What are the precise temperature control requirements for the extruder during the production of PE pipes?
Release Time : 2025-12-31
In the PE pipe production process, temperature control of the extruder is a core factor determining the quality and performance of the pipe. Its accuracy directly affects the plasticizing effect, melt flowability, and the physical properties of the final product. Temperature control needs to be implemented throughout multiple functional sections of the extruder, from raw material feeding to melt forming. The temperature setting at each stage must be closely matched with the raw material characteristics, equipment structure, and process objectives to achieve stable and efficient production.
In the raw material feeding stage, i.e., the feeding section of the extruder, temperature control needs to balance solid conveying efficiency with the pre-plasticizing requirements of the raw material. The temperature at this stage is usually set relatively low to ensure that the raw material enters the screw smoothly in a solid form, avoiding premature softening that could lead to bridging or blockage. Simultaneously, moderate preheating can improve the flowability of the raw material, preparing it for the subsequent plasticizing stage. If the temperature is too low, the raw material conveying resistance increases, potentially causing equipment overload; if the temperature is too high, the raw material will melt prematurely, compromising conveying stability.
After entering the melting section, temperature control becomes crucial in the plasticizing process. At this stage, the raw material needs to be gradually heated to transform from a solid state to a uniform molten state. The temperature setting needs to be adjusted according to the melt index, molecular weight distribution, and additive type of the raw material. Excessively low temperatures can lead to poor plasticization, leaving unmelted particles in the melt and affecting the mechanical properties of the pipe. Excessively high temperatures can cause thermal degradation of the raw material, resulting in defects such as bubbles and discoloration, and even damaging the molecular chain structure, reducing the pipe's pressure resistance and durability. Therefore, temperature control at this stage needs to be precise to a critical range that completely melts the raw material while avoiding thermal damage.
The metering section is the final heating area of the extruder, and its temperature setting must balance melt homogenization and conveying stability. Precise temperature control at this stage ensures uniform melt temperature, avoiding melt viscosity fluctuations caused by localized overheating or undercooling. Excessively high temperatures will decrease melt viscosity, potentially causing extrusion bulging and affecting pipe dimensional accuracy; excessively low temperatures will increase melt viscosity, increasing extrusion resistance and even causing melt fracture. Furthermore, the metering section temperature needs to be controlled in conjunction with the die temperature to create a stable melt pressure gradient, ensuring pipe forming quality.
The die and orifice, as the final channel for melt forming, directly determine the appearance and dimensional accuracy of the pipe through temperature control. The die head temperature needs to be slightly higher than the metering section to compensate for heat loss during melt flow and to prevent melt sagging or dripping due to excessive heat. The die temperature needs to be fine-tuned according to the pipe specifications and extrusion speed to ensure the melt has suitable viscoelasticity upon exiting the die, allowing for smooth shaping while avoiding surface roughness or internal stress concentration caused by excessively low temperatures. The temperature difference between the die and mandrel must also be controlled within a reasonable range to prevent uneven pipe wall thickness or excessive ovality.
While the vacuum shaping stage does not directly involve extruder temperature control, it needs to be coordinated with it. The water temperature in the vacuum shaping sleeve must be lower than the melt temperature to quickly cool and solidify the pipe surface, while avoiding brittleness or internal stress accumulation caused by excessively low temperatures. The difference between the extruder outlet temperature and the vacuum shaping water temperature needs to be precisely controlled to ensure that the pipe releases internal stress and maintains dimensional stability during the shaping process. If the extruder temperature is too high or the setting water temperature is too low, the pipe may deform due to uneven shrinkage; conversely, insufficient setting may occur, resulting in ripples or collapse on the pipe surface.
The cooling stage is the critical step in the pipe's transformation from a molten state to a solid state. Its cooling rate and temperature gradient must form a closed loop with the extruder temperature control. The cooling water temperature must be gradually reduced to avoid stress concentration caused by excessive temperature differences between the inside and outside of the pipe. The difference between the extruder outlet temperature and the initial cooling water temperature must be controlled within a reasonable range to ensure that the pipe releases heat slowly during cooling, avoiding increased brittleness or performance degradation due to rapid cooling. Furthermore, the cooling water flow rate and its uniformity must be coordinated with the extruder temperature control to ensure consistent cooling rates across all parts of the pipe, maintaining dimensional accuracy and surface quality.
Extruder temperature control in PE pipe production is a complex system involving multiple sections and parameters, requiring precise setting and dynamic adjustment based on raw material characteristics, equipment structure, and process objectives. From the low-temperature conveying in the feeding section, the gradient heating in the melting section, and the homogenization control in the metering section, to the matching of the forming temperature between the die head and the die, and then to the coordinated cooling in the vacuum shaping and cooling stages, the temperature control of each link must be aimed at achieving the best quality of the pipe. Through meticulous management and process optimization, we ensure that the PE pipe meets high standards in terms of performance, size, and appearance.