As widely said, the smallest things can a time make the greatest impact. Such is the case of a Journal Bearing in the operation of machines used in industrial applications.

The current trend in industries is the use of high speed, high load machinery that causes high heat generation between the surfaces in contact during relative movement as a result of friction.  This operating condition requires a machine member that eliminate this heat generated by friction as it could prove dangerous to the operation of the machine.

To avoid any ambiguity, I would like to define what friction is. **Friction** is simply the resistance offered by a surface when in contact with another surface. As a result of this opposing resistance or force, heat is usually generated between the mating surfaces. A close example is when we rub our palms against each other, heat is generated from that action.

The worrying thing is the effect of this generated heat afterward. When heat is highly generated, the surfaces in contact begin to wear off and could lead to misalignment and if severe, a breakdown of the machine.

So, how does a Journal Bearing help out here? Well, let’s see that together!

<center>![Bearing](http://maxpixel.freegreatpicture.com/static/photo/1x/Chrome-Steel-Bearing-Machine-part-Metallic-2314582.jpg)</center>
<center><sup><sub>[Maxpixel CC0: Chrome Steel Bearing Machine-part Metallic](http://maxpixel.freegreatpicture.com/Chrome-Steel-Bearing-Machine-part-Metallic-2314582)</sub></sup></center>

<center>**WHAT IS A BEARING?**</center>

According to Khurmi (2005), **Bearings** are machine elements that constrain relative motion and reduce friction between moving parts. In a simpler language, a Bearing is a machine element that helps transmit motion between two moving parts and reduces friction while performing this function. 

How does it do this right? This is simply possible due to the lubricant that is usually interposed between the surfaces that meet during relative motion. 

Bearings are usually categorized based on the kind of motion transmitted, type of operation, or to the directions of the loads (forces) applied to the parts. Common types of Bearings include the plain bearing, ball bearing, roller bearing and the fluid (journal) bearing. In this post, we would be focusing on Journal Bearing.

<center>**WHAT IS A JOURNAL BEARING?**</center>
<br/><div class="pull-left"><center><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/Hydrodynamic_lubrication_attitude_angle.svg/547px-Hydrodynamic_lubrication_attitude_angle.svg.png" /><br/><br/><em><sup><sup><a href="https://upload.wikimedia.org/wikipedia/commons/b/ba/Hydrodynamic_lubrication_attitude_angle.svg">Wikipedia Creative Commons: Hydrodynamic Bearing lubrication</a></sup></sup></em></center></div>
According to Bulapari (2004), **Journal bearings** are known as a type of fluid film bearings in which the surfaces in contact (or the mating surfaces) - the journal and the sleeve (bearing), are completely separated by a layer of fluid lubricant.

In a simpler language, a Journal Bearing is an example of the fluid film bearing which is made up of a stationary bearing (or shell) and a freely rotating journal having an interposed lubricant between the clearance existing between the bearing and journal. The lubricant can either be a solid, liquid or gas.

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The main advantage of this type of Bearing is the ability of the interposed lubricant to help reduce frictional resistance and wear and in some cases to carry away the heat generated in the bearing. 

<center>**CLASSIFICATION OF JOURNAL BEARING**</center>

Journal Bearing is broadly classified into two main types. These are:

* Hydrodynamic Journal Bearing
* Hydrostatic Journal Bearing

These two main types of Journal Bearing are extensively used to support the rotating shaft in high-speed machinery like turbines, pumps, electric motors etc.

<center>**HYDRODYNAMIC JOURNAL BEARING**</center>

The basic concept behind the operation of a hydrodynamic Journal Bearing is the manner in which the lubricant is distributed within the clearance existing between the rotating shaft and the stationary shell. The working operation of a Journal bearing can be explained as below.

At the start, when there exists a non-rotating shaft in a Journal bearing subjected to a downward applied load, both the shaft and the rigid sleeve are in contact due to the self-weight.

As the Journal begins to rotate, the lubricant is charged into the journal bearing in the direction of motion and its continuous flow induces a pressure generation in the converging portion of the bearing system. This generated pressure is known as the **Hydrodynamic Pressure.**

This pressure, as it increases due to the increasing speed of the shaft, reduces the inflow and increase the outflow of the lubricant in the bearing system and induces flow continuity. When the pressure is sufficiently high, it causes the journal to lift away from the bearing surface and causes a pumping action in the lubricant. The pumped lubricant thus ensures that there is no contact existing between the stationary sleeve and the rotating shaft and hence, **Hydrodynamic Lubrication** is achieved.

Hydrodynamic Journal Bearing for its special kind of operation is commonly employed in various industrial applications that require high-speed operation.
 
<center>**HYDROSTATIC JOURNAL BEARING**</center>

This type of Journal Bearing differs in the mode by which lubricant is supplied into the clearance between the outer sleeve and the journal. Here, an externally pressurized lubricant - usually by a pump, is interposed between the mating surface while the bearing begins or is in operation. 

The main advantage of this type of bearing is that it is good for start-up position of a bearing operation. Unlike the hydrodynamic Journal bearing in which metal to metal contact exist before the lubricant gets pressurized and circulated around the rotating journal, the lubricant is usually supplied even at start-up in a hydrostatic Journal bearing hence ensuring no metal to metal contact at any stage in the journal bearing operation. This makes it best suitable for extremely low speed and high load applications. Also, through the pressurized pumping of lubricant into the lubricating film, any wear debris existing in that field is duly flushed away and further wear is prevented.


<center>**APPLICATION OF JOURNAL BEARING**</center>

Journal Bearings are widely used in applications where the bearing speed is tending to 3000rpm and above. 

According to Malcolm (2001), when considering a machine that runs above 3000RPM or has a power that exceeds 500HP, turbomachinery users and designers should consider using fluid film (Journal) bearings in parts where relative motions occur.

Also, according to Vats (2014),  machinery with large operating power having speeds and high loads like steam turbines, compressors, and motors employs Journal Bearing as a rotor support.

Journal Bearing aids alignment, effective relative motion and wear prevention. So, it accounts for almost over 90% of the bearing types improvised in machine engines and parts. Other areas of application of Journal Bearing includes; Internal Combustion Engines, centrifugal pumps, Turbine shafts of most jet engines, in crankshaft of an automobile engine, etc.

<center>**ADVANTAGES OF JOURNAL BEARING**</center>

The prevention of friction and wear are the major functions of bearings in a machine component. However, there exist many other useful advantages that it offers in machine operation. Some of which includes;

* Provision of Damping in the Bearing system. This is required in order to pass through the critical speed and it also aids in suppressing instabilities and sub-synchronous vibration.

* It enables machines to be able to withstand shock loads and other types of sudden loads

* It helps to reduce noise when the machine is in operation

* It helps to reduce transmitted vibration

* It gives machine members very long life under normal load conditions

<center>**DISADVANTAGES OF JOURNAL BEARING**</center>

As advantageous as Journal Bearings are, there are however some shortcomings in relation to other types of bearings and in some applications. Some of these disadvantages are:

* It is characterized by higher friction and hence, power loss than in rolling element type

* In Journal Bearing, the radial positioning of the rotor is less precise

* It cannot run for any length of time if starved of lubricant e.g. when a lube system failure occurs

* They are susceptible to some particular contamination

<center>**CONCLUSION**</center>

Bearings are of great importance in mechanical systems and machinery. Without them, the machines will easily wear out due to friction and would constantly need replacement. 

Journal Bearings are extensively used in high speed, high load operations for their friction eliminating phenomenon made possible by the presence of an interposed lubricant which prevents metal to metal contact.

Thanks for reading. I hope you found it useful.

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<center>**REFERENCES**</center>

1. Khurmi R. S. and Gupta J. K., “A Textbook of Machine Design”, pp 962-993

2. Balupari R. S. (2004), “Validation of Finite Element Program for Journal Bearings – Static and Dynamic properties”, University of Kentucky Masters’ Theses Paper 325.

3. Malcolm E. and Leader P. (2001), “Understanding Journal Bearings”, Applied Machinery Dynamics Co., Durango, Colorado, pp 1-26

4. Vats P., Sharma B. C. (2014), “Heat Transfer through Journal Bearing: A Case Study”, International Journal of Research in Engineering and Technology, Vol 3, Issue 10, pp 216-230

5. [Wikipedia | Bearing](https://en.wikipedia.org/wiki/Bearing_(mechanical))

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