The difference between concentric layer twist (regular twist) and bundle twist of wire and cable

Stranding includes not only the stranding and bundling of conductors, but also the stranding (cabling) of insulated cores, as well as the stranding of cable core components. Based on this, only the stranding and stranding of conductors are described and discussed in this paper. , that is, the conductor is twisted.

1. Overview of Conductor Stranding

Conductor stranding refers to twisting several single wires of the same diameter or different diameters together according to a certain direction and certain rules to form a whole stranded core. Because a single wire is not easy to bend and has poor flexibility, it brings difficulties to production, transportation, installation, laying and use; second, the single wire has a large cross-section and a large eddy current loss, which affects the power transmission effect. The use of conductor stranding effectively avoids these problems.

When the stranded wire is used directly as a wire, it is called a bare stranded wire, such as a steel-cored aluminum stranded wire; if it is used as a conductor of an insulated wire and cable, it is called a stranded wire.

1. Characteristics of conductor stranding

1.1 Good flexibility

As wires and cables are used in different occasions, the current carrying capacity is different, and the cross-section of the wire is also large and small. As the cross-section of the wire increases, the diameter of the wire also increases, making it difficult to bend the wire. When twisted together, the bending ability of the wire can be improved, and the processing, manufacturing, installation and laying of the wire and cable can be facilitated.

1.2 Good stability

A stranded core in which a plurality of single wires are twisted in a certain direction and a certain rule, because the position of each single wire in the stranded wire is alternately located in the elongation area of the upper part of the stranded wire and the compression area of the lower part of the stranded wire, when the stranded wire is stranded. When both ends of the wire are bent downward, the elongation force and compression force of each single wire are equal, and the single wire will not be stretched and compressed, and the stranded wire will not be deformed. If multiple single wires are not twisted but combined into a wire bundle in parallel, when the wire bundle is bent, the upper single wire will be embedded in the wire bundle, and the lower single wire will also be compressed to the center of the wire bundle due to the change in length, thus changing the shape of the wire harness.

 1.3 Good reliability

Using a single wire as a conductor of a wire and cable is susceptible to material inhomogeneity or defects in manufacturing that affect the reliability of a single conductive core. Using a core of multiple single wires twisted, such defects can be dispersed and not affected. It will concentrate on a certain point of the wire, and the reliability of the wire is much stronger, especially at the joint of the wire.

1.4 High strength

The strength of the stranded wire is higher than that of the single wire with the same cross-section compared with the multiple stranded wires of the same cross-sectional size.

2. Conductor stranding form

Conductor stranding includes the stranding and bundling of conductors, and its stranding forms are mainly divided into regular stranding and irregular stranding (bundle wires).

Regular stranding can be divided into regular concentric single wire stranding and regular concentric strand stranding (complex stranding). Regular concentric single-wire stranded wire can be divided into two types: ordinary stranded wire (copper, aluminum stranded wire) and combined stranded wire (steel core aluminum stranded wire).

2.1 Regular concentric single wire stranding

2.1.1 Ordinary stranded wire

Single wires of the same diameter are regularly twisted layer by layer in the manner of concentric circles, and the twist direction of each layer is opposite, and their central layer is usually a single wire or 2~5 single wires of the same diameter. The twisted cores are twisted with one or more layers of single wires on top of them.

2.1.2 Combination Stranded Wire

The representative product of the combined stranded wire is the steel-cored aluminum stranded wire for overhead transmission lines, which is made of single wires of the same diameter and different materials or different diameters and different materials. 2.1.3 Regular concentric strand stranding (complex stranding)

Multi-stranded wire is a stranded wire that is normally concentrically stranded by multiple ordinary stranded wires or bundles. The twisting direction of the stranded wire is generally opposite to that of the strands.

2.2 Irregular single wire stranding (bundle wire)

The bundled wire is a stranded wire made of multiple single wires twisted together in the same twisting direction and not according to the twisting law.

Because the stranding of the bundled wire is all in one direction, which is different from the twisting of one layer to the left and one layer to the right of the ordinary stranded wire, the bundled wire is softer than the ordinary stranded wire.

2. Wire bundles and strands

1.1 Characteristics of the beam line

The bundle line is irregularly stranded, and it is formed by twisting multiple single wires together in the same twist direction. The position of each single wire in the bundle wire is not fixed, so it is difficult to keep the shape of the bundle wire composed of more than 7 single wires. ;Because each single wire in the bundle is twisted in one direction, when bending, the sliding margin between the single wires is large, and the bending resistance is small, so the bending performance of the bundle is good, for wire and cable products that require flexibility, Most of the cores are used.

1.2 Calculation of the weight of the beam line

The formula for calculating the beamline weight is:

kmkgKZdW /42ρπ⋅⋅⋅ =

Where: W — beam weight; kg/km

d — diameter of a single wire in the bundle; mm

Z — the number of single wires in the bundle;

ρ—the density of the conductor (the copper conductor is 8.89g/cm3);

K — the twisting factor of the beam wire (1.006~1.008).

2. Basic parameters commonly used in twisted wire calculation

2.1 Strand pitch h

The axial length of a single wire in a stranded wire that makes one turn around the center of the stranded wire is called the stranded wire pitch. There is an included angle (acute angle) h α between the single wire in the stranded wire and the radial direction of the stranded wire, which is called the twisting angle. Strand pitch, strand cross section circumference hD π (for strand diameter) and strand one pitch single-wire development length form a right triangle.

2.2 Pitch diameter ratio m

The pitch-diameter ratio is the ratio of the pitch length of the stranded wire to the outer diameter of the stranded wire, which is expressed by: hDm D hm=

Pitch diameter ratio is one of the important parameters of stranded wire. A larger pitch-diameter ratio, that is, a larger twisting angle, reflects a small degree of twisting; otherwise, the degree of twisting is large. Conductors with small pitch-diameter ratios have tighter twists, more stable structure, good conductor bendability and softness, that is, bending α is allowed.

Small radius; but slow production. If the pitch-diameter ratio is too small, the single wire in the stranded wire will also have local arching, which will affect the stability of the stranded wire. When twisting conductors, the pitch ratio of the outermost layer should be the smallest and gradually increase towards the inner layer.

2.3 Stranding coefficient λ and twisting rate k

In a pitch of the stranded wire, the unrolled length of the single wire is longer than the length of one pitch. The twisting coefficient Lh λ is the ratio of the unwrapped length of the single wire to the pitch of the twisted wire in a pitch of the stranded wire, and Lh λ is A value greater than 1. And the ratio of the difference between the length of the single wire and the pitch and the pitch, when expressed as a percentage, is called the twisting rate, which is expressed by: k twisting coefficient αλsin1h==L

Twisting rate %100)1(%100×−=×−=λhhLk

The larger the twisting rate is, that is, the same length of single wire is twisted, and a longer wire is required, which is mainly used for the calculation of production materials and material consumption. k

To sum up, pitch-diameter ratio, twisting rate k, etc. are all important parameters of the stranding process, which are related to the quality of stranding, product stability, strength, resistance, and material consumption and productivity. m

3. Twisting direction and twisting law of conductor stranding

3.1 Stranding direction

The twisting direction is divided into right and left directions. The specific method is to open the palm (the palm is facing you), and make the four fingers parallel to the axis of the twisted thread. If the direction is the same, the twist direction is the right direction, that is, the Z direction; if the extended left thumb direction is the same as the oblique out direction of the single line, the twist direction is the left direction, that is, the S direction. Figure 2

a) Right direction (Z direction) b) Left direction (S direction)

Fig. 2 Judgment diagram of twisted wire direction

3.2 Twisting law

In concentric regular stranding, in addition to the opposite direction of each layer, when the number of single wires in the central layer is fixed, the number of single wires in each layer is also fixed.

The outermost layer of aluminum stranded wire and steel core aluminum wire is twisted to the right, and the outermost layer of the copper-aluminum conductor core for electrical equipment wires and cables and power cables is twisted to the left.

Except for the exception that the center layer is 1 single wire, the other center layers are concentric regular stranding of 2 to 5 single wires. The structure with five roots is unstable, and the structure with one central layer is the most stable and has the largest filling factor.

According to the calculation, the number of single wires in each layer of concentric stranding is always 6.28 more than its adjacent inner layer, whichever is the integer, that is, it is always 6 more, no matter how many layers there are, and no matter the number of central layers is 2~ Any one of the 5 strands conforms to this twisting law. The only exception is that when the center layer is 1, the number of single wires of the first layer of strands is 6, which is only 5 more than the single wire of the central layer. root. Table 1 lists the calculation formulas for the outer diameter of the stranded wire, the number of single wires in each layer and the total number of stranded wires when the number of central single wires is different. Table 1 Calculation formula of stranded wire

4. About back-twist stranding and non-back-twist stranding

There are two methods of conductor stranding, untwisted and untwisted.

Back-twist stranding is a special device on the reel frame equipped with a pay-off reel (twist back device) to keep the pay-off reel always in a horizontal position when the machine rotates. , without torsion.

Non-retraction twisting is that the reel frame with the pay-off reel is fixed on the winch cage. When the winch cage rotates one turn (360°), the pay-off reel rotates along with it, and the single wire or the insulated core is also twisted by 360°. .

Untwisted stranding is often used for stranded wire cores that are not tightly compressed. The single wire in the stranded wire has no internal torsional stress, and the stranded wire structure is stable. Untwisted stranding is mostly used to compress round cores and fan-shaped cores.

5. About pressing special-shaped conductors

Hard structure conductors can be divided into two types: compressed and non-compressed, and when the compressed conductor is more than 50mm2, it can be made into a compressed special-shaped structure. The surface of the compressed conductor is smooth, the electric field is more uniform, and the outer diameter can also be reduced. , Save the manufacturing cost of the product, and the high-voltage cable must be a compact circular structure. The compacted shaped conductors produced by the company are semi-circular, fan-shaped (90°, 100°, 120°) and corrugated.

3. Conductor stranding equipment

The composition of the twisting equipment is basically the same, except for the main engine, there are pay-off, traction, take-up, transmission system and control system, etc. The composition of the twisting equipment will not be described in detail in this article. The company has 12 stranding machines, 3 pipe stranding machines (400/6, 400/8, 500/6), and 2 frame stranding machines (500/12+18+24, 630/6+12+18+24) ), 1 fork winch (500/12+18), 6 tow machines (two each of 400, 500, and 630). The specification of the stranding machine is indicated by the number of pay-off reels on which the twisted single wire is placed in the unit and the outer diameter of the side plate of the pay-off reel. For example, the 400/6 type tube stranding machine can be installed with six 400mm diameter reels. According to the principle of regular stranding, the rear section is equipped with 6 more pay-off reels than the front section. For example, the four-stage type of 6+12+18+24 can install 60 pay-off reels. Since the wire bundle plays a major role in the wire take-up part, the type of wire bundle machine is named according to the form of the wire bundle part.

Because the double traction mechanism is reliable, the twisted wire has no slippage and no damage to the surface of the twisted wire, so it is widely used.

1. Pipe stranding machine

The pipe stranding machine is a high-speed stranding machine with untwisting, which is widely used in the stranding production of copper, aluminum wire and steel-cored aluminum stranded wire. There are two types of pipe stranding machines used by the company: 6-reel and 8-reel, and the diameter of the pay-off reel has two specifications: 400mm and 500mm. The pipe stranding machine is mainly composed of a pay-off frame, a strand cage, a die base, a meter counter, a traction wheel, and a wire take-up frame. The cradle frame of the pipe stranding machine is arranged in a line along the axis of the unit, and the outside is a tubular cylinder that can rotate left and right, and a window for loading and unloading reels is opened on the wall of the cylinder.

During the twisting process of the pipe stranding machine, since the pay-off reel does not rotate, after the single wire is released from the pay-off reel, it passes through the guide wheel and the pipe wall to the doubling die. With the rotation of the pipe body, the single wire does not wind itself. The axis of the tube is rotated, and there is no single-line torsion, so the stranding process of the pipe stranding machine belongs to the back-twist stranding.

Because only the cylinder body rotates, it is light in weight and has a small radius of rotation, so it can achieve a very high speed. The disadvantage is that the rotating body of the unit is relatively long. When the cylinder rotates one turn, the core is twisted to produce a pitch.

Calculation formula of pitch of pipe stranding machine:

1000nvh×=

Where:— Stranding pitch (mm ) h

v — Outlet speed (m/min)

n — Twisting cage speed (r/min)

Table 2 Conventional conductors produced by the company's stranded wire equipment

2. Fork winch

The fork stranding machine is a non-twisting device, which is suitable for conductors for products that have little deformation and no effect on single wires. The twisting cage part is composed of a fork frame and a hollow shaft. Three pay-off reels can be installed on each fork-shaped frame. The fork frames are staggered to reduce the length and area of the pay-off. It is compact, the pay-off reel is close to the rotating hollow shaft, there is no floating cradle part of the cage winch, and the rotational inertia is small, so the speed can be increased, and the productivity is relatively high.

3. Frame stranding machine

The frame stranding machine is composed of stranding body, doubling die base, pressing die base, meter counter, traction device, wire take-up rack and electrical control cabinet. The twisted body consists of a twisted body gearbox and a twisted cage. The winch gearbox is used to obtain different cage speeds, and cooperate with the traction gearbox to obtain different pitches. The main shaft of the winch gearbox is the winch spindle, which greatly improves the rigidity of the whole frame and meets the requirements of high-speed rotation of the winch. The gearbox has a built-in gear pump, so that all gears and bearings are well lubricated. The winch cage is composed of 6, 12, 18 and 24 frames respectively. The frame, front and rear winches and intermediate supports form the main body of the winch, which can rotate forward and reverse to meet different production needs. The front winch is also a brake disc, which adopts a pneumatic disc-type caliper brake device. The outgoing end of the twisted cage is equipped with an automatic signalling device for contact disconnection.

The wire reels of the frame stranding machine are divided into four vertical frames. The central axis is not loaded by the weight of the wire reels. The wire reels are distributed at an angle of 90° in the circumferential direction of the winching cage. The turning radius of the cage is small, and its speed is doubled compared with the cage winch of the same specification. The winch does not need a supporting wheel, but is supported by large bearing seats at both ends. The equipment has low noise. , Clamped by pneumatic or electric, it is easy to operate, shortens the auxiliary time, and is conducive to the realization of mechanization and automation of the upper and lower coils. Single-line pay-off tension is controlled by pneumatic tension, which can be adjusted automatically. The disadvantage is that it cannot be reversed.

4. Beaming machine

The diameter of the single wire is required to be very thin, and the wire produced is particularly soft and twisted. The above-mentioned various stranding machines cannot be used, but only the stranding machine can be used. A plurality of single-line pay-off reels are placed on the fixed bracket in layers and rows, and together they enter the host of the bundling and take-up reels through the distribution board. The single wire is twisted by the rotation of the rotor. Due to the operation of the harness machine

Both are in the take-up part, and the speed changers are installed in the rotating hurdles.