EN ISO 8251:2018

SLOVENSKI STANDARD
01-december-2018
1DGRPHãþD
SIST EN ISO 8251:2012
Anodizacija aluminija in aluminijevih zlitin - Meritve obrabne obstojnosti anodno
oksidiranih prevlek (ISO 8251:2018)
Anodizing of aluminium and its alloys - Measurement of abrasion resistance of anodic
oxidation coatings (ISO 8251:2018)
Anodisieren von Aluminium und Aluminiumlegierungen - Messung der Abriebfestigkeit
von anodisch erzeugten Oxidschichten (ISO 8251:2018)
Anodisation de l'aluminium et de ses alliages - Détermination de la résistance à
l'abrasion des couches d'oxyde anodiques (ISO 8251:2018)
Ta slovenski standard je istoveten z: EN ISO 8251:2018
ICS:
25.220.20 Površinska obdelava Surface treatment
77.120.10 Aluminij in aluminijeve zlitine Aluminium and aluminium
alloys
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 8251
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2018
EUROPÄISCHE NORM
ICS 25.220.20 Supersedes EN ISO 8251:2011
English Version
Anodizing of aluminium and its alloys - Measurement of
abrasion resistance of anodic oxidation coatings (ISO
8251:2018)
Anodisation de l'aluminium et de ses alliages - Anodisieren von Aluminium und
Détermination de la résistance à l'abrasion des couches Aluminiumlegierungen - Messung der Abriebfestigkeit
d'oxyde anodiques (ISO 8251:2018) von anodisch erzeugten Oxidschichten (ISO
8251:2018)
This European Standard was approved by CEN on 19 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8251:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 8251:2018) has been prepared by Technical Committee ISO/TC 79 "Light
metals and their alloys" in collaboration with Technical Committee CEN/TC 132 “Aluminium and
aluminium alloys” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2019, and conflicting national standards shall
be withdrawn at the latest by March 2019.
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.
This document supersedes EN ISO 8251:2011.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 8251:2018 has been approved by CEN as EN ISO 8251:2018 without any modification.

INTERNATIONAL ISO
STANDARD 8251
Third edition
2018-08
Anodizing of aluminium and its
alloys — Measurement of abrasion
resistance of anodic oxidation
coatings
Anodisation de l'aluminium et de ses alliages — Détermination de la
résistance à l'abrasion des couches d'oxyde anodiques
Reference number
ISO 8251:2018(E)
©
ISO 2018
ISO 8251:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 8251:2018(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Characteristics of abrasion tests . 2
4.1 General . 2
4.2 Abrasive-wheel-wear test . 2
4.3 Abrasive jet test . 2
4.4 Falling sand abrasion test . 2
5 Abrasive-wheel-wear test . 2
5.1 Principle . 2
5.2 Apparatus . 3
5.2.1 Abrasive-wheel-wear test apparatus . 3
5.2.2 Abrasive strip . 3
5.2.3 Eddy-current meter . 3
5.2.4 Balance . 3
5.3 Procedure . 3
5.3.1 Standard specimen. 3
5.3.2 Test specimen . 4
5.3.3 Test procedure . 4
5.4 Expression of results . 5
5.4.1 General. 5
5.4.2 Wear resistance . 5
5.4.3 Mass wear resistance . 5
5.4.4 Wear index . 5
5.4.5 Mass wear index . 6
6 Abrasive jet test . 6
6.1 Principle . 6
6.2 Apparatus . 6
6.2.1 Abrasive jet test apparatus . 6
6.2.2 Abrading medium . 7
6.2.3 Eddy-current meter . 7
6.2.4 Balance . 7
6.3 Procedure . 7
6.3.1 Standard specimen. 7
6.3.2 Test specimen . 7
6.3.3 Calibration of apparatus . 8
6.3.4 Calibration of jet nozzle . 8
6.3.5 Determination . 9
6.3.6 Use of a reference specimen . 9
6.4 Expression of results . 9
6.4.1 General. 9
6.4.2 Abrasive jet factor . 9
6.4.3 Mean specific abrasion resistance . 9
6.4.4 Relative mean specific abrasion resistance .10
7 Falling sand abrasion test .10
7.1 Principle .10
7.2 Apparatus .10
7.2.1 Falling sand abrasion test apparatus .10
7.2.2 Ohmmeter .11
7.2.3 Abrading medium .11
ISO 8251:2018(E)
7.3 Test specimen .11
7.3.1 Sampling.11
7.3.2 Size .11
7.3.3 Treatment before testing .11
7.4 Test environment .11
7.5 Test conditions .11
7.6 Test procedure .11
7.6.1 General.11
7.6.2 Electrical conductivity method .11
7.6.3 Spot diameter method .12
7.7 Expression of results .12
7.7.1 Electrical conductivity method .12
7.7.2 Spot diameter method .13
8 Test report .13
Annex A (normative) Preparation of the standard specimen .14
Annex B (informative) Other expressions of results for the abrasive-wheel-wear test .16
Annex C (informative) Depth survey of abrasion resistance .19
Annex D (informative) Design of abrasive-wheel-wear test apparatus.22
Annex E (informative) Design of abrasive jet test apparatus .24
Annex F (informative) Design of falling sand abrasion test apparatus.27
Bibliography .29
iv © ISO 2018 – All rights reserved

ISO 8251:2018(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 of 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 79, Light metals and their alloys,
Subcommittee SC 2, Organic and anodic oxidation coatings on aluminium.
This third edition cancels and replaces the second edition (ISO 8251:2011), which has been technically
revised. The main technical changes are as follows:
— preparation for test specimens has been added;
— for expression of results, loss of mass has been added;
— some expressions of results have been moved to Annex B;
— standard specimen made of PMMA sheet has been added.
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.
ISO 8251:2018(E)
Introduction
The resistance of anodic oxidation coatings to abrasion is an important property. As it is dependent upon
the composition of the metal, the thickness of the coating and the conditions of anodizing and sealing,
it can give information about the quality of the coating, its potential resistance to erosion or wear and
its performance in service. For example, the effect of an abnormally high anodizing temperature, which
could cause potential deterioration in service by chalking of the surface layers, can be readily detected
by means of an abrasive wear resistance test.
The use of the term “abrasion resistance” is a convention of the industry. Strictly, the property should
be described as “wear resistance”. There are different types of wear including abrasive wear and
erosive wear.
vi © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 8251:2018(E)
Anodizing of aluminium and its alloys — Measurement of
abrasion resistance of anodic oxidation coatings
1 Scope
This document specifies the following tests:
a) abrasive-wheel-wear test, determining the abrasion resistance of anodic oxidation coatings with
abrasive wheel on flat specimens of aluminium and its alloys;
b) abrasive jet test, determining the comparative abrasion resistance of anodic oxidation coatings
with jet of abrasive particles on anodic oxidation coatings of aluminium and its alloys;
c) falling sand abrasion test, determining the abrasion resistance of anodic oxidation coatings with
falling sand on thin anodic oxidation coatings of aluminium and its alloys.
The use of abrasive-wheel-wear test and abrasive jet test for coatings produced by hard anodizing is
described in ISO 10074.
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 6344-1, Coated abrasives — Grain size analysis — Part 1: Grain size distribution test
ISO 7583, Anodizing of aluminium and its alloys — Terms and definitions
ISO 7823-1, Plastics — Poly(methyl methacrylate) sheets — Types, dimensions and characteristics —
Part 1: Cast sheets
ISO 8486-1, Bonded abrasives — Determination and designation of grain size distribution — Part 1:
Macrogrits F4 to F220
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7583 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
standard specimen
specimen produced in accordance with specified conditions
Note 1 to entry: The conditions are specified in Annex A.
ISO 8251:2018(E)
4 Characteristics of abrasion tests
4.1 General
In the scope of this document, there are three kinds of abrasion tests: abrasive-wheel-wear test (4.2),
abrasive jet test (4.3) and falling sand abrasion test (4.4).
4.2 Abrasive-wheel-wear test
Determination of the abrasion resistance by movement of a test specimen relative to an abrasive paper
under a specified pressure. The wear resistance or the wear index of the layers of oxide near the surface,
or of the whole oxidation coating thickness, or of any selected intermediate zone may be determined by
the test described.
NOTE 1 Abrasive-wheel-wear test determines the resistance to abrasive wear.
This test is applicable to all anodic oxidation coatings of thickness more than 5 μm on flat aluminium or
its alloy specimens.
This test does not apply to concave or convex specimens; these may be examined using the abrasive jet
test which will give an average value for the abrasive resistance of the coating.
NOTE 2 Minimum test specimen dimensions of 50 mm × 50 mm are normally used.
4.3 Abrasive jet test
Determination of the comparative abrasion resistance by the impact of abrasive particles projected onto
a test specimen. The mean specific abrasion resistance of anodic oxidation coatings can be determined.
NOTE 1 Abrasive jet test determines the comparative resistance to erosive wear.
This test is applicable to all anodic oxidation coatings of thickness more than 5 μm on aluminium or its
alloys. It is primarily intended for surfaces which are not flat. If suitable flat test surfaces are available,
the abrasive-wheel-wear test is the preferred test. Production components may be tested without
cutting if the apparatus chamber can accommodate these.
NOTE 2 This test is particularly suitable for small test specimens because the individual test area required is
only about 2 mm in diameter.
4.4 Falling sand abrasion test
Determination of the abrasion resistance by the impact of freely falling abrasive particles onto anodic
oxidation coatings.
This test is suitable to thin anodic oxidation coatings, generally less than 15 µm.
NOTE Falling sand abrasion test determines the resistance to erosive wear.
5 Abrasive-wheel-wear test
5.1 Principle
The anodic oxidation coatings on a test specimen are abraded, under defined conditions, by reciprocal
motion against a strip of silicon carbide paper attached to the outer circumference of a wheel. After each
double stroke, the wheel turns through a small angle to bring an unused portion of the abrasive strip
into contact with the test area. The decrease in coating thickness or mass obtained is used to calculate
the wear resistance, mass wear resistance, wear index or mass wear index. This result is compared
with that obtained using a standard specimen or reference specimen.
2 © ISO 2018 – All rights reserved

ISO 8251:2018(E)
The measuring method of coating thickness normally requires an eddy-current meter with a probe of
less than 12 mm diameter. If this is not available, the method of loss in mass should be used.
NOTE A complete presentation of the wear characteristics of the anodic oxidation coatings can be obtained
by progressively abrading the test area, until the substrate metal is revealed, and then constructing a graph to
show the relation between the coating thickness removed and the number of double strokes used. This is referred
to as a depth survey of the anodic oxidation coatings (see Annex C).
The testing environment should be at room temperature and the relative humidity should be under 65 %.
5.2 Apparatus
5.2.1 Abrasive-wheel-wear test apparatus
The apparatus consists of a clamping device or pressure plate for holding the test specimen level and
rigid, and a 50 mm diameter wheel to the outer circumference of which is attached a 12 mm wide strip
of silicon carbide paper. The force between the wheel and the test surface shall be capable of being
varied from zero to at least 4,9 N with an accuracy of ± 0,05 N. The abrasive action is produced either
by the fixed wheel sliding to and fro in a horizontal plane in parallel contact with the test surface over a
30 mm length or, alternatively, by the test specimen sliding in a similar way over the stationary wheel.
Typical apparatus is illustrated in Figure D.1.
After each double stroke, the wheel is advanced through a small angle to bring a fresh area of the silicon
carbide paper into contact with the specimen surface before making the next double stroke. The angle
of rotation is such that, after 400 ds, the wheel will have made one complete revolution. At this stage,
the strip of silicon carbide paper shall be renewed. The relative speed of movement shall be (40 ± 2) ds
per minute. The number of double strokes can be registered by means of a counter, and provision is
normally made for the apparatus to switch off automatically after a preset number of double strokes
has been reached (400 ds maximum). The test specimen surface shall be kept free from loose powder or
abrasion detritus during the test.
5.2.2 Abrasive strip
The abrasive strip consists of P320 silicon carbide paper (the specification of which shall be in
accordance with ISO 6344-1) 12 mm wide. Its length, 158 mm, shall be such that it covers the abrasive
wheel without overlapping, and it shall be bonded into position.
NOTE P320 paper is 45 μm grade (320 mesh).
5.2.3 Eddy-current meter
An eddy-current meter with a suitable diameter probe is described in ISO 2360.
5.2.4 Balance
Use a laboratory balance with a readability of 0,1 mg.
5.3 Procedure
5.3.1 Standard specimen
Prepare the aluminium standard specimen specified in Annex A.
If agreed between the interested parties, a standard specimen made of poly(methyl methacrylate)
(PMMA) sheet in accordance with ISO 7823-1 may be used.
NOTE Aluminium standard specimen and PMMA standard specimen specified in Annex A have different
abrasion resistance, about five times difference. For the purpose of comparison of the loss of mass, PMMA
standard specimen is used by adjusting the number of double strokes.
ISO 8251:2018(E)
5.3.2 Test specimen
5.3.2.1 Sampling
The test specimen shall be taken from a significant surface of the product, and shall not be taken near
an edge of the part for possible distortion and/or non-uniformity.
Where it is impossible to test the product itself, a test specimen may be used. However, in this case, the
test specimen used shall be one which is representative of the product, and it shall be made from the
same material and prepared under the same conditions of finishing as those used for the preparation of
the product.
The aluminium alloy, the manufacturing conditions (kind and temper of the material), and the surface
condition before treatment shall be the same as those of the product.
Pretreatment, anodizing and sealing shall be performed in the same baths and under the same
conditions as the treatment of the product.
5.3.2.2 Size
The standard size of the test specimen should be 50 mm × 50 mm.
5.3.2.3 Treatment before testing
The test specimen shall be clean, free from dirt, stains and other foreign matters. Any deposits or stains
shall be removed with a clean, soft cloth or similar material which is wetted by water or an appropriate
organic solvent such as ethanol. An organic solvent which can corrode the test specimen or generate a
protective film on the test specimen shall not be used.
5.3.3 Test procedure
5.3.3.1 The standard specimen and/or the test specimen shall be tested by the following procedure.
The abrasive strips used for the test specimen shall be the same lot as the one for the standard specimen.
A reference specimen may be used by agreement between the interested parties (see Annex B).
5.3.3.2 Select the test area of the standard specimen and/or the test specimen to be abraded. Measure
the anodic oxidation coating thicknesses of the standard specimen and/or the test specimen in each of
at least three positions along the test area by means of the eddy-current meter and calculate an average
thickness value (d ). For change in mass, weigh the mass (m ) of the standard specimen and/or the test
1 1
specimen to the nearest 0,1 mg by means of the balance.
5.3.3.3 Clamp the standard specimen and/or the test specimen into the position on the apparatus. If
the test specimen is not rigid, bond it firmly with an adhesive to a rigid metal sheet with a flat surface
before carrying out the test.
5.3.3.4 Attach a new abrasive strip to the circumference of the abrasive wheel. Adjust the force between
the wheel and the test surface to 3,9 N ± 0,1 N.
5.3.3.5 Allow the apparatus to run for 400 ds or an adequate number of double strokes corresponding
to the coating thickness and the kind of aluminium alloys.
5.3.3.6 Remove the standard specimen and/or the test specimen from the apparatus, wipe carefully to
remove any debris. Determine the average thickness value (d ) or weigh the mass (m ). A 3 mm length at
2 2
4 © ISO 2018 – All rights reserved

ISO 8251:2018(E)
one extremity of the test area can be subject to extra wear because of the continual wheel rotation which
takes place at this point; this area should be ignored when taking the thickness measurements.
Freshly exposed anodic oxidation coatings can gain in mass by absorbing water vapour. The
determination shall be carried out as early as possible after the test is finished.
5.3.3.7 Carry out at least two further tests on the same standard specimen and/or the test specimen
with test areas that are not overlapped. Follow the procedure specified in 5.3.3.2 to 5.3.3.6.
Determine the average thickness and/or mass of at least three standard specimens and/or test
specimens, before abrasion (d and/or m ) and after abrasion (d and/or m ).
1 1 2 2
5.4 Expression of results
5.4.1 General
The expression of results should be chosen from 5.4.2 to 5.4.5.
Other expression of results may be chosen by agreement between the interested parties (see Annex B).
5.4.2 Wear resistance
The wear resistance, R , in double strokes per micrometre, can be expressed using Formula (1):
W
N
R = (1)
W
dd−
where
N is the number of double strokes;
d is the average thickness, in micrometres, before abrasion;
d is the average thickness, in micrometres, after abrasion.
5.4.3 Mass wear resistance
The mass wear resistance, R , in double strokes per milligram, can be expressed using Formula (2):
MW
N
R = (2)
MW
mm−
where
N is the number of double strokes;
m is the average mass, in milligrams, before abrasion;
m is the average mass, in milligrams, after abrasion.
5.4.4 Wear index
The wear index, I , can be expressed using Formula (3):
W
dd−
12tt
I = (3)
W
dd−
12ss
ISO 8251:2018(E)
where
d is the average thickness, in micrometres, of the test specimen before abrasion;
1t
d is the average thickness, in micrometres, of the test specimen after abrasion;
2t
d is the average thickness, in micrometres, of the standard specimen before abrasion;
1s
d is the average thickness, in micrometres, of the standard specimen after abrasion.
2s
5.4.5 Mass wear index
The mass wear index, I , can be expressed using Formula (4):
MW
mm−
12tt
I = (4)
MW
mm−
12ss
where
m is the average mass, in milligrams, of the test specimen before abrasion;
1t
m is the average mass, in milligrams, of the test specimen after abrasion;
2t
m is the average mass, in milligrams, of the standard specimen before abrasion;
1s
m is the average mass, in milligrams, of the standard specimen after abrasion.
2s
6 Abrasive jet test
6.1 Principle
Dry silicon carbide particles are projected in a stream of dry air or inert gas under carefully controlled
conditions onto a small area of the surface to be tested. The test is continued until the substrate metal
is exposed, after which the abrasion resistance of the coating is expressed from either the time taken
or the mass of silicon carbide used. The result is compared with that obtained using an aluminium
standard specimen or reference specimen.
6.2 Apparatus
6.2.1 Abrasive jet test apparatus
NOTE The abrasive jet test apparatus is shown in Figures E.1 and E.2.
6.2.1.1 Abrasive jet nozzle, consisting essentially of two glass or metal tubes supported rigidly and
coaxially. The outer tube is connected to a supply of clean, dry, compressed air or inert gas, which can
be delivered at a carefully regulated flow rate. Dry abrasive particles are supplied to the inner tube, at
the exit end of which they mix with the air stream to form an abrasive jet which is directed onto the test
specimen.
No restriction is placed upon the design of the abrasive jet nozzle, except that it shall give reproducible
results in successive tests, and that it shall allow consistent measurements to be made.
NOTE A number of satisfactory designs of the jet nozzle have been constructed but it has proved difficult in
practice to manufacture a series of jets which give identical results, or to make any that are not subject to drift
and variations. Designs that have proved satisfactory are shown in Annex E.
6 © ISO 2018 – All rights reserved

ISO 8251:2018(E)
6.2.1.2 Test specimen support, comprising an inclined platform on which the test specimen is firmly
and rigidly supported such that the angle between the plane of the test area and that of the jet axis is in
the range 45° to 55°. The jet is usually vertical.
NOTE E.2 describes an apparatus where the angle is 55°. The larger angle produces a less elliptical test area,
more rapid abrasion and a sharper end point.
6.2.1.3 Air or inert gas supply, fed to the outer tube from a compressor or gas cylinder and controlled
accurately by means of a regulating valve and a manometer situated near the apparatus. The air or inert
gas shall be dry, or have constant low humidity.
NOTE 1 The inert gas can be dried by passing it through tubes containing silica gel. Compressed air passed
through a holding reservoir where condensed water vapour is collected will have a satisfactory and fairly
constant humidity.
NOTE 2 The pressure is typically 7,5 kPa ± 0,5 kPa.
6.2.1.4 Hopper, for storage of the abrading medium and capable of supplying this at a steady rate of
20 g/min ± 1 g/min to 30 g/min ± 1 g/min.
6.2.2 Abrading medium
Silicon carbide particles of a grade recommended by the manufacturer of the apparatus should be used.
A suitable grade of abrasive is 125 μm mesh size: F100 in accordance with ISO 565 and ISO 8486-1.
The abrading medium shall be free from moisture and shall be dried before use and passed through a
coarse sieve (for example, of 180 μm or 300 μm nominal aperture size) to ensure freedom from large
particles or fibres which might interfere with the rate of abrasive flow.
The dried medium may be re-used up to 50 times; after each use, the medium should be dried, passed
through a coarse sieve and stored in a clean, tightly closed container.
NOTE Ambient humidity has little effect on the test result, but can have a very considerable effect if the
medium is re-used without drying.
The testing environment should be at room temperature and the relative humidity should be under 65 %.
6.2.3 Eddy-current meter
An eddy-current meter with a suitable diameter probe is described in ISO 2360.
6.2.4 Balance
Use a laboratory balance with an accuracy of 1 g.
6.3 Procedure
6.3.1 Standard specimen
Prepare the aluminium standard specimen specified in Annex A.
6.3.2 Test specimen
6.3.2.1 Sampling
See 5.3.2.1.
ISO 8251:2018(E)
6.3.2.2 Size
The standard size of the test specimen should be about 100 mm × 100 mm.
6.3.2.3 Treatment before testing
See 5.3.2.3.
6.3.3 Calibration of apparatus
6.3.3.1 Select and mark the areas of the standard specimen to be abraded. Accurately measure the
anodic oxidation coating thickness (d) in each test area by means of an eddy-current meter.
6.3.3.2 Fix the standard specimen in position in the test apparatus with the selected test area beneath
the jet orifice and at the correct angle to the jet axis.
6.3.3.3 Fill the hopper with sufficient silicon carbide for the test. If the abrasion resistance is being
determined in terms of the mass of abrading medium used, weigh the hopper and abrading medium to
the nearest 1 g using the balance.
6.3.3.4 Set the air or gas pressure, to the specified (or selected) value, which shall be accurately
maintained throughout each test and any series of tests.
The air or gas pressure should be adjusted to give a rate of abrasion that is convenient for both the
standard specimen being tested and for the test specimen. The preferred pressure, is normally
indicated by the instrument manufacturer but it may be varied this for very soft, hard or thin coatings.
6.3.3.5 Start the flow of abrading medium and simultaneously start a timer. Throughout the test,
ensure that the abrading medium flows freely.
6.3.3.6 Keep the standard specimen under observation; when a small black spot appears in the centre
of the abraded area and rapidly enlarges to approximately 2 mm in diameter terminate the test by
stopping the abrading medium flow and the timer simultaneously. It is recommended that the end point
be determined by using a circuit tester to measure the electrical resistance at the abraded area on the
standard specimen.
6.3.3.7 Record the time, in seconds, taken for the test. If required, weigh the hopper and residual
abrading medium, calculate the mass in grams. The results give the abrasion of the standard specimen
(S ) in either seconds or grams.
s
6.3.3.8 Carry out at least two further tests on other parts of the standard specimen. Follow the
procedure specified in 6.3.3.1 to 6.3.3.7.
6.3.4 Calibration of jet nozzle
6.3.4.1 General
Since individual jets can vary with use and one with another, it is necessary to correct each set of
measurements by means of calibration determinations using a standard specimen as in 6.3.3. This
enables the abrasive jet factor for the set of measurements to be calculated.
6.3.4.2 Change of jet
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