What are Couplings? Types of Couplings and their application

Couplings – You might have an idea or two about couplings but today here in this article, we will know about them in detail. We will be discussing what are couplings, what are the types of couplings & their applications. So let’s begin.

What are Couplings?

In simple words, couplings are mechanical devices used to transmit power/torque from one shaft to another shaft.

Why do we need couplings?

Power can be transmitted by means of various gear arrangements or drives only if the shafts are parallel.
Couplings are used when the shafts are in a straight line and are to be connected end to end to transmit power.

General application OR Uses-

  • To transmit power from driving shaft to driven shaft.
  • To connect or couple 2 components which are manufactured separately eg. output motor shaft and generator.
  • To introduce extra flexibility while transmitting power in case of space restrictions.
  • To introduce protection against overloads.
  • To reduce the transmission of shock loads from one shaft to another by using flexible couplings.

Types of Couplings-

Here are the different types of couplings which are most widely used in industries and machines-

1.Muff or Sleeve coupling

Sleeve coupling with labelled parts

Sleeve couplings are nothing but just sort of thick hollow cylinder/pipe called as sleeve or muff. The sleeve is manufactured keeping the diameter of the shaft in mind so that the shaft fits perfectly into the sleeve. The driver & driven, both the shafts are then inserted into each side of the sleeve. Also two or more threaded holes are provided into the sleeve as well as in both of the shaft’s end so that they don’t move in the longitudinal direction when the bolts are inserted into them. Also the keyway and key ensure that the shaft and sleeve don’t slip.
The sleeve coupling is easy to manufacture as there are less number of parts.
They are used where the shafts don’t require any alignments and load capacity is light to medium duty.

2.Split Muff coupling

split muff coupling- a type of coupling
Split muff coupling with parts labelled.

In split muff coupling, the sleeve or muff isn’t a single different part instead it is split into 2. The muffs are semi-cylindrical in shape which then fits over the shaft. Threaded holes are provided on the muffs so that both the shafts can be joined with steel bolts or studs.
The special feature of this coupling is that it can be assembled and disassembled without changing the position of the shaft.
They are used for medium to heavy-duty load with moderate speed.

3.Flange coupling

flanged coupling - a type of coupling
Flange coupling with labelled parts

Flange coupling is also easy to manufacture coupling and is similar to sleeve coupling. Here, there are flanges on either side of the 2 sleeves. Both the flanges consist of an equal number of threaded holes for bolting purposes. The flanges are then joined together with bolts and nuts. A key section is also provided on the hub and shafts so that there is no slipping condition.
A tapered key is used here. This ensures that the hub doesn’t loosen up or move backward and stays attached to the shafts.
Flange couplings are used for medium & heavy-duty industrial applications.

Animation of the 2 most flexible coupling at the end of the article!

4.Bush Pin type flexible coupling

Bush pin coupling - a type of flexible coupling
Bush pin type flexible coupling with labelled parts

You could say that this coupling is an upgraded version of flange coupling. The only difference between them is the usage of rubber bushings. Slightly thick rubber bushings are designed so that the studs or bolts perfectly fit inside it and bushing fits perfectly inside the holes provided.
The major advantage of using this coupling is that it can be used for slightly misaligned shafts. The rubber bushings add a certain amount of flexibility to the coupling which also helps to absorb shocks and vibrations.
Bush pin-type couplings are used where there is a little amount of angular, parallel or axial misalignment.
They are used in medium-duty applications in electric motors & machines.

5.Gear coupling

Gear coupling

The gear coupling is another modified version of the flange coupling. In gear coupling, the flange and hub are different parts assembled together instead of a single part as in flange coupling.
The hubs are externally splined but they are so thick and deep that you can regard them as gear teeth. Also the flanges have internal teeth. The gear ratio is 1:1 and are meshed together. The single joint gear couplings are limited to lower angular misalignments.
Gear couplings are used for heavy-duty applications where the requirement of torque transmission is higher.

6.Fluid coupling

working of fluid coupling with labelled parts
Fluid coupling with labelled parts

Fluid coupling consists of 2 parts – a pump & a turbine. Both of these have blades mounted inside at a certain angle. The pump is mounted on the end of driver shaft while the turbine on the driven shaft.
The fluid enters into the pump through its centre and when the drive shaft rotates, due to centrifugal force it is pushed outwards. The casing is such that it diverts the motion of fluid into the turbine and the turbine blades along with the turbine start rotating. This way the pump and the turbine both make a coupling.
When an extra part called a reactor is introduced between the pump and the turbine, surprisingly the device becomes a torque converter which is an alternative to manual clutch in automatic transmission systems in cars! Learn more about automatic transmissions & how they work!
It is widely used in marine and industrial applications where controlled start-up of the power transmission is very essential.

7.Rzeppa joint

Types of couplings- Rzeppa joint, an example of constant velocity joint
An animation of a Rzeppa joint

This is sooo cool! The Rzeppa joint/coupling also called as CV coupling(constant velocity) is a type of coupling in which the driven shaft rotates at the same speed as the driver one. Also it is able to transmit power through variable angles. The joint is protected by applying grease on it and is covered by rubber boots.
Rzeppa joint is used in vehicles with independent rear suspension. In India, if you notice, you can see these joints near the rear wheels of rickshaws and tuk-tuks or chhakdas.

8.Universal joint or Hooke’s joint

Universal joint, the most widely and versatile coupling.
Animation of a Universal joint

By Van helsing – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1499089

As the name suggests, this type of coupling can be used anywhere. The universal joint can transmit power even at high parallel or angular misalignments. It consists of a pair of hinges close together perpendicular to each other connected by cross shafts. Unlike Rzeppa joint, the universal joint is not a constant velocity joint. This means that RPM of drive and driven shaft won’t be same at every angle.
Universal joints are used in machines where there are space restrictions or high flexibility is needed.

A good example would be the usage of this joint for transmission of power from the engine to the rear differential via propeller shaft. You could clearly see the universal joint under the trucks! And it really feels so fascinating to watch it in running condition


Application Examples: Couplings

Though couplings are well-known and commonly used components in many rotary motion applications, the sheer variety of couplings can make selection rather daunting. While coupling usage is straightforward, most of the design time is spent in selecting the correct coupling type for an application.

Jaw Coupling Application

The Jaw Coupling is designed to transmit torque while dampening system vibrations and accommodating misalignment. In this particular example we have a coupling used to connect a motor shaft to the drive roller of a conveyor. The Jaw coupling is a good choice for this application since high accuracy and zero back lash are not requirements. At the same time Jaw couplings have good misalignment characteristics and can transmit high torque.

Flexible Coupling Application

Flexible couplings are used to transmit torque from one shaft to another when the two shafts are slightly misaligned. In this example, the test fixture is using torque transducer as torque senor for measuring torque. In this example, the flexible couplings are used to connect the motor and torque sensor with the work piece. These two couplings need to minimize any misalignment error since the torque sensor needs to lay as flat as possible. They also need to protect the sensor from overloading. Major characteristic of the flex couplings are very low or zero backlash, good torsion rigidity as good lateral and angular misalignment capabilities making them very suitable for this application.Flexible CouplingDisc Coupling Application

By definition, a disc coupling is a high performance motion control (Servo) coupling designed to be the torque transmitting element (by connecting two shafts together) while accommodating for shaft misalignment. It is designed to be flexible, while remaining torsionally strong under high torque loads. In this example, the coupling is used as part of the slide table in the welding station. The coupling connects the servo motor to ball screws that move the work piece table to the required position or positions. The disc coupling used here was recommended to be used with servo motors due to its low backlash, high torsion rigidity, and good allowable misalignment and torque capabilities.Disc Coupling Couplings are standard machine components that require correct selection based on application requirements and user preference, installation, and regular inspection.

During operation, the user should watch for external signs such as abnormal noise and vibration that indicate premature coupling failure. This helps with understanding what caused the failure and how and what to correct prior to installing a new coupling. During their life span, couplings should also be checked for signs of wear and fatigue.

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