Tension Springs & Extension Springs
Like compression springs, tension springs absorb and store energy.
But tension springs work in the opposite manner to compression springs They resist stretching or tensile forces. When the ends are pulled apart, the spring tries to bring them back together.
Unlike compression springs, most tension springs - also known as extension springs - are always under some degree of tension, even when under no load. This initial tension is what determines how tightly together the spring is coiled when there is no load applied. They have hooks or loops at each end to allow them to be connected to other components. An example of tension springs in use are those seen in trampolines.
Another common type of tension or extension spring is the drawbar spring. In a drawbar, the load is applied at the ends of long steel loops that pass through the spring’s centre and are hooked around the opposite end, compressing the spring on loading.
Drawbar springs are excellent for use in potential overload situations and offer a built-in definite stop that will continue to carry a static load after reaching the maximum extended length.
As with compression springs, the applications for tension springs and extension springs are varied. Some of the most common uses include trampolines, carburettors, garage door assemblies, medical devices, farm machinery, and toys.
At the John Bradley spring works, tension springs can be manufactured from wire ranging from 0.3mm to 16mm and in diameters ranging from 3mm to 150mm.
They can be made with a variety of different ends, each suited to different applications. These include loop, hook, double twisted full loop ends, straight-cut, threaded inserts, extended twist loops, expanded eyes, reduced eyes, rectangular ends and teardrop-shaped ends.
The ends on a tension spring can vary in distance from the body of the spring. The length of the ends can be used to determine the overall tension of the spring when used in its application.
Extension springs can be manufactured with varying initial tension to suit different applications. Tension springs supplied by John Bradley are custom made to individual requirements.