Complete Production Process of Cable (Strand)
I Characteristics of stranded wire
1. Good softness; It can reduce the damage caused by bending, vibration and swing, which is beneficial to installation.
2. Good reliability: the defects of single wires constituting the twisted wire cannot be concentrated at the same place, so the influence of single wire defects on the performance of the twisted wire is much weaker than that of a single conductor.
3. High strength: when the same rod is used for pulling, the deformation of drawn thin wire is greater than that of thick wire, so the strength of thin wire is high. The strength of stranded wire is higher than that of single conductor with the same cross section.
II Classification and use of stranded wire
A common stranded wire
1. Aluminum stranded wire: the conductor is light in weight and good in conductivity, and is used for overhead power lines with less stress.
2. Hard copper stranded wire: excellent electrical performance, used for overhead transmission lines.
3. Aluminum alloy stranded wire: the tensile strength is large, twice that of aluminum stranded wire, and the conductivity is 10% lower than that of aluminum stranded wire. It is used for general lines and large crossing transmission lines in glaciers, mountains, hills and other regions.
4. Aluminum clad steel strand: superior mechanical performance, used for large crossing lines.
B combined strand
1. Steel cored aluminum strand: high tensile strength. It is used for overhead transmission lines, distribution lines, heavy ice areas and large span transmission lines.
2. Anticorrosive steel cored aluminum strand: the performance is the same as that of steel cored aluminum strand. The steel core is anticorrosive and can extend the service life of the conductor. It is used in salt water lakes, coastal areas, industrial areas and areas with heavy corrosion atmosphere.
3. Steel cored aluminum clad steel strand: improve the corrosion resistance of steel core, extend the service life of conductor, and be used for large crossing lines or lightning wires.
4. Compressed steel cored aluminum strand: it has large tensile strength, smooth conductor surface, and can be used for transmission lines to increase the span of poles and towers.
C Special strand
1. Expanded ACSR: increase the outer diameter, save metal and reduce corona, which is used for high-voltage transmission lines and high-altitude areas.
2. Expanded hollow conductor: with larger outer diameter, it can save metal and reduce corona, and is used in high-voltage substation.
3. Vibration elimination and gap type conductor: each stranding layer is separated and can eliminate vibration by itself, which is used in storm prone areas.
4. Anti ice and snow strand: It has strong anti ice and snow ability and is used in heavy ice area.
5. Copper brush wire: stable in structure, good in flexibility, twisted and compounded, used for motor lead wire.
6. Bare copper flexible stranded wire: the stranded wire shall be regularly twisted, bundled, and stranded without or after being stranded, it shall be formally twisted and stranded, and used to connect the motor and electrical equipment parts.
7. Copper braided wire: the wire is soft, and it is used for connecting mobile electrical equipment and batteries of automobiles and tractors.
8. Aluminized steel cored aluminum strand: basically the same as steel cored aluminum strand. It can reduce the potential difference between zinc and aluminum and avoid electric field distortion.
9. Weather resistant insulated overhead line: overhead line with polyethylene sheath. Used to pass through trees or cities.
10. Conductive wire core: mostly used for power cable 。 It can be divided into hard, soft and extra soft.
① Hard core: for Marine cable , power cable, etc;
② Flexible core: for Mining cable ， Rubber sheathed cable Etc;
③ Extra flexible wire core: used for frequently moving wires and cables and conductive wire cores with special requirements.
III Stranding method
There are two stranding methods for conductive wire core: untwisted stranding and untwisted stranding.
The core twisted with untwisting method has no torsional internal stress, so it is mostly used for the untwisted stranded wire to avoid the internal stress spreading when the single wire breaks.
Stranding without untwisting is mostly used for compacting cores. Because the residual stress generated by self twisting is elastic deformation and the compacting is plastic deformation, the internal stress can disappear after compaction.
IV Stranding direction
No matter the twisting direction of bare stranded wire is concentric or multi stranded, its outermost layer is specified as right direction（ Z shape); The outermost layer of stranded insulated conductor is left (S-shaped). The twisting direction of the adjacent two layers must be opposite whether it is right or left. This is to unify the product, facilitate connection, and prevent loose single line.
V Parallel die
The parallel die is an important control point of the stranded wire: the diameter uniformity of the stranded wire, whether there is snaking, missing root, jumping phenomenon are all shown here.
The parallel die is generally composed of two semicircles. The inner hole of the steel mold is chrome plated, and the hard wood mold can also be used. Practice has proved that wood mold is more practical, and steel mold is not only expensive, but also mainly for scribing, which is easy to cause burrs on the wire core.
The function of the parallel die is to make the stranded wire core diameter and shape. Experience shows that the hole diameter of the parallel die is slightly smaller than the calculated outer diameter 0.1~0.3mm is appropriate.
VI Compaction
The compaction process is mainly used for the stranding of insulated conductors, and bare wires are generally not compacted.
Purpose of compaction: (1) Increase the filling coefficient, reduce the geometric size of the conductor, and save insulation and sheath materials;
(2) Improve the smoothness of the conductor surface and even the electric field on the conductor surface;
⑶ Reduce the chance of forming gaps in the cable.
Compaction process: the compaction process of round stranded conductor is vertical compaction in the first and third layers, and horizontal compaction in the second and fourth layers; 1、 The second compaction amount is 80%, three and four rollers play a rounding role, and the compaction amount is 20%; Compared with the non compacted conductor, the outer diameter of the round compacted conductor can be reduced by 7.2~9.17%, and the filling coefficient (normal stranding) can be increased from 75% to 90~93%. Sector stranded conductor 25～50mm two Vertical compaction can be carried out only once; 70 mm two and After stranding the outermost layer of the above conductors, three layers of compaction shall be carried out, namely, vertical, horizontal and vertical compaction. The first layer of compaction shall be 85%, the second one is for shaping (both sides), and the third one is for shaping; The filling coefficient of compact sector conductor can reach 90~93%.
Comparison between compacted conductor and non compacted conductor:
（ 1) Process characteristics: improve efficiency, reduce consumption, and have stable structure;
（ 2) Electric field intensity: can play the role of uniform electric field;
（ 3) Softness: decreased;
（ 4) Consumption of structural materials: reduced. Plastic cable saves about 1.8% of material consumption.
7、 Structure size, process parameters and appearance quality control
1. Geometric dimension
The geometric dimension is controlled to ensure that the cross-sectional area of the conductor, that is, the DC resistance of the conductor, does not exceed the specified value. Because when the resistance value exceeds the specified value, the current carrying capacity of the cable will be reduced, which is not allowed. If the size is smaller than the specified value or the cross-sectional area is small, the DC resistance of the conductor needs to be measured for arbitration. If the resistance is qualified, even if the cross-sectional area of the conductor is small, it can still be regarded as qualified products.
2. Stranding pitch and sector section shape are asymmetric
Asymmetrical deviation of sector section shape will distort the electric field distribution and make the cable diameter out of round.
3. Welding
Single wires in stranded conductors are allowed to be welded. However, the distance between two adjacent welding points in the same layer shall not be less than 300mm。
When two single wires with the same diameter are welded, the welding current should be appropriate to prevent the section at the welding point from overheating and reducing the mechanical and electrical properties of the single wire.
The welding process shall be short and fast. The welding point shall be properly trimmed without protrusions and burrs. Its diameter shall be within the allowable tolerance of single line.
The whole core welding is not allowed for all kinds of stranded conductor cores; Solid core 25mm two Welds with sectional area of or above shall be separated.
4. Appearance
The conductor surface shall be smooth and clean, free of burrs, scratches, jumpers, wings and other defects that damage the insulation layer (no feeling when touched by hand). The surface shall be free of oil stain and dust, or free discharge will be caused there.
Pay attention to oxidation discoloration and mechanical damage of conductor core during storage.
