What are the effects of unsatisfactory cable insulation thickness?

In many national network notification suppliers' announcements, we often see such a notice from cable companies that the thickness of the insulation cable produced is unqualified. What effect does the thickness of the specific insulation layer have on the cable?

1. Reduce the service life of wire and cable products

This problem is easy to understand. After long-term operation, especially in direct burial, immersion in water, exposure to open air or corrosive environment, due to the corrosion of external media for a long time, the insulation level and mechanical of the sheath at the thinnest point. The level will drop. Coupled with the routine sheath test or line ground fault, the thinnest point may be broken down. In this way, the protective effect of the cable jacket is lost. In addition, the internal consumption can not be ignored, the wire and cable will generate a lot of heat when it is energized for a long time. Here is a little common sense: the conductor is allowed to work at 70 °C, and the long-term use temperature of PVC should not exceed 65 °C. Therefore, wire and cable are actually in the "internal and external troubles" situation.

2, increased the difficulty of the laying process

With the development of global industry, more and more environmental requirements require high-voltage cable products to have a small outer diameter. In the process of laying, it is necessary to consider leaving a gap, so as to dissipate the heat generated after the wire and cable are energized, and the thickness of the sheath. Too thick will increase the difficulty of laying, so the thickness of the sheath is strictly in accordance with the relevant standards, otherwise it can not protect the wire and cable. Nor can we blindly pursue its thickness.

According to the above two kinds of analysis, it is not difficult to see that the quality of the product is good or bad, and its first characteristic is reflected in the appearance quality of the product. No matter which product or semi-finished product, it must pay attention to the appearance in production. Quality, strict control and inspection. The sheath is the appearance of the cable, and its appearance requirements are smooth and round, uniform gloss, no eccentricity (not exceeding the specified deviation), no mechanical damage, flattening, no visible objects, bubbles, sand holes, obvious particles, bamboo Section shape, twist shape, etc. In addition to meeting the above quality requirements, the sheath thickness also has a certain impact on the cable quality.

It is well known that the role of the cable sheath is to protect the insulated core of the cable from damage under external force and to protect it. If the thinnest point of the cable jacket does not meet the requirements, the cable jacket will be damaged if it has not reached the normal maximum external destructive force.

If the thickness of the sheath in the production is lower than the standard requirements, it is unqualified, and the thickness exceeds the standard requirement and is also unqualified. For example: the cable type is DLD-KYJV22 3*1.5mm2, and the average thickness of the sheath is 1.7mm. The thickness of this model is 1.2mm according to the requirements of GB9330-88. How to control the thickness of the cable sheath?

1) Calculate the thickness of the control sheath according to the standard, and calculate the formula: D (outer diameter before extrusion) × 0.035 +1; 2) measure the thickness of the sheath on-line: thickness of the sheath = (perimeter after extrusion of the sheath - before extrusion) Perimeter)/2π or sheath thickness = (perimeter after extrusion of sheath - circumference before extrusion sheath) × 0.1592; 3) thinnest point of single core sheath: nominal value × 85% - 0.1;

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

5) Improve the temperature of the low-density polyethylene sheathed extruder and increase the stress cracking resistance. Because the extrusion temperature is too high, the plastic may be burnt or “slip” phenomenon; in addition, the shape stability of the extrusion layer is poor. The shrinkage rate increases, and even causes discoloration and bubble formation of the extruded plastic layer; 6. Eliminate friction and overheating of the extruder body and screw cooling system to maintain the heat balance during the extrusion process and stabilize the extrusion pressure. The plastic is evenly stirred to improve the quality of plasticization.

In summary, in the production process, we only carefully control the thickness of the sheath according to the standard requirements, so as to save resources, reduce material consumption, increase profits, and ensure cable quality and quality. Cheap products.