In terms of door springs, Alcomex uses SH or DH (Statically or Dynamically High load) qualities, in accordance with EN 10270-1, although the values set out in the EN 10270-1 are the lower thresholds. The EN 10270-1/2/3 classifies the indications of steel types in three different categories:
Group 1: steel types that are designated on the basis of their usage and mechanical or physical properties.
Group 2: steel types that are designated on the basis of their chemical composition.
Group 3: corrosion resistant materials (RVS)
In terms of industrial springs we have the following standard wire qualities, in the most common thicknesses:
| Material | Active ingredient | Normal temperature range |
|---|---|---|
| Carbon steel (C75, C85, C100) | 1.1200 / 1.1248 / 1.1269 / 1.1274 | [Temp -40°C up to +120°C] |
| Inox (301, 316, 17-7 PH) | 1.4310 / 1.4401 / 1.4568 | [Temp -150°C up to +250°C] |
| Inconel (X750, 718, 625, 600) | 2.4669 / 2.4668 / 2.4856 / 2.4816 | [Temp -200°C up to +550°C] |
| Hastelloy (C4, C276) | 2.4610 / 2.4819 | [Temp -100°C up to +500°C] |
| MP35N | Body implantable | [Temp -200°C up to +320°C] |
| Beryllium copper | 2.1247 | [Temp -190°C up to +160°C] |
| Phosphor bronze | 2.1020 | [Temp -190°C up to +80°C] |
| Brass | 2.0321 | [Temp -190°C up to +120°C] |
During the application analysis it is decided which spring application will be used. The working environment of the spring may be such corrosive that certain materials would simply “dissolve”.
As an alternative for expensive material, often the wire/spring is made suitable for an application by use of a surface treatment. The most widely used surface treatments are: galvanising, phosphating, nickelling, chroming, powder-coating, tinning and silvering/gilding. All of these surface treatments add specific properties to the spring, lengthening the lifespan without adversely affecting the mechanical properties.
The maximum strength provided by a spiral spring is mainly determined by the thickness (plus related tensile strength) of the wire and the diameter of the windings. The size of the maximum stroke and related spring constant can be influenced by increasing the number of windings, or by lowering it.
Spring constant: c=∆F/∆f=(G * d^4)/(8 * Dm^3* n)
Spring force: F=c*f=(G * d^4* f)/(8 * Dm^3* n)
d = wire thickness;
Dm = diameter center to center (of the wire);
n = active windings
The use of a different material in cost-driven applications is often too expensive, partly because the more “exotic” materials are limitedly available in wire or strip steel. Since corrosion has a negative impact on the wire thicknesses (and, as such, the functioning), good knowledge of the application and various surface treatments is a requirement with regard to tailor-made springs.
The application of surface treatments is not without risk and if not performed well, the materials may become brittle. This phenomenon is called hydrogen embrittlement and occurs in all cases where hydrogen can develop at the surface of the steel. The effect of hydrogen embrittlement on steel is that the steel will break already at a much lower tensile strength than usual, despite the fact that the steel shows normal durability values in regular lifespan tests. Hydrogen embrittlement may occur if springs are exposed: non-oxidising acids or cathodic cleaning and coating. Leaf springs that have hardened after moulding are sensitive to this.
The risk of embrittlement is reduced as the tensile strength and hardness decrease. Generally, embrittlement does not occur on steel with a tensile strength of < 1,000 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.
