There are various ways of connecting a Shaft and Housing to transmit the torque such as spline, keyway, and shrink fit. It depends on the choice of designer, his past experience, type of application (shock load or smooth drive), cost factors, amount of torque, etc. to choose the way to connect the shaft and housing. The most common practical example of this type of fit is the mounting gear on a shaft. Shrink Fitting is one of the common ways of connecting the hub with the shaft for heavy torque transmission. There are several pros and cons of this method. Considering the positive sides, there is no need for cutting the keyway or making a spline on the shaft and housing which is a costly affair, moreover, there is no stress concentration at the sharp edge like in the case of the keyway. On the other hand, it may not be easy to separate the shaft and housing that are fitted by shrink fit at a later stage, also it requires fitment skills of shop floor people and correct theoretical calculation of shaft & housing tolerances by the designer as excess tolerance will result in cylindrical stresses at contact surfaces and less tolerance will result in insufficient grip. So In general, when the hub and shaft are not be separated or mounted permanently then this method is used. Two parts (shaft and hub) are forced together either at room temperature or by heating the hub / cooling the shaft. Only smaller diameter shaft and hub can be press-fitted at room temperature but larger size shafts and hub require a huge amount of force for shrink fit so temperature differential must be used. Hot and cold parts can be slipped together with little axial force and when parts equilibrate at room temperature, their dimensional change creates the desired interference for frictional contact. Another method used to connect hub and shaft is by hydraulically expanding the hub by pressurized oil delivered by passageways in the shaft, this method is also used to separate hub and shaft. Elastic deformation due to interference fit results in a large amount of friction forces between parts. This friction force helps in transmitting the shaft torque to the hub and resists the axial motion of parts as well.
Another important consideration while designing the components of Sharink Fit is that the stresses (generated after mounting) need to be kept below the yield strengths of the shaft and hub material to avoid deformation or even cracks.
