posted June 16, 2003 03:43 PM               

Welcome to the single screw forum. You'll find lots of information on this topic in papers presented at SPE's ANTEC's, check out this link: http://www.4plasticsresearch.org

Powder and regrind tend to be less easy to process than spherical granules, crammers and vacuum venting barrels can help. Close control of feed, feed throat, screw (in the feed zone) and the feed zone barrel temps plays a big part too. As do the coefficents of friction of the barrel, screw and material.

posted June 17, 2003 10:58 AM               

Below is a clip from a chapter I wrote on single screw compounding for Hanser's "Plastics Compounding" text. Hope it helps...

"Feed stock morphology greatly influences compaction and the differences between pellet and powder feed stocks should be understood. Pellets tend to compact nicely as the outer surface of the solid plug undergoes deformation to conform to the constraints of the barrel I.D. By contrast, powder feed stocks exhibit initial point contact against the barrel I.D. as the irregular particle shape travels along the screw axis. Only after peaks have undergone deformation can the valleys be forced against the barrel wall for effective melting and subsequent melt removal. As a consequence, it is common for powder materials to exhibit a longer time rate of melting than a pellet feed stock. In addition, the greater interstitial area and lower bulk density in powder feed stocks allow a greater volume of air to be trapped, insulating the solid plug. This can delay melting even further and may make devolatization much more difficult."

tom

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Thomas Black
PPS, Inc.