Joining two shafts is done with mechanical couplings. Couplings should be capable of transmitting the rated torque capacity of the shaft while accommodating any misalignment between the shafts.
Rigid couplings are simple and low cost. But they demand almost perfect alignment of the mating shafts. The shafts must also have stable bearing supports. Misalignment, whether present initially or developed from wear, causes undue forces and accelerated wear on the shafts, coupling, shaft bearings, or machine housing.
In most coupling applications, misalignment is the rule rather than the exception. It comes from such sources as bearing wear, structural deflection, thermal expansion, or settling machine foundations. When misalignment is expected, a flexible coupling must be used.
Common selection factors include:
- Amount of torque
- Positive shaft engagement
- Misalignment tolerance
- Lubrication/maintenance
- Ease of installation/removal
- Operation under adverse conditions
- Service life
- Cost
