CEN/TR 17856:2022

SLOVENSKI STANDARD
01-september-2022
Merjenje premaznih lastnosti neorientirane elektropločevine
Measurement of the coating properties of non-oriented electrical steel
Bestimmung der Beschichtungseigenschaften bei nicht kornorientiertem Elektroband und
-blech
Mesures des propriétés de vernis d’aciers électriques à grains non orientés
Ta slovenski standard je istoveten z: CEN/TR 17856:2022
ICS:
77.140.40 Jekla s posebnimi Steels with special magnetic
magnetnimi lastnostmi properties
77.140.50 Ploščati jekleni izdelki in Flat steel products and semi-
polizdelki products
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TR 17856
TECHNICAL REPORT
RAPPORT TECHNIQUE
July 2022
TECHNISCHER REPORT
ICS 77.140.40; 77.140.50
English Version
Measurement of the coating properties of non-oriented
electrical steel
Mesures des propriétés de vernis d'aciers électriques à Bestimmung der Beschichtungseigenschaften bei nicht
grains non orientés kornorientiertem Elektroband und -blech

This Technical Report was approved by CEN on 10 July 2022. It has been drawn up by the Technical Committee CEN/TC 459/SC
8.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17856:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Curing . 5
5 Weldability . 5
6 Surface insulation . 6
7 Thermal endurance . 6
8 Corrosion resistance . 6
9 Friction coefficient . 7
10 Compressibility . 7
11 Adhesion . 7
12 Hardness . 8
13 Flexibility . 8
14 Thickness . 8
15 Break down voltage . 9
Bibliography .10

European foreword
This document (CEN/TR 17856:2022) has been prepared by Technical Committee CEN/TC 459 “ECISS -
European Committee for Iron and Steel Standardization” , the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.

Through its sub-committee CEN/TC 459/SC 8 “Steel sheet and strip for electrical applications” (secretariat: DIN).
Introduction
EN 10342 describes the electrical steel coating types. The electrical steels ordered according to standards
EN 10106, EN 10265, EN 10303, EN 10341 are supplied either with or without such a coating.
The measurements necessary to qualify these coatings are based on different standards, which are not
necessarily dedicated to electrical steel coatings. The lack of a clear description of which evaluation
methods to use, with which calibration methods, sample preparation, etc. brings inconsistency in
obtained measurement results. The purpose of this technical report is to overcome the problem of
differences in coating qualification results, by combining the aspects of Non-Oriented Electrical Steel
coating testing in a clear guideline.
In particular, the non-oriented fully processed electrical steels in high efficiency applications, such as
electric traction, benefit from the clarifications that this technical report brings to the specific coating
challenges, of such high power density machines.
1 Scope
This document describes the qualification methods, relevant for the non-oriented electrical steel coatings
described in EN 10342. In particular, it describes the testing methods, sample preparation, calibration
methods, that are necessary to obtain reliable results that can be considered a reference for quality
evaluation.
This document applies only to the coatings of non-oriented electrical steels.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Curing
A properly cured coating cannot be wiped off and its testing is therefore a resistance against solvents
such as ethanol or methyl ethyl ketone, in a wipe test. Other methods use spectrometry. The wipe test,
also called solvent rub test, as described in ASTM D5402-19:2019 Method A (Standard Method) or
EN 13523-11 represents common practice. The ASTM reference uses a manual rubbing, whereas the EN
reference uses a mechanical rubbing system. The outcome of the test can be interpreted as following:
— some discolouration and polishing effect is allowed, localized at the rubbed area;
— the coating is considered properly cured when it is not removed down to the substrate, when it does
not smear out, when it does not become soft, when it does not become tacky.
5 Weldability
The welding performance of a coating depends on its coating type, coating thickness, the substrate and
welding process. TIG weldability is a well-established process. The use of laser welding has become
further established for electrical steels, due to its advantages such as limited Heat Affected Zone.
The SEP 1210 was established for welding testing of the TIG process. It eliminates the steel substrate
effect by testing the coatings using a low Si grade in 0,50 mm gauge. The use of a standardized sample
geometry, a standardized welding test process, allows considering the welding speed and current as a
measure for the coating’s TIG weldability.
For laser welding such standardized test has not been identified yet.
6 Surface insulation
The surface insulation measurement occurs according to EN 60404-11. This document is written within
the series of EN 60404 and reflects well all aspects to be taken into account for electrical steel coatings.
It refers to measurements at room temperature, which are generally communicated.
It can be relevant to verify the insulation level of the coating at the operating temperature of the electrical
machine, in which the insulated steel lamination will be used. ASTM A717-12 allows for heating the
sample using a hot plate, during the Franklin measurement described in EN 60404-11. Clearly such
specific measurement remains within the purpose of an approval procedure and is not performed for
certification purposes.
7 Thermal endurance
The thermal endurance measurement occurs according to IEC 60404-12. This document is written within
the series of EN 60404 and reflects well all aspects to be taken into account for electrical steel coatings.
The application cases to be considered are:
— continuous temperature resistance;
— stress relief annealing;
— refurbishing;
— Al- or Cu- die casting.
The aspects of the coating relevant as thermal endurance measurement are:
— adhesion;
— surface insulation resistance;
— compressibility.
8 Corrosion resistance
Corrosion testing needs to be identified for the relevant application conditions of the non-oriented
electrical steel application. The medium / temperature / time profile of the test is set accordingly. The
application cases to be considered are:
air, at elevated temperatures, according to IEC 60404-12;
— humidity;
— refrigerants;
— transformer oil.
IEC 60404-12 uses the flexibility test and the surface insulation resistance measurement, after the
corrosion treatment, to evaluate the coating.
9 Friction coefficient
The friction coefficient of coated non-oriented electrical steels preferably is not too low, because a too
slippery surface presents a risk in electrical steel coil stability, but it also preferably is not too high,
because a too high friction surface does not allow for sufficiently fluent movement of the electrical steel
through the punching presses. Hence the friction coefficient is a relevant property.
The testing reference standards used are either the ASTM D202 (or TAPPI T815) for inclined plane
testing or the ASTM D1894:2014 for horizontal testing (method of assembly e in Figure 1). Neither of
these standards are written for coated steel sheets but rather for sheets of paper (ASTM D202) or plastic
(ASTM D1894). They propose testing the surface of the sample against a reference surface of a selected
reference testing block with a selected weight and surface state. The reference block can be replaced by
a second sample of the material to be tested, hence having bilateral contact of the tested coated electrical
steel surfaces. The ASTM D202 detects the onset of movement by increasing the inclination of the plane;
the ASTM D1894 by increasing the motor pulling force. Hence the criterion evaluated thus rather is the
static friction coefficient (although the motor pulling force can also be used as measure for the kinetic
coefficients). The testing methodologies identified allow for comparative testing in the process of coating
approval procedures, based on in-house experience. Both the inclined plane and horizontal testing
method yield for the different types of coatings for fully-processed non-oriented electrical steels, a
coherent evaluation method. They can both identify which coatings are of a lower or higher friction
nature. They are not suited for individual production coil assessment due to the lack of established
industry reference criteria and standards. Its testing remains within the purpose of an approval
procedure and is not performed for certification purposes.
10 Compressibility
The compressibility of non-oriented electrical steel coatings is a test necessary to evaluate the in-life
behaviour of a non-oriented electrical steel stack. It combines a stacking factor measurement as described
in EN IEC 60404-13, at a specific time/temperature exploitation condition, as described in IEC 60404-12.
11 Adhesion
The cross-cut test according to EN ISO 2409 is suitable for testing adhesion of steel coatings. However,
this cross cut test is hardly discriminating in non-oriented electrical steel coatings and therefore gives no
relevant results.
The outcome of the bending test, is depending on the flexibility of the coating, its adhesion to the electrical
steel substrate, the type of electrical steel substrate and the bending radius of the cylindrical mandrel.
The flexibility test is described in Clause 13.
Given there is no practice of an adhesion testing method that brings relevant grading of non-oriented
electrical steel coatings, it is common practice to refer to the flexibility testing, to identify adhesion
performance. For certification purposes of coating adhesion, the flexibility testing of Clause 13 is
commonly used, using a cylindrical mandrel radius of 5 mm. (It is clear that in such case the substrate
impact can affect
...