In comparison with desiccant dryers, the VBD
vacuum dryer consumes up to 80% less energy,
dries resin in one-sixth the time, and substantially
reduces the heat history to which polymer is exposed.
The speed with which the VBD system removes
moisture makes properly dried polymer available for
production only 35 minutes after a cold start.
VBD vacuum dryers use gravity to move material
through three vertically arranged stages of the
drying process, with the discharge of material from
one stage to the next controlled by high-speed
slide-gate valves with an accuracy per dispense
of +/- 4 grams. The vessels for the three stages are,
from top to bottom: a heating hopper that brings
resin to a target temperature; a vacuum vessel in
which vacuum reduces the boiling point of water,
causing moisture within the pellets to volatilize and
be forced out of the pellet into the low-pressure
environment surrounding it; and a heavy insulated
material retention hopper with transparent shroud
to protect dry material. For hygroscopic materials, a
membrane purge option is available.
The vacuum vessel and retention hopper are mounted
on load cells that monitor the weight of material at
two critical points, making possible precise control
over material consumption and documentation of
process conditions for certification to customers.
VBD™-600 vacuum dryer
.
www.maguire.com
TUBE NEWS March 2018
7