How to control the uniformity of crosslinking degree in the production of cross-linked polyolefin insulated wire?
Release Time : 2025-12-25
Cross-linked polyolefin insulated wire plays a crucial role in power transmission due to its excellent electrical properties, heat resistance, and mechanical strength. Its core performance depends on the uniformity of cross-linking. Uneven cross-linking distribution can lead to localized decreases in insulation heat resistance, insufficient mechanical strength, and even insulation aging or breakdown risks. Therefore, controlling the uniformity of cross-linking is a critical step in the production process, requiring coordinated optimization from multiple dimensions, including process parameters, equipment design, and material selection.
The cross-linking process of cross-linked polyolefin insulated wire is a core factor affecting uniformity. In chemical cross-linking, the dispersion uniformity of the cross-linking agent directly affects the cross-linking degree distribution. If the cross-linking agent is not sufficiently mixed in the insulation material, excessively high local concentrations will lead to over-cross-linking, while insufficient concentrations will result in inadequate cross-linking. Therefore, high-precision mixing equipment is needed to ensure the cross-linking agent is fully integrated with the polyolefin substrate, and the mixing time and temperature must be strictly controlled to avoid premature decomposition of the cross-linking agent due to excessively high temperatures. Irradiation cross-linking requires precise control of the electron beam energy and dosage. Excessive electron beam energy can penetrate the insulation layer, leading to over-crosslinking internally and insufficient surface crosslinking; uneven dosage can cause significant differences in crosslinking degree within the same cross-section. Therefore, a uniform irradiation system, such as an electron accelerator combined with a scanning device, is required to ensure uniform energy coverage of the insulation layer.
Temperature control is another key factor in ensuring uniform crosslinking degree. The crosslinking reaction of cross-linked polyolefin insulated wire is extremely sensitive to temperature; temperature fluctuations directly affect the crosslinking speed and degree. In chemical crosslinking, if the extruder temperature is too high, the crosslinking agent may decompose prematurely, leading to localized crosslinking failure; if the temperature is too low, the crosslinking reaction is slow, affecting production efficiency. Therefore, a segmented temperature control system is required, setting a reasonable temperature gradient based on the characteristics of the crosslinking agent to ensure that the insulation layer gradually completes the crosslinking reaction during extrusion. During irradiation crosslinking, the insulation layer temperature must be maintained within a suitable range to avoid thermal degradation or a decrease in crosslinking degree due to excessive temperature.
Equipment design is equally crucial for uniform crosslinking degree. The screw structure of the extruder must be matched with the characteristics of the insulation material to ensure uniform plasticization during extrusion, avoiding differences in crosslinking degree due to uneven plasticization. Mold design requires optimized flow channel structure to reduce variations in material residence time within the mold and prevent excessive local crosslinking due to prolonged residence time. For irradiation crosslinking, the beam uniformity of the electron accelerator directly affects the crosslinking degree distribution; therefore, equipment calibration is necessary to ensure stable beam intensity and scanning speed.
Material selection is fundamental to controlling the uniformity of crosslinking. The molecular weight distribution and crystallinity of the polyolefin substrate affect the uniformity of the crosslinking reaction. An excessively wide molecular weight distribution leads to inconsistent crosslinking rates, while excessively high crystallinity may hinder the penetration of the crosslinking agent. Therefore, polyolefin raw materials with narrow molecular weight distribution and moderate crystallinity should be selected, and the formulation should be optimized by adding appropriate amounts of plasticizers or modifiers to improve the material's processing performance and crosslinking reactivity. The selection of crosslinking agents also requires careful consideration; crosslinking agents with good compatibility should be chosen based on the type of polyolefin and process conditions to avoid uneven crosslinking due to differences in reactivity.
Environmental control during production is equally crucial. Environmental factors such as humidity and oxygen content can affect the stability of the crosslinking reaction. For example, excessive humidity may cause hydrolysis of the crosslinking agent, reducing crosslinking efficiency; oxygen may trigger oxidation reactions, affecting the electrical properties of the insulation layer. Therefore, production must be carried out in a dry, clean environment, equipped with dehumidification and inert gas protection devices to reduce the interference of environmental factors on the uniformity of crosslinking.
Quality inspection is the final checkpoint to ensure the uniformity of crosslinking. Online detection technologies, such as infrared spectroscopy and thermal elongation testing, must be used to monitor the crosslinking distribution of the insulation layer in real time. For critical products, destructive testing, such as cross-sectional observation and performance testing, is also required to verify the uniformity of crosslinking. By establishing a strict quality control system, deviations in the production process can be promptly identified and corrected to ensure that the crosslinking degree of each batch of products meets the standard requirements.