IEC 60424-1:2015

IEC 60424-1 ®
Edition 2.0 2015-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Ferrite cores – Guidelines on the limits of surface irregularities –
Part 1: General specification
Noyaux ferrites – Lignes directrices relatives aux limites des irrégularités de
surface –
Partie 1: Spécification générale

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or

your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie

et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des

questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing more than 30 000 terms and
Technical Specifications, Technical Reports and other definitions in English and French, with equivalent terms in 15
documents. Available for PC, Mac OS, Android Tablets and additional languages. Also known as the International
iPad. Electrotechnical Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a More than 60 000 electrotechnical terminology entries in
variety of criteria (reference number, text, technical English and French extracted from the Terms and Definitions
committee,…). It also gives information on projects, replaced clause of IEC publications issued since 2002. Some entries
and withdrawn publications. have been collected from earlier publications of IEC TC 37,

77, 86 and CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: csc@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient plus de 30 000 termes et définitions en
Spécifications techniques, Rapports techniques et autres
anglais et en français, ainsi que les termes équivalents dans
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
15 langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
Plus de 60 000 entrées terminologiques électrotechniques, en
La recherche avancée permet de trouver des publications IEC
en utilisant différents critères (numéro de référence, texte, anglais et en français, extraites des articles Termes et
comité d’études,…). Elle donne aussi des informations sur les Définitions des publications IEC parues depuis 2002. Plus
projets et les publications remplacées ou retirées. certaines entrées antérieures extraites des publications des

CE 37, 77, 86 et CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
csc@iec.ch.
IEC 60424-1 ®
Edition 2.0 2015-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Ferrite cores – Guidelines on the limits of surface irregularities –

Part 1: General specification
Noyaux ferrites – Lignes directrices relatives aux limites des irrégularités de

surface –
Partie 1: Spécification générale

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.100.10 ISBN 978-2-8322-3028-2

– 2 – IEC 60424-1:2015 © IEC 2015

CONTENTS
FOREWORD . 3

INTRODUCTION . 5

1 Scope . 6

2 Normative reference . 6

3 Terms and definitions. 6

4 Examples of irregularities . 7

5 Locations and functions of core parts and surfaces . 7
5.1 General . 7
5.2 Mating surfaces . 7
5.3 Centre post . 8
5.4 Outer walls or legs . 8
5.5 Back wall, bottom and back surfaces . 8
5.6 Wire-slot area . 8
5.7 Wire-way area . 8
5.8 Clamping recess area . 8
6 Area and length reference for visual inspection . 8
7 Limits of surface irregularities . 11
7.1 General . 11
7.2 Chips and ragged edges . 11
7.3 Cracks . 11
7.4 Flash. 11
7.5 Pull-outs . 11
7.6 Pores . 11
7.7 Crystallites . 11
8 Sectional specifications . 11
Bibliography . 13

Figure 1 – Examples of surface irregularities . 7
Figure 2 – Location of main core parts and surfaces – Example of RM-core type . 7

Table 1 – Area and length reference for visual inspection . 10

Table 2 – IEC 60424 sectional specifications . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
FERRITE CORES –
GUIDELINES ON THE LIMITS OF SURFACE IRREGULARITIES –

Part 1: General specification
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60424-1 has been prepared IEC technical committee 51: Magnetic
components and ferrite materials.
This second edition cancels and replaces the first edition published in 1999. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of pores in 3.5 and crystallites in 3.6.

– 4 – IEC 60424-1:2015 © IEC 2015

The text of this standard is based on the following documents:

FDIS Report on voting
51/1107/FDIS 51/1123/RVD
Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 60424 series, published under the general title Ferrite cores –
Guidelines on the limits of surface irregularities, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
Due to the method of manufacture and the physical nature of the products, ferrite cores can be

expected to exhibit some degree of physical irregularities such as chips, ragged edges, cracks,

flashing, and pull-out.
The permissible extent of these surface irregularities will depend on the type, position and size

of the defect and on the function of the core. Thus, in order to establish limits of surface

irregularities for a given series of ferrite cores, for example RM-cores, pot-cores, E-cores, U-

cores and ring-cores, it is necessary to prepare a particular specification for each, setting out

in detail the permissible extent of the various types of irregularities.

All surfaces of the core should be clean and free from loose ferrite particles or any other
foreign matter. This is more critical for mating surfaces that should make good contact with one
another. Stains, discolorations, surface crazing or crystallization are acceptable if they do not
affect the normal performance of the core. The irregularities described below are considered
as being detectable without the use of any magnifying equipment.
Surface irregularities limits are set for control of cosmetic appearance, and not for control of
magnetic performance. Surface irregularities do not substantially affect core magnetic function,
nor do they affect reliability. Reliability should be assessed for wound magnetics, rather than
for cores alone. See IEC 60401-3 for more details concerning the reliability of ferrite cores and
devices built with them.
– 6 – IEC 60424-1:2015 © IEC 2015

FERRITE CORES –
GUIDELINES ON THE LIMITS OF SURFACE IRREGULARITIES –

Part 1: General specification
1 Scope
This part of IEC 60424 gives guidelines on the allowable limits of surface irregularities of ferrite
cores.
This standard should be considered as a general specification useful in the dialogue between
ferrite core manufacturers and customers about surface irregularities.
2 Normative reference
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
Void.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
chips and ragged edges
areas with missing surface material that are generally caused by mechanical impact during
handling
3.2
crack
surface irregularity which has a width much smaller than its length, and penetrates into the
core
3.3
flash
sharp feather-edge wall extending beyond the intended contour surface of the core
3.4
pull-out
consequence of the removal of a surface layer of the core due to die “sticking”
3.5
pores
holes left on the surface of cores after sintering and surface finishing
3.6
crystallites
grains of abnormal size distinguishable on the surface, often with sparkling facets

4 Examples of irregularities
Figure 1 shows different examples of surface irregularities on an RM-core.

Cracks
Ragged edges
Example of flash
Chips
Pull-out
IEC
Figure 1 – Examples of surface irregularities
5 Locations and functions of core parts and surfaces
5.1 General
Figure 2 shows the location of main core parts and surfaces on an RM-core.
Mating surfaces (see 5.2)
Centre post (see 5.3)
Wire-slot area (see 5.6)
Outer walls and legs (see 5.4)
Bottom surface (see 5.5)
Wire-way area (see 5.7)
Back wall (see 5.5)
Back surface (see 5.5)
Clamping recess area (see 5.8)
IEC
Figure 2 – Location of main core parts and surfaces – Example of RM-core type
5.2 Mating surfaces
These surfaces are generally ground in order to limit the residual air gap between the two core
halves. Consequently, irregularities on these surfaces have to be considered as major ones,
and carefully evaluated with regard to their influence on the magnetic properties of the
complete circuit.
– 8 – IEC 60424-1:2015 © IEC 2015

5.3 Centre post
This should be considered as the most important part of the core due to its function of carrying

the total flux generated by the winding. The centre post of ferrite cores is generally circular

(with or without a hole) or rectangular.

5.4 Outer walls or legs
The main function of the outer walls (for example pot-cores) or the outer legs (for example E-
cores) is to guide the magnetic flux in a closed magnetic circuit.

5.5 Back wall, bottom and back surfaces
The back wall has the same magnetic function as the outer walls or legs; it may include wire-
slots and wire-way areas (for example on RM-cores), the shapes and dimensions of which are
dictated by the winding and isolation requirements.
Besides accommodating clamping, the back surface (ground or not) serves as a reference
plane for grinding the mating surface to achieve its required parallelism, flatness and
smoothness.
5.6 Wire-slot area
The wire-slot area is the lateral area of the outer walls, interfacing with the cut-out portion.
5.7 Wire-way area
The wire-way area is located on the bottom (inside) surface of the back wall, also called the
floor. The wire-way runs radially from the centre post to the edge of the back wall, centred with
respect to the wire-slot areas. The purpose of the wire-way is to provide a path for leads to
reach from the inside of the coil to terminals on the outside.
5.8 Clamping recess area
The clamping recess areas on the back walls accommodate clamping clips, affording secure
mounting, and preventing mechanical interference from the clip above the plane of the back
wall.
6 Area and length reference for visual inspection
Irregularities such as chips, cracks and pull-out should be compared to five simple geometries
which are shown in Table 1.
Such a table should be used as a reference for evaluation by operators either at the outgoing
stage (core manufacturers) or at the incoming inspection (customers).
Other methods than visual inspection can be used, such as computerized optical detection.
NOTE The minimum area and length considered are respectively 0,5 mm and 1 mm.
Recommended resolutions are as follows:
a) for area
2 2
– 0,5 mm up to 5 mm
2 2 2
– 1 mm from 5 mm to 10 mm
2 2 2
– 2,5 mm from 10 mm to 20 mm
2 2 2
– 5 mm from 20 mm to 50 mm
b) for length
– 1 mm from 1 mm to 5 mm
– 2,5 mm from 5 mm to 10 mm
– 10 – IEC 60424-1:2015 © IEC 2015

Table 1 – Area and length reference for visual inspection

IEC
7 Limits of surface irregularities

7.1 General
In each particular specification relevant to a standardized core series, generic rules for the

calculation of limits should be defined for every kind of irregularity and for all core parts and

surfaces.
For guidance on the limits of irregularities, refer to the sectional specifications of IEC 60424-2

to IEC 60424-8, where limits per core size are given in suitable tables, along with identification

of irregularity types on figures and drawings.

7.2 Chips and ragged edges
The simplest way of performing inspection on these two types of irregularities is to compare a
chip to a reference area limit and a ragged edge to a reference length.
The limits of chips are generally defined as a percentage of the related surface of the core.
The apparent area of a chip is considered to be the area of that chip.
The ragged edge length is generally limited to a percentage of the common perimeter of the
respective two surfaces.
7.3 Cracks
The limits of cracks are generally defined as a percentage of the specified core section
thickness.
The length of a crack is considered to be the actual length visible on the surface without
magnification.
7.4 Flash
Generally, no limit is defined but the critical places where flash is not allowed should be listed.
7.5 Pull-outs
The limits of pull-outs are generally defined as a percentage of the respective surface area.
The apparent area of a pull-out, neglecting actual depth, is considered to be the area of that

pull-out.
7.6 Pores
The limits of pores are generally defined as a percentage of the specified core.
7.7 Crystallites
The limits of crystallites are generally defined as a
...