Combined compression and extension spring replaces wire wound spring
21 July 2013
Abssac was recently called upon to retro-fit a spring in a fuel control system. The spring unit should compress and extend 2mm but deliver an accurate spring rate over a set life time.
The existing wire wound spring was not providing an accurate spring rate over time and each spring had to be rate tested and certified before fitting. Normal rate accuracies were ranging from +/-15% and were not linear in rate.
Abssac's machined spring is machined from a single piece of material. This not only allows one, two, three or more spring elements to be machined into the single part but, due to the geometry of the coil, the spring rate is totally linear. In fact spring rate tolerance can be as good as +/- 1% if required with a machined spring.
After the preliminary discussion between the customer and an Abssac application engineer, a drawing of the concept spring was forwarded to be reviewed. A few minor changes were then needed, as the customer considered incorporating attachment designs into the single piece stainless steel spring.
All other dynamic parameters were easily improved upon over those of the existing wire wound spring, and a final configuration was then proposed.
Two test samples were sent to verify the installation and complete life testing. The machined spring offered improved efficiency and reduced parts inventory; moreover, each spring supplied was certified on rate allowing it to be fitted straight into the application.
Solving this project has led to several other spring applications of the same physical configurations, but with varying spring rates and materials.
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