the opportunity for achieving greater
process capability in mixing that result in significantly higher output and better properties at
high levels of consistency and efficiency.
Conclusion
References:
1. Booy M. L (1978), Polymer Engineering and
Science, Sep 1978
2. Erdmenger R (1966), U.S. Patent 3,254,367,
June 7, 1966
3. Padmanabhan (2004), U. S. Patent 6.783,270,
Aug 31, 2004
4. Padmanabhan et al (2005), “Effect of Element
Geometry…”, ANTEC 2005
5. Tadmor et. al. (1979), Principles of Polymer
Processing, John Wiley, N.Y
6. Padmanabhan et al(2009),“Shear Uniformity…”,
ANTEC 2009
7. Padmanabhan et al (2009), “Special Intake
Elements…”, ANTEC 2009
This article is contributed by:
Dr. Babu Padmanabhan is the Chief Knowledge
Officer of STEER Engineering Private Limited. He
has done Ph.D in Mechanical Engineering from
Virginia Polytechnic Institute and State University,
Blacksburg, VA.
See: www.drbabupadmanabhan.com
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The availability of shovel elements
and fractional lobed elements provide
the opportunity for achieving greater
process capability in mixing.
“Whatever the mind of man can
conceive and believe, it can achieve.”
W . Clement Stone