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Technical calculation tool

Technical calculation for Service life

Required service life

Enter the required service life of the bearing.

Using a bearing with too long service life is not necessarily economical.

The required service life would better be set in consideration of the machine on which the bearing is to be used or of operating conditions.

The following table shows required service life used for calculation. The figures have been obtained from experience.

Operating condition Application Recommended service life
Short or intermittent operation Household electric appliance, electric tools,agricultural equipment, heavy cargo hoisting equipment 4000 - 8000
Not extended duration, but stable operation required Household air conditioner motors,construction equipment, conveyers, elevators 8000 - 12000
Intermittent but extended operation Rolling mill roll necks, small motors,cranes 8000 - 12000
Motors used in factories, general gears 12000 - 20000
Machine tools, shaker screens, crushers 20000 - 30000
Compressors, pumps, gears for essential use 40000 - 60000
Daily operation more than 8 hrs.
or continuous extended operation
Escalators 12000 - 20000
Centrifugal separators, air conditioners, air blowers, woodworking equipment,passenger coach axle journals 20000 - 30000
Large motors, mine hoists, locomotive axle journals, railway rolling stock traction motors 40000 - 60000
Paper manufacturing equipment 100000 - 200000
24 hrs. operation (no failure allowed) Water supply facilities, power stations, mine water discharge facilities 100000 - 200000

Required safety coefficient

The safety coefficient is designated, based on empirical data, so as to ensure safety in relation to basic static load rating.

Safety coefficient=Basic static load rating/Static equivalent load

Operating conditions fs(min.)
Ball bearings Roller bearings
With bearing rotation When high accuracy is required 2 3
Normal operation 1 1.5
When impact load is applied 1.5 3.0
Without bearing rotation (occasional oscillation) Normal operation 0.5 1
When impact load or uneven distribution load is applied 1 2

Lubrication conditions

Lubrication oil conditions used to calculate corrected rating life in consideration of factor aISO are entered here.

Operating temperature Enter the temperature of lubrication oil (or bearing) during operation.
Kinematic viscosity during operation Enter the kinematic viscosity of lubrication oil at operating temperature.

* If kinematic viscosity at operating temperature is unknown, click the "Calculation of kinematic viscosity during operation" button. It enables the entry of kinematic viscosity of lubrication oil during operation.

Temperature conditions (1) and (2) Enter any temperature to (1) and (2). However, the two settings should be different.
Kinematic viscosity at temperatures (1) and (2) Enter the kinematic viscosity of lubrication oil at temperatures (1) and (2).

Operating conditions

Operation conditions for calculation of corrected rating life in consideration of factor aISO are set here.


Enter the magnitude of load that work on a bearing (radial load and axial load) and bearing rotation speed. (To calculate these loads, refer to category 3.2 of the "Bearing info.")

(To calculate these loads, refer to category 3.2 of the "Bearing info.")

Generally, loading conditions are not always constant; they fluctuate in many patterns.

To take account of these fluctuating loads, enter the conditions according to the number of such variations (variation patterns).

How long the individual operating conditions are used should also be considered. Enter at what ratio each condition is used in operation.

Life modification factor for reliability a1

Reliability is "the percentage of the number of bearings that attain a specific life or that are expected to exceed this life in relation to the total number of identical bearings tested through operation under the same conditions." Values of a1 used to calculate a modified rating life with a reliability of 90% or higher (a failure probability of 10% or less) are shown below.

Life modification factor for reliability a1
Reliability (%) 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 0.080
99.95 L0.05m 0.077

(Citation from JIS B 1518:2013)

Contamination factor ec

If solid particles in the contaminated lubricant are caught between the raceway and the rolling elements, indentations may form on one or both of the raceway and the rolling elements. These indentations will lead to localized increases in stress, which will decrease the life. This decrease in life attributable to the contamination of the lubricant can be calculated from the contamination level as contamination factor ec.

Dpw shown in this table is the pitch diameter, which is expressed simply as Dpw = (D + d)/2.

For information such as details on special lubricating conditions or detailed investigations, contact JTEKT.


Values of contamination factor ec
Contamination level ec
Dpw < 100mm Dpw ≧ 100mm
Extremely high cleanliness: The size of the particles is approximately equal to the thickness of the lubricant oil film, this is found in laboratory-level environments. 1 1
High cleanliness: The oil has been filtered by an extremely fine filter, this is found with standard grease-packed bearings and sealed bearings. 0.8~0.6 0.9~0.8
Standard cleanliness: The oil has been filtered by a fine filter, this is found with standard grease-packed bearings and shielded bearings. 0.6~0.5 0.8~0.6
Minimal contamination: The lubricant is slightly contaminated. 0.5~0.3 0.6~0.4
Normal contamination: This is found when no seal is used and a coarse filter is used in an environment in which wear debris and particles from the surrounding area penetrate into the lubricant. 0.3~0.1 0.4~0.2
High contamination: This is found when the surrounding environment is considerably contaminated and the bearing sealing is insufficient. 0.1~0 0.1~0
Extremely high contamination 0 0

(Citation from JIS B 1518:2013)

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