1、Designation: E 703 98 (Reapproved 2004)e1Standard Practice forElectromagnetic (Eddy-Current) Sorting of NonferrousMetals1This standard is issued under the fixed designation E 703; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorially replaced the terms calibration with standardization and test with examination where applicable in Janu
3、ary2004.1. Scope1.1 This practice describes a procedure for sorting nonfer-rous metals using the electromagnetic (eddy-current) method.The procedure is intended for use with instruments usingabsolute or comparator-type coils for distinguishing variationsin mass, shape, conductivity, and other variab
4、les such as alloy,heat treatment, or hardness that may be closely correlated withthe electrical properties of the material. Selection of samples toevaluate sorting feasibility and to establish standards is alsodescribed.1.2 This standard does not purport to address all of thesafety concerns, if any,
5、 associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 105 Practice for Probability Sampling of Materials
6、E 122 Practice for Choice of Sample Size to Estimate aMeasure of Quality for a Lot or ProcessE 1316 Terminology for Nondestructive Examinations3. Terminology Definitions3.1 Definitions of terms relating to electromagnetic exami-nation are given in Terminology E 1316.4. Summary of Practice4.1 The tec
7、hniques that are primarily used in electromag-netic sorting employ the absolute (single-) and comparative(two-) coil methods using either encircling or probe coils. Thedecision of whether to use single-coil or two-coil operation isusually based on empirical data. In the absolute-coil method(encircli
8、ng or probe), the equipment is standardized by placingstandards of known properties in the test coil. The value of theexamined electrical parameter, which may be correlated withalloy, heat treatment temper, or hardness, is read on the displayof an indicator. In the comparative coil method (encirclin
9、g orprobe coils), the test specimen in one coil is compared with areference piece in a second coil to determine whether the testspecimen is within or outside of the required limits.4.1.1 Absolute Coil Method:4.1.1.1 Encircling CoilSamples of known classification(standards) are inserted consecutively
10、 in the test coil, and thecontrols of the instrument are adjusted to obtain an appropriateresponse. Typically, three samples would be used representingthe upper, lower, and mid-range for which standardization isrequired. The examination is then conducted by inserting thespecimens to be sorted into t
11、he test coil, and observing theinstrument response.4.1.1.2 Probe CoilThe probe coil is placed consecutivelyon the standards of known properties and the controls of theinstrument are adjusted for appropriate response (see 4.1.1.1).The examination is then conducted by placing the probe on thespecimens
12、 to be sorted and observing the instrument response.4.1.2 Comparative Coil Method:4.1.2.1 Encircling CoilKnown reference pieces (stan-dards) representing the minimum or maximum limits, or both,of acceptance or sorting category are inserted in the referenceand test coil. The instrument controls are a
13、djusted for appro-priate responses. The examination is then conducted by insert-ing specimens to be sorted in the test coil, leaving the knownreference in the reference coil and observing the instrumentresponse.4.1.2.2 Probe CoilBoth probe coils are placed on thereference pieces (standard) represent
14、ing the minimum or maxi-mum limits, or both, of acceptance or sorting category. Theinstrument controls are adjusted for appropriate responses. Theexamination is then conducted by placing the test probe on the1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing an
15、d is the direct responsibility of Subcommittee E07.07 onElectromagnetic Methods.Current edition approved January 1, 2004. Published February 2004. Originallyapproved in 1979. Last previous edition approved in 1998 as E 703 - 98.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or
16、contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.specimens to be so
17、rted (the other probe is left on the referencestandard) and observing the instrument response.4.2 The range of instrument response must be so adjusted inthe initial step that the anticipated deviations will be within therange of readout.4.3 Both absolute and comparative methods using encir-cling coi
18、l(s) require comparing the specimens to be examinedwith the reference piece(s). Two or more samples representingthe limits of acceptance may be required. In the absolutemethod, the electrical reference signal from the instrument isadjusted with the standard in the coil. In the comparativemethod, any
19、 electromagnetic condition, that is not common tothe test specimen and the standard, will produce an imbalancein the system. The comparative method is usually more stablesince it suppresses most of the interferences.4.4 The examination process may consist of manual inser-tion of one specimen after a
20、nother into the test coil or anautomated feeding and classifying mechanism may be em-ployed. In automated setups, it is sometimes necessary toestablish empirically the time required for the test specimen toremain in the test coil while the reading is being taken,especially if low frequencies are emp
21、loyed.5. Significance and Use5.1 Absolute and comparative methods provide a measurefor sorting large quantities of nonferrous parts or stock withregard to composition or condition, or both.5.2 The comparative or two-coil method is used whenhigh-sensitivity examination is required. The advantage of t
22、hismethod is that it almost completely suppresses interferences.5.3 The ability to accomplish these types of separationssatisfactorily is dependent upon the relation of the electriccharacteristics of the nonferrous parts to their physical condi-tion.5.4 These methods may be used for high-speed sorti
23、ng in afully automated setup where the speed of examination mayapproach many specimens per second depending on their sizeand shape.5.5 Successful sorting of nonferrous material dependsmainly on the variables present in the sample and the properselection of frequency and fill factor.5.6 The accuracy
24、of a sort will be affected greatly by thecoupling between the test coil field and the examined partduring the measuring period.6. Interferences6.1 The influence of the following variables must be con-sidered for proper interpretation of the results:6.1.1 The correlation shall be established so that
25、electricalproperties of various groups do not overlap and are welldefined in the standardization procedure used.6.1.2 The examination frequency must be selected to pro-vide a well-defined separation of variables.6.1.3 The temperature of the standard and test specimenshall be controlled within limits
26、 that will permit a well-definedrange of conductivity or permeability, or both, for which thecorrelation of the group or groups is valid. Cooling of thestandard when high field strengths are used or allowing testspecimens to cool or heat to an established ambient range, orboth, may be required.6.1.4
27、 The geometry, mass, and thickness of the standard andtest specimen shall be controlled within limits that will permitsorting.6.1.5 Magnetic permeability variations can interfere whensorting paramagnetic materials.6.1.6 Signal response can result from a change in relativemotion between the test spec
28、imen and the test coil, such as thelength of time the specimen is in a test coil (see 4.4).6.1.7 Conductivity has an unambiguous relationship tohardness for certain alloys. However, when alloys are mixed,identical conductivity does not necessarily indicate the samehardness.6.1.8 Care must also be ex
29、ercised in using conductivity tosort overheated parts quenched at a high temperature as theconductivity reading for acceptable parts may repeat at a largeincrease in temperature.6.1.9 Lift-off can result in a change in the test system outputwith probe coils. This effect is a change in the magneticco
30、upling between the test specimen and probe coil. Care mustbe exercised to prevent this effect from interfering withexamination results; either mechanical or electronic compen-sation must be used.6.1.10 For certain heat-treatable (aluminum) alloys, conduc-tivity values can also repeat themselves duri
31、ng the aging cycleat a constant temperature. Thus, for such alloys, conductivity isnot unique as a monitor of temper, etc.7. Apparatus7.1 Electronic ApparatusThe electronic apparatus shallbe capable of energizing the test coils with alternating currentsof suitable frequencies and power levels and sh
32、all be capable ofsensing changes in the electromagnetic response of the coils.Equipment may include any suitable signal-processing devices(phase discriminator, filter circuits, etc.) and the output may bedisplayed by meter, oscilloscope, recorder, signaling devices,or any suitable combination requir
33、ed for the particular appli-cation.7.2 Test coils may be of the encircling or probe-coil typeand shall be capable of inducing an electromagnetic field in thetest specimen and standard, and sensing changes in the electricor magnetic characteristics of the test specimen.7.2.1 When selecting the test c
34、oil, the objective should be toobtain a coil fill factor as large as possible. This means that theinside of the test coil should be filled by the test specimen asmuch as possible. This is of primary importance for examina-tions requiring high sensitivity.7.2.2 For complicated test specimen shapes, a
35、 correspond-ing insert shall be provided to ensure that each test specimencan be placed in the same position within the test coil. Theseinserts, as well as any other accessories, should consist ofnon-ferromagnetic, electrically nonconductive material.7.3 Mechanical Handling Apparatus A mechanical de
36、-vice for feeding and sorting the test specimens may be used toautomate a particular application.E 703 98 (2004)e128. Sampling8.1 Sampling (see Practices E 105 and E 122) is a method toobtain assurance that materials are of satisfactory quality.Instead of 100 % inspection, a portion of the material
37、isexamined to show evidence of the quality of the whole. Thereare two important needs for this approach: first, the finalinspection or examination is made to assure that productsdelivered are in conformance with specification requirements;second, to control parts and assemblies while they are beingp
38、rocessed. Statistical acceptance sampling tables and statisticalprocess-control sampling tables have been developed to meetthese needs.8.2 Acceptance sampling may be conducted on an accept/reject (or attributes) basis; that is, determining whether or notthe units of the sample meet the specification
39、. Examination ofthe samples may also be conducted on a measurements (orvariables) basis; that is, determining actual readings on theunits in the sample. The majority of acceptance sampling iscarried out on a sampling by attributes basis and the usualacceptance sampling table is designed for accept/r
40、eject.8.3 Process control sampling may be conducted on materialduring the course of production to prevent large quantities ofdefective parts being found in the acceptance examinations.Many parts and materials are subjected to several successivemachining or processing operations before they become fi
41、n-ished units. Parts can be most effectively controlled duringproduction by examining small samples of these parts atfrequent regularly scheduled intervals. The object of thisprocess check is to provide a continuous picture of the qualityof parts being produced. This helps prevent production ofdefec
42、tive parts by stopping and correcting the problem as soonas it begins to appear in the manufacturing process and therebykeeping the process in control. Sampling may be by attributesor by variables and process control sampling tables are used.The measurements (variables) control chart is by far the m
43、osteffective process control technique.8.4 Statistical sampling tables have four definite features:(1) specification of sampling datathat is, the size of thesamples to be selected, the conditions under which the samplesare to be selected, and the conditions under which the lot willbe accepted or rej
44、ected; (2) protection affordedthat is, theelement of risk that the sampling schedules in a given table willreject good lots or accept bad ones; (3) disposal procedurethat is, a set of rules that state what is to be done with lots aftersampling has been completed; and (4) cost requiredthat is,average
45、 inspection cost required to accept or reject a lot.9. Test Specimen or Sample (Standards)9.1 Two known samples of the precise size and configura-tion of the product to be examined are usually used to set up forsorting by the absolute coil method (see 10.2). Three knownsamples of the precise size an
46、d configuration are usually usedfor sorting by the comparative coil (see 10.3) method.9.2 Three known samples are usually required for a three-way mix (see 10.4).9.3 The sample should be selected to represent the extremesof acceptable and unacceptable groups or a range of hardnessor conductivity to
47、assure no overlap in the sort.9.4 Other arrangements can be used and are acceptable butare not described in this procedure.10. Standardization10.1 The electromagnetic sorting method is primarily one ofcomparison between specimens. Empirical data and physicalexaminations on samples representing prope
48、rties to be sepa-rated determine the validity of the sort. The standardizationprocedure shall be based on the properties of the samplerequiring separation. The sort may require more than oneoperation.10.2 When using the absolute coil method (encircling),insert the known acceptable standard to a fixe
49、d position in thecoil and adjust the test instrument to get an on-scale meter oroscilloscope reading, or both. Replace the acceptable standardwith a known unacceptable standard in the same exact positionand adjust the sensitivity of the instrument to maximize theindicated difference reading without exceeding 90 % of theavailable scale range.10.3 When using the comparative coil method (encircling),select a reference piece (usually one that falls within theacceptable limits of the specimens being examined), place it inthe reference coil and set this coil and piece in a locatio
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