Answer
Hysteresis is the difference between the loading and unloading curves and represents energy lost to friction. In multi-turn wave springs, hysteresis is primarily caused by 'inter-turn friction'. As the spring is compressed, the waves in adjacent turns must slide slightly against each other. If the spring is unlubricated or if the surface finish is rough, this friction resists motion, causing the 'loading' force to appear higher and the 'unloading' force to appear lower. High hysteresis is problematic in precision control valves where accurate positioning is required. To minimize it, engineers can specify a multi-turn spring with 'Gap' ends (to allow expansion) and use a high-performance dry-film lubricant to reduce the coefficient of friction between the turns.
