shaft coupling

A shaft coupling is a mechanical device used to connect two shafts at their ends for the purpose of transmitting power (torque and motion) from a driving shaft to a driven shaft. In addition to power transmission, couplings are designed to accommodate minor shaft misalignments, absorb shock loads, and dampen vibrations, thereby protecting connected components like bearings and seals from premature wear and failure.

Functions of Shaft Couplings
Power Transmission: The primary function is the efficient transfer of rotational power from the power source (e.g., motor, engine) to the equipment being driven (e.g., pump, gearbox).
Accommodating Misalignment: Couplings provide mechanical flexibility to tolerate minor misalignments (parallel/radial, angular, and axial/end-play) that inevitably occur during installation, operation, and due to thermal expansion.
Shock and Vibration Dampening: Many coupling types (especially flexible and elastomeric designs) can absorb shock loads and dampen vibrations, which reduces noise and extends the service life of the entire mechanical system.
System Protection: They can protect expensive machinery components from overload by allowing slippage or failure at a specific torque limit, and can also prevent heat transfer between shafts.
Ease of Maintenance: Couplings allow for the connection of separately manufactured units, simplifying assembly, disassembly, and maintenance procedures.
Types of Shaft Couplings
Shaft couplings are broadly classified into two main categories: rigid and flexible.
Rigid Couplings
Rigid couplings are used to connect two shafts that are perfectly, or near-perfectly, aligned, providing a strong, uncompromising connection that cannot tolerate misalignment.
Sleeve (Muff) Coupling: The simplest and most cost-effective type, consisting of a hollow cylinder fitted over the shaft ends and secured with keys and set screws.
Flange Coupling: A robust connection where each shaft is keyed to a flange, and the two flanges are bolted together, often used for heavy-duty, large-diameter shafting.
Split-Muff (Clamp) Coupling: Features a sleeve made of two halves clamped around the shafts with bolts, allowing for easier assembly and disassembly without moving the machinery.
Flexible Couplings
Flexible couplings accommodate varying degrees of misalignment, absorb shocks, and dampen vibrations through bending or the use of resilient elements.
Elastomeric Couplings (e.g., Jaw, Tyre, Pin-Bush): These use flexible materials like rubber or polyurethane to transmit torque through compression or shear, offering excellent vibration damping and electrical insulation.
Metallic Element Couplings (e.g., Gear, Disc, Diaphragm, Grid, Beam): These derive their flexibility from the sliding of parts (gear/grid) or the bending of flexible metallic discs/diaphragms, often suitable for high-speed and high-torque applications.
Universal Joint (U-Joint): A specialized joint designed to transmit power between shafts intersecting at a significant angle (up to 45 degrees or more), commonly found in vehicle drive trains.
Fluid Couplings: These transmit torque using hydraulic fluid without direct mechanical contact, providing very smooth power transmission and overload protection.
Selection Considerations
Selecting the appropriate coupling involves considering factors such as torque requirements, maximum speed (RPM), amount of expected misalignment, stiffness, inertia, shock absorption capacity, and environmental conditions.