Melt block problems
Vol.19 #3, Nov. 1992
Due to the reverse temperature profile (hotter at feed end), which is typically used for polypropylene, material can build up in the feed section of the screw. This can cause a melt block which will result in a reduction in throughput of the extruder and can be observed by gauge loss and drive load reduction.
In heavy sheet extrusion of polypropylene, if this problem should occur, the problem can possibly be resolved by cutting edge trim into ice cube size chunks and dumping a bucket full down the feed throat. These large pieces of polypropylene will often times scour the melt block away and eliminate the need to remove the screw and hand clean the screw.
See also
Melt blocking
Reversed temperature profile 1
Reversed temperature profile 2
Worn barrel