What is a torsion spring?

A torsion spring is a tightly coiled helical spring which stores and releases energy to resist force applied through torque.

Nothing lasts forever. However, JB Springs’ compression, torsion and tension springs are designed with a view to them having a very long lifespan – potentially outlasting other components within their application.

The following factors can cause failure in compression springs and tension springs as well as torsion springs, however, this blog will focus on how they affect the performance of torsion springs:

Overstressing

Incorrect direction of operation

Too small an inside diameter

Too large a body length

Overstressing

All springs can become overstressed; in the case of torsion springs, these become overstressed if they are subjected to too much deflection or if they are used in the wrong direction (Figure 1), and this can result in spring failure. People commonly underestimate the required size of the spring to achieve the desired deflection and/or torque (in terms of wire size, spring diameter and the number of coils).

Additionally, when calculating the required strength (torque) for the torsion spring design, it is very important to consider the distance from the pivot point to where any load is applied; the torque (Nmm) is the product of the load (N) and the distance (mm) from the pivot. The legs are typically the first part of the spring to either deform or break, due to spring fatigue.

Incorrect direction of operation

A torsion spring should always operate in the opposite direction to the wind direction. For example, a right-hand (clockwise) wound torsion spring should work going anti-clockwise and vice-versa (Figure 1). Another way of thinking about this is the spring should always “close up” in operation. If a spring works in the wrong direction, it will become overstressed very quickly and is likely to fail.

Too small torsion spring inside diameter

As the spring deflects, the inside diameter (Figure 2) will reduce. This is particularly important when the spring operates over a spigot. If the spring design does not consider the inside diameter, the spring may bind and be unable to perform optimally. Stresses then transfer to the spring legs and risk breakage or deformation.

Too large torsion spring body length

As a torsion spring deflects, it effectively adds coil and the body length (axial length) increases as a result. If there is insufficient space, the spring will bind – leading to deformation and/or spring leg breakage.

These are some of the most common pitfalls to look for and avoid when it comes to designing torsion springs. There is an (almost) infinite number of designs for the legs, which can further complicate the spring design.

We recommend that spring designs are trialled to confirm they meet the requirements of the application. If you find you require further assistance in spring design or spring manufacture, please get in touch with us at JB Springs by phone, email or simply filling in the form on our Contact Page. JB Springs use 128 years of experience as spring manufacturers UK to advise on optimal spring design and produce and provide quality springs and wireform parts for a range of industries and applications.