Greetings! Today at The Mechanical post we’ll see the types of shaft couplings, their construction, assembly, advantages, disadvantages and applications. So let’s get started.
What is coupling?
This is because very long shafts tend to bend due to their own weight. This can cause vibrations, noise and eventually the shaft might break.
To prevent this, shafts are connected by the coupling which connects two shafts together and helps to transmit power.
Functions of coupling
- Must disconnect easily for repairs or maintenance.
- It must be easy to connect the shafts and must hold them properly.
- Coupling must be able to connect shaft units, which are manufactured separately. For e.g. A motor shaft and a generator shaft.
- To compensate for misalignment of connected shafts.
- To introduce mechanical flexibility ( such as in case of flexible coupling ).
- To reduce and absorb transmission of shock loads from one shaft to another shaft.
- To provide protection against overloads.
- To change the vibration characteristics of rotating members, whenever required.
Requirements of a good coupling:
- Coupling should be easy to assemble and dismantle.
- Coupling should be able to transmit 100% power from one shaft to the other shaft without any power losses.
- Coupling should hold the shafts in perfect alignment.
- Coupling should be able to absorb and reduce shock and vibration when transmitting power from one shaft to another.
- Coupling should not have projected parts or have a minimum number of projected parts.
Factors to be considered while selecting a coupling:
- Misalignment of the shaft.
- Operating conditions.
- Operating torque and speed of shafts.
- Protections against overload.
- Durability and reliability.
- Cyclic operation.
- The direction of rotation.
Types of coupling:
- It is used to connect two shafts, which are in perfect alignment.
- It consists of two flanges with hubs, one keyed to the driving shaft and other two the driven shaft. Two flanges are bolted together.
- When the required length of the shaft is too long and is difficult to manufacture such long shaft, then two or more shafts of suitable length are connected with the help of sleeve or muff coupling.
- For motor-pump sets, motor-gear box sets etc.
- It is used to connect two shafts having both lateral and angular misalignment.
- Its construction is similar to a rigid coupling, except that, a flexible element, such as rubber bush is inserted between the coupled parts.
- Rubber bush is provided with brass lining to avoid excessive wear. These bushes absorb the misalignment between the shaft.
- Bushed pin-type coupling.
- Universal coupling.
- Oldham coupling.
What is the difference between rigid coupling and flexible coupling?
Now let’s talk in detail about each coupling starting off with Sleeve or muff coupling.
Sleeve or muff coupling
Sleeve or muff coupling consists of a sleeve or muff which is a type of hollow cylinder. The internal diameter of the muff is equal to the external diameter of the shaft.
The two shafts which are to be coupled have keyways built into them. A gib headed key is used to connect the shafts to the muff.
Assembly of sleeve or muff coupling
In this way, the sleeve or muff coupling is assembled. This type of coupling is used for small diameter shafts.
Advantages of muff coupling
- Its the simplest type of coupling with only 2 parts i.e muff and key.
- It is compact in size.
- It has no projecting parts which make it safe for usage.
- It is economical.
Disadvantages of sleeve/muff coupling
- The main disadvantage of a rigid coupling is that it cannot tolerate any misalignment in the axes of the shafts.
- It is difficult to assemble or dismantle as the sleeve has to be shifted over a shaft or shaft ends.
- It is not able to absorb shocks or vibrations during power delivery.
Split-muff or clamp coupling
|Image source- Grabcad|
Advantages of clamp coupling
- Coupling’s strength is more as compared to muff coupling.
- It can transmit more torque than the muff coupling.
- It can be easily assembled and dismantled.
- It is small in size diametrically.
Disadvantages of clamp coupling
- Its cost is more as compared to muff coupling due to more parts.
- As it contains nuts and bolts, it becomes unsafe. Thus protection must be provided.
- It cannot absorb shocks and vibrations.
Flange coupling (Protected type)
|Image source- Grabcad|
Advantages of flange coupling
- Simple in construction
- Is capable of transmitting high torque as compared to muff coupling.
- Is suitable for high speed.
- Easy to assemble and dismantle.
Disadvantages of Flange coupling
- It cannot tolerate misalignment, the shafts need to be perfectly aligned.
- It cannot absorb or withstand shocks or vibrations.
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Bush pin type flexible coupling
Advantages of bush pin type flexible coupling
- Its construction is simple
- It absorbs shock and vibration during power transmission.
- This type of coupling can handle misalignment of 0.5 mm laterally and 1.5 degree angular misalignment.
Disadvantages of Bush pin type flexible coupling
- It is not economical i.e. its cost is high due to more components.
- Radial space required by the coupling is more as compared to other couplings.
The Oldham coupling is another type of flexible coupling designed for shafts with misalignment. It was invented by John Oldham in Ireland in the year 1821.
Advantages of Oldham’s coupling
- Its size is compact.
- Easy to assemble.
- In case of excessive load, the centre disc will be the one to break first. Thus preventing the failure of other important machine components.
- The centre disc can be replaced easily and is inexpensive.
- It can effectively absorb shocks and vibrations.
- It can tolerate misalignment in shafts.
- Due to the presence of plastic centre disc, the coupling becomes electrically insulated.
- It is economical.
Disadvantages of Oldham’s coupling
- It cannot tolerate angular misalignment.
- It cannot tolerate high torque.
- Due to the sliding movement, the centre disc is subjected to wear, thus after a particular time period, it has to be replaced.
Applications of Oldham’s coupling
- It is used in a stepper motor.
- In robotics.
- Servo motor applications.
- In printers and xerox machines.
By Van helsing – Own work, CC BY 2.5,
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