In the extrusion process of PVC wire for household appliances, precise temperature control is crucial for reducing appearance defects and improving product quality. As a heat-sensitive polymer, PVC's thermal stability directly affects the width of the processing window, and the appearance quality of the wire (such as surface smoothness, color uniformity, and the presence of streaks or bubbles) is closely related to the matching degree of temperature parameters. Optimizing temperature parameters requires comprehensive consideration of equipment characteristics, material properties, and process logic to form a systematic solution.
The temperature zoning design of the extruder must match the plasticizing characteristics of PVC. Typically, the extruder barrel is divided into a feeding section, compression section, melting section, metering section, and die section. The temperature of each section needs to be set according to the functional differences. The feeding section, as the initial heating zone for the material, needs to provide sufficient external heat to quickly vitrify the PVC powder, forming a preliminary compacted block structure, preventing material slippage in the screw channel due to excessively low temperatures, which could cause feeding fluctuations. The compression and melting sections are critical areas for the transformation of PVC from a glassy state to a viscous flow state. Temperatures need to be gradually increased to promote molecular chain deentanglement, but localized overheating leading to degradation must be avoided. The metering section requires balancing internal and external heat to prevent excessive shear heating and carbonization of the melt, while ensuring melt temperature uniformity to reduce stress concentration caused by temperature fluctuations.
The die temperature is a direct factor affecting the appearance of PVC wire. Too low a die temperature leads to insufficient melt flow, resulting in streaks or pitting on the surface; too high a temperature may cause melt fracture, producing a sharkskin effect or scorch marks. Furthermore, the die temperature needs to be coordinated with the traction speed to ensure rapid solidification of the melt after leaving the die, avoiding bending or diameter fluctuations caused by uneven cooling. For PVC wire, surface smoothness directly affects insulation performance and aesthetics; therefore, die temperature optimization needs to be combined with die material and surface treatment processes, such as using chrome-plated dies or laser drilling technology to reduce melt adhesion.
Temperature parameter optimization needs to be deeply coupled with screw design. The compression ratio, length-to-diameter ratio, and shear element layout of the screw directly affect the plasticizing efficiency and temperature distribution of the material. For example, a high compression ratio screw can enhance shear heat generation and appropriately reduce the external heat setting; while a screw with a large length-to-diameter ratio requires segmented temperature control to avoid degradation due to excessive material residence time. For fine-diameter products such as PVC wire, the screw design must balance plasticizing uniformity and low shear to prevent molecular chain breakage caused by excessive shear, resulting in decreased PVC wire strength or surface roughness.
The sensitivity of material formulation to temperature parameters also needs to be optimized. The type of PVC resin, plasticizer, and filler ratio all affect its processing temperature range. For example, a high-filler system requires a higher processing temperature to promote dispersion, but may cause filler agglomeration or surface precipitation; while a high-plasticizer system requires a lower temperature to prevent plasticizer volatilization or migration. Household appliance wires have special requirements for flame retardancy and heat resistance. Flame retardants or heat-resistant modifiers are often added to the formulation. The decomposition temperature of these additives may be lower than that of the PVC itself, necessitating temperature parameter adjustments to avoid premature decomposition and resulting appearance defects.
The stability of temperature control depends on equipment precision and closed-loop process management. Extruders must be equipped with high-precision temperature control modules to ensure that temperature fluctuations in each section are controlled within ±2℃, preventing quality fluctuations caused by temperature drift. Simultaneously, a temperature-quality correlation database should be established, and the correspondence between temperature parameters and appearance defects should be analyzed through SPC statistical process control to achieve dynamic adjustment of process parameters. For example, if periodic stripes are found on the wire surface, the cause can be traced back to the matching degree of screw speed and temperature, and the defect can be eliminated by optimizing the temperature gradient.
Environmental factors also have a significant impact on temperature parameters. Workshop temperature, humidity, and ventilation conditions can alter the pre-drying effect of PVC materials and the heat exchange efficiency during extrusion. For example, high humidity environments may cause materials to absorb moisture, requiring higher processing temperatures to remove it, but this can lead to degradation. Conversely, low-temperature environments necessitate longer preheating times to prevent unstable extrusion due to uneven material temperatures. PVC wire production for household appliances requires constant temperature and humidity workshops equipped with dehumidification and drying systems to ensure material moisture content is below 0.1%, reducing the difficulty of adjusting temperature parameters from the outset.
Continuous improvement is a long-term strategy for optimizing temperature parameters. Using tools such as Design of Experiments (DOE) and Taguchi methods, the interactions between parameters like temperature, rotational speed, and traction speed are systematically explored to establish multi-objective optimization models. For instance, with surface finish, diameter tolerance, and energy consumption as optimization objectives, the optimal temperature combination is determined using response surface methodology. Simultaneously, an AI visual inspection system is introduced to monitor wire appearance defects in real time, feeding the inspection data back to the temperature control system, forming a closed-loop optimization mechanism to continuously improve product quality stability.
