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 a_DIN was renamed as a_ISO 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 C_r for radial bearings
• a constant, concentrically acting axial load C_a 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 and L_10h to ISO 281 ➤ Equation and ➤ Equation
• expanded adjusted rating life L_nm to ISO 281 ➤ link

Basic rating life

L₁₀ or L_10h

The basic rating life in millions of revolutions (L₁₀) is determined in accordance with ➤ Equation, the basic rating life in operating hours (L_10h) 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 F_a but also a radial force F_r. The equivalent dynamic axial load P_a 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 L_nm 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 L_na. 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 L_nm 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 C_u

The fatigue limit load C_u 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 C_u serves as a calculation value for determining the life adjustment factor a_ISO 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 C_u.

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 a_ISO

Influences on the life adjustment factor

The standardised method for calculating the life adjustment factor a_ISO 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 e_C ≧ 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 e_C ＜ 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 a_ISO ≦ 3. If the value a_ISO 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 a_ISO ≦ 50. This limit value also applies if e_C · C_u/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 a_ISO 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 d_M = (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 L_nm ➤ 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 e_C

The life adjustment factor for contamination e_C 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 e_C). No account is taken of other contamination such as that caused by water or other fluids. Under severe contamination (e_C → 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 e_C. 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 e_C

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

d_M = 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 k_a ➤ Table.
2. Factor k_a ➤ Table.

Factor k_a for axial cylindrical roller bearings

Series	Factor ka
K811	1,4
K812	0,9
K893	0,7
K894	0,5

Factor k_a 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 a_ISO. 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/a_ISO 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 C_0r for radial bearings
• a constant, concentrically acting axial load C_0a 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.

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.