Coupling | Types, Advantages, Disadvantages, Applications

What is a coupling?

A coupling is a mechanical device which is used to hold two rotating shafts together. It is a permanent joint, unlike clutch which can be disengaged on the will of operator.

With the help of couplings, we can join two shafts which are intersecting, colinear or parallel (with a small distance).

Rotating coupling

Oldham coupling is used to connect two parallel shafts which are a small distance apart.

Oldham coupler

Difference between clutch and coupling:

We all know that a clutch (which is generally used in automobiles) is also used for connecting two rotating shafts but there is a basic difference between a clutch and coupling. In clutch we can disengage the rotating shaft at our will whenever we want but in coupling it is not possible.

Practical example of coupling:

In our domestic electricity generator, we see that a shaft is rotated by an engine by converting chemical energy of fuel into mechanical energy. This rotating shaft of engine is then connected with the shaft of an electric alternator with the help of a coupling. And finally, the electric alternator converts mechanical energy of shaft into electric energy.

Here coupling is an important part which transmits rotating motion of engine shaft to electric alternator shaft.

Requirements of a good coupling

It should be capable of transmitting torque from driving shaft to driven shaft
It should align the shafts properly
It should be able to dismantle for the purpose of maintenance
It should provide safety to man and machine in case of coupling failure

Types of couplings

There are two types of couplings

Rigid coupling
Flexible coupling

A flexible coupling can accommodate a slight misalignment between shafts (up to 0.5-degree angular misalignment and 5 mm axial misalignment) but a rigid coupling cannot tolerate any such misalignment.

Examples of rigid coupling muff coupling, clamp coupling, rigid flange coupling etc.

Example of flexible coupling is Bushed pin flexible coupling.

Difference between rigid and flexible couplings

Flexible coupling can accommodate a slight misalignment between shafts but a rigid coupling cannot accommodate any misalignment
Flexible coupling can absorb shocks and vibrations but a rigid coupling cannot absorb shocks and vibrations
Rigid coupling is simple and inexpensive but flexible couplings are expensive

Some common types of couplings are discussed below.

Muff coupling

A muff coupling is also known as a sleeve or box coupling. It is a type of rigid coupling. It consists a sleeve and a key which is used to join input and output shafts.

Advantages of muff coupling

It is simple, it has only two parts a sleeve and a key
Since it has no projecting parts hence it is safe to use
It has compact construction
It is cheaper compared to other types of couplings

Disadvantages of muff coupling

It is difficult to assemble or dismantle
Since it is a rigid coupling so it cannot accommodate any misalignment
Due to absence of flexible elements it can not absorbs shocks and vibrations
It requires more axial space compared with other types of couplings

Clamp coupling

It is also known as compression or split muff coupling. It is a type of rigid coupling. It is same as muff coupling the only difference is in clamp coupling sleeve is divided into two axially symmetric parts. Which are assembled together to form a coupling.

Advantages of clamp coupling

It is Easy to assemble and dismantle
It is easy to remove without axial displacement of any shaft
Its diametrical dimensions are small compared to muff coupling

Disadvantages of clamp coupling

Dynamic balancing is difficult hence it is not suitable for high speed applications
It is Not suitable for shock loads
Necessary to provide a guard for safety

Rigid flange coupling

As the name suggests it is a rigid coupling. It has two flanges one on driving shaft and one on driven shaft. These two flanges are joined together with the help of nut and bolt.

Advantages of rigid flange coupling

It has High torque transmitting capacity
It is easy to assemble and dismantle
It has simple construction and it is easy to design and manufacture

Disadvantages of rigid flange coupling

It can not tolerate misalignment between shafts
It can not used where shocks and vibrations are present
It requires some radial space

Bushed pin flexible coupling

As the name suggests it is a type of flexible coupling. It consists two flanges mounted each on input and output shaft. Both the flanges are connected with rubber bush in between, which provides resistance to shocks and slight misalignment.

Advantages of Bushed pin flexible coupling

It can tolerate slight misalignment
It can work with shocks and vibrations
It can be used for transmitting high torques
It is simple in construction
It can easily be assembled or dismantled

Disadvantages of Bushed pin flexible coupling

It has high cost due to additional parts
It requires more radial space compared with other types of couplings

Also read:

What are riveted joints?

What are threaded joints?

What is a power screw?

Image source:

Rotating coupling: Attribution: By Occupational Safety and Health Administration part of the U.S. Department of Labor – OSHA web site, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11137887

Oldham coupler: Attribution: By Van helsing – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2533766