ASTM E703-98(2004)e1
(Practice)Standard Practice for Electromagnetic (Eddy-Current) Sorting of Nonferrous Metals
Standard Practice for Electromagnetic (Eddy-Current) Sorting of Nonferrous Metals
SIGNIFICANCE AND USE
Absolute and comparative methods provide a measure for sorting large quantities of nonferrous parts or stock with regard to composition or condition, or both.
The comparative or two-coil method is used when high-sensitivity examination is required. The advantage of this method is that it almost completely suppresses interferences.
The ability to accomplish these types of separations satisfactorily is dependent upon the relation of the electric characteristics of the nonferrous parts to their physical condition.
These methods may be used for high-speed sorting in a fully automated setup where the speed of examination may approach many specimens per second depending on their size and shape.
Successful sorting of nonferrous material depends mainly on the variables present in the sample and the proper selection of frequency and fill factor.
The accuracy of a sort will be affected greatly by the coupling between the test coil field and the examined part during the measuring period.
SCOPE
1.1 This practice describes a procedure for sorting nonferrous metals using the electromagnetic (eddy-current) method. The procedure is intended for use with instruments using absolute or comparator-type coils for distinguishing variations in mass, shape, conductivity, and other variables such as alloy, heat treatment, or hardness that may be closely correlated with the electrical properties of the material. Selection of samples to evaluate sorting feasibility and to establish standards is also described.
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:E703–98 (Reapproved 2004)
Standard Practice for
Electromagnetic (Eddy-Current) Sorting of Nonferrous
Metals
This standard is issued under the fixed designation E 703; 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—Editorially replaced the terms calibration with standardization and test with examination where applicable in January
2004.
1. Scope decision of whether to use single-coil or two-coil operation is
usually based on empirical data. In the absolute-coil method
1.1 This practice describes a procedure for sorting nonfer-
(encircling or probe), the equipment is standardized by placing
rous metals using the electromagnetic (eddy-current) method.
standards of known properties in the test coil. The value of the
The procedure is intended for use with instruments using
examined electrical parameter, which may be correlated with
absolute or comparator-type coils for distinguishing variations
alloy, heat treatment temper, or hardness, is read on the display
in mass, shape, conductivity, and other variables such as alloy,
of an indicator. In the comparative coil method (encircling or
heat treatment, or hardness that may be closely correlated with
probe coils), the test specimen in one coil is compared with a
the electrical properties of the material. Selection of samples to
reference piece in a second coil to determine whether the test
evaluate sorting feasibility and to establish standards is also
specimen is within or outside of the required limits.
described.
4.1.1 Absolute Coil Method:
1.2 This standard does not purport to address all of the
4.1.1.1 Encircling Coil—Samples of known classification
safety concerns, if any, associated with its use. It is the
(standards) are inserted consecutively in the test coil, and the
responsibility of the user of this standard to establish appro-
controls of the instrument are adjusted to obtain an appropriate
priate safety and health practices and determine the applica-
response. Typically, three samples would be used representing
bility of regulatory limitations prior to use.
the upper, lower, and mid-range for which standardization is
2. Referenced Documents
required. The examination is then conducted by inserting the
specimens to be sorted into the test coil, and observing the
2.1 ASTM Standards:
instrument response.
E 105 Practice for Probability Sampling of Materials
4.1.1.2 Probe Coil—The probe coil is placed consecutively
E 122 Practice for Choice of Sample Size to Estimate a
on the standards of known properties and the controls of the
Measure of Quality for a Lot or Process
instrument are adjusted for appropriate response (see 4.1.1.1).
E 1316 Terminology for Nondestructive Examinations
The examination is then conducted by placing the probe on the
3. Terminology Definitions
specimens to be sorted and observing the instrument response.
4.1.2 Comparative Coil Method:
3.1 Definitions of terms relating to electromagnetic exami-
4.1.2.1 Encircling Coil—Known reference pieces (stan-
nation are given in Terminology E 1316.
dards) representing the minimum or maximum limits, or both,
4. Summary of Practice
of acceptance or sorting category are inserted in the reference
and test coil. The instrument controls are adjusted for appro-
4.1 The techniques that are primarily used in electromag-
priate responses. The examination is then conducted by insert-
netic sorting employ the absolute (single-) and comparative
ing specimens to be sorted in the test coil, leaving the known
(two-) coil methods using either encircling or probe coils. The
reference in the reference coil and observing the instrument
response.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
4.1.2.2 Probe Coil—Both probe coils are placed on the
structive Testing and is the direct responsibility of Subcommittee E07.07 on
reference pieces (standard) representing the minimum or maxi-
Electromagnetic Methods.
Current edition approved January 1, 2004. Published February 2004. Originally mum limits, or both, of acceptance or sorting category. The
approved in 1979. Last previous edition approved in 1998 as E 703 - 98.
instrument controls are adjusted for appropriate responses.The
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
examination is then conducted by placing the test probe on the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E703–98 (2004)
specimens to be sorted (the other probe is left on the reference specimens to cool or heat to an established ambient range, or
standard) and observing the instrument response. both, may be required.
4.2 The range of instrument response must be so adjusted in
6.1.4 The geometry, mass, and thickness of the standard and
the initial step that the anticipated deviations will be within the
test specimen shall be controlled within limits that will permit
range of readout.
sorting.
4.3 Both absolute and comparative methods using encir-
6.1.5 Magnetic permeability variations can interfere when
cling coil(s) require comparing the specimens to be examined
sorting paramagnetic materials.
with the reference piece(s). Two or more samples representing
6.1.6 Signal response can result from a change in relative
the limits of acceptance may be required. In the absolute
motion between the test specimen and the test coil, such as the
method, the electrical reference signal from the instrument is
length of time the specimen is in a test coil (see 4.4).
adjusted with the standard in the coil. In the comparative
6.1.7 Conductivity has an unambiguous relationship to
method, any electromagnetic condition, that is not common to
hardness for certain alloys. However, when alloys are mixed,
the test specimen and the standard, will produce an imbalance
identical conductivity does not necessarily indicate the same
in the system. The comparative method is usually more stable
hardness.
since it suppresses most of the interferences.
6.1.8 Care must also be exercised in using conductivity to
4.4 The examination process may consist of manual inser-
sort overheated parts quenched at a high temperature as the
tion of one specimen after another into the test coil or an
conductivity reading for acceptable parts may repeat at a large
automated feeding and classifying mechanism may be em-
ployed. In automated setups, it is sometimes necessary to increase in temperature.
establish empirically the time required for the test specimen to
6.1.9 Lift-off can result in a change in the test system output
remain in the test coil while the reading is being taken,
with probe coils. This effect is a change in the magnetic
especially if low frequencies are employed.
coupling between the test specimen and probe coil. Care must
be exercised to prevent this effect from interfering with
5. Significance and Use
examination results; either mechanical or electronic compen-
sation must be used.
5.1 Absolute and comparative methods provide a measure
for sorting large quantities of nonferrous parts or stock with
6.1.10 Forcertainheat-treatable(aluminum)alloys,conduc-
regard to composition or condition, or both.
tivity values can also repeat themselves during the aging cycle
5.2 The comparative or two-coil method is used when ataconstanttemperature.Thus,forsuchalloys,conductivityis
high-sensitivity examination is required. The advantage of this
not unique as a monitor of temper, etc.
method is that it almost completely suppresses interferences.
5.3 The ability to accomplish these types of separations
7. Apparatus
satisfactorily is dependent upon the relation of the electric
7.1 Electronic Apparatus—The electronic apparatus shall
characteristics of the nonferrous parts to their physical condi-
be capable of energizing the test coils with alternating currents
tion.
ofsuitablefrequenciesandpowerlevelsandshallbecapableof
5.4 These methods may be used for high-speed sorting in a
sensing changes in the electromagnetic response of the coils.
fully automated setup where the speed of examination may
Equipment may include any suitable signal-processing devices
approach many specimens per second depending on their size
(phase discriminator, filter circuits, etc.) and the output may be
and shape.
displayed by meter, oscilloscope, recorder, signaling devices,
5.5 Successful sorting of nonferrous material depends
or any suitable combination required for the particular appli-
mainly on the variables present in the sample and the proper
cation.
selection of frequency and fill factor.
7.2 Test coils may be of the encircling or probe-coil type
5.6 The accuracy of a sort will be affected greatly by the
and shall be capable of inducing an electromagnetic field in the
coupling between the test coil field and the examined part
test specimen and standard, and sensing changes in the electric
during the measuring period.
or magnetic characteristics of the test specimen.
7.2.1 When selecting the test coil, the objective should be to
6. Interferences
obtain a coil fill factor as large as possible. This means that the
6.1 The influence of the following variables must be con-
inside of the test coil should be filled by the test specimen as
sidered for proper interpretation of the results:
much as possible. This is of primary importance for examina-
6.1.1 The correlation shall be established so that electrical
tions requiring high sensitivity.
properties of various groups do not overlap and are well
7.2.2 For complicated test specimen shapes, a correspond-
defined in the standardization procedure used.
ing insert shall be provided to ensure that each test specimen
6.1.2 The examination frequency must be selected to pro-
can be placed in the same position within the test coil. These
vide a well-defined separation of variables.
inserts, as well as any other accessories, should consist of
6.1.3 The temperature of the standard and test specimen
non-ferromagnetic, electrically nonconductive material.
shall be controlled within limits that will permit a well-defined
range of conductivity or permeability, or both, for which the 7.3 Mechanical Handling Apparatus— A mechanical de-
vice for feeding and sorting the test specimens may be used to
correlation of the group or groups is valid. Cooling of the
standard when high field strengths are used or allowing test automate a particular application.
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E703–98 (2004)
8. Sampling 9.4 Other arrangements can be used and are acceptable but
are not described in this procedure.
8.1 Sampling(seePracticesE 105andE 122)isamethodto
obtain assurance that materials are of satisfactory quality.
10. Standardization
Instead of 100 % inspection, a portion of the material is
10.1 Theelectromagneticsortingmethodisprimarilyoneof
examined to show evidence of the quality of the whole. There
comparison between specimens. Empirical data and physical
are two important needs for this approach: first, the final
examinations on samples representing properties to be sepa-
inspection or examination is made to assure that products
rated determine the validity of the sort. The standardization
delivered are in conformance with specification requirements;
procedure shall be based on the properties of the sample
second, to control parts and assemblies while they are being
requiring separation. The sort may require more than one
processed. Statistical acceptance sampling tables and statistical
operation.
process-control sampling tables have been developed to meet
10.2 When using the absolute coil method (encircling),
these needs.
insert the known acceptable standard to a fixed position in the
8.2 Acceptance sampling may be conducted on an accept/
coil and adjust the test instrument to get an on-scale meter or
reject (or attributes) basis; that is, determining whether or not
oscilloscope reading, or both. Replace the acceptable standard
the units of the sample meet the specification. Examination of
with a known unacceptable standard in the same exact position
the samples may also be conducted on a measurements (or
and adjust the sensitivity of the instrument to maximize the
variables) basis; that is, determining actual readings on the
indicated difference reading without exceeding 90 % of the
units in the sample. The majority of acceptance sampling is
available scale range.
carried out on a sampling by attributes basis and the usual
10.3 When using the comparative coil method (encircling),
acceptance sampling table is designed for accept/reject.
select a reference piece (usually one that falls within the
8.3 Process control sampling may be conducted on material
acceptable limits of the specimens being examined), place it in
during the course of production to prevent large quantities of
thereferencecoilandsetthiscoilandpieceinalocationsothat
defective parts being found in the acceptance examinations.
it will not be accidentally disturbed during the sorting opera-
Many parts and materials are subjected to several successive
tion. For this method, when used with a two-way mix, choose
machining or processing operations before they become fin-
two standards, one of which represents the acceptable and the
ished units. Parts can be most effectively controlled during
other the unacceptable group. Place the acceptable standard at
production by examining small samples of these parts at
a fixed position in the test coil coinciding with the position of
frequent regularly scheduled intervals. The object of this
the reference piece in the reference coil and balance the
process check is to provide a continuous picture of the quality
instrument. Replace this acceptable standard with one repre-
of parts being produced. This helps prevent production of
senting the unacceptable group and adjust the test instrument’s
defective parts by stopping and correcting the problem as soon
phase, sensitivity, and coil current, to maximize the indicator
as it begins to appear in the manufacturing process and thereby
reading without exceeding 90 % of the available scale range.
keeping the process in control. Sampling may be by attributes
Reinsert the acceptable standard and alternately readjust the
or by variables and process control sampling tables are used.
instrument controls to retain a null value for the acceptable
The measurements (variables) control chart is by far the mos
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