09 Nov, 2021

A muff couplings are also known as sleeve couplings and are a simple type of rigid couplings. It contains a hollow cylinder within the same diameter from inside as the shaft. With the medium of a gib head key, it is tailored over the ends of two shafts. 

The transmission of power from one shaft to another is done by one medium of a key or sleeve or a muff.

In diverse applications, the shafts need to be connected for rotation transmission. The inside of the sleeve has a bore diameter that is slightly more than the shaft diameter surface of the inner sleeve that is tapered. 

However, this tapper is matched on the bore of the outer sleeve. The annular space is closed with the help of a nut and sealing ring at the end of the outer sleeve.

Muff coupling advantages, disadvantages, design, and its applications

The outer sleeve is hydraulically driven on the inner sleeve when the coupling is in the position. For forced lubrication, oil is supplied at 200 bar at two points and 300 bar oil is supplied for driving the outer sleeve. 

At the release of the outer sleeve at the required position, the forced lubrication is released and drained. After this, the hoses are disconnected and plugs are fitted.

Advantages of Muff Couplings

A muff coupling which is also known as sleeve or box couplings is a rigid coupling that contains a sleeve and a key to connect the input and output shafts. It is a kind of inflexible coupling. In this article, we will have a detailed discussion on the advantages, disadvantages, design and application of muff couplings.

·         Muff Couplings can handle a lot of torque and have no backlash.

·         It has slowed down development

·         They are appropriate when misalignment isn’t present or desired, use this application

·         It can be disassembled or removed without causing damage to the shafts

·         It is less expensive than other coupling options

·         Except for the key head, it has no protruding parts

·         The sleeve’s external surface is smooth, which ensures the operator’s safety

·         Designing and manufacturing is straightforward

·         It features a tiny radial dimension and a compact design

To install the sleeve or Muff Couplings, the driven or drive shaft’s position should be changed. To lock the key position, there are some Allen screws also provided. After a discussion over the benefits of Muff Couplings, let us discuss the drawbacks of Muff Couplings.

Disadvantages of Muff Couplings

·         It is unable to assimilate stuns and vibrations due to the lack of adaptive components.

·         It necessitates increasingly pivotal space contrasted and various types of couplings

·         Because it is a rigid connection, it cannot accommodate any misalignment

·         Collecting or destroying it is difficult

·         When compared to flange coupling, it requires more axial space

·         It’s difficult to assemble or dismantle a muff coupling

Application of Muff Couplings

All couplings have the same basic function: to transmit power, correct axial movement, and accommodate misalignment. Couplings are also used to cushion shock or vibration. Muff Couplings are known for their semi-versatile purpose.

They are less expensive and are not difficult to keep up with. Muff couplings depend on these simple functions to follow:

·         The destroying and amassing is simple

·         When you combine a high torque age with a high RPM, you get greater noticeable power

·         It doesn’t require any greasing

·         It is used when the shafts don’t require any alignment and the load capacity is light to medium

·         They’re not difficult to introduce when combined with the Taper bolt shrub

Design of Muff Couplings

Muff coupling is a type of rigid coupling, which is made up of cast iron. It is made up of a hollow cylinder with the same inner diameter as the shaft. A buried key is used to fit it over the ends of the two shafts. 

With the help of a key and sleeve, the transmission of power takes place from one shaft to another.

While Muff Couplings are designed in the below methods:

·  The outer diameter of the sleeve should be 2 times the diameter of the shaft + 13mm, and the length of the sleeve should be 3.5 times the diameter of the shaft.

Design of a sleeve

The sleeves is made with the idea of a hollow shaft in mind.

T: The coupling’s torque will be communicated

TC: Permissible shear stress for the cast iron material of the sleeve

In the case of cast iron, a safe shear stress value is 14 MPa

The torque is transmitted by a hollow section,

T = π / 16 × τc {(D^4 – d^4) / D } = π / 16 × τc × D3 (1 – k^4)      … (Q k = d/D)

Design of a key

Designing of keys for coupling is done in the same way. The dimensions determine the width and thickness of the coupling key. 

The length of the coupling key is at least equal to the length of the sleeve (i.e. 3.5 d). The coupling key is usually made into two parts so that the length of the key in each shaft,

l = L / 2 = 3.5 d / 2

The induced shearing and crushing stresses can be checked once the length of the key is fixed in each shaft. We know that torque is transmitted, but we don’t know how much torque is transmitted.

T = l × w × τ × d / 2     … (Considering shearing of the key)

 I  =  l × t/2 × σc × d / 2    … (Considering crushing of the key)

Price of Muff Couplings

Muff couplings help to maximize performance and extend the machine’s projected life by accurately aligning the two shafts and holding them firmly in place. Sleeve couplings are the most cost-effective and simple to utilize. 

The sleeve is slipped over the shafts, bringing them together in the centre of the connection. The lowest price for Muff Couplings is from INR $3 to $40.

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