ASTM E977-05(2023)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E977 − 05 (Reapproved 2023)
Standard Practice for
Thermoelectric Sorting of Electrically Conductive Materials
This standard is issued under the fixed designation E977; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.1.3 direct instrumentation—a system that specifically
measures and displays the voltage (or an arbitrary unit)
1.1 This practice covers the procedure for sorting materials
generated between the electrodes when they are at different
using the thermoelectric method, which is based on the
temperatures and in contact with the material.
Seebeck effect. The procedure relates to the use of direct- and
comparator-type thermoelectric instruments for distinguishing
2.1.4 electrode—the conductors used in thermoelectric sort-
variations in materials which affect the thermoelectric proper- ing instruments used to generate the Seebeck effect with the
ties of those materials.
material under test.
1.2 While the practice is most commonly applied to the
2.1.5 Seebeck effect—the thermoelectric electromotive force
sorting of metals, it may be applied to other electrically
(emf) produced in a circuit connecting two dissimilar conduc-
conductive materials.
tors at two points of different temperatures; the magnitude of
this emf is a function of the chemistry of the materials, surface
1.3 Thermoelectric sorting may also be applied to the
metallurgical structure, and the temperature at the junctions.
sorting of materials on the basis of plating thickness, case
See Fig. 1.
depth, and hardness.
1.4 This standard does not purport to address all of the
3. Summary of Practice
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.1 The two techniques that are primarily used in thermo-
priate safety, health, and environmental practices and deter- electric sorting are direct and comparative instrumentation. In
mine the applicability of regulatory limitations prior to use.
the direct instruments, equipment is standardized by placing
1.5 This international standard was developed in accor- materials with known chemistry and metallurgical structure in
dance with internationally recognized principles on standard- the test system. The value of the thermoelectric voltage (or
ization established in the Decision on Principles for the arbitrary unit) is read on the scale of an indicator. In the
Development of International Standards, Guides and Recom-
comparative instruments, the thermoelectric response of the
mendations issued by the World Trade Organization Technical test piece is compared with that of a known standard(s) and the
Barriers to Trade (TBT) Committee. response indicates whether the piece is within the acceptance
limits.
2. Terminology
3.1.1 Both kinds of instrumentation require comparing the
pieces to be examined with the known standard(s). Two or
2.1 Descriptions of Terms:
more samples representing the acceptance limits may be
2.1.1 acceptance limits—the thermoelectric response that
required.
establishes the group into which the material being examined
3.1.2 Direct Thermoelectric Instrumentation—A known
belongs.
standard(s) is inserted in the system and the controls of the
2.1.2 comparative instrumentation—a system that uses elec-
instrument are adjusted to obtain a voltage (or arbitrary unit)
trode assemblies (probes), associated electronics, and known
reading(s). The process is then continued by inserting the
standards to measure a thermoelectric response from an
pieces to be sorted into the system, and observing the instru-
electrically-conductive material; this response is compared
ment reading(s).
with that of the reference standard.
3.1.3 Comparative Instrumentation—Known standards rep-
resenting the acceptance limits are inserted into the system.
The instrument controls are adjusted for appropriate response.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
The process is then continued by inserting the pieces to be
structive Testing and is the direct responsibility of Subcommittee E07.10 on
sorted in the system, and observing the instrument response.
Specialized NDT Methods.
Current edition approved Dec. 1, 2023. Published December 2023. Originally
3.2 In both instruments, the range of the instrument re-
approved in 1984. Last previous edition approved in 2019 as E977 – 05 (2019).
DOI: 10.1520/E0977-05R23. sponse must be adjusted during standardization so that any
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E977 − 05 (2023)
FIG. 1 Typical Circuit Used in Thermoelectric Material Sorting Instruments
anticipated deviation from the known standard(s) will be 5.1.3 Contaminates that will electrically insulate material
recognized as within the required acceptance limits. being examined, such as rust, grease, oil, mill scale; or surface
coatings such as paint, plastic, and so forth, must be removed
3.3 The examination process may consist of manual inser-
to ensure clean contact between the material and the electrodes
tion of one piece after another into the system, or an automated
of the device.
feeding and classifying mechanism may be employed.
5.1.4 Extreme temperature differences between the stan-
4. Application
dard(s) and the pieces will alter the emf generated. Known
4.1 Thermoelectric techniques provide a method for sorting
standard(s) should be at the same temperature as the pieces
large quantities of conductive materials. The ability to accom-
being examined.
plish satisfactorily these types of separations is dependent upon
5.1.5 The geometry and mass of the standard and part need
the relation of the thermoelectric voltages with regard to
not be a consideration to permit sorting. Fixturing may be
composition, condition, structure, and processing.
required where the part mass is insufficient to provide an
4.2 Comparative instrumentation is used when high-
adequate heat sink (for example, thin foil, small-diameter wire,
sensitivity testing is required. The advantage of this method is
small bearings, etc.).
that it reduces internal or external disturbances such as
5.1.6 Interference may be caused by radio frequency pro-
temperature variations of the material or probes, or both.
duced by devices such as arc welders or radio and radar
4.3 The success of an attempted sort will be affected by
transmitters. This interference may be observed when the
instrument factors such as
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