Official Answer
Answer
A spiral retaining ring will begin to expand and lift out of its groove if the centrifugal force exceeds the ring's 'clinging' force. The maximum allowable RPM $N$ is calculated as $N = \sqrt{\frac{4.8 \times 10^{11} E t G^2}{w (D_o^3 R_m)}}$, where $E$ is the Modulus of Elasticity, $t$ is the thickness, $G$ is the groove depth, $w$ is the radial wall, $D_o$ is the outer diameter, and $R_m$ is the mean radius. If the application speed exceeds this value, a self-locking feature (a tab and slot) is required to mechanically prevent the ring from expanding radially. This is critical in high-speed automotive transmissions and aerospace turbine shafts.
