Rolling-Element Bearings Calculation and selection using SKF Bearing Catalogue

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Principle of the Rolling-Element Bearings is very old.

This picture shows the principle of a Rolling-Element Bearing of today.

This picture shows how the people in ancient Mesopotamia moved huge stones.

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Modern Rolling Bearings

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• Outer ring

• Inner ring

• Rolling Elements

– Balls & Cage

– Rollers & Cage

Industrial revolution

• Development of modern Bearing

• Better material and better manufacturing methods resulted in better bearings

• Big need for rolling bearings

• Sewing machines’ and bicycle manufactures the biggest bearing consumers

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The diagram shows statistics of patents applications for bicycle bearings in England

This picture shows a drawing from a French patent of 1802.

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Tapered rollerThrust bearing(konisktaxialrullager)

Thrustball bearing(axialkullager)

Sven Wingquist and the Self-aligning ball bearing

• Maintenance engineer at Gamelstadensfabriker

• Frequent failures in deep groove ball bearings

• Reason: misaligning of the shafts of belt transmissions

• Invented a new bearing to accept missaligning

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Drawing of the Swedish patent number 25406 from 1907 by Sven Wingquist.Self-aligning ball bearing (Sfäriskt kullager)

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The Spherical roller bearing

• Development period: from 1919 to 1935

• Invented by Arvid Palmgren

• SKF’s research budget was bigger the research budget of whole Royal Technical Institute in Stockholm

• SKF calculations theory become world standard in 1947. (developed by Palmgren and mathematic Prof. G. Lundberg from RTI)

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Bearings are divided in two groups dependent on rolling elements.

Ball Bearings & Roller Bearings

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Stress concentration

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Loads and bearing types

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3

2

2

210

)11

(

578,0

RR

F

p

L

RRF

p

)11

(

564,0 210

Maximum contact pressure

For two spheres For two Cylinders

Low load

Ball bearings

Middle sized loads;

Ball or roller bearings

High load

Roller bearings

Bearings are also divided in two groups dependent on load direction.

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Radial load

Radial bearings

(radiallager) Example

Axial loadThrust bearings

(axiallager)

Example

Three groups of Rolling Element Bearing (Rolling Bearings)

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1. Radial Ball Bearings

Deep groove

ball bearing

Self-aligning

ball bearing

Angular contact

ball bearing

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2. Radial Roller Bearings

Cylindrical Roller Bearing & Spherical Roller Bearing

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Tapered Roller Bearing & Needle Roller Bearing

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3. Thrust (axial) BearingsShaft washer, Housing washer, Rolling element, and cage

Shaft

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Thrust ball bearing, Cylindrical roller thrust bearing & Spherical roller thrust bearing

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Use of bearings

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Selecting bearing size using the life equations

(SKF p. 64-65)

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L10 = basic rating life (at 90% reliability),

millions of revolutions

L10h = basic rating life (at 90% reliability),

operating hours

p = exponent of the life equation

p = 3 for ball bearings

p = 10/3 for roller bearings

n = rotational speed, rpm

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p

SKFnmhP

C

naaL

60

10000001

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Example: Self-aligning ball bearing (SKF p. 544)

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Sample problem:

Unsealed bearing: use SKF lubricating grease LGMT 2

c = 0,2

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SKF 6214 (SKF p. 330)

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SKF 6214 (SKF p. 331)

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(SKF p. 316)

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(diagram 1-4, SKF p. 66-69)

But first, we have to follow some steps:

Step 1: required kinematic Viscosity

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Step 2: Actual viscosity

SKF greases – LGMT 2(Table 4, SKF p.250)

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Diagram with logarithmic scale on y-axis

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Step 3:

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Step 4: to find factor for different levels of contaminations(Table 4, SKF p. 74)

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p

SKFnaahP

C

naaL

60

10000001

hours435752347

763

125060

100000050L

3

mh10

,

,

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hours26145347

763

125060

10000003L

3

mh10

,

,

Tolerances required for mounting and running of the bearings

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Tolerances and fits

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International Tolerance Grades or IT Grades

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Run-outs

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Total run-outs

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