What is COUPLING in mechanical engineering - ITI ONLINE NOTE

 Couplings 

1- Shaft transportation problem are usually available up to 7 meters length more length causes as.

2- To have greater length, it is necessary to join two or more pieces of shafts by means of couplings.

3- Connect the ends of two shafts together. 

4- Transmit power from one shaft to other shaft. 

5- Reduce the vibrations. 

6- Provide mechanical flexibility.

7- Permit misalignment of shafts.

Requirements of couplings 

1- It should be easy to connect or disconnect. 

2- It should transmit full power of shaft.

3- It should hold the shafts in perfect alignment. 

4- It should have no projecting parts. 

Types of couplings 

1- Rigid Couplings.

2- Flexible Couplings.

Rigid couplings 

1- It is used to connect two shafts which are perfectly aligned. 

Types of rigid couplings 

1- Sleeve or muff coupling. 

2- Clamp or split muff couplings. 

3- Flange coupling. 

> Protected type .

> Un protected type .

> Marine type 

Sleeve or muff coupling

1- Sleeve or muff coupling is the simplest type of rigid coupling, made of cast iron.

2- It consists of a hollow cylinder whose inner diameter is the same. as that of the shaft. 

3- It is fitted over the ends of the two shafts by means of a gib head key. 

4- The power is transmitted from one shaft to the other shaft by means of a key and a sleeve.

Disadvantages 

1- It is difficult in disassembly. 

2- The coupling cannot be removed without shifting the shafts axially.

Clamp coupling or split muff coupling 

1- This type of coupling consists of two halves of sleeves held together by bolts. 

2- To create a pressure (bearing pressure) between the surfaces of the shaft and the coupling, there is a small clearance at the jointing surface of the coupling. 

3- When tightening the bolts, force exerted by the bolts create the pressure between the shaft and sleeve, which develops the forces of friction. 

4- These forces of friction transmit the required torque.

Advantages 

1- This coupling is meant for heavy duty applications. 

2- It is easy to disassemble this coupling. 

3- The coupling can be removed without shifting the shafts axially.

Flanged coupling(un protected type) 

1- This is a standard form of coupling and is extensively used. 

2- It consists of two cast-iron flanges, keyed to the ends of the two shafts and fastened together by means of a number of tight-fitting-bolts. 

3- Sunk taper keys of rectangular or square cross-section are commonly used for the purpose. For ensuring correct alignment, one of the shafts is extended so that its end partly enters the flange keyed to the other shaft. 

4- The two shafts thus remain in a straight line.

5- Flange couplings are simple in design and cheap to manufacture. 

6- They transmit great torques (in àpplication like steam turbo generators, vertical hydro turbines, marine propellers) and are employed to connect shafts of diameter 18 to 200 mm.

Types of flange coupling 

Protected type of flange coupling 

1- In a protected type flange coupling, the protruding bolts and nuts are protected by flanges on the two halves of the coupling, in order to avoid danger to the workman.

2- The thickness of the protective circumferential flange (ta) is taken as 0.25d. 

3- The other proportions of the coupling are same as for unprotected type flange coupling. 

Marine type flange coupling 

1- In a marine type flange coupling, the flanges are forged integral with the shafts.

2- The flanges are held together by means of tapered headless bolts, numbering from four to twelve depending upon the diameter of shaft. 

3- Thickness of flange = d/3.

4- Taper of bolt = 1 in 20 to 1 in 40.

5- Pitch circle diameter of bolts, D1 = 1.6d.

6- Outside diameter of flange, D2 = 2.2d.

Flexible couplings

1- Used to connect two shafts have both lateral and angular misalignment.

Types of flexible couplings 

1- Bushed pin type.

2- Universal type.

3- Old ham coupling.

Bushed pin flange coupling.

1- It absorbs shocks and permits small amount of angular and lateral misalignment .

2- A bushed-pin flexible coupling is a modification of the rigid type of flange coupling, the coupling bolts are known as pins. 

3- The rubber or leather bushes are used over the pins. 

4- The two halves of the coupling are dissimilar in construction. 

5- A clearance 5 mm is left between the face of the two halves of the coupling. 

6- There is no rigid connection between them and the drive takes place through the medium of the compressible rubber or leather bushes.

Universal coupling 

1- It permits small angular misalignment.

2- A universal or Hooke's coupling is used to connect two shafts whose axes intersect, it can be even 20 - 30°. 

3- The inclination of the two shafts may be constant, but in actual practice, it varies when the motion is transmitted from one shaft to another. 

4- The main application of the universal or Hooke's coupling is found in the transmission from the gear box to the differential or back axle of the automobiles. 

5- In such a case, we use two Hooke's coupling, one at each end of the propeller shaft, connecting the gear box at one end and differential on the other end. 

6- A Hooke's coupling is also used for transmission of power to different spindles of multiple drilling machine.

7- It is used as a knee joint in milling machines.

Hooke's coupling 

1- The apparatus consists of an identical Hooks coupling at each end of a shaft. 

2- The axis of each coupling can be independently varied relative to the main shaft axis. 

3- Each coupling has a pointer and protractor scale so that the angular difference between the input and output shafts can be determined for a range of shaft angular positions.

4- A wide variety of angular settings for single or double couplings is possible. 

5- The couplings are mounted on a free standing pressed steel base. 

6- This equipment is part of a experimentally confirm basic engineering principles. 

7- Great care has been given to each item so as to provide wide experimental scope without unduly complicating or compromising the design. 

8- Each piece of apparatus is self-contained and compact. 

9- Setting up time is minimal, and all measurements are made with the simplest possible instrumentation, so that the student involvement is purely with the engineering principles being taught. 

10- A complete instruction manual is provided describing the apparatus, its application, experimental procedure and typical test results.