Most springs are fitted either within a hole or over a rod, in both cases to ensure that they remain in place and work only in the direction intended. They are found in all sizes, allowing them to be used in a huge range of applications. These include large-scale presses, car engines and industrial machinery. At the other end of the scale, precision-made compression springs just a few millimetres in length are crucial for almost all electronic devices, ranging from mobile phones to hospital scanners.
As long ago as the 1940s, informational films were being produced demonstrating how difficult it would be to live in a world without springs, and how many everyday products would become impossible to make. Whether it’s the activation button on a ballpoint pen, the suspension of your car or the firing mechanism of a pistol, springs are the unsung heroes of the modern world – and in the last half-century, they have become even more ubiquitous. Many devices require a variety of different sizes and strengths of spring, all working in harmony.
Here are some of the major classes of compression spring:
These springs are particularly favoured where space is at a premium, since the cone shape reduces the solid height of the spring and so allows it to be used in confined spaces. Their tapered design produces a telescoping effect, which means that the force exerted by the springs upon compression is not constant. They are very popular in the car industry, especially within internal combustion engines, since their shape is inherently stable, resulting in dependability under repeated, heavy strain and a reduction in vibration. Conical springs’ stability also means they can be made to very tight tolerances, making them perfect for use with small shafts or holes.
These are found mostly in firearms. They have a rather sharp-edged, angular appearance which is suited to the actions needed to release a bullet from its chamber and fire it on a press of the trigger. This type of spring is rarely found away from the shooting range: although magazine springs have occasionally been used in other fields, their specialist design makes them unsuitable for most general applications.
Torsional compression springs
This type of spring is used when there is a need for both radial and lateral forces to be addressed. A common example is in the traditional design of mousetrap: when open, the trap is held in suspense against its catch (the lateral force). However, when the trap is triggered, the removal of the catch allows a strong radial force to be exerted, which snaps the trap shut at high speed. Larger versions of torsion springs are used in cars’ anti-roll bars, while many projectors use thousands of tiny springs in their digital micromirror devices.
These springs come in two versions: convex and concave, with the latter sometimes known as “hourglass springs” after their appearance. They are effectively two conical springs stuck together – and, as with conical springs, they offer non-linear compression. They offer very good lateral stability under pressure, and their low solid height saves space over traditional straight springs. It is possible to place these springs so that they rub against each other in use; this can help reduce resonance but is likely to increase wear.