Today's KNOWLEDGE Share : Twin-screw extruders, workhorses in compounding for over a century, are often misunderstood.

Today's KNOWLEDGE Share

Twin-screw extruders, workhorses in compounding for over a century, are often misunderstood.


Here are five common myths and misperceptions that can create scaleup and manufacturing challenges.


Myth 1: TSE performance is always very sensitive to wear. Twin-screw extruders are generally less sensitive to wear than single-screw extruders due to self-wiping effects and positive forward conveying. Wear is often localized, with a rough rule of thumb allowing up to 3-5% wear on screw elements' OD.


Myth 2: A twin-screw vent stuffer always fixes a vent flow problem. Vent stuffers are useful for polymer formulations with unmelt material that tends to accumulate in the vent due to high vapor velocities, but they do not address issues from non-optimized screw design or backups in the pumping zone.


Myth 3: You can scale any process from lab to commercial in one step. The comparative surface-to-volume ratios of small to large TSEs make scaling challenging, particularly without experience. Processes may be volume-limited, heat-transfer-limited, or torque-limited, requiring adjusted formulas.


Myth 4: Liquid injection is difficult on a TSE. It is possible to inject more than 70% of liquid into a polymer on a commercial scale, using staged injection points and various pumps to mix pellets, powders, and liquids.


Myth 5: Specific torque is the most important torque-related parameter. Specific torque calculations do not reflect free volume, which depends on the OD/ID ratio of the screws.


Debunking these myths can improve TSE operations and performance. Read the full article for detailed insights. https://lnkd.in/gtuNAtBt


source : Plastics technology


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