Screw Position
Vol.20 #2, July 1993
When troubleshooting fluctuating extrusion head pressure or cyclic extruder output (if the extruder does not have a head pressure gage) and the feed throat is not bridged, have the head opened up.
Ensure that the screw is as far back into the barrel as required for picking up a full channel of pellets at the feed throat each revolution of the screw. Frequently a screw design is blamed and temperature profiles are changed when the problem is the screw has not been fully seated into the thrust bearing, particularly after cleaning of small diameter screws, resulting in only one half or only a portion of the first feed channel being open to the feed throat for a portion of each revolution of the screw.
See also:
- Check new screws
- Screw design
- Screw inspection
- Screw wear
- Thrust bearing
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Extrusion Hints