Hydraulically Fitted Hubs, Theory And Practice
The transmission of torque from a shaft to a hub can be efficiently accomplished through the use of friction. The advantages of this system over a keyed connection are: (1) the significant reduction of stress concentrations in the shafts and hubs, (2) an increase in the torque that can be transmitted, and (3) the ease of hub removal. The disadvantages of this system are: (1) it requires more care at installation, and (2) it can generate high shaft stresses if misused. The theory of transmission of torque through the use of friction is relatively simple. A hub having a bore slightly smaller than the shaft on which it will be installed is expanded radially either through heating or through hydraulic pressure. Sufficiently expanded, the hub can slide on the shaft and then is allowed to resume its original diameter; however, the shaft prevents this from happening. In the process, a high contact pressure is created at the interface. It is this pressure, the contact area, and the coefficient of friction that generates the tangential force which permits the torque transmission. The contact pressure at the interface also generates high stresses in the parts. These stresses must be carefully calculated in order to avoid immediate failure of the hubs, or fatigue failure of the shafts. The practice of hydraulic installation and removal is simple if a few rules are religiously followed. The most important ones are: (1) very good contact pattern at the interface, (2) cleanliness of the parts and oil, (3) accurate measurements of pressures and motion, and (4) observance of safety rules. This paper gives the formulae necessary for the calculation of the torque that can be transmitted through an interference fit, and for the calculation of the generated stresses. The second part gives the rules that have to be followed for a safe installation and removal of the hub, and illustrations showing various methods in use.
Calistrat, Michael M. (1980). Hydraulically Fitted Hubs, Theory And Practice. Texas A&M University. Gas Turbine Laboratories. Available electronically from