In many announcements of the State Grid notifying suppliers, we can often see such a notification from cable companies: the thickness of the insulation layer of the power cable produced is not qualified. So what is the impact of the thickness of the specific insulation layer on the cable? What kind of sheath is qualified? How can we make qualified cables in production? Let's take a look at it.

Hazard of unqualified cable sheath thickness

1, reduce the service life of wire and cable products

This is easy to understand, after long-term operation, especially directly buried, immersed in water, exposed to the open air or easily corroded environment, due to the corrosion of the external medium for a long time, the insulation level and mechanical level of the thinnest point of the sheath will decline. Coupled with routine sheath testing or line grounding failures, the thinnest point may be broken down. In this way, the cable sheath almost loses its protective effect on the cable.

In addition, the internal consumption can not be ignored, wire and cable long-term power will produce a lot of heat, also become a major factor affecting its service life.

(Here to add a little common sense: the allowable working temperature of the conductor is 70 ° C, and the long-term use temperature of PVC should not exceed 65 ° C.)

2, increase the difficulty in the laying process

With the development of global industry, it is increasingly required that high-voltage cable products must be small in the outer diameter, and it is necessary to consider leaving a gap in the laying process, so as to dissipate the heat generated after the wire and cable are energized, and the thickness of the sheath will increase the difficulty of laying. Therefore, the thickness of the sheath requires strict compliance with the relevant standards, otherwise it can not play the role of protecting the wire and cable, but at the same time, it can not blindly pursue its thickness, ignoring the relevant requirements of the actual laying.

Compliance standards for cable sheaths

According to the above two analysis, it is not difficult to see that the quality of the product is good or bad, its first feature is reflected from the appearance quality of the product, no matter what kind of product, or semi-finished products, in the production must pay attention to the appearance quality, the implementation of strict control and inspection.

Sheath is the appearance of the cable, its appearance requirements are smooth and round, uniform luster, no deviation of the core (shall not exceed the specified deviation), no mechanical damage, flattening, no visual visible debris, bubbles, sand holes, obvious particles, bamboo, twist shape, etc. In addition to meeting the above quality requirements, the thickness of the sheath also has a certain impact on the quality of the cable.

If the thickness of the sheath in the production of the cable is lower than the standard requirements, it is unqualified, and the thickness exceeds the standard requirements. For example, the cable model is DDR-KYJV223 *1.5mm2, and the average thickness of the sheath measured is 1.7mm. If this type is referred to the GB9330-88 standard, the thickness should be 1.2mm.

Precautions for sheath production

Calculate the thickness of the control sheath according to the standard, the calculation formula is: D (outer diameter before extrusion) ×0.035+1;

Online measurement of sheath thickness: sheath thickness = (circumference after sheath extrusion - circumference before sheath extrusion)/2π or sheath thickness = (circumference after sheath extrusion - circumference before sheath extrusion)×0.1592;

Single core sheath thinnest point: nominal value ×85%-0.1;

The thinnest point of multi-core sheath: nominal value ×80%-0.2;

Increase the temperature of the low density polyethylene sheath extruder, improve the stress cracking strength, because the extrusion temperature is too high, easy to make the plastic scorch, or "slip" phenomenon; In addition, the shape stability of extruded cladding is poor, the shrinkage rate increases, and even causes the discoloration and bubbles of extruded plastic layer.

Do a good job of the extruder body and screw cooling system to eliminate friction overheating, in order to maintain the heat balance in the extrusion process, stabilize the extrusion pressure, promote the plastic mixing evenly, improve the plasticizing quality.

To sum up, in the production process, we only after careful operation of the equipment, according to the standard requirements of strict control of the thickness of the sheath, can not only save resources for the enterprise, reduce material consumption, increase profits, but also to ensure the quality of the cable, to create high-quality and inexpensive products.


Qingdao Tianxing Cable Co., Ltd. is a technology enterprise specializing in the production of wire and cable in Shandong Province, with more than 150 sets of domestic excellent cable production equipment and testing equipment, excellent production technology, modern testing equipment, to ensure stable product quality and timely supply. The company's main products are power cable, mineral cable, high life wire and cable, radiation crosslinked cable, control cable, computer cable, photovoltaic cable, communication cable, data cable, low smoke halogen free cable, flame retardant series wire and cable.

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