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Rolling element bearings -design

Prof NDL Burger

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Rolling element bearingKNOW AND

UNDERSTAND YOURCATALOGUE

RESULTS IF YOU DONOT

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Rolling element bearing

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Rolling element bearing Size of bearing is determined according to the

load capacity and the life of the bearing Basic load rating Co Static load rating C - Dynamic load rating

C express the life for 1 000 000 cycles with areliability of 90% - ISO standard

Co Used to determine the static load carrying

capability of the bearing slow rotation or staticloading in big machines Maximum is specified at a point of deformation of

0.0001 x rolling element diameter

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Rolling element bearing Failures are normally Wear Corrosion

Seal failure not necessary due to fatigue Overloading (pitting)

Equivalent dynamic load P = XVFr + yFa Fr actual radial load X radial load factor Fa actual axial load Y Axial load factor V = 1 when inner ring rotates V = 1.2 when outer ring rotates

The equation for P isgeneric and the

actual values for Xand Y must beobtained for eachtype of bearing

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Back toexample

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Rolling element bearing

Equation can beused to determine

first bearing

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Rolling element bearing

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Rolling element bearing

a2 1 based on SKF/NTN materials

Can replace a2 and a3with a23 -

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Rolling element bearinga1

a3

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Rolling element bearing

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Rolling element bearing

Back to example

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Rolling element bearing

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Rolling element bearingDeep grove ball bearings

Back to

example

EQUIVALENT DYNAMIC BEARING LOAD

For single bearings and bearing pairs arranged

in tandem

P = Fr WHEN Fa/Fr < e

P = XVFr + YFa WHEN Fa/Fr > e

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Rolling element bearing

NB: These equations are bearing type specific

Deep grove ball bearings

Back to example

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Rolling element bearing Design of a rolling element bearing

Determine load on bearing radial and axial

Chose bearing

Check bearing for L10

life

Check bearing for static loading

Check bearing for Lna life

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Rolling element bearing Example

Fa = 1500 N Fr = 10 200 N

N = 1200 rpm

Inner ring rotates L10h (required) = 200

hours

Shaft diameter = 30 mm Normal loading

Normal silent operation

1500 N

10 200 N

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Rolling element bearing -

example Chose bearing 6006

C = 13.2kN, Co = 8.3kN (Bearing table) Fa/Co = 1500/8300 = 0.18

e = 0.325, X = 0.56, Y = 1.31 Fa/VFr = 1500/10 200 = 0.147 < e

Equivalent dynamic load

P = Fr = 10 200 N

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Rolling element bearing L10 = (C/P)

p= (13200/10200)3 = 2.16 x 106

cycles L10H = (1x10

6/60n)(C/P)p = 30 hours < 200hours

What now?

Redo for 6406 (Homework)

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Rolling element bearing - static Static

So = 1 Rolling element bearing

Po = 0.6 Fr + 0.5 Fa = 0.6x10200 + 0.5x1500Equivalent static load

= 6870 N < Fr Po = Fr = 10 200N

Co = 8300 N

So = Co/Po = 8300/10 200 = 0.81 < 1 Design is not OK (Re check with 6406)

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Rolling element bearing -

homework If the bearing operates at 80C determine

the Lna life (hours) of the bearing for areliability of 95%