Slewing ring bearing calculation

The size of the slewing ring required is dependent on the demands made on its:

Static and dynamic load carrying capacity.

Life

Operational reliability

Definition of static load carrying capacity

Slewing rings that undergo rotary motion only infrequently, undergo slow swivel motion, rotate only slowly or are subjected to load while stationary are dimensioned on the basis of their static load carrying capacity since the permissible load in these cases is determined not by material fatigue but by the loadinduced deformations at the contact points between the rolling elements and raceways.

The static load carrying capacity is described by:

the basic static load ratings C0 (see dimension tables)

the static limiting load diagrams Raceway and Fixing screws

The size of a statically loaded slewing ring for a particular application can therefore be checked in approximate terms using the basic static load ratings C0 and the static limiting load diagrams Raceway.

Checking the static load carrying capacity

The static load carrying capacity can be checked in approximate terms only when:

the load arrangement is in accordance with Figure3.

all the requirements stated in this publication are fulfilled in relation to

– flange rings and location

– fitting, lubrication and sealing.

Where load arrangements are more complex or the conditions are not fulfilled, please consult Schaeffler.

In order to check the static load carrying capacity, the following equivalent static operating values must be determined:

the equivalent static bearing load F0q

the equivalent static tilting moment load M0q.

Checking is possible for applications with or without radial load.

Determining the equivalent static bearing load without radial load and checking the static load carrying capacity in the static limiting load diagram Raceway.

If only axial and tilting moment loads are present, the following apply:

F0q = F0a· fA · fS

M0q = M0k· fA· fS

F0q-kN-Equivalent static axial bearing load

F0a-kN-Static axial bearing load

fA-Application factor

fS-Factor for additional safety

M0q-kNm-Equivalent static tilting moment load

M0k-kNm-Static tilting moment load.

Using the values for F0q and M0q, determine the load point in the static limiting load diagram Raceway.

The load point must be below the raceway curve.

In addition to the raceway, check the dimensioning of the fixing screws as well

Determining the equivalent static bearing load with radial load and checking the static load carrying capacity in the static limiting load diagram Raceway.

Radial loads can only be taken into consideration if the radial load F0r is smaller than the basic static radial load rating C0 according to the dimension table.

Calculate the load eccentricity parameter using the formula.

Determine the static radial load factor f0r.

This should be done as follows:

– determine the ratio F0r/F0a in Figure1 or Figure2

– from the ratio F0r/F0a and ε, determine the static radial load factor f0r from Figure1 or Figure2.

Determine the application factor fA according to Table 1,the safety factor fS if required.

Calculate the equivalent axial bearing load F0q and the equivalent tilting moment .

Using the values for F0q and M0q, determine the load point in the static limiting load diagram Raceway.

The load point must be below the raceway curve.

F0q = F0a·fA·fS·f0r

M0q = M0k·fA·fS·f0r

ε-Load eccentricity parameter

DM-mm-Rolling element pitch circle diameter (dimension tables)

f0r-Static radial load factor (see Figure1 or Figure2)

Application factors

The application factors fA in Table1 are empirical values.

They take account of the most important requirements – e.g.

The type and severity of operation, rigidity or running accuracy.

If the precise requirements of an application are known,

the values may be altered accordingly.

Application factors＜1 must not be used.

A large proportion of applications can be statically calculated using an application factor of 1 – e.g. bearings for gearboxes and rotary tables.

Safety factors

The factor for additional safety is fS = 1.

It is not normally necessary to factor in any additional safety in calculation.

In special cases, for example approval specifications, internal specifications, requirements stipulated by inspection bodies etc., the appropriate safety factor should be used.