This post is the first in our series of blogs exploring the main factors which affect the longevity of a spring.
The first question to ask is ‘could a spring last forever?’. And the answer is, yes it could do if: the operating stresses are not too high, the working temperature does not cause the spring to lose too much load, the environment does not cause corrosion, the spring is not abused, and the spring is well-made and free from imperfections. Yes, some springs could potentially last forever!
Considering the best spring material for its purpose
The lifespan of springs is directly impacted by wire material used in their manufacture. If an unsuitable material is chosen, both the performance and the longevity of the spring will be severely compromised as the spring may not be fit for the purpose. All solid materials have certain properties which lend themselves to the make-up of a spring – even wood demonstrates elastic potential in its use for making bows for firing arrows. These are considered to be one of the first representations of spring technology. We will now look at the main materials from which most springs are manufactured today.
Carbon steel is the favoured and most common material in spring production, as it is relatively inexpensive and widely available. It has high strength and its popularity stems from its high load capacity and consistent performance in high-pressure applications. Disadvantages of this material are its susceptibility to load less at high temperatures and the risk of corrosion.
For spring manufacturers, carbon steel is denoted by the standard EN10270-1 and there are various grades from SL (Static Low) up to DH (Dynamic High). The higher the tensile strength of carbon steel and the better the surface quality, the greater the fatigue life – i.e. the ability to withstand thousands, or even millions, of cycles without the risk of fracture – will be in a dynamic spring application.
Stainless steel is also a popular choice of spring material due to its ability to operate in temperatures up to 300 degrees Celsius, its resistance to corrosion and its subsequent suitability in these settings. It also provides durability and high yield strength – making it able to withstand intense stress while still maintaining its form. On the other hand, it is slightly weaker than materials such as carbon spring steel and more expensive. New stainless steels are in development to increase strength while retaining the resistance to relaxation during the application of temperature.
Silicon Chrome is suitable in situations where the spring is required to support a great amount of force and/or shock loads and high-stress applications, as it has high tensile strength – particularly at wire diameters exceeding 2mm. It is also able to perform in relatively high-temperature environments – higher than carbon less than stainless – therefore making it a suitable spring material for use in products including engine valve springs, firearm recoil springs and automotive suspension.
Examples of exotic materials include Inconel®, Elgiloy® and Nimonic®. These contain greater concentrations of elements such as nickel, chromium, cobalt and molybdenum, providing high strength, corrosion resistance (in environments in which stainless steel is at risk of corrosion), oxidation and high temperatures. These properties make them ideal materials to use in particularly aggressive environments – in which high temperatures and levels of corrosion are typically the two main aspects. One example would be their use in the oil and gas industry.
The first questions to ask are, “Would carbon steel work? If not, why not?”. This will usually indicate which material would be suitable. Once the operating stress has been calculated, it can be determined whether carbon steel has sufficient strength. Temperature causes relaxation (loss of load) in springs over time and this is commonly overlooked, so should be evaluated when choosing the appropriate material.
The next thing to consider is environment i.e. is it corrosive? If so, the material used to make the spring will need to be resistant to corrosion or coated with corrosion protection.
Opting for materials of a higher grade within a specification results in better quality springs with increased longevity – quality can be looked at in terms of the tensile strength of the material and the surface quality i.e. the fewer flaws in the surface, the better the quality of the material.
Ultimately, it entirely depends on the unique application in which the spring(s) will be used.
The flowchart below poses questions about the environments and applications in which a spring may operate, following the appropriate arrows to each answer will suggest a suitable material for the purpose. This should, however, be used purely as a guide as there are several additional caveats which should also be considered, including the prestressing of springs and the potential need to redesign those with high operating stresses.
For more information about springs, their longevity and our work producing them, visit www.jbsprings.co.uk or send an enquiry through our Contact Us page to find out how we can provide you with lean spring solutions. We’re always happy to help with any queries you may have about springs and their applications. You can also discover how our 48hr custom order service could provide you with the specific springs you require within two working days at https://jbsprings48.com/.