Coupling: Definition, Types and Shaft Coupling

What is a Coupling(shaft coupling)?

A coupling is a mechanical element that connects two shafts to accurately transmit the power from the drive side to the driven side while absorbing the mounting error or misalignment of the two shafts.

Coupling in the machine industry is interpreted as “a part that connects two shafts” and is generally called “coupling,” “shaft coupling,” or “joint.” By using a coupling, power can be transmitted, even between axes of different diameters.

The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects.

Couplings do not normally allow disconnection of shafts during operation, however, there are torque-limiting couplings that can slip or disconnect when some torque limit is exceeded.

Selection, installation, and maintenance of couplings can lead to reduced maintenance time and maintenance costs.

The role of a coupling (shaft fitting)

  • Transmit power
  • Absorb misalignment
  • Absorb vibrations to protect surrounding products
  • Do not transfer the heat of the motor, etc., to the driven side.

What is Shaft Coupling?

A shaft coupling is a mechanical component that connects the driveshaft and driven shaft of a motor, etc., to transmit power. Shaft couplings introduce mechanical flexibility, providing tolerance for shaft misalignment.

As a result, this coupling flexibility can reduce uneven wear on the bearing, equipment vibration, and other mechanical troubles due to misalignment.

Types Of Coupling

Different types of Coupling are:

  • Rigid Coupling: They are used to connect two perfectly aligned shafts.
  • Flexible Coupling: They are used to connect two shafts having lateral and angular misalignment.
  • Fluid Coupling or Hydraulic Coupling: They transmit power from one shaft to another shaft, acceleration, and deceleration of hydraulic fluid.

Types of Shaft Coupling

Different Types of Shaft coupling are:

  • Beam coupling
  • Sleeve or Muff Coupling
  • Split Muff coupling
  • Flange coupling
  • Disc coupling
  • Bushed Coupling
  • Diaphragm Coupling
  • Grid Couplings
  • Roller Chain Coupling
  • Gear coupling
  • Tyre Couplings
  • Jaw Couplings
  • Oldham Coupling
  • Universal Coupling
  • Bellows Coupling

1. Beam coupling

A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset, and even axial motion of one shaft relative to the other.

This design utilizes a single piece of material and becomes flexible by removing material along a spiral path resulting in a curved flexible beam of helical shape.

Since it is made from a single piece of material, the Beam Style coupling does not exhibit the backlash found in some multi-piece couplings. Another advantage of being an all machined coupling is incorporating features into the final product while still keeping the single piece’s integrity.

Changes to the lead of the helical beam provide changes to misalignment capabilities and other performance characteristics such as torque capacity and torsional stiffness. It is even possible to have multiple starts within the same helix.

The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical, and aerospace.

Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steel, and titanium. The most common applications are attaching rotary encoders to shafts and motion control for robotics.

2. Sleeve or Muff Coupling

This is the simplest type of hard coupling, made of cast iron. It consists of a hollow cylinder whose inner diameter is similar to the shaft. Power is transmitted from one shaft to another through a key and a sleeve.

Therefore, all elements must be strong enough to transmit torque. Two threaded holes are provided to lock the coupling in position.

3. Split Muff coupling

It is also known as split muff coupling. In this case, the muff or sleeve is made into two halves and bolted together. Half of the muff is made of cast iron. The shaft ends are designed to separate each other, and a single key is directly fitted to the keys of both shafts.

Types of Coupling

Half of the muff is fixed from the bottom and the other half from the top. Both parts are held together using mild steel studs or bolts and nuts. The number of bolts can be two, four, or six. Nut Muff is admitted to the casting bodies.

This coupling can be used for heavy-duty and medium speeds. The advantage of this coupling is that there is no need to change the position of the shaft for combining or assembling the coupling.

4. Flange Coupling

A flange coupling is usually applied to a coupling consisting of two different cast irons. Each flange is mounted at the end of the shaft and is keyed. The face is rotated at right angles to the axis of the shaft. One of the flanges has an approximate part, and the other flange has a similar recess.

This helps to align the shaft and maintain alignment. The two flanges are joined together using bolts and nuts. Flange coupling is adopted for heavy loads and is therefore used on large chefs. There are three types of flange couplings:

  • Unprotected Type Flange Coupling: In an unprotected type flange coupling, each shaft is placed on a flange with a counter-fad key, and the flanges are coupled together via bolts. Generally, three, four, or six bolts are used. The keys vibrate at right angles along the circumference of the shaft to split the weakening effect caused by the keys. Normal ratio for coupling an unprotected type of cast iron flange.
  • Protected Type Flange Coupling: A shielded type flange coupling consists of protruding bolts, and flanges protect the nuts on the two halves of the coupling to avoid danger to the workman. The thickness of the protective perimeter flange is taken as 0.25 D. Other ratios of coupling are similar to The unprotected type of flange coupling.
  • Marine Type Flange Coupling: In a marine type flange coupling, the flanges are forged integral with the shaft. The flanges are held together using pointed headless bolts, a number from four to twelve depending on the diameter of the shaft.

5. Disc Coupling

The operation of the principle of disk coupling is the torque transmitted through the flexing disk elements. It operates through tension and compression of the corded segment on a common bolt circle alternately bolted between the drive and the driven side.

These couplings usually include two hubs, two disk packs, and a center member. A single disk pack can accommodate angular and axial misalignment. A two-disk pack is required to accommodate parallel misalignment.

  • Allows angular parallel and axial disorientation
  • is a true limited end float design
  • a zero-backlash design
  • high-speed rating and balance

6. Bushed Coupling

Bushing flexible coupling is a modification of rigid coupling type flange coupling. The coupling bolts are known as pins. Rubber or leather bushes are used on top of pins. Also, there is a variation in the construction of two parts of the coupling.

There is a 5 mm clearance remaining between the faces of the two halves of the coupling. And there is no rigid connection between them, and the drive is through compressed rubber or leather bushes.

Types of Shaft Coupling

7. Diaphragm Coupling

Diaphragm couplings use a single or single series of plates or diaphragms for flexible members. It transmits torque from the outside diameter of a flexible plate to the inside of a spool or piece of the spacer and then from inside to outside diameter.

The deflection of the outer diameter relative to the inner diameter occurs when the diaphragm is subjected to misalignment. Axial displacement, for example, attempts to stretch the diaphragm resulting in elongation and bending of the diaphragm profile.

  • Allows for angular, parallel, and high axial misalignments
  • High torque, used in high-speed applications

8. Grid Coupling

The grid couplings consist of 2 radial slated hubs meshed with a serpentine strip of spring steel that allows the grid to be twisted and flexed by the steel strength of an elastomer.

Grid couplings transmit torque and adjust the axial misalignment parallel from one hub to another through rocking and sliding a tapered grid in the mating hub slots.

Grid cross-sections are usually tapped for better hub contact and easier assembly. Since there is movement between the contact hub and the grid metal parts, lubrication is required.

9. Roller Chain Coupling

Roller chain type couplings have two radial sprocket hubs that connect the strands of a double pitch roller chain. Chain couplings are used for low to medium torque and speed applications. The mesh of diffuse teeth and chains transmits torque, and the associated clearances accommodate angular, parallel, and axial misalignment.

Chain couplings require periodic lubrication depending on the application. Lubrication is usually brushed on the chain, and a casing is used to help maintain lubrication at the coupling.

10 Gear Coupling

Gear couplings transmit the largest torque and the highest amount of torque in the smallest diameter of any flexible coupling. Each coupling has two hubs that have large external gear teeth.

Hubs are forged with two internally trimmed sleeves that are bolted together. Gear couplings accommodate angular and axial misalignments by moving and sliding gear teeth crowned against the mating sleeve teeth.

Parallel misalignment is accommodated by two adjacent hub / sleek flex points. Gear couplings require periodic lubrication depending on the application.

They are sensitive to lubrication failures, but if properly installed and maintained, the service life of these couplings is 3 to 5 years, and in some cases, they can last for decades.

Coupling Types

11. Tyre Couplings

These couplings have a rubber or polyurethane element connected to two hubs. The rubber element transmits torque in shear.

  • Reduces transmission of shock loads or vibration.
  • High misalignment capacity
  • Easy assembly w/o moving hubs or connected equipment
  • Moderate to high-speed operation
  • Wide range of torque capacity

12. Jaw Coupling

The jaw coupling is a material flexing coupling that transmits torque thru compression of an elastomeric spider insert placed between two intermeshing jaws.

  • Flex element is commonly made of NBR, polyurethane, Hytrel, or Bronze
  • Accommodates misalignment
  • Transmits torque
  • Used for torsional dampening (vibration)
  • Low torque, general-purpose applications

13. Oldham Coupling

Oldham coupling is a form of flexible coupling designed for applications that must be free of backlash. They are also being used as a replacement for direct jaw couplings. Oldham couplings have three discs.

Two of the discs, typically made of aluminum or stainless steel, are attached on either side of the drive, while the third is made of one of several different plastics sandwiched between the tongue and groove design. Is done.

The tongue and groove on one side is the tongue and groove on the other side. Often springs are used to reduce the backlash of the coupling. Oldham couplings have many other advantages, including their compact size and potential for electrical isolation through plastic center discs.

Couplings can act as a fuse for a machine. If the torque limit is exceeded, the center disc of the coupling will first break apart, thereby avoiding torque transmission and potential damage to more costly machine components.

Flexible Coupling

14. Universal (or Hooke’s) Coupling

A universal or hook coupling is used to connect two shafts whose axes intersect at a small angle. The bending of the two shafts may be constant, but in actual practice, it changes when the momentum is transferred from one shaft to another.

The main application of universal or hook coupling is found in transmission from the gearbox to automobiles’ differential or back axle.

In such a case, we use a coupling of two hooks, connecting the gearbox at one end and the differential at the other end at each end of the propeller shaft. The coupling of a hook is also used to transmit electricity to the various spindles of several drilling machines. It is used as a knee joint in a milling machine.

15. Bellows Couplings

Bellows couplings also adapt to speed control applications. They consist of several metal determinations that provide high torsional stiffness that is important for the state of applications.

Torsional rigidity reduces the level of angular and parallel misalignment that they can adjust with beam couplings, although torque transmission capability is the same.

Use of coupling

Shaft couplings are used in machinery for many purposes, the most common of which are the following:

  • For connection to shafts of units manufactured separately as a motor and generator and provide for repair or disconnection for option.
  • To provide shaft misalignment or to introduce mechanical flexibility.
  • To reduce the transmission of shock loads from one shaft to another.
  • To introduce protection against overload.
  • It should not have any projecting parts.

Requirements of a good coupling

A good shaft coupling should have the following requirements:

  • It should be simple to connect or disconnect.
  • It must transmit full power from one shaft to another shaft without damage.
  • It should hold the shaft in the correct alignment.
  • It should decrease the transmission of shock loads from one shaft to another.
  • It should not have any projecting parts.

Coupling maintenance and failure

Coupling maintenance requires a regularly scheduled inspection of each coupling. It consists of:

  • Performing visual inspections,
  • checking for signs of wear or fatigue
  • cleaning couplings regularly
  • Checking and changing lubricant regularly if the coupling is lubricated. This maintenance is required annually for most couplings and more frequently for couplings in adverse environments or demanding operating conditions.
  • Documenting the maintenance performed on each coupling, along with the date.

Even with proper maintenance, however, couplings can fail. Underlying reasons for failure, other than maintenance, include:

  • Improper installation
  • Poor coupling selection
  • Operation beyond design capabilities.

The only way to improve coupling life is to understand what caused the failure and to correct it prior to installing a new coupling. Some external signs that indicate potential coupling failure include:

  • Abnormal noise, such as screeching, squealing, or chattering
  • Excessive vibration or wobble
  • Failed seals are indicated by lubricant leakage or contamination.


What is a Coupling?

A coupling is a mechanical element that connects two shafts to accurately transmit the power from the drive side to the driven side while absorbing the mounting error or misalignment of the two shafts.

What coupling means?

coupling is a device used to connect two shafts at their ends to transmit power. In a more general context, a coupling can also be a mechanical device that connects the ends of adjacent parts or objects.

What is Shaft Coupling?

A shaft coupling is a mechanical component that connects the driveshaft and driven shaft of a motor, etc., to transmit power. Shaft couplings introduce mechanical flexibility, providing tolerance for shaft misalignment.

What are the Types of Coupling?

Types of Coupling:
1. Beam coupling
2. Sleeve or Muff Coupling
3. Split Muff coupling
4. Flange coupling
5. Disc coupling
6. Bushed Coupling
7. Diaphragm Coupling
8. Grid Couplings