Conductors and insulators: how electrical wires and cables are made

The main components of electrical cables are the conductors, usually drawn wires made of copper, aluminum or alloys, and insulation.

A cable usually has a specific cross-section containing many wires. However, taken separately, the wires will be too fragile and may break. Therefore, they group together to form flexible conductors.
The thinner the wires, the more flexible the conductor. This first step is called "grouping".

Grouping process

At this stage, the wires are continuously twisted around a common longitudinal axis with simultaneous longitudinal movement in one direction according to agreed parameters. This process creates uniformly structured, flexible and stable wire assemblies called bundles.

This process usually uses a double twist machine. After pulling the coils from the pay-off devices installed outside the machines, the wires pass through the ceramic holes of the plate installed in front of the grouper and converge concentrically at one point.

Here the bundle of wires is rotated once around its axis and guided through a nipple or die whose hole profile ensures that each wire occupies its assigned position in the assembly. The bundle of wire then passes along a guide roller into a semicircular rotor arc, which rotates continuously around the take-up spool. The rotational movement of the nose and the movement of the wire bundle caused by the capstan result in the "first turn" of the wire bundle. As it exits the bow, the bundle of wire is guided along the next guide roller to the spool holder and finally wound onto the take-up spool. This is when the “second turn” occurs and the connection is created.

The rotor speed and the pull-out speed are critical to the lay length, i.e. the measured length in the axial direction in which the assembly element makes one revolution around its axis. The working speed is measured in lays per minute and is known as the laying speed. The product of the laying factor and the laying length equals the production volume.

The main parameters of this process are:
1. forces acting on wires and bundles;
2. wire tension as a result of this;
3. consistency of lay length;
4. loss of deformation;
5. beam concentricity.

To make cross strands or cables that require more conductors, more specialized equipment such as rigid stranding machines is required. Each of these machines has several stands containing a certain number of bobbins arranged radially around a common longitudinal axis. Each cell rotates around its axis independently of other cells in speed and direction.

At the end of the strand line, a large pull pin is used to pull the stranded wires through, and a winder winds them onto spools.

Shielding and armoring

Sometimes electrical cables may require additional elements such as armor to protect the cables from external damage and shields to isolate the signals circulating in the cable from external interference. Shielding and armoring are carried out by covering the cable with concentric tubular sheaths.

Another operation sometimes necessary to protect the cable is braiding. The weaving process is carried out on a braiding machine.

Braiding machines

Braiding machines for making electrical cables can be divided into two categories: vertically oriented and horizontally oriented machines. In the first case, the product to be woven is raised vertically above the machine. In the second case, production is carried out parallel to the floor; Large, rigid braided cables can be produced in this way.

Typical braiding materials are round or flat wires, uncoated or coated, made from copper, aluminum or stainless steel, as well as man-made yarns and fibers.

The operating principle is based on the complex movements of the spool holders on which the braided spools are secured and the path of the braided materials that must be woven around the moving cable.

Modern braiding machines are equipped with infinitely variable adjustment of line speed and braiding pitch, as well as an automatic central lubrication system. In addition to braid, it is sometimes necessary to use a foil jacket to increase the shielding and durability of the braided cable. If the braiding machine is equipped with an integrated tape device, both processes can be carried out in one working step. The benefits include saving space, eliminating rewinding processes and improving product quality.

Modern braiding machines with built-in electronic controls can operate for many hours or even days without operator intervention.

Cable sheath

Electrical cables at the end of the entire process may require an outer protective coating called a "jacket", which can be made of polymers, rubber or lead and is applied as insulation by high temperature extrusion.