How Fit and Function Affect Spring Longevity

Categories: Design and Innovation, Engineering, Manufacturing, News, Springs, Springtelligence|856 words|4.3 min read|By |Published On: October 27th, 2020|

It is fundamental to optimal spring operation and spring longevity that it fits and works freely within the space available. While this may sound obvious, insufficient space for a spring to operate within is a common cause of spring failure.

How Fit and Function of Compression Springs Affects Spring Longevity

Compression springs often fit over a rod, within a bore, or sometimes both. It is imperative that the spring does not rub on either of these. This will prevent the spring from operating properly and will cause increased stress and eventual breakages.

The inside diameter (ID) of a compression spring, including any tolerances, should always be greater than the maximum rod size (again, allowing for any tolerances). It is likely that the end coils, especially if ground, will affect this and should therefore be monitored. The video below details what spring tolerance is and how it affects the functionality of a spring.

In spring design, you must consider the dimension tolerances for the outside diameter (OD) within a specified bore. Also, bear in mind compression spring diameter expansion upon its compression. The video below demonstrates the importance of allowing for the OD expansion of a compression spring.

How Fit and Function of Tension Springs Affect Spring Longevity

It is unusual (though not unheard of) for a tension spring to operate over something – like a rod or spigot – as tension springs are usually closed coiled. Also, as the spring extends, the OD reduces; so if the spring – including tolerance for the OD – fits in the bore available, it will work within it.

The type, form and orientation of torsion spring ends need considering to ensure the spring fits and operates correctly (see diagram below). A simple example is if an end needs to fit through a hole in a mating component. This requires a sufficiently large gap to ensure this is achievable. Similarly, if the fittings for a spring are at 90 degrees, this should be specified in the spring design.

As a tension spring extends, the diameter tries to reduce. If the ends are fixed, this puts a torsional stress on the ends of the spring – which are its weakest points. There are a number of ways to overcome this potential problem and allow the ends to rotate – one option is separate, coned-in ends. Another is joining two spring sections by a central rod, or attaching centre hooks to allow some rotation upon applying load.

Tension Spring Parameters

How Fit and Function of Torsion Springs Affect Spring Longevity

Torsion spring leg design needs to suit the spring application to achieve spring operation and spring longevity. There are three main types of ends on torsion springs: axial, tangential and radial (or a combination).

The form of the end can vary from simple, straight legs to very complex shapes – depending on the intended application.

A torsion spring should always work by closing, so the direction of coiling is very important to get correct; should it operate the ‘wrong way’, the spring is likely to fatigue very quickly and ultimately fail. Discover more about spring coiling direction in our Springtelligence video below.

As a torsion spring deflects, the ID reduces and the body length of the spring increases. It is imperative to consider these factors when designing a spring. If the spring binds onto the shaft, or within the lateral space, the stresses transfer to the spring’s legs and they may break.

Compression spring OD expansion, torsion spring ID reduction and increase in body length are calculable for any deflection.

Operating Stresses

It’s imperative to consider the space available for a spring to operate in.  If there is insufficient space for the spring to operate within, the laws of physics can unfortunately be unforgiving! It is always a good idea to take spring design into consideration at an early stage in any new project.

As we touched upon in our previous blog post, different materials and grades can allow for greater stresses to be accommodated in a design. However, always evalute the working stresses for any type of spring to establish the optimal design and fit.

In summary, the application affects each type of spring differently during the respective uses. You should always allow sufficient space for the spring to work effectively and consider how the application affects the spring’s performance.

To find out more about springs, spring longevity and spring applications, visit our other website pages and blogs, or to request a quote please get in touch with us.