The feed zone of the plastics extruder is where the plastic raw material first enters the barrel with the rotating screw. It is an important part of the overall extrusion process. There are specific controls that can be adjusted to control the feed and forward conveying of the plastic through the barrel of the extruder.
The feed zone has several control variables affecting the forward conveying of the plastic. These are:
- The method of feeding the plastic into the extruder
- The feed zone temperature
- The screw temperature
Extruders can be filled with plastic raw material in two ways. They can be flood-fed or starve-fed.
Most single screw extruders are flood fed. This means they rely on gravity to entirely fill the feed section of the screw with the raw material.
Extruders can also be starve-fed. This means the plastic raw material is fed into the extruder at a metered rate. Starve feeding can provide a more consistent feed rate. It is sometimes done to eliminate a surging problem.
The temperature of the barrel is an important control variable in the feed zone.
The goal of the temperature settings in the feed zone of the single screw extruder is to begin raising the plastic’s temperature and cause the plastic particles in contact with the extruder barrel surface to become sticky. To cause a forward travel in this zone, the plastic should stick to the barrel and slide on the rotating extruder screw.
The extruder screw is often cored in the feed zone to allow for internal temperature control. If the screw is cored, the flow rate and temperature of the fluid circulated in the core are control variables.
For more information on all aspects of optimizing the operation of the single screw extruder see Paulson Training Program’s Extrusion Technology interactive video program which is currently used in over 1,000 extrusion plants worldwide. This comprehensive course is available both in DVD formal and online through Paulson’s InSite360 training portal.