Innovative FRIGECO
Extruder Design Increases
Output
While the extruder is the melt supply devise
in most extrusion processes, the basic
design has not evolved much over the last
few years. Its purpose is to supply molten
material at a constant melt temperature and
at a constant volumetric rate. The typical
extruder is made up of three geometric
sections:
The feed section or solids
conveying, the transition or melting section
and the metering or pumping section.
For this discussion we will concentrate on
the areas of re-design on the Frigeco
Extruder:
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shear in the material and therefore an
increase in melt temperature. The
combination of rotational speed, adequate
cooling and accurate temperature control
will keep the shear rate down and prevent
localized overheating.
It is in this area that Frigeco engineers have
done the most extensive research and
redesign. In the past you had these basic
options:
The typical extruder barrel is made from
heavy wall alloy steel tubing. Normal
practice is to have a smooth outside
diameter
and
clamp
on
aluminum
heater/cooling blocks (fig. 1).
Feeding Zone
Extruder Barrel and Screw Profile
Thermoregulation
Stable & Reactive Electronics
Increased Output & Lower Energy
Consumption.
The actual melting takes place in the
feeding zone. Most plastics are poor
conductors of heat and are melted by
shearing the material against the barrel
rather than by heat conduction. Consistent
flow of material into the extruder barrel is
obtained by controlling the temperature of
the feed throat. However, you cannot rely on
plant water supply which can vary from 38F
(3C) in the winter to 75F (24C) in the
summer. These fluctuations in temperature
will affect melt temperature and cause
product variations. Therefore, controlling the
temp-erature of the feed throat is essential
to constant solids conveying. The Frigeco
grooved feed throat, integral cooling jacket
and closed loop water temperature control
circuit provide a constant feeding zone
temperature. The next section is the
transition zone where a large amount of
heat will be generated. Much of the heat
necessary to plasticize the material comes
from the rotation of the screw. The faster
the screw rotates, the higher the surface
speed of the screw, the greater amount of
Fig.1
A plenum chamber is provided for each
zone and the barrel is cooled by air
convection. Unfortunately, the thermal
exchange capacity is considerably reduced
with clamp on heaters with finned surfaces
due to the low heat transfer coefficient
between the two elements (barrel and
heater) and furthermore in this case, it is
necessary to cool the heater first and then
the barrel.
Another option is to place fins on the barrel
directly such as the figure below. This
system is also ineffective since there is
limited space to place the fins, the heaters
are placed on the outside of the fins which
further reduces the effective heat transfer
efficiency (fig. 2).
Fig.2
and that of the melt. Therefore, the
temperature of the barrel detected by the
thermocouple may not be an accurate
representation
of
the
actual
melt
temperature.
The Frigeco Barrel:
The cooling grooves on re-designed Frigeco
extrusion barrels are made directly on the
barrel so that the air from the fans acts
directly on the zone to be cooled. In the first
three zones the grooves are closer together
in order to have the greatest heat
dissipation. The last two sections the
grooves are not as close together in order to
guarantee the highest efficiency of heating
and cooling. The grooves are made in the
barrel in order to increase the overall
efficiency and to create cooling air
turbulence.
In addition, large circulating fans have been
added in order to remove heat. These fans
are not in a straight line. They are offset
along the longitudinal axis of the barrel in
order to provide better air distribution, better
suction side clearance for the fans, and
through suitable ducts provide space for
larger CFM fans
The
Frigeco
System:
Temperature
Control
On conventional thermoregulation systems
the thermocouple are placed into drilled
holes partway into the extruder barrel wall in
order to detect the temperature: during line
speed changes and resulting screw speed
changes, there are significant differences
between the extruder barrel temperature
Would it not be better to measure the melt
temperature since that is what you are
trying to control?
The thermocouples on the new (Patented)
thermoregulation system of Frigecoʼs
Extruders barrels are placed in direct
contact with the melt, thus detecting the
exact melt temperature and not the barrel
temperature.
In this way the thermocouple reading and
melt temperature will always be precise,
during speed changes (when there are large
differences in temperature between the
extruder barrel and the melt) (3), and during
normal operations.
In short, common systems control steel
temperature, while Frigecoʼs new system
controls melt temperature, which is of the
utmost importance in HFFR processing.
Another factor which improves the quality of
our Extruders thermoregulation is the noise
reduction on weak signals transmitted by
the thermocouples in the detection phase.
Considering that the thermocouples transmit
the value of the detected temperature
expressed in mV, it is clear that the distance
between the detection and the reception
point of the signal becomes critical. In fact,
the voltage drop due to distance creates an
error which, when added to the potential
drops generated at each electrical
connection point (where there is a small
loss on each point), the total error becomes
significant. Generally, the connections
between machines and electrical panels
require at least 2 or 3 connections on
terminals and about 60 to 100 feet of FeCo
cable. Our solution needs a very short
connection
(max
5-6
feet)
without
interruption on the thermocouple cable,
which is connected directly to the
thermoregulation unit mounted on the
extruder (see below).
From there a common Profibus cable
transmits the data to the PLC after the
signal has been processed and converted
into digital. It is easy to understand how
voltage drop is negligible in our solution,
providing an extremely fast and high
precision measurement.
Another important feature is the electronics
which controls the temperature regulation.
The Frigeco electronics control system
provides PID algorithems dedicated to each
specific material. In fact, it is also possible
to place into memory, parameters that are
automatically learned by the system when
running new materials.
Once your process is stable, you can enter
the system, which of course is password
protected, and you can save the new
process and PID parameters and assign a
description to it so it can be retrieved at a
later date
Frigeco Feeding Zone & Extrusion Screw
The feed throat of the extruder is
asymmetrical with longitudinal grooves of a
specific length and profile to increase the
quantity of material being conveyed into the
extruder.
The feed throat is thermoregulated in order to guarantee that the
feeding conditions do not change with time
or with changes in atmospheric conditions.
The Frigeco extrusion screws are designed
to provide the rate of production required for
the exact polymer to be extruded. Most of
the screws are drilled for cooling and the
end of the screw is equipped with a tapped
hole so a rotary joint can be attached.
Most Materials, even difficult to process
material such as HFFR, LSOH, etc. can be
processed without the need for screw
cooling due to the highly efficient cooling
capacity of the extruder barrel which
provides optimum performance.
Extruder Reducer
All of the Frigeco extruders are equiped with
robust gear reducers. The medium and
large gear reducers are supplied with oil
cooling systems and are fitted with
oversized thrust bearings which are
guanteed for 20 years even under the most
extreme conditions.
The drive motor is directly couple to the
input of the gear reducer which eliminates
the need for belts and pulleys. The AC
motors externally ventilated and therefore
there is no need for a filter. The result is a
machine that will require very little
maintenance.
The use of the AC motor and inverter allows
the machine to generate greater torque at
the low end while allowing it to increase
RPM up to and above 100 Hertz.
Why does all of this matter!
The advantage of this system is that we
were able to achieve higher output at
comparable RPM, and we were able to
achieve higher outputs by increasing the
screw RPM and still be able to control
perfect melt temperature control.
The tests were done on a 120 mm 25:1 L/D
Frigeco extruder.
The test was conducted using a halogenfree, low smoke flame retardant compound.
The main characteristics are the following:
Density:
Tensile strength:
Oxygen Index:
Melt Flow Index:
1.49 gr/cm3
12.0 n/mm2
37%
8.0 gr/10 min.
In order to prove the accuracy of the new
temperature control system we added a set
of conventional deep well thermocouples
and monitored the difference between the
conventional temperature control system
and the new Frigeco design. What we found
is illustrated below:
As you can see zone one is set at 137C.
The recorded temperature of the Frigeco
system is 135C while the traditional system
is 122C. We found this difference to be
relatively consistent across the entire barrel
profile. Conversely the Frigeco temperature
measurement was consistent with the actual
temperature.
We increased the RPM from 30 rpm, the
stated RPM of competitive systems, to 60
RPM as shown on the previous illustration
and recorded the results.
Conclusion:
The Frigeco re-design was initiated to
provide a more accurate temperature
control system for the extrusion process.
The result of this study has reinforced our
hypothesis that the equipment re-design
enables the user to control real melt
temperature and due to the tighter control
on melt temperature you are able to
increase output without degrading the
material.
Our results have shown that we were able
to increase screw speed from 30 rpm with a
production output of 482 kg/hour to 65 RPM
and an output of 1164 kg/hour while
maintaining a constant melt temperature.
For additional information contact us at:
Headquarters & Manufacturing Plant
Mario Frigerio S.p.A.
Via Ghislanzoni 73
23900 Lecco (LC) Italy
Tel: 011+39 0341 3581
In some cases where increased output is
not required, you have the option of going
down one size of extruder, decreasing your
capital cost and decreasing the amount of
energy required by the process.
Manufacturing Plant
Fridea S.r.l.
Zona Industriale Pagliare
63078 Spinetoli (AP) Italy
Tel: 011+39 0736 891701
Sales and Service
Frigeco USA, Inc.
67 Beaver Avenue
Annandale, New Jersey 08801
Tel: 908-894-5801
Fax: 908-894-5809
Website: www.frigeco.com