What is the quantitative relationship between the degree of crosslinking control of XLPE cable material and the mechanical strength of the cable?
Release Time : 2026-01-26
As the core insulation material of power cables, the degree of crosslinking in XLPE cable material significantly impacts its mechanical strength throughout the entire material modification process. The crosslinking process transforms linear polyethylene molecular chains into a three-dimensional network structure through chemical or physical means. This structural change directly determines the material's creep resistance, tensile strength, and elongation at break. The core of crosslinking degree lies in balancing the density of crosslink bonds between molecular chains: insufficient crosslinking leads to slippage of molecular chains under stress, causing thermal creep at high temperatures, insulation shrinkage and deformation, and a significant decrease in mechanical strength; excessive crosslinking, on the other hand, causes stress concentration due to over-binding of molecular chains, making the material brittle, reducing impact resistance, and even leading to cracking during processing due to excessive internal stress.
The degree of crosslinking has a dual effect on improving the tensile strength of XLPE. Within a moderate crosslinking range, the crosslink bonds formed between molecular chains act as "molecular bridges," effectively transferring stress and ensuring uniform stress distribution during stretching, thus significantly improving tensile strength. This strengthening mechanism stems from the inhibitory effect of the crosslinked network on molecular chain slippage, requiring the material to overcome a higher energy barrier before failure. However, when the degree of crosslinking exceeds a critical value, excessive constraint on the molecular chains causes the crosslinking points to become stress concentration points, thus reducing tensile strength. At this point, the failure mode of the material changes from molecular chain slippage to crosslink bond breakage, macroscopically manifested as brittle fracture.
Elongation at break, as a key indicator of material toughness, is negatively correlated with the degree of crosslinking. Moderate crosslinking can limit the excessive extension of molecular chains, preventing irreversible deformation under stress and thus maintaining a certain elongation at break. However, when the crosslinking is too high, the degrees of freedom of the molecular chains are severely restricted, and the material cannot absorb energy through the extension of molecular chains during stretching, leading to a sharp drop in elongation at break. This loss of toughness is particularly evident when cables are bent or subjected to external impact, potentially causing insulation cracking and threatening the operational safety of the cable.
The degree of crosslinking in XLPE cable material also has a significant impact on the creep resistance of XLPE. Creep is a slow plastic deformation that occurs in materials under long-term stress and is crucial for the long-term stability of cables. Moderate crosslinking, by forming a stable crosslinked network, effectively inhibits the thermal motion of molecular chains and significantly reduces the creep rate. This inhibitory effect is particularly pronounced at high temperatures, preventing uneven thickness or separation of the insulation layer from the conductor due to creep. However, excessively low crosslinking leads to active thermal motion of the molecular chains, accelerating creep deformation and potentially causing localized overheating or electric field concentration in the cable; excessively high crosslinking, on the other hand, can cause material cracking due to internal stress accumulation.
The uniformity of crosslinking degree has a decisive influence on the spatial distribution of mechanical strength. During cable production, the crosslinking reaction may exhibit a crosslinking degree gradient due to uneven temperature, pressure, or raw material distribution. This non-uniformity leads to an imbalance in the internal stress distribution of the insulation layer, easily causing localized stress concentration under stress and reducing overall mechanical strength. For example, the inner insulation layer may be more fully crosslinked due to slower heat dissipation, while the outer layer has a lower crosslinking degree, forming a "soft outside, hard inside" structure, which is prone to cracking of the outer layer during bending. Therefore, optimizing crosslinking process parameters to achieve axial and radial uniformity of crosslinking degree is crucial for improving the mechanical reliability of cables.
The crosslinking degree of XLPE cable material is closely related to the long-term thermal aging performance of XLPE. In high-temperature operating environments, cross-linking bonds may break due to thermal oxidation or electrical stress, leading to a decrease in the degree of cross-linking. This degradation process weakens the connections between molecular chains, reduces mechanical strength, and may even cause insulation layer delamination. Moderate cross-linking can improve the thermal stability of cross-linking bonds and slow down the aging process; however, excessive cross-linking may accelerate aging due to excessive initial internal stress. Therefore, a balance must be struck between the degree of cross-linking and thermal stability through the addition of antioxidants or optimization of cross-linking agents.
Cross-linking degree control is a core aspect of optimizing the mechanical properties of XLPE cables. By precisely controlling cross-linking process parameters, such as cross-linking temperature, time, and cross-linking agent dosage, the degree of cross-linking can be optimized within a suitable range, thus balancing tensile strength, elongation at break, creep resistance, and thermal aging stability. Simultaneously, attention must be paid to the uniformity of the degree of cross-linking to avoid spatial uneven distribution of mechanical properties due to process defects. These measures collectively ensure the mechanical reliability of XLPE cables in complex operating environments, providing a crucial guarantee for the safe and stable operation of power systems.