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The
EXTRUDER
TIMES
Published by
CONSULTANC Y SERV I CES , I ND I A
The Background:
We have a co-rotating twin-screw extruder machine with following
specs: Barrel Dia 48mm. Do/Di ratio 1.49. Screw Speed 600 rpm. The temperature set
was @230°C. Actual temp 120°C. CaCO
3
more than 65% Filler from side feeder. Base
polymer PP from the main feeder. Side feeder output 255 kg/hr.
The Query:
Why is there a drastic temperature decrease of almost 90°C, once the barrel
temp reaches 140°C filler started coming out from the atmospheric vent? (Received from
Mr.Prakash H from Bangalore, India.)
Dear Mr. Prakash
The naturally occuring Calcium Carbonate (Chalk, Limestone, Marble) has a Specific heat
capacity of approximately 0.8 kJ/kg/ °C. When the calcite enters at room temperature
into the extruder at 225 Kg/hr, the total heat energy required to heat it up to operating
temperature will be 10 kW (assuming there is little moisture in the Calcite, with more
moisture, the heat-loss is even higher). This can also be interpreted as the cooling capac-
ity of the Calcite. The only way to heat the Calcite is by working it along with the polymer
as a result of the Screw action. This heating happens due to shear while the material
travels along the extruder. The loss of heat due to entry of Calcite cannot easily be
compensated by Barrel heating (since barrel heating is generally limited to standard
applications where the heat-transfer between the barrel and the melt is limited). This is
a normal phenomenon but if this not acceptable, a possible solution will be to pre-heat
the Calcite to operating temperature before entry into the extruder. Another solution is
to have higher heating capacity in the Side-feeder Barrel, say 5 or 6 kW as against the
normal range of 2.5-3 kW. It is possible that once the melt cool excessively, some convey-
ing efficiency is lost and the capacity of the extruder is reduced. This caused the extruder
to get over filled and the filler escapes with the gases in the atmospheric vent.
- Babu Padmanabhan
on behalf of ET expert panel.
For further queries on the subject you may write to: drbabu@steerworld.com.
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Printed and Published by: ET editorial coordinator KSRam on behalf of STEER CONSULTANCY SERVICES, 290, 4th
main, 4th phase, Peenya Ind. Area, Bangalore - 560 058, India.
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Plastindia 2006
February 9 - 14, New Delhi
NPE Society of the Plastics Industry Inc
June 19 - 23, 2006
McCormick Place, Chicago, IL, USA
Plastivision India 2007
7th National Exhibition and Seminar,
Mumbai
The Generation Next Co-rotating Twin-screw
Extruder is on display at Plastindia 2006, New Delhi.
February 9 - 11, Hall No, 15, Booth No. 11
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