Page 47 - Plastics News August - 2023

FEATURE

ment. For this experiment, a small the screw and sectioned, as shown in to the melt pool by the motion of
amount of color masterbatch is added Fig 3 and 4. the screw. About 80% of the melt-
to fresh resin at a ratio of about 200 A cross section early in the melting ing occurs at the barrel side, and the
parts fresh resin to one-part master- process is shown in Fig. 3. The white remainder occurs at the other edges
batch. The mix is added to the hop- regions were compacted pellet solids of the solid bed. This is why the melt-
per. at the moment that screw rotation ing process requires area at the barrel
When the discharge becomes fully was stopped. The black regions were wall and why the melting process is
tinted by the colorant, the rotation of molten resin. A thin melt film exists presented as a melting flux with units
the screw is stopped, and the barrel between the solid bed and the barrel of kg/ (hr. m2).
zones are placed on full cooling. The wall. The rotation of the screw causes The melting profile for a 21-diam long
die and transfer line are removed, viscous dissipation of energy to occur extruder is provided in Fig 4. Notice
and the pellets in the hopper are re- in this film. Some of the energy con- the solid bed becomes smaller, and the
moved using a vacuum cleaner. After ducts into the solid bed and melts ad- size of the melt pool becomes larger
the resin is solidified in the extruder, ditional resin. as melting progresses downstream.
the screw is pushed out, as shown by The newly molten resin is carried Eventually melting is completed. If the
Fig. 2 for an ABS terpolymer. Next, away in the melt film and conveyed screw speed is increased, the solid
the solidified resin is removed from bed will move downstream and into

PLASTICS NEWS 4747
August 2023 PLASTICS NEWS
August 2023