Many spring manufacturers produce their parts by applying strong pressure to wind steel wire under ambient temperature to obtain the desired functional forms. Following this step, however, the spring accumulates too much internal stress, which may weaken it, meaning it may no longer be optimal to support the load for which it was designed.
Stress relieving removes a large part of the produced internal tension and significantly prolongs the part’s service life, with no major complications. While this treatment is easy to do, particularly if we use an oven specifically designed for this type of treatment (as are those built by Pyromaître Inc.), it may be harder to verify its efficacy and to prove that the maximum amount of residual stress has indeed been removed. One scientific method, X-ray diffraction[i], can confirm and validate the anticipated outcomes by bombarding a sample of treated steel with X-rays and analyzing the intensity of these rays according to their projection into space. The result of the heat treatment is then evidenced by a curve produced by the synthesis of the diffraction analysis.
Atoms and X-rays: Seeing inside a crystal – http://undsci.berkeley.edu/article/0_0_0/dna_04
The equipment required to perform this type of test is relatively costly, and if adequate tools are not available, there may be delays in getting results, as few industries possess mechanical characterization labs similar to those found at university research facilities. Luckily, manufacturers have developed a simpler, more practical method to ensure optimal stress relief outcomes. These industries perform physical testing to determine the effects of expansion on their springs post-treatment. However, each type of spring must undergo individual testing to measure expansion post-treatment… which basically means that each case is different.
I’m looking at the relevant literature to see whether anyone in our field has introduced any new testing standards that (a) could be easily applied to the majority of spring models (length, width, and diameter) and (b) could confirm the success of a treatment. The greatest challenge in finding a general rule pertaining to expansion is that springs don’t expand in only one direction, which considerably increases the number of prediction errors regarding the deformations created by the treatment.
I have not given up just yet! I will continue looking into this. I hope that eventually I can write an interesting article on this issue. I will let you know before year’s end. If any of you happen to have expertise in this area or have read on the subject, feel free to share your thoughts here.
[i] Scientific American. X-Ray Crystallography: 100 Years at the Intersection of Physics, Chemistry, and Biology.