More about Extension Springs

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Extension springs are tightly coiled springs designed to resist a tensile, or stretching, force. When pulled outward, the spring will attempt to pull back into its coil. As the spring is extended further, its resistance increases. This means that extension springs exert a greater pull the wider their ends are extended. Compression springs work in the opposite manner. They exert an outward force when the ends are pushed together. One of the main advantages to a compression spring is that, typically, when they fail, they simply compress. An extension spring that fails, however, can cause much greater damage because it will drop whatever load has caused it to fail. Due to this problem, extension springs are only designated three-fourths of the maximum working stress of similar compression springs.

Common extension spring designs are straight-cut, loop, hook and double twisted full loop ends. They can be manufactured from a wide range of materials, including music wire, titanium, stainless steel, chrome silicon and exotics, such as Inconel and Monel. Virtually any custom size and material is available. Some of the most familiar uses of extension springs are in garage door assemblies, carburetors and trampolines. The design of choice, whether full loop or hook ends, is dependant upon the application and the shape of the components being held together.

One of the most interesting forms of extension spring is the drawbar spring. Although these springs are designed to resist stretching, they do so using a central compression spring. In a drawbar spring, two long, steel loops are pushed through the center of a normal compression spring. This creates a loop on each side, and the base of each loop is hooked over the side of the spring opposite to its loop. When the loops are pulled, they draw the central compression spring together. The central compression spring then pushes outward, thereby attempting to pull the two opposing loops back to their original position. Due to the superior strength of the steel loops, and the compression action of the central spring, failure of a drawbar spring does not usually result in release of the supported load.