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What is the effect of insulation layer thickness failure on the cable?
At many state-owned network announcements of suppliers, we can often see such a notification from cable companies: The thickness of the power cable insulation produced is not acceptable. What is the effect of the unqualified thickness of the specific insulation on the cable?
1, reduce the service life of wire and cable products
This problem is easy to understand. After long-term operation, especially under direct burial, immersed in water, exposed to open air or in corrosive environments, due to prolonged exposure to external media, the insulation level and mechanical properties of the thinnest point of the sheath The level will fall. Coupled with routine sheath testing or line ground faults, the thinnest point may be broken. In this way, the protective effect of the cable sheath will be lost. In addition, the internal consumption can not be ignored, long-term electricity will produce a large amount of heat wire and cable, add a little common sense here: conductor allowable working temperature is 70 °C, PVC long-term use temperature should not exceed 65 °C. Therefore, wire and cable are actually in the "internal and external problems" situation.
2, increased the difficulty of the laying process
With the development of the global industry, more and more environmental requirements of high-voltage cable products must be small outer diameter, in the laying of the process need to consider leaving gaps, in order to dissipate heat generated after the power cable cable, sheath thickness Too thick will increase the difficulty of laying, so the thickness of the sheath must be strictly in accordance with the relevant standards, otherwise it cannot protect the wire and cable. Nor can we pursue its thickness blindly.
Based on the above two analyses, it is not difficult to see that the quality of a product is good or bad. The first feature is reflected in the appearance quality of a product. No matter what kind of product or semi-finished product, the appearance must be valued in production. Quality, strict control and inspection of it. The sheath is the appearance of the cable, and its appearance requirements are smooth and round, uniform luster, no eccentricity (no more than the specified deviation), no mechanical damage, flattening, no visible debris, air bubbles, trachoma, obvious particles, bamboo Festival, twist-shaped and so on. In addition to meeting the above quality requirements, sheath thickness also has a certain influence on cable quality.
It is well known that the function of the cable sheath is to protect the insulated wire core of the cable from being damaged under the action of the external force and play a protective role. If the thinnest point of the cable sheath does not meet the requirement, the cable sheath will be damaged if the normal maximum external destructive force has not been reached.
If the thickness of the sheath in the production is lower than the standard requirement, it is unqualified, and if the thickness exceeds the standard, it is also unqualified. For example, the cable type is DLD-KYJV22 3*1.5mm2, and the average thickness of the jacket thickness measured is 1.7mm. The thickness of this type of model should be 1.2mm according to GB9330-88 standard. How to control the thickness of cable sheath?
1) Calculate the thickness of the control jacket according to the standard and calculate the formula: D (extrusion outer diameter) × 0.035+1;
2) On-line measurement of sheath thickness: Sheath thickness = (perimeter after the extruded sheath - perimeter before extrusion of the sheath)/2π or sheath thickness = (perimeter after the sheath is extruded - before extrusion of the sheath Perimeter)×0.1592;
3) The thinnest point of single-core sheath: nominal value × 85% -0.1;
4) The thinnest point of multi-core sheath: nominal value × 80% -0.2;
5) Improve the temperature of the low density polyethylene jacket extruder, improve the stress cracking strength, because the extrusion temperature is too high, easy to scorch the plastic, or "skid" phenomenon; In addition, the shape stability of the extruded layer is poor Increased shrinkage may even cause discoloration and bubbles in the extruded plastic layer;
6, to do a good job extruder body and screw cooling system to eliminate friction and overheating, in order to maintain the heat balance in the extrusion process, stabilize the extrusion pressure, promote uniform plastic mixing, improve the quality of plasticization.
To sum up, in the production process, we only strictly operate the equipment and strictly control the thickness of the jacket according to the standard requirements. This will not only save resources for enterprises, reduce material consumption, increase profits, but also guarantee the quality of cables and create high quality. Cheap products. (Source Network)