Worn barrel
Vol.19 #3, Nov. 1992
The clearance between the screw and barrel is a very important design criteria.
When the extruder is not performing as it should, low output, surging, melt blocks, etc., first check all of the obvious variables, such as temperature profiles, cooling, screw design, regrind bulk density, etc.
Don't neglect to check for a worn barrel ID.
See also
Barrel heaters
Early detection
Melt block problems