Effective heat management is critical in polymer extrusion, especially at high output rates. Heat is generated through viscous dissipation from shear and conducted from the heated barrel. This heat must be balanced with energy input requirements and polymer degradation limits.
Screw Cooling Techniques
Internal Screw Cooling
Some screw designs incorporate internal cooling channels, such as a hole in the screw core where water evaporates at the hot tip and condenses at the colder intake, cooling the tip and heating the dry blend. This helps manage melt temperature and minimizes degradation, particularly at the screw tip and adaptor.
Heat Balancing at High Output
High output rates often require high torque, which can limit the effectiveness of internal screw cooling if the screw core walls must be thickened for strength, reducing the cooling channel diameter. Insufficient cooling at high output can lead to higher risk of melt sticking, increased stabilizer requirements to prevent degradation, and even screw breakage.
Modern extruders are designed for lower specific energy input, meaning less heat needs to be removed by cooling. The energy that previously required heavy cooling can now be used to process more melt, increasing output while maintaining the same torque level. Eliminating external screw cooling holes allows for thicker, stronger screw shafts that can handle higher torque, further boosting potential output. Air cooling for the cylinder and closed internal screw cooling contribute to the 'maintenance free' concept by reducing reliance on fluids and pumps.
FAQ Section
Why is effective heat management in the extruder screw important, especially at high output?
Effective heat management prevents polymer degradation due to excessive temperatures caused by shear and barrel heat. At high outputs and torque, the risk of overheating, melt sticking, and even screw damage increases if heat is not adequately removed or balanced.
How have modern extruder designs improved heat balancing at high output?
Modern designs reduce the need for heavy cooling by optimizing specific energy input. By allowing more energy to be used for melting rather than requiring cooling, and by eliminating external cooling channels (which allows for stronger screws), they can process higher output at the same or even higher torque levels without risking overheating or degradation.
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Patrick van Bezouw
