ASTM E566-99

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 566 – 99
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.
1. Scope 3. Terminology
1.1 This practice covers the procedure for sorting ferrous 3.1 Standard terminology relating to electromagnetic ex-
metals using the electromagnetic (eddy-current) method. The amination may be found in Terminology E 1316, Section C:
procedure relates to instruments using absolute or comparator- Electromagnetic Testing.
type coils for distinguishing variations in mass, shape, conduc-
4. Summary of Practice
tivity, permeability, and other variables such as hardness and
4.1 The two techniques that are primarily used in electro-
alloy that affect the electromagnetic or magnetic properties of
the material. The selection of samples to determine sorting magnetic sorting employ the absolute (single-) and compara-
tive (two-) coil methods. The decision of whether to use
feasibility and to establish standards is also included.
1.2 This standard does not purport to address all of the single-coil or two-coil operation is usually determined by
empirical data. In the absolute-coil method, the equipment is
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- standardized by placing standards of known properties in the
test coil. The value of the tested parameter (for instance,
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. hardness, alloy, or heat treatment) is read on the scale of an
indicator. In the comparative-coil method, the test piece is
2. Referenced Documents
compared with a reference piece and the indication tells
2.1 ASTM Standards: whether the piece is within or outside of the required limits.
E 105 Practice for Probability Sampling of Materials 4.1.1 Absolute Coil Method—A sample of known classifi-
E 122 Practice for Choice of Sample Size to Estimate a cation is inserted in the test coil, and the controls of the
Measure of Quality for a Lot or Process instrument are adjusted to obtain an indication. The test is then
E 543 Practice for Agencies Performing Nondestructive continued by inserting the pieces to be sorted into the test coil,
Testing and observing the instrument indication.
E 1316 Terminology for Nondestructive Examinations 4.1.2 Comparative Coil Method—Known reference pieces
2.2 ASNT Documents: representing the minimum or maximum limits of acceptance,
SNT-TC-1A Recommended Practice for Qualification and or both, are inserted in the reference coil and test coil. The
Certification in Nondestructive Testing instrument controls are adjusted for appropriate indications.
ANSI/ASNT CP-189 ASNT Standard for Qualification and The test is then continued by inserting the pieces to be sorted
Certification of Nondestructive Testing Personnel in the test coil, leaving a known reference in the reference coil,
2.3 Federal Standard: and observing the instrument indication.
NAS-410 Nondestructive Testing Personnel Qualification 4.2 The range of instrument indication must be so adjusted
and Certification in the initial step that the anticipated deviations will be
recognized within the range of readout according to whether
two- or three-way sorts are to be accomplished.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
4.3 Both absolute and comparative methods require com-
structive Testing and is the direct responsibility of Subcommittee E07.07 on
paring the pieces to be tested with the reference piece(s). Two
Electromagnetic Methods.
or more samples representing the limits of acceptance may be
Current edition approved June 10, 1999. Published August 1999. Originally
published as E 566 – 76. Last previous edition E 566 – 94.
required. In the absolute method the electrical reference is
General information can be found in the Nondestructive Testing Handbook,
generated by a test piece. In the comparative method any
(Second Edition), Vol IV: Electromagnetic Testing, Society for Nondestructive
electromagnetic condition that is not common to the test
Testing, 1986.
Annual Book of ASTM Standards, Vol 14.02. specimen and the standard will produce an imbalance in the
Annual Book of ASTM Standards, Vol 03.03.
system. The comparative method usually is more stable, as it
Available from American Society for Nondestructive Testing, 1711 Arlingate
normally suppresses noise.
Plaza, P.O. Box 28518, Columbus, OH 43228–0518.
Available from Standardization Documents Order Desk, Building 4, Section D,
700 Robbins Avenue, Philadelphia, PA 19111–5904, ATTN: NPODS.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E566–99
4.4 The testing process may consist of manual insertion of 7.1.1 The correlation shall be established so that magnetic
one piece 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 piece used.
momentarily in the test coil while the reading is being taken, 7.1.2 In sorting magnetic materials, a magnetic field
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 part on the test (residual magnetism) shall be negated by
composition, condition, structure, or processing, or a combi- demagnetization of the part if it restricts the electromagnetic
nation thereof.
sort.
5.2 The comparative or two-coil method is used when
7.1.4 The temperature of the standard and test part shall be
high-sensitivity testing is required. The advantage of this
controlled within limits that will permit a well-defined range of
method is that it almost completely suppresses all internal or
conductivity or permeability, or both, for which the correlation
external disturbances such as temperature variations or stray
of the group or groups is valid. Cooling of the test standard
magnetic fields. The two-coil method is normally used when
when high field strengths are used or allowing test parts to cool
harmonic evaluation is employed for sorting.
or heat to an established ambient range, or both, may be
5.3 The ability to accomplish satisfactorily these types of
required.
separations is dependent upon the relation of the magnetic
7.1.5 The geometry and mass of the standard and test part
characteristics of the ferromagnetic parts to their physical
shall be controlled within limits that will permit sorting.
condition.
7.1.6 Speed Effects—See 4.4.
5.4 These methods may be used for high-speed sorting in a
fully automated setup where the speed of testing may approach
8. Apparatus
ten pieces per second depending on their size and shape.
8.1 Electronic Apparatus—The electronic apparatus shall
5.5 The success of sorting ferromagnetic material depends
be capable of energizing the test coils with alternating currents
mainly on the proper selection of magnetic field strength and
of suitable frequencies and power levels and shall be capable of
frequency of signal in the test coil, fill factor, and variables
sensing the changes in the electromagnetic response of the
present in the sample.
coils. Equipment may include any suitable signal-processing
5.6 The degree of accuracy of a sort will be affected greatly
devices (phase discriminator, filter circuits, etc.) and the output
by the coupling between the test coil field and the tested part
may be displayed by meter, scope, recorder, signaling devices
and the accuracy with which the tested part is held in the test
or any suitable combination required for the particular appli-
coil field during the measuring period.
cation.
5.7 When high currents are used in the test coil, a means
8.2 Test Coils may be of the encircling or probe-coil type
should be provided to maintain a constant temperature of the
and shall be capable of inducing electromagnetic field in the
test standard in order to minimize measurement drift.
test specimen and standard and sensing changes in the electric
and magnetic characteristics of the test specimen.
6. Basis of Application
8.2.1 When selecting the test coil, the objective should be to
6.1 Personnel Qualification—If specified in the contractual
obtain a coil fill factor as large as possible. This means that the
agreement, personnel performing examinations to this practice
inside of the test coil should be filled by the test piece as much
shall be qualified in accordance with a nationally recognized
as possible. This is of primary importance for tests requiring
NDT personnel qualification practice or standard, such as
high sensitivity.
ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, or a similar
8.2.2 For complicated test piece shapes, a corresponding
document and certified by the employer or certifying agency,
insert shall be provided to ensure that each test piece can be
as applicable. The practice or standard used and its applicable
placed in the same position within the test coil. These inserts,
revision shall be identified in the contractual agreement be-
as well as any other accessories, should consist of nonferro-
tween the using parties.
magnetic, electrically nonconductive material.
6.2 Qualification of Nondestructive Agencies—If specified
8.3 Mechanical Handling Apparatus—A mechanical device
in the contractual agreement, NDT agencies shall be qualified
for feeding and sorting the test specimens may be used to
and evaluated as described in Practice E 543. The applicable
automate the particular application.
edition of Practice E 543 shall be specified in the contractual
agreement.
9. Sampling
6.3 Acceptance Criteria—Since acceptance criteria are not
specified in this practice, they shall be specified in the 9.1 Sampling (see Practices E 105 and E 122) is a method to
obtain assurance that materials are of satisfactory quality.
contractual agreement.
Instead of 100 % inspection, a portion of the material is
7. Interferences
examined to show evidence of the quality of the whole. There
7.1 The specific influence of the following variables must be are two important needs for this approach: first, in the final
considered for proper interpretation of the results obtained: inspection or tests made to ensure that products delivered are in
E566–99
conformance with specification requirements; second, to con- and adjust the test instrument to get an on-scale meter or scope
trol parts and asemblies while they are being processed. reading, or both. Replace the acceptable standard with a known
Statistical acceptance sampling tables and statistical process- unacceptable standard in the same exact position and adjust the
control sampling tables have been developed to meet these sensitivity of the instrument to maximize the indicator differ-
needs. ence reading without exceeding 90 % of the available scale
9.2 Acceptance sampling may be conducted on an accept/ 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
reference piece (usually one that falls within the acceptable
the samples may also be conducted on a measurements (or
limits of the pieces being tested) and place it in the reference
variables) basis, that is, determining actual readings on the
coil in such a way that it will not be disturbed, and set this coil
units in the sample. The majority of acceptance sampling is
and reference piece out of the way. For this method, when
carried out on a sampling by the attributes basis and the usual
confronted with a two-way mix, choose two standards, one of
acceptance sampling table is designed for accept/reject criteria.
which represents the acceptable and the other the unacceptable
9.3 Process control sampling may be conducted on material
group. Place the acceptable standard to a fixed position in the
during the course of production to prevent large quantities of
test coil coinciding with the position of the reference piece in
defective parts being found in the acceptance tests. Many parts
the reference coil and balance the instrument. Replace this
and materials are subjected to several successive machining or
acceptable calibration standard with one representing the
processing operations before they become finished units. Parts
unacceptable group and adjust the test instrument’s phase,
can be most effectively controlled during production by exam-
sensitivity, and coil current; then index to maximize the
ining small samples of these parts at regularly scheduled
indicator reading without exceeding 90 % of the available scale
intervals. The object of this process check is to provide a
range. Reinsert the acceptable standard and alternately readjust
continuous picture of the quality of parts being produced. This
the instrument controls to retain a null value for the acceptable
helps prevent production of defective parts by stopping and
standard and maximum indication for the unacceptable stan-
correcting the problem as soon as it begins to appear in the
dard.
manufacturing process and thereby keeping the process in
11.4 For a three-way sort, it is best to have three standards,
control. Sampling may be by attributes or by variable and
two of which represent the high and low limits of acceptability
process control sampling tables. The measurements (variables)
for one group or one each of the two unacceptable groups. The
control chart is by far the most effective process control
third standard, of course, represents the acceptable lot of
technique.
material.
9.4 Statistical sampling tables have four definite features:
11.4.1 A typical case for the former usually consists of
(1) specifications of sampling data, that is, the size of the
hardness or case depth measurements where standards repre-
samples to be selected, the conditions under which the samples
senting maximum and minimum limits are required. In this
are to be selected, and the conditio
...