Flow Disturbances
If cast sheet has a periodic flow non-uniformity, check to seek if it is at the same frequency of the screw speed. (line speed/pitch of non-uniformity = screw rotational speed.) If so, examine or change the thrust bearing. A slightly damaged thrust bearing will result in a significant pulse in flow (the screw moves back and forth) that is proportional to screw speed.
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Extrusion Hints