Based on the specific functions of each heating zone, PVC extrusion is carried out using an extruder, with the entire process broadly divided into three sections: heating, temperature‑holding, and insulation. The heating and temperature‑holding stages primarily take place within the extruder, which is partitioned—by the venting port—into two relatively independent yet interconnected zones. The insulation zone comprises components such as the flow‑diverting core, the extrusion die body, and the die orifice.

Feed Zone Temperature: The feed zone is where the electric heater transfers heat to the barrel; the temperature displayed reflects the barrel temperature at that section, not the material temperature. Material temperature is typically much lower than the indicated temperature. When the material first enters the extruder via the feed screw, its temperature is around 30–40°C, and the temperature rise generated by shear heating still falls far short of the plasticization (glass transition) temperature. Meanwhile, as the material moves through the compression zone and passes the venting port, it must complete the transition from a glassy state to a viscous flow within the heating zone—ideally exhibiting an “orange‑peel” texture with no powdery residues and tightly adhering to the screw grooves—to prevent vacuum‑induced draw‑out or blockage of the vent. Therefore, the primary function of the feed zone is external heating, and the set temperature should be relatively high to ensure the electric heating bands supply sufficient external heat. At this stage, the heaters operate frequently, often running continuously. However, since the material has not yet reached the die and still requires time to pass through the feed zone, and because bridging may occur at the feed throat or wall‑sticking inside the machine, the set temperature should not be excessively high; a display reading above 185°C is advisable. Even if the feed zone temperature is set lower—say around 170°C or even lower—it is possible to produce products that meet internal quality standards. Yet, with insufficient external heat and excessive reliance on shear heating to raise melt temperature, wear on the barrel increases, shortening the service life of both the screw and the barrel—a trade‑off that ultimately proves disadvantageous. Our long-term observations during extruder maintenance reveal that, after one to two years of operation—sometimes even less—the barrel suffers severe wear, concentrated primarily in the single‑head sections following the heavily compressed double‑head portion, as well as in the wider working areas of the metering zone. Wear depths can reach 2–3 mm. At this point, yellow streaks appear in extrudate due to material backflow and prolonged residence at elevated temperatures. Adjusting clearances further exacerbates localized friction between the screw and barrel, leading to black streaks in the product and abnormal noises from the equipment, rendering normal operation impossible and necessitating replacement of the barrel and screw. Although this phenomenon is closely linked to substandard steel grades and inadequate heat‑treatment processes employed by manufacturers, a key contributing factor is the excessively low feed‑zone temperature, which intensifies shear forces in these regions and accelerates wear. Setting a higher temperature in the feed zone promotes better material melting and allows for more effective utilization of external heat, thereby reducing shear‑induced wear on the extruder. Extensive practical experience demonstrates that, with feed rate, extrusion speed, and metering‑zone temperature held constant, moderately increasing the feed‑zone set temperature can significantly narrow the gap between the metering‑zone’s displayed and set temperatures, clearly indicating that the feed‑zone temperature plays a role in modulating shear heating to some extent.