1、Designation: D7378 16Standard Practice forMeasurement of Thickness of Applied Coating Powders toPredict Cured Thickness1This standard is issued under the fixed designation D7378; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the thickness measurement ofdry coating powders applied to a variety of rigid substrat
3、es.Use of some of these procedures may require repair of thecoating powder. This practice covers the use of portableinstruments. It is intended to supplement the manufacturersinstructions for their operation of the gages and is not intendedto replace them. It includes definitions of key terms, refer
4、encedocuments, the significance and use of the practice, and theadvantages and limitations of the instruments.1.2 Three procedures are provided for measuring dry coat-ing powder thickness:1.2.1 Procedure AUsing rigid metal notched (comb)gages.1.2.2 Procedure BUsing magnetic or eddy current coatingth
5、ickness gages.1.2.3 Procedure CUsing non-contact ultrasonic powderthickness instruments.1.3 Coating powders generally diminish in thickness duringthe curing process. Some of these procedures therefore requirea reduction factor be established to predict cured film thicknessof powder coatings.1.4 Proc
6、edure A and Procedure B measure the thickness(height or depth) of the applied coating powders in thepre-cured, pre-gelled state. By comparing results to the mea-sured cured powder thickness in the same location, a reductionfactor can be determined and applied to future thicknessmeasurements of the s
7、ame coating powder.1.5 Procedure C results in a predicted thickness value of thecured state based on a calibration for typical coating powders.If the powder in question is not typical then an adjustment canbe made to align gage readings with the actual cured values asdetermined by other measurement
8、methods.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, associated with its use. It is theresponsibility of the user of this standard to estab
9、lish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4138 Practices for Measurement of Dry Film Thickness ofProtective Coating Systems by Destructive, Cross-Sectioning MeansD6132 Test Method
10、for Nondestructive Measurement of DryFilm Thickness of Applied Organic Coatings Using anUltrasonic Coating Thickness GageD7091 Practice for Nondestructive Measurement of DryFilm Thickness of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic, Nonconductive Coat-ings Applied to Non-Ferrous
11、 Metals3. 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 and the true thickness ofthe item being measured.3.1.2 adjustment, nthe physical act of aligning a gagesthickness readings to match those
12、of a known thickness sample(reduction of bias) in order to improve the accuracy of the gageon a specific surface, within a specific portion of its measure-ment range or to specific operating conditions.3.1.2.1 DiscussionAn adjustment will affect the outcomeof subsequent readings.3.1.3 coating powder
13、s, nfinely divided particles of resin,either thermoplastic or thermosetting, generally incorporatingpigments, fillers, and additives and remaining finely divided1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct
14、responsibility ofSubcommittee D01.51 on Powder Coatings.Current edition approved Dec. 1, 2016. Published March 2017. Originallyapproved in 2007. Last previous edition approved in 2010 as D7378 10. DOI:10.1520/D7378-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AS
15、TM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard wa
16、s developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1during stora
17、ge under suitable conditions, which, after fusingand possibly curing, give a continuous film.3.1.4 calibration, nthe high-level, controlled and docu-mented process of obtaining measurements on traceable cali-bration standards over the full operating range of the gage, thenmaking the necessary gage a
18、djustments (as required) to correctany out-of-tolerance conditions.3.1.4.1 DiscussionCalibration of coating thickness gagesis performed in a controlled environment using a documentedprocess by the equipment manufacturer, their authorized agent,or by an accredited calibration laboratory. The outcome
19、of thecalibration process is to restore/realign the gage to meet/exceedthe manufacturers stated accuracy and may result in thecreation of a calibration certificate recording the results of theprocess at the time of testing.3.1.5 powder coatings, ncoatings which are protective ordecorative, or both,
20、formed by the application of a coatingpowder to a substrate and fused in a continuous film by theapplication of heat or radiant energy.3.1.6 dry film thickness, nthe thickness of a cured coating(or coating layers) as measured from the surface of thesubstrate.3.1.7 micrometer (micron), none one-thous
21、andth of amillimeter (0.001 mm); 25.4 microns = 1 mil.3.1.8 mil, nan imperial unit of measure; one one-thousandth of an inch (0.001 in.); 1 mil = 25.4 microns.3.1.9 substrate, nthe base material, type of surface orcomponent that is being coated.3.1.10 uncured, adjthe physical state of coating powder
22、when particles are electrostatically held to a substrate.3.1.11 verification of accuracy, ncomparing predictedthickness values with actual cured thickness values and ensur-ing both are within their combined measurement tolerances.4. Summary of Practice4.1 The three procedures take measurements of ap
23、pliedcoating powders in the pre-cured, pre-gelled state. Eachprocedure employs different devices to measure the dry pow-der.4.2 Procedure AUses a metal notched gage to manuallydetermine the thickness of the coating powder. The gage isdragged through the powder a short distance. Powder thicknessis de
24、termined as being between the highest numbered tooth thatmade a mark and has powder clinging to it, and the nexthighest tooth that left no mark and has no powder clinging toit. Measurements can be made on a suitable rigid surface, metalor non-metal but marks will be made in the powder that maynot be
25、 covered when the powder flows in the cure process.4.3 Procedure BUses a conventional magnetic or eddycurrent coating thickness gage with a specially designedpowder probe to measure the thickness of the coating powder.Micro pins, which are integrated into the probe, penetrate thecoating powder down
26、to the substrate. The probe is manuallypressed down to the surface of the powder to effect a thicknessmeasurement. This procedure is applicable to flat, metalsubstrates only. Marks may be made in the powder that maynot be covered when the powder flows in the cure process.4.4 Procedure CUses a non-co
27、ntact ultrasonic powderthickness instrument to take a measurement of the appliedcoating powder to calculate and display a predicted curedthickness. Measurements can be made on any rigid surface.4.5 The thickness of dry coating powder diminishes duringthe curing process. To predict the cured powder c
28、oatingthickness, a correlation must be made between pre-cured andpost-cured thicknesses.4.5.1 Procedure A and Procedure B result in a thicknessmeasurement of the uncured coating powder only. A reductionfactor must then be used to predict the cured powder thicknessfor each particular coating powder.
29、This reduction factor isFIG. 1 Typical Correlation Between Pre- and Post-cured PowderD7378 162obtained by measuring the cured powder thickness at the samelocation where the uncured powder thickness measurementwas taken. For best accuracy, measurements before and aftercuring should be taken for diffe
30、rent thicknesses. A sample plotof measurement results is shown in Fig. 1. From this plot areduction factor can be determined and applied to all future drycoating powder thickness measurements to predict cured thick-ness. As coating powder properties may alter over time, thisvalue should be confirmed
31、 annually or when there is a changein powder suppliers.4.5.2 Procedure C does not provide a dry powder thicknessmeasurement. The user can make an adjustment to the instru-ment by measuring the cured powder thickness at the samelocation where the uncured powder thickness measurementwas taken and alig
32、n the gage readings with the cured coatingreadings.5. Significance and Use5.1 Many physical and appearance properties of the finishedcoating are affected by the film thickness. Film thickness canaffect the color, gloss, surface profile, adhesion, flexibility,impact resistance and hardness of the coa
33、ting. The fit of piecesassembled after coating can be affected when film thickness isnot within tolerance. Therefore coatings must be applied withincertain minimum and maximum film thickness specifications tooptimize their intended use.5.2 All procedures involve taking measurements of appliedcoating
34、 powders in the pre-cured, pre-gelled state to helpinsure correct cured film thickness. This enables the applica-tion system to be set up and fine-tuned prior to the curingprocess. In turn, this will reduce the amount of scrap andover-spray. Accurate predictions help avoid stripping andre-coating wh
35、ich can cause problems with adhesion andcoating integrity.5.3 Measurements of cured powder coating thickness can bemade using different methods depending upon the substrate.Non-destructive measurements over metal substrates can bemade with magnetic and eddy current coating thickness gages(see Practi
36、ce D7091). Non-destructive measurements overnon-metal substrates can be made with ultrasonic coatingthickness gages (see Test Method D6132). Destructive mea-surements over rigid substrates can be made with cross-sectioning instruments (see Practices D4138).6. Test Specimen6.1 The test specimen can b
37、e the coated part on which thepowder thickness is to be evaluated, or can be test panels ofsimilar material and shape on which it is desired to measure thecoating thickness.PROCEDURE AMETAL NOTCHED GAGES7. Apparatus7.1 Metal Notched Gage with at least one end (edge)consisting of a series of teeth ex
38、tending from the body andspaced from each other. The teeth are of different length. Twolegs or stand-offs extend beyond the teeth at both ends of therow of teeth to support the gage against the coated substrate(see Fig. 2). Several models are available to measure a broadrange of coating powder thick
39、nesses.NOTE 1Notched gages intended for measuring wet film thickness aregenerally not suitable for measuring powder thickness. They usually havesquare teeth with increments too fine for powder measurement.8. Procedure8.1 Select a test panel or choose a site for the thicknessmeasurement.8.2 Select a
40、gage model with a scale range of teeth heightcovering the range of estimated powder thickness. If thicknessis unknown, make a trial determination with a model thatcovers the range of approximately 50 to 300 microns (2 to 12mils).8.3 Push the gage perpendicularly into the dry coatingpowder so that th
41、e two stand-offs (end tabs) on both sides ofthe teeth rest firmly on the substrate.8.4 Keeping the gage perpendicular to the surface, drag thegage along the surface of the coated part for at least 1 cm (0.5in.) thereby generating lines in the powder where the teethtouch it.8.5 Remove the gage from t
42、he surface and examine themarks left in the powder. The powder thickness is consideredto be a range value between the highest numbered tooth thatmade a mark and has powder clinging to it, and the nexthighest tooth that left no mark and has no powder clinging toit.8.6 Using the reduction factor obtai
43、ned from a previouslyprepared correlation chart for that particular coating powder(see Fig. 1), convert the measured powder thickness value to apredicted cured thickness value.PROCEDURE BMAGNETIC OR EDDY CURRENTCOATING THICKNESS GAGES9. Apparatus9.1 Coating Thickness Gage BodyAn electronic device(ho
44、st unit) that accepts a probe to effect a thickness measure-ment.9.2 Powder ProbeA measuring probe connected to thecoating thickness gage body consisting of integrated microFIG. 2 A Metal Notched GageD7378 163pins, a deflection foil and operating on a magnetic or eddycurrent principle (see Fig. 3).1
45、0. Procedure10.1 Select a test panel or choose a site for thicknessmeasurement.10.2 Connect the probe to the coating thickness gage body.10.3 Verify gage accuracy on shims of known thickness andadjust if necessary according to the manufacturers instruc-tions.10.4 Place the probe onto the applied dry
46、 powder until themicro pins contact the substrate. Press down on the probe untilthe integrated deflection foil makes minor contact with thepowder.10.5 Record the thickness (powder height) value displayedon the coating thickness gage.10.6 Using the reduction factor obtained from a previouslyprepared
47、correlation chart for that particular coating powder(see Fig. 1), convert the measured powder thickness value to apredicted cured thickness value.PROCEDURE CNON-CONTACT ULTRASONICPOWDER THICKNESS INSTRUMENTS11. Apparatus11.1 Non-Contact Ultrasonic Powder ThicknessInstrumentSee Fig. 4.12. Procedure12
48、.1 Select a test panel or choose a site for thicknessmeasurement.12.2 Zero the probe of the instrument according to themanufacturers instructions.12.3 Position the probe of the instrument close to theapplied coating powder and take measurements following themanufacturers instructions.13. Report13.1
49、The following items should be reported:13.1.1 Gage type (manufacturer, model and serial number ifavailable),13.1.2 Measurement range of the instrument,13.1.3 Method of accuracy verification and adjustment (ifappropriate),13.1.4 Reduction factor calculations (Procedures A and B),13.1.5 Size and description of the test specimen,13.1.6 Results of a thickness determination,13.1.7 If more than one measurement is made and specificresults for each location are not needed, report the minimum,the maximum, and the average thickness, and13.1.8 Gage operators
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