1、Designation: B 499 09Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Test Method forMeasurement of Coating Thicknesses by the MagneticMethod: Nonmagnetic Coatings on Magnetic Basis Metals1This standard is issued under the fixed designation B 499;
2、the number immediately following the designation indicates the year 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.T
3、his standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers the use of magnetic instrumentsfor the nondestructive measurement of the thickness of non-magnetic coatings over ferrous or other magnetic base metals.It is intended to supplement man
4、ufacturersinstructions for theoperation of the instruments and is not intended to replacethem.NOTE 1Autocatalytically deposited nickel-phosphorus alloys contain-ing more than 8 % phosphorus are sufficiently nonmagnetic to bemeasured by this test method, as long as the measurement is made priorto any
5、 heat treatment.1.2 These instruments measure either the magnetic attrac-tion between a magnet and the basis metal, as influenced by thepresence of the coating (categorized as “magnetic pull-off”), orthe change in magnetic-flux density within the probe (catego-rized as “electronic”). These instrumen
6、ts cannot distinguish thethickness of individual layers. They can only measure thecumulative thickness of all layers beneath the probe down tothe base metal.1.3 Measurements made in accordance with this test methodwill be in compliance with the requirements of ISO Interna-tional Standard 2178 as pri
7、nted in 1982.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to
8、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 530 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Electrodeposited NickelCoatings on Magnetic and Nonm
9、agnetic Substrates2.2 International Standard:ISO 2178 Non-Magnetic Coatings on Magnetic SubstrateMeasurement of Coating ThicknessMagnetic Method33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 accuracy, nthe measure of the magnitude of errorbetween the result of a measurement
10、and the true thickness ofthe item being measured.3.1.2 adjustment, nthe physical act of aligning a instru-ments thickness readings to match those of a known thicknesssample (removal of bias), in order to improve the accuracy ofthe instrument on a specific surface or within a specific portionof its m
11、easurement 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 over the full operating range of the instru-ment, then making the necessary instrument ad
12、justments (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 authorized, trained calibration laboratoryin a controlled environment using a documented proces
13、s. 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 of a coating thicknessmeasuring instrument.1This test method is under the jurisdiction o
14、fASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved April 15, 2009. Published May 2009. Originallyapproved in 1969. Last previous edition approved in 2002 as B 499 96 (2002).2For referenced ASTM standar
15、ds, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, N
16、ew York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.5 verification of accuracy, nobtaining measurementson a reference standard pr
17、ior to instrument use for the purposeof determining the ability of the coating thickness instrument toproduce reliable values, compared to the combined instrumentmanufacturers stated accuracy and the stated accuracy of thereference standard.4. Summary of Test Method4.1 Magnetic pull-off instruments
18、employ an attraction prin-ciple and a stationary magnetic field. These mechanical instru-ments measure the force required to pull a permanent magnetfrom a coated magnetic metal substrate. The magnetic force ofattraction to the substrate beneath the coating is opposed by aspring or coil. Tension is a
19、pplied to the spring/coil until themagnetic attraction to the magnetic substrate is overcome. Theinstrument must be placed directly on the coated surface toobtain a measurement. The force holding the permanentmagnet to the magnetic base is inversely proportional to thethickness of the coating layer(
20、s) between the magnet and themagnetic base. For example, a thin coating applied to a ferroussubstrate will require greater spring tension to pull the magnetoff than will a thicker coating, since the magnet is closer to theferrous substrate with the thinner coating. This inverse rela-tionship is refl
21、ected on the nonlinear instrument scale.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 instru
22、ments determine the 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. For most nonferrous coatings on steel, themagnetic method is reliable for measuring coating thickness
23、nondestructively and is suitable for specification acceptancetesting and SPC/SQC applications.5.2 This test method should not be used to determine thethickness of electrodeposited nickel coatings on steel. TestMethod B 530 is suitable for that determination.6. Apparatus6.1 Coating Thickness Instrume
24、nt, based on magnetic prin-ciples, 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
25、 (typically polyester).7. Calibration 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 ofCalibr
26、ation showing traceability to 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 typicalfre
27、quency suggested by many instrument 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, calibr
28、ation accuracy shall be verified 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 Coating thickness standards of known thickness areavailable either as shims or foils or as coated specimens.7.4.1 Foi
29、ls:NOTE 2In the following paragraphs, the use of the word “foil willimply a nonmagnetic metallic or nonmetallic foil or shim.7.4.1.1 Because of the difficulty of ensuring adequate con-tact, foils are generally not recommended for the calibration,verification of accuracy, and adjustment of magnetic p
30、ull-offinstruments but they are suitable in some circumstancesprovided the necessary precautions are taken. They can nor-mally be used with other types of instruments.7.4.1.2 Foils are advantageous on curved surfaces and aremore readily available than coated standards. To preventmeasurement errors i
31、t is necessary to ensure that intimatecontact is established between foil and substrate. Resilient foilsshould be avoided to prevent indentation errors. Only nonfer-rous metal foils should be used for thicknesses less than 15 m(0.6 mil). Foils are subject to wear and indentation and,therefore, shoul
32、d be replaced frequently. Worn foils shall not beused.7.4.2 Coated StandardsThese calibration standards con-sist of nonconductive coatings of known, uniform thicknesspermanently bonded to the substrate material.7.4.3 The coating thickness of the standards used shallbracket the users highest and lowe
33、st coating thickness mea-surement requirement. Standards suitable for many applica-tions of the test method are commercially available and may beused provided the certified values are traceable to a NationalMetrology Institution.7.5 In some cases the calibration of the instrument should bechecked by
34、 rotating the probe in increments of 90 (see 8.1.8and 8.1.9).7.6 The basis-metal thickness for the test and the calibrationadjustment shall be the same if the critical thickness, defined in8.1.3, is not exceeded. It is often possible to back up the basismetal of the standard or of the test specimen
35、with a sufficientthickness of similar material to make the readings independentof the basis-metal thickness.7.7 If the curvature of the coating to be measured is such asto preclude calibration adjustment on a flat surface, thecurvature of the coated standard, or of the substrate on whichthe foil is
36、placed, shall be the same.8. Factors Affecting the Measuring Accuracy8.1 The following factors affect the accuracy of a coatingthickness measurement:B4990928.1.1 Coating ThicknessInherent to the test method is ameasurement uncertainty that, for thin coatings, is constant andindependent of the coatin
37、g thickness. The magnitude of thismeasurement uncertainty is primarily a function of test piecesurface finish (see 8.1.6 on surface roughness). For thicknessesgreater than about 25m (1 mil), this uncertainty is propor-tional to the coating thickness.8.1.2 Magnetic Properties of the Basis MetalMagnet
38、icthickness measurements are affected by variations in themagnetic properties of the basis metal. (For practical purposes,magnetic variations in low-carbon steel can often be consid-ered to be insignificant. To avoid the influences of severe orlocalized heat treatments and cold working, the instrume
39、ntshould be adjusted using a reference standard having a basismetal with the same magnetic properties as that of the testspecimen or, preferably and if available, with a sample of thepart to be tested before application of the coating.)8.1.3 Basis Metal ThicknessFor each instrument, there isa critic
40、al thickness of the basis metal above which themeasurements will not be affected by an increase in thethickness of the basis metal. Since it depends on the instrumentprobe (Note 3) and the nature of the basis metal, its valueshould be determined experimentally if not supplied by themanufacturer.NOTE
41、 3In this method “instrument probe” will also include the term“magnet.”8.1.4 Edge EffectsThe method is sensitive to abruptchanges in the surface contour of the test specimen. Therefore,measurements made too near an edge or inside corner will notbe valid unless the instrument is specifically calibrat
42、ed for sucha measurement. The effect may extend to about 20 mm (0.8 in.)from the discontinuity, depending on the instrument.8.1.5 CurvatureThe measurements are affected by thecurvature of the test specimen. The influence of curvaturevaries considerably with the make and type of instrument butalways
43、becomes more pronounced as the radius of curvaturedecreases. Instruments with two-pole probes may also producedifferent readings if the poles are aligned in planes parallel orperpendicular to the axis of a cylindrical surface. A similareffect can occur with a single-pole probe if the tip is unevenly
44、worn.8.1.6 Surface RoughnessMeasurements are influenced bythe surface topography of the basis metal and coating. Surfaceroughness becomes significant when the degree of roughness isgreater than 10 % of the coating thickness, causing increasedscatter in measurements. Therefore, it is necessary, on a
45、roughor scratched surface, to make a greater number of measure-ments at different positions to obtain an average value that isrepresentative of the mean coating thickness. If the basis metalis rough, it may also be necessary to check, and adjust ifnecessary, the zero of the instrument at several pos
46、itions on aportion of the uncoated, rough, basis metal.8.1.7 Direction of Mechanical Working of the Basis MetalMeasurements made by an instrument having a two-pole probeor an unevenly worn single-pole probe may be influenced bythe direction in which the magnetic basis metal has beensubjected to mech
47、anical working (such as rolling), the readingchanging with the orientation of the probe on the surface.8.1.8 Residual MagnetismResidual magnetism in the ba-sis metal affects the measurements made by instruments thatemploy a stationary magnetic field. Its influence on measure-ments made by instrument
48、s employing an alternating magneticfield is much smaller.8.1.9 Stray Magnetic FieldsStrong stray magnetic fields,such as are produced by various types of electrical equipment,can seriously interfere with the operation of instruments basedon magnetic principles.8.1.10 Foreign ParticlesMagnetic instru
49、ments of alltypes must make physical contact with the test surface and are,therefore, sensitive to foreign material that prevents intimatecontact between probe and coating surface. Both the testsurface and instrument probe should be kept free of foreignmaterial.8.1.11 Conductivity of CoatingMagnetic instruments em-ploying an alternating magnetic field operating frequenciesabove 200 Hz could produce eddy currents in thick, highlyconductive coatings that may interfere with the reading.8.1.12 PressureInstrument readings are sensitive to thepressure w
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