In my career there have been a handful of times where a custom compounder using single-screw extruders have asked me to design a screw for mixing large amounts of powdered additives into the virgin base resin. But single screws do not have the capability to convey  powder additives in volumes above 20% in a flood-feed condition.  Twin screws are built and design for processing large percentages of powder at the feed, and this is typically done in a starve-feed condition and also at very high screw rpms...normally, two and three times faster then single screws. 

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