Plasticator transition/melting zone

The melting (transition) section is where the softened plastic is transformed into a continuous melt. It can occupy from 5 to 50 percent of the screw length. This usual compression zone has to be sufficiently long to make sure that the plastic is melted. A straight compression-type screw is one having no feed or metering section. For certain plastics, particularly TSs, there tends to be no compression zone since overheating and solidification of the melt could occur in the screw or barrel. 

Melting zone n. In a well-designed extruder screw, the section, to be coincident with the transition section, in which most, if not all, of the melting of the feedstock occurs. The pumping section, in which the plastic is presumed to be fully melted, is sometimes called the melt zone. 

With crystalline types [not amorphous (Chapter 1)], melt leaving the die (and moving to a ring-shaped zone where the film approaches its diameter) changes from a hazy to a transparent (amorphous) condition. The level at which this transition occurs is the frost line. This zone is characterized by a frosty appearance to the film caused by the film temperature falling below the softening range of the plastic. 

Transition section (transition zone, compression section) n. In a metering-type screw for a single-screw extruder the section of decreasing channel volume per turn between the feed and metering sections, in which the plastic is changing state from a loosely packed bed of particles-cwm-voids, to a void-free melt. The transition may be... 

The feed zone conveys plastic forward to the transition zone and has a constant root diameter. The root diameter tapers through the transition zone, which compresses the granules forcing air back toward and out of the feed throat and hopper. The main purpose of the transition zone is to compress the plastic and provide the shear heating to drive the melting process. Ideally, by the end of the... 

Polymers behave differently in the transition section. The lower the flowability in the plastic state, the more sensitive the material is during the melting process. In the transition zone, approx. 80% of the total energy is dissipated in unfilled thermoplastics [35]. 

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