A shaft coupling is a mechanical device used to connect two rotating shafts together so that power can be transmitted from one shaft to the other. Couplings are essential components in machines where two pieces of equipment—such as a motor and pump, engine and compressor, or gearbox and conveyor—must operate as one combined unit.

Shaft couplings also perform several secondary functions that improve machine health, efficiency, and safety.

Functions of Shaft Coupling

They are widely used in industrial, marine, automotive, and power plant applications for the following purposes:

✔ 1. Connecting Separately Manufactured Equipment

Often, machines like motors, gearboxes, and pumps are built separately. Shaft couplings allow them to be connected without complicated alignment processes.

✔ 2. Allowing Misalignment

Couplings absorb:

Angular misalignment
Parallel (offset) misalignment
Axial movement

This protects bearings and prolongs equipment life.

✔ 3. Shock Load Dampening

Couplings reduce the effect of vibration, sudden torque changes, and load impacts. This is especially important in:

Crushers
Compressors
Reciprocating machinery

✔ 4. Overload Protection

Some couplings act as mechanical fuses, breaking or slipping during overload conditions to protect critical machinery.

✔ 5. Easy Assembly & Disassembly

Couplings allow quick separation of shafts for:

Maintenance
Repairs
Equipment replacement

Types Of Shaft Coupling

1. Rigid Coupling

They are used to connect two shafts which are perfectly aligned.

Types of Rigid Coupling

(a) Sleeve or Muff Coupling

(b) Flange Coupling

2. Flexible Coupling

They are used to connect two shafts having lateral and angular misalignment.

Types of Flexible Coupling

(a) Bushed pin type coupling

(b) Oldham Coupling

(d) Gear Coupling

(e) Tyre Coupling

(f) Jaw Coupling

(g) Bellow Coupling

3. Fluid Coupling or Hydraulic Coupling

They are used to transmit power from one shaft to another shaft by means of acceleration and deceleration of hydraulic fluid.

Types of Fluid Coupling

(a) Constant Speed Type Fluid Coupling

(b) Variable Speed Type Fluid Coupling

Requirements Of A Good Shaft Coupling

It should be easy to connect or disconnect.
It should transmit the full power from one shaft to other shaft without losses.
It should hold the shaft in perfect alignment.
It should reduce transmission of shock loads.
It should have no projecting parts.

How to Select the Right Shaft Coupling

Before selecting a coupling, consider:

1. Torque Requirement

Coupling must handle both running and peak torque.

2. Misalignment Levels

Different couplings tolerate different misalignment types.

3. Operating Speed

High-speed machines require balanced, low-vibration couplings.

4. Environment

Heat, chemicals, moisture, and dust affect coupling materials.

5. Maintenance Needs

Elastomer couplings need inspection; metallic ones need lubrication.