As discussed in a recent column on Plastic Technology Online, the role of barrel heat in the extrusion process is often misunderstood. While it’s commonly assumed that the barrel primarily generates the heat needed for melting, the reality is more nuanced.

In single-screw extruders, melting primarily occurs due to shear heating of the polymer, rather than direct heat transfer from the barrel. This process involves the rotation of a polymer-filled screw within the barrel, creating friction and generating heat. Picture the screw as a round shaft turning inside a heated tube filled with a highly viscous material.

Polymers, known for their insulating properties, pose a challenge for heat conduction. While some heat from the barrel does contribute to melting, it must first pass through the layer of polymer in the screw channel, which can impede efficient melting.

The ratio of shear heating to heat conducted from the barrel depends largely on the gap between the screw and the barrel. Generally, larger screws with deeper channels rely more on shear heating for melting.

Understanding this interplay between shear heating and barrel heat is crucial for optimizing the extrusion process and achieving desired melt properties in the final product.

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Article with all rights reserved, courtesy of ptonline.com.