Page 246 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 217

Figure 3-90. Interference fits required for various shaft/hub diameter ratios to reach
required interference-fit pressures.

Maximum Combined Stresses

Experience shows that highly satisfactory interference fits are generally reached
when the material at the hub bore reaches about 80% of the yield stress. The maxi-
mum combined stress is composed of compressive and tensile components and, for a
conventional coupling hub, occurs at the bore. Its value can be expressed as:

(3-11)

where c = dlD. Studies have indicated that coupling hubs with c values of 0.4 or
lower will operate quite well even if the full yield stress value is reached by the max-
imum combined stress at the coupling bore.49

Hub Mounting by Thermal Expansion

Thermal expansion of hubs is accomplished through application of heat. Immer-
sion in high flashpoint heat-transfer oil, heating in an oven atmosphere, or soaking in