ASTM D5796-20

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Designation: D5796 − 10 (Reapproved 2015) D5796 − 20
Standard Test Method for
Measurement of Dry Film Thickness of Thin-Film Coil-
Coated Systems by Destructive Means Using a Boring
Device
This standard is issued under the fixed designation D5796; 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
1.1 This test method covers the measurement of dry film thickness (DFT) of coating films by microscopic observation of a
precision-cut, shallow-angle crater bored into the coating film. This crater reveals cross sectional layers appearing as rings, whose
width is proportional to the depth of the coating layer(s) and allows for direct calculation of dry film thickness.
1.1.1 The Apparatus, Procedure, and Precision and Bias discussions include Method A and Method B. Method A involves the
use of an optical measurement apparatus which is no longer commercially available, but remains a valid method of dry film
measurement. Method B is a software driven measurement procedure that supersedes Method A.
1.2 The substrate may be any rigid, metallic material, such as cold-rolled steel, hot-dipped galvanized steel, aluminum, etc. The
substrate must be planar with the exception of substrates exhibiting “coil set,” which may be held level by the use of the clamping
tool on the drilling device.
NOTE 1—Variations in the surface profile of the substrate may result in misrepresentative organic coating thickness readings. This condition may exist
over substrates such as hot-dipped, coated steel sheet. This is true of all “precision cut” methods that are used to determine dry film thickness of organic
coatings. This is why several measurements across the strip may be useful if substrate surface profile is suspect.
1.3 The range of thickness measurement is 0 to 3.5 mils (0 to 89 μm).
NOTE 2—For DFT measurements of films greater than 3.5 mils (89μm), but less than 63 mils (1600 μm), a 45° borer may be used in accordance with
this test method, with the exception of 6.8, where the micrometer reading would provide a direct read-out, and division by ten would be unnecessary per
4.3.1 Method A.
1.4 Measurements may be made on coil-coated sheet, certain formed products, or on test panels.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D3794 Guide for Testing Coil Coatings
3. Significance and Use
3.1 Measurement of dry film thickness of organic coatings by physically cutting through the film and optically observing and
measuring the thickness offers the advantage of direct measurement as compared with nondestructive means.
This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.53 on Coil Coated Metal.
Current edition approved June 1, 2015July 1, 2020. Published June 2015July 2020. Originally approved in 1995. Last previous edition approved in 20102015 as
D5796 – 10.D5796 – 10 (2015). DOI: 10.1520/D5796-10R15.10.1520/D5796-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5796 − 20
3.2 Constituent coating layers of an overall thickness of a coating system can usually be measured individually by this test
method, provide adhesion between each layer is sufficient. (However, this can be difficult in cases where the primer, topcoat, or
multiple coating layers have the same, or very similar, appearance.)
4. Apparatus
4.1 Dry Film Thickness Device, It is an apparatus consisting of either a manual or automated carbide-tipped drill that raises and
lowers the boring tip perpendicular to the surface to be tested, a cleaning brush, a marking device (optional), and a video imaging
system, which is attached to a microscope that views the crater formed by the boring device.
4.2 Carbide Borer Bit, The configuration is designed to provide a very smooth circular incision in the paint film at a precise
angle to the surface (see Fig. 1).
4.3 Optical Magnification:
4.3.1 Method A, Video Camera—It is attached to an illuminated microscope and conveys the image onto a closed-circuit
television (CCTV) monitor, so that it is an easy matter to line up the cross-hair on the enlarged image. This very effectively
minimizes error or lack of consistency on the part of the operator in lining up the cross-hair.
4.3.2 Method B, Computer Monitor—It is attached to a microscope with external lighting and conveys the image via software
onto a computer monitor. The monitor and software enlarge the image for viewing and measuring, while the computer retains the
picture as an image file, if the user desires.
4.4 Microscope—The measurement is performed by first boring a shallow-angle crater of known configuration through the
coating(s) film into the substrate. The microscope facilitates viewing and measuring the crater.
4.5 The instrument is calibrated by taking measurements on a standard, which is traceable to a national standards institution.
Calibration is a procedure that is done during setup and will require recalibration if changes are made to the microscope, boring
device, or the camera system. Calibration verification should be done at intervals agreed upon between the user and the consumer,
but no less often than indicated by the manufacturer of the measuring device.
5. Test Specimens
5.1 If multiple coats of paint are to be measured, successive contiguous coats should be of contrasting colors to aid sharp
discrimination of interfaces (see 3.2).
5.2 Generally, test specimens shall be prepared (as test panels) or chosen (as sites on a coil-coated sheet) to be representative
of localized coating thickness and variability.
5.3 If test panels are to be laboratory prepared, this should be done using accepted industry practices, in accordance with Guide
D3794.
6. Procedure
6.1 Select a test panel or choose a site for thickness measurement.
6.2 Using an appropriate surface marker of contrasting color, mark a line on the surface about 25-mm long and 12-mm wide.
In most cases, the use of a marker is not necessary, but for certain colors, usually whites, its use may be desirable. Depending upon
NOTE 1—The drawing is not to scale. It is for illustration purposes only.
NOTE 2—θ = 5° 42 ft 38 in. = 5.710593°
Tan θ = A ⁄B = 0.1
A = 0.1B
FIG. 1 Typical Crater Formed by Boring Device
The sole source of supply of the dry film thickness device known to the committee at this time is DJH Designs, 2366 Wyecroft Rd., Unit D4, Oakville, Ont., Canada
L6L 6M1. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration
at a meeting of the responsible technical committee, which you may attend.
The manufactured angle formed between the surface of the coating and the substrate is 5° 42 ft 38 in. and the resulting crater is circular.
The supplier of the standard used to generate the precision statement and used for calibration (silver-plated, copper substrate) is DJH Designs. The DJH Designs standard
is traceable to the NRC, Montreal Road Building M-36, Ottawa, Canada, K1A 0R6. An additional acceptable standard for calibration (copper and chromium coating on steel,
SRM 1357) may be obtained from NIST, Standard Reference Materials Program, Building 202, Room 204, Gaithersburg, Maryland 20899. All standards must be traceable
to the National Research Council or the National Institute of Science and Technology.
The marker Sanford Sharpie, a registered trademark of Sanford, used by the committee at this time for this test method is Sanford Corp., Bellwood, IL 60104.
D5796 − 20
the coating and the type of marker used, it is possible for the marker to be absorbed into the coating, up to 0.2-mils (5-μm) deep.
This effect can make it difficult to determine the position of the top edge of the crater. External fluorescent lighting may be
positioned to enhance the image and eliminate the need for a marker. The use of a marker, lighting, or marker and lighting shall
be agreed upon between the user and customer.
6.3 Select the appropriate borer bit. A typical bit used for coil coatings has a depth range of 0 to 2 mils, but others are available.
The bit type and depth range shall be agreed upon between the user and customer.
6.4 Place the test panel on the borer stage (align the marked line, if required) so that it is positioned under the bit. Clamp the
panel into place.
6.5 With a small brush, clean debris from the borer bit, the “depth stop surface,” and the surface of the test panel. Debris in these
areas will result in a shallower and smaller crater, with consequently inaccurate results.
6.6 Adjust the depth control wheel so that the carbide borer bit just penetrates the metallic substrate, to avoid undue wear on
the borer
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