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.

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.

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.

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).

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/aISO can be omitted from the equations ➤ Equation to ➤ Equation.

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.

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 aDIN was renamed as aISO but without any change to the calculation method.

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

Bearing loadsexplained

Do not overspecify the bearings, otherwise it may not be possible to observe the requisite minimum load. Recommended minimum load ➤ section and product chapter.

➤ Table shows guide values for the contamination factor eC. 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.

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

The equivalent dynamic load P on a bearing subjected to combined load (with a radial and axial load) is calculated in accordance with ➤ Equation.

Viscosity ratio ➤ link For κ ＞ 4 calculation should be carried out using κ = 4. This calculation method cannot be used for κ ＜ 0,1

SKFbearingload calculation

For practical purposes, the life adjustment factor should be restricted to aISO ≦ 50. This limit value also applies if eC · Cu/P ＞ 5. For a viscosity ratio κ ＞ 4, the value κ = 4 should be used; if κ ＜ 0,1, the calculation is not valid.

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.

The operating values calculated here already take account of the life adjustment factors aISO. They must not be applied again when calculating the adjusted rating life.

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.

Static load capacity ofbearingformula

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 Fa but also a radial force Fr. The equivalent dynamic axial load Pa is thus determined in accordance with ➤ Equation.

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.

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:

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.

Bearingload capacity chart

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.

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 life adjustment factor for contamination eC takes account of the influence of contamination in the lubrication gap on the rating life ➤ Table.

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.

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.

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.

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.

The calculation of the expanded adjusted rating life Lnm 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 Lna. 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.

Bearingload calculation pdf

The basic rating life in millions of revolutions (L10) is determined in accordance with ➤ Equation, the basic rating life in operating hours (L10h) is determined in accordance with ➤ Equation.

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 operating life is defined as the life actually achieved by the bearing. It may differ significantly from the calculated life.

How to calculate radial load onbearing

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.

Bearingaxial load

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 eC). No account is taken 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.

Under normal contact conditions, this load causes a permanent deformation at the contact points of approx. 1/10 000 of the rolling element diameter.

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.

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 reference viscosity ν1 is determined from the mean bearing diameter dM = (D + d)/2 and the operating speed n ➤ Figure.

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

Radial load calculation formula

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.

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.

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.

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.

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.

The basic dynamic load ratings for rolling bearings are matched to empirically proven performance standards published in previous FAG and INA catalogues.