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1. BEARING

1.1. DEFINITION

A bearing is a device to allow constrained relative motion between two or more parts, typically

rotation or linear movement.

Bearings may be classified broadly according to the motions they allow and according to their 

 principle of operation as well as by the directions of applied loads they can handle.

Figure 3.1 : Taper Roller Bearing

1.2.TYPES OF BEARINGS:- 

There are many different types of bearings.

Type Description Friction Stiffness Speed Life Notes

Plain

bearing  

Rubbing

surfaces,

usually with

Depends on

materials and

construction,

Good,

 provided

wear is

Low to

very high

Low to very high

- depends upon

application and

Widely used,

relatively high

friction,

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lubricant; some

 bearings use

 pumped

lubrication and

 behave

similarly to

fluid bearings.

PTFE has

coefficient of 

friction

~0.05-0.35,

depending

upon fillers

added

low, but

some

slack is

normally

 present

lubrication suffers from

stiction in

some

applications.

Depending

upon the

application,

lifetime can

 be higher or 

lower than

rolling

element

 bearings.

Rolling

element

bearing  

Ball or rollers

are used to

 prevent or 

minimize

rubbing

Rolling

coefficient of 

friction with

steel can be

~0.005

(adding

resistance due

to seals,

 packed

grease,

 preload and

misalignment

can increase

friction to as

much as

0.125)

Good, but

some

slack is

usually

 present

Moderate

to high

(often

requires

cooling)

Moderate to high

(depends on

lubrication, often

requires

maintenance)

Used for 

higher 

moment loads

than plain

 bearings with

lower friction

Jewel Off-center Low Low due Low Adequate Mainly used

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negligible if 

magnetic

field is quasi-

static

external

 power.

Flexure

bearing  

Material flexes

to give and

constrain

movement

Very low LowVery

high.

Very high or low

depending on

materials and

strain in

application.

Usually

maintenance

free.

Limited range

of movement,

no backlash,

extremely

smooth

motion

Stiffness is the amount that the gap varies when the load on the bearing changes, it is distinct

from the friction of the bearing.

Table 3.1: Types of bearing

1.1.TAPERED ROLLER BEARING

Tapered roller bearings are designed in such a way that vertices of the cone for each roller and

those for the inner and outer raceways coincides on the bearing axis or extensions of the

raceways and rollers converge at a common point on the axis of rotation. This results in true

rolling motion of the rollers on the raceways at every point along the rollers.

The tapered roller bearings support radial loads and axial loads from one direction only. The line

contact between rollers and raceways provide the bearings with a high load carrying capacity.

Steep angle tapered roller bearing with exceptionally steep cone angle enables the bearings to

take heavier axial load.

The bearings are of separable type, enabling separate mounting of cups and cones. Since the

tapered roller bearings can absorb thrust loads in one direction only, these bearings should

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generally be installed as opposed mountings. The correct amount of radial and axial clearance is

obtained by adjusting the two bearings against each other.

Besides, double row and four row tapered roller bearings are also widely used for heavy loads

such as rolling mills.

The inner and outer ring raceways are segments of cones and the r ollers are also made with a

taper so that the conical surfaces of the raceways and the roller axes if projected, would all meet

at a common point on the main axis of the bearing.

Figure3.2 : Taper Roller Bearing

This conical geometry is used as it gives a larger contact patch, which permits greater loads to be

carried than with spherical (ball) bearings, while the geometry means that the tangential speeds

of the surfaces of each of the rollers are the same as their raceways along the whole length of 

the contact patch and no differential scrubbing occurs. When a roller slides rather than rolls, it

can generate wear at the roller-to-race interface, i.e. the differences in surface speeds creates a

scrubbing action. Wear will degenerate the close tolerances normally held in the bearing and can

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lead to other problems. Much closer to pure rolling can be achieved in a tapered roller bearing

and this avoids rapid wear.

The rollers are guided by a flange on the inner ring. This stops the rollers from sliding out at high

speed due to their momentum.

The larger the half angles of these cones the larger the axial force that the bearing can sustain.

Tapered roller bearings are separable and have the following components: outer ring, inner ring,

and roller assembly (containing the rollers and a cage). The non-separable inner ring and roller 

assembly is called the cone, and the outer ring is called the cup. Internal clearance is established

during mounting by the axial position of the cone relative to the cup.

1.1.1.  RAW MATERIAL:

The Races & Rolling elements of Bearing are subjected to stress on a very small contact surface

must be of such material also as to with stand wear and have high elastic Limit & fatigue Limit.

The raw material being used by the Industry for Manufacturing of various Bearing components

are as under:

CUP AND CONE

The raw material used in the Manufacturing of bearing Races is SAE 52100 high Carbon

Chrome bearing steel, which has composition similar to EN-31 (100 CR 6 As per BIS

specification). The raw material for Bearing Races is in the form of Rods & Seamless Hollow

Tubes.

This is a Spheroids Annealed Steel. Approx. 80% of the Seamless Hollow tubes are purchased

 by the Industry from M/s. Indian Seamless Metal tube PUNE, while the rest of the tube used in

the cluster is imported material.

The Steel bar are purchased from M/s. Indian Seamless Steel & Alloy Pune & M/s. Mahindra

Ugine Steel Company KHAPOLI (Maharashtra).

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Some of the units are buying the steel scrap rod for manufacturing bearing races.

Bearing Races material and their heat treatment are required to be selected carefully, taking

account the mechanical strength and required life of the Bearing,

Approximate required composition for bearing races are Constitute % Composition

Carbon 0.95 to 1.1

Chromium 1.4 to 1.6

Manganese 0.50 max.

Silicon 0.15 to 0.35

Sulphur 0.025 (Max.)

Phosphorous 0.05

CAGE'S

Cage is used to return balls at proper distance to prevent them from containing each other and to

 prevent a temperature rise and resultant damage due to friction.

The Material for manufacturing cages is CRCA Strips of C2015 Bearing grade steel having

carbon percentage at0.08% max. and Magnesium ranging from 0.25% to 0.45%