Couplings are categorized as rigid or flexible. What determines the categories?

The categorization of couplings into rigid or flexible primarily relates to the needs of the connected components. Rigid couplings are designed to maintain an exact alignment between two shafts, which is critical for applications where precision and minimal movement are required. Such situations demand stability and reliability that rigid couplings provide, effectively transmitting torque without allowing for any misalignment.

On the other hand, flexible couplings are used in scenarios where some degree of misalignment or movement between components may occur. These couplings can accommodate angular, parallel, or axial misalignment and serve to absorb shock loads while reducing stress on connected shafts. The requirements of the connected components, including their operational conditions and tolerances for misalignment, dictate the need for either rigid or flexible couplings.

This understanding of alignment, movement, and operational needs highlights why the choice of coupling type is fundamentally based on the requirements imposed by the connected components rather than solely on material or structural properties.