akhil mahajan 15me63r16 - elearn.fnu.ac.fj

Akhil Mahajan

15ME63R16

A bearing is a device that is used to enablerotational or linear movement, while reducingfriction and supporting shafts.

All bearing are provided with somelubrication arrangement to reduced frictionbetween shaft and bearing.

◦ Rolling or anti-friction bearing : -

Due to less contact area rollingfriction is much lesser than thesliding friction, hence thesebearings are also known asantifriction bearing.

◦ Plain or slider bearing : -

In which the rotating shaft has asliding contact with the bearing.Due to large contact areafriction 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 tosupport axial loads like verticalshafts.

Does not withstand any radialload, also with this it is notsuitable for higher speeds.

They are used in gear sets like incar transmissions between gearsand between housing and therotating shafts.(Lay shafts)

Cylindrical bearings offerhigher load capacities thanball bearings of the same sizeas they make line contactrather than point contact withtheir rings.

Not suitable for axial loading,cheaper to manufacture, usedfor heavy and sudden loading,high speed and continuousservice.

Used in gearboxes

Tapered roller bearings useconical rollers that run onconical races.

High radial and axial loadratings at moderate speed.

Mounted in pairs with opposedtaper to counter the axialcomponent.

Taper roller bearings are used inthe wheel bearings of mosttrucks, buses, cars, and so on.

Rollers used in spherical rollerbearings are thicker in themiddle and narrow at the ends.

They can adjust to supportmisaligned loads so, alsoknown as self aligning rollerbearings.

Important uses of sphericalbearings have been in carsuspensions, trackballs,computer mouse, heavymachinery, sewing machines,drive shafts, etc.

• Needle roller bearings are slendercylindrical rollers that have highestload capacity for a given radial spaceof all rolling-element bearings.

• Needle roller bearings are ideal forapplications where moderate radialload carrying capacity is requiredbut radial space is limited.

• Needle bearings are primarily usedin engine components like pumps,compressors, rocker arm pivots, andtransmissions, universal joint .

COMPARISON TABLE FOR DIFFERENT ANTI-FRICTION BEARINGS

Just a bearing surface andno rolling elements.Therefore the journal slidesover the bearing surface.

Plain bearings, in general,are the least expensive typeof bearing. They are alsocompact and lightweight,and they have a high load-carrying capacity

Pedestal bearing

Footstep bearing

Journal bearing

Shaft, or "journal",rotates in the bearingwith a layer of oil orgrease separating thetwo parts through fluiddynamic effects.

Simple journal is simply ablock of cast iron with ahole for the shaftproviding running fit. Anoil hole is drilled at thetop for lubrication.

◦ Two types of lubrication used in journal bearings:

Hydrodynamic lubrication

Hydrostatic Lubrication

Journal (Sleeve) Bearings

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 pressureis continuously applied to forcefluid lubricant through inletchannels into chambers betweenthe bearing surfaces.

That means these bearingsurfaces are always separated bya thin lubricant film whichprevents any friction betweenthe bearing surfaces.

This allows highly preciseposition control in the sub-micrometre range.

In this the bush of soft material like brass or gun metalis provided and the body or main block is made of castiron.

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 arunning fit for the shaft.

Applications: turbines, large diesel engines, supportingcrankshafts etc.

It is a split type of bearing. This type of bearing is used forhigher speeds, heavy loads and large sizes.

This bearing facilitates the placements and removal of the shaftfrom the bearing.

Unlike the solid bearing which are to be inserted end-wise andhence are kept near the ends of the shaft, these can be placedanywhere.

This bearing ensures a perfect adjustment for wear in thebrasses 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 havenoiseless operation. They can be easily machined,occupy small radial space and have vibrationdamping properties. Also they can cope withtapped foreign matter.

Disadvantages are they require large supply oflubricating oil, they are suitable only for relativelow temperature and speed; and starting resistanceis much greater than running resistance due toslow build up of lubricant film around the bearingsurface.

http://bearingsindustry.com/Hydrostatic%20Bearings-An%20Introduction.PDF

https://en.wikipedia.org/wiki/Fluid_bearing#Hydrodynamic_lubrication

Prof. M.M. Mayuram & Prof. K. Gopinath, IIT Madras, NPTEL Modules/Lecturesnptel.ac.in/courses/IIT-MADRAS/Machine_Design_II/pdf/5_3.pdf

Dr. Rajiv Tiwari, IIT Guwahati, Theory & Practice of Rotor Dynamics, NPTEL Modules/Lecturesnptel.ac.in/courses/112103024/7

Dr. Harish Hirani, IIT Delhi, Tribology, NPTEL Modules/Lectures nptel.ac.in/courses/112102014/40