Zero-meter screw

Figure 8.33 shows an extruder screw without a metering section the so-called zero-meter screw [8]. 

This screw is more appropriate for a plasticating unit of an injection molding machine. The zero-meter screw is used to reduce the temperature build-up in the material by deepening the depth of the channel in the melt conveying zone of the extruder. The obvious drawback is that the pressure generating capability of the screw will be adversely affected, but this is not a major concern in injection molding applications. In other applications, however, the approach outlined in Section 8.3 is recommended. An extension of the zero-meter screw is the zero-feed zero-meter screw shown in Fig. 8.34. 

The exact opposite of the zero-feed zero-meter screw is the very rapid compression screw, shown in Fig. 8.35. 

Figure 8.34 Zero-feed zero-meter extruder screw...

HSEI twin-screw extruders are starve fed with the output rate is determined by the feeder(s), which meter pellets, liquids, powders, and fibers into the process section. The extruder screw rpm is independent of the feed rate and is used to optimize compounding efficiencies. Because the pressure gradient is controlled, and zero for... 

The screw consists of at least five distinct geometrical sections. The first three sections, feed, compression, and metering, are the same as on a conventional screw. After the metering section there is a rapid decompression followed by the extraction section, which, in turn, is followed by a rapid compression and a pump section. Two important functional requirements for good devolatilization are zero pressure in the polymer under the vent port and completely molten polymer under the vent port. 

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