In a number of national websites, we can often see the cable company's announcement that the insulation thickness of the electric cable is not qualified.How does the thickness of the concrete insulating layer affect the cable?
1. Reduce the service life of cable products
This question is easy to understand, after running for a long time, especially directly buried, soaked in water, exposed in the open air or susceptible to corrosion environment, due to long time to be medium corrosion, sheathed the thinnest point of insulation and mechanical level will fall.Combined with routine protective test tests or a line grounding fault, the thinnest points may be punctured.Thus, the protective effect of the cable sheath will be lost.In addition, internal consumption also cannot ignore, long-term electric wire and cable will generate a lot of heat, it adds a little common sense: conductor allowed working temperature is 70 ℃, polyvinyl chloride (PVC) long-term use of temperature should not exceed 65 ℃.So cable is actually in the situation of "internal and external problems".
2. Increased difficulty in laying process
With the development of global industry, more and more environmental requirements must be outside diameter is small, high voltage cable products in the process of laying there need to consider the gaps, so you can send out the heat generated by the electric wire electric cable after electrify, too thick sheath thickness will increase the difficulty of laying, so the thickness of sheath requirements strictly comply with relevant standards, otherwise unable to protect the wire and cable.Also cannot blindly pursue its thickness
According to the above two kinds of analyses we see not hard, product quality, the advantages and disadvantages, the first characteristic is reflected from the appearance of the product quality, whatever the product, or semi-finished products, must pay attention to appearance quality in the production, the strict control and inspection.Sheath is the appearance of the cable, the requirement is smooth and rounded appearance, uniform luster, unbiased core () shall not exceed the stipulated deviation, no mechanical damage, flattening, perception of visible without sundry, bubble, sand holes, clear grain, bamboo, twist, etc.In addition to the above quality requirements, the sheath thickness has some influence on cable quality.
It is well known that the effect of cable sheath is to protect the insulated wire core of the cable from damage and protect it.If the cable sheath is not as thin as required, the cable sheath will be damaged in the absence of normal maximum external damage.
If the sheath thickness of the cable is lower than the standard in the production, the thickness exceeds the standard and is not qualified.For example, the cable model is DLD-KYJV22 3*1.5mm2 and the average thickness of the sheath thickness is 1.7mm. The thickness should be 1.2mm in reference to the standard gb9330-88 standard.How to control the thickness of cable sheath?
1) according to the standard calculation control sheath thickness, the calculation formula: D (extrusion front diameter) * 0.035+ 1;
2) online measurement of sheath thickness: sheath thickness = (girth of the perimeter of the protective sleeve) /2 PI or sheath thickness = (girth of the circumference of the sheath after the sheath, the circumference of the sheath) x 0.1592;
3) the thinnest point of single core sheath: the nominal value (x 85%- 0.1);
4) the thinnest point of multi-core sheath: nominal value x 80%- 0.2;
5) improve the temperature of low density polyethylene sheath extruder, improve the stress cracking strength, because the extrusion temperature is too high, make the plastic coke burn, or appear "skid" phenomenon;In addition, the shape stability of the extruded layer is poor, the shrinkage rate is increased, and it can even cause discoloration and air bubbles in the plastic layer.
6. Make the extruder fuselage and screw cooling system eliminate the friction heat, to maintain the heat balance in the extrusion process, stabilize extrusion pressure, promote the mixing of plastic and improve the plasticizing quality.
To sum up, in the process of production, we only after careful operation equipment, according to the standard requires strict control of sheath thickness, both for the enterprise to save resources, reduce material consumption, increase profits, and can ensure the quality of cable, create a high quality and low price products.