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There are several types of mechanical springs including the compression spring, extension spring, torsion spring, constant force spring and belleville spring. Each type of spring undergoes a change in shape or size when a load is applied. Energy is stored in the spring until the load is removed. The most simplistic spring is the tension bar, which absorbs a force uniformly through its structure and deforms only slightly. An example of a tension bar is the spokes on a bicycle wheel.
Compression springs are mechanical springs that oppose compression forces. It typically squeezes together to absorb the force and expands once the load has been removed. Compression springs are used in car suspensions and switches.
Extension springs are mechanical springs that stretch beyond their rest positions when a load is applied. After the load is removed, they contract back to their original size. Typically, an extension spring has a loop at each end to attach to various objects, such as a screen door hinge or garage door hinge.
Torsion springs are mechanical springs that rotate around an axis to create a load. As the load is released, the spring rotates back to its starting position. This type of spring is usually used in mouse traps.
A type of spring that releases a controlled amount of energy, instead of the quick burst associated with torsion springs, is the constant force spring. Generally, it is made of a band of steel that is wrapped around itself in the shape of a spiral. A torsion spring is capable of producing a rotational force that lasts over a long period of time. The mechanical springs that are found in clocks are typically constant force springs. They are also found in wind-up toys. Constant force springs can unravel dramatically if they are removed from their structure, since they contain a lot of stored energy.
If an application requires more power, a constant force spring can be designed to work over a fewer number of rotations. It is generally constructed from a thicker band of steel and can be dangerous if removed from its intended application. This type of spring is typically used in the reclining mechanisms of car seats.
The belleville spring, also known as the belleville washer, is a flat, disk-shaped spring with a hole in the center. It is typically used with a bolt to maintain pretension, which reduces the stress on the bolt when a load is applied. When stacked on top of each other, several belleville springs can generally accommodate higher loads.