ISO 4378-2:2024
(Main)Plain bearings — Terms, definitions, classification and symbols — Part 2: Friction and wear
Plain bearings — Terms, definitions, classification and symbols — Part 2: Friction and wear
This document specifies the most commonly used terms relating to friction and wear of plain bearings with their definitions and classification. For some terms and word combinations, their short forms are given, which can be used where they are unambiguous.
Paliers lisses — Termes, définitions, classification et symboles — Partie 2: Frottement et usure
L'ISO 4378-2:2017 spécifie les termes les plus couramment utilisés en matière frottement et d'usure de paliers lisses, ainsi que leur définition et leur classification. Les formes abrégées données pour certains termes peuvent être employées dans les cas où elles ne créent aucune ambiguïté possible quant à leur interprétation. Les termes suffisamment explicites par eux-mêmes ne sont pas définis.
General Information
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Standards Content (Sample)
International
Standard
ISO 4378-2
Fourth edition
Plain bearings — Terms, definitions,
2024-11
classification and symbols —
Part 2:
Friction and wear
Paliers lisses — Termes, définitions, classification et symboles —
Partie 2: Frottement et usure
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms .1
3.2 Terms related to types and characteristics of external friction and classification .3
3.2.1 Classification according to the presence of relative motion .3
3.2.2 Classification according to the mode of relative motion .4
3.2.3 Classification according to the presence of lubricant .5
3.3 Terms related to types and characteristics of wear process and classification .5
3.3.1 Mechanical wear .5
3.3.2 Mechano-chemical wear .7
3.3.3 Other wear .7
3.4 Terms related to phenomena and processes in friction and wear .8
3.5 Terms related to vibration and vibration-related terms regarding a rotating shaft
supported by plain bearings .9
Bibliography .10
Index .11
iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 6, Terms
and common items.
This fourth edition cancels and replaces the third edition (ISO 4378-2:2017), which has been technically
revised.
The main changes are as follows:
— editorial revision of the document: instead of referencing the parts in the figure by subclause number,
the part numbers have been used and the names in the key have been shown;
— addition of Bibliography and an alphabetical index.
A list of all parts in the ISO 4378 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
As there is a large number of multiple designations in the domain of plain bearings, there is a considerable
risk of error in the interpretation of standards and technical literature.
This document is an attempt to establish a uniform basic system of designations of friction and wear.
In addition, this document is specifically intended for the field of plain bearings the content can be adopted
in general to the field of tribology and being adopted to other machinery elements.
v
International Standard ISO 4378-2:2024(en)
Plain bearings — Terms, definitions, classification and
symbols —
Part 2:
Friction and wear
1 Scope
This document specifies the most commonly used terms relating to friction and wear of plain bearings with
their definitions and classification.
For some terms and word combinations, their short forms are given, which can be used where they are
unambiguous.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General terms
3.1.1
external friction
force and its phenomenon of resistance to the relative motion between two bodies, originating at the contact
area of their surfaces and directed tangentially to them
3.1.2
internal friction
force and its phenomenon of resistance to the relative motion of particles or mass of a body with respect to
other particles or mass in the same body
3.1.3
friction
force and its phenomenon of resistance to the relative motion working tangentially with respect to the
common boundary between two bodies when, under the action of an external force, one body moves or is at
rest relative to the surface of the other
Note 1 to entry: See Figure 1.
Key
F friction force (3.1.4)
P normal force
W weight of material
α friction angle (3.1.6)
Figure 1 — Friction
3.1.4
friction force
force that resists relative motion between two bodies
Note 1 to entry: See Figure 1.
3.1.5
coefficient of friction
ratio of the friction force (3.1.4) between two bodies to the normal force pressing these bodies together
3.1.6
friction angle
angle, the tangent of which is equal to the ratio of the friction force (3.1.4) to the normal force, or coefficient
of friction (3.1.5)
Note 1 to entry: See Figure 1.
3.1.7
wear
phenomenon of a loss of substance from a solid body surface in frictional conditions
3.1.8
wear process
process of a loss of substance from a solid body surface in frictional conditions, which appears as a gradual
decrease of body dimensions and/or change of shape
Note 1 to entry: Rarely, in a broader sense, is there a process of permanent increase of body dimensions on the surface
without loss of substance.
3.1.9
wear rate
amount of wear (3.1.7) per unit sliding distance or per interval of time
Note 1 to entry: A distinction is made between “momentary” (at a definite moment) and “mean” wear rate (during a
definite interval of time).
3.1.10
specific wear rate
wear intensity
value of amount of wear (3.1.7) divided by the product of sliding distance (or time) and load; that is, the ratio
of wear rate (3.1.9) to the load
Note 1 to entry: Wear can be expressed in the units of length, volume, mass, etc.
Note 2 to entry: Wear intensity is distinguished as “momentary” or as “mean” wear intensity.
3.1.11
mild wear
normal wear
type of adhesive wear (3.3.1.3) characterizing in generation of smooth surface with a little surface damage
and minute wear (3.1.7) particles of several microns of less
3.1.12
severe wear
excessive wear
type of adhesive wear (3.3.1.3) characterizing that produces significant transfer and large-sized wear (3.1.7)
debris accompanied by intense adhesion (3.4.2) between friction (3.1.3) surfaces
3.2 Terms related to types and characteristics of external friction and classification
3.2.1 Classification according to the presence of relative motion
3.2.1.1
static friction
friction (3.1.3) and its phenomena that occur between two contacting bodies before the start of relative
motion under increasing external force
Note 1 to entry: See Figure 2.
Note 2 to entry: Friction that occurs at an extremely low sliding speed is also referred to as static friction.
Key
1 position of the curve corresponding to maximum static friction (3.2.1.2)
f friction (3.1.3)
L sliding distance
a
The solid line represents static friction.
b
The dotted line represents dynamic friction (3.2.1.3).
Figure 2 — Friction according to relative motion
3.2.1.2
maximum static friction
friction (3.1.3) and its phenomena that occur between two contacting bodies just before the start of relative
motion under gradually increasing external force
Note 1 to entry: See Figure 2.
3.2.1.3
dynamic friction
friction (3.1.3) and its phenomena between two bodies in relative motion
Note 1 to entry: See Figure 2.
3.2.2 Classification according to the mode of relative motion
3.2.2.1
sliding motion
relative motion between two bodies in contact when the contact areas of both bodies move with different
magnitudes and/or directions of tangential velocity
3.2.2.2
sliding friction
force and its phenomena of resistance to the sliding motion (3.2.2.1) between two bodies
Note 1 to entry: See 3.1.3.
3.2.2.3
sliding velocity
difference between tangential velocities of two bodies in contact, at their contact point, during sliding
3.2.2.4
sliding surface
body surface subjected to sliding motion (3.2.2.1)
3.2.2.5
rolling motion
relative motion between two bodies in contact when the contact areas of both bodies move with the same
magnitude and direction of tangential velocity
3.2.2.6
rolling velocity
tangential velocity at the common contact point between bodies that are rolling relative to each other
3.2.2.7
rolling friction
force and its phenomena of resistance to the rolling motion (3.2.2.5) between two bodies
3.2.2.8
combined rolling and sliding friction
dynamic friction (3.2.1.3) that occurs between two contacting bodies when rolling motion (3.2.2.5) and
sliding motion (3.2.2.1) take place simultaneously within the contact area
3.2.2.9
traction
force and its phenomena that occur during the rolling motion (3.2.2.5) of a body on another body, accompanied
by sliding at the contact area in the tangential direction, and which are utilized for power transmission
3.2.2.10
traction force
force that occurs during the rolling motion (3.2.2.5) of a body on another body, accompanied by sliding at the
contact area in the tangential direction
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