The cable that we usually do is round, but the round cross-linked polyethylene insulated core must fill the gap with the filling material when it is cabled. It virtually increases the outer diameter of the cable, and also increases the material of the subsequent process. Dosage. If the conductor is changed into a fan shape, after the fan-shaped insulated wire core is cabled to form a round shape, the cable packing material of the cable core can be greatly reduced, and the cable outer diameter is also reduced, so that the amount of material used in the subsequent process is reduced. This reduces the cost of cable manufacturing.
With the rapid development of the national economy and technological advancement, the market has put forward high quality and low price requirements for wire and cable products. This requires the study of existing conventional products and the full exploration of potential to create greater technical and economic benefits. At present, the conductors of cross-linked polyethylene insulated power cables (hereinafter referred to as cross-linked cables) are mostly circular compacted-stranded conductors, and the process control and operation of the conductors of the structure during insulation extrusion and multi-core cabling are relatively simple, but The circular insulated core must be filled with voids when filling the cable to ensure the roundness of the cable appearance of the finished cable. This increases the outer diameter of the cable while increasing the auxiliary materials for the cable. This virtually increases the amount of material used in the subsequent process and increases the manufacturing cost of the cable. In the new cable national standard, due to the abolition of the original stipulation that the XLPE insulated power cable conductor is a circular tight pressure limit, taking into account the above additional material usage, if the conductor is changed into a fan shape, the fan-shaped insulated wire core is made into The back of the cable is just formed into a round shape, which can not only greatly reduce the cable filling material of the cable core, but also reduce the external diameter of the cable, so that the amount of material in the subsequent process can also be reduced, thereby reducing the manufacturing cost of the cable.
l Technical key According to the above situation, the corresponding cable structure is designed. The key problem is that because the radius of curvature of the outer surface of the fan-shaped conductor is smaller than that of the circular conductor of the same section, the local electric field strength of adjacent insulation layers is high. To solve this problem better, the sector conductor cross-section must be optimized. The semi-conductive shield and insulating layer of the cross-linked cable are extruded into three-layer co-extruded, and the eccentricity is not easy to control when a conventional circular pressed conductor is used for three-layer co-extrusion, not to mention the three-layer co-extrusion of the sector-shaped conductor. The difficulty of the process can be imagined. After repeated trials and trials, we finally designed a three-layer co-extrusion die, which basically solved the difficulties in the process of insulation extrusion of fan-shaped conductors.
2 The design and test of the process tooling is usually a single-layer extrusion when the fan-shaped conductor is extruded in the plastic cable. Generally, a circular extrusion die can be used directly. The insulation extrusion of the CCV unit is a three-layer co-extrusion, and the flow state of the rubber compound is more complicated. In order to obtain a good insulating shape, a suitable mold must be used. Anhui Wanbang Special Cable Co., Ltd. has adopted the following four test programs.
2.1 The core mold sets are all fan-shaped and squeezed. After the actual extrusion, it is found that although the core and die are fan-shaped, the thickness of the extruded insulation layer is extremely uneven, and the insulation thickness at the fan-shaped two wings is the smallest. The thickness of the insulating layer at the fan-shaped surface is relatively large. As a result, the appearance of the insulated wire core is not obvious in a fan shape, but is close to a circle. The reason for the analysis is that the extrusion die causes the molten rubber to have pressure in the flow channel, and because the fan shape at the die outlet makes the pressure at the outlet uneven, there is a big difference in the amount of glue on the cross-section, resulting in the fan shape being not Obviously rounded.
2.2 The mold core is round, the mold is fan-shaped, and the semi-extrusion tube is adjusted multiple times. The thickness of the insulated wire core is generally uniform and the appearance is basically fan-shaped. However, due to the small pressure of the squeeze tube mold, Extrusion, the rubber and the conductor can not be well combined, causing the plastic material to droop; the head of the vacuum, the plastic material sagging disappeared, but in the fan-shaped surface of the phenomenon of tendons. The reason for the analysis of the striated ribs is that the flow channel pressure at the die mouth is not uniform, and there is a large pressure difference between the two straight edges and the circular arc edge around the scallop, resulting in difficult control of the thickness.
2.3 The mold core and the mold sleeve are all round, and the vacuum tube is still used for squeezing the tube mold head. After the insulation is adjusted, the sectorial cross-section of the insulation layer is basically formed, and the thickness of the fan-shaped periphery is substantially uniform. However, after the insulated wire core was cross-linked and cooled by the cross-linked pipe, it was found that the fan-shaped insulating layer appeared to be thin at both wings and thick at both straight edges. According to the analysis, the polyethylene layer extruded on the fan-shaped conductor enters into the cross-linked pipe, but before the cross-link curing has been formed, it remains in a molten state for quite some time. Therefore, due to the effect of surface tension, the thickness of the periphery of the fan-shaped layer is made. Change has occurred.
2.4 The mold core is circular and the mold sleeve is elliptical. Extrusion tube mold is intended to increase the insulation extrusion thickness at two corners of the sector. After extruding, cross-linking and cooling, the thickness of the periphery of the sector is substantially uniform, but the thickness of the arc edge is slightly thinner than the two straight sides. To make the thinnest points meet the requirements of the national standard, the overall extrusion thickness has to be increased.
3 Trial production results After repeated trial and comparison, the final design of the extrusion die with a circular core and an elliptical die set was used to extrude a batch of YJV22-8.7/10 kV 3 x 240 mm insulated cores. Cables and other processes made of cables and passed performance tests have been delivered to users.
4 Cost comparison and analysis Taking the YJV228.7/lokV3×240mm cross-connected cable as an example, the comparative analysis of the fan-shaped conductor and the circular conductor for the 10kV cross-connected cable has resulted in a material cost savings of 836 yuan per kilometer of fan-shaped conductor cross-linked cable. . If 10kV three-core cross-connected cables are calculated every year for 500km, then RMB 418,000 will be saved each year.
5 Concluding remarks After measurement, the outer diameter of the cable core after the insulated wire core is cabled is reduced, but the reduction is not ideal. The main reason is that although the sector shape of the insulation layer is relatively good, there is still a large deviation at the arc edge, which results in the core diameter of the core after cabling being large, which is not ideal. Therefore, in the future, molds and runners should be further improved to maximize the insulation thickness of the fan-shaped conductors in order to achieve the minimum cable and finished product outside diameter. Significantly reduce costs. This will bring greater profits to the company.
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