A coupling is a mechanical device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings are fundamental components in various mechanical systems, from industrial machinery and automotive applications to household appliances and precision instruments. They serve not only to transmit torque but also to accommodate misalignment, absorb shock loads, and provide other critical functions in power transmission systems.

Types of Couplings

Rigid Couplings

Rigid couplings are used when precise shaft alignment is required and no misalignment is expected. They provide a solid connection between two shafts, ensuring zero relative motion. Common types include sleeve couplings, flange couplings, and clamp couplings. While they offer high torque capacity and simplicity, they cannot compensate for any misalignment, making them suitable only for applications where shafts are perfectly aligned.

Flexible Couplings

Flexible couplings are designed to accommodate various types of misalignment while transmitting torque. They can handle angular, parallel, and axial misalignments to different degrees. Major categories include:

Jaw Couplings: Use elastomeric spiders to absorb shock and accommodate misalignment

Gear Couplings: Consist of two hubs with external gear teeth and a sleeve with internal teeth, allowing for high torque transmission and some misalignment

Disc Couplings: Use flexible metal discs to transmit torque while accommodating misalignment

Universal Joints (U-Joints): Allow for large angular misalignment but require proper phasing

Oldham Couplings: Use a floating disc to accommodate parallel misalignment

Special Purpose Couplings

These include fluid couplings, magnetic couplings, and safety couplings. Fluid couplings use hydraulic fluid to transmit torque smoothly, while magnetic couplings provide contactless power transmission. Safety couplings (shear pin or overload couplings) are designed to disconnect or slip when torque exceeds a predetermined limit, protecting machinery from damage.

Key Functions and Characteristics

Power Transmission

The primary function of any coupling is to transmit rotational power from one shaft to another. The torque capacity, speed rating, and efficiency are critical parameters that determine coupling selection.

Misalignment Compensation

Shafts are rarely perfectly aligned due to manufacturing tolerances, thermal expansion, or foundation settling. Flexible couplings can accommodate:

Angular misalignment: Shafts at an angle to each other

Parallel misalignment: Shafts with offset centers

Axial misalignment: End movement along the shaft axis

Vibration Damping and Shock Absorption

Many couplings, particularly those with elastomeric elements, can absorb vibrations and dampen shock loads, protecting connected equipment from sudden torque spikes.

Thermal Expansion Accommodation

In applications with temperature variations, couplings can compensate for the differential expansion of connected components.