As highlighted in the article “To Produce Quality Extrusions, Get Control Over Melt Temperature” on Plastics Technology Online, the melt temperature plays a pivotal role in the extrusion process. It is the absolute temperature that influences the entire plastic flow, shaping the quality of the final product.
To ensure accurate melt temperature readings, the importance of correctly setting zone temperatures is emphasized. In extrusion, the objective is to achieve a homogeneous melt temperature at the screw’s tip after undergoing shearing, heating, melting, and pumping. Attempting to uniformly cool the melt in subsequent stages, such as an adapter, rotator, or die, is crucial for maintaining consistency in the final extruded product.
The recommendation is to use a flush-tipped melt thermocouple or one integrated into a pressure gauge to measure the plastic melt accurately. The article suggests a practical approach to verify the accuracy of the thermocouple by comparing the melt temperature with the zone temperature after raising the zone temperature by about 30°F (17°C).
Understanding the unique flow characteristics of plastic melt, the article explains that the plastic flow through an adapter tube is typically parabolic, with the hotter material flowing up the middle and cooler material surrounding it. A crucial point is made about the non-Newtonian behavior of plastic melt, debunking the misconception that it flows like water. The emphasis is on the thermocouple’s placement within the round flow cavity for accurate temperature measurement, with practical recommendations for immersion tip dimensions.
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