How are cables produced
Cable manufacturing technology depends on its design. The more complex the design, the more process steps are required. At the same time, for each technological operation a certain type of equipment is required.
The following operations are required to manufacture a cable:
- Drawing of a wire (coarse wire drawing machine)；
- Annealing of the wire after drawing (annealed installation, usually combined with a wire drawing machine);
- Twisting single wires into a conductive core (twisting machine for aluminum or copper wires);
- Cable insulating of different colors on each core (insulating extrusion line);
- Twisting insulated cores into a cable workpiece (twisting machine for insulated cores).
- Application of filler or belt insulation (hose extrusion line).
- Laying-on of screens, armor of various types (winding or braiding machines).
- Laying on the sheath or protective hose (hose extrusion line).
- Rewinding the finished cable to shipping containers for testing, packaging and transportation to the consumer (rewinding lines for deliveries on drums, coiling lines for deliveries in coils).
Calculation of the cable design, determination of the required number of technological operations, the choice of equipment for each operation is best entrusted to a competent engineer.
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How to choose the size of the extruder.
-One of the main characteristics of an extruder is its productivity, i.e., the ability to squeeze a certain amount of molten material per unit time. Extruders of the same diameter may have different capacities depending on the design.
The most productive extruders are generally more expensive.
Depending on the tasks facing the manufacturer - the required speeds, the required production volumes, etc., the extruder is selected according to the following basic principle:
The cable design is calculated, where the material consumption is indicated, for example, for insulation, in kg / km. Next, the productivity of the extruder is taken in kg / h. It is pided by material consumption and the linear speed of the output in km / h is obtained.
V = 0,8хP/m
where V is the linear speed, km / h
P - maximum extruder productivity, kg / h
m - material consumption per unit length, kg / km.
0.8 - safety factor.
As a rule, extruders are suitable for insulation of a smaller size, for a sheath - need a larger.
For which purpose cable is twisted?
Both conductive conductors and insulated conductors in the cable must be twisted to give the cable the necessary flexibility for bending.
In addition, for communication cables designed to transmit high-frequency signals, twisting is necessary as protection against interference.
Any cable has three main parameters: d.c. resistance, capacitance and inductance. All of them adversely affect the signal passing through the cable. Aiming to reduce the cable resistance as much as possible, manufacturers increase its cross-section, without thinking about the fact that they increase the reactive components of the impedance - the capacitance and inductance. Meanwhile, an increased active resistance, although is not preferred, but it does less harm than reactive resistance, since it does not depend on frequency.
The original matrix geometry of inpidual small-diameter conductors woven into two spirals with an oncoming twist, in contrast to parallel conductors (the worst case), ensures their intersection at an angle of 90, practically bringing the areas of electromagnetic interaction of neighboring conductors to a point. Due to this, the capacitance between the conductors becomes the minimum possible, and mutual induction is absent. The entire electromagnetic flow is concentrated inside the spiral, and the fields created by the currents of the forward and reverse conductors are mutually compensated. Thus, we can say about the absence of inductance, forasmuch as its influence is not manifested. D.C. resistance due to the large number of parallel-connected conductors is also very small.
The twisting of communication cables (including computer) are being done mainly to control interference.
What kind of twisting machines are used in the cable industry?
- You can set the rotation of the pay-off.
In this machine, the pitch is provided by the rotational speed and linear speed.
It has large geometric dimensions → low productivity.
But it provides better twisting, since twisting to the forming device.
- You can set the rotation of the take-up device.
It's hard to create a layered cable
Less twisting quality, but higher productivity.
- You can set the rotation of both the take up and pay off device in opposite directions.
Here we get significantly more performance.
- Twist on the frame (the fastest machines, but do not provide concentric layer).
- single (twisting at one point). It's used for twisting up to 12 wires.
- - pay-off unit
- - twisting frame
- –take-up unit
- double (twisting at two points)
- - pay-off unit
- - Twisting frame
- Twist on the rotor ("Cigar"). ↑ Performance and ↑ (Concentric layer).
The cradles are arranged sequentially one after another inside the rotor along its axis, therefore the rotor has a small diameter, and this allows to achieve large turns of the twisting part. The center of gravity of the cradles, together with the coils, is a bit lower than the axis of rotation of the rotor. Therefore, the cradles remain almost stationary during rotation of the rotor. The twisting of wires on tubular-type machines occurs without untwisting.
Tubular-type machines can be designed for 6, 12, 18 and 24 wire spools. Tubular-type machines with a large number of spools are more convenient to carry out from separate independent sections that can work separately or all together.
- SZ-twisting, for twisting insulated cores. From 2 to 100 wires, conductors of a small section. Very high performance.
- Twisting process and equipment requirements
The performance is affected by the mass of the torsion part and its dimensions.
- Equality of wire tension.
If there is too much deviation, then the wire will become tangled. With the same tension of the wires, the deviation of the wires from the straight line will be the same, which will not lead to crowding.
- Inadmissibility of wire break
Wire break control device and welding machine are needed.
- Drum flange
The main performance of the pay-off device in a twisting machine (from 100 to 1200 mm.)
Equipment for twisting conductors.
- Pay-off unit
- Take-Up unit
Twisting wires with a diameter up to 0.1 mm.
Provides small pitches even at high twist speeds. The rotation frequency of the torsion part reaches 2500 rpm. Only 1 + 6 can be twisted.
Orderly twisting machine.
Wire twisting is performed on twisting machines, which, depending on the device of the twisting part, can be pided into three types:
1 - stranding-pay-off device; 2 - calibers; 3 - sealing rollers; 4 - traction device; 5 - take-up device; 6 - stationary pay-off device; 7 - supporting stand;8 - support roller; 9 - untwisting device; 10 – separator
The stranding part of the machine is made in the form of a cage, consisting of several parallel metal rings mounted on a hollow shaft in the center of the cage. In the cage between the rings, pay-off devices for coils with wire are installed. These devices are called cradles. The axles of the cradles are installed in bearings located in the rings of the cage, so the cradles can freely rotate relative to the rings, which allows twisting the strands with untwisting. A distinctive feature of cage-type twisting machines is the presence of an untwisting device in the cages. Two types of untwisting devices are used, providing 360 ° untwisting.
In a cradle there is a device for braking a bobbin when it is unwound. In one stand 6, 12, 18 and 24 cradles can be placed. Neighboring cages rotate in different directions at different speeds, with smaller cages having higher speeds, since the first lays overlap in smaller pitches. If one or more wires (for example, a seven-wire workpieces) is located in the center of the core, then the transfer coils with these wires are installed in front of the machine.
Cage-type machines are the most versatile of all types of twisting machines. They can be twisted with twist and without twist, they can be used to impose wire armor on the cable, etc.
Disadvantages of cage twisting machines are: low speeds, large dimensions and difficulties in changing the pay-off coils. The low speeds of rotation of the cages are explained by the presence of coils with a wire of large mass located at a great distance from the axis of the cage, as well as by the presence of an untwisting mechanism. The efforts arising from the rotation of the cages cannot be well balanced; therefore, stands are a kinematically unbalanced system. The rotation frequency of the cages is in the range of 70-240 rpm, which allows to obtain a linear speed of the product in the range of 10-60 m / min.
Rigid and disс-type machines.
Rigid type machine.
1 - Pay-off bobbin;
2 - Cage frame.
1 – Disc;
2 – pay-off bobbin;
3 – Separator;
4 –.Disc drive
Rigid machines are a variant of cage machines that do not have a untwisting device, which greatly simplifies their design. In the stranding part, the pay-off coils with wire are located as close as possible to the axis of rotation, this allows you to increase the speed to 180-350 rpm. These machines are widely used for twisting round and shaped conductors of power cables. In disc machines, metal discs mounted on a hollow shaft are used as a stranding device. Coils with wire are fixed on axes or half shafts placed parallel or perpendicular to the plane of the disc. Pay-off coils in disc machines are located at a sufficiently large distance from the center, so the speed of the discs is limited.
Both disk and rigid-frame machines are mainly used for twisting shaped cores. They are convenient due to their compactness, simplicity and ease of maintenance.
Disc twist part:
- with the frontal arrangement of coils.
1 - Rotor;
2 - pay-off coil;
3 — Wire;
4 - Separator;
5 - Caliber;
6 - Take-up device;
7 - Window for loading coils;
High quality of proper twist, rotor speed 3000 - 3500 rpm.
The torsion device of tubular-type machines is a cast tubular or cigar-shaped rotor assembled from rods, inside of which cradles are placed with pay-off coils with wire installed in them.
The cradles are arranged sequentially one after another inside the rotor along its axis, so the rotor has a small diameter, and this allows to achieve large revolutions of the torsion part.
The gravity center of the cradles, together with the coils, is somewhat lower than the axis of rotation of the rotor. Therefore, the cradles remain almost stationary during rotation of the rotor. The wire gets off the coil, passes along the guide rollers along the rotor body and enters the separator. The twisting of the wires is carried out using the rotor body, which rotates the wires passing along it around the axis of the twisted product. Coils with center wires can be located at the rear or front of the rotor. When twisting the wires, the position of the coils does not change, which causes the wires to rotate in the eyes of the rotor relative to its body. Thus, the twisting of wires on tubular-type machines occurs without twisting.
Tubular-type machines can be designed for 6, 12, 18 and 24 wire spools.
1.7 General design of the machine for twisting current-conducting conductor.
1 - Pay-off, for the central wire or core;
2 - Disk twisting part;
3 - Separator;
4 - Calibers;
5 - Lantern torsion part;
6 - Sealing device;
7 - Traction device;
8 - Meter's counter;
9 - Take-up device.