Chemistry Reference
In-Depth Information
Figure 10.3.
Image of a 16mm corotating twin-screw extruder (model Nano-16). Reproduced
with permission from American Leistritz Extruder Corp., USA.
rate
es
causing higher bulk density in the lower section of the feeding vessel with lower bulk
density in higher regions of the feeding hopper. Variable auger screw designs allow
process optimization to be performed for a volumetric feeder, the requirement being that
consistent
-
rpm relationship may not be constant, for instance, when feed material densi
flow must be achieved. The changing vertical height of powder in the hopper
can affect the output of the volumetric feeder.
A loss-in-weight feeder is set to deliver material at a measured
”
rate with real-time feed rate control. The hopper and feeding module are mounted on a
load cell that measures weight at frequent intervals. The measured mass
“
mass per unit time
ow data are
used by the controller to adjust the motor speed (or vibratory tray for some units) as
necessary to maintain mass
flow within the control limits.
When performing extended processing, recharging of the feed hopper is required.
The action of recharging the hopper creates simultaneous weight loss and weight gain
that will confound the controller input data. Loss-in-weight feeders manage this need
with a function to enter a temporary feeding mode that uses the historical mass
ow data
to continue feeding at a predicted rate. Once charging is complete, real-time control can
be reactivated.
