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Load carrying capacity and life

“Expanded calculation of the adjusted rating life”

Schaeffler introduced the “Expanded calculation of the adjusted rating life” in 1997. This method was standardised for the first time in DIN ISO 281 Appendix 1 and has been a constituent part of the inter­national standard ISO 281 since 2007. As part of the international standardisation work, the life adjustment factor aDIN was renamed as aISO but without any change to the calculation method.

Fatigue theory as a principle

The basis of the rating life calculation in accordance with ISO 281 is Lundberg and Palmgren's fatigue theory which always gives a final rating life.

However, modern, high quality bearings can exceed by a considerable margin the values calculated for the basic rating life under favourable operating conditions. Ioannides and Harris have developed a further model for fatigue in rolling contact that expands on the Lundberg and Palmgren theory and gives a better description of the performance capability of modern bearings.

Values which must be taken into account in the “Expanded calculation of the adjusted rating life”

The method “Expanded calculation of the adjusted rating life” takes account of the following influences:

  • the bearing load
  • the fatigue limit of the material
  • the extent to which the surfaces are separated by the lubricant
  • the cleanliness in the lubrication gap
  • additives in the lubricant
  • the internal load distribution and frictional conditions in the bearing

The influencing factors, especially those relating to contamination, are extremely complex. A great deal of experience is essential for an accurate assessment. As a result, please consult Schaeffler for further advice.

The tables and diagrams in this chapter can only give guide values.

Dimensioning of rolling bearings

The required size of a rolling bearing is dependent on the demands made on its:

  • rating life
  • load carrying capacity
  • operational reliability

Dynamic load carrying capacity and life

Basic dynamic load ratings

The dynamic load carrying capacity is described in terms of the basic dynamic load ratings. The basic dynamic load ratings are based on DIN ISO 281.

The basic dynamic load ratings for rolling bearings are matched to empirically proven performance standards published in previous FAG and INA catalogues.

The fatigue behaviour of the material determines the dynamic load carrying capacity of the rolling bearing.

Dynamic load carrying capacity

The dynamic load carrying capacity is described in terms of the basic dynamic load rating and the basic rating life.

Factors influencing the fatigue life

The fatigue life is dependent on:

  • the load
  • the operating speed
  • the statistical probability of the first appearance of failure

Basic dynamic load rating C

The basic dynamic load rating C applies to rotating rolling bearings. It is:

  • a constant radial load Cr for radial bearings
  • a constant, concentrically acting axial load Ca for axial bearings

The basic dynamic load rating C is that load of constant magnitude and direction which a sufficiently large number of apparently identical bearings can endure for a basic rating life of one million revolutions.

Calculation of the rating life

Calculation methods

The methods for calculating the rating life are:

Basic rating life

L10 or L10h

The basic rating life in millions of revolutions (L10) is determined in accordance with ➤ Equation, the basic rating life in operating hours (L10h) is determined in accordance with ➤ Equation.

Rating life in revolutions

Rating life in operating hours

Legend

L10 106

The basic rating life in millions of revolutions, that is reached or exceeded by 90% of a sufficiently large number of apparently identical bearings before the first indications of material fatigue appear

L10h h

The basic rating life in operating hours, that is reached or exceeded by 90% of a sufficiently large number of apparently identical bearings before the first indications of material fatigue appear

C N

Basic dynamic load rating, see product tables

P N

Equivalent dynamic bearing load

p -

Life exponent; for roller bearings: p = 10/3 for ball bearings: p = 3

n min-1

Operating speed (nominal speed)

Equivalent dynamic bearing load

The basic rating life L10 in accordance with ➤ Equation is defined for a load of constant magnitude acting in a constant direction. In the case of radial bearings, this is a purely radial load, while in the case of axial bearings it is a purely axial load.

Equivalent dynamic load P is identical to the combined load occurring in practice

If the load and speed are not constant, equivalent operating values can be determined that induce the same fatigue as the actual loading conditions.

Equivalent operating values for variable load and speed ➤ section.

Equivalent dynamic radial bearing load

The equivalent dynamic load P on a bearing subjected to combined load (with a radial and axial load) is calculated in accordance with ➤ Equation.

Equivalent dynamic radial bearing load

Legend

P N

Equivalent dynamic radial bearing load

X -

Radial load factor; see product tables

Fr N

Radial load

Y -

Axial load factor; see product tables

Fa N

Axial load

The calculation in accordance with ➤ Equation cannot be applied to radial needle roller bearings, axial needle roller bearings and axial cylindrical roller bearings. Combined loads are not permissible with these bearings.

For radial needle roller bearings ➤ Equation, for axial bearings ➤ Equation.

Equivalent dynamic radial bearing load

Legend

P N

Equivalent dynamic radial bearing load

Fr N

Radial load

Equivalent dynamic axial bearing load

In axial bearings with α = 90°, only axial loads are possible

Axial deep groove ball bearings, axial cylindrical roller bearings, axial needle roller bearings and axial tapered roller bearings with the nominal contact angle α = 90° can only support purely axial forces. For concentric axial load ➤ Equation.

Equivalent dynamic axial bearing load

Legend

Pa N

Equivalent dynamic axial bearing load

Fa N

Axial load


In axial bearings with α ≠ 90°, axial and radial loads are possible

Axial angular contact ball bearings, axial spherical roller bearings and axial tapered roller bearings with the nominal contact angle α ≠ 90° can support not only an axial force Fa but also a radial force Fr. The equivalent dynamic axial load Pa is thus determined in accordance with ➤ Equation.

Equivalent dynamic axial bearing load

Legend

Pa N

Equivalent dynamic axial bearing load

X -

Radial load factor; see product tables

Fr N

Radial load

Y -

Axial load factor; see product tables

Fa N

Axial load

Expanded adjusted rating life

The calculation of the expanded adjusted rating life Lnm was standardised for the first time in DIN ISO 281 Appendix 1 and included in the global standard ISO 281 in 2007. It replaces the previously used adjusted rating life Lna. Computer-aided calculation to DIN ISO 281 Appendix 4 has been specified since 2008 in ISO/TS 16281 and standardised in DIN 26281 since 2010.

The expanded adjusted rating life Lnm is calculated in accordance with ➤ Equation.

Expanded adjusted rating life

Legend

Lnm 106

Expanded adjusted rating life in millions of revolutions in accordance with ISO 281:2007

a1 -

Life adjustment factor for a requisite reliability other than 90% ➤ Table

aISO -

Life adjustment factor for operating conditions

κ -

Viscosity ratio

eC -

Life adjustment factor for contamination

Cu kN

Fatigue limit load; see product tables

C kN

Basic dynamic load rating; see product tables

P kN

Equivalent dynamic bearing load

p -

Life exponent

Fatigue limit load Cu

The fatigue limit load Cu in accordance with ISO 281 is defined as the load below which, under laboratory conditions, no fatigue occurs in the material. The fatigue limit load Cu serves as a calculation value for determining the life adjustment factor aISO and not as a design criterion. With poor lubrication or contamination of the lubricant in particular, it is also possible for the material to undergo fatigue at loads which are significantly below the fatigue limit load Cu.

Life adjustment factor a1

The values for the life adjustment factor a1 were redefined in ISO 281:2007 and differ from the previous data ➤ Table.

Life adjustment factor a1

Requisite reliability

Expanded adjusted
rating life

Life adjustment factor

%

Lnm

a1

90

L10m

1

95

L5m

0,64

96

L4m

0,55

97

L3m

0,47

98

L2m

0,37

99

L1m

0,25

99,2

L0,8m

0,22

99,4

L0,6m

0,19

99,6

L0,4m

0,16

99,8

L0,2m

0,12

99,9

L0,1m

0,093

99,92

L0,08m

0,087

99,94

L0,06m

0,08

99,95

L0,05m

0,077

Life adjustment factor aISO

Influences on the life adjustment factor

The standardised method for calculating the life adjustment factor aISO essentially takes account of:

  • the load on the bearing
  • the lubrication conditions (viscosity and type of lubricant, speed, bearing size, additives)
  • the fatigue limit of the material
  • the type of bearing
  • the residual stress in the material
  • the environmental conditions
  • contamination of the lubricant

Life adjustment factor for operating conditions

Legend

aISO -

Life adjustment factor for operating conditions ➤ Figure to ➤ Figure

eC -

Life adjustment factor for contamination ➤ Table

Cu N

Fatigue limit load; see product tables

P N

Equivalent dynamic bearing load

κ -

Viscosity ratio ➤ link For κ > 4 calculation should be carried out using κ = 4. This calculation method cannot be used for κ < 0,1

Taking account of EP additives in the lubricant

In accordance with ISO 281, EP additives in the lubricant can be taken into consideration in the following way:

  • For a viscosity ratio κ < 1 and a contamination factor eC ≧ 0,2, calculation can be carried out using the value κ = 1 for lubricants with EP additives that have proven effective. Under severe contamination (contamination factor eC < 0,2), the effectiveness of the additives under these contamination conditions must be demonstrated. The effectiveness of the EP additives can be demonstrated in the actual application or on a rolling bearing test rig FE8 to DIN 51819-1.
  • If the EP additives are proven effective and calculation is carried out using the value κ = 1, the life adjustment factor must be restricted to aISO ≦ 3. If the value aISO calculated for the actual value κ is greater than 3, this value can be used in calculation

For practical purposes, the life adjustment factor should be restricted to aISO ≦ 50. This limit value also applies if eC · Cu/P > 5. For a viscosity ratio κ > 4, the value κ = 4 should be used; if κ < 0,1, the calculation is not valid.

The life adjustment factor aISO can – depending on the bearing type – be determined from ➤ Figure to ➤ Figure.

Life adjustment factor aISO for radial roller bearings

aISO = life adjustment factor

Cu = fatigue limit load

eC = contamination factor

P = equivalent dynamic bearing load

κ = parameter for the lubrication regime (viscosity ratio)

Life adjustment factor aISO for axial roller bearings

aISO = life adjustment factor

Cu = fatigue limit load

eC = contamination factor

P = equivalent dynamic bearing load

κ = parameter for the lubrication regime (viscosity ratio)

Life adjustment factor aISO for radial ball bearings

aISO = life adjustment factor

Cu = fatigue limit load

eC = contamination factor

P = equivalent dynamic bearing load

κ = parameter for the lubrication regime (viscosity ratio)

Life adjustment factor aISO for axial ball bearings

aISO = life adjustment factor

Cu = fatigue limit load

eC = contamination factor

P = equivalent dynamic bearing load

κ = parameter for the lubrication regime (viscosity ratio)

Viscosity ratio κ

The viscosity ratio κ is an indication of the quality of lubricant film formation ➤ Equation.

Viscosity ratio

Legend

κ -

Viscosity ratio

ν mm2/s

Kinematic viscosity of the lubricant at operating temperature

ν1 mm2/s

Reference viscosity of the lubricant at operating temperature


Reference viscosity

The reference viscosity ν1 is determined from the mean bearing diameter dM = (D + d)/2 and the operating speed n ➤ Figure.

Nominal viscosity

The nominal viscosity of the oil at +40 °C is determined from the required operating viscosity ν and the operating temperature ϑ, ➤ Figure. In the case of greases, ν is the operating viscosity of the base oil.

In the case of heavily loaded bearings with a high proportion of sliding contact, the temperature in the contact area of the rolling elements may be up to 20 K higher than the temperature measured on the stationary ring (without the influence of any external heat sources).

Taking account of EP additives in calculation of the expanded adjusted rating life Lnm ➤ link.

ν1 for n < 1 000 min-1 or n ≧ 1 000 min-1

The reference viscosity ν1 is calculated for n < 1 000 min-1 in accordance with ➤ Equation, for n ≧ 1 000 min-1 in accordance with ➤ Equation. By differentiating between these cases, the effect of starvation at high speeds is taken into account.

Reference viscosity

Reference viscosity

Legend

ν1 mm2/s

Reference viscosity of the lubricant at operating temperature

n min-1

Operating speed

dM mm

Mean bearing diameter dM = (D + d)/2


ν1 for synthetic oils

In accordance with ISO 281:2007, the equations ➤ Equation and ➤ Equation can also be used in approximate terms for synthetic oils, such as oils based on synthetic hydrocarbons (SHC) for example.

Reference viscosity ν1

ν1 = reference viscosity

dM = mean bearing diameter; (d + D)/2

n = operating speed

ν/ϑ diagram for mineral oils

ν = operating viscosity

ϑ = operating temperature

ν40 = viscosity at +40 °C

Life adjustment factor for contamination

Contamination factor eC

The life adjustment factor for contamination eC takes account of the influence of contamination in the lubrication gap on the rating life ➤ Table.

The rating life is reduced by solid particles in the lubrication gap and is dependent on:

  • the type, size, hardness and number of particles
  • the relative lubrication film thickness
  • the bearing size

Due to the complex interactions between these influencing factors, it is only possible to give approximate guide values. The values in the tables are valid for contamination by solid particles (factor eC). No account is taken of other contamination such as that caused by water or other fluids. Under severe contamination (eC → 0) the bearings may fail due to wear. In this case, the operating life is substantially less than the calculated life.

➤ Table shows guide values for the contamination factor eC. The values are given in DIN ISO 281. An aid to selecting the appropriate cleanliness class is given in DIN ISO 281 Appendix 3. This appendix also gives guidance on achieving the individual cleanliness classes.

Guide values for the contamination factor eC

Contamination

Contamination factor eC

dM < 100 mm

dM ≧ 100 mm

from

to

from

to

Very high cleanliness:

  • Particle size within the order of magnitude
    of the lubricant film thickness
  • Laboratory conditions

1

1

High cleanliness:

  • Oil filtered through extremely fine filter
  • Sealed, greased bearings

0,8

0,6

0,9

0,8

Standard cleanliness:

  • Oil filtered through fine filter

0,6

0,5

0,8

0,6

Slight contamination:

  • Slight contamination of oil

0,5

0,3

0,6

0,4

Typical contamination:

  • Bearing contaminated by wear debris
    from other machine elements

0,3

0,1

0,4

0,2

Heavy contamination:

  • Bearing environment is heavily contaminated
  • Bearing environment inadequately sealed

0,1

0

0,1

0

Very heavy contamination

0

0

dM = mean bearing diameter (d + D)/2

Requisite minimum load

In order to prevent damage due to slippage, a minimum radial or axial load must be applied to the bearings ➤ Table.

Recommended minimum radial and axial load for rolling bearings

Bearing type

Recommended minimum load

Deep groove ball bearings

P > C0 /100

Angular contact ball bearings

P > C0 /100

Self-aligning ball bearings

P > C0 /100

Cylindrical roller bearings

P > C0 /60

Tapered roller bearings

P > C0 /60

Barrel roller bearings

P > C0 /60

Spherical roller bearings

P > C0 /100

Toroidal roller bearings,
full complement or with cage

P > C0 /75

Needle roller bearings

P > C0 /60

Axial deep groove ball bearings

Axial cylindrical roller bearings 1)

Axial needle roller bearings

Axial spherical roller bearings2)

  1. Factor ka ➤ Table.
  2. Factor ka ➤ Table.

Factor ka for axial cylindrical roller bearings

Series

Factor

ka

K811

1,4
K812 0,9
K893 0,7
K894 0,5


Factor ka for axial spherical roller bearings

Series

Factor

ka

292..-E

0,6

293..-E1(E)

0,9

294..-E1(E)

0,7

Equivalent operating values

Equivalent operating values for non-constant loads and speeds

The rating life equations assume a constant bearing load P and constant bearing speed n. If the load and speed are not constant, equivalent operating values can be determined that induce the same fatigue as the actual loading conditions.

The operating values calculated here already take account of the life adjustment factors aISO. They must not be applied again when calculating the adjusted rating life.

Variable load and speed

If the load and speed vary over a time period T, the speed n and the equivalent bearing load P ➤ Equation and ➤ Equation are calculated as follows. If only a basic rating life is to be calculated, the terms 1/aISO can be omitted from the equations ➤ Equation to ➤ Equation.

Equivalent speed

Equivalent bearing load

Variation in steps

If the load and speed vary in steps over a time period T, n and P are calculated as follows ➤ Equation and ➤ Equation.

Equivalent speed

Equivalent bearing load

Variable load at constant speed

If the function F describes the variation in the load over a time period T and the speed is constant, P is calculated as follows ➤ Equation.

Equivalent bearing load

Load varying in steps at constant speed

If the load varies in steps over a time period T and the speed is constant, P is calculated as follows ➤ Equation.

Equivalent bearing load

Constant load at variable speed

If the speed varies but the load remains constant, the following applies ➤ Equation.

Equivalent speed

Constant load with speed varying in steps

If the speed varies in steps, the following applies ➤ Equation.

Equivalent speed

Swivel motion

The equivalent speed is calculated in accordance with ➤ Equation.

If the swivel angle is smaller than twice the pitch angle of the rolling elements, there is a risk of false brinelling.

Equivalent speed

Legend

n min-1

Equivalent speed

T min

Time period under consideration

P N

Equivalent bearing load

p -

Life exponent;
for roller bearings: p = 10/3
for ball bearings: p = 3

aISO i,
aISO(t)
-

Life adjustment factor aISO for current operating condition

ni, n(t) min-1

Bearing speed for current operating condition

qi %

Duration of operating condition as a proportion of the total operating period;
qi = (Δti/T) · 100

Fi, F(t) N

Bearing load during the current operating condition

nosc min-1

Frequency of swivel motion

φ °

Swivel angle ➤ Figure

Swivel motion, swivel angle

Complete swivel motion =  2 · φs

φs = swivel angle of the bearing

φa = swivel angle at which every point on the outer raceway is overrolled

Guide values for dimensioning

Guide values for rating life

The values for the recommended rating life are guide values for normal operating conditions ➤ Table to ➤ Table. In addition, the tables give the operating life values that are usually achieved in practice at various mounting locations.

Do not overspecify the bearings, otherwise it may not be possible to observe the requisite minimum load. Recommended minimum load ➤ section and product chapter.

Motor vehicles

Mounting location

Recommended rating life

h

Ball bearings

Roller bearings

from

to

from

to

Motorcycles

400

2 000

400

2 400

Passenger car powertrains

500

1 100

500

1 200

Passenger car gearboxes
protected against contamination

200

500

200

500

Passenger car wheel bearings

1400

5  00

1 500

7 000

Light commercial vehicles

2 000

4 000

2 400

5 000

Medium commercial vehicles

2 900

5 300

3 600

7 000

Heavy commercial vehicles

4 000

8 800

5 000

12 000

Buses

2 900

11 000

3 600

16 000

Internal combustion engines

900

4 000

900

5 000

Rail vehicles

Mounting location

Operating life

Millions of kilometres

from

to

Wheelset bearings for freight wagons

0,1

0,1

Urban transport vehicles

1

2

Passenger carriages

2

3

Goods wagons

1

2

Tipper wagons

1

2

Powered units

2

3

Locomotives, external bearings

2

4

Locomotives, internal bearings

2

4

Shunting and industrial locomotives

0,5

1

Gearboxes for rail vehicles

0,5

2

Shipbuilding

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Marine thrust bearings

20 000

50 000

30 000

80 000

Marine shaft bearings

50 000

200 000

30 000

80 000

Large marine gearboxes

14 000

46 000

20 000

75 000

30 000

80 000

Small marine gearboxes

4 000

14 000

5 000

20 000

5 000

20 000

Boat propulsion systems

1 700

7 800

2 000

10 000

2 000

10 000

Agricultural machinery

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Tractors

1 700

4 000

2 000

5 000

5 000

10 000

Self-propelled machinery

1 700

4 000

2 000

5 000

2 000

6 000

Seasonal machinery

500

1 700

500

2 000

500

2 000

Construction machinery

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Dozers, loaders

4 000

7800

5 000

10 000

5 000

10 000

Excavators,
travelling gear

500

1 700

500

2 000

500

2 000

Excavators, slewing gear

1 700

4 000

2 000

5 000

2 000

5 000

Vibratory road rollers,
unbalance generators

1 700

4 000

2 000

5 000

5 000

30 000

Vibrator bodies

500

1 700

500

2 000

500

2 000

Electric motors

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Electric motors
for household appliances

1 700

4 000

500

1000

Series motors

21 000

32 000

35 000

50 000

20 000

30 000

Large motors

32 000

63 000

50 000

110 000

40 000

50 000

Wind energy generators

100 000

200 000

Generators

40 000

50 000

continued ▼

Electric motors

Mounting location

Recommended rating life

Operating life

h

km

Ball bearings

Roller bearings

from

to

from

to

from

to

Electric traction motors for 14 000 21 000 20 000 35 000
mainline operations

2 000 000

2 500 000

trams

1000 000

1000 000

suburban and underground trains

1500 000

1500 000

continued ▲

Rolling mills, steelworks equipment

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Rolling mill frames

500

14 000

500

20 000

2 000

10 000

Rolling mill gearboxes

14 000

32 000

20 000

50 000

20 000

40 000

Roller tables

7 800

21 000

10 000

35 000

20 000

40  000

Centrifugal casting machines

21 000

46 000

35 000

75 000

30 000

60 000

Machine tools

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Headstock spindles,
milling spindles

14 000

46  000

20 000

75 000

10 000

30 000

Drilling spindles

14 000

32  000

20 000

50 000

1 000

20 000

External grinding spindles

7 800

21  000

10 000

35 000

10 000

20  000

Hole grinding spindles 500 2 000

Workpiece spindles
in grinding machines

21 000

63  000

35 000

110 000

20 000

30 000

Machine tool gearboxes

14 000

32 000

20 000

50 000

10 000

20 000

Presses, flywheels

21 000

32 000

35 000

50 000

20 000

30  000

Presses, eccentric shafts

14 000

21 000

20 000

35 000

10 000

20 000

Electric tools and
compressed air tools

4 000

14 000

5 000

20 000

100

200

Woodworking machinery

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Milling spindles and cutter blocks

14 000

32 000

20 000

50 000

10 000

20 000

Saw frames,
main bearings
35 000 35 000
Saw frames,
connecting rod bearings
10 000 20 000

Circular saws

4 000

14 000

5 000

20 000

10 000

20 000

Gearboxes in general machine building

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Universal gearboxes

4 000

14 000

5 000

20 000

5 000

20 000

Geared motors

4 000

14 000

5 000

20 000

5 000

20 000

Large gearboxes,
stationary

14 000

46 000

20 000

75  000

20 000

80 000

Conveying equipment

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Belt drives,
mining

75 000

150 000

10 000

30 000

Conveyor belt rollers,
mining

46 000

63 000

75 000

110 000

10 000

30 000

Conveyor belt rollers,
general

7 800

21000

10 000

35 000

10 000

30 000

Belt drums

50 000

75 000

10 000

30 000

Bucket wheel excavators,
travel drive

7 800

21 000

10 000

35 000

5 000

15 000

Bucket wheel excavators,
bucket wheel

75 000

200 000

30 000

50 000

Bucket wheel excavators,
bucket wheel drive

46 000

83 000

75 000

150 000

30 000

50 000

Winding cable sheaves

32 000

46 000

50 000

75 000

50 000

80 000

Sheaves

7 800

21 000

10 000

35 000

8 000

30 000

Tunnel-boring machines:
drill head main bearings

5 000

10 000

Pumps, fans, compressors

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Ventilators, fans

21 000

46 000

35 000

75 000

20 000

100 000

Large fans

32 000

63 000

50 000

110 000

>10 000

Piston pumps

21 000

46 000

35 000

75 000

20 000

50 000

Centrifugal pumps

14 000

46 000

20 000

75 000

20 000

50 000

Hydraulic axial and
radial piston engines

500

7 800

500

10 000

1 000

20 000

Gear pumps

500

7 800

500

10 000

1 000

20 000

Compressors

4 000

21 000

5 000

35 000

30 000

80 000

Centrifuges, stirrers

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Centrifuges

7 800

14 000

10 000

20 000

40 000

60 000

Large stirrers

21 000

32 000

35 000

50 000

40 000

50 000

Textile machinery

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Spinning machines,
spinning spindles

21 000

46 000

35 000

75 000

10 000

50 000

Weaving and
knitting machines

14 000

32 000

20 000

50 000

10 000 50 000

Plastics processing

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Plastics worm extruders

14 000

21 000

20 000

35 000

20 000

100 000

Rubber and
plastics calenders

21 000

46 000

35 000

75 000

20 000 100 000

Crushers, mills, screens

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Jaw crushers

20 000

35 000

25 000

40 000

Gyratory crushers,
roll crushers

20 000

35 000

25 000 40 000

Rigid hammer mills,
hammer mills,
impact crushers

50 000

110 000

40 000

40 000

Tube mills

50 000

100 000

100 000

100 000

Vibration grinding mills

5 000

20 000

30 000

60 000

Grinding track mills

50 000

110 000

60 000

100 000

Vibrating screens

10 000

20 000

10 000

30 000

Briquette presses

35 000

50 000

40 000

40 000

Rotary kiln radial
support rollers

50 000

110 000

100 000

Roller presses

40 000

40 000

Paper and printing machinery

Mounting location

Recommended rating life

Operating life

h

h

Ball bearings

Roller bearings

from

to

from

to

from

to

Paper machinery,
wet section

110 000

150 000

50 000

100 000

Paper machinery,
dry section
150 000 250  000
Guide rolls 50 000 120 000 150 000 250 000
Dryer rolls 50 000 150 000 150 000 250 000
M.G. cylinders 50 000 200 000 150 000 250 000

Paper machinery,
refiners

80 000

120 000

50  000

100 000

Paper machinery,
calenders

80 000

110 000

50 000

100 000

Printing machinery

32 000

46 000

50 000

75 000

30 000

60 000

Static load carrying capacity

Plastic deformation limits the static load carrying capacity

If high, static or shock loads occur, the raceways and rolling elements may undergo plastic deformation. This deformation limits the static load carrying capacity of the rolling bearing with respect to the permissible noise level during operation of the bearing.

Basic static load rating

If a rolling bearing operates with only infrequent rotary motion or completely without rotary motion, its size is determined in accordance with the basic static load rating C0.

In accordance with DIN ISO 76, this is:

  • a constant radial load C0r for radial bearings
  • a constant, concentrically acting axial load C0a for axial bearings

The basic static load rating C0 is that load under which the Hertzian pressure at the most heavily loaded point between the rolling elements and raceways reaches the following values:

  • for roller bearings, 4 000 N/mm2
  • for ball bearings, 4 200 N/mm2
  • for self-aligning ball bearings, 4 600 N/mm2

Under normal contact conditions, this load causes a permanent deformation at the contact points of approx. 1/10 000 of the rolling element diameter.

Static load safety factor

In addition to dimensioning on the basis of the fatigue life, it is advisable to check the static load safety factor. Guide values and shock loads occurring during operation in accordance with ➤ Table must be taken into consideration.

Static load safety factor

Legend

S0 -

Static load safety factor; guide values ➤ Table

C0r, C0a N

Basic radial or axial static load rating; see product tables

P0r, P0a N

Radial or axial equivalent static bearing load ➤ Equation

Guide values for static load safety factor

Guide values for the requisite static load safety factor S0 are given in DIN ISO 76:2009-01 and in ➤ Table. Guide values for axial spherical roller bearings and high precision bearings: see corresponding product description. For drawn cup needle roller bearings, S0 ≧ 3 is necessary.

Static load safety factor S0 for ball and roller bearings – guide values

Operating conditions and application

Static load safety factor

S0

min.

Ball bearings

Roller bearings

Low-noise, smooth running, free from vibrations, high rotational accuracy

2

3

Normal, smooth running, free from vibrations, normal rotational accuracy

1

1,5

Pronounced shock loading1)

1,5

3

  1. If the order of magnitude of the shock loading is not known, the values used for S0 should be at least 1,5. If the order of magnitude of the shock loading is known precisely, lower values are possible.

Equivalent static bearing load

The equivalent static load P0 is a calculated value. It corresponds to a radial load in radial bearings and a concentric axial load in axial bearings.

P0 induces the same load at the centre point of the most heavily loaded contact point between the rolling element and raceway as the combined load occurring in practice.

Equivalent static bearing load

Legend

P0 N

Equivalent static bearing load

X0 N

Radial load factor; see product tables or product description

Fr, Fa N

Largest radial or axial load present

Y0 N

Axial load factor; see product tables or product description

The calculation cannot be applied to radial needle roller bearings, axial needle roller bearings and axial cylindrical roller bearings. Combined loads are not permissible with these bearings.

In the case of radial needle roller bearings and all radial cylindrical roller bearings: P0 = F0r.
For axial needle roller bearings and axial cylindrical roller bearings: P0 = F0a.

Operating life

The operating life is defined as the life actually achieved by the bearing. It may differ significantly from the calculated life.

Possible factors influencing the operating life

This may be due to wear or fatigue as a result of:

  • deviating operating data
  • misalignments between the shaft and housing
  • insufficient or excessive operating clearance
  • contamination
  • insufficient lubrication
  • excessive operating temperature
  • oscillating bearing movement with very small swivel angles (false brinelling)
  • high vibration and false brinelling
  • very high shock loads (static overloading)
  • prior damage during mounting

The operating life cannot be calculated

Due to the wide variety of possible installation and operating conditions, it is not possible to precisely predetermine the operating life. The most reliable way of arriving at a close estimate is by comparison with similar applications.