The quality of a 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 paid attention to in production, and strict control and inspection must be implemented. The sheath is the appearance of the cable, and its appearance requirements are smooth and round, uniform in luster, no eccentricity (not exceeding the specified deviation), no mechanical damage, flattening, no visible sundries, bubbles, blisters, obvious particles, bamboo Section shape, twist shape, etc. In addition to meeting the above quality requirements, the thickness of the sheath also has a certain influence on the quality of the cable. If the thickness of the sheath is lower than the standard requirements, it is of course unqualified, but if the thickness exceeds the standard requirements, it is also unqualified. For example: the cable model is ZR-KVVP 4*1.5mm2, and the average thickness of the sheath is measured to be 1.6mm. If this model refers to the GB9330-88 standard, the thickness should be 1.2mm. The reasons for disqualification are as follows: 
(1) Reduce the service life. After the cable is laid, it will be energized for a long time, which will generate heat energy. The allowable working temperature of the conductor is 70 °C. The long-term use temperature of PVC should not exceed 65 °C. If it is in summer, the working temperature will rise, and these temperatures will pass through the external The sheath is emitted, the thickness of the sheath increases, and the heat energy is difficult to dissipate, which will affect the service life of the cable. Due to the action of heat, the insulating layer undergoes a series of physical and chemical changes, and the original excellent performance is lost. , resulting in a significant decrease in insulation performance, and even a short circuit, affecting the normal operation of the unit. (2) Defects in material properties. Material properties are not reflected by thickness. According to the requirements of GB8815-2002 standard, If one of its indicators does not meet the standard, flame retardant PVC material, then its oxygen index is lower than 30. (3) There is a problem with the cable structure. If the density of conductors, insulating layers, and weaving is controlled according to the standard requirements, and appropriate fillers are selected to make them round, how can the sheath be squeezed so thick? (4) Increase the difficulty of cable laying. At present, cable laying is mainly based on bridge or pipe. Now many enterprises are implementing tight cable requirements and small outer diameter. During the laying process, there can be gaps to dissipate heat energy to ensure that the outer sheath of the cable is not damaged. Otherwise, it will be given to the construction unit. And cable laying brings certain difficulties.
To sum up, the thickness of the sheath should be controlled according to the standard, which not only saves resources, reduces material consumption, and increases profits for enterprises, but also ensures the quality of cables and creates high-quality and low-cost products.
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