Good spring indices for polymer springs

[Enea Sacco]

When designing a metal spring, usually a spring index of between 4-25 is wanted. But I was unable to find a similar range for polymer springs. Can anyone recommend a range?

 

[rickfischer51]

Spring index is driven by the method of manufacture. How are you going to manufacture your plastic spring and what kind of tolerances do you need to hold? Consider that metal coil springs are typically wound from drawn metal wire or bar. The winding can be done hot or cold, and the material could be cold or hot drawn. Things like tolerance on wire diameter, level of springback, tool wear, forming temperature will all affect the final dimensions. Think in terms of how this will apply to a polymer.

How will this spring be used? If the spring will be cycled, fatigue is an issue, and calculating fatigue life in a polymeric component is not straight forward. If the spring will be continuously loaded, creep must be considered. The reality is that polymers are a poor choice for a spring, and there must be an unusually compelling reason to to consider this.

Rick Fischer
Principal Engineer
Argonne National Laboratory