How does temperature-induced relaxation affect the preload of a wave spring over its service life?

Relaxation is the gradual loss of load when a spring is held at a constant deflection over time, exacerbated by high temperatures. The rate of relaxation follows an Arrhenius relationship, where the loss in load $\Delta P$ increases exponentially with temperature $T$. For a carbon steel spring at $250^{\circ}F$, relaxation might be $5-10\%$ over 1000 hours. If the application requires a precise preload (e.g., in a mechanical seal), the spring must be 'heat set' by the manufacturer. This involves compressing the spring at a temperature higher than the operating temperature, which pre-relaxes the material and stabilizes the load for service.