A coupling is a mechanical device used to connect two shafts together at their ends for the primary purpose of transmitting power from one shaft to the other. Couplings are fundamental components in a vast array of machinery and mechanical systems.

Primary Functions

While the basic function is to connect two shafts, couplings are designed to serve several key purposes:

Power Transmission: The core function is to transmit rotational motion and torque (e.g., from a motor to a pump or a gearbox).

Accommodate Misalignment: Perfect, permanent alignment between two shafts is often impossible to maintain due to factors like thermal expansion, shaft deflection, or mounting errors. Couplings can accommodate various types of misalignment:

Angular Misalignment: The shafts meet at an angle.

Parallel Misalignment: The shafts are parallel but their axes are offset.

Axial Misalignment (End Float): The shafts move closer or further apart along their axis.

Absorb Shock and Vibration: Some flexible couplings can dampen shock loads and vibrations from the driving side, protecting the driven component.

Provide a Mechanical Fuse: Certain couplings, like shear pin couplings, are designed to fail under excessive load, protecting more expensive components in the system from damage.

Main Types of Couplings

Couplings can be broadly classified into two categories:

1. Rigid Couplings

Purpose: Used when precise shaft alignment is required and guaranteed. They do not tolerate any misalignment.

Application: Primarily in applications where shafts are supported by multiple bearings and alignment is rigidly maintained.

Examples:

Sleeve or Muff Coupling: A simple cylindrical sleeve that fits over the ends of the two shafts.

Flanged Coupling: Two flanged hubs are attached to each shaft and bolted together.

2. Flexible Couplings

Purpose: To transmit torque while accommodating misalignment, absorbing shock, and damping vibration.

Application: The vast majority of industrial applications (e.g., connecting motors to pumps, compressors, conveyors).

Examples (there are many, each with specific advantages):

Jaw Coupling: Uses a spider-shaped elastomeric insert between two metal hubs. Popular for general-purpose applications.

Gear Coupling: Consists of two geared hubs connected by a sleeve with internal gears. Excellent for high-torque applications.

Flexible Disc Coupling (Beam Coupling): Uses a single or multiple helical cuts in a metal disc to accommodate misalignment. Often made of stainless steel.

Oldham Coupling: Uses a floating disc with tenons to connect two hubs. Good for parallel misalignment.

Universal Joint (U-Joint): Allows for large angular misalignment.

Fluid Coupling: Uses hydraulic fluid to transmit power, providing very smooth acceleration and overload protection.