Spring is a device that recovers its shape after an outside force changes that shape and is then removed. Most springs are in the shape of a cylindrical coil or a flat spiral. They are made of metals–commonly steel and bronze.
A coil spring is made by bending a length of wire into the coil shape, then annealing and hardening it. Annealing, a process of heating and cooling, removes internal pressures, called stresses, that result from the bending of the wire.
A coil spring resists forces that tend to elongate or compress the coil. The amount of resistance is proportional to the force applied to the spring.
Adding alloys containing elements such as chromium, nickel, tungsten, and cobalt to steel wire used in springs increases the springs’ ability to withstand heat. Stainless-steel springs will perform well at temperatures up to about 500 °F (260 °C). An alloy of nickel and chromium has been used at 900 °F (480 °C).
