The Importance of Plasticization and Melting in Twin Screw Extruders

In twin screw extruders, the plasticization and melting of resin are primarily achieved through the complex interactions of various heat-generating mechanisms driven by the high shear stress exerted by the two screws. This plasticization and melting process constitutes a significant portion of the total energy consumption within the extruder and is a critical factor influencing the dispersion state of different types of plastics and nanoparticles.

The plasticization and melting process can be categorized into four key heat-generation mechanisms:

1. Heat from Plastic Deformation
2. Heat from Viscous Dissipation
3. Heat from Friction
4. Heat Transfer from Heaters

Each mechanism impacts material melting and processability in the solid conveying and melting zones of the extruder. Their intricate interplay determines the process efficiency and the quality of the final product.

Heat from Plastic Deformation

When materials undergo plastic deformation, their internal crystalline and molecular structures are altered, releasing energy as heat. This phenomenon is particularly pronounced in materials with high strength, where significant heat is generated during deformation.

In twin-screw extruders, similar effects occur during pellet heating, where the deformation of pellets generates heat, accelerating melting. Heat from plastic deformation is induced by sustained stress at specific temperatures and pressures, helping to raise the internal energy of the material to the melting point.

Heat from Viscous Dissipation

Viscous dissipation occurs when highly viscous materials are sheared, generating internal friction that converts energy into heat. This phenomenon is especially important in the extrusion of polymers and high-viscosity materials, where increased shear stress leads to greater heat production.

In twin-screw extruders, viscous dissipation plays a critical role in the melting process, contributing to polymer flowability and ensuring uniform internal temperature distribution.

Heat from Friction

Frictional heat is generated when materials and machine components come into contact and engage in relative motion. Inside a twin-screw extruder, pellets and molten materials repeatedly interact with the screws and barrel, producing frictional heat.

This frictional heat is particularly important in the initial stages of heating, aiding in the gradual transition of pellets into a molten state.

Heat Transfer from Heaters

Extruders are typically equipped with heaters on the barrel surrounding the screws. These heaters provide the necessary energy to initiate material melting. Heat transfer occurs as conduction from the external heaters through the screws and barrel to the pellets, facilitating the melting process.

Heater-induced heat is especially critical in the early stages of the melting process, allowing for precise temperature control as materials transition into a molten state.

Twin Screw Extruders by Technovel
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As a world-first innovation, we have developed a new type of horizontal multi screw extruder. Our Quad screw and Octa screw extruders are already being utilized across various industries. Even in the field of conventional twin screw extruders, we offer a wide lineup ranging from ultra-compact models—such as the world’s smallest 6 mm diameter screw and our best-selling 15 mm model—to large-scale production machines.

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