Coil spring

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A compression coil spring
A tension coil spring
A selection of conical coil springs

A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of a helix which returns to its natural length when unloaded.

Coil springs are a special type of torsion spring, the material of the spring acts in torsion when the spring is compressed or extended.

The two usual types of coil spring are:

  • Tension coil springs which are designed to resist stretching. They usually have a hook or eye form at each end for attachement.
  • Compression coil springs are designed to resist being compressed. A typical use for compression coil springs is in car suspension systems.

Metal coil springs are made by winding a wire around a shaped former - a cylinder is used to form cylindrical coil springs.

Oxy-cut spring showing deformation due to loss of tempering in adjacent turn

Many types of coil spring are wound in an annealed (soft) condition and then tempered to achieve their strength as a spring. Over time, this tempering can be lost and the spring will sag because it can no longer withstand the loads applied. Such springs can be re-set by annealing, returning to their original length (or deliberately setting them to a different length) and then re-tempering. Damage to springs, such as using oxy-acetylene to cut the end off a car suspension spring to lower a vehicle's ride height, can destroy the tempering in localised areas of the spring.