How to determine the right material for spring solutions?
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Depending on the application and the requirements set, the choice is made to use a certain material or a specific surface treatment. Mechanical, thermodynamic properties and corrosion resistance play a major part, but at Alcomex we obviously also look into the availability and costs. An exotic material, that might be perfect though for a specific spring application, is often far too costly or not available in terms of wire.
Knowledge of materials and surface treatment
Within the technology department of Alcomex, wire manufacturers are always consulted when options are sought to improve the existing materials. Over the years, the wire used by Alcomex has significantly improved (for example higher tensile strength versus the EN 10270-1). This way we can allow the application of greater forces to the springs we design. In addition to improving the mechanical properties, we also study whether it is possible to make springs suitable for a certain use by applying a specific surface treatment. A simple example of this is the evaporation of gold; here, springs are provided with a thin layer of gold, which guarantees corrosion resistance (in addition, gold is a great conductor of electricity and is fairly abrasion-resistant). However, the limiting factor in this example is the costs which are too high for most purposes.
The extensive alcomex testing programme
Since applications become increasingly more challenging, for Alcomex the knowledge of materials has become more important over the years. Specific demands with regard to temperature and corrosion resistance and “foreseeable lifespan” make the testing of the behaviour of material an essential factor.
At Alcomex we use an extensive testing programme to determine the lifespan and relaxation. In consultation with our partners, it is even possible to tests springs in the application directly. One of the examples regarding the direct testing in the customer’s application, was the question: “What is the lifespan of an INOX 316 compression spring at 80°C in water vapour containing 40% sulphuric acid (H2SO4)?” The results of the test showed that after 80 hours, the INOX 316 springs were heavily corroded and, as such, no longer capable of providing enough strength.
The solution for this specific application, chosen by Alcomex, in consultation with the partner, was the use or ordinary spring steel with a special coating. After testing, this resulted in a lifespan of approximately 2,000 hours.
Springs in a certain application coming into contact with relatively high temperatures is another challenge that Alcomex faces regularly. By heating springs continuously (approx. 250°C), they are in fact calcined tension-free constantly, where tension-free calcining is part of the production process and serves a purpose. However, heating continuously, up to 250°C, is a different matter. At even higher temperatures the mechanical properties, and thus the spring constant (N/mm), quickly deteriorate, in other words, the springs will no longer function the way they were intended to.
Obviously there are standard materials available, but sometimes even they do not suffice, so that the solution should be sought in the total design that the spring is part of.
Changing Elasticity modulus under temperature
(E(application)=E20 * [1-r *(t-20)] => t [temp-application] at 20°C ambient temperature and r=0.25×10¯³ for spring steel and r=0.4×10¯³ for INOX).
For this kind of specific cases it is important to look at the entire system and only then choose the material. Because often, after a simple adjustment in the design, an existing material can be chosen for the springs. For example, the application of cooling fins or insulation may sometimes be enough to guarantee the desired service life of the spring.
Each market segment has its specific technical requirements, as well as numerous applications, so it is impossible to discuss all of them. We can however state that in its existence Alcomex’s technical team has already overcome many a problem. In addition, we are always looking for new techniques and surface treatments that we can use, together with our years of experience, for our customers.
By: Marco Dekker | Head of Research & Development
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