In order to improve the softness and integrity cables, two or more single wires are stranded in the specified direction. This process is called stranding. The entire stranding process is divided into conductor stranding, cabling, braiding, armoring and rewinding. Problems in any process will directly affect the quality of the cable.
So what should you pay attention to during the stranding process? Which links are prone to problems? Next, Lint Top will introduce what should be paid attention to during the stranding process.
1. What are the quality requirements for stranded conductor?
The stranded wire core should be tight, round and straight, the surface of the copper wire should be free of oxidation and blackening, the pitch should be even, the joints should be flat, the wiring should be neat, the wire diameter should meet the tolerance requirements, and the length should meet the requirements.
2. What preparations should be done before stranding production?
(1) Check whether all parts of the rotating machine are normal and whether there are obstacles in the running parts;
(2) Check whether the electromechanical equipment, electrical switches, and hurdle insurance are normal;
(3) Select the stranding die according to the requirements of the work dispatch order and process card , replace the pitch gear, replace the twist direction measurement wire diameter, etc.
3. What is back-twisting? Under what circumstances is the effect significant?
Stranding with back-twist means that each reel is always kept in a horizontal position with a unique device (back-twisting mechanism) to ensure that each single wire does not produce self-twisting deformation during the twisting process. This is called back-twisting stranding. Back-twisting will only have good results when the single wire diameter is larger, the pitch is larger, and the single wire is harder.
4. What two requirements must the structure of the fan-shaped wire core meet?
(1) The single wires on the central layer should also be arranged on the center line of the sector. If this requirement cannot be ensured, when the wire core is bent, these single wires will be stretched or compressed, causing the single wires to bulge, resulting in the shape change of the sector-shaped wire core.
(2) Sliding requirements: that is, the single wires on the outer periphery of the sector should be able to slide on the central layer. This is because the sector-shaped wires wrapped with insulation do not twist back when twisted into the cable core, and the single wires on the outer periphery strive to slide around the central plane. Therefore, if this requirement cannot be met, the single line will also jump up, destroying the shape of the sector line.
5. For stranded wires twisted in concentric layers, the twisting directions of adjacent layers are set to be opposite. Why?
(1) The stranded wires are round. If adjacent layers are twisted in the same direction, it is easy for the single wires of the outer layer to be embedded in the inner layer, thus destroying the complete circular structure.
(2) When the stranded wire is under tension, the rotational torque generated by each layer is opposite and can offset each other, preventing the single wires of each layer from rotating in the same direction and causing loose strands. It can also prevent the stranded wire from looping when it is not tightened. .
(3) In the steel core aluminum stranded wire, the AC impedance can be reduced, corona phenomenon and power loss are reduced.
6. Why is the entrance of the die hole like a trumpet when cabling?
There are two advantages to having a trumpet shape at the entrance of the die hole: (1) to gradually compress the stranded cable core; (2) to avoid scratching the cable core.
7. What is the main difference between drum twister and cradle type laying up machine?
The stranding part of the cradle type laying up machine is integrated with the pay-off device, while the stranding part of the drum twister is not, but is connected with the traction device and the take-up device.
8. In terms of structure, what are the wrapping forms for cable wrapping?
There are three types: simple type, planar type, tangent type or semi-tangential type.
9. Use a trial fraction to show the relationship between the wrapping pitch h (mm), the forward speed of the cable core V (m/min) and the number of revolutions of the wrapping head around the cable core n (rev/min).
h=V/n=1000(mm)
10. What is the difference between unilay stranding and concentric stranding?
The twisting direction of each layer of the unilay stranded cable core is the same, and the stranding distance is larger, which is about 1.5 times that of the concentric stranding. The number of units in each layer of the cable core does not follow the n+6 rule. The reason is that the cable core must be completely filled and deformed, so that each unit no longer maintains its original round shape. The number of units on each floor basically follows the n+4 rule.
11. What is cabling? How many kinds of deformations do insulated wire cores undergo when they are cabled?
The process of stranding multiple insulated wire cores according to certain rules is called cabling. When the insulated wire core is stranded into a cable, there are two types of deformation: one is the bending deformation produced by the wire core around the cylinder, and the other is the torsional deformation produced around the spiral direction.
12. Why adopt cabling with back-twist for round wire cable?
For round wire core cabling, back-twisting is often used to reduce the deformation of the wire core, avoid damage to the insulation layer due to deformation, and make the cable more flexible.
13. What are the main performance requirements for auxiliary materials in the power cable cabling process?
Auxiliary materials during the cabling process of power cables include filling rope, tightening tape and shielding tape, etc. They should have heat resistance, non-absorbent properties, and no corrosion. The tightening tape used for filling should have considerable mechanical properties meet the process requirements.
14. What are the general principles for selecting sector-shaped wire core cable cabling die? What should we pay attention to during the specific operation process?
The first die is 1.0~3.0mm larger than the outer diameter of the cable, and the second die is 0~0.6mm smaller than the outer diameter of the cable. The third die is 0~0.2mm smaller than the outer diameter of the cable.
When actually using the die, you should also pay attention to the fact that the cable cannot swing in the die, the cable core does not feel loose when turned by hand, and the heat generated by the friction between the die and the insulated core should not be hot to your hands. The surface of the insulated wire core coming out of the die should be smooth and free of damage and other traces.
15. After the control cable of a certain specification was cabled, it was found that the conductor was thinned or even broken. What are the main reasons?
The reasons are as follows: (1) The tension of the pay-off is too large; (2) The wire is pinched by the wire nozzle; (3) There is a bulge on the wire core insulation, which is partially thick; (4) The wire joint is not stable; (5) The take-up tension is too high.
16. What causes the fan-shaped insulated wire core to turn over and how to prevent it?
The reasons for the fan-shaped insulated wire core turning over are: (1) Insufficient pre-twisting angle; (2) The wire core is turned over when the wire core is loaded on the pay-off, and the wire core is thick; (3) The wire core is twisted back when release from the pay-off.
Preventive methods: (1) Adjust the distance between the pre-twist spring die and the wire core guide wheel; (2) Adjust the pre-twist angle; (3) Arrange the wire on the pay-off, and turn the bobbin over if necessary, so that the cables are arranged neatly and not loosely.