ASTM D7378-07

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D7378–07
Standard Practice for
Measurement of Thickness of Applied Coating Powders to
Predict Cured Thickness
This standard is issued under the fixed designation D7378; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This practice describes the thickness measurement of
bility of regulatory limitations prior to use.
dry coating powders applied to a variety of substrates. Use of
some of these procedures may require repair of the coating
2. Referenced Documents
powder. This practice is intended to supplement the manufac-
2.1 ASTM Standards:
turers’ instructions for the operation of the gages and is not
D4138 PracticesforMeasurementofDryFilmThicknessof
intended to replace them. It includes definitions of key terms,
Protective Coating Systems by Destructive, Cross-
reference documents, the significance and use of the practice,
Sectioning Means
and the advantages and limitations of the instruments.
D6132 Test Method for Nondestructive Measurement of
1.2 Three procedures are provided for measuring dry
Dry FilmThickness ofApplied Organic Coatings Using an
coating powder thickness:
Ultrasonic Gage
1.2.1 Procedure A—Using rigid metal notched (comb)
D7091 Practice for Nondestructive Measurement of Dry
gages.
Film Thickness of Nonmagnetic Coatings Applied to
1.2.2 Procedure B—Usingmagneticoreddycurrentcoating
Ferrous Metals and Nonmagnetic, Nonconductive Coat-
thickness gages.
ings Applied to Non-Ferrous Metals
1.2.3 Procedure C—Using non-contact ultrasonic powder
thickness instruments.
3. Terminology
1.3 Coating powders generally diminish in thickness during
3.1 Definitions of Terms Specific to This Standard:
the curing process. These procedures therefore require a
3.1.1 accuracy, n—the measure of the magnitude of error
reduction factor be established to predict cured film thickness
between the result of a measurement and the true thickness of
of powder coatings.
the item being measured.
1.4 Procedure A and Procedure B measure the thickness
3.1.2 adjustment, n—the physical act of aligning a gage’s
(height or depth) of the applied coating powders in the
thickness readings to match those of a known thickness sample
pre-cured, pre-gelled state. By comparing results to the mea-
(removal of bias) in order to improve the accuracy of the gage
sured cured powder thickness in the same location, a reduction
on a specific surface, within a specific portion of its measure-
factor can be determined and applied to future thickness
ment range or to specific operating conditions.
measurements of the same coating powder.
3.1.3 coating powders, n—finely divided particles of resin,
1.5 Procedure C results in a predicted thickness value based
either thermoplastic or thermosetting, generally incorporating
on a calibration for typical coating powders. If the powder in
pigments, fillers, and additives and remaining finely divided
question is not typical then a calibration adjustment can be
during storage under suitable conditions, which, after fusing
made to align gage readings with the actual cured values as
and possibly curing, give a continuous film.
determined by other measurement methods.
3.1.4 calibration, n—the high-level, controlled and docu-
1.6 The values stated in SI units are to be regarded as the
mented process of obtaining measurements on traceable cali-
standard. The values given in parentheses are for information
brationstandardsoverthefulloperatingrangeofthegage,then
only.
making the necessary gage adjustments (as required) to correct
1.7 This standard does not purport to address all of the
any out-of-tolerance conditions.
safety concerns, if any, associated with its use. It is the
3.1.4.1 Discussion—Calibration of coating thickness gages
is performed in a controlled environment using a documented
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
Related Coatings, Materials, and Applications and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D01.51 on Powder Coatings. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved July 1, 2007. Published July 2007. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7378-07. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7378–07
processbytheequipmentmanufacturer,anauthorizedagent,or it.Measurementscanbemadeonasuitablerigidsurface,metal
by an authorized, trained calibration laboratory. The outcome or non-metal but marks will be made in the powder that may
of the calibration process is to restore/realign the gage to not be covered when the powder flows in the cure process.
meet/exceed the manufacturer’s stated accuracy and may result 4.3 Procedure B—Uses a conventional magnetic or eddy
in the creation of a calibration certificate recording the results current coating thickness gage with a specially designed
of the process at the time of testing. powder probe to measure the thickness of the coating powder.
3.1.5 powder coatings, n—coatings which are protective or Micro pins, which are integrated into the probe, penetrate the
decorative, or both, formed by the application of a coating coating powder down to the substrate. The probe is manually
powder to a substrate and fused in a continuous film by the pressed down to the surface of the powder to effect a thickness
application of heat or radiant energy. measurement. This procedure is applicable to metal substrates
3.1.6 dry film thickness, n—the thickness of a coating (or only. Marks may be made in the powder that may not be
coating layers) as measured from the surface of the substrate. covered when the powder flows in the cure process.
3.1.7 micrometer (micron), n—one one-thousandths of a 4.4 Procedure C—Uses a non-contact ultrasonic powder
millimeter (0.001 mm); 25.4 microns = 1 mil. thickness instrument to take a measurement of the coating
3.1.8 mil, n—an imperial unit of measure; one one- powder to calculate and display a predicted cured thickness.
thousandths of an inch (0.001 in.); 1 mil = 25.4 microns. Measurements can be made on any rigid surface.
3.1.9 substrate, n—the base material, type of surface or 4.5 The thickness of dry coating powder diminishes during
component that is being coated. the curing process. To predict the cured powder coating
3.1.10 uncured, adj—the physical state of coating powder thickness, a correlation must be made between pre-cured and
when electrostatically held, but not yet fused, to a substrate. post-cured thicknesses.
3.1.11 verification of accuracy, n—obtaining measurements 4.5.1 Procedure A and Procedure B result in a thickness
on a reference standard prior to gage use for the purpose of measurement of the uncured coating powder only. A reduction
determiningtheabilityofthecoatingthicknessgagetoproduce factor must then be used to predict the cured powder thickness
reliablevalues,comparedtothecombinedgagemanufacturer’s for each particular coating powder. This reduction factor is
stated accuracy and the stated accuracy of the reference obtained by measuring the cured powder thickness at the same
standard. location where the uncured powder thickness measurement
was taken. For best accuracy, measurements before and after
4. Summary of Practice
curing should be taken for different thicknesses.Asample plot
4.1 The three procedures take measurements of applied of measurement results is shown in Fig. 1. From this plot a
coating powders in the pre-cured, pre-gelled state. Each reduction factor can be determined and applied to all future dry
procedure employs different devices to measure the dry pow- co
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