DS-APR22-PG34+36_Layout 1 12/04/2022 15:36 Page 1
FEATURE
SPRINGS & SHOCK ABSORBERS HEADING teXt Standfirst
Wave goodbye to spring specification confusion
During the harsh Alaskan winter, up to 60% of a wood frog’s body
freezes solid. So that their cells don’t shrink or die, the animals have adapted to build up high glucose concentrations in their organs and tissues. When specifying a spring, material choice will determine its
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suitability for the environment to ensure that, like the wood frog, it can withstand extremes. Justin Lawrence, applications engineer at TFC, examines the properties of different wave spring material choices can you take the heat?
wave spring utilises a sinusoidal waveform to generate the required axial force. A Crest-to-Crest wave
spring has multiple turns to build up the free height of the spring to achieve the required deflection characteristics. Wave springs are made from flat wire,
which takes up less vertical space, significantly reducing working heights within an assembly. However, the choice of material affects the design and will normally be dictated by the operating temperature and environment where the spring must function. When specifying a wave spring, the choice
of materials ranges from standard carbon spring steel, through a variety of stainless steels, to more exotic nickel-chromium alloys. To make an informed decision regarding what material is best for your application, a good understanding of the properties of each alloy with respect to temperature and corrosion resistance is essential.
3 DESIGN SOLUTIONS APRIL 2022 4
The first environmental factor that can influence the material choice is temperature. When springs are used in environments close to or outside their recommended operating temperatures, it can lead to permanent deformation, or in the case of extreme cold, to a brittle fracture. For applications operating at ambient
temperatures, SAE 1070-1090 carbon tempered steel’s maximum recommended temperature of 121˚C will probably serve you well. This standard material is widely used in many industrial applications. Tensile and yield strength are maximised because of the oil’s tempered martensitic structure. If elevated temperatures are involved, 17-7
Ph/C stainless steel offers up to 343˚C as a maximum recommended temperature. Spring properties are achieved by precipitation hardening condition C to condition CH900. A286 stainless steel, or maybe Inconel 718, are the pinnacle of heat resistant alloys,
boasting maximum recommended temperatures of over 500˚C. However, these materials come with a much lower tensile strength, meaning careful consideration throughout the design process is critical to ensure the springs will function correctly. For extreme low temperatures, such as
those in cryogenic systems, choice of material is equally important. In these applications, 300 series stainless steels or Nickel alloys are normally preferred.
corrosion resistance
Corrosion, which occurs when metals react with their surroundings, can also cause springs to fail by leading to microscopic cracks. Corrosion is a much more relevant threat to carbon steel, which is vulnerable to atmospheric damage when not properly sealed. For improved performance 17-7, stainless steel has a similar corrosion resistance to 302 stainless, whilst offering excellent spring properties. 316
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