ISO 20056-2:2017

INTERNATIONAL ISO
STANDARD 20056-2
First edition
2017-12
Rolling bearings — Load ratings for
hybrid bearings with rolling elements
made of ceramic —
Part 2:
Static load ratings
Roulements — Charges de base pour roulements hybrides avec
éléments roulants en céramique —
Partie 2: Charges statiques
Reference number
ISO 20056-2:2017(E)
©
ISO 2017

---------------------- Page: 1 ----------------------
ISO 20056-2:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 20056-2:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Static load rating . 3
5.1 General . 3
5.2 Basic static radial load rating of radial ball bearings . 3
5.3 Basic static axial load rating of thrust ball bearings . 4
5.4 Basic static radial load rating of radial roller bearings . 5
5.5 Basic static axial load rating of thrust roller bearings . 5
5.6 Discontinuities in load ratings . 5
5.7 Consideration of special material properties . 5
6 Static equivalent load . 5
6.1 General . 5
6.2 Radial ball bearings . 5
6.3 Thrust ball bearings . 5
6.4 Radial roller bearings . 5
6.5 Thrust roller bearings . 5
7 Static safety factor . 6
Annex A (informative) Calculation of the Hertzian parameters for point contact .7
Annex B (informative) Guide values of the factor f for ball bearings . 8
0
Annex C (informative) Discontinuities in the calculation of basic static load ratings .10
Annex D (informative) Material properties and material classification .11
Bibliography .13
© ISO 2017 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 20056-2:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 4, Rolling bearings, Subcommittee SC 8,
Load ratings and life.
A list of all the parts in the ISO 20056 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 20056-2:2017(E)

Introduction
Hybrid bearings are rolling bearings with raceways consisting of commonly used rolling bearing steel
and rolling elements made from silicon nitride (for definitions, see ISO 5593). Due to the higher modulus
of elasticity of the ceramic rolling elements, hybrid bearings have a noticeably smaller contact ellipse at
the same load than rolling bearings with rolling elements made of rolling bearing steel. This will lead to
higher contact stresses at the same load.
Since the second edition of ISO 76 in 1987, the static capacity of rolling bearings is defined by a
permissible Hertzian contact stress in the highest loaded contact. In rolling bearings made of steel,
this contact stress will lead to a permanent plastic deformation at raceway and rolling element of
approximately 1/10 000th of the rolling element diameter. In hybrid bearings, no significant plastic
deformation will occur at the rolling element, resulting in a smaller total plastic deformation in the
rolling contact. Therefore, in accordance with industrial practice, slightly higher permissible Hertzian
stresses are defined for hybrid bearings. The guideline values of the static safety factor, S , have been
0
increased accordingly to maintain the same overall safety for the raceway.
© ISO 2017 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 20056-2:2017(E)
Rolling bearings — Load ratings for hybrid bearings with
rolling elements made of ceramic —
Part 2:
Static load ratings
1 Scope
This document specifies methods of calculating the static load ratings for hybrid bearings with bearing
rings made of contemporary, commonly used, high quality hardened bearing steel, in accordance
with good manufacturing practice, and a full set of rolling elements made of silicon nitride (Si N ) in
3 4
[4]
contemporary, commonly used material and manufacturing quality. For balls, ISO 26602, together
[1] [2] [4]
with ISO 3290-2, is applicable. For rollers, ISO 12297-2 is applicable, and ISO 26602 is applicable
in an analogous way.
For applications where hybrid bearings are used, guideline values of the static safety factor, S ,
0
according to Table 1 and Table 2 are observed.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 76:2006, Rolling bearings — Static load ratings
ISO 5593, Rolling bearings — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5593 and ISO 76, and the
following, apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
basic static radial load rating
C
0r
radial load which corresponds to a calculated contact stress at the centre of the most heavily loaded
rolling element/raceway contact of
— 4 600 MPa for all radial ball bearings including radial self-aligning ball bearings, and
— 4 200 MPa for all radial roller bearings
Note 1 to entry: In the case of a single-row angular contact bearing, the radial load rating refers to the radial
component of that load which causes a purely radial displacement of the bearing rings in relation to each other.
© ISO 2017 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 20056-2:2017(E)

Note 2 to entry: The contact stress limits given in this subclause are only valid for rolling elements made of
silicon nitride with a modulus of elasticity of 300 000 MPa or higher. For rolling elements made of ceramics with
a lower modulus of elasticity, the contact stress limits per ISO 76 should be applied.
3.2
basic static axial load rating
C
0a
static centric axial load which corresponds to a calculated contact stress at the centre of the most
heavily loaded rolling element/raceway contact of
— 4 600 MPa for all thrust ball bearings, and
— 4 200 MPa for all thrust roller bearings
Note 1 to entry: For a tapered roller, the applicable diameter is equal to the mean value of the diameters at the
imaginary sharp corners at the large end and at the small end of the roller.
Note 2 to entry: For an asymmetrical convex roller, the applicable diameter is an approximation of the diameter
at the point of contact between the roller and the ribless raceway at zero load.
Note 3 to entry: The contact stress limits given are only valid for rolling elements made of silicon nitride with a
modulus of elasticity of 300 000 MPa or higher. For rolling elements made of ceramics with a lower modulus of
elasticity, the contact stress limits according to ISO 76 should be applied.
4 Symbols
C basic static load rating, in N
0
C basic static axial load rating, in N
0a
C basic static radial load rating, in N
0r
D pitch diameter of ball or roller set, in mm
pw
D nominal ball diameter, in mm
w
D roller diameter applicable in the calculation of load ratings, in mm
we
E modulus of elasticity of ceramic rolling elements, in MPa (E = 300 000 MPa)
Ce Ce
E modulus of elasticity of rolling bearing steel, in MPa (E = 207 000 MPa, according to ISO 76)
St St
complete elliptic integral of the second kind
E()χ
F bearing axial load (axial component of actual bearing load), in N
a
F bearing radial load (radial component of actual bearing load), in N
r
relative curvature difference
F()ρ
f factor for calculation of basic static load rating
0
i number of rows of rolling elements
complete elliptic integral of the first kind
K()χ
L effective roller length applicable in the calculation of load ratings, in mm
we
P static equivalent axial load, in N
0a
P static equivalent radial load, in N
0r
2 © ISO 2017 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 20056-2:2017(E)

r cross-sectional raceway groove radius of outer ring or housing washer, in mm
e
r cross-sectional raceway groove radius of inner ring or shaft washer, in mm
i
S static safety factor
0
w correction factor for different material combinations
X static radial load factor
0
Y static axial load factor
0
Z number of rolling elements in a single-row bearing; number of rolling elements per row of
a multi-row bearing with the same number of rolling elements per row
α nominal contact angle, in degrees
γ
auxiliary parameter, γα=×DDcos/
wpw
v Poisson's ratio of ceramic rolling el
...