Official Answer
Answer
The installation stress $σ_i$ occurs when the ring is expanded over a shaft or contracted into a bore. It is calculated by $σ_i = \frac{E · t · (D_g - D_i)}{D_m^2}$. To prevent 'permanent set' (where the ring doesn't snap back to its original diameter), $σ_i$ must be less than the yield strength $σ_y$ of the material. For $17-7PH$ CH900, $σ_y \approx 200$ ksi. If the calculation shows $σ_i > σ_y$, the ring must be redesigned with more turns (which reduces the thickness $t$ per turn) or a larger free diameter. In the field, using a tapered 'Installation Cone' and 'Plunger' is essential to ensure the ring is expanded uniformly and not beyond the calculated limit.
