1、Designation: D 7378 07Standard Practice forMeasurement of Thickness of Applied Coating Powders toPredict Cured Thickness1This standard is issued under the fixed designation D 7378; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 substrates.
3、 Use ofsome of these procedures may require repair of the coatingpowder. This practice is intended to supplement the manufac-turers instructions for the operation of the gages and is notintended to replace them. It includes definitions of key terms,reference documents, the significance and use of th
4、e practice,and the advantages and limitations of the instruments.1.2 Three procedures are provided for measuring drycoating powder thickness:1.2.1 Procedure AUsing rigid metal notched (comb)gages.1.2.2 Procedure BUsing magnetic or eddy current coatingthickness gages.1.2.3 Procedure CUsing non-contac
5、t ultrasonic powderthickness instruments.1.3 Coating powders generally diminish in thickness duringthe curing process. These procedures therefore require areduction factor be established to predict cured film thicknessof powder coatings.1.4 Procedure A and Procedure B measure the thickness(height or
6、 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 in a predict
7、ed thickness value basedon a calibration for typical coating powders. If the powder inquestion is not typical then a calibration adjustment can bemade to align gage readings with the actual cured values asdetermined by other measurement methods.1.6 The values stated in SI units are to be regarded as
8、 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 practices and determine the
9、 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 4138 Practices for Measurement of Dry Film Thicknessof Protective Coating Systems by Destructive, Cross-Sectioning MeansD 6132 Test Method for Nondestructive Measurement ofDry Film Thickness ofApplied
10、 Organic Coatings Using anUltrasonic GageD 7091 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 Standard:3.1.1 a
11、ccuracy, 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(removal of bias) in order to improve the accuracy o
12、f the gageon a specific surface, within a specific portion of its measure-ment range or to specific operating conditions.3.1.3 coating powders, nfinely divided particles of resin,either thermoplastic or thermosetting, generally incorporatingpigments, fillers, and additives and remaining finely divid
13、edduring 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 on traceable cali-bration standards over the full operating range of the gage, thenmaking the ne
14、cessary gage adjustments (as required) to correctany out-of-tolerance conditions.3.1.4.1 DiscussionCalibration of coating thickness gagesis performed in a controlled environment using a documented1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials,
15、and Applications and is the direct responsibility ofSubcommittee D01.51 on Powder Coatings.Current edition approved July 1, 2007. Published July 2007.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStand
16、ards 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.process by the equipment manufacturer, an authorized agent, orby an authorized, trained calibrat
17、ion laboratory. The outcomeof the calibration process is to restore/realign the gage tomeet/exceed 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 protec
18、tive ordecorative, or both, 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 coating (orcoating layers) as measured from the surface of the substrate.3.1.7 micrometer (
19、micron), none one-thousandths of amillimeter (0.001 mm); 25.4 microns = 1 mil.3.1.8 mil, nan imperial unit of measure; one one-thousandths 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 physica
20、l state of coating powderwhen electrostatically held, but not yet fused, to a substrate.3.1.11 verification of accuracy, nobtaining measurementson a reference standard prior to gage use for the purpose ofdetermining the ability of the coating thickness gage to producereliable values, compared to the
21、 combined gage manufacturersstated accuracy and the stated accuracy of the referencestandard.4. Summary of Practice4.1 The three procedures take measurements of appliedcoating powders in the pre-cured, pre-gelled state. Eachprocedure employs different devices to measure the dry pow-der.4.2 Procedure
22、 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 clinging to it, and the nexthighest tooth that left n
23、o 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 magnetic or eddycurrent coating thickness gage with
24、 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 effect a thicknessmeasurement. This procedure is appl
25、icable 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 calculate and display a predicted cured thickness.Mea
26、surements 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 Procedure A and Procedure B result in a thicknessmeasurem
27、ent 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 the uncured powder thickness measurementwas taken. F
28、or 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 thickness measurements to predict cured thick-ness.4
29、.5.2 Procedure C does not provide a dry powder thicknessmeasurement. The user can make a calibration adjustment tothe instrument by measuring the cured powder thickness at thesame location where the uncured powder thickness measure-ment was taken and aligning the gage readings with the curedcoating
30、readings.FIG. 1 Typical Correlation Between Pre- and Post-cured PowderD73780725. 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 resista
31、nce 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 use.5.2 All procedures involve taking mea
32、surements 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-spray. Accurate predictions help avoid
33、 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 with magnetic and eddy current coating
34、 thickness gages(see Practice D 7091). Non-destructive measurements overnon-metal substrates can be made with ultrasonic coatingthickness gages (see Test Method D 6132). Destructive mea-surements over rigid substrates can be made with cross-sectioning instruments (see Test Method D 4138).6. Test Spe
35、cimen6.1 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 Gage with at least one end (edge)co
36、nsisting 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 models are available to measure a br
37、oadrange 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 panel or choose a site for the th
38、icknessmeasurement.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 Push the gage perpendicularly into
39、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 lines in the powder where the teethtou
40、ch 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 and has no powder clinging toit.8.6
41、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 GAGES9. Apparatus9.1 Coating Thickness
42、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 eddycurrent principle (see Fig. 3).10. P
43、rocedure10.1 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 and adjust if necessary accordingto the manufacturers instructions.10.4 Place the probe onto the applied dry powder until themicro pins conta
44、ct 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.FIG. 2 A Metal Notched GageD737807310.6 Using the reduction factor obtained from a previouslyprepare
45、d 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. Procedure
46、12.1 Select a test panel or choose a site for thicknessmeasurement.12.2 Verify instrument accuracy and adjust if necessaryaccording to the manufacturers instructions.12.3 Position the probe of the instrument close to theapplied coating powder and take a measurement following themanufacturers instruc
47、tions.12.4 If a correction to the reading is required to allow for theparticular characteristics of the powder then follow the manu-facturers 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 ran
48、ge of the instrument,13.1.3 Method of accuracy verification and adjustment (ifappropriate),13.1.4 Reduction factor calculations,13.1.5 Results of a thickness determination,13.1.6 If more than one measurement is made and specificresults for each location are not needed, report the minimum,the maximum
49、, and the average thickness, and13.1.7 Gage operators name.14. Keywords14.1 coating powder; coating thickness; film thickness;powder coating; powder thickness; thickness prediction;ultrasonicFIG. 3 A Powder ProbeFIG. 4 A Non-contact Ultrasonic Powder Thickness InstrumentD7378074ASTM 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 infringeme
