ASTM Int'l Issues Coating Thickness Standard - ASTM D 7378
December 10, 2007 // Published as a news service by IHS
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ASTM International Committee D01 on Paint and Related Coatings, Materials and Applications developed ASTM D 7378 - Practice for Measurement of Thickness of Applied Coating Powders to Predict Cured Thickness.
The 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 precured, pregelled state while Procedure C (ultrasonic) results in a predicted thickness value based on a calibration for typical coating powders, said ASTM International.
"Many physical and appearance properties of the finished coating are affected by the film appearance," said 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 important that coatings must be applied within certain minimum and maximum film thickness specifications to optimize their intended use, according to ASTM International.
"The three procedures described in [ASTM] D 7378 involve taking measurements of applied coating powders in the precured, pregelled state to help insure correct cured film thickness," said 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 said that accurate predictions help avoid stripping and recoating that can cause problems with adhesion and coating integrity.
ASTM D 7378 will be beneficial in 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 on many washer and dryer parts.
- The automotive industry uses powder coating on wheels, bumpers, decorative trim and engine parts.
- Architectural powder coating on buildings provides a finish that has more color, is longer lasting and more durable.
- Products like golf clubs, shelving, lawn mowers, garden tools and metal toys benefit from the economics of powder coating.
ASTM D 7378 is under the jurisdiction of Subcommittee D01.51 on Powder Coatings.
Source: ASTM International.