Screw feed zone

Z-N catalyst See catalyst, Ziegler-Natta. zone A location in a plasticating screw. See screw feed zone screw metering screw transition zone, zone axis A group of crystal planes that are all parallel to one line is called the zone axis. 

Single-screw extruders are commonly used for the conversion of polymers into prodncts such as pipe, cables, film and so on. It is used for compounding with a modification of the screw, feed zone and mixing zone. The compounding operation can be synchronised with product extrusion in a single operation. 

Screw Feed zone Compression zone Metering zone Head Die... 

As the screw turns, it conveys the pellets from the feed zone towards the melting zone. A combination of external heating and mechanical work melts the polymer as it is transported towards the metering zone. The metering zone pumps a uniform stream of molten polymer to a forming device, such as a profile die. Other types of extruders that employ two or more screws are commonly used for compounding polymer blends. The principles of twin screw extrusion will be discussed in Chapter 12. 

Why does the channel depth of the screw generally decrease as you move from the feed zone to the metering zone of an extruder ... 

The modified screw was placed back into the injection-molding press and evaluated for performance. The barrel temperatures were maintained at 245, 255, 260, and 260 °C for the feed zone through the last barrel zone, respectively. This temperature setting was lower than that used for the original screw. The screw was rotated at a speed of 235 rpm, and the back pressure was set so that the pressure at the tip was 10 MPa. The 0.244 kg part and runner system was plasticated in 4.2 s for a specific rate of 0.89 kg/(h-rpm). All parts produced were completely free of the splay defect. The modifications were able to eliminate the bubbles and the unmelted material. 

Extrusion of tubes, hose, and profiles is done on standard extruders for rubber. The usual temperature pattern is a gradual increase of temperature from the feed zone to the die. The die temperature is typically 100°C (212°F) and the screw temperature is approximately the same as the temperature of the feed zone.37 Processing aids are almost always required to improve the surface appearance and to increase the extrusion rate. Extrusion represents only a small proportion (about 10%) of the total consumption of fluorocarbon elastomers.37... 

Feed Zone This is the part of the screw that picks up the plastic at the feed opening (throat) plus an additional portion downstream. Many screws, particularly for extruders, have an initial constant lead and depth section, all of which is considered the feed section. This section can be welded onto the barrel or a separate part bolted onto the upstream end of the barrel. The feed section is usually jacked for fluid heating and/or cooling. 

Transition Zone-. It is the section, also called the compression zone, of a screw between the feed zone and metering zone in which the flight depth decreases in the direction of discharge. In this zone the plastics starts in both solid and molten state with target to have all molten upon leaving this zone. 

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