In the quality reports of the cable industry, we often see problems about the thickness of the cable insulation layer not meeting the standard. So, what are the effects of a sheath layer that is too thin or too thick on the cable? What kind of sheath is considered qualified? How do we ensure that the cable jacket meets the standards during the manufacturing process?
The hazard of unqualified cable sheaths
1. Affect the life and safety of the cable
During long-term operation of cables, especially in harsh environments, such as direct burial, underwater, open air or corrosive environments, the thinnest point of the sheath layer may be eroded by external media, resulting in deterioration of insulation and mechanical properties. In addition, the heat generated by the energizing of the cable also accelerates the aging of the sheath. If the sheath layer is too thin, it may not be able to effectively protect the core in the event of cable failure, thus shortening the life of the cable.
2. Increase the difficulty of laying
With the development of industry, high-voltage cable products require a smaller outer diameter for easy laying. An excessively thick jacket layer increases the volume of the cable, making it difficult to leave the necessary voids to dissipate heat during laying, thus making it more difficult to lay. Therefore, the thickness of the sheath layer needs to be strictly controlled within a reasonable range, neither too thin nor too thick.
What does a qualified sheath look like?
A qualified sheath layer should first of all be smooth, rounded, and uniform in appearance, with no eccentricity, mechanical damage, or visible impurities. The thickness of the jacket is also crucial for the quality of the cable. If the thinnest point of the sheath layer is not up to standard, damage may occur before the maximum external destructive force is reached.
In the production process, how to ensure that the thickness of the sheath layer is qualified?
The thickness of the sheath is calculated and controlled according to the standard, using the formula e.g. d(outer diameter before extrusion) 0035+1。
*Measure sheath thickness using the formula: sheath thickness (perimeter after sheath extrusion – circumference before sheath extrusion) 2 or sheath thickness ()01592。
Thinnest point of single-core sheath: nominal value 85%-01；Thinnest point of multi-core sheath: 85%-01。
Increase the temperature of the low-density polyethylene sheath extruder to improve the stress crack resistance and avoid the plastic scorching or "slipping" phenomenon caused by the extrusion temperature being too high.
Do a good job in the extrusion body and screw cooling system to eliminate friction and overheating, maintain the thermal balance in the extrusion process, stabilize the extrusion pressure, and improve the plasticizing quality.
In summary, only through precise operation and strict thickness control can the quality of the cable sheath be ensured, which not only saves resources and reduces costs for enterprises, but also ensures the quality of cables and produces cost-effective products.