They are almost always manufactured out of copper that is at least 99.9% pure. Copper is a smooth, shiny, soft and malleable metal that is desired for its formability, chemical resistance, low oxidization rate and its conductive properties.
Copper coils are usually sold in large bundles and can be easily shaped, twisted and bent without the use of heat, tools or high force. They may be layered, annealed, or coated with plastic resin. Other specifications include temper (the hardness or softness of the copper), thickness and width. Copper coils are used as components of many different systems within engineering, heating, cooling, electrical, refrigeration and heat exchanging applications.
The crafts and jewelry making industries also use thin copper coil to make many different hand made products. Capillary tubing is made of copper coil, and is part of refrigeration and air conditioning systems, that act as metering devices. They are also found in relay switches as the winding part of the relay that produces a magnetic field to actuate the mechanism.
All copper coil, whether it has a solid profile or is hollow in the middle, exhibits seamless, uniform wall thickness. They are easy to form from billets, preforms and copper sheets that have been heated and forced through a mold in the shape of the coil. This process is known as extrusion. Thin copper coil, which is essentially wire that has been wound, is extruded several times through successively smaller and smaller molds until the desired thickness has been obtained. Extrusion produces a moderate amount of waste material, but it can be reused to form other copper products.
After the copper material has been extruded, it is annealed or heat treated, depending on how hard or soft it should be. It is then automatically wound into a circular or spiral pattern, cut and is ready to ship. One of the most widely used applications for copper coil is as an electromagnetic coil, which is a copper coil that acts as a conductor. It is wound around a core, forming an inductor. A single loop of wire is referred to as a turn, and by definition, coil must be comprised of multiple turns.