Rolling-element Bearings.pptx

8/13/2019 Rolling-element Bearings.pptx

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Introduction

A rolling-element bearing, also known as

a rolling bearing,is a bearing which carries a

load by placing rolling elements (such as balls

or rollers) between two bearing rings.


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Introduction

The relative motion of the pieces causes the

round elements to roll with very little rolling

resistance and with little sliding.

One of the earliest and best-known rolling-

element bearings are sets of logs laid on the

ground with a large stone block on top.


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Introduction

As the stone is pulled, the logs roll along the

ground with little sliding friction. As each log

comes out the back, it is moved to the front

where the block then rolls on to it.

It is possible to imitate such a bearing by

placing several pens or pencils on a table and

placing an item on top of them.


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Introduction

A rolling element rotary bearing uses a shaft in

a much larger hole, and cylinders called

"rollers" tightly fill the space between the

shaft and hole.

As the shaft turns, each roller acts as the logs

in the above example. However, since the

bearing is round, the rollers never fall outfrom under the load.


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Introduction

Rolling-element bearings have the advantage

of a good tradeoff between cost, size, weight,

carrying capacity, durability, accuracy, friction,

and so on.


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Structure

Rolling-element

bearings have 4

main parts:

Outer ring

Inner ring

Balls/roller

Cage/retainer


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Structure

Typical rolling-element

bearings range in size

from 10 mm diameter

to a few metresdiameter, and have

load-carrying capacity

from a few tens of

grams to many

thousands of tonnes.


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Types of rolling elements

There are five types of rolling-elements that

are used in rolling element bearings:

balls

cylindrical rollers

tapered rollers

spherical rollers

needles


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Ball bearing

is a bearing that uses balls to maintain the

separation between the bearing races.

The purpose of a ball bearing is to reduce

rotational friction

and support radial

and axial loads.


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Cylindrical roller

Roller bearings typically have higher load capacity

than ball bearings, but a lower capacity and higher

friction under loads perpendicular to the primarysupported direction.

If the inner and outer

races are misaligned, the

bearing capacity often

drops quickly compared

to either a ball bearing

or a spherical roller bearing.


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Needle

Needle roller bearings use very long and thincylinders. Often the ends of the rollers taper to

points, and these are used to keep the rollerscaptive, or they may be hemispherical and notcaptive but held by the shaft itself or a similararrangement.

Since the rollers are thin, the outside diameter ofthe bearing is only slightly larger than the hole inthe middle.


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Needle

However, the

small-diameter

rollers must bendsharply where they

contact the races,

and thus the

bearing fatigues

relatively quickly.


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Tapered roller

Tapered rollerbearings use conical

rollers that run onconical races,support both radialand axial loads, andgenerally can carryhigher loads thanball bearings due togreater contact area.


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Spherical roller

Spherical roller bearings have an outer ring with

an internal spherical shape. The rollers are thicker

in the middle and thinner at the ends. Sphericalroller bearings can thus adjust to support both

static and dynamic misalignment.


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Rolling-element Bearings.pptx

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