Measuring the thickness of dry coating powders is an important factor in the manufacture of a variety of products. ASTM International Committee D01 on Paint and Related Coatings, Materials and Applications has developed a new standard for this purpose: D 7378, Practice for Measurement of Thickness of Applied Coating Powders to Predict Cured Thickness. D 7378 is under the jurisdiction of Subcommittee D01.51 on Powder Coatings.

The new standard references three methods for measuring thickness – comb, magnetic and ultrasonic. Procedures A (comb) and B (magnetic) measure the thickness of the applied coating powders in the pre-cured, pre-gelled state, while Procedure C (ultrasonic) results in a predicted thickness value based on a calibration for typical coating powders.

“Many physical and appearance properties of the finished coating are affected by the film appearance,” said David Beamish, general manager of DeFelsko Corp. and Committee D01 member. “Film thickness can affect the color, gloss, surface profile, adhesion, flexibility, impact resistance and hardness of the coating.” Because the fit of pieces assembled after coating can be affected when film thickness is not within tolerance, it is essential that coatings must be applied within certain minimum and maximum film thickness specifications to optimize their intended use.

“The three procedures described in D 7378 involve taking measurements of applied coating powders in the pre-cured, pre-gelled state to help ensure correct cured film thickness,” noted Beamish. “This enables the application systems to be set up and fine-tuned prior to the curing process. In turn, this will reduce the amount of scrap and over-spray.” Beamish also noted that accurate predictions help avoid stripping and recoating that can cause problems with adhesion and coating integrity.

Beamish noted that there is currently good representation from powder coating suppliers and instrument manufacturers in the subcommittee, but that stronger participation from users of powder coatings is sought.

For more information about the new standard, contact David Beamish, DeFelsko Corp., Ogdensburg, N.Y. at 315.393.4450 or dbeamish@defelsko.com.

Committee D01 will meet January 20-22, 2008, in Ft. Lauderdale, FL. For membership or meeting information, contact Jeffrey Adkins, technical committee operations, ASTM International, at 610.832.9738 or jadkins@astm.org.

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