As discussed in the informative article “To Produce Quality Extrusions, Get Control Over Melt Temperature,” published on Plastics Technology Online, melt temperature is a critical factor in the extrusion process.
In the world of extrusion, melt temperature is the one absolute temperature. It’s the temperature at which plastic materials melt and flow, and it plays a pivotal role in the entire process. All other temperatures, such as zone temperatures, either contribute to achieving the desired melt temperature or are influenced by it.
To ensure quality extrusions, it’s crucial to monitor and control the melt temperature accurately. One primary objective in extrusion is to produce a consistent, homogenous melt temperature at the screw’s tip. This melt has undergone shearing, heating, melting, and pumping processes. It’s then pushed through a screen pack, and its temperature is measured. Attempting to uniformly cool this melt after measurement can be challenging and lead to variations in melt temperature at the die.
To accurately measure melt temperature, it’s vital to use a melt thermocouple that’s flush-tipped or integrated into a pressure gauge. This ensures that the measurement is focused on the plastic melt, not the surrounding steel. In the plastic flow through an adapter tube, the material typically takes on a parabolic shape, with the hottest material flowing in the center and cooler material surrounding it. It’s essential to remember that plastic melt doesn’t behave like water; it’s a viscous substance with unique flow characteristics.
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