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A bearing is a device that is used to enable rotational or linear movement, while reducing friction and supporting shafts.
All bearing are provided with some lubrication arrangement to reduced friction between shaft and bearing.
Rolling or anti-friction bearing : -
Due to less contact area rolling friction is much lesser than the sliding friction, hence these bearings are also known as antifriction bearing.
Plain or slider bearing : -
In which the rotating shaft has a sliding contact with the bearing. Due to large contact area friction is high.
Ball and roller arranged between the surfaces of two races. These provide rolling action between the races.
the radius of the track for balls is slightly greater 5 to 10 % than that of the ball themselves.
Note that the rotating surfaces rotate in opposite directions.
Incorporates hardened steel balls and rollers (52100 chrome steel).
Hence ball and rolling bearing are more suitable to drives subject to frequent starting and stopping as they save power.
Ball Bearing Single row deep groove ball bearing Double row deep groove ball bearing
Angular contact ball bearing Single row angular contact bearing Double row angular contact bearing
Thrust Bearing Single row thrust bearing Double row thrust bearing
Roller Bearing Cylindrical roller bearing Tapered roller bearing Spherical roller bearing Needle roller bearing
A Ball bearing is a common type of rolling bearing.
Point contact; support radial and axial loads.
Used for applications where the load is relatively small.
Ball bearings are often used in individual cages to reduce friction in axle assemblies or in a series to absorb the weight placed on a moving part.
Designed for axial and radial loading; used in pairs.
These bearing are used where the thrust load is equal to or greater than
radial load.
Thrust bearings are designed to support axial loads like vertical shafts.
Does not withstand any radial load, also with this it is not suitable for higher speeds.
They are used in gear sets like in car transmissions between gears and between housing and the rotating shafts.(Lay shafts)
Cylindrical bearings offer higher load capacities than ball bearings of the same size as they make line contact rather than point contact with their rings.
Not suitable for axial loading, cheaper to manufacture, used for heavy and sudden loading, high speed and continuous service.
Used in gearboxes
Tapered roller bearings use conical rollers that run on conical races.
High radial and axial load ratings at moderate speed.
Mounted in pairs with opposed taper to counter the axial component.
Taper roller bearings are used in the wheel bearings of most trucks, buses, cars, and so on.
Rollers used in spherical roller bearings are thicker in the middle and narrow at the ends.
They can adjust to support misaligned loads so, also known as self aligning roller bearings.
Important uses of spherical bearings have been in car suspensions, trackballs, computer mouse, heavy machinery, sewing machines, drive shafts, etc.
• Needle roller bearings are slender cylindrical rollers that have highest load capacity for a given radial space of all rolling-element bearings.
• Needle roller bearings are ideal for applications where moderate radial load carrying capacity is required but radial space is limited.
• Needle bearings are primarily used in engine components like pumps, compressors, rocker arm pivots, and transmissions, universal joint .
Just a bearing surface and no rolling elements. Therefore the journal slides over the bearing surface.
Plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load- carrying capacity
Pedestal bearing
Footstep bearing
Journal bearing
Shaft, or "journal", rotates in the bearing with a layer of oil or grease separating the two parts through fluid dynamic effects.
Simple journal is simply a block of cast iron with a hole for the shaft providing running fit. An oil hole is drilled at the top for lubrication.
Two types of lubrication used in journal bearings:
Hydrodynamic lubrication
Hydrostatic Lubrication
Load is transferred through a lubricant in sliding contact
Fluid film at the point of minimum thickness decreases in thickness as the load increases
Pressure within the fluid mass is greatest at some point approaching minimum clearance and lowest at the point of maximum clearance
Film thickness at the point of minimum clearance increases with the use of more viscous fluids
With a given load and fluid, the thickness of the film will increase as speed is increased
In this type an external pressure is continuously applied to force fluid lubricant through inlet channels into chambers between the bearing surfaces.
That means these bearing surfaces are always separated by a thin lubricant film which prevents any friction between the bearing surfaces.
This allows highly precise position control in the sub- micrometre range.
In this the bush of soft material like brass or gun metal is provided and the body or main block is made of cast iron.
When the bush gets worn out it can be easily replaced. The outside of the bush is a driving fit (interference fit) in the hole of the casting where as the inside is a running fit for the shaft.
Applications: turbines, large diesel engines, supporting crankshafts etc.
It is a split type of bearing. This type of bearing is used for higher speeds, heavy loads and large sizes.
This bearing facilitates the placements and removal of the shaft from the bearing.
Unlike the solid bearing which are to be inserted end-wise and hence are kept near the ends of the shaft, these can be placed anywhere.
This bearing ensures a perfect adjustment for wear in the brasses by screwing the cap.
Suitable for supporting a vertical shaft with axial loads.
In a footstep bearing a gun metal bush having a collar on top and shaft rests on a gun metal disc placed at the bottom in the bush.
The disc is prevented from rotation with the help of a pin fitted in the sole. The disc act as a thrust bearing whereas the bush fitted in the casting supports the shaft in position. The bush can take radial loads, if any, on the shaft.
The disadvantage of footstep bearing is that it cannot be efficiently lubricated and there is unequal wear on the bottom disc.
Plain bearing are cheap to produce and have noiseless operation. They can be easily machined, occupy small radial space and have vibration damping properties. Also they can cope with tapped foreign matter.
Disadvantages are they require large supply of lubricating oil, they are suitable only for relative low temperature and speed; and starting resistance is much greater than running resistance due to slow build up of lubricant film around the bearing surface.
http://bearingsindustry.com/Hydrostatic%20Bearings- An%20Introduction.PDF
Prof. M.M. Mayuram & Prof. K. Gopinath, IIT Madras, NPTEL Modules/Lectures nptel.ac.in/courses/IIT-MADRAS/Machine_Design_II/pdf/5_3.pdf
Dr. Rajiv Tiwari, IIT Guwahati, Theory & Practice of Rotor Dynamics, NPTEL Modules/Lectures nptel.ac.in/courses/112103024/7
Dr. Harish Hirani, IIT Delhi, Tribology, NPTEL Modules/Lectures nptel.ac.in/courses/112102014/40