Extension Springs

Extension springs are coiled springs that are intended to stretch with the application of force. Though of a similar shape and appearance, they perform the opposite role of compression springs, which are designed to contract along one axis with the application of force. Extension springs, in essence, counter a tension load by expanding along one axis. Unlike a normal, uncoiled strip of metal, an extension spring has already absorbed energy during its coiling/manufacturing process. This potential for work counters the tension that is applied to one or either end of the extension spring, allowing the elastic spring to gradually expand outward along its axis. In general, tightly coiled extension springs have a greater capacity to resist tension than springs that have noticeable gaps between their coils. It is therefore common for such springs to have no visible gaps between their coils.

In practice, extension springs are used in many devices that involve two physically separate units that are intended to be gradually separated, such as with the faces of various types of doors, hatches, and cases. An extension spring that connects between a frame and a cabinet door, for instance, allows the door to be opened or closed gradually, thereby avoiding damage to any attached mirrors or woodwork. Likewise, extension springs are routinely used to slow and eventually stop any object that is intended to roll or slide down a slot or track, such as is seen in many industrial and household applications.