An elastic coupling, also known as a flexible coupling, is a mechanical device used to connect two rotating shafts, typically from a driving machine (like an electric motor) to a driven machine (like a pump, gearbox, or fan). Its primary function is to transmit torque from one shaft to another while accommodating for minor misalignments and mitigating the transmission of shock loads and vibrations.
Unlike rigid couplings, which hold shafts in a fixed, precise alignment, elastic couplings incorporate a flexible element. This element is the core of its functionality, providing the necessary "give" to handle real-world installation and operational challenges.
Key Functions and Benefits
The design of elastic couplings provides several critical advantages in power transmission systems:
Compensation for Misalignment: It is virtually impossible to achieve and maintain perfect alignment between two machines due to manufacturing tolerances, thermal expansion, and shaft deflection under load. Elastic couplings can accommodate three primary types of misalignment:
Parallel Misalignment: When the two shafts are parallel but their centerlines are offset.
Angular Misalignment: When the centerlines of the two shafts intersect at an angle.
Axial Misalignment (End Float): When the two shafts move slightly towards or away from each other along their axis.
Vibration Damping and Shock Absorption: The flexible element acts as a damper, absorbing torsional vibrations and shock loads caused by sudden torque changes (e.g., during startup or from an uneven load). This protects both the driving and driven equipment from damage and reduces wear.
Protection of Connected Equipment: By dampening vibrations and shocks, the coupling serves as a sacrificial component. It is often designed to be the weakest link, failing before more expensive components like motor bearings or gearboxes, thus preventing catastrophic failure.
Torque Transmission: The fundamental purpose remains the efficient transmission of rotational power (torque) between the connected shafts.
Common Types of Elastic Couplings
Various designs exist, each utilizing different materials and principles for flexibility. Some of the most common types include:
Jaw Couplings (Spider Couplings): Feature two metal hubs with interlocking jaws. A flexible, elastomeric spider (typically made of polyurethane, Hytrel, or NBR) is inserted between the jaws. This spider compresses to accommodate misalignment and dampen vibrations. They are compact, easy to install, and very popular.
Beam Couplings (Helical Couplings): Made from a single piece of material (often stainless steel) with a helical cut pattern. This design allows for flexibility in all directions of misalignment while maintaining zero backlash, making them ideal for precision applications like servo motors and encoders.
Tire Couplings: Consist of a rubber or polyurethane element that resembles a tire, bolted between two metal hub halves. They excel at absorbing high levels of vibration and shock and can accommodate significant parallel and angular misalignment.
Pin and Bushing Couplings: Use a rubber or polyurethane bushing inserted into holes in the coupling flanges. A pin passes through the bushing to transmit torque. The elasticity of the bushing provides the flexibility. These are often used in heavy-duty applications.
Oldham Couplings: Comprise three parts: two hubs and a central floating disc. The disc has tongues on opposite sides that fit into slots on the hubs. While often considered a rigid coupling, a plastic or elastomeric center disc can add an element of flexibility and damping.
