The cable sheath cannot be too thin or too thick. What does it take to be qualified?

Hazards of unqualified sheath thickness

1. Reduce the service life of wire and cable products

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

In addition, routine sheath test detection or line grounding fault may cause the thinnest point to be broken down. In this way, the protective effect of the cable sheath will be lost. In addition, the internal consumption cannot be ignored. The long-term power supply of wires and cables will generate a lot of heat.

Here is a little common sense: the allowable operating temperature of the conductor is 70℃, and the long-term use temperature of polyvinyl chloride should not exceed 65℃. So wires and cables are actually in a situation of "internal and external troubles".

2. Increased difficulty in the laying process

With the development of global industry, more and more environments require high-voltage cable products to have a small outer diameter. In the process of laying, it is necessary to consider leaving gaps so that the heat generated by the wires and cables after power is turned on can be dissipated. The thickness of the sheath is too thick, which will increase the difficulty of laying. Therefore, the thickness of the sheath must strictly comply with the relevant standards, otherwise it will not be able to protect the wires and cables. You can't just pursue its thickness.

What kind of sheath is qualified?

Based on the above two analyses, it is not difficult to see that the quality of the product is good or bad, and its first feature is reflected in the appearance quality of the product. No matter what kind of product or semi-finished product, the appearance quality must be emphasized in production, and it must be strictly controlled and inspected.

The sheath is the appearance of the cable. Its appearance requirements are smooth and round, uniform gloss, no core deviation (not exceeding the specified deviation), no mechanical damage, flattening, no visible debris, bubbles, sand holes, obvious particles, bamboo joints, twists, 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.

It is well known that the function of the cable sheath is to protect the insulated core of the cable from damage under the action of external force. If the thinnest point of the cable sheath does not meet the requirements, the cable sheath will be damaged before the normal maximum external destructive force is reached.

If the sheath thickness of the cable is lower than the standard requirement during production, it is unqualified, and the thickness exceeds the standard requirement. For example: the cable model is DLD-KYJV22 3*1.5mm2, and the average sheath thickness is measured to be 1.7mm. If this model refers to the GB9330-88 standard requirements, the thickness should be 1.2mm.

A few points to note in sheath production

1. Control the sheath thickness according to the standard calculation Calculation formula: D (outer diameter before extrusion) × 0.035 + 1

2. Online measurement of sheath thickness

Sheath thickness = (circumference after extrusion - circumference before extrusion) / 2π

or Sheath thickness = (circumference after extrusion - circumference before extrusion) × 0.1592

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

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

5. Increase the temperature of the low-density polyethylene sheath extruder to improve the stress cracking resistance, because the extrusion temperature is too high, which can easily cause the plastic to burn or "slip"; in addition, the shape stability of the extruded layer is poor, the shrinkage rate increases, and it may even cause the extruded plastic layer to change color and bubbles to appear.

6. Do a good job of the extruder body and screw cooling system to eliminate friction overheating, so as to maintain the thermal balance during the extrusion process, stabilize the extrusion pressure, promote uniform mixing of the plastic, and improve the plasticization quality.

To sum up, in the production process, we only need to carefully operate the equipment and strictly control the sheath thickness according to standard requirements. This can not only save resources for the enterprise, reduce material consumption, increase profits, but also ensure the quality of the cable and create high-quality and low-cost products.