G & O Spring tips – Hot Prestressing
How to further reduce your springs relaxation and increase fatigue performance
Hot prestressing is a superior version of pre-stressing which adds significant complexity. This process is normally used when a spring is operating at an elevated temperature and relaxation becomes an issue.
The process consists of clamping the spring at its solid height and heat treating it (clamped) at its maximum operating temperature for a period of time. What this does is to artificially age the spring (without reducing its life) which in turn reduces its length. This length reduction has to be calculated by the manufacturer as the spring length needs to be correct after the process to ensure that the spring forces are correct.
In very sensitive applications it is best practice to leave the springs clamped prior to use because if stored for any period of time without an applied stress the springs can ‘grow’ back towards their original pre hot prestressing length.
Using this process can actually mean that springs are stronger at the end of their life than when they were installed as it drastically improves relaxation performance.
Hot prestressing can be applied to compression, extension, clock and torsion springs which will all benefit from the procedure.
How to: To check if your spring has been correctly hot pre-stressed measure the free length, then compress the spring carefully to solid height (avoid crushing) between two parallel plates, then measure the free length again. If the spring loses height then it has not been properly pre-stressed (scragged). If the spring has not been stored clamped then it is important that you scrag the spring 5 times (this will help to reverse any growth the spring has seen in storage).
The software we use to design springs allows us to predict the benefits that this process offers, contact us for a free spring design review.
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