Tech Tips
Vol. 31 #2, Fall 2004
When polymers enter the feed section of a screw they are typically 40-50% air by volume. As the screw moves the polymer forward and compacts it into a solid all of that air must exit back through the hopper. There are a number of hopper mounted devices such as blenders, gravimetric feeders, driers, compact hoppers, etc. which can prevent the free flow of air out of the system.
When trapped air is encountered in the extrudate always make sure that there is an adequate exit route for the air before looking into screw design or other more complicated issues.
– Jim Frankland Milacron, Inc.
Return to
Extrusion Hints