Page 28 - Plastics News April 2021

FeAtures

the items that minimize the time to change screws. wider operating window, but it is still limited. A simple
Such items are a screw pusher, lifting equipment, quick- test is to run the types of recycle common to your
disconnect adapter/die, and easily movable downstream business and compare the outputs. One type will always
equipment such as the pelletizer so there is space to run at higher outputs, so simply compare the change in
easily remove the screw. Even though many may look at output to the time to change screws. When the proper
that as time lost, the improvement in processing rate equipment is available, screw changes can be kept to
and melt quality can easily make up the difference 1-2 hr, depending on the size of the extruder.
Barrier screws tend to be less flexible on a variety of Don’t forget about the purging time when trying to run
polymer types of recycle than conventional single- different polymers on the same screw. The combination
flighted screws, because their basic concept is to be of the lost time and wasted polymer alone can equal the
designed for a specific melting rate and energy input. cost to change screws.
Conventional single-flighted screws generally have a (Courtesy: PT)

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