Understanding Flexible vs. Rigid Couplings

Mechanical couplings are used to connect two rotating shafts and transmit power. Couplings can be broadly classified into two main categories: rigid couplings and flexible couplings.

• Rigid Couplings: These couplings are used to connect shafts when perfect alignment is maintained. They do not allow for any misalignment or vibration between the shafts. They essentially make the two shafts behave as a single, long shaft.
• Flexible Couplings: These couplings are used to connect shafts that may have some degree of misalignment (angular, parallel, or axial) or require damping of vibration. They provide flexibility to accommodate these imperfections without causing excessive stress on the shafts or bearings.

Analyzing the Given Couplings

Let's examine each option provided in the question to determine if it is a flexible coupling or not.

• Oldham's coupling: This is a type of flexible coupling used to connect two parallel shafts that are misaligned. It uses a central floating disc with tongues that fit into grooves on the flanges mounted on the shafts. It specifically accommodates parallel misalignment. Therefore, Oldham's coupling is a flexible coupling.
• Universal coupling: Also known as a Cardan joint or Hooke's joint, this is a flexible coupling used to connect two shafts whose axes are inclined at an angle to each other. It allows for angular misalignment between shafts. Therefore, a Universal coupling is a flexible coupling.
• Bushed pin flexible coupling: This coupling consists of two flanges, one with pins and the other with holes fitted with rubber or flexible bushes. The pins from one flange pass through the bushes in the other. The flexibility comes from the rubber bushes, which can absorb shock, damp vibration, and accommodate slight angular, parallel, and axial misalignments. Therefore, a Bushed pin flexible coupling is a flexible coupling.
• Compression coupling: This is a type of rigid coupling. It connects two shafts end-to-end using tapered sleeves or mufflers that are compressed onto the shafts by nuts or bolts. It relies on friction and compression to hold the shafts firmly together and transmit torque. It requires the shafts to be in good alignment and does not accommodate misalignment or vibration. Therefore, a Compression coupling is not a flexible coupling.

Conclusion

Based on the analysis, Oldham's coupling, Universal coupling, and Bushed pin flexible coupling are all types of flexible couplings designed to accommodate various forms of misalignment and vibration. The Compression coupling, however, is a rigid coupling that requires precise shaft alignment.

Therefore, the coupling that is not a flexible coupling is the Compression coupling.