1、Designation: B499 09 (Reapproved 2014) Endorsed 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 d
2、esignation B499; 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 revisio
3、n or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 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 inten
4、ded to supplement manufacturersinstructions 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 measuremen
5、t is made priorto any 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 “electron
6、ic”). These instruments 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
7、 Standard 2178 as printed 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
8、 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:2B530 Test Method for Measurement of Coating Thicknessesby the Magnetic Method: Electrodeposited Nickel Coat-ings
9、on Magnetic and Nonmagnetic 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 resu
10、lt of a measurement 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 spec
11、ific portionof 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 over the full operating range of theinstrument, then making the neces
12、sary instrument adjustments(as required) 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
13、 documented process. Theoutcome of the calibration process is to restore/realign theinstrument to meet/exceed the manufacturers stated accuracy.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 o
14、nTest Methods.Current edition approved May 1, 2014. Published May 2014. Originallyapproved in 1969. Last previous edition approved in 2009 as B499 09. DOI:10.1520/B0499-09R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
15、 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, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、 C700, West Conshohocken, PA 19428-2959. United States13.1.4 reference standard, na specimen of known thicknessused to verify the accuracy of a coating thickness measuringinstrument.3.1.5 verification of accuracy, nobtaining measurementson a reference standard prior to instrument use for the purpose
17、of 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 employ an attraction prin-ciple and a
18、 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 applied to the spring/coil until thema
19、gnetic 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(s) between the magnet and themagnetic
20、 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 reflected on the nonlinear instrument sca
21、le.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 the effect on themagn
22、etic 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 thicknessnondestructively and is suitable for
23、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 B530 is suitable for that determination.6. Apparatus6.1 Coating Thickness Instrument , based on magneticprinciples, comm
24、ercially 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. Calibration
25、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 to a Nation
26、al 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 instrument ma
27、nufacturers.7.2 Before use, each instruments calibration accuracy shallbe verified in accordance with the instructions of themanufacturer, employing suitable thickness standards and, ifnecessary, any deficiencies found shall be corrected.7.3 During use, calibration accuracy shall be verified atfrequ
28、ent 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 Foils:NOTE 2In the following paragraphs, th
29、e use of the word “foil willimply a nonmagnetic metallic or nonmetallic foil or shim.7.4.1.1 Because of the difficulty of ensuring adequatecontact, foils are generally not recommended for thecalibration, verification of accuracy, and adjustment of mag-netic pull-off instruments but they are suitable
30、 in some circum-stances provided the necessary precautions are taken. They cannormally 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 it is necessary to ensure that intimateco
31、ntact 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, should be replaced frequently. Worn foils sha
32、ll not beused.7.4.2 Coated Standards These 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 lowest coating thickness mea-surement requi
33、rement. 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 rotating the probe in increments of 90
34、 (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 with a sufficientthickness of similar m
35、aterial 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, theB499 09 (2014)2curvature of the coated standard, or of the substrate on whichthe foil is placed, shall be the sam
36、e.8. Factors Affecting the Measuring Accuracy8.1 The following factors affect the accuracy of a coatingthickness measurement:8.1.1 Coating ThicknessInherent to the test method is ameasurement uncertainty that, for thin coatings, is constant andindependent of the coating thickness. The magnitude of t
37、hismeasurement 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 MetalMagneticthickness measurements are af
38、fected 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 instrumentshould be adjusted using a re
39、ference 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 is acritical thickness of the basis metal
40、 above which the measure-ments will not be affected by an increase in the thickness of thebasis metal. Since it depends on the instrument probe (Note 3)and the nature of the basis metal, its value should be deter-mined experimentally if not supplied by the manufacturer.NOTE 3In this method “instrume
41、nt 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 calibrated for sucha measurement.
42、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 becomes more pronounced as
43、 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 unevenlyworn.8.1.6 Surface Roughne
44、ssMeasurements 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 roughor scratched surface,
45、 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 positions on aportion of the
46、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 mechanical working (such as ro
47、lling), 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 instruments employing an alternating
48、 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 instruments of all typesmust mak
49、e 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 with which the probe is ap
