Wire

A wire is a long, thin, and flexible bar of metal. While most wires are cylindrical, they can also be made in square, hexagonal, or flattened rectangular shapes.

These different shapes serve specific purposes. Some are used for decoration, while others are designed for technical tasks. For example, flattened wire is used to make edge-wound coil springs, like a Slinky toy.

Wires are also essential for carrying electricity and telecommunications signals. In these roles, a wire might be a single solid piece or many strands bundled together into a cable.

To create wire, manufacturers use a process called drawing. This involves pulling metal through a small hole in a hard tool called a die or a draw plate.

By passing the metal through progressively smaller dies, the wire reaches its desired diameter. For very fine work, dies are made from precious stones like diamonds or rubies. These materials do not change size easily, which ensures the wire diameter remains accurate. If a metal die becomes too large, workers can hammer the hole back to its original size and then use a punch to drift it out. Sometimes, wire is also annealed, which means it is heat-treated to make it easier to draw or to improve its conductivity.

Electrical wires require protection to prevent short circuits. They are usually covered with insulating materials like plastic, rubber-like polymers, or varnish.

In modern manufacturing, an extruder is used to apply this insulation or jacketing. In the past, workers used treated cloth, paper, or oil-based products for insulation. For more complex setups, two or more wires can be wrapped concentrically to form a coaxial cable. This type of cable is often protected by additional layers of lead, aluminum sheathing, or steel taping.

To add these layers, stranding or covering machines wind the material onto the wire as it passes through at high speeds.

Humans have been shaping metal wire for thousands of years. In ancient Egypt, during the 2nd Dynasty, people used a strip drawing technique. They pulled metal strips through holes in stone beads to create thin, hollow tubes.

In the Bronze and Iron Ages in Europe, people used swaging to create square or hexagonal wires. Swaging involves striking a metal rod between grooved blocks or an anvil. By the middle of the 2nd millennium BCE, gold jewelry often featured wires with spiral seam lines. These were made by twisting strips and then rolling them between flat surfaces to make them solid. By the 8th to 10th centuries AD, the drawing method became the standard in the Old World.

In Great Britain, wire drawing has a long history dating back to the medieval period. For example, wire was used to make wool cards and pins in England.

The first wire mill in Great Britain was established at Tintern around 1568. Despite these mills, fine wire was often still drawn by hand well into the early 20th century. The complexity of wire manufacturing is seen in the way strands are organized. For instance, a large 2/0 wire can be made from 5,292 individual strands of No. 36 gauge wire. These strands are built up by first creating bundles of seven strands, then grouping those bundles into larger sets.

There are two primary forms of wire: solid and stranded.

Solid wire, or single-strand wire, consists of one continuous piece of metal. It is cheaper to make and provides great mechanical ruggedness. It is also resistant to corrosive environments because it has less surface area exposed to the elements. Stranded wire, however, is composed of many small wires bundled together. This makes the wire much more flexible and resistant to metal fatigue. Stranded wire is necessary for items that move often, such as computer mouse cables, musical instrument cables, or headphone wires.

The number of strands in a bundle affects how the wire performs. The simplest stranded wire uses 7 strands, with one in the center and six surrounding it. If a wire must undergo constant, repeated movement, such as in an assembly robot, manufacturers must use between 70 and 100 strands.

For high-frequency electrical applications, special types like litz wire are used. Litz wire features individual strands that are insulated and twisted in specific patterns to improve performance. This complexity allows wire to function in everything from massive submarine cables to the tiny components inside a smartphone.