A helical spring is a coiled mechanical device which stores and releases energy to absorb impacts or shock and to resist either compression or pulling forces between objects. It is typically cylindrically shaped and features varying numbers of coils according to its intended use. The wires used to manufacture helical springs are generally specially tempered after their construction to give the spring its compression characteristics. The tags or ends of the wire may either be cut flush with the coils or extend beyond the spring axis as attachment points. Helical springs are generally used in several distinct applications.
A helical spring is typically a cylinder shaped spring with any number of progressive coils. Helical springs may also be cone shaped according to their intended use but still follow the same basic progressive coil design. These springs are usually formed around steel jigs while the wire is still annealed or soft, then tempered or hardened to produce the resilient, resistive qualities of the finished spring. With extended use the tempering may be degraded to the point where the helical spring stretches or sags and no longer functions. Depending on the financial implications, a worn spring may either be replaced or re-tempered to restore its original characteristics.
Helical springs are generally used in two different applications. The first is the role of compression spring which offers resistance to forces moving two components towards each other. Typical applications are car suspension and mattress springs. Compression springs typically have their ends trimmed in such a way that they lie flush with last coils on each end allowing for easy mounting.
The second common use for the helical spring is as a tensioning element. Springs used in this role resists forces moving two objects away from each other. A couple of common tension spring applications include spring scales and automatic door closers. The ends of a tension spring extend beyond the axis of the spring and are typically equipped with a loop to allow for fastening.
The helical spring may also be used in applications where the energy stored in a compressed spring imparts percussive impact. These applications typically see the percussive work piece pulled back against the spring tension then released to strike another object. This cycle may be completed in a single action or the striker may be locked in place with the spring under tension for later use. Common examples of these uses include firearm firing pins, detonators on anti-personal ordinance, and automatic center punches.