In the announcement of many State grid 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. How does the thickness of the specific insulation layer not meet the standard affect the cable? What kind of sheath is qualified? How do we make qualified cables in production?

The hazard of unqualified 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 protective effect of the cable sheath will be lost. In addition, the internal consumption can not be ignored, wire and cable long-term power will produce a lot of heat.

A little common sense is added here: the allowable working temperature of the conductor is 70 ° C, and the long-term use temperature of PVC should not exceed 65 ° C. So the wire and cable is actually in the "internal troubles and foreign troubles" situation.

2, increase the difficulty in the laying process

With the development of global industry, more and more environmental requirements of high-voltage cable products must be small outside diameter, in the laying process need to consider leaving a gap, so as to dissipate the heat generated after the wire and cable power, the thickness of the sheath is too thick will increase the difficulty of laying, so the thickness of the sheath is strictly in line with the relevant standards, otherwise it can not play a role in protecting the wire and cable. Nor can we blindly pursue its thickness.

What kind of sheath is acceptable?

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.

As we all know, the role of the cable sheath is to protect the insulated wire core of the cable from damage under the action of external forces, and play a protective role. If the thinnest point of the cable sheath does not meet the requirements, the cable sheath is damaged under the action of the normal maximum external destructive force.

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 DLD-KYJV22 3*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.

Several points to pay attention to in the production of sheathing

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

2. Measure the sheath thickness online

Sheath thickness = (perimeter after sheath extrusion - perimeter before sheath extrusion)/2π or sheath thickness = (perimeter after sheath extrusion - perimeter before sheath extrusion)×0.1592

3. Thinnest point of single core sheath: nominal value ×85%-0.1

4. The thinnest point of multi-core sheath: nominal value ×85%-0.1

5. Increase the temperature of the low-density polyethylene sheath extruder and 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 the extruded cladding is poor, the shrinkage rate increases, and even causes the discoloration and bubbles of the extruded plastic layer.

6. Do a good job of extrusion 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, so that not only for the enterprise to save resources, 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.