A torsion spring can be closed or open wound and are usually designed to wind up. As a torsion spring winds up, the coil diameter will decrease and the body length will increase.
Typical application of larger type torsion springs is assisting in the raising and lowering of ramp doors – usually on the rear of commercial vans, horseboxes etc.
An example of a ramp spring is shown below – these can be used singly or in series, depending on the weight requirements.
There is a range of stress (and, therefore, force) for any spring index that can be held without problems. If the designer needs an extension spring with no initial tension he should design the spring with space between the coils.
TORSION SPRINGS – Custom made – bespoke design.
Torsion springs are usually made for a specific application eg. ramp springs, ratchet springs, hinge springs, tail lift springs, skip springs and many other engineering applications.
Materials are generally Stainless steel type 302 or 316, or high carbon alloys.’