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An expansion spring is a device that uses a coil of wire to store energy through expansion. These devices are the opposite of compression springs; they do the same thing through contraction. As the spring is placed under load, it becomes longer. The coils begin to expand outwards from one another, typically because one end is connected to a stationary object and the other is connected to an energetic object. The process of expansion stores energy within the coil, and when it returns to its original shape, it releases that energy back into its environment.
Regardless of the way they are used, springs of any kind are designed to hold, store and move energy. The energy within the springs can be of nearly any kind. Electrical current moves through wire coils, typically without deforming the spring, and mechanical energy is stored within the spring’s body, generally causing a physical change.
An expansion spring is designed to become longer as the spring stores more energy. It will typically start in a tight coil with all the layers stacked on top of one another. As energy enters the spring, it will grow longer as it stores the force. If the spring returns to its original shape, that means it has imparted the energy it was storing onto something else.
In typical usage, an expansion spring is placed between two connected objects where at least one does not have a fixed position. As the objects move apart in relation to one another, the spring expands. In this case, the spring is storing part of the energy generated by the objects as they move. As the spring grows larger, it stores more and more energy, which will slow the moving objects until they stop. The spring then releases its energy to pull the objects towards one another until it reaches its original shape and size.
The other common spring design, a compression spring, operates the same way but in reverse. As objects move closer to one another, the spring will shorten until it releases its energy and moves the objects apart. Unlike an expansion spring, a compression spring doesn’t need to have a permanent connection to an object to impart energy to it.
The term ‘expansion spring’ is also used when referring to a spring that bridges two electrical connections in place of a useful device. At any time, the user can remove the spring and place a component within the area, thereby expanding its functionality. This term is uncommon, but is occasionally used by non-native English speakers and in some types of electrical jargon.