What causes a loss of feed, and how is it corrected?
Loss of feed may be caused by polymer that is stuck to the screw flight and/or root diameter in the feed and/or transition zones of the screw. This problem is commonly referred to as roping, which can occur when the screw heats up too much in the feed and transition zones. Preventing Loss of Feed • Screw cooling, lowering the first barrel zone temperature, and the use of feed-throat cooling will help prevent loss of feed. • When extruding Eastman Provista™ copolymer, be sure to start with a screw speed of at least 10 rpm when pellets are first poured. Slower speeds give the pellets more time to stick to an uncooled screw. Correcting Loss of Feed With the screw turning at 15 to 20 rpm: • Empty the feed hopper. • Apply cooling on the screw and feed throat. • Raise the first barrel zone temperature to 260°C (500°F). • Feed large pieces of profile into the throat to help break the material free. • Once the polymer flow appears to be established, slowly starve-feed pellets to the screw unti
