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Principles Rolling bearings Shaft guidance systems Track roller guidance systems Monorail guidance systems
Top
Schaeffler KG 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.
Top
Fatigue theory as aprinciple
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
of fatigue in rolling contact that expands on the Lundberg/Palmgren theory
and gives a better description of the performance capability of modern
bearings.
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 the Engineering Service of Schaeffler Group
Industrial should be consulted for further advice.
The tables and diagrams can only give guide values.
Top
Dimensioning ofrolling bearings
The required size of a rolling bearing is dependent on the demands made
on its:
rating life
load carrying capacity
operational reliability.
Top
Dynamic loadcarrying capacity and life
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 and those published in previous
FAG and INA catalogues.
The fatigue behaviour of the material determines the dynamic load carrying
capacity of the rolling bearing.
Load carrying capacity and lifeFatigue theory as a principleDimensioning of rolling bearingsDynamic load carrying capacity and lifeCalculation of the rating lifeEquivalent operating valuesRequired rating lifeOperating lifeAxial load carrying capacity of cylindrical roller bearingsStatic load carrying capacity
medias® professional – Product catalogue
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The dynamic load carrying capacity is described in terms of the basic
dynamic load rating and the basic rating life.
The fatigue life is dependent on:
the load
the operating speed
the statistical probability of the first appearance of failure.
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.
Top
Calculation of the rating life The methods for calculating the rating life are:
basic rating life L10 and L10h to ISO 281, see link
adjusted rating life Lna to DIN ISO 281:1990 (no longer a constituent part
of ISO 281), see link
expanded adjusted rating life Lnm to ISO 281, see link.
Basic rating life The basic rating life L10 and L10h is calculated as follows:
L10 106 revolutionsThe basic rating life in millions of revolutions is the life reached or exceeded by 90% ofa sufficiently large group of apparently identical bearings before the first evidence ofmaterial fatigue developsL10h hThe basic rating life as defined for L10 but expressed in operating hoursC NBasic dynamic load ratingP NEquivalent dynamic bearing load for radial and axial bearingspLife exponent; for roller bearings: p = 10/3 for ball bearings: p = 3n min–1
Operating speed.
Equivalent dynamic load
The equivalent dynamic load P is a calculated value. This value is constant
in size and direction; it is a radial load for radial bearings and an axial load
for axial bearings.
The load value P gives the same rating life as the combined load occurring
in practice.
P NEquivalent dynamic bearing loadFr NRadial dynamic bearing loadFa NAxial dynamic bearing loadXRadial factor given in the dimension tables or product descriptionYAxial factor given in the dimension tables or product description.
This 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.
TopAdjusted rating life
The adjusted rating life Lna can be calculated if, in addition to the load and
speed, other influences are known such as:
special material characteristics
lubrication
or
if a requisite reliability other than 90% is specified.
This calculation method was replaced in ISO 281:2007 by the calculation of
the expanded adjusted rating life Lnm, see link.
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Lna 106 revolutionsAdjusted rating life for special material characteristics and operating conditions with arequisite reliability of (100 – n) %L10 106 revolutionsBasic rating lifea1Life adjustment factor for a requisite reliability other than 90%. In ISO 281:2007, thevalues for the life adjustment factor a1 have been redefined, see tablea2Life adjustment factor for special material characteristics. For standard rolling bearingsteels: a2 = 1a3Life adjustment factor for special operating conditions; in particular lubrication, Figure 1.
The viscosity ratio κ is determined according to the formula on link.
Good cleanliness and suitable
additives
Very high cleanliness and low load
Contamination in the lubricant
a3 = life adjustment factor
κ = viscosity ratio
Figure 1
Life adjustment factor a3
Viscosity ratio The viscosity ratio κ is an indication of the quality of lubricant film formation:
ν mm2s–1
Kinematic viscosity of the lubricant at operating temperatureν1 mm2s–1
Reference viscosity of the lubricant at operating temperature.
The reference viscosity ν1 is determined from the mean bearing diameter
dM = (D + d)/2 and the operating speed n, Figure 2.
The nominal viscosity of the oil at +40 °C is determin ed from the required
operating viscosity ν and the operating temperature ϑ, Figure 3. 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).
Taking account of EP additives in calculation of the expanded adjusted
rating life Lnm: see link.
ν1 = reference viscosity
dM = mean bearing diameter
n = speed
Figure 2
Reference viscosity ν1
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ν = operating viscosity
ϑ = operating temperature
ν40 = viscosity at +40 °C
Figure 3
V/T diagram for mineral oils
TopExpanded adjusted rating life
The calculation of the expanded adjusted rating life Lnm was standardised
in DIN ISO 281 Appendix 1. Since 2007, it has been standardised in the
worldwide standard ISO 281. Computer-aided calculation in accordance
with DIN ISO 281 Appendix 4 has been specified since 2008 in
ISO/TS 16 281.
Lnm is calculated as follows:
Lnm 106 revolutionsExpanded adjusted rating life to ISO 281a1Life adjustment factor for a requisite reliability other than 90%, see tableaISOLife adjustment factor for operating conditionsL10 106 revolutionsBasic rating life, see link.
The values for the life adjustment factor a1 were redefined in ISO 281:2007
and differ from the previous data.
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
The standardised method for calculating the life adjustment factor aISO
essentially takes account of:
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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 in the lubricant.
aISOLife adjustment factor for operating conditions,Figure 4 to Figure 7eCLife adjustment factor for contamination, see tableCu NFatigue limit loadP NEquivalent dynamic bearing loadκ
Viscosity ratio, see linkFor κ > 4, calculation should be carried out using κ = 4.For κ < 0,1, this calculation method cannot be used.
Taking account of EP additives in thelubricant
In accordance with ISO 281, EP additives 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. With severe contamination
(contamination factor eC < 0,2), the effectiveness of the additives under
these contamination conditions must be proven. The effectiveness of the
EP additives can be demonstrated in the actual application or on a
rolling bearing test rig FE 8 to DIN 51 819-1.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 κ is greater than 3, this value can be used in
calculation.
Figure 4
Life adjustment factor aISO
for radial roller bearings
Figure 5
Life adjustment factor aISO
for axial roller bearings
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Figure 6
Life adjustment factor aISO
for radial ball bearings
Figure 7
Life adjustment factor aISO
for axial ball bearings
TopFatigue limit load
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.
TopLife adjustment factor
for contamination
The life adjustment factor for contamination ec takes into consideration the
influence of contamination in the lubrication gap on the rating life, see
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 nature of the interaction between these influencing
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factors, only an approximate guide value can be attained. The values in the
tables are valid for contamination by solid particles (factor eC). They do not
take account 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.
Factor eC
Contamination Factor eC
dM <<<<
100 mm1)dM ≧≧≧≧
100 mm1)
Extreme cleanliness
Particle size within lubricant film
thickness
Laboratory conditions
1 1
High cleanliness
Oil filtered through extremely fine filter
Sealed, greased bearings
0,8 to 0,6 0,9 to 0,8
Standard cleanliness
Oil filtered through fine filter
0,6 to 0,5 0,8 to 0,6
Slight contamination
Slight contamination of oil
0,5 to 0,3 0,6 to 0,4
Typical contamination
Bearing contaminated with abraded
material from other machine elements
0,3 to 0,1 0,4 to 0,2
Heavy contamination
Bearing environment is heavily
contaminated
Bearing arrangement is insufficiently
sealed
0,1 to 0 0,1 to 0
Very heavy contamination 0 0
______
1 dM = mean bearing diameter (d + D)/2.
Top
Equivalent operating values
The rating life formulae 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 conditions.
The equivalent operating values calculated here already take account of
the life adjustment factors a3 or 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 equivalent
bearing load P are calculated as follows:
Variation in steps
If the load and speed vary in steps over a time period T, n and P are
calculated as follows:
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TopVariable 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:
TopLoad varying in steps and
constant speed If the load varies in steps over a time period T and the speed is constant, P
is calculated as follows:
TopConstant load at variable speed If the speed varies but the load remains constant, the following applies:
TopConstant load with
speed varying in steps If the speed varies in steps, the following applies:
TopUnder oscillating bearing motion The equivalent speed is calculated as follows:
The formula is valid only if the angle of oscillation is greater than twice the
angular pitch of the rolling elements. If the angle of oscillation is smaller,
there is a risk of false brinelling.
Figure 8
Angle of oscillation φ
TopSymbols, units and definitions
n min–1
Mean speedT minTime period under considerationP NEquivalent bearing loadpLife exponent;for roller bearings: p = 10/3for ball bearings: p = 3ai, a(t)Life adjustment factor aISO for current operating condition,see linkni, n(t) min–1
Bearing speed for current operating conditionqi %
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Duration of operating condition as a proportion of the total operating period;qi = (∆ti/T) · 100Fi, F(t) NBearing load during the current operating conditionnosc min–1
Frequency of oscillating motionφ °Angle of oscillation, Figure 8.
Top
Required rating life If no information is available on the rating life, the guide values from the
following tables may be used.
Do not overspecify the bearing. If the calculated life is > 60 000 h, this
normally means that the bearing arrangement is overspecified. Pay
attention to the minimum load for the bearings; see the design and safety
guidelines in the product sections.
Motor vehicles
Mounting location Recommended rating life in
h
Ballbearings
Rollerbearings
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 1 400 5 300 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 Recommended rating life in h
Ball bearings Roller bearings
from to from to
Wheelset bearings for freight wagons 7 800 21 000 - -
Tram carriages - - 35 000 50 000
Passenger carriages - - 20 000 35 000
Goods wagons - - 20 000 35 000
Tipper wagons - - 20 000 35 000
Powered units - - 35 000 50 000
Locomotives, external bearings - - 35 000 50 000
Locomotives, internal bearings - - 75 000 110 000
Gearboxes for rail vehicles 14 000 46 000 20 000 75 000
Shipbuilding
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Marine thrust blocks - - 20 000 50 000
Marine shaft bearings - - 50 000 200 000
Large marine gearboxes 14 000 46 000 20 000 75 000
Small marine gearboxes 4 000 14 000 5 000 20 000
Boat propulsion systems 1 700 7 800 2 000 10 000
Agricultural machinery
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Tractors 1 700 4 000 2 000 5 000
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Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Self-propelled machinery 1 700 4 000 2 000 5 000
Seasonal machinery 500 1 700 500 2 000
Construction machinery
Mounting location Recommended rating life in
h
Ball
bearings
Roller
bearings
from to from to
Dozers, loaders 4 000 7 800 5 000 10 000
Excavators, travelling gear 500 1 700 500 2 000
Excavators, slewing gear 1 700 4 000 2 000 5 000
Vibratory road rollers, imbalance
generators
1 700 4 000 2 000 5 000
Vibrator bodies 500 1 700 500 2 000
Electric motors
Mounting location Recommended rating life in
h
Ball bearings Roller bearings
from to from to
Electric motors for household
appliances
1 700 4 000 - -
Series motors 21 000 32 000 35 000 50 000
Large motors 32 000 63 000 50 000 110 000
Electric traction motors 14 000 21 000 20 000 35 000
Rolling mills, steelworks equipment
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Roll stands 500 14 000 500 20 000
Rolling mill gearboxes 14 000 32 000 20 000 50 000
Roller tables 7 800 21 000 10 000 35 000
Centrifugal casting machines 21 000 46 000 35 000 75 000
Machine tools
Mounting location Recommended rating life inh
Ball bearings Roller bearings
from to from to
Headstock spindles, milling spindles 14 000 46 000 20 000 75 000
Drilling spindles 14 000 32 000 20 000 50 000
Grinding spindles 7 800 21 000 10 000 35 000
Workpiece spindles in grinding
machines
21 000 63 000 35 000 110 000
Machine tool gearboxes 14 000 32 000 20 000 50 000
Presses, flywheels 21 000 32 000 35 000 50 000
Presses, eccentric shafts 14 000 21 000 20 000 35 000
Electric tools and compressed air tools 4 000 14 000 5 000 20 000
Woodworking machinery
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Milling spindles and cutter blocks 14 000 32 000 20 000 50 000
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Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Saw frames, main bearings - - 35 000 50 000
Saw frames, connecting rod bearings - - 10 000 20 000
Circular saws 4 000 14 000 5 000 20 000
Gearboxes in
general machine building
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Universal gearboxes 4 000 14 000 5 000 20 000
Geared motors 4 000 14 000 5 000 20 000
Large gearboxes, stationary 14 000 46 000 20 000 75 000
Conveying equipment
Mounting location Recommended rating life inh
Ball bearings Roller
bearings
from to from to
Belt drives, mining - - 75 000 150 000
Conveyor belt rollers, mining 46 000 63 000 75 000 110 000
Conveyor belt rollers, general 7 800 21 000 10 000 35 000
Belt drums - - 50 000 75 000
Bucket wheel excavators, travel drive 7 800 21 000 10 000 35 000
Bucket wheel excavators, bucket wheel - - 75 000 200 000
Bucket wheel excavators, bucket wheel
drive
46 000 83 000 75 000 150 000
Winding cable sheaves 32 000 46 000 50 000 75 000
Sheaves 7 800 21 000 10 000 35 000
Pumps, fans, compressors
Mounting location Recommended rating life inh
Ball bearings Roller bearings
from to from to
Ventilators, fans 21 000 46 000 35 000 75 000
Large fans 32 000 63 000 50 000 110 000
Piston pumps 21 000 46 000 35 000 75 000
Centrifugal pumps 14 000 46 000 20 000 75 000
Hydraulic axial and radial piston
engines
500 7 800 500 10 000
Gear pumps 500 7 800 500 10 000
Compressors 4 000 21 000 5 000 35 000
Centrifuges, stirrers
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Centrifuges 7 800 14 000 10 000 20 000
Large stirrers 21 000 32 000 35 000 50 000
Textile machinery
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Spinning machines, spinning spindles 21 000 46 000 35 000 75 000
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Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Weaving and knitting machines 14 000 32 000 20 000 50 000
Plastics processing
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Plastics worm extruders 14 000 21 000 20 000 35 000
Rubber and plastics calenders 21 000 46 000 35 000 75 000
Crushers, mills, screens
Mounting location Recommended rating life in
h
Ball
bearings
Roller bearings
from to from to
Jaw crushers - - 20 000 35 000
Gyratory crushers, roll crushers - - 20 000 35 000
Rigid hammer mills, hammer mills,
impact crushers
– – 50 000 110 000
Tube mills - - 50 000 100 000
Vibration grinding mills - - 5 000 20 000
Grinding track mills - - 50 000 110 000
Vibrating screens - - 10 000 20 000
Briquette presses - - 35 000 50 000
Rotary furnace track rollers - - 50 000 110 000
Paper and printing machinery
Mounting location Recommended rating life in h
Ball bearings Roller bearings
from to from to
Paper machinery, wet section - - 110 000 150 000
Paper machinery, dry section - - 150 000 250 000
Paper machinery, refiners - - 80 000 120 000
Paper machinery, calenders - - 80 000 110 000
Printing machinery 32 000 46 000 50 000 75 000
Top
Operating life The operating life is defined as the life actually achieved by the bearing. It
may differ significantly from the calculated value.
This may be due to wear or fatigue as a result of:
deviations in operating conditions
misalignment between the shaft and housing
insufficient or excessive operating clearance
contamination
insufficient lubrication
excessive operating temperature
oscillating bearing motion with very small angles of oscillation (false
brinelling)
high vibration and false brinelling
very high shock loads (static overloading)
prior damage during installation.
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.
Top
Axial load carrying capacity Radial cylindrical roller bearings used as semi-locating and locating
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of cylindrical roller bearings bearings can support axial forces in one or both directions in addition to
radial forces.
The axial load carrying capacity is dependent on:
the size of the sliding surfaces between the ribs and the end faces of the
rolling elements
the sliding velocity at the ribs
the lubrication on the contact surfaces
the tilting of the bearing.
Ribs subjected to load must be supported across their entire height.
The permissible axial load Fa per must not be exceeded, in order to avoid
unacceptably high temperatures.
The limiting load Fa max must not be exceeded, in order to avoid
unacceptable pressure at the contact surfaces.
The ratio Fa/Fr must not exceed a value of 0,4. For bearings of TB design,
the value 0,6 is permissible.
Continuous axial loading without simultaneous radial loading is not
permissible.
Bearings of TB design
In the case of bearings of TB design, the axial load carrying capacity has
been significantly improved through the use of new calculation and
manufacturing methods.
Optimum contact conditions between the roller and rib are ensured by
means of a special curvature of the roller end faces. As a result, axial
surface pressures on the rib are significantly reduced and a lubricant film
with improved load-carrying capabilities is achieved. Under normal
operating conditions, wear and fatigue at the rib contact running and roller
end faces is completely eliminated. The axial frictional torque is reduced by
up to 50%. The bearing temperature during operation is therefore
significantly lower.
TopPermissible and
maximum axial load Fa per and Fa max are calculated as follows:
Bearings of standard design
Bearings of TB design
Bearings of standard and TB design
Fa per NPermissible axial loadFa max NAxial limiting loadkSFactor dependent on the lubrication method,see tablekBFactor dependent on the bearing series,see tabledM mmMean bearing diameter (d + D)/2n min–1
Operating speed.
Misalignment of the bearing
Misalignment caused by shaft deflection for example, may lead to
alternating stresses on the inner ring ribs. In this instance, the axial load
must be restricted to Fas in accordance with the formula where the bearing
is tilted up to a maximum of 2 angular minutes.
For more severe tilting, a separate strength analysis is required.
Factor kS
for lubrication method
Lubrication methods1) Factor
kS
Minimal heat dissipation, drip feed oil lubrication, oil mist
lubrication, low operating viscosity (ν < 0,5 · ν1)
7,5 to
10
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Lubrication methods1) Factor
kS
Little heat dissipation, oil sump lubrication, oil spray lubrication,
low oil flow
10 to
15
Good heat dissipation, recirculating oil lubrication (pressure oil
lubrication)
12 to
18
Very good heat dissipation,
recirculating oil lubrication with oil cooling,
high operating viscosity (ν > 2 · ν1)
16 to
24
______
1
The precondition for these kS values is the reference viscosity ν1 according to the
section Oil lubrication. Doped oils should be used such as CLP (DIN 51 517) and
HLP (DIN 51 524) of ISO-VG classes 32 to 460 and ATF oils (DIN 51 502) and
gearbox oils (DIN 51 512) of SAE viscosity classes 75 W to 140 W.
Bearing factor kB
Series FactorkB
SL1818, SL0148 4,5
SL1829, SL0149 11
SL1830, SL1850 17
SL1822 20
LSL1923, ZSL1923 28
SL1923 30
NJ2..-E, NJ22..-E, NUP2..-E, NUP22..-E 15
NJ3..-E, NJ23..-E, NUP3..-E, NUP23..-E 20
NJ4 22
Top
Static load carryingcapacity
Very high static loads or shock loads can cause plastic deformation on the
raceways and rolling elements. This deformation limits the static load
carrying capacity of the rolling bearing with respect to the permissible noise
level during operation of the bearing.
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.
According to 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 limit life, it is
advisable to check the static load safety factor. The guide values and
shock loads occurring in operation to table must be taken into
consideration, see table, link.
The static load safety factor S0 is the ratio between the basic static
load rating C0 and the equivalent static load P0:
S0Static load safety factorC0 (C0r,C0a)
N
Basic static load ratingP0 (P0r, P0a) NEquivalent static load on the radial or axial bearing, see link.
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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.
Guide values
for static load safety factor
Operating conditions Static load safety factorS0
for roller
bearings
for ball
bearings
Smooth, low-vibration, normal operation
with minimal demands for smooth running;
bearings with slight rotary motion
≧ 1 ≧ 0,5
Normal operation with higher requirements
for smooth running
≧ 2 ≧ 1
Operation with pronounced shock loads ≧ 3 ≧ 2
Bearing arrangement with high
requirements for running accuracy and
smooth running
≧ 4 ≧ 3
Equivalent static 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.
P0 NEquivalent static bearing loadF0r NRadial static bearing loadF0a NAxial static bearing loadX0Radial factor given in the dimension tables or product descriptionY0Axial factor given in the dimension tables or product description.
This 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.
For radial needle roller bearings and all radial cylindrical roller bearings,
P0 = F0r.
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