Load capacity and life time
Static load rating C0
The calculations of the static load ratings are based on DIN ISO 76.
The static load rating C0 is the load at which the Hertz pressure between rolling elements and raceways reaches the following value at the point of highest load:
■ For roller bearings 4.000 N/mm2
For rolling element bearings, this is the load limit of a material that causes a permanent deformation of 0.0001 times (0.01%) the rolling element diameter. If the load exceeds the static load rating, the function, noise level and accuracy of a bearing arrangement will be adversely affected.
Static load safety factor S0
The calculation of the static load safety factor must be executed separately for the radial and axial bearing parts. The static load safety factor for machine tool applications should be S0 ≥ 4 in order to avoid permanent plastic deformations in the bearing.
Static limiting load diagrams
The static limiting load diagrams serve to:
■ Check the selected bearing size under predominantly static load
■ Determine the tilting moment MK which the bearing can support in addition to the axial load.
The static limiting load diagrams take into account the static load safety factor S0 ≥ 4 as well as the screw and bearing ring strength.
Example:
Static limiting load diagram
| 1 | Bearing/size |
| 2 | Permitted range |
| 3 | Non-permitted range |
| Fa | Axial load [kN] |
| MK | Maximum tilting moment in [kNm] |
Dynamic load rating C
The calculations of the dynamic load ratings are based on DIN ISO 281.
The dynamic load rating C is the load of invariable magnitude and direction at which a sufficiently large quantity of identical bearings achieves a nominal life time of one million revolutions.
Life time
The life time is calculated using the following procedures:
Nominal life time L10 in millions of revolutions according to ISO 281:
nominal life time L10h in operating hours according to ISO 281:
| L10 [106] = | Nominal life time in millions of revolutions reached or exceeded by 90% of a sufficiently large quantity of identical bearings before the first signs of material fatigue appear |
| L10h [h] = | Nominal life time in operating hours reached or exceeded by 90% of a sufficiently large quantity of identical bearings before the first signs of material fatigue appear |
| C [N] = | Dynamic load rating, see product tables |
| P [N] = | Dynamic equivalent bearing load |
| p [-] = | Life time exponent; for roller bearings: p = 10/3 |
| n [min-1] = | Operating speed |
The calculation of the extended modified life time Lnm is carried out via computer-aided calculation according to DIN ISO 281 Supplement 4. It has been specified in ISO/TS 16281 since 2008 and standardised in DIN 26281 since 2010.
| Lnm [106] = | Extended modified life time in millions of revolutions according to ISO 281:2007 |
| a1 [-] = | Life time coefficient for a survival probability of 90% = 1 |
| aISO [-] = | Life time coefficient for the operating conditions |
| ϰ [-] = | Viscosity ratio |
| eC [-] = | Life time coefficient for contamination |
| Cu [kN] = | Fatigue limit load |
| C [kN] = | Dynamic load rating, see product tables |
| P [kN] = | Dynamic equivalent bearing load |
| p [-] = | Life time exponent; for roller bearings: p = 10/3 |
We will be happy to carry out these calculations for you. The following information is required for the calculation:
■ Details on application (drawings, sketches, specifications)
■ Workpiece dimensions and weight
■ Details on the load cycle (cutting forces, speeds, operating durations)
Service life
The service life is the achieved life time of the bearing. It can deviate significantly from the calculated life time.
Possible factors influencing the service life are wear or fatigue caused by:
■ Deviating operating data
■ Misalignment between the shaft and the housing
■ Operating clearance too small or too large
■ Contamination
■ Insufficient lubrication
■ Excessive operating temperature
■ Oscillating bearing movements with very small swivel angles (ripple formation)
■ Vibration stress and ripple formation
■ Very high impact loads (static overload)
■ Pre-damage during assembly.
The service life cannot be determined mathematically.
Due to the variety of possible assembly and operating conditions, the service life cannot be calculated exactly.
It can be estimated most reliably by a comparison with similar installation cases.