COUPLING AND KEYS

I have seen the importance of Coupling and Keys in my industrial life and i am compelled to write this blog about coupling and keys so that we may share information about this very precious subject i.e. Coupling and Keys

Let us see what we want to understand about the coupling and key 

1. Various types of couplings 

2. Advantage and disadvantage of various couplings 

3. Various types of keys and their standard specifications 

4. Understanding the concept of splines and determine suitable load

5. Universal joints and their application areas

6. Shaft attachment mechanisms e.g. Clamps, setscrews and cross pins

First I would like to focus on key, so let’s go ahead towards the basic concept of key 

This blog is based on coupling and keys for shaft and we will focus the various types of keys here as well as design and selection process that we must adopted.

Keys 

Keys are normally used for connecting two member mechanically, let us consider gear coupling and shaft , in this case coupling hub and shaft will be mechanically connected by means of key. i have seen various types of keys but commonly flat keys are used in 

Flat Keys 

Normally we use flat key in number of applications, let us understand what is flat key. 

Standard dimensions of square and flat keys

Shaft diameter (inch)	Square key size (inch) , h or w	Flat key size (inch) , w*h
½* to 9/15	1/8	1/8 x 3/32
5/8 to 7/8	3/16	3/16x 1/8
15/16 to 1*1/4	1/4	1/4 x 3/15
1*5/16 to 1*3/8	5/16	5/16x1/4
1*7/16 to 1*3/4	3/8	3/8 x1/4
1*13/16 to 2*1/4	1/2	1/2 x3/8
2*5/46 to 2*3/4	5/8	5/8  x 7/16
2*7/8 to 3*1/4	3/4	3/4 x 1/2
3*3/8 to 3*3/4	7/8	7/8 x 5/8
3*7/8 to 4*1/2	1	1 x 3/4
4*3/4 to 5*1/2	1*1/4	1-1/4 x 7/8
5*3/4 to 6	1*1/2	1*1/2 x 1

Various types of key

There are various types of keys and their classification depends on method of manufacturing.

Square and rectangular parallel key

This type of key is highly recommended these days for various applications. We will come to know about the cross section of key and then we can decide whether key is square or rectangular. Selection of size of key depends on the diameter of shaft and we have already discussed some standard size of key for various size of shaft in above table.

Tapered key

Such type of keys will have varying rectangular cross-section. The fundamental idea of adopting taper keys is basically for the easiness of assembly as well as for removal of the key.

Gib Head Key

Such type of keys are very similar with tapered key but there will be one difference , in case of gib head key there will be a head that will be provided at bigger end side of  key and this type of keys are used where we need frequent removal of keys with easiness.

Woodruff keys

Such type of key is called as woodruff because of the process of manufacturing of key and there will be a semi-circular key seat over the surface of shaft and it will hold the key. The key will be in the circular section shape. But we must understand that such type of key will have a lesser shear strength as compared to square or rectangular key.

Circular Keys 

such type of keys are in circular shape and in this case there will be semi circular hole in shaft and hub for fixing the circular keys , circular keys are also known as Pin keys.

Key design

Let us consider the torque transmitted by the key 

Couplings

A coupling is used for connecting one shaft end with another shaft end for transmitting the power from one shaft to another shaft.

Coupling Classifications 
There are mainly two types of couplings in general 

1. Rigid coupling - Such type of couplings are used for aligned shaft 
2. Flexible coupling - Such type of couplings are used for non aligned shaft 

Rigid coupling

There will not be any allowable misalignment between both connecting shafts and members in case of rigid couplings.

1. Flanged

2. Split Coupler

3. Keyed

4. Friction

Flanged Coupling

There will be key for connecting shaft with coupling hub and then coupling flanges will be coupled together by bolts

Split Coupler
 

In this type of coupling , we use same process i.e. key will be used for fixing the coupling with shaft and then coupling will be coupled together with bolts.

Keyed Coupler

Grooves will be cut over the shaft and with the fixed member and we will use one key for connecting two parts together.

Friction Coupling

Clutch not engaged  

 

Clutch in engaged condition

Flexible coupling

Such type of couplings are used for non aligned connecting member

1. Constant Velocity
2. Universal

3. Flexible

Constant Velocity

this type of couplings are used where we can not use universal coupling and both connecting members are at more than 20 degrees.

Universal

This type of couplings are very suitable for connecting two members those are not aligned and we may use this coupling up to misalignment angle 40 degrees.

Flexible Coupling

In this type of coupling , both connecting shaft will be bolted over a rubber disc and we may use this type of coupling where misalignment angle not more than 3 degree as only rubber disc flexibility will compensates the misalignment angle.

We studied coupling and key and these two parts are basic components in any industry

Let us go ahead towards another technical blog

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