Most other coil spring varieties are either compression or torsion springs, which are used to store and transmit compressive and rotational force, respectively. Instead, extension springs resist linear pulling forces.
Extension spring components are used in tape cassette players, balance scales, trampolines, washing machines, garage doors and in many other products and processes. They usually feature hooks, rings, eyelets or other shapes to which other components can be attached. Extension springs always attached two objects to each other and allow for the controlled movement of those objects relative to each other.
In a trampoline, for example, when a force is exerted on the surface to which the extension springs are attached, the elasticity of the spring allows for its extension to a certain point. Because the spring is attached both to a moving part and to a stationary part, the moving part is restricted in its motion. After extending to a certain point, the extension spring retracts, pulling the moving surface back with it. All extension springs, with few minor exceptions, perform according to similar basic principles.
In contrast to compression springs, extension springs are compact when resting and extended when under stress. They are designed so that their spiral wires are contiguous when there is no weight load and stretched apart when loaded. Extension springs are 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 elastic ability of a spring enables it to return to its original position; however, this capability diminishes with use. Stainless steel is used as a spring composition material when the spring is intended for use in conditions that involve frequent or constant exposure to moisture or corrosive chemicals.
Stainless steel is by nature strong and corrosion resistant, which makes it appropriate for use as a spring composition material in harsh environments. In general, the larger the spring wire, the stronger the spring is. Decreasing the diameter of the coil is another way to increase spring strength. They come in many different sizes are used in a variety of applications.