1、Designation: B 530 09Standard 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 () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Departmen
3、t of Defense.1. Scope*1.1 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. It is intended to supplement manufacturersinstructions for the operation of the in
4、struments and is notintended to replace them.1.2 These instruments measure either the magnetic attrac-tion between a magnet and the coating-substrate combination(categorized as “magnetic pull-off”), or the change in magneticflux density within the probe (categorized as “electronic”).1.3 For this tes
5、t method, there are two types of coating-substrate combinations that can be encountered: TypeA, nickelcoatings on a magnetic substrate, and Type B, nickel coatingson a nonmagnetic substrate.1.4 The effective measuring ranges of instruments using theprinciple of magnetic attraction are up to 50 m (2
6、mils) forType A coatings, and up to 25 m (1 mil) for Type B coatings.For gages based on change in magnetic flux density principles,the effective ranges are much greater, and measurements up to1 mm (40 mils) or more, can be made on both types ofcoatings.1.5 Measurements made in accordance with this t
7、est methodwill be in compliance with the requirements of ISO Stan-dard 2361 as printed in 1982.1.6 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.7 This standard does not purport to address all of thesafety concerns, if any,
8、 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:2B 487 Test Method for Measurement of Metal and Oxide
9、Coating Thickness by Microscopical Examination of CrossSectionB 499 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB 748 Test Method
10、for Measurement of Thickness of Me-tallic Coatings by Measurement of Cross Section with aScanning Electron Microscope2.2 ISO International Standard:ISO 2361 Electrodeposited Nickel Coatings on Magneticand Nonmagnetic SubstratesMeasurement of CoatingThicknessMagnetic Method33. Terminology3.1 Definiti
11、ons of Terms Specific to This Standard:3.1.1 accuracy, nthe measure of the magnitude of errorbetween the result of a measurement and the true thickness ofthe item being measured.3.1.2 adjustment, nthe physical act of aligning an instru-ments thickness readings to match those of a known thicknesssamp
12、le (removal of bias), in order to improve the accuracy ofthe instrument on a specific surface or within a specific portion1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current
13、edition approved April 15, 2009. Published June 2009. Originallyapproved in 1970. Last previous edition approved in 2002 as B 530 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume infor
14、mation, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100
15、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of its measurement range. An adjustment will affect theoutcome of subsequent readings.3.1.3 calibration, nthe high-level, controlled and docu-mented process of obtaining measurements on traceable cali-bration standards o
16、ver the full operating range of the instru-ment, then making the necessary instrument adjustments (asrequired) to correct any out-of-tolerance conditions.3.1.3.1 DiscussionCalibration of coating thickness instru-ments is performed by the equipment manufacturer, an autho-rized agent, or by an authori
17、zed, trained calibration laboratoryin a controlled environment using a documented process. Theoutcome of the calibration process is to restore/realign theinstrument to meet/exceed the manufacturers stated accuracy.3.1.4 reference standard, na specimen of known thick-ness used to verify the accuracy
18、of a coating thicknessmeasuring instrument.3.1.5 verification of accuracy, nobtaining measurementson a reference standard prior to instrument use for the purposeof determining the ability of the coating thickness instrument toproduce reliable values, compared to the combined instrumentmanufacturers
19、stated accuracy and the stated accuracy of thereference standard.4. Summary of Test Method4.1 Magnetic pull-off instruments are mechanical instru-ments that measure the force required to pull a permanentmagnet from magnetic material. The magnetic force of attrac-tion to the magnetic coating or coati
20、ng-substrate combinationis opposed by a spring or coil. Tension is applied to thespring/coil until the magnetic attraction to the material isovercome. The instrument must be placed directly on thecoated surface to obtain a measurement. The force holding thepermanent magnet to the magnetic material i
21、s inversely pro-portional to the thickness of the coating layer(s) between themagnet and the magnetic material. For example, a thin nickellayer applied to a nonmagnetic substrate will require lessspring tension to pull the magnet off than will a thicker nickellayer, since the thinner coating has wea
22、ker magnetic strength.4.2 Electronic instruments measure a change in magneticflux density within the probe to produce a coating thicknessmeasurement. The instrument probe must be placed directly (ina perpendicular position) on the coated surface to obtain ameasurement. These instruments determine th
23、e effect on themagnetic field generated by the probe due to the proximity tothe substrate.5. Significance and Use5.1 The thickness of a coating is often critical to itsperformance. This magnetic method is suitable for measuringnondestructively the thickness of some nickel coatings and forspecificati
24、on acceptance.5.2 This method requires that the magnetic properties of thecoating and its substrate be the same as those of the referencestandards used for the calibration adjustment of the instrument.5.3 This method should not be used to determine thethickness of autocatalytically deposited nickel-
25、phosphorus al-loys containing more than 8 % phosphorus on steel. Thosecoatings are sufficiently nonmagnetic for Test Method B 499 tobe suitable for that determination, as long as the measurementis made prior to any heat treatment.6. Apparatus6.1 Coating Thickness Instrument, based on magnetic prin-c
26、iples, commercially available, suitable to measure coatingthickness accurately.6.2 Coating Thickness Standards, with assigned valuestraceable to a National Metrology Institution. They may becoated or plated steel plates, or may be foils or shims of flat,non-metallic sheet (typically polyester).7. Ca
27、libration and Standardization7.1 Calibration of coating thickness instruments is per-formed by the equipment manufacturer, an authorized agent, orby an authorized, trained calibration laboratory in a controlledenvironment using a documented process. A Certificate ofCalibration showing traceability t
28、o a National MetrologyInstitution can be issued. There is no standard time interval forre-calibration, nor is one absolutely required, but a calibrationinterval can be established based on experience and the workenvironment. A one-year calibration interval is a typicalfrequency suggested by many ins
29、trument manufacturers.7.2 Before use, each instruments calibration accuracy shallbe verified in accordance with the instructions of the manufac-turer, employing suitable thickness standards and, if necessary,any deficiencies found shall be corrected.7.3 During use, calibration accuracy shall be veri
30、fied atfrequent intervals, at least once a day. Attention shall be givento the factors listed in Section 8 and to the proceduresdescribed in Section 9.7.4 Reference standards shall be coated standards obtainedby electroplating nickel adherently onto a substrate. Thecoating thickness of the reference
31、 standards shall bracket theusers highest and lowest coating thickness measurementrequirement.7.5 The substrate and the coating of the standard shall havethe same magnetic properties as those of the test specimen (see8.2, 8.3, 8.11 and 8.12).7.5.1 To assure the similarity of the magnetic properties
32、ofthe nickel deposit and for Type A coatings on steel substrate,reference standards shall be produced and measured by anothersuitable test method, such as cross sectioning or the coulom-etric test method from a specimen produced under identicalconditions as the test specimen to be measured. To confi
33、rm thesimilarity of the magnetic properties of the substrate to those ofthe standards, a comparison of the readings obtained with thebare basis metal of the standard to that of the test specimen isrecommended.7.5.2 In the same manner, the similarity of the magneticproperties of the coating of the te
34、st specimen to that of thestandard can be established by verifying with the crosssectioning (Test Methods B 487 or B 748) or coulometric (TestMethod B 504) methods that the thickness reading obtained onthe test specimen by means of the properly adjusted instrumentcorresponds to the actual thickness
35、determined by one or bothof the above methods.B 530 0927.6 Where indicated, the accuracy of the instrument shouldbe checked by rotating the probe in increments of 90 (see 8.7and 8.8).7.7 For Type A coatings, the basis metal thickness for thetest and the calibration adjustment shall be the same if th
36、ecritical thickness, defined in 8.3, is not exceeded. Whenpossible, back up the basis metal of the standard, or the testspecimen, with a sufficient thickness of similar material tomake the readings independent of the basis metal thickness.7.8 If the curvature of the coating to be measured is such as
37、to preclude calibration adjustment on a flat surface, thecurvature of the coated standard shall be the same as that of thetest specimen.8. Factors Affecting the Measuring Accuracy8.1 Coating ThicknessInherent in the method is a mea-suring uncertainty that, for thin coatings, is constant andindepende
38、nt of the coating thickness; for thicknesses greaterthan about 50 m (2 mils), this uncertainty is proportional tothe coating thickness.8.2 Magnetic Properties of the Basis Metal (Type A coat-ings only)Magnetic thickness measurements are affected byvariations in the magnetic properties of the basis m
39、etal. Forpractical purposes, magnetic variations in low-carbon steel canoften be considered to be insignificant. To avoid the influencesof severe or localized heat treatments and cold working, theinstrument should be adjusted using a reference standardhaving a basis metal with the same magnetic prop
40、erties as thatof the test specimen or, preferably and if available, with asample of the part to be tested before application of the coating.8.3 Basis Metal Thickness (Type A coatings only)Foreach instrument, there is a critical thickness of the basis metalabove which the measurements will not be aff
41、ected by anincrease in that thickness. Since it 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.”8.4 Edge EffectThe metho
42、d is sensitive to abrupt changesin the surface contour of the test specimen. Therefore, mea-surements made too near an edge or inside corner will not bevalid, unless the instrument is specially adjusted for such ameasurement. This also applies to measurements made ongeometrically limited areas, such
43、 as narrow conductors onprinted circuit boards.8.5 CurvatureMeasurements are affected by the curvatureof the test specimen. 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
44、two-pole probes may also producedifferent readings, depending on whether the poles are alignedin planes parallel or perpendicular 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, t
45、herefore, be valid unless the instrument isspecifically adjusted for such measurements.8.6 Surface Roughness:8.6.1 Measurements 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
46、 to point. In this case, it is necessary to make manyreadings at different positions to obtain an average value that isrepresentative of the mean coating thickness.8.6.2 If the basis metal is magnetic and rough, it may also benecessary to check, and adjust if necessary, the zero of theinstrument at
47、several positions on a sample of the uncoatedrough substrate.8.6.3 If the roughness of the substrate surface is small,relative to the coating thickness, its effect will probably benegligible.8.7 Direction of Mechanical Working of the Basis Metal(Type A coatings only) Measurements made by an instrume
48、nthaving a two-pole probe or an unevenly worn single-pole probemay be influenced by the direction in which the magnetic basismetal has been subjected to mechanical working, such asrolling. The reading may change with the orientation of theprobe on the surface.8.8 Residual Magnetism (Type A coatings
49、only)Residualmagnetism in the basis metal affects the measurements madeby instruments that employ a stationary magnetic field. Itsinfluence on measurements made by reluctance instrumentsemploying an alternating magnetic field is much smaller.8.9 Stray Magnetic FieldStrong stray magnetic fields,such as those produced by various types of electrical equip-ment, can seriously interfere with the operation of instrumentsbased on magnetic principles.8.10 Foreign ParticlesThe probes of magnetic instru-ments of all types must make physical contact with the testsu
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