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Coating Thickness Standard Describes Measurement Procedures

January/February 2008
Update

Committee D01 on Paint and Related Coatings, Materials and Applications

Coating Thickness Standard Describes
Measurement Procedures

Coating Thickness

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,” says David Beamish, general manager, 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 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 esure correct cured film thickness,” notes 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 notes that accurate predictions help avoid stripping and recoating that can cause problems with adhesion and coating integrity.

D 7378 will be beneficial in a variety of industries that use coating powders, including the following:

  • The appliance industry benefits from powder coating on exterior panels of household appliances where it has replaced porcelain enamel;
  • The automotive industry uses powder coating on wheels, bumpers, decorative trim and numerous engine parts;
  • Architectural powder coating on buildings provides a superior, more colorful, longer lasting and more durable finish;
  • Everyday products like golf clubs, shelving, lawn mowers, garden tools and metal toys benefit from the economics of powder coating.

Beamish says that the subcommittee welcomes new members. “D01.51 is responsible for maintaining and updating a number of active standards and work items,” says Beamish. “A small number of industry users and suppliers are active in committee work but more participation is being encouraged.” He notes that there is currently good representation from powder coating suppliers and instrument manufacturers but that stronger participation from users of powder coatings is sought.

CONTACT

Technical Information: David Beamish, DeFelsko Corp., Ogdensburg, N.Y.

Phone: 315/393- 4450

ASTM Staff: Jeffrey Adkins

Phone: 610/832-9738