Answer
In slip clutches, wave springs provide the normal force $F_n$ required to generate friction torque $T = \mu F_n R_e n$, where $\mu$ is the friction coefficient, $R_e$ is the effective radius, and $n$ is the number of friction surfaces. The installation must ensure that the spring applies a perfectly axial load. Any non-parallelism in the mating plates will cause uneven wear and 'chatter'. Because slip clutches generate significant heat, the wave spring must be isolated from direct contact with the friction material if possible, or manufactured from a high-temperature alloy like Inconel X-750. Furthermore, the spring rate should be chosen to be relatively flat (low $k$) to maintain consistent torque even as the friction linings wear down and the spring's operating height increases.
