Main processes of wires and cables
Wires and cables are produced through three processes: drawing, twisting, and coating. The more complex the model specifications, the higher the repeatability.
1. drawn
In metal pressure processing, the technical processing method of forcing the metal through the mold (pressure wheel) under the action of external force, the metal cross-sectional area is compressed, and the required cross-sectional area shape and size is obtained is called metal drawing.
The drawing process is divided into: single wire drawing and twisted drawing.
2. twisted
In order to improve the flexibility and integrity of wires and cables, intertwining two or more single wires in a specified direction is called twisting.
The stranding process is divided into: conductor stranding, cabling, braiding, steel wire armoring and winding.
3. Cover
According to different performance requirements for wires and cables, special equipment is used to cover the outside of the conductor with different materials. Coating process points:
A. Extrusion packaging: rubber, plastic, lead, aluminum and other materials.
B． Longitudinal packaging: rubber, wrinkled aluminum strip materials.
C. Wrapping: ribbon-shaped paper tape, mica tape, alkali-free glass fiber tape, non-woven fabric, plastic tape, etc., linear cotton yarn, silk and other fiber materials.
D． Dip coating: insulating paint, asphalt, etc.
3. Basic process flow of plastic wire and cable manufacturing
1. Copper and aluminum single wire drawing
Copper and aluminum rods commonly used in wires and cables are passed through one or several drawing holes of the drawing mold using a wire drawing machine at room temperature, so that the cross section is reduced, the length is increased, and the strength is improved. Wire drawing is the first process for every wire and cable company, and the main process parameter of wire drawing is mold matching technology.
2. Monofilament annealing
When copper and aluminum monofilaments are heated to a certain temperature, they recrystallize to improve the toughness and reduce the strength of the monofilaments to meet the requirements of wires and cables for conductive cores. The key to the annealing process is to prevent oxidation of the copper wire.
3. conductor stranding
In order to improve the flexibility of wires and cables and facilitate laying and installation, the conductive wire core is made of multiple single wires twisted together. From the stranding form of conductive cores, 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 conductor is twisted and compressed at the same time, so that the ordinary round shape is transformed into a semicircle, a fan shape, a tile shape and a compressed round shape. This type of conductor is mainly used in power cables.
4． insulation extrusion
Plastic wires and cables mainly use extruded solid insulation layers. The main technical requirements for plastic insulation extrusion are:
4.1. Eccentricity: The deviation value of the extruded insulation thickness is an important indicator of the level of extrusion technology. Most product structural dimensions and their deviation values are clearly specified in the standards.
4.2. Smoothness: The surface of the extruded insulation layer must be smooth, and there must be no poor quality problems such as rough surface, scorch, or impurities.
4.3. Density: The cross-section of the extruded insulation layer must be dense and strong, with no pinholes visible to the naked eye and no bubbles.
5. Cabled
For multi-core cables, in order to ensure the molding degree and reduce the appearance of the cable, it is generally necessary to twist them into a circle. The mechanism of stranding is similar to that of conductor twisting. Due to the large pitch diameter of the twisting, most of them adopt the non-backtwisting method. Technical requirements for cable formation: first, to prevent special-shaped insulated cores from turning over and causing cable twisting; second, to prevent the insulation layer from being scratched.
Most cables are accompanied by the completion of two other processes when they are cabled: one is filling to ensure the roundness and stability of the cable after being cabled; the other 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 the armor, the insulation layer needs to be properly protected. The inner sheath is divided into: extruded inner sheath (isolation sleeve) and wrapped inner sheath (cushion). The wrapping cushion layer replaces the binding tape and is carried out simultaneously with the cabling process.
7． armor
Cables laid underground may be subject to a certain amount of positive pressure during work, so an inner steel tape armored structure can be selected. When laying cables in situations where there is both positive pressure and tension (such as in water, vertical shafts or soil with a large drop), a structural type with internal steel wire armor should be selected.
8. outer sheath
The outer sheath is a structural part that protects the insulation layer of wires and cables from corrosion by environmental factors. The main function of the outer sheath is to improve the mechanical strength of wires and cables, prevent chemical corrosion, moisture-proof, waterproof and immersion, and prevent cable burning. According to the different requirements for the cable, the extruder is used to directly extrude the plastic sheath.
