According to Plastics Technology Online, the process of melting in single-screw extruders relies primarily on shear heating of the polymer, rather than heat from the barrel. Although the barrel generates heat, the challenge lies in conducting that heat through the polymer in the screw channel for effective melting.

Shear heating occurs as a polymer-filled screw rotates within the barrel. Visualize the screw as a round shaft without flights turning inside a heated tube filled with highly viscous material. The degree of shear heating versus heat conducted from the barrel for melting depends significantly on the gap between the shaft and tube. Larger screws with deeper channels tend to rely more on shear heating.

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