Official Answer
Answer
Loss of free height, or 'set,' occurs when the operating stress exceeds the material's elastic limit. This often happens if the spring was compressed to its solid height $H_s$ during installation, even if the operating height $H_1$ is safe. The stress at solid height $\sigma_s$ must be calculated. If $\sigma_s > \sigma_{yield}$, the spring will undergo plastic deformation. To troubleshoot, we perform a 'Presetting' process during manufacturing where the spring is compressed to solid 3 times. This induces beneficial residual compressive stresses. If the spring still loses height, the material must be upgraded to a higher-strength alloy (e.g., from 302 to 17-7PH) or the wave count $N$ increased to reduce the stress per wave.
