Coil springs are coiled metal or plastic cords used to store or absorb mechanical energy. Coil springs are among the most widely recognizable spring configurations, and their design is one of the simplest among all spring configurations. They are usually composed of a rounded cord, as opposed to the flat strips used in flat springs, and they can be coiled to varying degrees of tightness.
Coil springs are sometimes also called helical springs because of their helical shape. Conical coil springs, cylindrical coil springs and other coil spring shapes can be found in use throughout industry, commerce and in consumer products contexts. They are important tools in many different kinds of complex industrial equipment as well as in simple hand tools. In commerce, simple coil springs are important to the function of office utilities like staplers and even printers. Very small coil springs can be found in pens and mechanical pencils, and very large coil springs are used to suspend the North American Aerospace Defense Command's facilities deep within Cheyenne Mountain in Colorado. Coil springs can also be used as torsion springs, transferring and storing mechanical energy through a twisting motion. Many mousetrap varieties involve the use of coil torsion springs.
The two different types of coil springs are compression and extension springs. Compression springs compress under a load, whereas extension springs lengthen, or extend, under the weight of a load. Extension springs are used primarily to keep two components together, while compression springs are used to keep components from touching. The basic design of each of the two kinds of coil springs differs in an essential way. The spiral wires in compression springs are not touching when in a relaxed position and only become so under the stress of weight. In contrast, extension springs are designed so that their spiral wires are contiguous when there is no weight load and stretched apart under the stress of a weighted load. Coil springs can be made of various steel materials, including stainless steel, hard drawn steel, steel music wire and spring steel. Spring steel is a special kind of steel with increased elasticity and return properties. The elasticity of a spring enables it to return to its original position; however, this capability diminishes with use. In general, the larger the wire, the stronger the spring is. Spring strength can also be increased by making the coil diameter of the spring smaller.
