In the production of polyester insulated lead wire, precisely controlling the uniformity of the insulation layer thickness is crucial for ensuring the electrical performance, mechanical strength, and service life of the conductor. Uneven insulation layer thickness can lead to localized electric field concentration, increasing the risk of breakdown, or increasing costs due to material waste. Therefore, multi-dimensional optimization is necessary, encompassing raw material selection, equipment precision, process parameters, and environmental control.
The quality of raw materials directly affects the molding effect of the insulation layer. As the main component of the insulation layer, the molecular weight distribution, melt index, and additive ratio of polyester resin must strictly match production requirements. For example, resin with too low a molecular weight has excessive fluidity, easily leading to thickness fluctuations during extrusion; while excessive use of additives such as lubricants or plasticizers may cause uneven surface tension in the insulation layer, resulting in localized accumulation or depressions. Therefore, it is necessary to screen for raw material formulations with optimal equipment compatibility through laboratory trials and long-term production verification to reduce thickness deviations from the source.
The precision of the extrusion equipment is key to controlling the insulation layer thickness. Twin-screw extruders, due to their efficient plasticizing capacity and stable extrusion pressure, are the preferred choice for polyester insulated lead wire production. The screw's compression ratio, length-to-diameter ratio, and die flow channel design need to be customized according to the conductor specifications. For example, the flow channel surface needs ultra-precision polishing to avoid resin degradation or changes in flow resistance due to friction; the die lip gap needs to be calibrated to the micron level using a laser measuring instrument to ensure uniform extrusion of molten polyester. Furthermore, extruders equipped with online diameter gauges can monitor the outer diameter of the insulation layer in real time and automatically adjust the screw speed or traction speed through a feedback system to achieve dynamic thickness compensation.
Optimization of process parameters needs to consider both equipment characteristics and material properties. The extrusion temperature needs to be set in segments according to the polyester's melting point and viscosity curve, typically divided into a feeding section, a compression section, a metering section, and a die zone. Too low a temperature will lead to insufficient resin plasticization and fluctuations in extrusion pressure; too high a temperature may cause material decomposition, producing bubbles or coke particles. Matching the traction speed and extrusion speed is equally important; a large speed difference will cause the insulation layer to stretch and thin, while a small speed difference may lead to excessive thickness due to buildup. Determining the optimal parameter combination through orthogonal experimental design can significantly improve thickness uniformity.
Controlling the cooling process is crucial for the structural stability of the insulation layer. After extrusion, the polyester insulation layer undergoes multi-stage cooling water baths, with the cooling rate adjusted according to the conductor diameter and insulation thickness. Excessive cooling can lead to residual internal stress and subsequent cracking; insufficient cooling can cause the insulation layer to sag and deform due to gravity. A gradient cooling process, using a higher water temperature initially to slow the cooling rate and then gradually decreasing the temperature in subsequent stages to fix the shape, effectively reduces thickness deviation. Simultaneously, the cooling water baths must be equipped with a circulating filtration system to prevent impurities from scratching the insulation layer surface.
Online detection and feedback mechanisms are the last line of defense for ensuring thickness uniformity. Laser diameter gauges or X-ray thickness gauges can measure the insulation layer thickness non-contactly, with a sampling frequency of over a thousand times per second to ensure real-time data. The detection data is transmitted to the central control system via industrial Ethernet. After comparison with the preset thickness range, the system automatically triggers adjustment commands. For example, when an area is detected to have excessive thickness, the system can reduce the screw speed or increase the traction speed in that area, forming a closed-loop control. Furthermore, the online detection equipment is calibrated regularly to avoid misjudgments due to instrument drift.
Temperature and humidity control in the production environment is equally crucial. Polyester materials are sensitive to moisture; moisture absorption can lead to roughness or blistering of the insulation layer surface. Production workshops must be equipped with constant temperature and humidity systems, maintaining the temperature at 23±1℃ and humidity at 50±5% to minimize the impact of environmental factors on material performance. Simultaneously, raw materials and semi-finished products must be stored in a dry environment to prevent thickness fluctuations during extrusion due to moisture absorption.
By systematically optimizing key aspects such as raw materials, equipment, processes, testing, and the environment, the uniformity of insulation layer thickness in polyester insulated lead wire can be significantly improved. This not only helps improve the electrical safety and mechanical reliability of the conductor but also reduces production costs and enhances the product's competitiveness in the high-end market. In the future, with the in-depth application of intelligent manufacturing technologies, such as machine vision-based thickness defect identification and big data-based process parameter prediction, insulation layer thickness control will move towards a more precise era of automation.
