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CRB Bearing Selection

Bearing selection

Selection of Cooper bearings must take into account both radial and axial loads, which are considered independently as the effect of the axial load on the radial load-bearing surfaces is small enough to discount at normal working loads and speeds.

The thrust or axial load is taken by the end face of the rollers and the flanged shoulders of the inner race assembly and outer race. The ability of the fixed (GR) unit to handle thrust loads is dependent upon specific pressure, velocity of contact areas and lubrication.

Calculating bearing loads

The bearing loads are affected by one or more of the following:

1. Weight of components such as shafting, flywheels, sheaves, pulleys, gears, etc.

2. Tension resulting from belt or chain drives.

3. Tangential, separating and axial loading developed by gears.

4. Inertia loading resulting from acceleration or deceleration.

5. Centrifugal forces developed in rotary or out of balance motion.

Selection for radial load

The radial load ratings listed here are based on ISO standards. The system establishes a common basis for calculating load ratings for all anti-friction bearings. The radial load rating is denoted by Cr.

Selection for radial load is determined independently from the axial load. Determine the radial load, speed and minimum life required. Generally the shaft size has been predetermined. Selection of the bearing can be made using the following formula:

Cr ≥ P x fn x fL x fd
where Cr = radial dynamic rating.
P = calculated effective radial load.
fn = speed (rpm) factor.
fL = life (hours) factor.
fd = dynamic or service factor. 

fn = (rpm x 0.03)0.3 or find from scale on the chart.
fL = (L10 hours/500)0.3 or find from scale on the chart.

L10 hours is the expected life in hours of 90% of similar bearings under similar operating conditions. 

Note: The product of fn x fL should not be less than 1.0.

Alternatively, bearing life may be calculated by the equation:

L10 = [Cr/(P x fd)]10/3
where: L10 = expected life of 90% of similar bearings under similar operating conditions, in millions of revolutions.
When the equivalent radial load equals the Cr rating, multiplied by the service factor, the L10 life will be 1 million revolutions.

If high temperatures (above 100°C) are involved, please refer to temperature section. 

Bearing life requirements (L)

Suggested lives and factors for specific operating conditions are shown below.

Operating conditions Life factor
Life hours
8 hour daily working 3.0-4.0 20,000- 50,000
Continuous operation main drives, large electrical machinery, flywheels, mining 4.4-5.0 70,000-100,000
Continuous operation and an exceptionally high degree of reliability 5.0-6.0 100,000-200,000


Continuous operation and an exceptionally high degree of reliability

We recommend that bearings are specified to provide an L10 life of at least 10,000 hours, except for bearings selected on the basis of static rating.

Dynamic factor
The appropriate dynamic factor fd may be taken from the table below.

Conditions fd
Steady load or small fluctuations 
1.0 - 1.3
Light shock 1.3 - 2.0
Heavy shock, vibration or reciprocation 2.0 - 3.5


Life adjustment factors for critical applications
The basic L10 life, obtained by using the equations or tables shown here, are adequate for normal applications. 

Bearings for most normal applications are specified using the L10 life as above. For reliability greater than 90%, replace L10 in the above equations with Lna where

Lna = a1 x L10 and is given below.

Reliability % 95 96 97 98 99
  a1 0.62 0.53 0.44 0.33 0.21


Minimum radial load
The radial load must exceed a certain value in order to prevent the rollers skidding rather than rolling. 

Cooper bearings are able to operate at lower loads than other types of rolling element bearings. Minimum radial loads are generally Cr/65 for GR bearings and Cr/120 for EX bearings.

Lower loads can be accommodated under certain conditions. Please refer to our technical department.

Basic static load ratings (Cor)
The values of Cor given in this publication have been calculated in accordance with ISO standards. The basic static load rating is defined as that static (radial) load which corresponds to a contact stress of 4,000 MPa (580,000 psi) at the centre of the most heavily loaded roller/raceway contact and produces a permanent deformation of 0.0001 times the roller diameter.

Where rotation is very slow (less than 5 rpm) or intermittent, bearing size can be selected based on the static load carrying capacity. The requisite basic static load rating can be determined from:

Cor = So x P
where: Cor = basic static radial load rating (kN)
P = effective bearing load (kN)
So = static safety factor 

Bearing static safety factors, So

Type of operation Requirements for smooth running
Low Normal High
Vibration free 1 1.2 3
Normal 1 2 3.5
High shock loads 2.5 3 4


Selection for axial load

Selection for axial load is considered independently from the radial load. Determine the axial load applied to the bearing. Knowing the speed and desired shaft size, select a bearing using the following formula:

Ca > (fda x fdn x Pa) / fb
where Ca = axial rating
fda = dynamic or service factor
Pa = calculated axial load
fdn = Velocity (dn) factor (see scale on the chart)
fb = bearing factor (see scale on the chart) 

The dynamic or service factor fda may be 1 for peak overload periods and 1.1 to 1.2 for general running (depending on smoothness), where the load is accurately known. An allowance for any inaccuracies in the calculated loads must be made to ensure that the bearing axial capacity is not exceeded.

Retaining rings or recessed journals are required when Pa>0.5Ca for 01/01E, 02 and 03 Series bearings, and if Pa>0.2Ca for 100 Series bearings.

If the axial load exceeds 40% of the radial load, please consult our technical department.

The axial load capacity is decreased by 50% if the lubricant does not have extreme pressure (EP) additives.

The normal range for standard bearings is 0° to 100°C. Where the temperature rise is mainly from the shaft, increased diametric clearance may be necessary. 

Above 100°C, special consideration must be given to material, design, lubrication and seals. Above 120°C, special heat treatment of the bearing parts is required.

A reduction in radial capacity occurs at temperatures above (150°C) which can be seen below.

°C 170 200 250
% reduction 5 15 25


For temperatures above 100°C or below 0°C, please consult our technical department.


The SKF Cooper upgraded E-series

The SKF Cooper upgraded E-series includes an extended range of series 01 and 02 bearings in bore sizes up to 150 mm, complementing the entire product range with sizes up to 300 mm.

Read more