ASTM E566-99(2004)e1
(Practice)Standard Practice for Electromagnetic (Eddy-Current) Sorting of Ferrous Metals
Standard Practice for Electromagnetic (Eddy-Current) Sorting of Ferrous Metals
SIGNIFICANCE AND USE
Absolute and comparative methods provide a means for sorting large quantities of ferrous parts of stock with regard to composition, condition, structure, or processing, or a combination thereof.
The comparative or two-coil method is used when high-sensitivity testing is required. The advantage of this method is that it almost completely suppresses all internal or external disturbances such as temperature variations or stray magnetic fields. The two-coil method is normally used when harmonic evaluation is employed for sorting.
The ability to accomplish satisfactorily these types of separations is dependent upon the relation of the magnetic characteristics of the ferromagnetic parts to their physical condition.
These methods may be used for high-speed sorting in a fully automated setup where the speed of testing may approach ten specimens per second depending on their size and shape.
The success of sorting ferromagnetic material depends mainly on the proper selection of magnetic field strength and frequency of signal in the test coil, fill factor, and variables present in the sample.
The degree of accuracy of a sort will be affected greatly by the coupling between the test coil field and the test specimen and the accuracy with which the specimen is held in the test coil field during the measuring period.
When high currents are used in the test coil, a means should be provided to maintain a constant temperature of the reference specimen in order to minimize measurement drift.
SCOPE
1.1 This practice covers the procedure for sorting ferrous metals using the electromagnetic (eddy-current) method. The procedure relates to instruments using absolute or comparator-type coils for distinguishing variations in mass, shape, conductivity, permeability, and other variables such as hardness and alloy that affect the electromagnetic or magnetic properties of the material. The selection of specimens to determine sorting feasibility and to establish standards is also included.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E566–99 (Reapproved 2004)
Standard Practice for
Electromagnetic (Eddy-Current) Sorting of Ferrous Metals
This standard is issued under the fixed designation E 566; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorial changes were made to provide consistent terminology in May 2004.
1. Scope NAS-410 Qualification and Certification of Nondestructive
Testing Personnel
1.1 This practice covers the procedure for sorting ferrous
metals using the electromagnetic (eddy-current) method. The
3. Terminology
procedure relates to instruments using absolute or comparator-
3.1 Standard terminology relating to electromagnetic ex-
type coils for distinguishing variations in mass, shape, conduc-
amination may be found in Terminology E 1316, Section C:
tivity, permeability, and other variables such as hardness and
Electromagnetic Testing.
alloy that affect the electromagnetic or magnetic properties of
the material. The selection of specimens to determine sorting
4. Summary of Practice
feasibility and to establish standards is also included.
4.1 The two techniques that are primarily used in electro-
1.2 This standard does not purport to address all of the
magnetic sorting employ the absolute (single-) and compara-
safety concerns, if any, associated with its use. It is the
tive (two-) coil methods. The decision of whether to use
responsibility of the user of this standard to establish appro-
single-coil or two-coil operation is usually determined by
priate safety and health practices and determine the applica-
empirical data. In the absolute-coil method, the equipment is
bility of regulatory limitations prior to use.
standardized by placing standards of known properties in the
test coil. The value of the tested parameter (for instance,
2. Referenced Documents
hardness, alloy, or heat treatment) is read on the scale of an
2.1 ASTM Standards:
indicator. In the comparative-coil method, the test specimen is
E 105 Practice for Probability Sampling of Materials
compared with a reference specimen and the indication tells
E 122 Practice for Calculating Sample Size to Estimate,
whether the test specimen is within or outside of the required
with a Specified Tolerable Error, the Average for Charac-
limits.
teristic for a Lot or Process
4.1.1 Absolute Coil Method—A specimen of known classi-
E 543 Practice for Agencies Performing Nondestructive
fication is inserted in the test coil, and the controls of the
Testing
instrument are adjusted to obtain an indication. The method is
E 1316 Terminology for Nondestructive Examinations
then continued by inserting the test specimens to be sorted into
2.2 ASNT Documents:
the test coil, and observing the instrument indication.
SNT-TC-1A Recommended Practice for Personnel Qualifi-
4 4.1.2 Comparative Coil Method—Known reference speci-
cation and Certification in Nondestructive Testing
mens representing the minimum or maximum limits of accep-
ANSI/ASNT CP-189 Standard for Qualification and Certi-
4 tance, or both, are inserted in the reference coil and test coil.
fication of Nondestructive Testing Personnel
The instrument controls are adjusted for appropriate indica-
2.3 AIA Standard:
tions. The method is then continued by inserting the test
specimens to be sorted in the test coil, leaving a known
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- reference in the reference coil, and observing the instrument
structive Testing and is the direct responsibility of Subcommittee E07.07 on
indication.
Electromagnetic Methods.
4.2 The range of instrument indication must be so adjusted
Current edition approved May 1, 2004. Published June 2004. Originally
in the initial step that the anticipated deviations will be
approved in 1976. Last previous edition approved in 1999 as E 566 - 99.
General information can be found in the Nondestructive Testing Handbook,
recognized within the range of readout according to whether
(Second Edition), Vol IV: Electromagnetic Testing, Society for Nondestructive
two- or three-way sorts are to be accomplished.
Testing, 1986.
3 4.3 Both absolute and comparative methods require com-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM paring the test specimens with the reference specimen(s). Two
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
4 5
AvailablefromTheAmericanSocietyforNondestructiveTesting(ASNT),P.O. Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518. Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E566–99 (2004)
or more specimens representing the limits of acceptance may 6.3 Acceptance Criteria—Since acceptance criteria are not
be required. In the absolute method the electrical reference is specified in this practice, they shall be specified in the
generated by a test specimen. In the comparative method any contractual agreement.
electromagnetic condition that is not common to the test
specimen and the reference specimen will produce an imbal-
7. Interferences
ance in the system. The comparative method usually is more
7.1 Thespecificinfluenceofthefollowingvariablesmustbe
stable, as it normally suppresses noise.
considered for proper interpretation of the results obtained:
4.4 The testing process may consist of manual insertion of
7.1.1 The correlation shall be established so that magnetic
one specimen after another into the test coil, or an automated
or electrical properties, or both, of various groups do not
feeding and classifying mechanism may be employed. In
overlap and are well defined in the standardization procedure
automated setups, it is sometimes necessary to stop each
used.
specimen momentarily in the test coil while the reading is
7.1.2 In sorting magnetic materials, a magnetic field
being taken, especially if low test frequencies are employed.
strength and test frequency must be used that will result in a
well-defined separation of variables being tested.
5. Significance and Use
7.1.3 When examining magnetic materials at low field
5.1 Absolute and comparative methods provide a means for
strength, any influence from the previous magnetic history of
sorting large quantities of ferrous parts of stock with regard to
the test specimen (residual magnetism) shall be negated by
composition, condition, structure, or processing, or a combi-
demagnetization of the specimen if it restricts the electromag-
nation thereof.
netic sort.
5.2 The comparative or two-coil method is used when
7.1.4 The temperature of the reference specimen and test
high-sensitivity testing is required. The advantage of this
specimen shall be controlled within limits that will permit a
method is that it almost completely suppresses all internal or
well-defined range of conductivity or permeability, or both, for
external disturbances such as temperature variations or stray
which the correlation of the group or groups is valid. Cooling
magnetic fields. The two-coil method is normally used when
of the reference specimens when high field strengths are used
harmonic evaluation is employed for sorting.
or allowing test specimens to cool or heat to an established
5.3 The ability to accomplish satisfactorily these types of
ambient range, or both, may be required.
separations is dependent upon the relation of the magnetic
7.1.5 The geometry and mass of the reference standard and
characteristics of the ferromagnetic parts to their physical
test specimen shall be controlled within limits that will permit
condition.
sorting.
5.4 These methods may be used for high-speed sorting in a
7.1.6 Speed Effects—See 4.4.
fully automated setup where the speed of testing may approach
ten specimens per second depending on their size and shape.
8. Apparatus
5.5 The success of sorting ferromagnetic material depends
8.1 Electronic Apparatus—The electronic apparatus shall
mainly on the proper selection of magnetic field strength and
be capable of energizing the test coils with alternating currents
frequency of signal in the test coil, fill factor, and variables
ofsuitablefrequenciesandpowerlevelsandshallbecapableof
present in the sample.
sensing the changes in the electromagnetic response of the test
5.6 The degree of accuracy of a sort will be affected greatly
coils. Equipment may include any suitable signal-processing
bythecouplingbetweenthetestcoilfieldandthetestspecimen
devices (phase discriminator, filter circuits, etc.) and the output
and the accuracy with which the specimen is held in the test
may be displayed by meter, scope, recorder, signaling devices
coil field during the measuring period.
or any suitable combination required for the particular appli-
5.7 When high currents are used in the test coil, a means
cation.
should be provided to maintain a constant temperature of the
8.2 Test Coils may be of the encircling or probe-coil type
reference specimen in order to minimize measurement drift.
and shall be capable of inducing an electromagnetic field in the
6. Basis of Application
test specimen and reference specimen and sensing changes in
the electric and magnetic characteristics of the test specimen.
6.1 Personnel Qualification—If specified in the contractual
agreement, personnel performing examinations to this practice 8.2.1 When selecting the test coil, the objective should be to
obtain a coil fill factor as large as possible. This means that the
shall be qualified in accordance with a nationally recognized
nondestructive testing (NDT) personnel qualification practice inside of the test coil should be filled by the test specimen as
much as possible. This is of primary importance for tests
or standard, such as ANSI/ASNT-CP-189, SNT-TC-1A, NAS-
410, or a similar document and certified by the employer or requiring high sensitivity.
8.2.2 For complicated test specimen shapes, a correspond-
certifying agency, as applicable. The practice or standard used
and its applicable revision shall be identified in the contractual inginsertshallbeprovidedtoensurethateachspecimencanbe
placed in the same position within the test coil. These inserts,
agreement between the using parties.
6.2 Qualification of Nondestructive Agencies—If specified as well as any other accessories, should consist of nonferro-
magnetic, electrically nonconductive material.
in the contractual agreement, NDT agencies shall be qualified
and evaluated as described in Practice E 543. The applicable 8.3 Mechanical Handling Apparatus—Amechanical device
edition of Practice E 543 shall be specified in the contractual for feeding and sorting the test specimens may be used to
agreement. automate the particular application.
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E566–99 (2004)
9. Sampling 11. Standardization
11.1 Theelectromagneticsortingmethodisprimarilyoneof
9.1 Sampling(seePracticesE 105andE 122)isamethodto
comparison between specimens. Empirical data and physical
obtain assurance that materials are of satisfactory quality.
tests determine classification. The standardization procedure
Instead of 100 % inspection, a portion of the material is
shall be governed by the properties of the material requiring
examined to show evidence of the quality of the whole. There
separation.
are two important needs for this approach: first, in the final
11.2 Whenusingtheabsolutecoilmethod,inserttheaccept-
inspection or examinations made to ensure that products
delivered are in conformance with specification requirements; able reference standard to a fixed position in or relative to the
test coil and adjust the instrument to get an on-scale meter or
second, to control parts and assemblies while they are being
processed. Statistical acceptance sampling tables and statistical scope reading, or both. Replace the reference standard with an
unacceptable reference specimen in the same exact position
process-control sampling tables have been developed to meet
these needs. and adjust the sensitivity of the instrument to maximize the
indicator difference reading without exceeding 90 % of the
9.2 Acceptance sampling may be conducted on an accept/
available scale range.
reject (or attributes) basis, that is, determining whether or not
11.3 When using the comparative coil method, select a
the units of the sample meet the specification. Examination of
referencespecimen(usuallyonethatfallswithintheacceptable
the samples may also be conducted on a measurements (or
limits of the specimens being tested) and place it in the
variables) basis, that is, determining actual readings on the
referencecoilinsuchawaythatitwillnotbedisturbed,andset
units in the sample. The majority of acceptance sampling is
this coil and reference specimen out of the way. For this
carried out on a sampling by the attributes basis and the usual
method, when confronted with a two-way mix, choose two
acceptance sampling table is designed for accept/reject criteria.
specimens, one of which represents the acceptable and the
9.3 Process control sampling may be conducted on material
other the unacceptable group. Place the acceptable specimen to
during the course of production to prevent large quantities of
a fixed position in the test coil coinciding with the position of
defective parts being found in the acceptance tests. Many parts
the reference specimen in the reference coil and balance the
and materials are subjected to several successive machining or
instrument. Replace this acceptable specimen with one repre-
processing operations before they become finished units. Parts
senting the unacceptable group and adjust the test instrument’s
can be most effectively controlled during production by exam-
phase, sensitivity, and coil current; then index to maximize the
ining small samples of these parts at regularly scheduled
indicatorreadingwithoutexceeding90 %oftheavailablescale
intervals. The object of this process check is to provide a
range. Reinsert the acceptable specimen and alternately read-
continuous picture of the quality of parts being produced. This
just the instrument controls to retain a null value for the
helps prevent production of defective parts by stopping and
acceptable specimen and maximum indication for the unac-
correcting the problem as soon as it begins to appear in the
ceptable specimen.
manufacturing process and thereby keeping the process in
11.4 For a three-way sort, it
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