Understanding the term coupling

The term “coupling” is common in the engineering world, it is known as a part that connects two shafts together in order to accurately transmit power. The transmission is done from the drive side to the driven side while absorbing the mounting error (misalignment), etc. of the two shafts. Coupling is used in almost all industrial machines that require power transmissions, such as motors, pumps, generators, and compressors.

Today you’ll get to know the definition, applications, functions, diagram, working, types, and requirements of a good coupling.

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What is coupling?

In simple words, couplings are mechanical devices used to transmit power/torque from one shaft to another shaft. Coupling can also be seen as a device used to connect two shafts together at their ends so that power can be transmitted. However, the primary purpose of couplings is to join two pieces of rotating equipment, allowing some degree of misalignment or end movement, or both. The device is rigid or flexible according to the alignment accuracy and torque requirement.

In a general context, the coupling is a mechanical device that serves to connect the ends of adjacent parts or objects. Normally, they do not allow disconnection of shafts during operation, but torque-limiting couplings are available. These couplings can slip or disconnect when some torque limit is exceeded. In essence, coupling maintenance time and cost can be reduced the application requirement, selection, installation, and maintenance.

Note: power can be transmitted by means of various gear arrangements or drives, that is 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.

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Applications of coupling

Just as earlier mentioned, shaft couplings are used in almost all industrial machinery for several purposes. The primary function is for power transfer from one end to another end. For example, a motor transferring power to a pump through coupling. Below are the general applications of coupling.

• To transmit power from the driving shaft to the driven shaft.
• Couplings connect or couple two components that are separately manufactured, i.e., output motor shaft and generator.
• It reduces the transmission of shock loads from one shaft to another by using flexible couplings.
• Couplings are also used to introduce extra flexibility while transmitting power in case of space restrictions.
• To introduce protection against overloads.

Requirements of a good coupling

Below are the requirements to consider to know a good coupling system.

• Coupling should be able to transmit torque from driven shaft to driven shaft.
• It should align the shafts properly.
• Couplings should provide safety to man and machine in case of coupling failure.
• Couplings should be able to dismantle for the purpose of maintenance.
• Finally, couplings should be adjustable.

Diagram of coupling:

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Types of coupling

The various types of coupling are rigid, sleeve or muff, clamp or split-muff is also known as compression coupling, flange coupling, flexible, bushed pin-type, universal, and Oldham coupling. Some other types of coupling include gear, bellow, jaw, diaphragm, fluid, constant speed, and variable speed coupling.

Rigid coupling:

Rigid couplings are employed when two shafts are perfectly aligned. They are only suitable in close alignment. Their examples include sleeve or muff coupling, split-muff coupling, and flange coupling.

Sleeve or muff coupling:

In the construction of these types of couplings, shaft, key, sleeve or muff are the major components. Also, a hollow cylinder whose inner diameter is equal to the shaft is used. A gib head key is used to fix it over the ends of the two shafts. Power transmission occurs through one shaft to the other shaft by means of a key and a sleeve. All the elements must be strong enough to transmit the torque.

Clamp or split-muff or compression coupling:

These types of couplings are also known as split muff coupling. The muff or sleeve is made in two helves and is bolted together and they are made of cast iron. Stud is also used to connect the halves. Both shaft’s ends are connected to each other and a key is fitted in the keyway located on the shafts. One end of the muff is attached from below and the other end is connected from above, held together by bolts and nuts.

Flange coupling:

Flange coupling comprises two cast iron flanges fitted at the end of each shaft. These flanges are bolted together with bolts to complete the drive. Bringing two tubes together in a sealed manner can represent these types of flange coupling. In their construction, one of the flanges has a projected portion part and the other flange has a similar recess. The flange ends are brought together to make correct alignment without causing resistance in the material being passed through them.

These types of coupling help to bring the shaft into the same line and to maintain alignment. Bolt and nuts are used to couple the two flanges together. These couplings are typically used in pressurized piping systems and they are employed too heavy loads. The various types of flange coupling are unprotected and protected types of flange coupling, and marine flange coupling.

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Flexible coupling:

Flexible types of couplings are used to connect two shafts that have both lateral and angular misalignment. Examples of flexible couplings are bushed pin-type coupling, universal coupling, Oldham coupling, gear coupling, bellow coupling, jaw couplings, diaphragm couplings.

Bushed pin-type coupling:

The bushed pin types of couplings are used for slightly parallel misalignment, angular misalignment, or axial misalignment of the two shafts. They are much related to that of rigid flange coupling, in fact, the modification. They consist of two halves that are dissimilar in construction known as pins, rubber bushes which are used over pins.

Universal coupling:

These types of coupling are known as Hooke’s coupling. They are used when two shafts axis intersects at a small angle and the inclination between the two shafts can be constant. This can only occur in actual practice and changes when the motion is transferred from one shaft to another. Universal couplings are widely used in the transmission of power. They can be found in the transmission from the gearbox to the differential of the automobile. In these cases, two universal joints are used on each end; one at the end of the propeller shaft of the gearbox and the differential to another end. Universal coupling is also used in transmitting power to different spindles of multiple drilling machines and milling machines.

Oldham coupling:

Oldham couplings are used where two shafts have a lateral misalignment. They consist of two flanges A and B with slots and a middle floating part E with two tongues T1 and T2.  The middle part of the device is fixed by means of pins which are attached to flanges and floating parts. The T1 tongue fits into flange A allows back and forth motion and T2 is fitted into flange B and allows for vertical motion of the parts.

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Gear coupling:

The gear couplings are the modified version of flange couplings. The gear coupling is designed to transmit high torque due to the large size of teeth. Their flange and hub are separately assembled together instead of a single part as flange coupling. In their construction, each joint has a 1:1 gear ratio internal and external gear pair. Furthermore, gear couplings are limited to angular misalignments about 0.01 – 0.02 inches in parallel and 2 degrees in angular. Gear couplings and universal joints are similarly used in heavy-duty applications where high torque transmission is required.

Bellow coupling:

These types of couplings are flexible coupling with twin coupling ends known as hubs. They have excellent torsional rigidity to accurately transmit velocity, angular position, and torque. Bellow couplings are usually made up of stainless steel. They are used where high precision positioning is required. Bellow couplings are designed with thin walls and have minor flexibility angular, axial, or parallel misalignment. The hubs are welded to coupling below.

Jaw coupling:

Jaw couplings are used for general purpose power transmission and are also used in motion control applications. They are designed to transmit torque while reducing system vibrations and adjusting misalignment, which further protects other components from damage. Jaw couplings are beneficial because they can handle angular misalignment and reactionary loads due to misalignment. Also, they have good torque to outside diameter capability and they are good chemical resistance and decent dampening capability.

Diaphragm coupling:

These types of couplings are non-lubricated coupling used in high-performance turbomachinery and transmitting torque. They are also used in serving misalignment between equipment shafts. Diaphragm couplings transmit torque from the outside to inside diameter and vise versa. They use a single or a series of plates for the flexible members and allows angular, axial, or parallel misalignment. Diaphragm couplings are used when high torque and high speed are required. Finally,

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Fluid coupling:

Fluid types of coupling are also known as hydraulic coupling. They are hydrodynamic devices used to transmit rotating mechanical power through the acceleration and deceleration of hydraulic fluid. there is an impeller on the driving shaft (input) of the device and a runner is located on the driven shaft (output). The impeller act as a pump and the runner acts as a turbine.

Working principle of coupling

The working of a coupling device is less complex and can be easily understood. It is used to connect two shafts of the same or different diameters together. The motor is transmitting power from the drive side and the propeller is on the driven side. The coupling does not transfer the heat etc. of the motor to the driven side. Flexible coupling can be separated into two groups; metallic and elastomeric. The metallic types use freely fitted parts that roll or slide against one another or, on the other hand. Also, non-moving parts bend to take up misalignment.

On the other hand, elastomeric types also gain flexibility from resilient, non-moving, elastic, or plastic elements transmitting torque between metallic hubs. Watch the video below to clearly understand the working of coupling.

Advantages of coupling

Below are the benefits of coupling in their various application.

• Designs are less complex.
• They absorb mounting errors between the axes of the driving side (turning side)
• Transmission of power.
• Absorbs vibration from the driving side and protects surrounding products.
• Do not transfer heat from the motor on the drive side, etc. to the driven side.

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Conclusion

That is all for this article, where the definition, applications, functions, diagram, working, types, and requirement of a good coupling were explained. The advantages of couplings are also discussed. I hope you get a lot from the reading, if so, kindly share with other students. Thanks for reading, see you next time.