Standard Qualification Requirements for Cable Sheathing

First of all, we need to understand the situation and harm of cable sheath failure.

Hazard of unqualified jacket thickness

1. Reduce the service life of wire and cable products

This is easy to understand. After long-term operation, especially in direct burial, immersion in water, exposure to open air or corrosive environment, the insulation level and mechanical level of the sheath at the thinnest point due to long-term corrosion by external media. Will fall.

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, internal consumption can not be ignored, and the long-term energization of the wire and cable will generate a lot of heat.

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 the 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 you blindly pursue its thickness.

What kind of jacket sheath qualifies?

According to the above two kinds of analysis, it is not difficult to see whether 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. 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 if 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.

Points to note in the production of the jacket

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

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

The thinnest point of the single core sheath: nominal value × 85% - 0.1.

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

Improve the temperature of the low-density polyethylene sheathed extruder and improve 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 and shrinks. The rate increases and even causes discoloration of the extruded plastic layer and the occurrence of bubbles, etc.

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

In summary, in the production process, we only carefully operate the equipment and strictly control the thickness of the sheath according to the standard requirements, which not only saves resources for the enterprise, reduces material consumption, increases profits, but also guarantees cable quality and creates high quality. Cheap products.

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