Selecting a spring design with appropriate durability ensures your end product will function reliably for as long as required.
In order to ensure that your spring component offers suitable longevity, you will need to think carefully about your application. For example, an automotive suspension system might be expected to last several decades and withstand harsh conditions. On the other hand, a spring used in wearable electronics might be relatively well protected and need to last just a few years thanks to the kind of rapid technological advances that prompt frequent consumer upgrades.
When looking to match the lifespan of your spring component with your end product, you will need to take these elements into consideration. Regardless of the application, there are two main variables that can impact longevity in spring design: spring material and spring finish.
In this article, we will explore how surface finishing can improve the performance and durability of your spring design, but first, a word on spring materials.
MATERIAL SELECTION IN SPRING DESIGN
When choosing the right materials for your spring design, there are some important factors to consider including a spring’s behaviour under stress, its conductivity, operating temperature, and working conditions.
In industrial applications, for example, springs may be exposed to harsh environments or corrosive substances. Aerospace designs may be subject to high temperatures, while medical implants might require a biocompatible spring design.
As a result, a variety of metals are used in spring fabrication, each with different characteristics, however, common materials include stainless steel, which can withstand hot temperatures and protect against oxidation, or low-alloy steels, which offer durability under stress.
The important thing to remember is that choosing the right material ensures that your spring’s behavioural dynamics are efficient, robust and matched to the anticipated working life of the application.
SPRING DESIGN FINISHES
In addition to the spring material itself, you may be able to significantly enhance the performance and reliability of your spring by opting for a surface treatment.
Some examples of the benefits choosing the right spring design finish can bring include:
- Deliver additional resistance in humid or corrosive environments
- Reduce friction between spring coils
- Minimising wear and improving performance in dynamic applications.
- Surface treatments can even be used to improve the appearance of a spring or provide colour coding in applications where visual aesthetics make a difference.
Whether you require a solution for cosmetic reasons or to increase durability, there are several spring finishing options available.
Types of Spring Finishes
Barrelling or Rumbling
The first treatment that many springs undergo is that of barrelling or rumbling to remove any sharp edges or burrs. This process involves tumbling the springs in a rotating container along with an abrasive media to smooth the spring’s surface. Not only does this improve the look of springs, but it can also enhance their performance and prepare them for further treatment.
Plating Processes
Thanks to its low cost and effective results, electroplating is one of the most popular spring treatments. During this process the spring is immersed in an electrolytic solution containing metal ions. When an electric current is passed through the solution, these metal ions are attracted to the spring and deposited in a thin, uniform layer on its surface. Common metals used in spring electroplating include zinc, nickel, chrome, and gold, depending on the application requirements.
As an alternative to electroplating, it is also possible to fabricate spring components using pre-plated wire. This is achieved by drawing the spring wire through molten metal prior to coiling. The advantage of this is that it provides a consistent coating thickness along the entire length of the wire ensuring uniform protection. Not only that, it can also simplify the manufacturing process by eliminating the need for a separate plating step post-manufacture.
Powder coatings
Powder coating offers an alternative to plating, providing a durable and corrosion-resistant finish, which enhances the lifespan of your spring. It offers a uniform coating thickness, improves aesthetics, and allows for customisation in colour, however, the coating itself is thicker than electroplating and may increase spring dimensions. Complex spring geometries can therefore pose a challenge during the coating process.
Compared to other coating methods, initial setup costs can be higher, although the long-term benefits in terms of performance often outweigh these disadvantages.
PTFE and Parylene
In some applications, it may be advisable to apply a PTFE or Parylene coating to protect springs. These coatings are ideal where low friction, corrosion resistance and biocompatibility are essential, which makes them an ideal choice in medical devices, precision instruments or aerospace designs.
Polytetrafluoroethylene (PTFE) offers a high melting point, low coefficient of friction, and resistance to almost all chemicals. It can be used as a surface treatment on springs to reduce wear, prevent corrosion and minimise friction during use.
Parylene is a crystalline polymer which results in a thin film coating. It is applied as a vapour and can conform to complex designs, providing even coverage with a high mechanical strength.
SOURCING A CUSTOM SPRING DESIGN
When thinking about both the materials selection and spring finishing process, it is important to consider compatibility issues prior to manufacture.
Without careful planning and thinking through the end use, you could choose a material or finish that may compromise your design. Significantly different coefficients of thermal expansion could lead to instability. Worse still, chemical incompatibility between the spring material and coating could even result in premature corrosion or degradation.
At best, this means paying to manufacture another batch of springs, or delaying your product launch, and at worst, could result in failures in action. It is important to consult a spring manufacturer with both spring design and coating or plating expertise. With suggestions on spring design and a thorough testing process, they should be able to ensure your final spring design offers optimal performance and durability – no matter what your intended application.
With over 40 years’ experience in custom spring design and manufacture, SCS offers a collaborative approach to finding the right spring materials and protective finishes for your design.
Contact us today to find out how we could improve the long-term reliability of your project.
