1、Designation: B 530 02Standard Test Method forMeasurement of Coating Thicknesses by the MagneticMethod: Electrodeposited Nickel Coatings on Magnetic andNonmagnetic Substrates1This standard is issued under the fixed designation B 530; the number immediately following the designation indicates the year
2、 oforiginal adoption or, in the case of revision, the 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.This standard has been approved for use by agencies of the Departme
3、nt of Defense.1. Scope1.1 This test method covers the use of magnetic instrumentsfor the nondestructive measurement of the thickness of anelectrodeposited nickel coating on either a magnetic or non-magnetic substrate.1.2 These instruments measure either the magnetic attrac-tion between a magnet and
4、the coating-substrate combination,or the reluctance of a magnetic flux path passing through thecoating and the basis metal.1.3 For this test method, there are two types of coating-substrate combinations that can be encountered: Type A, nickelcoatings on a magnetic substrate, and Type B, nickel coati
5、ngson a nonmagnetic substrate.1.4 The effective measuring ranges of instruments using theprinciple of magnetic attraction are up to 50 m for Type Acoatings, and up to 25 m for Type B coatings. For reluctancegages, the effective ranges are much greater, and measurementsup to 1 mm or more, can be made
6、 on both types of coatings.1.5 Measurements made in accordance with this test methodwill be in compliance with the requirements of ISO Stan-dard 2361 as printed in 1982.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility o
7、f 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 ISO International Standard:ISO 2361 Electrodeposited Nickel Coatings on Magneticand Nonmagnetic SubstratesMeasurement o
8、f CoatingThicknessMagnetic Method23. Significance and Use3.1 The thickness of a coating is often critical to itsperformance. This magnetic method is suitable for measuringnondestructively the thickness of some nickel coatings and forspecification acceptance.3.2 This method requires that the magnetic
9、 properties of thecoating and its substrate be the same as those of the calibrationstandards.4. Factors Affecting the Measuring Accuracy4.1 Coating ThicknessInherent in the method is a mea-suring uncertainty that, for thin coatings, is constant andindependent of the coating thickness; for thicknesse
10、s greaterthan about 50 m, this uncertainty is proportional to the coatingthickness.4.2 Magnetic Properties of the Basis Metal (Type A coat-ings only)Magnetic thickness measurements are affected byvariations in the magnetic properties of the basis metal. Forpractical purposes, magnetic variations in
11、low-carbon steel canoften be considered to be insignificant. To avoid the influencesof severe or localized heat treatments and cold working, theinstrument should be calibrated using a calibration standardhaving a basis metal with the same magnetic properties as thatof the test specimen or, preferabl
12、y and if available, with asample of the part to be tested before application of the coating.4.3 Basis Metal Thickness (Type A coatings only)Foreach instrument, there is a critical thickness of the basis metalabove which the measurements will not be affected by anincrease in that thickness. Since it
13、depends on the instrumentprobe (Note 1) and the nature of the basis metal, its valueshould be determined experimentally, if it is not supplied bythe manufacturer.NOTE 1The term “instrument probe” also includes the term “magnet.”4.4 Edge EffectThe method is sensitive to abrupt changesin the surface c
14、ontour of the test specimen. Therefore, mea-surements made too near an edge or inside corner will not bevalid, unless the instrument is specially calibrated for such ameasurement. This also applies to measurements made ongeometrically limited areas, such as narrow conductors on1This test method is u
15、nder the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onGeneral Test Methods.Current edition approved Sept. 10, 2002. Published November 2002. Originallypublished as B 530 70. Last previous edition B 530 96.2Available fr
16、om American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.printed circuit boards.4.5 CurvatureMeasurements are affected by the curvatureof the test specime
17、n. The influence of curvature varies consid-erably with the make and type of instrument, but alwaysbecomes more pronounced as the radius of curvature de-creases. Instruments with two-pole probes may also producedifferent readings, depending on whether the poles are alignedin planes parallel or perpe
18、ndicular to the axis of a cylindricalsurface. A similar effect can occur with a single-pole probe, ifthe tip is unevenly worn. Measurements made on curved testspecimens may not, therefore, be valid unless the instrument isspecifically calibrated for such measurements.4.6 Surface Roughness:4.6.1 Meas
19、urements are influenced by the surface topogra-phy of the substrate and the coating, and a rough or scratchedsurface will give individual instrument readings that all varyfrom point to point. In this case, it is necessary to make manyreadings at different positions to obtain an average value that is
20、representative of the mean coating thickness.4.6.2 If the basis metal is magnetic and rough, it may also benecessary to check the zero of the instrument at severalpositions on a sample of the uncoated rough substrate.4.6.3 If the roughness of the substrate surface is small,relative to the coating th
21、ickness, its effect will probably benegligible.4.7 Direction of Mechanical Working of the Basis Metal(Type A coatings only)Measurements made by an instrumenthaving a two-pole probe or an unevenly worn single-pole probemay be influenced by the direction in which the magnetic basismetal has been subje
22、cted to mechanical working, such asrolling. The reading may change with the orientation of theprobe on the surface.4.8 Residual Magnetism (Type A coatings only)Residualmagnetism in the basis metal affects the measurements madeby instruments that employ a stationary magnetic field. Itsinfluence on me
23、asurements made by reluctance instrumentsemploying an alternating magnetic field is much smaller.4.9 Stray Magnetic FieldStrong stray magnetic fields,such as those produced by various types of electrical equip-ment, can seriously interfere with the operation of magneticthickness instruments.4.10 For
24、eign ParticlesThe probes of magnetic instru-ments of all types must make physical contact with the testsurface and are, therefore, sensitive to foreign material thatprevents intimate contact between the probe and the coatingsurface. Both the test surface and the instrument probe shouldbe kept free o
25、f foreign material.4.11 Magnetic Properties of the Coating Magnetic thick-ness measurements are affected by variations in the magneticproperties to the coating. These properties depend on theconditions under which the deposit is produced, the type andcomposition of the coating, and its stress. The m
26、agneticproperties of multiple-layer nickel coatings will also depend onthe relative thickness of each of the layers.4.11.1 A heat treatment at 400C for 30 min will equalizethe magnetic permeability of dull (Watts) nickel coatings of thesame composition. Bright nickel deposits may or may not havethe
27、same magnetic properties after heat treatment.4.12 Nickel Coatings on the Back of the Substrate (Type Bcoatings only)Nickel coatings on the back of the substratecan affect the measurements, depending on the thickness of thesubstrate.4.13 PressureInstrument readings are sensitive to thepressure with
28、which the probe is applied to the test specimen.No deformation of the coating or probe should be allowed.Errors that sometimes are encountered with the use of manualprobes can be avoided by employing spring-loaded probes thatexert a relatively constant pressure.4.14 Probe OrientationInstrument readi
29、ngs may be sen-sitive to the orientation of the magnet in relation to the field ofgravity of the earth. Thus, the operation of an instrument in ahorizontal or upside-down position may require a differentcalibration, or may be impossible.5. Calibration of Instruments5.1 Before use, each instrument sh
30、all be calibrated inaccordance with the instructions of the manufacturer, employ-ing suitable thickness standards. During use, the calibrationshall be checked at regular intervals, at least once a day.Attention shall be given to the factors listed in Section 4 and tothe procedures in Section 6.5.2 T
31、he calibration standards shall be coated standardsobtained by electroplating nickel adherently onto a substrate.The coating thickness of the calibration standards shall bracketthe users highest and lowest coating thickness measurementrequirement.5.3 The substrate and the coating of the standard shal
32、l havethe same magnetic properties as those of the test specimen (see4.2, 4.3, 4.12 and section 4.12.1).5.3.1 To assure the similarity of the magnetic properties ofthe nickel deposit and for Type A coatings the steel substrate,calibration standards shall be produced by another suitable testmethod, s
33、uch as cross sectioning or the coulometric testmethod from a specimen produced under identical conditionsas the test specimen to be measured. To confirm the similarityof the magnetic properties of the substrate to those of thestandards, a comparison of the readings obtained with the barebasis metal
34、of the standard to that of the test specimen isrecommended.5.3.2 In the same manner, the similarity of the magneticproperties of the coating of the test specimen to that of thestandard can be established by verifying with the coulometricor microscopical method that the thickness reading obtained ont
35、he test specimen by means of the properly calibrated instru-ment corresponds to the actual thickness determined by one orboth of the above methods.5.4 Where indicated, the calibration of the instrumentshould be checked by rotating the probe in increments of 90(see 4.7 and 4.8).5.5 For Type A coating
36、s, the basis metal thickness for thetest and the calibration shall be the same if the criticalthickness, defined in 4.3, is not exceeded. When possible, backup the basis metal of the standard, or the test specimen, with asufficient thickness of similar material to make the readingsindependent of the
37、 basis metal thickness.5.6 If the curvature of the coating to be measured is such asto preclude calibration on a flat surface, the curvature of theB 530 022coated standard shall be the same as that of the test specimen.6. Procedure6.1 Operate each instrument in accordance with the instruc-tions of t
38、he manufacturer. Give appropriate attention to thefactors listed in Section 4.6.2 Check the calibration of the instrument at the test siteeach time the instrument is put into service, and at regularintervals during use, to assure proper performance.6.3 Observe the following precautions:6.3.1 Basis M
39、etal Thickness (Type A coatings only)Check whether the basis metal thickness exceeds the criticalthickness. If not, either use the back-up method of 5.5, or makesure that the calibration has been made on a standard havingthe same thickness and magnetic properties as the test speci-men.6.3.2 Edge Eff
40、ectsDo not make readings close to an edge,hole, inside corner, etc., of a specimen, unless the validity ofthe calibration for such a measurement has been demonstrated.6.3.3 CurvatureDo not make readings on a curved surfaceof a specimen, unless the validity of the calibration for such ameasurement ha
41、s been demonstrated.6.3.4 Number of Readings:6.3.4.1 For each measurement, make at least 3 readings,removing the probe after each reading, and average thereadings. If any 2 of the readings differ from each other bymore than 5 % of the average reading or 2 m, whichever is thegreater, then the measure
42、ment shall be discarded and repeated.6.3.4.2 The substrate or coating, or both, may be too roughto meet this criterion. In such a case it may be possible toobtain a valid measurement by averaging a number of readings.To be valid under this test method, the validity of such aprocedure must be demonst
43、rated (see Appendix X1).6.3.4.3 Instruments of the attractive force type are sensitiveto vibrations, and readings that are obviously erroneous shouldbe rejected.6.3.5 Direction of Mechanical Working (Type A coatingsonly)If the direction of mechanical working has a pro-nounced effect on the reading,
44、make the measurement on thetest specimen with the probe in the same orientation as thatused during calibration. If this is impossible, make fourmeasurements at various orientations by rotating the probe inincrements of 90.6.3.6 Residual Magnetism (Type A coatings only)Whenresidual magnetism is prese
45、nt in the basis metal, it is necessary,when using instruments employing a stationary magnetic field,to make measurements in two orientations differing by 180. Itmay also be necessary to demagnetize the test specimen to getvalid results (see 4.7 and 4.8).6.3.7 Surface CleanlinessBefore making measure
46、ments,clean any foreign matter such as dirt, grease, and corrosionproducts from the surface without removing any coatingmaterial. When making measurements avoid any areas havingvisible defects that are difficult to remove, such as welding orsoldering flux, acid spots, dross, or oxide.6.3.8 Technique
47、sThe readings obtained may depend onthe technique of the operator. For example, the pressure appliedto a probe or the rate of applying a balancing force to a magnetwill vary from one individual to another. Such effects can bereduced or minimized either by having the instrument cali-brated by the sam
48、e operator who will make the measurement,or by using constant pressure probes.6.3.9 Positioning of the Probe:6.3.9.1 In general, place the instrument probe perpendicularto the specimen surface at the point of measurement. For someinstruments of the attractive force type, this is essential. Withsome
49、instruments, however, it is desirable to tilt the probeslightly and select the angle of inclination giving the minimumreading.6.3.9.2 If, on a smooth surface, the readings obtained varysubstantially with the angle of inclination, it is probable thatthe probe is worn and needs to be replaced. If a magneticinstrument is to be used in horizontal or upside-down position,calibrate it for that position.7. Report7.1 The report should include the following information:7.1.1 A reference to this standard,7.1.2 Type of instrument used,7.1.3 Size and description o
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