151-Chap 11-1 Rolling Bearings (11-1 to 11-7)(v2)

7/24/2019 151-Chap 11-1 Rolling Bearings (11-1 to 11-7)(v2)

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Chapter 11-Rolling Contact Bearing 2

earings

Rolling Contact Bearings

Sliding CB

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Arif_ME308-132 Chapter 11-Rolling Contact Bearing 3

History

1.

As far back as 1100 BC the Assyrians and Babyloniansused rollers inserted between enormous stones andground to reduce friction.

2. The wheel based on sliding motion came later.

3. Some historians mention that lubricated chariot

wheels existed before 1400 BC.4. The bicycle introduced the need for rolling elements

(1817).

Rolling Bearing


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Bearing Types

Rolling ElementPure radial load

(Cylindrical roller bearings)

Pure Thrust load(Cylindrical and Ball)

Combination load

(Deep groove ball, Tapered roller,

Angular contact bearings)

Sliding (Journal)

Bearings

Pure radial

Pure Thrust

Combination

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Other Types

Magnetic bearings

Fluid/Air bearings

Micro/Nano

bearings

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http://upload.wikimedia.org/wikipedia/commons/b/b4/Hydrostatic_bearing.GIF


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Journal Bearings

Radial

(Plain Bearings, sleeves)

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Thrust Journal Bearing

Thrust

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Why Rolling-Contact Bearings?

RCB are used to minimize the friction

resulting from relative motion performed

under load.

RCB are used to describe bearings in

which the main load is transferred throughrolling elements.

Typical applications

Gear Box

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Inner and outer races are typically pressed onto shafts or hubs

with slight interference fit to make them move with shafts

(inner race) or remain stationary (outer race)

Ball

Bearing Nomenclature

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Ball Bearing Types



Notes on Bearings

Bearings maybe obtained with shields on one or bothsides. Shields provide a degree of protection againstdirt.

Some bearings are manufactured with seals in one orboth sides. If sealed on both sides, bearings arelubricated at the factory.

Starting friction is almost twice the running friction.

Bearings are manufactured to take eitherpure radial

load,pure thrust loador a combination of both. Bearing makers usually provide manuals to describe

the various types. (www.skf.com, www.fag.com,www.timken.com )

Arif_ME308-132
http://www.skf.com/http://www.fag.com/http://www.timken.com/http://www.timken.com/http://www.fag.com/http://www.skf.com/


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Ball Bearings

Angular ball bearings have higher thrust load capacity in

one direction than Radial ball bearings


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Roller Bearings

Roller bearings have higher load capacity than ball bearings

Roller bearings require prefect geometry

Straight roller bearing (radial cylindrical) cannot take thrust loads

Tapered roller bearings combine the advantage of ball and straight

roller bearings, they take radial and thrust loadings.

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Roller bearings: Needle Bearings

Needle bearings have very high load ratings and require less space

Needle bearings can be used with and without races

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Characteristics of ball Bearings

Type Approximate range of

bore sizes, mm

Relative capacity Limiting

speedfactor

Tolerance

to mis-alignment

Minimum Maximum Radial Thrust

Conrad or deep

groove

3 1060 1.00a0.7 1.0 015

Maximum capacity

or filling notch

10 130 1.2-1.4a0.2 1.0 03

Self-aligning

internal

5 120 0.7b0.2 1.0 230

Self-aligning

external

- - 1.0a0.7 1.0 High

Double row,

maximum

6 110 1.5a0.2 1.0 0.3

Double row, deep

groove

6 110 1.5a1.4 1.0 0

aTwo directions

bOne direction

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Rolling Contact Bearing Materials

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Ch i i f A l


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Type A ppr oxima te

maximum

size mm

Rela tive ca pa city Limiting

speed fa ctor

Tolerance

to mis-

alignment

Ra dia l Thr ust

One-directionalthrust

320 b1.00-1.15 a,b1.5-2.3 b1.1-3.0 02

Duplex, back toback

320 1.85 c1.5 3.0 0

Duplex, face toface

320 1.85c1.5 3.0 0

Duplex, tandem 320 1.85a2.4 3.0 0

Two directional or

split ring

110 1.15c1.5 3.0 02

Double row 140 1.5c1.85 0.8 0

aOne direction

bDepends on contact angle

cTwo directionsdIn other direction

Characteristics of Angular

Contact Ball Bearings

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Type Approxi m at e range of

bore si zes mm

R el at i ve capaci t y Lim i t i ng

speed

factor

Tolerance

to mis -

al ignment

Mi ni m um Maxi m um R adi al Thrus t

Seperable outer

ring, nonlocating

(N)

10 320 1.55 0 1.20 05

Seperable inner

ring, nonlocating

(NU)

12 500 1.55 0 1.20 05

Seperable inner

ring, one direction

locating (NJ)

12 320 1.55 aLocating 1.15 05

Seperable inner

ring, two-direction

locating (NUP)

20 320 1.55 bLocating 1.15 05

aOne directionbTwo directions

Characteristics of Cylindrical

Roller Bearings

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Characteristics of Spherical Roller Bearings

R lli C B i


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Rolling Contact Bearings

In selecting these types of bearings, thedesigner should take into consideration the

following:

The available space

The load and its characteristics

The desired life

The required speed

The cost

Not to design rolling bearings but to select proper

bearings for the application

Objective:

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Bearing Life

Assuming perfect mounting, adequate lubricationand protection thus failure will occurby fatigue

Bearings are subjected to millions of repeatedcontact stress (Hertezian) cycles causing spalling

(flaking or pitting) on ball or raceway. (Video 1& 3

)

Failure Criteria:

1. SKF: failure happens when a pit of diameter10-4

diameter of ball or roller is observed.2. Timken Co.: failure happens when 10-2 in2 of

surface is spalled

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Simulation of progression of fatigue


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Simulation of progression of fatigue

failure

Flake

pit

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151-Chap 11-1 Rolling Bearings (11-1 to 11-7)(v2)

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Transcript of 151-Chap 11-1 Rolling Bearings (11-1 to 11-7)(v2)