In power cord production, the extrusion process is crucial for controlling wire diameter uniformity. The key lies in achieving stable wire diameter output through equipment optimization, parameter control, mold design, and real-time feedback mechanisms.
The core of the extrusion process is the continuous operation of a single-screw extruder. The insulation or sheathing surrounding the power cord conductor requires the extruder to melt plastic pellets into a viscous fluid state, which is then extruded through the annular gap between the core and sleeve. During this process, the screw speed, barrel temperature distribution, and the pull-off mechanism all play a synergistic role in determining wire diameter uniformity. Unstable screw speed or fluctuating pull-off speeds can lead to periodic variations in wire diameter, resulting in bamboo-like defects. Improper temperature control can cause plastic decomposition or poor plasticization, affecting wire diameter consistency.
Temperature control is a crucial parameter in the extrusion process. In power cord production, plastic undergoes three temperature zones: feeding, melting, and homogenization. The feeding section uses a low temperature to prevent premature melting of the plastic, which can lead to poor feeding. The melting section requires a significant temperature increase to transform the plastic from a granular solid into a viscous fluid. The homogenization section maintains the highest temperature to ensure that any remaining polymer components are fully plasticized. Excessively high temperatures can cause plastic scorching, bubbles, or surface roughness; excessively low temperatures can lead to uneven plasticization and fluctuations in wire diameter. Therefore, the temperature profile must be dynamically adjusted based on the plastic type (e.g., polyethylene, polyvinyl chloride), and thermal balance must be maintained through staged cooling.
Screw design and speed matching are key to achieving wire diameter uniformity. The screw's compression ratio, aspect ratio, and flight structure directly impact the plasticization of the plastic. A low compression ratio screw reduces shear heating and prevents material overheating; a screw with a high aspect ratio prolongs the plasticization time and improves mixing uniformity. Furthermore, the screw speed must be coordinated with the pull-out speed: excessively high speeds can cause melt pressure fluctuations, resulting in thinner wire diameters; excessively low speeds can lead to insufficient output, resulting in glue accumulation or empty pipes. In practice, a PID control algorithm is used to adjust the screw speed in real time to ensure that the extrusion output matches the pull-out output. Mold design plays a crucial role in controlling wire diameter. The mold core and sleeve must be matched to each other, taking into account the plastic's expansion rate and cooling shrinkage. Extruded cores are suitable for high-viscosity materials, but smaller sleeves are required to offset melt expansion. Semi-extruded cores achieve a smoother surface finish by increasing the sleeve's inner diameter. The length and diameter of the sleeve's sizing zone must be precisely calculated: a short sizing zone will result in unstable wire diameter, while an excessively long zone may cause wire thinning due to increased friction. Furthermore, mold concentricity must be kept within a tight range to avoid eccentricity that could cause the wire to be thicker on one side and thinner on the other.
The stability of the traction device and pay-off and take-up system is the ultimate guarantee for wire diameter uniformity. The traction speed must be uniform and stable, forming a closed-loop control with the screw speed. Fluctuations in the traction speed will cause periodic variations in wire diameter. Excessive traction tension can cause the wire to stretch and thin. The pay-off and take-up device must be equipped with a tension control system to ensure the conductor is centered and the tension is constant, preventing diameter fluctuations caused by conductor misalignment or sudden tension changes. In practice, crawler-type or roller-type pullers are often used, coupled with a magnetic powder clutch to achieve constant tension winding.
Real-time detection and closed-loop feedback are the technical support for wire diameter uniformity. Online diameter gauges use laser or capacitive sensors to monitor wire diameter changes in real time and transmit the data to a central control system. When wire diameter deviation is detected, the system immediately adjusts the screw speed or pull-out speed, forming a "measure-compare-correct" closed-loop control mechanism. This feedback mechanism keeps wire diameter fluctuations within a minimal range, significantly improving product qualification rates.
Controlling wire diameter uniformity in the power cord extrusion process requires coordinated improvements across multiple dimensions, including equipment accuracy, parameter optimization, mold design, and real-time feedback. By precisely controlling key parameters such as temperature, screw speed, and pull-out tension, combined with high-precision molds and a closed-loop feedback system, stable wire diameter output can be achieved, meeting the quality requirements of the high-end power cord market.
