What is Bearing?
A bearing is a mechanical element which allows motion between two rotating parts, with minimum friction.
An example of such rotating parts is shaft and its housing.
Function of bearing
A good bearing is expected to do the following functions.
It should ensure free rotation with minimum friction
It should support rotating parts and maintain them in the correct position
Bearing should transmit the forces acting on rotating parts to the frame of the machine
Classification of Bearings
There are several bases for classification of bearings, we will discuss all of them one by one.
- Depending on the direction of force
- Radial bearing
- Axial bearing
- Depending on the type of friction
- Sliding contact bearing
- Roller contact bearing
- Sliding contact bearing
- Sliding contact bearings are also known as sleeve bearings, journal bearings or plain bearings.
This type of bearing surface of shaft slides over the surface of a bush which results in wear and friction.
To reduce the friction rotating surfaces are separated by a film of lubricating oil. The bush is made of special material like bronze or white metal.
- Applications of sliding contact bearings
- Concrete mixtures, rope conveyors and marine installations
- Steam and gas turbines
- Large size electric motors
- Centrifugal pumps
- Crankshaft bearings in petrol and diesel engines
- Types of sliding contact bearings
- On the basis of the type of lubrication applied in sliding contact bearings, they can be classified into two types.
- Hydrodynamic lubrication bearings
- Hydro-static lubrication bearings
- Rolling contact bearing
- Rolling contact bearings are also known as anti-friction bearings or simply ball bearings.
To reduce friction, rolling devices such as balls or rollers are placed between moving surfaces.
In this type of bearing sliding, contacts are replaced by rolling contacts.
- Functions of rolling contact bearings
- Rope shaves, crane hooks, and hoisting drums
- Small size electric motors
- Front and rear axles of automobiles
- Machine tool spindles
- Types of rolling contact bearings
- On the basis of load and use requirements, ball bearings can be classified in the following types.
- Deep groove ball bearing
- Cylindrical roller ball bearing
- Angular contact bearings
- Self-aligning bearings
- Spherical roller bearing
- Taper roller bearing
- Thrust ball bearing
Selection of bearing type
To select a proper bearing for our application is a very important thing. Here is a quick guide for selecting the right bearing.
Too low and medium loads select ball bearing, and for heavy load select roller bearings
In case of misalignment between shafts self-aligning ball bearings or roller
Bearings are used for medium thrust load,
Radial thrust bearings are selected and for heavy thrust loads
Cylindrical thrust bearings are used
For situations where we have both axial and radial component of load,
We use deep groove ball bearing, angular contact bearing,
And spherical roller bearing for high-speed applications deep groove ball bearings,
Angular contact bearings and cylindrical roller bearings are recommended
When the rigidity of the system is our main requirement like in machine tools we use double row cylindrical roller bearing or taper roller bearing
When noise reduction is the main criteria we use deep groove ball bearing
Static load carrying capacity
Before determining the static load carrying capacity of a ball bearing, let us first understand what a static load is.
Static load is defined as the load acting on a bearing when the shaft is stationary.
The static load carrying capacity of a shaft is defined as the static load
Which corresponds to a total permanent deformation of balls and races,
At the most heavily stressed point of contact, equal to 0.0001 of the ball diameter.
Dynamic load-carrying capacity
The dynamic load-carrying capacity of a bearing is defined as the
Radial load in radial bearing (or thrust load in the thrust bearing)
That can be carried for a minimum life of one million revolutions.
Needle bearings are the cylindrical roller bearings with a
Very small diameter compared to the length of the roller.
They are also known as Quill bearings.
The length to diameter ratio of a needle bearing is more than four.
Advantages of needle bearings
They can be used to replace sleeve bearings
They are compact and lightweight
Compared to their size they have large load carrying capacity
They have large load carrying capacity particularly at low speeds
There are two basic types of bearing failure.
Breakage of parts
The breakage of parts happens due to misalignment or overload.
Through selecting the right bearing, this form of bearing failure can be easily avoided.
Surface destruction of bearings can be further classified into the following.
Guidelines for lubricating ball bearing
We need to lubricate ball bearing from time to time, for smooth movement of balls. To find suitable lubrication for your application, here is a quick guide.
When the temperature is less than 100-degree Celsius grease is suitable. For temperature above 100-degree Celsius oil is suitable.
Grease is suitable for low and moderate loads and for heavy loads oil is suitable.
In case we already have a central lubrication system present in the machine, we can use the same forbearing. No need for any extra lubrication system for bearings.
When the product of bore (in mm) * speed (rpm) is below 200000, grease is suitable, for higher values oils are suitable.