Twisting: The process of twisting multiple smaller diameter single wires into larger cross-sectional conductive wire cores according to certain rules.
　
1. There are two types of stranding: regular stranding and irregular stranding.
Regular stranding can be divided into regular concentric single wire stranding and regular concentric strand stranding. Regular concentric single wire stranding:
(1) Ordinary stranded wire: Use single wires of the same diameter and lay them in concentric circles, layer by layer in a regular manner, with each layer twisted in the opposite direction.
(2) Composite stranded wire: It is made of single wires of the same diameter, different materials, or different diameters and materials. (Representative products such as overhead wires)
Regular concentric stranded wire: It is a stranded wire that is concentric twisted by multiple ordinary strands or bundle wires.
Irregular stranding (bundle wire): A stranded wire formed by multiple single wires twisted together in the same direction without following the stranding pattern. The positions of each single wire are not fixed to each other, and the shape of the bundle wire is also difficult to maintain roundness.
　
2. The biggest difference between bundle wire and ordinary stranded wire is that each single wire of ordinary stranded wire has a fixed position, and is twisted layer by layer in a regular manner; The individual strands of the bundle are not twisted together in a fixed position according to the twisting pattern.
　
3. The characteristics of irregular stranding (bundle wire): Due to the fact that each single wire in the bundle wire is twisted in one direction, there is a large sliding margin between each single wire during bending, and the bending resistance is small. Therefore, the bending performance of the bundle wire is particularly good. For wire and cable products that require flexibility and frequent movement, bundle wire is used as the conductor core.
　
4. Characteristics of stranded wire cores:
⑴ Good softness; The use of multiple smaller diameter single wire twisted cores can improve the bending capacity of cables, making it easier for the processing, manufacturing, installation, and laying of wires and cables.
⑵ Good stability; A wire core composed of multiple single wires twisted in a certain direction and with regular twisting rules. Due to the fact that each single wire in the stranded wire is alternately located in the elongation zone above the stranded wire and the compression zone below the stranded wire, deformation does not occur when the stranded wire is bent.
⑶ Good reliability; Using a single wire as a conductor for wires and cables is susceptible to material unevenness or defects generated during stranding, which can affect the reliability of the conductor core. Defects such as using multiple single wire twisted cores are dispersed and do not concentrate at a single point in the conductor, resulting in much stronger reliability of the conductor core.
High strength; Compared to multiple stranded wire cores with the same cross-sectional size, the strength of stranded wire cores is higher than that of single wires.
　
5. Explanation of terms:
(1) Pitch: The distance that a single wire advances in an axial direction by one cycle.
(2) Pitch diameter ratio: The ratio of the pitch length of the stranded wire to the diameter of the stranded wire.
(3) The relationship between pitch and strand softness: The smaller the pitch, the better the strand softness, while the larger the pitch, the worse the strand softness.
(4) Twist in coefficient: The ratio of the actual length of a single wire unfolded to the pitch length in a single pitch of the stranded wire.
(5) Twisting direction of the stranded wire: right (Z direction) left (S direction)
(6) Compression conductor: Common compression conductors include compression circular, sector shaped, and compression tile shaped (five core cables) and semi circular (two core cables)
　
6. Tightening purpose:
(1) Tightly pressed fan-shaped conductor: reducing the outer diameter of the cable saves product costs and reduces cable weight.
(2) Tightly pressed circular conductors: improve the surface quality of stranded conductors, reduce the conductor diameter, increase the conductor filling coefficient, and ensure that the surface of the tightly pressed conductor is smooth, round, and free of burrs, with a uniform electric field on the conductor surface. Save materials and reduce costs.
　
7. Conductor classification:
According to the GB/T3956 "Conductors of Electric Cables" standard, there are four types of conductors: the first, second, fifth, and sixth. The first type is a solid conductor, and the second type is a twisted conductor, both of which are suitable for fixed laying of cables; The 5th and 6th types are stranded conductors, used for conductors of flexible cables and cords. The 6th type is softer than the 5th type.