BS 5645:1987 download.Specification for Static load ratings for rolling bearings [ISO title: Rolling bearings Static load ratings].
Permanent deformations appear in rolling elements and raceways of rolling hearings under static loads of moderate magnitude and increase gradually with increasing load,
It is often impractical to establish whether the deformations appearing in a bearing in a specific application are permissible by testing the bearing in that application. Other methods are therefore required to establish the suitability of the bearing selected.
Experience shows that a total permanent deformation of 0.000 1 of the rolling element diameter, at the centre of the most heavily loaded rolling elcmentfraceway contact, can be tolerated in most bearing applications without the subsequent bearing operation being impaired. The basic static load rating is, therefore, given a magnitude such that approximately this deformation occurs when the static equivalent load is equal to the load rating.
Tests in different countries indicate that a load of the magnitude in question may be considered to correspond to a calculated contact stress of:
— 4 600 MPa’) for self-aligning ball bearings,
— 4 200 MPa for all other ball bearings, and
— 4 000 MPa for all roller bearings.
at the centre of the most heavily loaded rolling element/raceway contact. The formulae and factors for the calculation of the basic static load ratings are based on these contact stresses.
The permissible static equivalent load may be smaller than, equal to or greater than the basic static load rating, depending on the requirements for smoothness of operation and friction, as well as on actual contact surface geometry. Bearing users without previous experience of these conditions should consult the bearing manufacturers.
1 Scope and field of application
BS 5645 specifies methods of calculating the basic static load rating and the static equivalent load for rolling bearings within the size ranges shown in the relevant international standards. manufactured from good quality hardened steel, in accordance with good manufacturing practice and basically of conventional design as regards the shape of rolling contact surfaces.
Calculations carried out in accordance with this international standard do not yield satisfactory results for bearings in which, because of application conditions and/or because of internal design, there is a considerable truncation of the area of contact between the rolling elements and the ring raceways. The same limitation applies where application conditions cause deviations from a normal load distribution in the bearing, for example misalignment. preload or extra large clearance. Where there is reason to assume that such conditions prevail, the user should consult the bearing manufacturer for recommendations and evaluation of static equivalent load.
4.2.1.2 When calculating the static equivalent radial load for wo or more imilar single-row radial or
angular contact ball hearings mounted side by side on the same shaft such that they operate as a unit
(paired or stack mounting) in “tandem” arrangement, the X0 and Y0 values for a single-row bearing and the
Fr and F5 values for the total loads on the arrangement shall be used.
5 Thrust ball bearings
5.1 Basic static axial load rating
The basic static axial load rating for single. or double-direction thrust ball bearings is given by the formula 10ZDsina
where the values of f are given in Table 1 and Z is the number of balls carrying load in one direction. The formula applies to bearings with a cross-sectional raceway groove radius not larger than 0.54 D.
The load-carrying ability of a bearing is not necessarily increased by the use of a smaller groove radius, but is reduced by the use of a larger groove radius. In the latter case, a correspondingly reduced value of f shall be used.
5.2 Static equivalent axial load
The static equivalent axial load for thrust ball bearings with a 90° is given by the formula P0p2.3Ftana4’F5
This formula is valid for all ratios of radial load to axial load in the case of double-direction bearings. For single-direction bearings, it is valid where F,JF5 0.44 cota and gives satisfactory but less conservative values of P for F1JF5 up to 0.67 cota.
Thrust ball bearings with a = 90° can support axial loads only. The static equivalent axial load for this type of bearing is given by the formula
P05F5
6 Radial roller bearings
6.1 Basic static radial load rating
The basic’ static radial load rating for radial roller bearings is given by the formula
The static equivalent radial load for radial roller bearings with a = 00. and subjected to radial load only, is given by the formula
NOTE The ability of radial roller beanngs with a = 00 to support axial loads varies considerably with bearing design and execution. The bearing user should therefore consult the bearing manufacturer for recommendations regarding the evaluation of equivalent load in recea whore bearings with a 0° are aubjoc-td to axial lead.
6.2.1 Bearing combinations
6.2.1.1 When calculating the static equivalent radial load for two similar single-row angular contact roller bearings mounted side by side on the same shaft such that they operate as a unit (paired mounting) in “back-to-back” or ‘face-to-face” arrangement, the X() and Y, values for a double-row bearing and the Fr and Fa for the total loads on the arrangement shall be used.
6.2.1.2 When calculating the static equivalent radial load for two or more similar single-row angular contact roller bearings mounted side by side on the same shaft such that they operate as a unit (paired or stack mounting) in “tandem” arrangement, the X0 and values for a single-row bearing and the F and a values for the total loads on the arrangement shall be used.
7 Thrust roller bearings
7.1 Basic static axial load rating
The basic static axial load rating for single. and double-direction thrust roller bearings is given by the formula
where Z is the number of rollers carrying load in one direction.
In cases where rollers have different lengths, ZL is taken as the sum of the lengths, defined in 2.7, of all the rollers carrying load in one direction.
7.1.1 Bearing combinations
The basic static axial load rating for two or more similar single-direction thrust roller bearings mounted side by side on the same shaft such that. they operate as a unit (paired or stack mounting) in “tandem” arrangement, properly manufactured and mounted for equal load distribution, is the number of bearings times the rating of one single-direction bearing.