Basic process flow of plastic wire and cable manufacturing
1. Copper and aluminum single wire drawing
The copper and aluminum rods commonly used for wires and cables can reduce the section, increase the length and improve the strength by using the wire drawing machine to pass through the die holes of one or several drawing dies at room temperature. Wire drawing is the first process of wire and cable companies, and the main process parameter of wire drawing is die matching technology.
2. Single wire annealing
When the copper and aluminum monofilament is heated to a certain temperature, the toughness of the monofilament is improved and the strength of the monofilament is reduced by recrystallization, so as to meet the requirements of wires and cables for conductor cores. The key of annealing process is to eliminate the oxidation of copper wire
3. Stranding of conductor
In order to improve the flexibility of wires and cables and facilitate laying and installation, the conductive wire core is twisted by multiple single wires. From the stranding form of conductor core, it can be divided into regular stranding and irregular stranding. Irregular stranding is divided into bundle stranding, concentric compound stranding, special stranding, etc.
In order to reduce the occupied area of the conductor and reduce the geometric size of the cable, the compact form is adopted while stranding the conductor, so that the ordinary circle can be changed into a semicircle, fan-shaped, tile shaped and compact circle. This kind of conductor is mainly used in power cables.
4. Insulation extrusion
Extruded solid insulation layer is mainly used for plastic wires and cables. The main technical requirements of plastic insulation extrusion are as follows:
4.1. Eccentricity: the deviation value of extruded insulation thickness is an important symbol reflecting the extrusion process level. Most product structure dimensions and their deviation values are clearly specified in the standard.
4.2. Smoothness: the surface of the extruded insulating layer shall be smooth without surface roughness, scorching and impurities
4.3. Densification: the cross section of the extruded insulating layer shall be dense and solid, and there shall be no needle holes visible to the naked eye, so as to eliminate the existence of bubbles.
For multi-core cables, it is generally necessary to twist them into a circle in order to ensure the formability and reduce the shape of the cable. The mechanism of stranding is similar to that of conductor stranding. Because the stranding pitch diameter is large, no untwisting mode is mostly adopted. Technical requirements for cable forming: first, prevent the twisting of cable caused by turning over of special-shaped insulated core; The second is to prevent the insulating layer from being scratched.
Most cables are completed with the completion of two other processes: one is filling to ensure the roundness and stability of cables after cable completion; One is binding to ensure that the cable core is not loose.
6. Inner sheath
In order to protect the insulated wire core from being damaged by armor, it is necessary to properly protect the insulating layer. The inner protective layer is divided into extruded inner protective layer (isolation sleeve) and wrapped inner protective layer (cushion). Wrapping cushion instead of binding belt shall be carried out synchronously with cable forming process.
If the cable is laid underground, it may bear certain positive pressure during work, and the inner steel strip armored structure can be selected. When the cable is laid under both positive pressure and tension (such as in water, vertical shaft or soil with large drop), the structural type with inner steel wire armor shall be selected.
8. Outer sheath
The outer sheath is a structural part to protect the insulating layer of wires and cables from environmental factors. The main function of the outer sheath is to improve the mechanical strength, chemical corrosion prevention, moisture-proof, water-proof and human immersion of wires and cables, and prevent cable combustion. According to different requirements for cables, the plastic sheath is directly extruded by extruder.
Max Xu- China Wire Machinery Expert.