1、Designation: D7378 10Standard 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 is intended to supplement themanufacturers instructions for the operation of the gages andis not intended to replace them. It includes definitions of keyterms, reference documents, the significance and use of t
4、hepractice, and the advantages 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 dryfilm thickness gages.1.2.3 Procedure CUsing non-co
5、ntact 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 Procedure A and Procedure B measure the thickne
6、ss(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 same coating powder.1.5 Procedure C results
7、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 methods.1.6 The values stated in SI units a
8、re 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 establish appro-priate safety and health practic
9、es 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 for Nondestructive Measurement ofDry Film T
10、hickness ofApplied Organic Coatings Using anUltrasonic GageD7091 Practice for Nondestructive Measurement of DryFilm Thickness of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic, Nonconductive Coat-ings Applied to Non-Ferrous Metals3. Terminology3.1 Definitions of Terms Specific to This
11、 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 of a known thickness sample(reduction of bias) in order to imp
12、rove 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 powders, nfinely divided particles of resin,either thermoplastic or
13、thermosetting, generally incorporatingpigments, fillers, and additives and remaining finely dividedduring storage 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
14、 on traceable cali-bration standards over the full operating range of the gage, thenmaking the necessary gage adjustments (as required) to correctany out-of-tolerance conditions.1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications a
15、nd is the direct responsibility ofSubcommittee D01.51 on Powder Coatings.Current edition approved Dec. 1, 2010. Published January 2011. Originallyapproved in 2007. Last previous edition approved in 2007 as D7378 - 07. DOI:10.1520/D7378-10.2For referenced ASTM standards, visit the ASTM website, www.a
16、stm.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4.1
17、 DiscussionCalibration of coating thickness gagesis performed in a controlled environment using a documentedprocess by the equipment manufacturer, an authorized agent, orby an authorized, trained calibration laboratory. The outcomeof the calibration process is to restore/realign the gage tomeet/exce
18、ed the manufacturers stated accuracy and may resultin the creation of a calibration certificate recording the resultsof the process at the time of testing.3.1.5 powder coatings, ncoatings which are protective ordecorative, or both, formed by the application of a coatingpowder to a substrate and fuse
19、d in a continuous film by theapplication of heat or radiant energy.3.1.6 dry film thickness, nthe thickness of a coating (orcoating layers) as measured from the surface of the substrate.3.1.7 micrometer (micron), none one-thousandth of amillimeter (0.001 mm); 25.4 microns = 1 mil.3.1.8 mil, nan impe
20、rial 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 powderwhen particles are electrostatically held to a substrate.3.1.11 verificat
21、ion of accuracy, ncomparing predictedthickness values with actual cured thickness values and ensur-ing both are within their combined tolerances.4. Summary of Practice4.1 The three procedures take measurements of appliedcoating powders in the pre-cured, pre-gelled state. Eachprocedure employs differ
22、ent 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 determined as being between the highest numbered tooth thatmade a mark and has powder c
23、linging 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 covered when the powder flows in the cure process.4.3 Procedure BUses a conventional
24、 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 to the substrate. The probe is manuallypressed down to the surface of the powder to e
25、ffect a thicknessmeasurement. This procedure is applicable to metal substratesonly. Marks may be made in the powder that may not becovered when the powder flows in the cure process.4.4 Procedure CUses a non-contact ultrasonic powderthickness instrument to take a measurement of the coatingpowder to c
26、alculate and display a predicted cured thickness.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 coatingthickness, a correlation must be made between pre-cured andpost-cured thicknesses.4.5.1 Proce
27、dure 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. This reduction factor isobtained by measuring the cured powder thickness at the samelocation where
28、the uncured powder thickness measurementwas taken. For best accuracy, measurements before and aftercuring should be taken for different 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
29、thickness measurements to predict cured thick-ness.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 align th
30、e gage readings with the cured coatingreadings.FIG. 1 Typical Correlation Between Pre- and Post-cured PowderD7378 1025. 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 profil
31、e, adhesion, flexibility,impact resistance and hardness of the coating. 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 us
32、e.5.2 All procedures involve taking measurements of appliedcoating 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
33、-spray. Accurate predictions help avoid stripping andre-coating which 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
34、 with magnetic and eddy current coating thickness gages(see Practice 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
35、 (see Practices D4138).6. Test Specimen6.1 The test specimen can be 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 G
36、age with at least one end (edge)consisting of a series of teeth extending 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 mo
37、dels are available to measure a broadrange of coating powder thicknesses.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
38、 panel or choose a site for the thicknessmeasurement.8.2 Select a 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 P
39、ush the gage perpendicularly into the dry coatingpowder so that the 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 line
40、s in the powder where the teethtouch it.8.5 Remove the gage from the 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 an
41、d has no powder clinging toit.8.6 Using the reduction factor obtained 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 GAGES
42、9. Apparatus9.1 Coating Thickness Gage BodyAn electronic device(host 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 micropins, a deflection foil and operating on a magnetic or eddycu
43、rrent principle (see Fig. 3).FIG. 2 A Metal Notched Gage FIG. 3 A Powder ProbeD7378 10310. 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 necessar
44、y according to the manufacturers instruc-tions.10.4 Place the probe onto the applied dry 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 co
45、ating thickness gage.10.6 Using the reduction factor obtained 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 CNON-CONTACT ULTRASONICPOWDER THICKNESS INSTRUMENTS11. A
46、pparatus11.1 Non-Contact Ultrasonic Powder ThicknessInstrumentSee Fig. 4.12. Procedure12.1 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 coat
47、ing powder and take measurements following themanufacturers instructions.13. Report13.1 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 (ifappr
48、opriate),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 av
49、erage thickness, and13.1.8 Gage operators name.14. Keywords14.1 coating powder; coating thickness; film thickness;powder coating; powder thickness; thickness prediction;ultrasonicASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at an
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