The following list of problems and possible remedies reflects my own experiences over several hundred extrusion runs, both lab and production facilities.
It must be realized that, like automobiles, no two extruders of the same design will run exactly the same.

For example, differences in flight clearance with varying amounts of screw and barrel wear will affect the temperaure setings required to run a given formulation. Therefore, remedies described should be considered as suggestions, with the need for possible adjustments for differences in extruder behavior kept in mind.

PROBLEMS AND POSSIBLE REMEDIES

A - IN THE HOPPER & EXTRUDER THROAT

 1.  Bridging, or interrupted powder flow to screws, causing erratic flow out of die 
 (a) Powder blend too warm (freshly mixed) - let stand for 24 hours.
 (b) Possible moisture  contamination.
 (c) Crammer necessary for single-screw extrusion to force-feed screw.       
 (d) Vibrator on hopper helpful,especially with highly filled blends.

 2.  Foreign objects in blend.  
 (a) Always use hopper magnets for metallic contamination!  Nonmetallic materials should pass through with minimal damage to extruder screws and barrel.

 3.  At a given feeder setting, and during long extrusion runs, powder level in extruder throat gradually decreases - resulting in starved screws. 
 (a) Powder gradually builds up on feeder screw flights through static charge, or compression, which decreases volume transport to extruder.  Feeder screw should be cleaned periodically.

 4.  Momentary interruption of powder flow to screws, causing several empty screw flights - generally seen as a drastic drop in amperage.  
 (a) Quickly slow down haul-off (since flow out of die slows down), and turn off vacuum to prevent powder in vacuum lines.  If done quickly, the line may hold together.  Gradually increase haul-off sped as flow from die increases and turn on vacuum again as normal powder feed is resumed.