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  1. The effect of temperature and corrosion on springs

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    One of the challenges that we, as a spring manufacturer, have little influence on is the combination of the demanded lifespan and the conditions under which the spring is required to function. Depending on the system requirements, we first assess which material is sufficiently resistant to corrosion and whether this is useable in the application. At the same time Alcomex decides, within the specified temperature range, whether the chosen material still has sufficient mechanical properties to function. Finding the right combination for this is often a difficult task.

    The various literature makes material specifications available. The most common are:

    Material Active ingredient Normal temperature range
    Carbon steel (C75, C85, C100) 1.1248 / 1.1269 / 1.1274 [-40°C tot +120°C]
    Inox (301, 316, 17-7 PH) 1.4310 / 1.4401 / 1.4568 [-150°C tot +250°C]
    Inconel (X750, 718, 625, 600) 2.4669 / 2.4668 / 2.4856 / 2.4816 [-200°C tot +550°C]
    Hastelloy (C4, C276) 2.4610 / 2.4819 [-100°C tot +500°C]
    MP35N Body implantable [-200°C tot +320°C]
    Beryllium copper 2.1247 [-190°C tot +160°C]
    Phosphor bronze 2.1020 [-190°C tot +80°C]
    Brass 2.0321 [-190°C tot +120°C]


    Material and surface treatment as a solution

    After the first screening, the application of the spring is examined. It may so happen that the work environment of the spring is such corrosive that certain materials simply “dissolve”. The strength of springs and spring products is largely determined by the thickness of the wire in relation to the tensile strength [N/mm2]. The thickness of the wire and tensile strength have an effect on the spring constant, thus the functioning of the spring, and in addition the lifespan is influenced. Issues can often be solved by choosing a different material. But be aware, for cost-driven applications, often this is too expensive, since certain, more exotic materials are simply not available in wire or narrow strip.

    Often surface treatment can be chosen as an alternative solution for a specific medium. The most common surface treatments are: galvanising, phosphating, nickelling, chroming, powder-coating, tinning and silvering/gilding. All of these surface treatments add specific properties to the spring, as a result of which the lifespan is extended and the product made suitable for the application, with the principle that the mechanical properties are not being adversely affected.

    Hydrogen embrittlement in spring materials

    The application of surface treatments is not without risk and if implemented incorrectly, this may lead to embrittlement of the materials. This phenomenon is called hydrogen embrittlement and occurs in all cases where hydrogen is able to develop on the surface of the steel. The effect of hydrogen embrittlement on steel is that the steel will break at a much lower tensile strength than usual, despite the steel showing enormous durability properties during normal lifespan tests. Hydrogen embrittlement could be caused by processes for surface treatments and occurs when springs are exposed to non-oxidising acids or cathodic cleaning and coating. Remark: leaf springs that have hardened after moulding are sensitive to this.

    The risk of embrittlement is reduced as the tensile strength and hardness are diminished. Generally, embrittlement does not occur on steel with a tensile strength of < 1000 N/mm ² or a hardness of < 30 Vickers. Most of the hydrogen can be removed by an additional thermal treatment (continuous warming). The thickness of the material determines the temperature and the duration of this thermal treatment:

    Material thickness < 3 mm 170°C – 180°C, 5 hours

    Material thickness < 12 mm 190°C – 210°C, 4 hours

    The implementation of surface treatments is hardly ever without risk. Alcomex always carries out these treatments in consultation with specialised partners, in order to guarantee the quality of our spring products and solutions.

    By: Marco Dekker | Head of Research & Development


    Do you have a specific challenge regarding high temperatures or corrosion? Get in contact with us!

  2. 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


    Submit your challenge to us? Get in contact with us!


  3. Market leader through research & development – part 2

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    From troubleshooter with a lot of experience to partner in “predictive maintenance”

    In cooperation with our strategic partners, we investigate the specific technical requirements that our springs programme should comply with, to determine the lifespan of your springs in advance. For our customers we try, for instance, to prevent sudden production interruption and attempt to realise a situation of planned maintenance, together with you.

    The expected lifespan of all the springs in our standard programme is in accordance with the DIN and 13906. In case of springs, custom made for you, we look beyond the standard norms, because they depend on your specific situation and use. For instance chemical composition of the material and corrosion resistance play a significant role at high temperatures or in an aggressive environment. Alcomex has extensive expertise in the area of surface treatment, including: galvanising, anodising, phosphating and special surface-treatment processes.

    Based on our many years of practical experience, knowledge of engineering and internal testing, we have developed a complete programme in order to be able to determine the lifespan of extension, compression and torsion springs, matched to your application/use. The programme developed by us is based on several variables, including:

    • Application
    • Specific customer demands
    • Spring configuration
    • Chemical composition
    • Conversion degree
    • Ductility of the wire
    • Surface treatment
    • Thermal treatment

    Did you miss previous episodes in the research & development series? Read part 1 here! or read more of part 3 here!

    By: Marco Dekker | Head of Research & Development

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